STEREOCHEMISTRY OF COMPLEXES WITH N-ALKYLATED AMINO ACIDS. VIII. CRYSTAL STRUCTURE AND CONFORMATIONAL ANALYSIS OF AQUABIS(L-N,N-DIMETHYLTHREONINATO)COPPER(II) DIHYDRATE

Abstract

The structure of blue, monoclinic (space group P2₁) crystals of aquabis(L-N,N-dimethylthreoninato)copper(II) dihydrate was determined by X-ray diffraction and refined to R = 0.030. The coordination around the copper(II) atom is distorted square-pyramidal with threonine N and O atoms in trans orientations (Cu-O 1.930(3) and 1.926(3)Å, Cu-N 2.042(3) and 2.055(3)Å, O-Cu-O 163.9, N-Cu-N 164.0°) and apical water (Cu-O(W) 2.206 Å). The shape of the coordination polyhedron was reasonably well reproduced with molecular mechanics calculations, yielding root-mean-square deviations of ten valence angles around copper to 4.5°. The calculated strain energy of the crystal conformation is about 21 kJ mol^? higher than the energy of the most stable conformer. This was tentatively attributed to the additional stabilization of molecular conformation by intermolecular hydrogen bonds in the solid state.