Mohammad A.
Abdulmalic
a,
Azar
Aliabadi
b,
Andreas
Petr
b,
Yulia
Krupskaya
b,
Vladislav
Kataev
b,
Bernd
Büchner
bc,
Ruslan
Zaripov
d,
Evgeniya
Vavilova
d,
Violeta
Voronkova
d,
Kev
Salikov
d,
Torsten
Hahn
e,
Jens
Kortus
e,
Francois
Eya'ane Meva
f,
Dieter
Schaarschmidt
a and
Tobias
Rüffer
*a
aTechnische Universität Chemnitz, Fakultät für Naturwissenschaften, Strasse der Nationen 62, D-09111 Chemnitz, Germany. E-mail: tobias.rueffer@chemie.tu-chemnitz.de
bLeibniz Institute for Solid State and Materials Research IFW Dresden, D-01171 Dresden, Germany
cInstitut für Festkörperphysik, Technische Universität Dresden, D-01062 Dresden, Germany
dZavoisky Physical-Technical Institute, Russian Academy of Sciences, 420029 Kazan, Russia
eTechnische Universität Bergakademie Freiberg, Institut für Theoretische Physik, D-09596 Freiberg, Germany
fDepartment of Pharmaceutical Sciences, Faculty of Medicine and Pharmaceutical Sciences, University of Douala, BP 2701, Cameroon
First published on 23rd March 2015
The diethyl ester of o-phenylenebis(oxamic acid) (opbaH2Et2) was treated with an excess of RNH2 in MeOH to cause the exclusive formation of the respective o-phenylenebis(N(R)-oxamides) (opboH4R2, R = Me 1, Et 2, nPr 3) in good yields. Treatment of 1–3 with half an equivalent of [Cu2(AcO)4(H2O)2] or one equivalent of [Ni(AcO)2(H2O)4] followed by the addition of four equivalents of [nBu4N]OH resulted in the formation of mononuclear bis(oxamidato) type complexes [nBu4N]2[M(opboR2)] (M = Ni, R = Me 4, Et 5, nPr 6; M = Cu, R = Me 7, Et 8, nPr 9). By addition of two equivalents of [Cu(pmdta)(NO3)2] to MeCN solutions of 7–9, novel trinuclear complexes [Cu3(opboR2)(L)2](NO3)2 (L = pmdta, R = Me 10, Et 11, nPr 12) could be obtained. Compounds 4–12 have been characterized by elemental analysis and NMR/IR spectroscopy. Furthermore, the solid state structures of 4–10 and 12 have been determined by single-crystal X-ray diffraction studies. By controlled cocrystallization, diamagnetically diluted 8 and 9 (1%) in the host lattice of 5 and 6 (99%) (8@5 and 9@6), respectively, in the form of single crystals have been made available, allowing single crystal ESR studies to extract all components of the g-factor and the tensors of onsite CuA and transferred NA hyperfine (HF) interaction. From these studies, the spin density distribution of the [Cu(opboEt2)]2− and [Cu(opbonPr2)]2− complex fragments of 8 and 9, respectively, could be determined. Additionally, as a single crystal ENDOR measurement of 8@5 revealed the individual HF tensors of the N donor atoms to be unequal, individual estimates of the spin densities on each N donor atom were made. The magnetic properties of 10–12 were studied by susceptibility measurements versus temperature to give J values varying from −96 cm−1 (10) over −104 cm−1 (11) to −132 cm−1 (12). These three trinuclear CuII-containing bis(oxamidato) type complexes exhibit J values which are comparable to and slightly larger in magnitude than those of related bis(oxamato) type complexes. In a summarizing discussion involving experimentally obtained ESR results (spin density distribution) of 8 and 9, the geometries of the terminal [Cu(pmdta)]2+ fragments of 12 determined by crystallographic studies, together with accompanying quantum chemical calculations, an approach is derived to explain these phenomena and to conclude if the spin density distribution of mononuclear bis(oxamato)/bis(oxamidato) type complexes could be a measure of the J couplings of corresponding trinuclear complexes.
On the other hand, mono-N- (type II) and di-N-substituted (type III) type I compounds and, thus, their subsequent mononuclear type V and VI complexes, cf. Scheme 1, have received less attention.3–6 Due to this, a limited number of corresponding trinuclear type VIII and IX complexes, cf. Scheme 1, have been reported so far.7,8a
As reported by Kahn,9 a slight tuning of the ligand skeleton that bridges neighbouring metals, mainly the replacement of the Lewis-basic heteroatoms of the oxamato fragments with less electronegative ones, can induce higher J couplings between neighbouring, e.g. CuII ions, as shown for a number of binuclear complexes.
In a recent study, we observed a direct proportionality between the spin density distribution of a type V complex, namely [nBu4N]2[Cu(opooMe)] (opooMe = o-phenylene(N′-methyl oxamidato)(oxamato)) (13), and the magnetic superexchange interactions of its corresponding trinuclear type VIII complex, namely [Cu3(opooMe)(pmdta)2](NO3)2·3MeCN (14).8a These results support the assumption, on the one hand, that the spin density distribution of mononuclear type IV and/or V complexes is a measure of the magnitude of J values of corresponding trinuclear type VII/VIII complexes.8a,10
On the other hand, the asymmetric type VIII complex 14 has been synthesized to verify whether the magnetic superexchange interactions between its oxamato or oxamidato bridged CuII ions are different or not. However, only one experimental J value of −130 cm−1 was determined, although, for example, from DFT calculations two different J values (−84 cm−1/−72 cm−1via the oxamidato/oxamato bridging unit) were derived.8b This observation agrees with the statement made by Kahn on how to induce higher J couplings.9 For example, we have already reported on the conversion of [nBu4N]2[Cu(opba)] (15) to [Cu3(opba)(pmdta)2(NO3)](NO3)·2MeCN (16, opba = o-phenylenebis(oxamato)) or the conversion of [nBu4N]2[Cu(obbo)] (17) to [Cu3(obbo)(pmdta)2(NO3)](NO3)·CH2Cl2·H2O (18, obbo = o-benzylbis(oxamato)) with J = −89 cm−1 and J = −111 cm−1, respectively.11,12 However, additional studies are required to verify this finding.
In order to elaborate further the interplay between the spin density distribution of mononuclear type IV–VI complexes and the magnetic superexchange interactions of their corresponding trinuclear type VII–IX complexes, we report here on the synthesis of the mononuclear type VI complexes [nBu4N]2[M(opboR2)] (M = NiII, R = Me (4), Et (5), nPr (6). M = CuII, R = Me (7), Et (8), nPr (9)). Diamagnetically diluted single crystals of 8@5 and 9@6 were prepared to estimate the spin density distributions of 8 and 9 from the HF tensors determined by ESR spectroscopy. From 7–9, the corresponding type IX complexes [Cu3(opboR2)(L)2](NO3)2 (L = pmdta, R = Me (10), Et (11), nPr (12)) were synthesized to determine their magnetic properties. The results obtained thereof are reported here, together with supporting DFT calculations.
For the synthesis of the mononuclear type VI complexes 4–9, a hot MeOH solution of [Cu2(OAc)4(H2O)2] or [Ni(OAc)2(H2O)4], respectively, was added to a suspension of either 1–3 in MeOH.13 Then, four equivalents of [nBu4N]OH were added, causing the complete dissolution of all suspended materials and the reaction mixture was stirred for 15 min at 60 °C. Complexes 4–9 were isolated after appropriate workup as yellow and red powders.13
The trinuclear type IX complexes 10–12 were synthesized conveniently according to Scheme 2 in MeCN. After reducing the volume of the reaction mixtures, the desired complexes were precipitated by the addition of THF. The purification was effectively achieved by re-dissolving the crude material in MeCN and precipitation by the addition of THF. This method was satisfactory to produce analytically pure complexes, cf. the Experimental part.
4A | 5A , | 6A/6Ba,c | 7A | 8A , | 9A | 10A/10Bc,d | 12A | |
---|---|---|---|---|---|---|---|---|
a M1 = Ni1. b For 5A/8A the labeling is as follows: N3 = N1A, C3 = C3A, O3 = O1A, N4 = N2A, C4 = C4A, O4 = O4A. Symmetry code “A”: −x, y, −z + ½. c The second entry belongs to analogous data of the crystallographically independent B molecule. d M1 = Cu1. | ||||||||
Bond lengths | ||||||||
N1–M1 | 1.8485(16) | 1.8546(15) | 1.855(7)/1.864(6) | 1.938(16) | 1.9374(17) | 1.934(6) | 1.953(9)/1.946(16) | 1.953(11) |
N2–M1 | 1.9033(16) | 1.9130(16) | 1.879(6)/1.877(6) | 1.952(17) | 1.9645(18) | 1.967(7) | 1.985(7)/1.952(16) | 1.986(13) |
N3–M1 | 1.8508(15) | 1.8546(15) | 1.879(7)/1.855(8) | 1.938(17) | 1.9374(17) | 1.936(7) | 1.926(9)/1.918(14) | 1.933(11) |
N4–M1 | 1.8989(16) | 1.9130(16) | 1.919(8)/1.950(6) | 1.953(17) | 1.9645(18) | 1.942(7) | 1.991(7)/1.948(17) | 1.992(12) |
C1–O1 | 1.237(2) | 1.247(2) | 1.250(8)/1.267(9) | 1.239(2) | 1.244(3) | 1.244(3) | 1.294(13)/1.28(4) | 1.297(17) |
C2–O2 | 1.247(2) | 1.255(2) | 1.275(8)/1.274(8) | 1.251(2) | 1.258(3) | 1.240(7) | 1.297(13)/0.93(5) | 1.278(19) |
C3–O3 | 1.239(2) | 1.247(2) | 1.217(12)/1.243(11) | 1.243(2) | 1.244(3) | 1.171(8) | 1.43(3)/1.198(13) | 1.262(16) |
C4–O4 | 1.245(2) | 1.255(2) | 1.312(15)/1.263(9) | 1.250(3) | 1.258(3) | 1.312(10) | 1.296(14)/1.206(14) | 1.300(17) |
C1–C2 | 1.544(3) | 1.539(3) | 1.524(11)/1.493(12) | 1.545(3) | 1.551(3) | 1.561(11) | 1.527(17)/1.34(4) | 1.47(2) |
C3–C4 | 1.541(3) | 1.539(3) | 1.44(2)/1.424(14) | 1.548(3) | 1.551(3) | 1.559(14) | 1.525(14)/1.396(13) | 1.47(2) |
Bond angles | ||||||||
N1–M1–N3 | 84.76(7) | 84.26(9) | 82.4(3)/84.2(3) | 82.20(7) | 81.97(10) | 80.8(3) | 81.3(3)/80.6(6) | 80.5(5) |
N2–M1–N4 | 106.16(7) | 108.24(10) | 107.7(3)/104.8(3) | 111.18(7) | 112.38(11) | 111.9(3) | 110.3(3)/108.1(6) | 112.9(5) |
N1–M1–N2 | 84.66(7) | 83.82(7) | 83.6(3)/85.8(3) | 83.30(7) | 83.03(7) | 83.2(3) | 83.9(3)/85.5(6) | 83.6(5) |
N3–M1–N4 | 84.47(7) | 83.82(7) | 86.3(4)/85.2(3) | 83.50(7) | 83.03(7) | 84.2(3) | 84.5(3)/85.9(6) | 83.4(5) |
N1–M1–N4 | 169.09(7) | 167.67(6) | 168.7(3)/168.8(3) | 165.23(7) | 164.04(7) | 164.9(3) | 165.8(3)/166.3(6) | 162.8(5) |
N2–M1–N3 | 169.21(7) | 167.67(6) | 166.0(3)/169.9(3) | 165.05(7) | 164.04(7) | 163.9(3) | 165.1(3)/165.9(6) | 163.2(5) |
O1–C1–N1 | 128.27(19) | 128.22(18) | 126.4(7)/123.8(9) | 128.7(2) | 128.4(2) | 128.2(10) | 131.3(14)/120(3) | 127.1(13) |
O1–C1–C2 | 121.98(17) | 121.40(18) | 123.2(6)/122.5(7) | 120.50(18) | 120.22(19) | 121.1(6) | 115.3(11)/124(2) | 119.0(13) |
N1–C1–C2 | 109.75(16) | 110.38(16) | 110.3(6)/113.6(7) | 110.79(18) | 111.38(18) | 110.7(7) | 113.4(11)/116(3) | 113.7(13) |
O2–C2–N2 | 126.97(19) | 128.00(19) | 127.8(7)/129.1(8) | 126.2(2) | 127.2(2) | 127.6(9) | 126.6(11)/126(4) | 124.2(15) |
O2–C2–C1 | 119.29(18) | 119.27(18) | 119.0(6)/118.1(8) | 118.68(19) | 118.5(2) | 117.4(7) | 115.7(9)/114(3) | 117.7(13) |
N2–C2–C1 | 113.70(16) | 112.72(17) | 113.1(6)/112.7(6) | 115.10(18) | 114.31(18) | 115.0(6) | 117.6(11)/120(3) | 118.1(15) |
O3–C3–N3 | 128.47(18) | 128.22(18) | 127.1(14)/121.6(11) | 128.3(2) | 128.4(2) | 132.8(13) | 129.5(14)/127(2) | 127.3(15) |
O3–C3–C4 | 121.69(17) | 121.40(18) | 120.9(11)/127.2(9) | 120.31(19) | 120.22(19) | 117.7(10) | 118.2(9)/119.4(18) | 119.8(12) |
N3–C3–C4 | 109.84(16) | 110.38(16) | 111.8(9)/111.2(7) | 111.42(18) | 111.38(18) | 109.4(7) | 112.2(11)/113.7(17) | 112.9(11) |
O4–C4–N4 | 127.21(19) | 128.00(19) | 115.8(15)/121.1(9) | 126.3(2) | 127.2(2) | 122.1(13) | 127.1(11)/115.0(19) | 124.5(13) |
O4–C4–C3 | 119.43(17) | 119.27(18) | 126.4(11)/119.4(8) | 119.0(2) | 118.5(2) | 122.0(8) | 114.5(9)/126(2) | 117.2(12) |
N4–C4–C3 | 113.33(16) | 112.72(17) | 117.7(9)/118.8(7) | 114.74(18) | 114.31(18) | 115.9(8) | 118.4(10)/118.9(17) | 118.1(12) |
For 6 the asymmetric unit comprises two crystallographically different [Ni(opbo(nPr)2)]2− dianionic complex fragments, denoted as 6A (comprising Ni1) and 6B (comprising Ni2). Related bond lengths and angles of 6A and 6B show differences of up to ca. 2% and ca. 6%, respectively. Additionally, in the case of 6A an anti-conformation of the nPr groups with respect to their orientation to the almost planar {Ni(opbo)} unit is observed, whereas for 6B a syn-conformation is found. Despite this, only data of 6A will be discussed. For completeness and comparison, Table 1 gives bond lengths and angles of both 6A and 6B. Fig. S1† displays the molecular structures of 6A and 6B. The 1D chains formed by 5′ and 8′ due to intermolecular hydrogen bonds are illustrated in Fig. S2 and S3,† while selected bond lengths and angles of these hydrogen bonds are given in Tables S1 and S2,† respectively.
For 5A and 8A crystallographically imposed C2 symmetry is observed. The C2 axes pass the M1 atom and the middle of the C3/C3A bond, cf. Fig. 1 and 2. In contrast, all other herein discussed [M(opboR2)]2− fragments exhibit C1 symmetry. Moreover, as revealed by entries in Table 3, related pairs of NiII/CuII containing complexes (4 and 7, 5 and 8, 6 and 9) can be regarded as isomorphic to each other. In the case of the related NiII/CuII pair of 6 (NiII, monoclinic, P2(1)) and 9 (CuII, monoclinic, P2(1)/c), unit cell parameters are in good agreement with each other, although the determined space group is different. It is verified that a solution/refinement of 6 in the space group P2(1)/c and of 9 in P2(1), respectively, is not possible. Responsible for this observation is the orientation of the nPr groups with respect to the planar {M(opbo)} units, cf. above. Despite this, the isomorphism of corresponding pairs indicates that a co-crystallization of them should be possible, cf. the Experimental part.
A common feature of 4A–9A is the coordination of the respective opboR24− ligands to the metal ions by their four deprotonated amido nitrogen atoms N1–N4, forming planar MN4 coordination units, cf. Fig. 1 and 2. The metal ions are located 0.004(1) Å (4A), 0.000 Å (5A), 0.006(5) Å (6A), 0.001(1) Å (7A), 0.0002(10) Å (8A) and 0.003(3) Å (9A), respectively, above/below the calculated mean planes of atoms N1–N4 with root mean square deviations (rmsd) from planarity of 0.033 Å (4A), 0.047 Å (5A), 0.001 Å (6A), 0.055 Å (7A), 0.081 Å (8A) and 0.023 Å (9A), respectively. The planarity of the MN4 coordination units is indicated further by the sum of the four bond angles around the metal ions of 360.05(14)° for 4A, 360.14(17)° for 5A, 360.0(7)° for 6A, 360.18(14)° for 7A, 360.41(16)° for 8A and 360.1(6)° for 9A, respectively. As observed and discussed for the related type IV complexes, cf. Scheme 1,14 a unique feature of planar complexes possessing 5-5-5 fused chelate rings around the respective metal ion is that three of the bond angles are rather small, whereas the fourth one is substantially larger. Indeed, this situation is observed as well for 4A–9A with the bond angles N1–M1–N3, N1–M1–N2 and N3–M1–N4 being in the range from 80.8(3)° (9A) to 86.3(4)° (6A) compared to the N2–M1–N4 bond angles in the range from 106.16(7)° (4A) to 112.38(11)° (8A).
The M–N bonds can be divided into M–Naryl and M–Nalkyl bonds with respect to the substituents at the N donor atoms. Especially for NiII-containing 4A and 5A the M–Naryl bond lengths (range: 1.8485(16) Å (4A) to 1.8546(15) A (5A)) are significantly shorter compared to the M–Nalkyl ones, although for 6A and the CuII-containing complex fragments 7A–9A this difference is not significant. The M–Naryl bond lengths of 7A–9A (range: 1.934(6) Å (9A) to 1.967(7) Å (9A) exceed those of 4A–6A (range: 1.8485(16) Å (4A) to 1.879(7) Å (6A)) dramatically, whereas a comparison of the M–Nalkyl bond lengths reveals minor differences only, cf. Table 1. Such differences have been observed for pairs of NiII/CuII-containing related type IV complexes as well and could be explained by the shorter ion radii of NiII (63 pm) compared to that of CuII (71 pm) in quadratic planar coordination environments.15
The molecular structures of the dicationic complex fragments [Cu3(opboR2)(pmdta)2]2+ of 10′ and 12′ (denoted in the following as 10A and 12A) are displayed in Fig. 3. Selected bond lengths and angles of the [Cu(opboR2)]2− and [Cu(pmdta)]2+ fragments of 10A and 12A are given in Tables 1 and 2, respectively. As described in the Experimental part, the trinuclear and dicationic complex fragment 10A has been refined as a whole disordered at two positions. Thus, the fragment with the major occupation factor is referred to as 10A, and the other as 10B. In the following we will describe 10A only, although Tables 1 and 2 refer to data of both 10A and 10B. In Table 4 selected crystallographic and structural refinement data of 10′ and 12′ have been summarized.
10A/10B | 12A | |
---|---|---|
a The averaged <τ> parameter refers to the combination of 10A/10B. | ||
Bond lengths | ||
Cu2–O1 | 1.946(16)/1.97(3) | 2.174(8) |
Cu2–O2 | 2.030(10)/2.31(3) | 1.982(9) |
Cu2–N5 | 2.046(8)/2.06(3) | 2.032(10) |
Cu2–N6 | 2.031(8)/2.007(19) | 2.004(10) |
Cu2–N7 | 2.195(6)/2.076(10) | 2.056(10) |
Cu3–O3 | 2.043(12)/2.02(3) | 2.179(8) |
Cu3–O4 | 1.957(14)/2.15(4) | 1.987(8) |
Cu3–N8 | 1.992(9)/2.208(16) | 2.058(10) |
Cu3–N9 | 2.050(7)/2.05(2) | 1.994(11) |
Cu3–N10 | 2.209(8)/1.963(13) | 2.077(11) |
Bond angles | ||
O1–Cu2–O2 | 83.3(4)/77.7(8) | 81.3(3) |
O1–Cu2–N5 | 140.6(7)/126.2(12) | 107.8(4) |
O1–Cu2–N6 | 99.6(4)/113.9(9) | 103.1(4) |
O1–Cu2–N7 | 97.9(6)/109.8(7) | 98.9(4) |
O2–Cu2–N5 | 88.0(4)/82.2(12) | 92.8(4) |
O2–Cu2–N6 | 173.7(4)/166.8(11) | 175.6(4) |
O2–Cu2–N7 | 98.4(3)/93.8(10) | 93.2(4) |
N5–Cu2–N6 | 86.2(4)/85.8(12) | 85.8(4) |
N5–Cu2–N7 | 121.5(3)/121.0(10) | 153.2(4) |
N6–Cu2–N7 | 86.8(3)/87.9(7) | 86.2(4) |
O3–Cu3–O4 | 86.5(7)/72.0(17) | 80.7(3) |
O3–Cu3–N8 | 127.8(7)/132.1(13) | 106.8(4) |
O3–Cu3–N9 | 99.4(7)/101.3(11) | 102.5(4) |
O3–Cu3–N10 | 105.7(6)/98.5(9) | 98.7(4) |
O4–Cu3–N8 | 89.8(4)/86.5(18) | 92.3(4) |
O4–Cu3–N9 | 173.9(5)/159.0(15) | 176.8(4) |
O4–Cu3–N10 | 92.4(5)/108.3(12) | 93.0(4) |
N8–Cu3–N9 | 88.1(4)/83.7(12) | 86.7(4) |
N8–Cu3–N10 | 126.5(4)/129.1(9) | 154.4(4) |
N9–Cu3–N10 | 84.2(3)/92.2(8) | 86.6(4) |
<τ> parameter | ||
0.644a | 0.373 |
4 | 5′ | 6 | 7 | 8′ | 9 | |
---|---|---|---|---|---|---|
a R int = ∑|Fo2 − Fo2(mean)|/∑Fo2, where Fo2(mean) is the average intensity of symmetry equivalent diffractions. b S = [∑w(Fo2 − Fc2)2]/(n − p)1/2, where n = number of reflections, p = number of parameters. c R = [∑(||Fo| − |Fc|)/∑|Fo|]; wR = [∑(w(Fo2 − Fc2)2)/∑(wFo4)]1/2. | ||||||
Chemical formula | C44H82N6NiO4 | C46H90N6NiO6 | C48H90N6NiO4 | C44H82CuN6O4 | C46H90CuN6O6 | C48H90CuN6O4 |
Formula weight (g mol−1) | 817.87 | 881.95 | 873.95 | 822.70 | 886.78 | 878.80 |
Crystal system | Triclinic | Monoclinic | Monoclinic | Triclinic | Monoclinic | Monoclinic |
Space group |
P![]() |
C2/c | P2(1) |
P![]() |
C2/c | P2(1)/c |
Unit cell dimensions (Å, °) | a = 10.7141(4) | 24.3834(7) | 13.5126(5) | 10.583(13) | 24.396(5) | 13.4875(6) |
b = 14.4059(5) | 13.4528(3) | 14.7246(4) | 14.534(3) | 13.432(3) | 14.6748(7) | |
c = 15.4535(6) | 15.9421(4) | 25.4056(7) | 15.609(15) | 15.919(3) | 25.6140(12) | |
α = 99.540(3) | 90 | 90 | 98.444(11) | 90.0 | 90 | |
β = 90.910(3) | 110.328(3) | 95.567(3) | 91.564(9) | 109.80(3) | 95.346(4) | |
γ = 102.522(3) | 90 | 90 | 102.014(12) | 90.0 | 90 | |
Volume (Å3) | 2292.92(15) | 4903.7(2) | 5031.0(3) | 2318.8(5) | 4908.4(19) | 5047.6(4) |
Measurement temperature (K) | 110 | 110 | 110 | 100 | 100 | 100 |
Radiation source | Cu Kα | Mo Kα | Cu Kα | Cu Kα | Mo Kα | Cu Kα |
Wavelengths (Å) | 1.54184 | 0.71073 | 1.54184 | 1.54184 | 0.71073 | 1.54184 |
Z | 2 | 4 | 4 | 2 | 4 | 4 |
Density (calculated) (Mg m−3) | 1.185 | 1.195 | 1.154 | 1.178 | 1.200 | 1.156 |
Absorption coefficient (mm−1) | 0.962 | 0.446 | 0.905 | 1.012 | 0.495 | 0.959 |
F(000) | 896 | 1936 | 1920 | 898 | 1940 | 1924 |
Reflections collected | 14![]() |
10![]() |
25![]() |
17![]() |
21![]() |
14![]() |
Independent reflections/Rinta | 7226, 0.0212 | 4298, 0.0232 | 14![]() |
6824, 0.0325 | 4293, 0.0225 | 7383, 0.0278 |
Index ranges | −10 ≤ h ≤ 12, | −28 ≤ h ≤ 22, | −12 ≤ h ≤ 15, | −11 ≤ h ≤ 11, | −28 ≤ h ≤ 28, | −15 ≤ h ≤ 10, |
−16 ≤ k ≤ 16, | −15 ≤ k ≤ 15, | −16 ≤ k ≤ 16, | −16 ≤ k ≤ 16, | −15 ≤ k ≤ 15, | −16 ≤ k ≤ 16, | |
−16 ≤ l ≤ 17 | −18 ≤ l ≤ 16 | −25 ≤ l ≤ 29 | −17 ≤ l ≤ 17 | −18 ≤ l ≤ 18 | −28 ≤ l ≤ 25 | |
θ range for data collection (°) | 3.19 to 61.99 | 2.96 to 25.00 | 3.47 to 61.98 | 3.91 to 60.63 | 2.96 to 25.00 | 3.29 to 59.99 |
Data/restraints/parameters | 7226/0/496 | 4298/9/275 | 14![]() |
6824/0/496 | 4293/9/274 | 7383/804/715 |
Goodness-of-fit on F2![]() |
1.009 | 1.039 | 0.961 | 0.939 | 1.070 | 0.974 |
Final R indices [I > 2σ(I)]c | R 1 = 0.0423, wR2 = 0.1171 | R 1 = 0.0344, wR2 = 0.0927 | R 1 = 0.0991, wR2 = 0.2531 | R 1 = 0.0345, wR2 = 0.0850 | R 1 = 0.0368, wR2 = 0.0933 | R 1 = 0.0883, wR2 = 0.2625 |
R indices (all data)c | R 1 = 0.0492, wR2 = 0.1195 | R 1 = 0.0452, wR2 = 0.0950 | R 1 = 0.1361, wR2 = 0.2794 | R 1 = 0.0497, wR2 = 0.0892 | R 1 = 0.0463, wR2 = 0.1013 | R 1 = 0.1498, wR2 = 0.2980 |
Flack x parameter | — | — | 0.10(5) | — | — | — |
Largest diff. peak/hole (e Å−3) | 0.452, −0.398 | 0.710, −0.272 | 1.638, −0.301 | 0.226, −0.283 | 1.188, −0.376 | 0.320, −0.407 |
10′ | 12′ | |
---|---|---|
a R int = ∑|Fo2 − Fo2(mean)|/∑Fo2, where Fo2(mean) is the average intensity of symmetry equivalent diffractions. b S = [∑w(Fo2 − Fc2)2]/(n − p)1/2, where n = number of reflections, p = number of parameters. c R = [∑(||Fo| − |Fc|)/∑|Fo|]; wR = [∑(w(Fo2 − Fc2)2)/∑(wFo4)]1/2. | ||
Chemical formula | C78H96B2Cu3N10O4 | C150H290Cl4Cu12N48O43 |
Formula weight (g mol−1) | 1449.89 | 4358.56 |
Crystal system | Triclinic | Monoclinic |
Space group |
P![]() |
P2(1)/c |
Unit cell dimensions (Å, °) | a = 13.7472(5) | 16.1788(11) |
b = 14.0699(5) | 29.4708(15) | |
c = 19.3586(8) | 11.2788(7) | |
α = 103.343(3) | 90.0 | |
β = 100.238(3) | 91.797(7) | |
γ = 91.599(3) | 90.0 | |
Volume (Å3) | 3576.0(2) | 5375.1(6) |
Measurement temperature (K) | 100 | 100 |
Radiation source | Cu Kα | Cu Kα |
Wavelengths (Å) | 1.54184 | 1.54184 |
Z | 2 | 2 |
Density (calculated) (Mg m−3) | 1.347 | 1.346 |
Absorption coefficient (mm−1) | 1.483 | 2.338 |
F(000) | 1526 | 2286 |
Reflections collected | 21![]() |
21![]() |
Independent reflections/Rint![]() |
11034, 0.0370 | 11546, 0.1117 |
Index ranges | −14 ≤ h ≤ 14, | −18 ≤ h ≤ 18, |
−16 ≤ k ≤ 16, | −33 ≤ l ≤ 34, | |
−22 ≤ l ≤ 16 | −13 ≤ k ≤ 13 | |
θ range for data collection (°) | 3.24 to 62.00 | 4.059 to 63.50 |
Data/restraints/parameters | 11![]() |
11![]() |
Goodness-of-fit on F2![]() |
1.039 | 0.939 |
Final R indices [I > 2σ(I)]c | R 1 = 0.0987, wR2 = 0.2442 | R 1 = 0.0994, wR2 = 0.2628 |
R indices (all data)c | R 1 = 0.1043, wR2 = 0.2479 | R 1 = 0.1419, wR2 = 0.2894 |
Largest diff. peak/hole (eÅ−3) | 0.713, −0.656 | 1.564, −0.703 |
The central CuII ions of 10A and 12A are all coordinated by four deprotonated amide N donor atoms to form CuN4 coordination units. The CuN4 units can be regarded as planar-quadratic, as calculations of mean planes of the N1–N4 atoms give the rmsd/hdp values as follows: 10A/12A (rmsd, hdp) = 0.0005 Å, N1 with 0.0005(4) Å/0.004 Å/N1 with 0.086(7) Å, respectively, with the Cu1 atoms placed nearly in the plane of the calculated N4 mean planes (10A: 0.007(3) Å. 12A: 0.008(7) Å). Additionally, the sum of bond angles of the CuN4 units amounts to 360.0(6)° (10A) and 360.4(10)° (12A), which indicates the CuN4 units to be planar.
As observed and discussed for 4A–9A, three bond angles of the CuN4 units are rather small; whereas the fourth one is substantially larger as described for 7A–9A, cf. above. This difference is not significant for 10A and 12A, cf. Table 1.
The central CuN4 units of 10A and 12A are obviously planar, although only the {Cu3(opbo)} fragment of 10A is planar in contrast to 12A, cf. Fig. 3. The deviation from planarity of the {Cu3(opbo)} fragment of 12A is not induced by the coordination of either counter anions and/or solvent molecules to the central Cu1 atoms. Indeed, for solvent free 10′ any coordination of the [BPh4]− anions is certainly not expected. Even in the case of 12′ no coordination of any species to the central Cu1 atoms is observed. It should be mentioned additionally that in the crystal structures of 10′ and 12′ no further intermolecular interactions are observed.
The terminal CuII ions of 10A and 12A are each coordinated by two O donor atoms of the respective oxamidato group as well as the three N donor atoms of the pmdta ligands, forming thus CuN3O2 coordination units. The geometries of these units are, with respect to their averaged τ parameters <τ>,16cf. Table 2, closer to the ideal trigonal-bipyramidal (10A) or to the ideal square-pyramidal coordination geometry (12A).
A further feature of these CuN3O2 coordination units needs to be discussed. For the related type VIII complex 148a it is observed that the largest bond angle of the CuN3O2 unit at the “oxamidato side” involves the O donor atom of the O⋯C⋯Nalkyl function and the middle N donor atom of the pmdta ligands. For the related CuN3O2 unit at the “oxamato side” the situation is different. Here, the largest bond angle involves the O donor atom of the O⋯C⋯Naryl function. This specific feature is furthermore usually observed for type VII complexes, as already explained along with the structural discussion of 14.8a For 10A and 12A it is then exclusively observed that the largest bond angles of the terminal CuN3O2 units involve the O donor atom of the O⋯C⋯Nalkyl function and the middle N donor atom of the pmdta ligands, cf. Fig. 3 and Table 2.
In summary it can be ruled out that a replacement of the two O donor atoms involved in the coordination of the central CuII ions of type VII complexes by N(R) donor atoms to give the corresponding type IX complexes leads to such trinuclear{Cu3(opbo)} fragments of which the central CuII ions are not coordinated by further co-ligands. Furthermore, this replacement rearranges the geometries of the terminal CuN3O2 units. Both observations compare well with the related type VIII complex 14,8a although certainly additional work is required to figure out if they are universally valid.
![]() | (1) |
Here, the first term represents the Zeeman interaction of an electron spin S with the external magnetic field B0, whereas g and μB stand for the g-tensor and Bohr magneton, respectively. The HF interaction between the electron spin S of CuII and the 63Cu, 65Cu and 14N nuclear spins ICu and IN is described by the second and the third term, respectively. Here, ACu and AN are the respective HF coupling tensors. Finally, Hi accounts for the nuclear Zeeman, hyperfine, and nuclear quadrupole interactions of further surrounding nuclei, such as, e.g., protons.
The isotropic ESR parameters of 8 and 9 were obtained from measurements of 1 mM acetone solutions. In Fig. 4 their ESR spectra are displayed together with the performed simulations. The ESR spectra of both 8 and 9 appear rather similar. Both spectra consist of four lines due to the onsite HF coupling of the electron spin of CuIIS = 1/2 to its own nuclear spin I (63,65Cu) = 3/2. From the modelling of the spectra, cf. Fig. 4, the isotropic g-factor, the 63Cu–HF coupling constants and the 14N–HF coupling constants were obtained, respectively. Experimentally determined isotropic ESR parameters are listed in Table 5. We note that in this work in the model calculations of ESR spectra based on the Hamiltonian (1) we took into account only the HF interaction of the electron spin of copper with the spins of the nitrogen nuclei and neglect much weaker interactions with more distant nuclei (the last term in (1)).
![]() | ||
Fig. 4 Experimental (E) and simulation (S) X-band ESR spectrum of 8 (up) and 9 (bottom) in acetone at f = 9.8 GHz (X-band) at room temperature. |
Complex | g ⊥ | g ∥ | g iso | A Cu⊥ | A Cu∥ | A Cuiso | A N⊥ | A N∥ | A Niso |
---|---|---|---|---|---|---|---|---|---|
8 | 2.036 | 2.162 | 2.082 | 43.4 | 611 | 225.8 | 36.9 | 50.2 | 40.8 |
9 | 2.04 | 2.159 | 2.086 | 54.9 | 622.5 | 237.9 | 37.6 | 48.8 | 40.9 |
In order to obtain anisotropic ESR parameters, the angular dependence of the ESR spectra of a single crystal of 9@6 at f = 9.56 GHz at room temperature was measured by rotation of the magnetic field B0 in the plane perpendicular to the molecular plane. For a single crystal of 8@5, the extreme orientations of the spectrum corresponding to the principal axes of the g- and HF-tensors were determined by measuring the angular dependence of the g-factor by rotating around an arbitrary axis and searching the direction of B0 for the minimum g-factor. This direction was chosen as a new axis about which the angular dependence of the g-factor and HF-coupling constants was measured. Finally, to check the correctness of the procedure, the direction of the maximum g-factor was chosen as the rotation axis and indeed no angular dependence is found. In this experiment the spectra were recorded with a rotation interval of 15°. Representative ESR spectra of a single crystal of 8@5 and 9@6, respectively, together with their simulation, are shown in Fig. 5.
![]() | ||
Fig. 5 Experimental (E) and simulation (S) X-band ESR spectrum of a single crystal of 8@5 (left) and 9@6 (right) at f = 9.56 GHz (X-band) at room temperature. The magnetic field is oriented parallel to the symmetry axis of the CuN4 unit, cf. Fig. 6. |
Both spectra consist of two quartet groups of lines owing to the HF-coupling with the 63,65Cu nuclear spin I (63,65Cu) = 3/2. Each group further represents a subset of lines. They arise due to transferred HF-coupling with the 14N nuclear spins I (14N) = 1 of the four N donor atoms which can be, cf. Fig. 6, classified into two equivalent groups. When the magnetic field is parallel to the normal of the molecular plane n (B0∥n), the largest g value and the largest copper HF constant are obtained. The smallest g value is obtained when the magnetic field lies in the molecular plane (B0⊥n). For this field geometry the line groups overlap because of the small 63,65Cu–HF coupling constant ACu⊥ in this direction. Therefore the extraction of the coupling parameters becomes very difficult.
![]() | ||
Fig. 6 Left: chemical structure of the studied complexes. Right: scheme of the principal axes of the Cu and N hyperfine tensors of the CuN4 unit. |
Owing to the above described difficulties, the values of ACu⊥ and AN∥ were estimated with the aid of the isotropic values using the relation Aiso = (2A⊥ + A∥)/3. For the investigated complexes, the following assumptions are taken:
gx = gy = g⊥, gz = g∥, Ax = Ay = A⊥ < Az = A∥ | (2) |
Principal values of g, ACu and AN of 8 and 9 obtained from modeling of the ESR spectra are listed in Table 5. In general, differences between values reported in Table 5 are not significant; the largest principal values for ACu were obtained for 9.
The principal axes of g and ACu coincide with their maximum components located perpendicular to the molecular plane. The maximum components of the 14N hyperfine tensors were found to lie parallel to the Cu–N bond vectors as sketched in Fig. 6. The principal values of g, ACu, and AN obtained from the ENDOR measurements are shown in Table 6. They agree reasonably well with the ESR data, cf. Table 5. Note that, unlike in the ESR experiment, the better resolution of the ENDOR method enables, with the help of the modeling of the spectra on the basis of (1) and (2), to estimate all four nitrogen HF tensors. They are presented in Table 6 and labeled as A, B, C and D. In agreement with the ESR results, AN⊥|<|AN∥ has been found for all four tensors. With the parameters listed in Table 6, satisfactory agreement with experimental ENDOR spectra has been achieved. Most optimal fits were obtained close to the orientation of the magnetic field parallel to the normal to the molecular plane, which is due to a better S/N ratio for this field geometry. Considering the data in Table 6, the nitrogen HF tensors can be grouped in pairs A–B and C–D with quite close values of the tensor components in each group, respectively. However, the ENDOR measurements indicate some differences in the HF parameters within each group, which is not evident in the static ESR data. The difference of the HF parameters between the two groups is substantial. The larger values of the HF constants of the group A–B enable to tentatively assign them to the N1 labeled Naryl donor atoms, cf. Fig. 6, since these values are closer to those of related type IV CuII-containing bis(oxamato) complexes comprising only two Naryl donor atoms.10 The smaller HF constants in the group C–D can then be associated with the N2 labeled Nalkyl donor atoms, cf. Fig. 6.
g ⊥ | g ∥ | A Cu⊥ | A Cu∥ |
---|---|---|---|
2.016 | 2.144 | 49 | 639 |
A | B | C | D | |
---|---|---|---|---|
A N∥ | 51.2 | 51.8 | 42.2 | 41.6 |
A N⊥ | 40.4 | 42.6 | 36.6 | 30.8 |
![]() | (3) |
![]() | (4) |
In these expressions Pκ is the Fermi contact term with P(63Cu) = μBgeμngn × 〈r−3〉 = 1164 MHz, that is, the dipolar HF coupling parameter of the unpaired electron,19 and Δg∥,⊥ = g∥,⊥ −2.0023. The parameter α2 is a covalency parameter, which describes the in plane metal–ligand σ bonding. The value of α2 can be determined by using eqn (3) and (4), cf. above, and the experimental Cu–HF coupling constants. The following normalization condition was used to determine α′:
(α2 + α′2−2αα′S = 1) | (5) |
For the complexes under study, the α2 and (α′/2)2 values are given in Table 7. The values of α2 and (α′/2)2 represent then the spin density on the CuII ion (ρCu (total)) and on the N-donor atom (ρN(total)), respectively.
Furthermore, the values obtained for the spin density on the CuII ion were compared with those deduced by the procedure of Morton and Preston.18 This approach was also used to calculate the spin density on the N donor atoms. According to this approach, the spin density ρ(s) and ρ(p) on the s and p orbitals (d orbitals for Cu) are proportional to the isotropic or Fermi contact contribution Aiso and the dipolar HF coupling constant Adip = Aiso − A⊥, respectively. The proportionality constants for many abundant nuclei can be found in the literature.18 Spin densities calculated according to Morton and Preston18 are also reported in Table 7. A more detailed description of these two models can be found in our previous work and Table 7 refers then additionally to corresponding data obtained for 13 and [nBu4N]2[Cu(opba)] (15).8a,10 To make a direct comparison possible, the spin densities on the s orbital of the N donor atom of 13 and 15 are recalculated with the isotropic N HF coupling constant for unit spin density taken from ref. 18.
Very similar spin densities on the CuII ion and N donor atoms of 8 and 9 are obtained, cf. Table 7. As observed earlier for 138a and 15,10 the unpaired electron is mainly localized on the CuII ion in both 8 and 9. Additionally, the averaged spin density on one individual N donor atom of 8 and 9 compares with that for 138a and 15.10 However, experimentally obtained data reported here for 8 and 9 do not follow the expected tendency that a replacement of O versus N donor atoms results in a lower spin density on CuII and higher spin densities on the N donor atoms9 when compared with 138a and 15,10vide infra.
Furthermore, since ENDOR measurements on 8@5 have enabled to resolve individual HF tensors A–D of the N donor atoms, the spin density on them was estimated according to the approach by Morton and Preston.18 The respective values are listed in Table 8.
A | B | C | D | ||||||||
---|---|---|---|---|---|---|---|---|---|---|---|
ρ(s) | ρ(p) | ρ(total) | ρ(s) | ρ(p) | ρ(total) | ρ(s) | ρ(p) | ρ(total) | ρ(s) | ρ(p) | ρ(total) |
2.43 | 6.48 | 8.91 | 2.52 | 5.58 | 8.1 | 2.12 | 3.42 | 5.54 | 1.9 | 6.48 | 8.38 |
One might expect the larger HF parameters of tensors A–B as compared with C–D to be reflected in larger spin densities ρ. This expectation is only partially met, since the value of ρ(total) for D appears to be the same as that for A–B. Most likely this is related to a limited accuracy of the ENDOR experiment for the field direction close to the molecular plane, which has led to an overestimate of the anisotropy (A∥ − A⊥) of tensor D and consequently to an overestimate of the partial spin density on the p orbital ρ(p). To remind, in the model of Morton and Preston,18ρ(p) is directly proportional to (A∥ − A⊥). Remarkably, the partial spin density on the s orbital ρ(s), which is determined by the isotropic part of the HF coupling Aiso = (A∥ + 2A⊥)/3, is similar for C and D and both are smaller compared to A and B, as expected.
Generally, the spin density on each N-donor atom, as estimated from ESR and ENDOR data, is smaller than those obtained from DFT calculations. However, an inequality of the HF tensors obtained from the ENDOR measurement is compatible with the DFT calculation data based on the structural data from crystallographic characterization and yield different spin densities on all four N-donor atoms, cf. below. Apparently, the different spin densities on the N atoms reflect their different local geometries, as revealed by different HF tensors.
![]() | (6) |
Here J12 and J13 denote the exchange integrals between the central and the terminal CuII spins and the first term stands for the Zeeman interaction. The values of J23 (the exchange integral between the two terminal CuII ions) in all investigated complexes were assumed to be negligibly small due to the large distance between the Cu2 and Cu3 atoms, cf. Fig. 3, and the large number of orbitals involved in the corresponding superexchange interaction between them. The analysis yields the best possible fit with the values J12 = J13 as shown in Fig. 8.
The J values of the type IV complexes 10–12 are with −96 to −132 cm−1, cf. Fig. 8, comparable with and even slightly larger in magnitude than J values of related type VII complexes such as, for example, those of 16/17 (−89 cm−1/−111 cm−1)11,12 and those of 14 (−130 cm−1),8b a type VIII complex. According to Kahn9 and others,22,23 a substitution of electronegative oxygen atoms vs. less electronegative nitrogen atoms should result in increased J couplings, the question arises whether the, in magnitude, somewhat larger J values reported here for the type IV complexes 10–12 as compared with the related type VII complexes are due to this mechanism. We will continue this discussion after displaying next the results obtained from accompanying DFT studies.
Second, the spin density distributions of 7A–9A and 7Acalc–9Acalc were calculated and the obtained values are given in Fig. 9. It has to be noticed that related N donor atoms of 7A, 8A and/or 9A do not have identical spin populations. For example, for the Naryl donor atoms of 7A, values of 14.7 and 14.0 were calculated as given in Fig. 9. Such differences are not observed for 7Acalc–9Acalc. The differences observed for 7A–9A are then attributed to distortions of the molecular geometries, as outlined above. Additionally, it has to be noticed that generally the spin population at the N donor atoms of 7A–9A is larger compared to related atoms of 7Acalc–9Acalc, whereas the spin population of the Cu atoms is smaller, cf. Fig. 9. That is most probably due to overemphasizing long Cu–N bond lengths of 7Acalc–9Acalc. Eventually, we do not aim to stress this point too much as corresponding data deviate by less than 10%. In the following we refer, however, to calculated data of 7Acalc–9Acalc only.
![]() | ||
Fig. 9 Selected values of the calculated and experimentally obtained spin population of 7A–9A together with corresponding values of 138a and 15.10 |
It is certainly of interest to compare the spin density distribution of 7A–9A with those already reported for 138a and 15,10 as done in Fig. 9. With respect to calculated values one can infer from Fig. 9 that the change of the CuN2O2 unit of 1510 by a CuN3O unit of 138a and finally by a CuN4 unit of 7A–9A results in a decrease of the remaining spin population at the Cu atoms (15: 55%, 13: 53.9, 7A–9A: 52.2% on average). This tendency could be expected, as according to Kahn the performed heteroatom substitution should result in a better overlap between the N donor atom orbitals to Cu compared to O donor atom orbitals.9 That tendency is, however, not reflected by a clear trend in the spin population at the donor atoms of the Cu atoms. For example, for 1510 a spin population at the Naryl donor atoms of 15% was calculated, whereas for the Naryl donor atoms of 7Acalc–9Acalc this value amounts to ca. 13.8%, cf. Fig. 9. Nevertheless, the described tendency for the spin population at the Cu atoms agrees with the expectation. In case there is an interplay between the spin density distribution of mononuclear complexes such as those in Fig. 9 and J values of their corresponding trinuclear complexes, this tendency would indicate higher J coupling for corresponding trinuclear complexes of 7A–9A compared to related complexes of 138a and 15.10
Finally, the calculated spin density distribution of 7A–9A should be compared with the estimates from the HF tensors. As reported before,8a the experimental approach according to Morton and Preston18 compares much better with calculated values than the Maki and McGarvey approach,17cf. Fig. 9. Certainly, the differences of the spin population at the Cu atoms of 8A/9A determined from the HF tensors and calculated values (exp. vs. calc. for 8A/9A = 57.1/57.5 vs. 52.2/52.0) are larger than the difference reported for 138a (51 vs. 53.9) and 1510 (54.6 vs. 55). This could be related to simplifications implicit in the experimental approaches17,18 which do not properly account for real local geometries of the complexes in question. In the approach of Maki and McGarvey,17 the anisotropic HF coupling constants are calculated for a square planar molecular geometry. In the approach of Morton and Preston,18 the HF coupling constants are calculated for a free atom. For both models, this sets a limitation for obtaining precise spin density values due to a deviation from the square planar geometry for the complexes under study. Nevertheless, they still remain reasonable qualitative approaches to obtain insight into the spin density distribution of CuII-containing type VI complexes. Furthermore, calculated spin densities of 8A/9A are different when compared to 8Acalc/9Acalc, cf. Fig. 9, due to different geometries. The geometry of 8A in 8@5 and of 9A in 9@6 cannot be determined, but it seems likely that both 8A and 9A do not have identical geometries inside the diamagnetic diluted materials as determined by their crystallographic characterization. Thus, the observed differences of the calculated spin density distribution of 7A–9A compared with those estimated from the HF tensors might be attributed to this effect as well.
Considering that the ESR spectra of type VI complexes reported here are much more complicated compared to type IV and type V complexes, the spin densities estimated from ESR and calculated spin density distribution reasonably complement each other. Moreover, the inequality of N donor atoms revealed for 8 in the ENDOR experiment, cf. above, is in good qualitative correspondence with the DFT results. Nevertheless, there remains the question whether the increase of the exchange interaction in type IX complexes compared to type VII complexes is related to a smaller electronegativity of N donor atoms. This will be briefly discussed next.
Unfortunately, 10 and 11 cannot be included in the following discussion. In the case of 10 this is due to the isolation as “[Cu3(opboMe2)(pmdta)2](NO3)2”, of which the magnetic properties were measured. As this material could not be characterized crystallographically, it was converted into “[Cu3(opboMe2)(pmdta)2](BPh4)2 (10′)” of which crystals were suitable for crystallographic studies. Compound 10′ displays then the same connectivity and coordination mode of the terminal Cu(pmdta) fragments as observed for 12. However, due to the use of BPh4− anions in the case of 10′ compared to NO3− anions in the case of 10, especially bond angles are expected to be modified by, for example, packing effects. Of 10′ itself, only very little quantities could be obtained. On the other hand, crystals of 11 were not suitable to determine the structure reliably, vide supra.
To identify the reason why the J values of type IX complexes exceed those of type VII complexes the following test should be instructive: supposing that the formerly established nearly linear relationship between J values and τ parameters of type VII complexes16,24 applies to corresponding type IX complexes as well, one could abstract the J value of 12 from Fig. 10 with −112 cm−1. From now on, we refer to that J value as Jabs. The experimentally determined J value of 12 with −132 cm−1 exceeds Jabs significantly. From this observation, one could already conclude that for the same τ parameter, J values of type IX complexes are larger when compared to type VII complexes, although the solid line in Fig. 10 displays an average estimate for type VII complexes. Additional support comes then from the calculated spin density distribution of especially 9A as the precursor of type IX12 compared to 1510 as the precursor of type VII16.11 Thereby, the Cu atom of 9Acalc exhibits a spin density of 52.0% compared to 55% calculated for 15.10 This striking difference could indeed be a consequence of the replacement of the O donor atoms of 15 by less electronegative N donor atoms in 9A, as proposed by Kahn.9
![]() | ||
Fig. 10 Representation of the experimentally determined J values of 16 (![]() ![]() ![]() |
Unfortunately, up to now, with 12 only one crystallographically characterized type IX complex can be described, the magnetic properties of which were determined. Due to this, it is not yet possible to conclude whether type IX complexes exhibit a related linear J versus τ dependence as observed for type VII complexes,16,24 keeping in mind that the bonding situation of the terminal CuN3O2 units is different. The different bonding situation of type IXversus type VII complexes might then have an impact on the magnetic superexchange coupling path, which cannot be ruled out here and points out that additional studies are required.
ESR studies of 8@5 and 9@6 allowed an estimation of the spin density distribution of 8A and 9A by two different approaches. Single crystal ENDOR measurements of 8@5 have enabled to resolve individual spin densities of the four N donor atoms of 8A as individual HF tensors could be observed. The spin densities estimated from HF tensors agree fairly when compared with quantum chemically calculated ones. Especially the inequality of the HF tensors obtained from the ENDOR measurement of 8@5 compares well with calculated spin densities of the N donor atoms of 8A in case that the crystallographically determined geometry of 8A is applied for calculation. These results proof at least that the spin densities of the two different types of N donor atoms of 8A/9A, namely the Naryl and Nalkyl type atoms, are significantly different.
From susceptibility measurements versus temperature, the J parameters of the trinuclear CuII-containing bis(oxamidato) complexes (type IX complexes) 10 (−96 cm−1), 11 (−104 cm−1) and 12 (−132 cm−1) have been determined. They appear larger in magnitude when compared to J values of reported type VII complexes.1 Our discussion of the spin density distribution favours the scenario that the enhancement of the exchange coupling J is related to the substitution of the O donor atoms in complexes of type VII by less electronegative N donor atoms in complexes of type IX. To this end, the present work supports earlier studies,8a,10 in which an interplay between the spin density distribution of mononuclear type IV and VI complexes and magnetic superexchange interactions of trinuclear complexes derived out of them had been proposed.
4. Yield: 1.32 g (81%). Anal. calcd (%) for 4 (C44H82N6NiO4, 817.85 g mol−1): C 64.62, H 10.11, N 10.28; found: C 64.02, H 10.59, N 9.88. IR: ν = 2959(m), 2870(m) (CH); 1622(s), 1589(s), 1576(s) (CO). 1H NMR: δ = 0.94 (t, 24H, Ha), 1.36 (m, 16H, Hb), 1.57 (m, 16H, Hc), 2.39 (s, 6H, H1,1′), 3.15 (t, 16H, Hd), 6.43 (dd, 2H, H6,6′), 7.95 (dd, 1H, H5,5′).
5. Yield: 1.25 g (74%). Anal. calcd (%) for 5 (C46H86N6NiO4, 845.91 g mol−1): C 65.31, H 10.25, N 9.93; found: C 64.96, H 10.40, N 9.90. IR: ν = 2958(m), 2872(m) (CH); 1619(s), 1587(m), 1572(s) (CO). 1H NMR: δ = 0.87 (t, 6H, H1,1′), 0.94 (t, 24H, Ha), 1.31 (m, 16H, Hb), 1.57 (m, 16H, Hc), 2.66 (q, 4H, H2,2′), 3.17 (t, 16H, Hc), 6.41 (dd, 2H, H7,7′), 7.97 (dd, 2H, H6,6′).
6. Yield: 1.53 g (88%). Anal. calcd (%) for 6 (C48H90N6NiO4, 873.96 g mol−1): C 65.97, H 10.38, N 9.62; found: C 65.22, H 10.50, N 9.79. IR: ν = 2961(m), 2870(m) (CH); 1618(s), 1584(s), 1570(s) (CO). 1H NMR: δ = 0.77 (t, 6H, H1,1′), 0.95 (t, 24H, Ha), 1.32 (m, 20H, H2,2′,b), 1.58 (m, 16H, Hc), 2.55 (m, 10H, H3,3′,DMSO), 3.17 (t, 16H, Hd), 6.41 (dd, 2H, H8,8′), 7.97 (dd, 1H, H7,7′).
7. Yield: 1.26 g (78%). Anal. Calcd (%) for 7 (C44H82CuN6O4, 822.71 g mol−1): C 64.24, H 10.05, N 10.22; found: C 64.11, H 9.97, N 10.13. IR: ν = 2960(m), 2881(m) (CH); 1616(s), 1587(s), 1568(s) (CO).
8. Yield: 1.44 g (85%). Anal. Calcd (%) for 8 (C46H86CuN6O4, 849.60 g mol−1): C 65.94, H 10.19, N 9.88; found: C 65.96, H 10.21, 9.68. IR: ν = 2964(m), 2880(m) (CH); 1614(s), 1583(s), 1561(s) (CO).
9. Yield: 1.42 g (81%). Anal. Calcd (%) for 9 (C48H90CuN6O4, 877.63 g mol−1): C 65.60, H 10.32, N 9.56; found: C 65.21, H 10.05, N 9.29. IR: ν = 2963(m), 2890(m) (CH); 1612(s), 1581(s), 1558(m) (CO).
Crystals obtained from slow diffusion of Et2O into CH2Cl2 solutions of 10 were of minor quality. Therefore, a metatheses reaction has been carried out. To a solution of 10 (0.0002 mol, 0.18 g) in MeOH (25 mL) was added a solution of NaBPh4 (0.0005 mol, 0.17 g) in MeOH (25 mL) in one portion with stirring. A pale green powder was precipitated immediately, which was filtered off, washed thoroughly with MeOH and Et2O and dried in vacuo. Slow diffusion of Et2O vapour in a solution of the obtained powder in MeCN–DMF (1:
1) mixture afforded single crystals of [Cu3(opboMe2)(pmdta)2](BPh4)2 (10′) suitable for X-ray crystallographic studies after three days. No further characterization of 10′ has been carried out.
Remark for the crystallization of 11: By allowing diffusion of Et2O into MeCN solutions of 11 well shaped single crystals have been obtained. However, these crystals were too weakly diffractive and/or display very diffuse diffraction at higher diffraction angles, independent whether classical sealed-tube or μF Cu Kα radiation was applied. Due to this, a reliable refinement of the structure of 11 in the solid state was not possible, even not by treating them as incommensurable modulated.31
Any trials to grow sufficiently large single crystals of 7@4 failed, although for both of the individual complexes 4 and 7 comparatively large single crystals could be obtained. The obtained needle-like single crystals of the cocrystallization of 7 and 4 were of dimensions of ca. 0.1 × 0.04 × 0.04 mm3 and were all orange coloured, which indicates that 7@4 was formed. Individual crystals were too small for an ESR characterization and a further characterization of them was not carried out.
In the case of 5′ and 8′ the positions of O-bonded hydrogen atoms were taken from the difference Fourier map and refined isotropically. Furthermore, for 5′ a comparatively large unrefined electron density peak is observed with ca. 0.7 e Å−3 at a distance of ca. 1.8 Å away from O3. This peak might indicate a disorder of the respective water molecule, although this disorder could not be refined reliably.
The absolute structure of 6 was established by anomalous dispersion effects with respect to the absolute structure parameter.30 Furthermore, the atoms C11, C13, C14 (0.84/0.16); the atoms C59, C60 (0.43/0.57); the atoms C69–C72 (0.34/0.66) and the atoms C73–C76 (0.72/0.28) are disordered and have been refined to split occupancies given in brackets. Although a number of atoms/groups could be refined disordered, trials to refine more atoms/groups as disordered did fail or gave non-reliable results. This is most probably due to the comparatively low number of observed vs. total reflections. The two highest unrefined electron density peaks Q1 (ca. 1.6 e Å−3) and Q2 (ca. 1.2 e Å−3) are located ca. 1.1 Å away from Ni2 and ca. 1.1 Å away from Ni1, respectively.
In the case of 9 the atoms C11, C13, C14 (0.47/0.53); the atoms C17–C20 (0.17/0.83); the atoms C21–C24 (0.32/0.68); the atoms C25–C28 (0.24/0.76); the atoms C33–C36 (0.65/0.35) and the atoms C37–C40 (0.37/0.63) are disordered and have been refined to split occupancies given in brackets. Several atoms here do have too large ADP max/min ratios or large Hirshfeld test differences and high Ueq values, respectively, when compared to neighbours. Furthermore, short intra and/or inter H⋯H contacts are observed. Most probably, all of these observations are due to further, but not reliable resolvable, disorder of atoms/groups. Additionally, the best suitable single crystal of 9 was, due to its plate-like shape, weakly diffractive only. Although long measurement times of individual frames have been applied by using Cu Kα radiation, the ratio between observed/unique reflections is with ca. 45% still poor. Due to icing problems, the measurement has been stopped at a resolution of θ = ca. 60°. These reasons might explain why further models of disorder could not be introduced.
Data of 4, 5′, 6, 7, 8′ and 9 have been deposited at the Cambridge Crystallographic Data Centre under CCDC deposition numbers CCDC 1035427–1035432, respectively.
In the case of 12′ the crystals were twinned. By applying CrysAlisPro version 1.171.37.3128b four different domains were applied for data integration. No further domains could be observed, whereby for domains I to IV the ratios 0.36, 0.32, 0.15 and 0.17, respectively, were finally determined. The SHELXL-2013 software29b was used for refinement and the command RIGU was applied. The two nitrate anions could be refined disordered over two positions (N11, O5–O7 (0.78/0.22), and N12, O8–O10 (0.34/0.66)). In addition, the atoms C11–C13 of one nPr group could be refined disordered with occupations of 0.40/0.60. Furthermore, in the VOIDS one Et2O and one CH2Cl2 molecule could be refined with occupation factors of 0.75 and 0.5, respectively. Thereby, the Et2O molecule was refined disordered over two positions with occupation factors for O11, C36–C39 of 0.52/0.48.
Data of 10′ and 12′ have been deposited at the Cambridge Crystallographic Data Centre under CCDC deposition numbers CCDC 1035433 and 1035435, respectively.
Electron Nuclear Double Resonance (ENDOR) experiments were performed with an X-band ESR spectrometer Elexsys E580 (Bruker) at a temperature of 20 K. A standard Davies ENDOR pulse sequence has been used: πmw–πrf–π/2mw–πmw–echo.32b In this pulse protocol the amplitude of the stimulated electron spin echo arising after the application of the microwave (mw) pulses πmw–π/2mw–πmw–echo is recorded as a function of the frequency of the intervening radiofrequency (rf) pulse in the MHz range. To obtain the optimal rf π-pulse length (πrf) the nutation experiments were performed. For all measurements the lengths of the inversion pulse πmw, radiofrequency pulse πrf and detection pulses π/2mw(πmw) were set to 400 ns, 7 μs and 16 ns (32 ns), respectively. Simulations of the ENDOR spectra were performed using the EasySpin (version 4.0.0)32c program of the Matlab 2007a package.
Footnote |
† Electronic supplementary information (ESI) available. CCDC 1035427–1035433, 1035435. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c4dt03579h |
This journal is © The Royal Society of Chemistry 2015 |