Recurrent H-bond graph motifs between metal tris-ethylenediamine cations and uncoordinated oxalate anions: fitting a three pin plug into a two pin socket

Keene, Tony D., Hursthouse, Michael B. and Price, Daniel J. (2012) Recurrent H-bond graph motifs between metal tris-ethylenediamine cations and uncoordinated oxalate anions: fitting a three pin plug into a two pin socket. CrystEngComm, 14 (1), 116-123. (doi:10.1039/c1ce05837a).

Abstract

The structures of four new compositionally related compounds are described; [Cu(en)(2)(H2O)(2)][ox] (1), [Cu(en)(3)][ox] (2), [Co(en)(3)](2)[ox](3)(H2O)(3.61) (3), and [Co(en(3))](2)[ox](3)(H2O)(7) (4) [en = 1,2-ethylenediamine, ox oxalate]. These materials all inhabit the broader structural landscape for compounds with a generic M-p(ox)(q)(en)(r)(H2O)(s) composition. Here the competing nature of the ligands; ethylenediamine, oxalate and water, results in complex solution chemistry. In addition the very different structure directing effects of each type of ligand yield a range of crystal architectures. In the present cases ethylenediamine displaces the oxalate dianion, which is non-coordinated in each of these compounds. Compound 3 has disordered water of crystallisation, and is a non-stiochoimetric hydrate, while compound 4 shows a correlated disorder in both ligand conformation and water site occupancies. The H-bond motifs linking pseudo 3-fold symmetric M(en)(3)(n+) cations to pseudo 2-fold symmetric ox(2-) anions shows frequent occurrence of particular motifs; notably the R-2(2)(8) and R-2(2)(9) graphs and a tendency to form bifurcated hydrogen bonds. The oxalate geometric parameters of twist and C-C bond length in our compounds are correlated with data from related structures in the CSD.

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Contributors

Author: Tony D. Keene

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