Ivan
Nemec
,
Radovan
Herchel
and
Zdeněk
Trávníček
*
Regional Centre of Advanced Technologies and Materials, Department of Inorganic Chemistry, Faculty of Science, Palacký University, Tř. 17. listopadu 12, CZ-77146 Olomouc, Czech Republic. E-mail: zdenek.travnicek@upol.cz
First published on 19th January 2015
X-ray crystal structures and magnetic properties of an isostructural series of iron(III) Schiff base complexes with the general formula [Fe(L5)(NCX)]·Solv (where H2L5 = N,N′-bis(2-hydroxy-naphthylidene)-1,6-diamino-4-azahexane, X = S, Solv = tetrahydrofuran, 1a; X = S, Solv = methanol and 0.5 pyrazine, 1b; X = S, Solv = butanone, 1c; Solv = N,N′-dimethylformamide, X = S (1d) or X = Se (1d′); X = S, Solv = dimethyl sulfoxide, 1e) are reported. In the crystals, the individual [Fe(L5)(NCX)] molecules are connected through weak C–H⋯O, C–H⋯π or C–H⋯S non-covalent contacts into 2D supramolecular networks, while the guest-solvent (Solv) molecules are trapped in the cavities between two adjacent layers, which are furthermore stabilized by N–H⋯O hydrogen bonds connecting the Solv oxygen atom with the amine group of the [Fe(L5)(NCX)] molecule, with the N⋯O distances varying from 2.921(6) Å (in 1d′) to 3.295(2) Å (in 1a). The magnetic properties of the complexes were tuned by the different Solv molecules and as a result of this, four new spin crossover (SCO) compounds with cooperative spin transitions are reported, which are accompanied by thermal hysteresis in two cases (1d and 1e): 1c, T1/2 = 84 K; 1d, T1/2↓ = 232 K, T1/2↑ = 235 K and 1e, T1/2↓ = 127 K, T1/2↑ = 138 K. The role of the N–H⋯O hydrogen bonding in the occurrence and tuning of SCO was also computationally studied using a topological analysis, and also by evaluation of non-covalent interaction (NCI) indexes. Both theoretical approaches showed a clear relationship between the strength of the N–H⋯O hydrogen bonds and T1/2, as already inferred from X-ray structural and magnetic data.
In general, the role of solvent molecules of crystallization (Solv) in the SCO process is still not clear, because there are several contrasting examples describing the influence of solvents. The presence of the guest molecules in the crystal lattice of the SCO compounds can dramatically affect their magnetic behaviour5 by changing the cooperative interactions with respect to the parent compound and therefore the lattice phonon distribution is affected.2 It can be also rationalized that non-covalent interactions, such as hydrogen bonds, may cause a charge redistribution on the ligands and consequently, a change in the ligand field strength can occur.6 The stabilization of the LS state is usually observed for the solvated samples and there are many examples of a downward shift of T1/2 (or just occurrence of SCO in the formerly LS-only solvated compounds) upon desolvation of the sample.7
In accord with these observations, the solvation of a sample usually tends to increase T1/2. Alternatively, upon guest molecule exchange, the variation in T1/2 and in steepness of the transition is observed, as has been reported recently in the remarkable single-crystal-to-single-crystal transformation studies.8 Rational tuning of the SCO behaviour by the lattice solvent exchange was reported first for the nanoporous metal–organic frameworks (MOFs) built by [Fe2(azpy)(NCS)4] molecules (azpy = trans-4,4′-azopyridine) in 2002 by Kepert et al.,9 and then, other similar studies have followed.10 The vapour and gas adsorption studies on {[Fe(PYZ)Ni(CN)4]} Hoffmann-type metal–organic frameworks (MOFs) revealed the relationship between the guest size and T1/2 (PYZ = pyrazine),11 and similar relationships were reported also for 0D supramolecular systems such as [Fe(4ditz)3](PF6)2·Solv (4ditz = 1,4-bis(tetrazole-1-yl)butane, Solv = CH3OH, CH3CH2OH) or [Fe(bdpt)2]·Solv (Hbdpt = 3-(5-bromo-2-pyridyl)-5-(4-pyridyl)-1,2,4-triazole), Solv = CH3OH, CH3CH2OH).12 Another possible Solv–SCO relationship was found in MOFs such as [Fe(bpbd)2(NCS)2]·Solv (bppd = 2,3-bis(4′-pyridyl)-2,3-butanediol, Solv = CH3CN, CH3OH, CH3CH2OH, CH3CH2OH (CH3)2CO), and it was shown that lower values of the Solv dielectric constants (εr) result in the LS state being more stabilized.13 The solvent–SCO relationship was documented also for Fe(III) SCO compounds several times but the systematic study is still missing.14
Recently, we have reported on the SCO phenomenon observed in a series of [Fe(L5)(L1)]·Solv compounds (Scheme 1, H2L5 = N,N′-bis(2-hydroxy-naphthylidene)-1,6-diamino-4-azahexane, L1 stands for pseudohalide ligands).15 The thiocyanate and selenocyanate complexes from the mentioned series, [Fe(L5)(NCX)]·CH3CN and [Fe(L5)(NCS)]·(CH3)2CO (X = S, Se), exhibited magnetic behaviour dependent on the presence of a solvent molecule incorporated into the crystal structure: the acetonitrile solvate showed SCO while the latter compound stayed in the HS state down to 2 K. In both cases, the solvent molecule is connected with the donor nitrogen amine atom from the L5 ligand via a hydrogen bond (the nitrogen/oxygen atom from the Solv molecules serves as an acceptor). In order to explore the influence of the co-crystallized Solv molecules on SCO in greater detail, we decided to investigate the properties of the aforementioned system utilizing various Solv molecules. In this work, we report on the crystal structures and magnetic properties of an isostructural (for bond lengths and selected structural parameters see Table 1, for crystallographic data see Table 2) series of [Fe(L5)(NCX)]·Solv complexes, where X = S, Solv = tetrahydrofuran (THF) (1a); X = S, Solv = methanol (MeOH) and 0.5 pyrazine (PYZ) (1b); X = S, Solv = butanone (MEK) (1c); X = S, Solv = N,N′-dimethylformamide (DMF) (1d); X = Se, Solv = DMF (1d′); X = S, Solv = dimethyl sulfoxide (DMSO) (1e). Moreover, previously published compounds 1f (X = S, Solv = 0.5 MeOH and 0.5 MEK) and 1g (X = S, Solv = acetone) were included in the discussion for comparative purposes.15,16 Apparently, the use of PYZ as a guest molecule deviates from the series because PYZ can potentially form a N–H⋯N hydrogen bond, while the other guests from the series are O-acceptors of hydrogen bonding. However, the use of this guest allowed us to study the influence of a methanol molecule on the magnetic behaviour of the [Fe(L5)(NCS)] molecule (vide infra), since the preparation of the pure methanol solvate is impossible by direct synthesis in methanol.17 The previously reported [Fe(L5)(NCX)]·CH3CN compounds were not included because they are not isostructural with compounds 1a–1g.
Fe–Nam | Fe–NNCX | Fe–Nima | Fe–Oa | α/° | Σ/° | |
---|---|---|---|---|---|---|
a The average values calculated from two bond lengths. | ||||||
1a | 2.2137(14) | 2.0849(15) | 2.082 | 1.939 | 84.5 | 59.3 |
1b | 2.209(2) | 2.085(2) | 2.080 | 1.945 | 85.8 | 61.5 |
1c | 2.1937(14) | 2.0908(16) | 2.069 | 1.942 | 84.7 | 56.8 |
1d 298 K | 2.183(3) | 2.086(3) | 2.068 | 1.941 | 82.5 | 58.8 |
1d 150 K | 2.0087(16) | 1.9447(17) | 1.925 | 1.884 | 84.6 | 25.5 |
1d′ 308 K | 2.173(3) | 2.096(4) | 2.064 | 1.935 | 82.0 | 56.6 |
1d′ 150 K | 2.003(4) | 1.942(4) | 1.927 | 1.884 | 83.3 | 25.3 |
1e | 2.185(2) | 2.077(2) | 2.077 | 1.940 | 87.5 | 56.1 |
1f Fe1 | 2.218(3) | 2.094(3) | 2.080 | 1.940 | 84.3 | 65.7 |
1f Fe2 | 2.210(3) | 2.082(3) | 2.078 | 1.944 | 81.0 | 56.6 |
1g | 2.205(2) | 2.088(2) | 2.077 | 1.941 | 83.2 | 60.0 |
1a | 1b | 1c | 1d 150 K | 1d 298 K | 1d′ 150 K | 1d′ 308 K | 1e | |
---|---|---|---|---|---|---|---|---|
a R 1 = ∑(|Fo|−|Fc|)/∑|Fo|. b wR2 = {∑[w(Fo2 − Fc2)2]/∑[w(Fo2)2]}1/2. | ||||||||
Formula | C32H33Fe1N4O3S1 | C31H31Fe1N5O3S1 | C32H33Fe1N4O3S1 | C31H32Fe1N5O3S1 | C31H32Fe1N5O3S1 | C31H32Fe1N5O3Se1 | C31H32Fe1N5O3Se1 | C30H31Fe1N4O3S2 |
M r/g mol−1 | 609.54 | 609.52 | 609.53 | 610.53 | 610.53 | 657.43 | 657.43 | 615.56 |
Crystal system | Triclinic | Triclinic | Triclinic | Triclinic | Triclinic | Triclinic | Triclinic | Triclinic |
Space group | P | P | P | P | P | P | P | P |
a | 10.0481(2) | 10.2159(4) | 10.2135(3) | 10.2652(3) | 10.2153(6) | 10.2722(7) | 10.2841(3) | 10.2094(3) |
b | 10.8818(2) | 10.6166(5) | 10.9173(3) | 11.4487(3) | 11.1783(6) | 11.4128(6) | 11.2785(3) | 11.0128(4) |
c | 13.1468(2) | 13.0796(5) | 13.0351(3) | 12.7914(4) | 13.2477(6) | 12.8071(9) | 13.2216(4) | 12.9469(4) |
α | 98.4710(10) | 83.965(4) | 98.967(2) | 106.073(2) | 100.939(4) | 105.151(5) | 101.184(3) | 98.641(3) |
β | 92.739(2) | 87.370(3) | 93.341(2) | 92.837(2) | 93.011(4) | 93.370(5) | 93.834(3) | 92.784(2) |
γ | 91.3720(10) | 89.972(4) | 90.673(2) | 97.652(2) | 93.339(4) | 96.060(5) | 92.497(2) | 95.509(3) |
V | 1419.48(4) | 1409.23(10) | 1432.94(7) | 1425.77(7) | 1479.62(14) | 1435.30(16) | 1498.57(7) | 1429.56(8) |
T/K | 100(2) | 100(2) | 100(2) | 150(2) | 298(2) | 150(2) | 308(2) | 160(2) |
ρ calc (g cm−1) | 1.426 | 1.436 | 1.413 | 1.422 | 1.370 | 1.521 | 1.457 | 1.430 |
μ (mm−1) | 0.639 | 0.652 | 0.640 | 0.644 | 0.621 | 1.835 | 1.758 | 0.713 |
F(000) | 638 | 636 | 638 | 638 | 638 | 674 | 674 | 642 |
Goodness of fit | 1.066 | 0.954 | 1.054 | 0.947 | 1.030 | 0.909 | 0.913 | 1.075 |
Data/restraints/param. | 4970/0/370 | 4943/0/371 | 5027/3/405 | 5015/0/370 | 5205/0/360 | 5026/0/372 | 5271/2/360 | 5009/0/363 |
r int/rσ | 0.0161/0.0204 | 0.0315/0.0553 | 0.0179/0.0218 | 0.0240/0.0314 | 0.0262/0.0428 | 0.0362/0.0658 | 0.0324/0.0593 | 0.0232/0.0321 |
R 1a/wR2b (all data) | 0.0345/0.0792 | 0.0620/0.0976 | 0.0367/0.0814 | 0.0438/0.0895 | 0.0802/0.1500 | 0.0839/0.1588 | 0.0855/0.1201 | 0.0533/0.1195 |
R 1a/wR2b (I > 2σ(I)) | 0.0286/0.0776 | 0.0396/0.0929 | 0.0298/0.0789 | 0.0328/0.0931 | 0.0522/0.1416 | 0.0616/0.1523 | 0.0467/0.1127 | 0.0412/0.1156 |
CCDC number | 943181 | 943182 | 943183 | 1030134 | 943184 | 1030135 | 943185 | 1030136 |
The presented series of the [Fe(L5)(NCX)]·Solv compounds is unique due to very similar structural frameworks of constitutive [Fe(L5)(NCX)] molecules (Fig. 1, see ESI, Fig. S1–S7†). Due to only very tiny structural differences (both at the molecular and supramolecular level) between the particular members of the series, the [Fe(L5)(NCX)] framework cannot be responsible for the differences in their magnetic behaviours, but the properties of the Solv molecules must be considered as the main perturbative term responsible for the (non)occurrence and characteristics of SCO.
Infrared spectra of 1a–1e are very similar for all the compounds in the series. The only differences between them originate from the presence of the different guest molecules of crystallization (in cm−1, ν(CO) = 1699 in 1c, 1663 in 1d, 1665 in 1d′, ν(O–H) = 3272 in 1b). The differences in the frequency of the ν(N–H) vibrations were also observed (between 3163 and 3242 cm−1). This should reflect different strengths of N–H⋯N hydrogen bonds within the present series (vide infra), but the obtained results are not very informative (see ESI, Fig. S8†), probably due to the broadness of the observed bands, which prevented us from performing a deeper study.
The Fe–O bond lengths are the shortest adopting values close to 1.94 Å. The LS structures were determined only for compounds 1d and 1d′. Both compounds possess very similar bond lengths and selected structural parameters (Table 1), which correspond well with the values found for the purely LS cyanido complexes reported previously.15,19,20
The crystal structures of 1a–1g are very similar. They are composed of the [Fe(L5)(NCX)] and Solv molecules which form a three-dimensional framework via C–H⋯O and C–H⋯π weak interactions. The essential part of the framework consists of a centrosymmetric dimer of two adjacent [Fe(L5)(NCX)] molecules interconnected by a rather weak C–H⋯O non-covalent contact between the CH group of the naphthalene ring and the phenolic oxygen atom (Fig. 1). Further small stabilization within the dimer is provided by an offset ring–ring stacking interaction of the naphthalene rings. The interconnections between the adjacent dimeric units, lying in the same layer, are provided by very weak C–H⋯π and C–H⋯S non-covalent contacts. The cavities with the Solv molecules are placed between the dimeric units (Fig. 1).
Each cavity is occupied by two same guest molecules in most of the cases, but two exceptions can be found within the present series: two CH3OH and one PYZ molecules in 1b, MEK and CH3OH in 1f. The Solv guests from the cavity are hydrogen bonded to the amine groups of the [Fe(L5)(NCX)] molecules from the upper, or lower {[Fe(L5)(NCX)]2}n layer. The cavities are of similar size with the volumes ranging from 224.4 Å3 in 1b to 295 Å3 in 1d′. The contraction of the framework induced by SCO is documented also by a change in the cavity size by approximately 13% (1d, 247.3 at 150 K vs. 283.3 Å3 at 298 K) and 16% (1d′, 247.0 Å3 at 150 K vs. 294.8 Å3 at 308 K). Additional stabilization of the Solv molecule is provided by weak contacts such as C–H⋯O and C–H⋯π interactions. In particular, the C–H⋯O contact between the CH group from Solv and the phenolic oxygen atom from the [Fe(L5)(NCX)] molecule is of importance, because together with the N–H⋯O hydrogen bond, these two contacts form ring synthons (Fig. 2): R22(6) in 1b and 1f (CH3OH molecules), R22(8) in 1c, 1f (MEK molecule), 1e and 1g, R22(9) in 1d and 1d′. It must be noted that the aliphatic chain (in most of the cases the C–H⋯O contact provided by the carbon atom C12, Fig. 2) from the L5 ligand also interacts with the solvent oxygen atom. Besides these dominant contacts other weak non-covalent C–H⋯O, C–H⋯S and C–H⋯π interactions can be found in the crystal structures of 1a–g.
The magnetic data for the purely HS compounds, 1a–c, 1f, are shown in ESI, Fig. S9–S11 and Table S1.† The magnetic behaviours observed for 1a–c, 1f and 1g are essentially similar. The effective magnetic moment at room temperature adopts slightly higher values (μeff ≈ 6.0–6.1μB) than the spin-only value calculated for S = 5/2 and g = 2.0 (5.92μB). The μeff values stay almost constant down to 20 K, where the zero-field splitting (ZFS) and/or weak magnetic interactions mediated through the non-covalent interactions start to dominate the magnetic behaviour and this is observed as an abrupt drop in the μeff values to ca. 5μB. The magnetic data were analysed using the following eqn (1),
Ĥ = D(Ŝz2 − Ŝ2/3) − zj〈Sa〉Ŝa + μBBgiŜi,a | (1) |
d(N⋯O)/Å | T 1/2/K | V solva/Å3 | ε rb | |
---|---|---|---|---|
a Molecular volumes calculated by the Molinspiration program predictions.28 b According to ref. 29. | ||||
1a | 3.295(2) | HS | 78.0 | 7.5 |
1b | 3.110(3) | HS | 37.2 | 33.0 |
1c | 2.988(2) | 84 | 81.5 | 18.6 |
1d 308 K | 2.941(2) | 232↓ 235↑ | 77.5 | 38.3 |
1d 150 K | 2.944(4) | |||
1d′ 308 K | 2.935(5) | 244 | 77.5 | 38.3 |
1d′ 150 K | 2.921(6) | |||
1e | 3.004(3) | 127↓ 138↑ | 71.4 | 47.2 |
1f Fe1 | 3.272(4) CH3OH | HS | 37.2 | 33.0 |
1f Fe2 | 3.154(4) MEK | 81.5 | 18.6 | |
1g | 3.143(3) | HS | 64.7 | 21.0 |
For example, any prediction fails in the case of the isostructural series, where the SCO complexes [Fe(pa)3]Cl2·Solv (pa = 2-picolylamine)5c have very similar surroundings of the [Fe(pa)3]2+ cation consisting of relatively strong N–H⋯Cl hydrogen bonds, and different Solv guests are involved in the supramolecular system only by weak non-covalent contacts. However, the difference between the aforementioned system and the present series must be emphasized. In contrast to the [Fe(pa)3]Cl2·Solv series, the 1a–1g compounds have a complex framework built by weak non-covalent contacts and the strongest contact is formed between the solvent molecule and the amine group, which is directly involved in the coordination of the metal centre. Therefore, a dominant role of this contact in influencing the ligand field strength might be expectable due to the charge transfer of the electron density from the acceptor to hydrogen bonding donor upon formation of the hydrogen bond.23
Finally, it should be pointed out that each solvent molecule has different intrinsic properties such as electron density distribution, vibrational states, basicity, polarity etc., which might affect the SCO behaviour or Solv⋯SCO complex interaction. Therefore, the accurate T1/2 prediction based only on the D⋯A distance is not expectable and this can be also documented within the 1a–g series in which 1e has a longer D–A distance but a higher T1/2 than 1c (Table 3).
(2) |
This parameter literally measures the difference between the LS and HS crystal structure of the SCO compound. It could be expected that the compounds exhibiting cooperative SCO behaviours might have changes in the crystal structure that are more pronounced (and the δxyz values higher) than those exhibiting gradual transitions. This can be understood on the basis of the elastic interaction model developed by Spiering et al.26 where the cooperativity is defined as the interaction between the LS and HS species in the SCO solids, which are expected to be stronger for molecules capable of forming a “larger” point defect in the crystal lattice upon spin transition. Furthermore, it can be expected that the use of this parameter should be valid for the compounds consisting of the SCO molecules with a similar second coordination sphere, i.e. with non-covalent interactions of similar strength, which is, as mentioned above, the case of the herein studied series of compounds. The LS and HS structures are available for two compounds in this work: 1d and 1d′. The δxyz values calculated for these compounds differ significantly: 0.0526 (1d) and 0.0463 (1d′). Only one SCO compound with determined LS and HS structures belonging to the group of [Fe(L5)(NCX)] compounds was reported previously: [Fe(L5)(NCSe)]·CH3CN.15 The δxyz value calculated for this compound is equal to 0.0300. Again, as in the case of the α parameter, the largest δxyz value is found for the most abrupt transition in 1d. In order to compare these values properly, it is necessary to define the abruptness of SCO. This can be done by utilizing a modification of the previously published SCO smoothness equation:27TS = T(xHS = 0.9) − T(xHS = 0.1): TS(1d) = 24 K, TS(1d′) = 45 K and TS([Fe(L5)(NCSe)]·CH3CN) = 76 K. The Ts values found for 1d, 1d′ and [Fe(L5)(NCSe)]·CH3CN agree with expected changes of abruptness in above mentioned compounds.
First, the non-covalent interaction (NCI) index was utilized to visualize both attractive (hydrogen bonding, van der Waals) and repulsive (steric) interactions based on the properties of the electron density using program NCIPLOT.36 The method is based on the analysis of the reduced gradient of density s, defined as
(3) |
In order to accomplish our intention, the NCIPLOT was used to calculate the NCI index for all available {[Fe(L5)(NCX)]⋯Solv} moieties 1a–g, utilizing their HS experimental single-crystal X-ray structures with optimized hydrogen atom positions. The keyword LIGAND was used to address only NCI between the complex and the solvent requiring the use of promolecular densities. The results are divided into two groups, purely HS compounds (1a, 1b, 1f, 1g) and SCO compounds (1c–e) – Fig. 4. As an example of NCI calculation, the molecular structure of {[Fe(L5)(NCS)]⋯DMF} (1d) is shown in Fig. 4c, together with NCI isosurfaces coloured according to the nature and strength of these interactions showing the N–H⋯O contact (orange-red colour), C–H⋯O and C–H⋯π contacts (green-blue colour) and O-lone-pair⋯O-lone-pair contact (blue colour). This 3D plot of NCI then can be transformed into a 2D plot, in which the above mentioned NCIs are represented by troughs (Fig. 4a and b). The troughs found approximately in the region of −0.015 < sign(λ2)ρ < +0.015 represents weak interactions. In the group of SCO compounds, the strongest and attractive interactions belonging to the N–H⋯O contact are found in the region of −0.027 < sign(λ2)ρ < −0.024 (Fig. 4d). Furthermore, the sign(λ2)ρ values of these troughs, corresponding to the strength of the N–H⋯O contact, nicely correlate with T1/2 (Fig. 5).
The indispensable role of this N–H⋯O contact is further demonstrated in Fig. 4b for purely HS compounds, in which there are no troughs in the region of −0.027 < sign(λ2)ρ < −0.024, which means that there are no N–H⋯O contacts that are strong enough. We can only observe the strong and attractive O–H⋯O contact in 1f between MeOH and phenolic oxygen atoms. This contact should act in an opposite direction (than the N–H⋯O contact) in charge transfer due to hydrogen bonding because the solvent molecule acts as a hydrogen bond donor. The strongest N–H⋯O contact is found in 1b, sign(λ2)ρ = −0.020, but evidently the strength of this contact is not sufficient to induce SCO behaviour.
To push further our effort to substantiate the role of the N–H⋯O contact in SCO behaviour within the presented series of complexes, we used another approach based on topological analysis using the total molecular electronic density ρ(r) and the Laplacian of ρ(r) (∇2ρ(r)) based on atoms in molecule (AIM) calculations.37 The single point energy DFT calculations on {[Fe(L5)(NCX)]⋯Solv} moieties resulted in the geometry-basis-wavefunction (GBW) files, which were then transformed to the MOLDEN format and analysed using a program Multiwfn 3.3.5 (A Multifunctional Wavefunction Analyzer).38 The so-called bond critical points (BCP) of the type (3,−1) were located in the N–H⋯O contacts and in these points, the potential energy density V(r) was calculated, because it was shown that the energy of hydrogen bonds (EHB) can be approximated as EHB = V(r)/2.39 The results depicted in Fig. 5 (right) proved that the energy of the N–H⋯O hydrogen bonds within the series of SCO compounds correlates with T1/2, showing that the stronger the N–H⋯O hydrogen bond in the HS X-ray structure is formed, the higher T1/2 is observed.
To summarize, both theoretical approaches based on ab initio calculations identified the N–H⋯O hydrogen bond strength (energy) as the key driving force for observing SCO in the isostructural series of the [Fe(L5)(NCX)]·Solv complexes.
Furthermore, the group of [Fe(L5)(NCX)]·Solv compounds is interesting not only for the above mentioned relationship in the host–guest system. These compounds are promising also due to the capability of the host [Fe(L5)(NCX)] framework to propagate cooperative interactions resulting in the occurrence of abrupt SCO with thermal hysteresis (1d, ΔT = 3 K, 1e, ΔT = 11 K). This, along with the possibility of exploiting the Solv guests as T1/2 tuners, gives an opportunity to prepare cooperative Fe(III) SCO compounds with T1/2 at ambient temperature.
The complex 1a was prepared by the reaction of [Fe(L5)Cl]17 (100 mg, 0.186 mmol) with KNCS (20 mg, 0.206 mmol) in tetrahydrofuran (10 cm3) and methanol (20 cm3). This solution was stirred and heated for 10 minutes. Then it was filtered through a paper filter and left to crystallize for several days. Yield (based on [Fe(L5)Cl]) = 74%.
The complex 1b was prepared by the reaction of [Fe(L5)Cl] (100 mg) with KNCS (20 mg, 0.206 mmol) in methanol (25 cm3) and 4 g of pyrazine was added afterwards. This solution was stirred and heated for 10 minutes. Then it was filtered through a paper filter and left to crystallize for several days. Yield (based on [Fe(L5)Cl]) = 12%.
The complexes 1c, 1d, 1d′ were prepared in the very same way. The precursor complex [Fe(L5)Cl] (100 mg, 0.186 mmol) was reacted with KNCS/Se (20 (S) or 30 (Se) mg, 0.206 mmol) in 20 cm3 of methanol and X ml of Solv (X = 10 cm3 MEK (1c), X = 3 cm3 DMF (1d, 1d′) and the resulting mixture was stirred and heated for 10 minutes. Then it was filtered through a paper filter and left to crystallize for several days. In the case of 1d and 1d′ the suitable single-crystals were obtained by slow diffusion of diethyl ether to the solution. Yields (based on [Fe(L5)Cl]) = 67% for 1c, 35% for 1d, 24% for 1d′.
The complex 1e was prepared by the reaction of [Fe(L5)Cl] (100 mg, 0.186 mmol) and KNCS (20 mg, 0.206 mmol) in the mixture of CH3OH and DMSO (5 cm3). This solution was stirred and heated for 10 minutes. Then it was filtered through a paper filter and the solution volume was reduced by nitrogen gas flow. When the first microcrystals appeared, the solution was left to crystallize for several days at −18 °C. Yield (based on [Fe(L5)Cl]) = 25%.
All prepared samples are of dark violet colour when ground. In liquid nitrogen, the samples exhibiting SCO turned green as reported previously for this group of compounds.41 Elemental analysis: 1a, Mr = 609.54, C32H33Fe1N4O3S1, Found: C, 62.9; H, 5.5; N, 9.1, requires C, 63.1; H, 5.5; N, 9.2%, IR mid (in cm−1): ν(N–H) = 3240 (w), ν(C–H)aromatic = 3039 (w), ν(C–H)aliphatic = 2974, 2926, 2871 (m), ν(NCS) = 2061 (vs), ν(CN) and ν(CC) = 1603, 1536, 1506 (vs); 1b, Mr = 609.52, C31H31Fe1N5O3S1, Found: C, 61.3; H, 5.3; N, 11.4, requires C, 61.1; H, 5.1; N, 11.5%, IR mid (in cm−1): ν(O–H) = 3272 (w), ν(N–H) = 3204 (w), ν(C–H)aromatic = 3049 (w), ν(C–H)aliphatic = 2973, 2926, 2865 (m), ν(NCS) = 2053 (vs), ν(CN) and ν(CC) = 1602, 1538, 1506 (vs); 1c, Mr = 609.53, C32H33Fe1N4O3S1, Found: C, 62.9; H, 5.4; N, 9.2, requires C, 63.1; H, 5.5; N, 9.2%, IR mid (in cm−1): ν(N–H) = 3242 (w), ν(C–H)aromatic = 3050 (w), ν(C–H)aliphatic = 2973, 2924, 2871 (m), ν(NCS) = 2057 (vs), ν(CO) = 1699, ν(CN) and ν(CC) = 1603, 1537, 1505 (vs); 1d, Mr = 610.53, C31H32Fe1N5O3S1, Found: C, 61.1; H, 5.2; N, 11.4, requires C, 61.0; H, 5.3; N, 11.5%, IR mid (in cm−1): ν(N–H) = 3166 (w), ν(C–H)aromatic = 3049 (w), ν(C–H)aliphatic = 2967, 2924, 2861 (m), ν(NCS) = 2058 (vs), ν(CO) = 1663, ν(CN) and ν(CC) = 1605, 1539, 1506 (vs); 1d′Mr = 657.42, C31H32Fe1N5O3Se1, Found: C, 56.7; H, 5.0; N, 10.5, requires C, 56.6; H, 4.9; N, 10.7%, IR mid (in cm−1): ν(N–H) = 3163 (w), ν(C–H)aromatic = 3046 (w), ν(C–H)aliphatic = 2967, 2926, 2859 (m), ν(NCSe) = 2060 (vs), ν(CO) = 1665, ν(CN) and ν(CC) = 1602, 1536, 1506 (vs); 1e, Mr = 615.57, C30H31Fe1N4O3S2, Found: C, 58.6; H, 5.1; N, 9.3, requires C, 58.5; H, 5.1; N, 9.1%, IR mid (in cm−1): ν(N–H) = 3167 (w), ν(C–H)aromatic = 3049 (w), ν(C–H)aliphatic = 2969, 2925, 2867 (m), ν(NCS) = 2060 (vs), ν(CN) and ν(CC) = 1603, 1537, 1506 (vs).
Magnetic susceptibility and magnetization measurements were done using a SQUID magnetometer (MPMS, Quantum Design) from T = 2 K at B = 0.1 T. The magnetization data were taken at T = 2.0 and 4.6 K. The effective magnetic moment was calculated as usual: μeff/μB = 798(χ′T)1/2 when SI units are employed. Analysis of magnetic data was done with the package POLYMAGNET.42 The visualization of non-covalent interactions based on NCIPLOT calculation was done with the help of a VMD program.43
Single crystal X-ray diffraction data were collected using an Oxford diffraction Xcalibur2 CCD diffractometer with a Sapphire CCD detector installed in a fine-focus sealed tube (Mo-Kα radiation, λ = 0.71073 Å) and equipped with Oxford Cryosystems nitrogen gas-flow apparatus. All structures were solved by direct methods using SHELXS9744 and SIR-9245 incorporated into the WinGX program package.46 For each structure, its space group was checked by the ADSYMM procedure of the PLATON47 software. All structures were refined using full-matrix least-squares on Fo2 − Fc2 with SHELXTL-9744 with anisotropic displacement parameters for non-hydrogen atoms. All the hydrogen atoms were found in differential Fourier maps and their parameters were refined using a riding model with Uiso(H) = 1.2 or 1.5 Ueq (atom of attachment). All the crystal structures were visualized using the Mercury software.48
Non-routine aspects of the structure refinement are as follows: some parts (carbon atoms) of the solvent molecules in the compounds 1c, 1d and 1d′ are disordered over two positions: 1c, C1SA/B, C2SA/B, C3SA/B, C4SA/B (occupancy factors, A:B = 0.51:0.49).
Footnote |
† Electronic supplementary information (ESI) available: Results of magnetic data analysis for the HS compounds, detailed crystal structure information for compounds 1a–1e. CCDC 943182–943185, 1030134–1030136. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c4dt03400g |
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