Magnetic Properties and Crystal Structure of a Linear-chain Copper(II) Compound with Bridging Chloride and Oxamidate Ligands

The compound [Cu2(L)Cl2] [H2L = N,N'-bis(3-amino-2,2-dimethylpropyl)oxamide] has been prepared and characterized by means of structural and magnetic measurements. The crystals are triclinic, space group P-1, with a = 6.630(1), b = 7.443(1), c = 9.702(1) angstrom, alpha = 95.38(1), beta = 102.72(1), gamma = 101.12(1)° and Z = 2. The structural unit comprises one independent copper ion bonded to one half of a trans-oxamidate ligand and one chloride ion. Two centres of symmetry lead to a polymeric molecule. The copper ions are in distorted square-pyramidal environments and the basal co-ordination sites are occupied by O,N,N' donors from the trans-oxamidate ligand and by a chloride ion. The fifth contact occurs with the chloride ion of an adjacent asymmetric unit. The nearest-neighbour Cu...Cu distance is 3.2989(9) angstrom and a remarkably acute angle is found at the bridging chloride [79.02(3)°]. The magnetic properties of the compound are well reproduced by the dimer model with pairwise interactions, owing to the overwhelming importance of the oxamidate bridge in determining the exchange coupling interactions [J = 409(3) cm-1]. The EPR spectra, however, indicate that the compound intimately behaves as an alternating chain.