Received 2 May 2006
The six-coordinate copper(II) ions in the title compound, [Cu(C2O4)(CH5N)], experience a Jahn-Teller distortion. The structure is a two-dimensional coordination network, with three crystallographically independent oxalate ions, two of them centrosymmetric, bridging CuII ions in three different coordination modes. Each Cu ion is also coordinated by methylamine which is involved in both intra- and interlayer hydrogen bonding.
The oxalate ligand is known for its chelating and bridging coordination modes. It is used by magnetochemists to mediate significant exchange interactions and can result in magnetically ordered materials (Coronado et al., 2000; Decurtins et al., 1993; Demunno et al., 1995; Hursthouse et al., 2004; Julve et al., 1984; Keene et al., 2004; Mathoniere et al., 1996; Price et al., 2001). We present here the structure of [Cu(ox)(CH3NH2)] (ox = oxalate), (I).
The asymmetric unit of (I) contains two Cu atoms, two methylamine molecules, and one complete and two halves of oxalate anions (Fig. 1). The CuII cations each have a CuNO5 coordination and show a large Jahn-Teller-induced tetragonal elongation. While the coordination environment of each CuII ion is very similar (Table 1), the coordination of the three oxalate ions differs significantly (Fig. 2). The structure of (I) is a complex two-dimensional coordination network that can best be viewed by initially considering only the short Cu-O/N contacts (<2.05 Å). The structure is built from two distinct copper oxalate chains. Chain A (Fig. 3) is formed from Cu1 and the oxalate containing C1 and C2; it consists of a simple alternation of these components, with a |-Cu1-oxB|n repeat unit and a CuCu separation of 5.530 (3) Å. Chain B (Fig. 3) is built from Cu2 and the crystallographically centrosymmetric oxalate anions containing C3 and C4. It has a more complex topology with a |-Cu2-oxA-Cu2-oxC-|n repeat unit and alternating CuCu separations of 5.537 (9) and 5.192 (9) Å. The longer Cu-O interactions link neighbouring chains into a corrugated two-dimensional structure in the bc plane (Fig. 4). The coordinated methylamine displays both intra- and interlayer hydrogen bonding (Table 2).
Surprisingly, there are very few structures that contain copper and either methyl- or ethylamine. Chemically, the most similar compound with a known structure is [Cu(NH3)(ox)] (Cavalca et al., 1972). Indeed, the structure of this compound shows remarkable similarity to that of (I). [Cu(NH3)(ox)] also has a two-dimensional character, being built from Cu(ox) chains with the type B structure described above. Here, neighbouring chains are linked through the long Cu-O interactions into a two-dimensional sheet structure, with a topology that is different from that seen in (I).
| || Figure 1 |
Fig. 1. The asymmetric unit of (I) and selected symmetry-equivalent atoms, showing the coordination of both metal ions and ligands. Displacement ellipsoids are drawn at the 40% probability level and H atoms have been omitted for clarity. [Symmetry codes: (i) 1 - x, -y, -z; (ii) 1 - x, -y, 1 - z; (iii) x, - y, + z; (iv) x, - y, - + z].
| || Figure 2 |
Schematic illustration of the three oxalate coordination modes seen in (I).
| || Figure 3 |
Two types of copper oxalate chain (A top and B bottom) from which the extended structure is built.
| || Figure 4 |
The complex two-dimensional Cu(ox) network, viewed along the a axis.
Single crystals of (I) were synthesized by dissolving synthetic mooloolite, viz. [Cu(ox)]·0.33H2O (1.000 g, 6.35 mmol), in an aqueous methylamine solution (20 ml, 40% w/w). The resultant dark-blue solution was further diluted with distilled water to a volume of 100 ml and left to evaporate. Blue crystals of (I) formed as a minor product amongst a large proportion of finely divided [Cu(ox)]·0.33H2O.
H atoms were positioned geometrically, with N-H = 0.90 Å for amine H and C-H = 0.96 Å for methyl H atoms, and were constrained to ride on their parent atoms, with Uiso(H) = xUeq(C,N), where x = 1.2 for amine H and x = 1.5 for methyl H atoms.
Data collection: DENZO (Otwinowski & Minor, 1997) and COLLECT (Hooft, 1998); cell refinement: DENZO and COLLECT; data reduction: DENZO and COLLECT; program(s) used to solve structure: SIR92 (Altomare et al., 1993) in WinGX (Farrugia, 1999); program(s) used to refine structure: SHELXS97 (Sheldrick, 1997) in WinGX; molecular graphics: DIAMOND (Brandenburg, 1999).
The authors are grateful to the EPSRC, the University of Glasgow and the University of Southampton for financial support.
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