Geometry and electronic structure of bis-(glycinato)-CuII•2H2O complexes as studied by density functional B3LYP computations

Geometry optimizations using the density functional method B3LYP with a variety of basis sets were performed on bis-(glycinato)-(CuBO)-B-II . 2H(2)O complexes. The geometry and electronic structure were probed with various basis sets and natural population analysis. Geometry optimizations should at least be performed with the all-electron basis set 6-311+G(d,p) or with C, H, N, O=6-311+G(d,p) and an effective core potential for Cu; spurious minima were found with smaller basis sets. Two real minima were found on these potential energy surfaces: a trans configurated complex of C-i symmetry, and a cis configurated complex with C-1 symmetry. In vacuo the trans structure is more stable by 18 kcal mol(-1), which reduces to 10 kcal mol(-1) in a dielectric medium representing water. The final geometries strongly depend on the number of hydrogen bonds formed between the coordinating water molecules and the amino and carboxylate functionalities, as formation of such hydrogen bonds competes with axial Cu-II... OH2 interactions.