Giacomo
Manfroni
a,
Bernhard
Spingler
b,
Alessandro
Prescimone
a,
Edwin C.
Constable
a and
Catherine E.
Housecroft
*a
aDepartment of Chemistry, University of Basel, Mattenstrasse 24a, BPR 1096, 4058-Basel, Switzerland. E-mail: catherine.housecroft@unibas.ch
bDepartment of Chemistry, University of Zurich, Winterthurerstr. 190, 8057-Zurich, Switzerland
First published on 23rd September 2022
The tetratopic 1,4-bis(2-phenylethoxy)-2,5-bis(3,2′:6′,3′′-terpyridin-4′-yl)benzene (1) and 1,4-bis(3-phenylpropoxy)-2,5-bis(3,2′:6′,3′′-terpyridin-4′-yl)benzene (2) ligands have been prepared and fully characterised. Combination of ligand 1 or 2 and [M(hfacac)2]·xH2O (M = Cu, x = 1; M = Zn, x = 2) under conditions of crystal growth by layering led to the formation of [Cu2(hfacac)4(1)]n·3.6n(1,2-Cl2C6H4)·2nCHCl3, [Zn2(hfacac)4(1)]n·nMeC6H5·1.8nCHCl3, [Cu2(hfacac)4(2)]n·nMeC6H5·2nH2O, [Cu2(hfacac)4(2)]n·2.8nC6H5Cl and [Cu2(hfacac)4(2)]n·2n(1,2-Cl2C6H4)·0.4nCHCl3·0.5nH2O. For each compound, single-crystal X-ray analysis revealed the assembly of a planar (4,4)-net in which the tetratopic ligands 1 or 2 define the nodes. The metal centres link two different bis(3,2′:6′,3′′-tpy) ligands via the outer pyridine rings; whereas copper(II) has N-donors in a trans-arrangement, zinc(II) has them in cis. This difference between the copper(II) and zinc(II) coordination polymers modifies the architecture of the assembly without changing the underlying (4,4)-network.
Although many examples of 1D-, 2D- and 3D-assemblies have been prepared from ligands containing one or more 4,2′:6′,4′′-tpy units, the coordination behaviour of 3,2′:6′,3′′-tpy ligands remains less exploited.1,5–25 We have reported three copper(II) 1D-coordination polymers [Cu2(hfacac)4(L1)2]n·n(1,2-Cl2C6H4) (Hhfacac = 1,1,1,5,5,5-hexafluoropentane-2,4-dione), [Cu2(hfacac)4(L1)2]n·nC6H5Cl, and [Cu(hfacac)2(L2)]n·nC6H5Cl, containing ditopic 3,2′:6′,3′′-tpy ligands with coordinatively innocent 4′-substituents. In [Cu2(hfacac)4(L1)2]n·n(1,2-Cl2C6H4) and [Cu2(hfacac)4(L2)2]n·nC6H5Cl the 3,2′:6′,3′′-tpy domains exhibit conformation C, while with [Cu(hfacac)2(L2)]n·nC6H5Cl conformation B is adopted (Scheme 1).26 Structures of ligands L1 and L2 are shown in Scheme 2.
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Scheme 2 The structures of ligands L1 and L2.26 |
One strategy for increasing the dimensionality of an assembly is to select metal centres which favour higher coordination numbers combined with ditopic 3,2′:6′,3′′-tpy or 4,2′:6′,4′′-tpy linkers. The resulting coordination network is thereby directed by the metal node.5,27 An alternative methodology to encourage the formation of 2D- and 3D-dimensional assemblies is by connecting multiple tpy domains to appropriate scaffolds. Two 3,2′:6′,3′′-tpy or 4,2′:6′,4′′-tpy units can be linked in a “back-to-back” fashion by any organic spacer, generating a tetratopic ligand.8,28 We decided to extend our investigations of [M(hfacac)2] coordination chemistry to tetratopic bis(tpy) ligands, and we recently demonstrated the assembly of a series of (4,4) nets based on 1,4-bis(n-alkyloxy)-2,5-bis(3,2′:6′,3′′-terpyridin-4′-yl)benzene ligands.29 A search of the Cambridge Structural Database (CSD v. 2021.3.0, April 2022) revealed only three other structures involving a bis(4,2′:6′,4′′-tpy) or bis(3,2′:6′,3′′-tpy) with a metal 1,3-diketonate. Yoshida et al. showed that ligand L3 (Scheme 3) combined with [Co(acacCN)2] (HacacCN = 2-acetyl-3-oxobutanenitrile) gives the 2D-dimensional (4,4) net [Co2(acacCN)4(L3)]n. The replacement of [Co(acacCN)2] by [Co(dbm)2] (Hdbm = 1,3-diphenylpropane-1,3-dione) leads to a 1D-chain [Co(dbm)2(L3)]n, in which L3 is bidentate through one pyridine N-donor from each tpy domain. The low connectivity is perhaps sterically induced by the presence of larger phenyl rings in [Co(dbm)2]. In contrast, in [Co2(acacCN)4(L4)]n, a change in the ligand from L3 to L4 (Scheme 3) with [Co(dbm)2] does not change the topology of the coordination network, but the networks exhibit 3-fold interpenetration in the solid state structure.25
In this work, we report the synthesis of two bis(3,2′:6′,3′′-tpy) ligands 1 and 2 (Scheme 4) with 1,4-phenylene spacers containing 2-phenylethoxy and 3-phenylpropoxy substituents attached to the phenylene moiety. We have already demonstrated that introducing alkyloxy groups enhances the solubility of the ligand in organic solvents which is beneficial for crystal growth. In addition, the nature of the alkyloxy group can influence the assembly and if terminal phenyl groups are present, they may participate in π–π stacking interactions within the solid state.5,8,28 Herein, we describe the reaction of 1 and 2 (potentially tetratopic ligands) with [M(hfacac)2] (M = Cu, Zn), a two connecting building block, to generate a series of 2-dimensional (4,4)-networks. The electron-withdrawing effect of the CF3 substituents improves the affinity of the complex towards coordination with the pyridine donors of the tetratopic ligands as well as improving its solubility in organic solvents.
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Scheme 4 Synthetic route to 1 and 2. Reagents conditions (see ESI† for full details): (i) n-BuLi, Et2O, 0 °C; dry DMF, warmed to room temperature, 22 h; (ii) 3-acetylpyridine, KOH, NH3, EtOH, RT, 6 days for 1 and 5 days for 2. |
Compound | 1a | 2a |
---|---|---|
Empirical formula | C24H22O4 | C26H26O4 |
Formula weight | 374.41 | 402.47 |
Crystal system | Monoclinic | Orthorhombic |
Space group | P21/n | Pbca |
a [Å] | 12.4540(7) | 9.0988(6) |
b [Å] | 5.4805(2) | 8.7410(6) |
c [Å] | 14.1111(7) | 27.1654(17) |
α [°] | 90 | 90 |
β [°] | 104.263(4) | 90 |
γ [°] | 90 | 90 |
V [Å3] | 933.45(8) | 2160.5(2) |
Z | 2 | 4 |
D c [g cm−3] | 1.332 | 1.237 |
T [K] | 150 | 150 |
Wavelength [Å] | 1.34143 | 1.54178 |
μ [mm−1] | 0.462 | 0.661 |
F(000) | 396 | 856 |
Crystal size [mm3] | 0.3 × 0.2 × 0.1 | 0.25 × 0.20 × 0.08 |
Crystal description | Yellow prism | Yellow plate |
θ range (data collect.) [°] | 3.694 to 56.730 | 5.853 to 69.871 |
Index ranges | −15 ≤ h ≤ 14, −4 ≤ k ≤ 6, −17 ≤ l ≤ 16 | −10 ≤ h ≤ 10, −10 ≤ k ≤ 9, −32 ≤ l ≤ 32 |
Measured Refl's. | 5213 | 14![]() |
Indep't Refl's | 1854 | 1995 |
R int | 0.0802 | 0.0334 |
Refl's I > 2σ (I) | 1614 | 1817 |
Completeness to θ | 98.7% to 53.597° | 99.6% to 67.679° |
Redundancy | 2.81 | 7.03 |
Absorption correction | Multi-scan | Multi-scan |
Max. and min. transmission | 0.218 and 0.000 | 0.753 and 0.695 |
Data/restraints/parameters | 1854/0/127 | 1995/0/136 |
Gof on F2 | 1.258 | 1.015 |
R 1 [I > 2σ (I)] | 0.1118 | 0.0354 |
wR2 [I > 2σ (I)] | 0.2784 | 0.0950 |
R 1 all data | 0.1152 | 0.0386 |
wR2 all data | 0.2849 | 0.0984 |
Largest diff. peak and hole [e Å−3] | 0.720 and −0.565 | 0.198 and −0.160 |
CCDC | 2162893 | 2162895 |
Compound | [Cu2(hfacac)4(1)]n·3.6n(1,2-Cl2C6H4)·2nCHCl3 | [Zn2(hfacac)4(1)]n·nMeC6H5·1.8nCHCl3 | [Cu2(hfacac)4(2)]n·nMeC6H5·2nH2O | [Cu2(hfacac)4(2)]n·2.8nC6H5Cl | [Cu2(hfacac)4(2)]n·2n(1,2-Cl2C6H4)·0.4nCHCl3·0.5nH2O |
---|---|---|---|---|---|
Empirical formula | C95.6H60.4Cl13.2Cu2F24N6O10 | C80.80H53.80Cl5.40F24N6O10Zn2 | C81H56Cu2F24N6O12 | C90.8H61Cl2.8Cu2F24N6O10 | C86.40H56.40Cl5.20Cu2F24N6O10.50 |
Formula weight | 2504.12 | 2046.87 | 1888.39 | 2078.39 | 2113.99 |
Crystal system | Monoclinic | Monoclinic | Triclinic | Triclinic | Triclinic |
Space group | P21/n | P21/n |
P![]() |
P![]() |
P![]() |
a [Å] | 11.9740(4) | 14.31144(10) | 8.9300(2) | 8.9544(2) | 9.0105(3) |
b [Å] | 24.5642(6) | 14.96748(10) | 15.7218(3) | 15.7417(4) | 15.1823(4) |
c [Å] | 19.0265(6) | 22.80527(13) | 16.4219(3) | 16.3905(4) | 19.9645(3) |
α [°] | 90 | 90 | 100.0302(15) | 100.053(2) | 109.391(2) |
β [°] | 94.874(3) | 93.1070(6) | 93.7146(16) | 94.071(2) | 92.202(2) |
γ [°] | 90 | 90 | 96.8981(18) | 97.071(2) | 100.595(2) |
V [Å3] | 5576.1(3) | 4877.85(5) | 2245.22(8) | 2247.46(10) | 2517.67(12) |
Z | 2 | 2 | 1 | 1 | 1 |
D c [g cm−3] | 1.491 | 1.394 | 1.397 | 1.536 | 1.394 |
T [K] | 130 | 160 | 160 | 160 | 160 |
Wavelength [Å] | 1.34143 | 1.54184 | 1.54184 | 1.54184 | 1.54184 |
μ [mm−1] | 4.547 | 2.854 | 1.554 | 2.342 | 2.676 |
F(000) | 2509 | 2057 | 954 | 1049 | 1063 |
Crystal size [mm3] | 0.20 × 0.14 × 0.08 | 0.613 × 0.384 × 0.227 | 0.156 × 0.085 × 0.067 | 0.504 × 0.178 × 0.075 | 0.135 × 0.08 × 0.018 |
Crystal description | Green plate | Colourless prism | Blue prism | Green prism | Green plate |
θ range (data collect.) [°] | 2.561 to 56.819 | 3.534 to 76.550 | 2.743 to 79.422 | 2.750 to 79.570 | 3.155 to 74.503 |
Index ranges | −13 ≤ h ≤ 14, −30 ≤ k ≤ 28, −23 ≤ l ≤ 18 | −18 ≤ h ≤ 17, −18 ≤ k ≤ 18, −28 ≤ l ≤ 28 | −10 ≤ h ≤ 8, −19 ≤ k ≤ 19, −20 ≤l ≤ 20 | −11 ≤ h ≤ 10, −18 ≤ k ≤ 15, −19 ≤ l ≤ 20 | −11 ≤ h ≤ 10, −18 ≤ k ≤ 18, −24 ≤ l ≤ 23 |
Measured Refl's. | 62![]() |
81![]() |
29![]() |
33![]() |
39![]() |
Indep't Refl's | 11![]() |
10![]() |
9228 | 8919 | 9979 |
R int | 0.1234 | 0.0282 | 0.0311 | 0.0466 | 0.0629 |
Refl's I > 2σ (I) | 8115 | 9342 | 8012 | 7542 | 6887 |
Completeness to θ | 99.8% to 53.597° | 100% to 67.684° | 97.7% to 67.684° | 95.1% to 67.684° | 97.7% to 67.684° |
Redundancy | 5.56 | 7.97 | 3.16 | 3.80 | 3.99 |
Absorption correction | Multi-scan | Gaussian | Gaussian | Gaussian | Gaussian |
Max. and min. transmission | 0.560 and 0.004 | 1.000 and 0.122 | 1.000 and 0.675 | 1.000 and 0.286 | 1.000 and 0.596 |
Data/restraints/parameters | 11![]() |
10![]() |
9228/202/731 | 8919/208/714 | 9979/571/882 |
Gof on F2 | 1.027 | 1.042 | 1.070 | 1.040 | 1.209 |
R 1 [I > 2σ (I)] | 0.1224 | 0.0797 | 0.0758 | 0.0932 | 0.0984 |
wR2 [I > 2σ (I)] | 0.3685 | 0.2452 | 0.2299 | 0.2661 | 0.2869 |
R 1 all data | 0.1547 | 0.0839 | 0.0830 | 0.1035 | 0.1225 |
wR2 all data | 0.4112 | 0.2527 | 0.2463 | 0.2839 | 0.3162 |
Largest diff. peak and hole [e Å−3] | 1.889 and −1.099 | 1.235 and −0.791 | 1.818 and −0.627 | 2.229 and −1.086 | 1.390 and −0.363 |
CCDC | 2162894 | 2162898 | 2162896 | 2162897 | 2162899 |
The 1H and 13C{1H} NMR spectra of intermediates 1a–1b and 1–2 were assigned using NOESY, COSY, HMQC and HMBC techniques (Fig. S1–S12†). The spectroscopic signatures are consistent with the structures displayed in Scheme 4. Melting point determination, ATR-IR spectroscopies (Fig. S13–S16†), UV-vis (Fig. S17†) and MALDI-TOF mass spectrometry (Fig. S18–S21†) and either HR-ESI mass spectrometry (Fig. S22–S23†) or elemental analysis complemented the characterisation (see ESI† for full details).
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Fig. 1 The molecular structures of (a) 1a and (b) 2a. H atoms are omitted for clarity, and thermal ellipsoids are drawn at 40% probability level. Symmetry code: i = 1 − x, −y, 1 − z. |
Intermolecular interactions in the crystal lattice in 1a arise from a combination of C–H⋯O hydrogen bonds, short C–H⋯π(arene) contacts, and arene–arene π-stacking. The C–H⋯O bonds arise from the oxygen atom of the aldehydes and the hydrogen atoms H5A and H5B attached to C5, with C⋯O distance of 3.12 Å (C–H⋯O range of 2.65–2.95 Å) and C–H⋯O angles range of 90.4–126.3°. Only one crystallographically independent π-stacking interaction occurs (Fig. 2a). The terminal phenyl ring containing C10 stacks with the neighbouring ring containing C10ii across an inversion centre (symmetry code ii = 1 − x, 1 − y, −z). The rings are offset with respect to each other and the centroid⋯centroid separation is 4.12 Å. The interactions are then supplemented by short C–H⋯π(arene) contacts.
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Fig. 2 (a) Face-to-face π-stacking between two molecules of 1a. H atoms are omitted for clarity. (b) C–H⋯O hydrogen bonding between molecules of 2a leads to ribbons. |
In contrast, the packing in 2a is dominated by C–H⋯O hydrogen bonds. Two CHO groups interact via a pair of C–H⋯O hydrogen bonds, generating a six-membered ring through a centrosymmetric arrangement; hydrogen bond metrics are C1ii⋯O1 = 3.27 Å (C1ii–H1ii⋯O1 = 2.52 Å), C1ii–H1ii⋯O1 = 135.9° (symmetry code ii = −x, −y, 1 − z). The interconnection of the CHO groups arranges the molecules into 1D ribbons as shown in Fig. 2b. The individual ribbons are parallel with respect to each other and the stacking is slightly staggered following an ABAB pattern (Fig. S24†). Weak short C–H⋯π(arene) interactions link the different stacks.
The self-association of aromatic aldehydes dimers via C–H⋯O interactions is rare. A search of the Cambridge Structural Database (CSD v. 2021.3.0, April 2022) for structures containing aromatic aldehydes reveals that only 157 out of 4039 crystal structures form dimers of the type found in 2a. Statistical analysis, using normalised H, reports mean distances of 2.57(10) and 2.58(9) Å for the pair of C–H⋯O interactions involved in dimer formation, with C–H⋯O angles of 130(14) and 129(14)°, respectively. In our case, a C–H⋯O distance of 2.42 Å and an angle of 133.6° (with normalised H) are consistent.
Coordination polymer | Solvent for [M(hfacac)2]·xH2O | Space group |
---|---|---|
[Cu2(hfacac)4(1)]n·3.6n(1,2-Cl2C6H4)·2nCHCl3 | 1,2-Dichlorobenzene | P21/n |
[Zn2(hfacac)4(1)]n·nMeC6H5·1.8nCHCl3 | Toluene | P21/n |
[Cu2(hfacac)4(2)]n·nMeC6H5·2nH2O | Toluene |
P![]() |
[Cu2(hfacac)4(2)]n·2.8nC6H5Cl | Chlorobenzene |
P![]() |
[Cu2(hfacac)4(2)]n·2n(1,2-Cl2C6H4)·0.4nCHCl3·0.5nH2O | 1,2-Dichlorobenzene |
P![]() |
Structural analysis confirmed the assembly of a 2D-coordination polymer in each case, comprising solvated coordination networks with the general formula [M2(hfacac)4(L)]n (M = Cu, Zn). From the reaction between 2 and [Cu(hfacac)2]·H2O, single crystals grew from three solvent combinations yielding [Cu2(hfacac)4(2)]n·nMeC6H5·2nH2O (from toluene/CHCl3), [Cu2(hfacac)4(2)]n·2.8nC6H5Cl (from chlorobenzene/CHCl3) and [Cu2(hfacac)4(2)]n·2n(1,2-Cl2C6H4)·0.4nCHCl3·0.5nH2O (from 1,2-dichlorobenzene/CHCl3). The first two are isostructural networks which crystallise in the triclinic space group P and possess comparable cell dimensions (a = 8.9300(2), b = 15.7218(3), c = 16.4219(3) Å, α = 100.0302(15), β = 93.7146(16), γ = 96.8981(18)° for [Cu2(hfacac)4(2)]n·nMeC6H5·2nH2O, and a = 8.9544(2), b = 15.7417(4), c = 16.3905(4) Å, α = 100.053(2), β = 94.071(2), γ = 97.071(2)° for [Cu2(hfacac)4(2)]n·2.8nC6H5Cl). Therefore, we only discuss in detail the structure of [Cu2(hfacac)4(2)]n·2.8nC6H5Cl. In [Cu2(hfacac)4(2)]n·2n(1,2-Cl2C6H4)·0.4nCHCl3·0.5nH2O, a change in conformation of the 3,2′:6′,3′′-tpy domains justifies a separate description of this structure. All five assemblies are (4,4)-nets, but two structurally distinct designs can be identified and are discussed separately: (4,4)-nets with a trans-arrangement of the {Cu(hfacac)2(N1)(N2)} units and a (4,4)-net with cis-arrangement of the {Zn(hfacac)2(N1)(N2)} units (Scheme 5).
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Scheme 5 Schematic representations of (a) trans-{Cu(hfacac)2(N1)(N2)} and (b) cis-{Zn(hfacac)2(N1)(N2)} fragments. N1 and N2 originate from two different bis(tpy) ligands. |
In [Cu2(hfacac)4(1)]n·3.6n(1,2-Cl2C6H4)·2nCHCl3 and [Cu2(hfacac)4(2)]n·2.8nC6H5Cl both ligand 1 and 2 adopt conformation B. Interestingly, with ligand 2, a solvent change from chlorobenzene (or toluene) to 1,2-dichlorobenzene leads to a conformational change of the tpy groups within the 2D-polymer (Fig. 3b and c, top). In fact, in [Cu2(hfacac)4(2)]n·2n(1,2-Cl2C6H4)·0.4nCHCl3·0.5nH2O, ligand 2 displays conformation C, although this does not lead to a significant change in the network (Fig. 3b and c, middle). In all three structures, the combination of ligand 1 or 2 with Cu(hfacac)2 leads to a 2D-net directed by the tetratopic ligands. The centroids of the phenylene spacers are the nodes of the network, whereas the copper centres act as linkers (Fig. 3, middle). The network in [Cu2(hfacac)4(1)]n·3.6n(1,2-Cl2C6H4)·2nCHCl3 contains a rhombic shortest circuit with internal angles of 87.0 and 93.0° and a node⋯node distance of 16.94 Å. The copper atoms are close to the plane of the (4,4)-net generating a small deformation in the structure (Fig. 3a, middle and bottom). In contrast, in [Cu2(hfacac)4(2)]n·2.8nC6H5Cl and [Cu2(hfacac)4(2)]n·2n(1,2-Cl2C6H4)·0.4nCHCl3·0.5nH2O, the shortest circuits are parallelograms (Fig. 3b and c, middle) with the copper centres lying in the plane (Fig. 3b and c, bottom). The conformational change of ligand 2 does not appear to play a crucial role in the assembly. Indeed, from [Cu2(hfacac)4(2)]n·2.8nC6H5Cl to [Cu2(hfacac)4(2)]n·2n(1,2-Cl2C6H4)·0.4nCHCl3·0.5nH2O, only minor changes occur in the distances and angles between the individual nodes (Table 5).
Compound | Node–node distance/Å | Internal angles of rhombus in (4,4) net/° |
---|---|---|
[Cu2(hfacac)4(1)]n·3.6n(1,2-Cl2C6H4)·2nCHCl3 | 16.94 | 87.0, 93.0 |
[Cu2(hfacac)4(2)]n·2.8nC6H5Cl | 16.42, 17.12 | 78.8, 101.2 |
[Cu2(hfacac)4(2)]n·2n(1,2-Cl2C6H4)·0.4nCHCl3·0.5nH2O | 16.17, 20.68 | 73.0, 107.0 |
All the structures considered in this section have phenylalkoxy groups pointing above and below the plane (Fig. 3, bottom). [Cu2(hfacac)4(1)]n·3.6n(1,2-Cl2C6H4)·2nCHCl3 and [Cu2(hfacac)4(2)]n·2n(1,2-Cl2C6H4)·0.4nCHCl3·0.5nH2O were crystallised in the same solvent mixture (from 1,2-dichlorobenzene/CHCl3) and with the same reagent concentrations. The only difference is in the length of the phenylalkoxy substituent, ligand 1 possesses a 2-phenylethoxy whereas ligand 2 possesses a 3-phenylpropoxy. Despite the difference of only one CH2 group, the network is significantly affected going from [Cu2(hfacac)4(1)]n·3.6n(1,2-Cl2C6H4)·2nCHCl3 to [Cu2(hfacac)4(2)]n·2n(1,2-Cl2C6H4)·0.4nCHCl3·0.5nH2O (Fig. 3a and c). It is important to note that, in [Cu2(hfacac)4(1)]n·3.6n(1,2-Cl2C6H4)·2nCHCl3, the peripheral phenyl ring is not involved in any significant interaction, whereas in [Cu2(hfacac)4(2)]n·2n(1,2-Cl2C6H4)·0.4nCHCl3·0.5nH2O, short C–H⋯π(arene) interactions link the pendant phenyl ring with the 1,2-dichlorobenzene molecule and the phenylene spacer of the ligand in the adjacent sheet (Fig. S28†). The 3-phenylpropoxy substituent also engages in weak interactions in the crystal structure of [Cu2(hfacac)4(2)]n·2.8nC6H5Cl, where the terminal phenyl ring stacks with the central arene spacer of the ligand 2 contained in a neighbouring (4,4)-net (Fig. S29†). In each lattice, the individual layers pack with the cavities running down the crystallographic a-axis (Fig. 4). The solvent molecules are accommodated within these open channels.
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Fig. 4 (a) Illustration of the void space in the crystal lattices of [Cu2(hfacac)4(2)]n·2.8nC6H5Cl (ca. 21% void) with channels following the a-axis. (b) Representation of the same structure with solvent molecules. The void was calculated from the structure without solvent molecules. Subsequently, the same structure with solvent molecules was superimposed on the one without, revealing the chlorobenzene in the channels. Contact surface map with probe radius = 1.2 Å. Calculations made with Mercury (v. 2021.3.0).32 |
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Scheme 6 With pairs of 3,2′:6′,3′′-tpy ligands in conformation C (Scheme 1), there are three possible coordination topology (I)–(III) at a Zn atom that does not lie on an inversion center. The labels in and out indicate the orientation of the lone pair of each coordinating N atom relative to the central N atom of the 3,2′:6′,3′′-tpy unit. Only limiting planar conformations are shown and coordinated oxygen atoms arise from [hfacac]− ligands. |
As with the complexes described in the previous section, ligand 1 behaves as a 4-connecting node, coordinating four different Zn(II) ions and directing the assembly of a planar (4,4)-net (Fig. 5a). The distance between adjacent ligand nodes (centroids of the phenylene spacers) is 15.11 Å and the internal angles of the rhombic shortest circuit are 59.4 and 120.6°. Compared to the copper(II) structures reported in this work, the topology of the zinc(II) network is identical. However, structural differences can be seen by examination of how the metal linkers and the phenylalkoxy tails are arranged. The zinc(II) centres are disposed alternately above and beneath the plane generated by the ligand nodes, while the 2-phenylethoxy chains are located in the plane (Fig. 5b). Each cavity of the network accommodates two 2-phenylethoxy tails, both originating from the same individual 2D-coordination polymer, and the pendant phenyl rings interact via face-to-face π-interaction across an inversion centre (Fig. S31†).
Note that a change from a trans to a cis arrangement of the N-donors on going from the Cu(II) to Zn(II) structures modifies the architecture of the assembly without changing the underlying (4,4)-network. On the other hand, we have recently reported a planar (4,4)-net with trans-{Cu(hfacac)2(N1)(N2)} domains lying above and below the plane displaying a similar arrangement of metal linkers.29 In [Zn2(hfacac)4(1)]n·nMeC6H5·1.8nCHCl3, viewed down the crystallographic b-axis, the individual layers are parallel to each other (Fig. S32†). The packing of the sheets shows a zig-zag arrangement with the CF3 groups protruding out of the plane. Interactions between the layers are dominated by short C–H⋯F–C contacts between 2-phenylethoxy substituents in one sheet and the CF3 groups from the neighbouring one. However, since the CF3 groups are disordered, a detailed discussion is not meaningful. Removal of the solvent molecules from the structure reveals cavities (Fig. 6) rather than open channels in which they are located.
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Fig. 6 Illustration of the void space in the crystal lattices of [Zn2(hfacac)4(1)]n·nMeC6H5·1.8nCHCl3 (ca. 33% void) following the a-axis. Contact surface map with probe radius = 1.2 Å. Calculations made with Mercury (v. 2021.3.0).32 |
The solid state IR spectra of the dried copper(II) coordination polymers are shown in Fig. S37–S40.† Not surprisingly, given the similarity of the structures, the absorption of the 1,3-diketonate and the fingerprint regions are almost identical.
In the copper(II) coordination polymers the metal ions display a trans-arrangement of the N-donor atoms. Differences, such as phenylalkoxy chain length or conformational changes in the 3,2′:6′,3′′-tpy groups, do not change significantly the motif and distinct features remain identical within the series. The Cu(II) centres are located near or in the plane (determined by the nodes) and the phenylalkoxy chains are directed outwards from the individual sheets. By contrast, in [Zn2(hfacac)4(1)]n·nMeC6H5·1.8nCHCl3, the Zn(II) centres have a cis-arrangement of the N atoms and are arranged alternately above and below the network. Pairs of 2-phenylethoxy tails are lodged in each cavity of the (4,4)-net interacting with each other via face-to-face π-interaction.
This work showed that the assembly of planar (4,4)-nets by combining ligands 1 or 2 with [M(hfacac)2]·xH2O (M = Cu, x = 1; M = Zn, x = 2) is independent upon the choice of the crystallization solvents. A switch from Cu(II) to Zn(II) influences the orientation of the metal linkers but does not change the topology of the network.
Footnote |
† Electronic supplementary information (ESI) available: Fig. S1–S12: NMR spectra of compounds 1a–1b and 1–2; Fig. S13–S16: IR spectra of compounds 1a–1b and 1–2; Fig. S17: absorption spectra; Fig. S18–S23: mass spectra; Fig. S24–S36: additional structural figures and PXRD; Fig. S37–S40: IR spectra of the copper(II) coordination polymers. CCDC reference numbers 2162893–2162899. For ESI and crystallographic data in CIF or other electronic format see DOI: https://doi.org/10.1039/d2ce01130a |
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