Geometry and electronic structure of bis-(glycinato)-Cu-II center dot 2H(2)O complexes as studied by density functional B3LYP computations

Geometry optimizations using the density functional method B3LYP with a var iety of basis sets were performed on bis-(glycinato)-(CuBO)-B-II . 2H(2)O c omplexes. The geometry and electronic structure were probed with various ba sis 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 minim a were found with smaller basis sets. Two real minima were found on these p otential 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 d ielectric medium representing water. The final geometries strongly depend o n the number of hydrogen bonds formed between the coordinating water molecu les and the amino and carboxylate functionalities, as formation of such hyd rogen bonds competes with axial Cu-II... OH2 interactions.