Distortion isomerism and plasticity of the coordination sphere of binuclear Cu(II) complexes: Crystal structure of the monoclinic isomer of [Cu2(2-bromopropionato)4(caffeine)2]

The crystal and molecular structure of monoclinic [di(caffeine)tetrakis(2-bromopropionato)dicopper(II)] 0.8 water was determined using direct methods and Fourier techniques. The complex crystallizes in space group C2/c and is dimeric with square pyramidal geometry at each copper(II) center. The Cu Cu distance is 2.674(1) . Experimental data are compared with those found in a similar triclinic [Cu2(2-bromopropionato)4(caffeine)2] complex. The isomers differ in the geometry of copper(II) and the inter-aromatic interaction of caffeine molecules. The correlation of Cu Cu distances vs. apical Cu-O bond length for dimeric copper(II) carboxylate complexes were interpreted by the bond-valence model. Minimum lengths of apical Cu-O bond and Cu Cu separation were predicted.