Simulation of Plasticity of Copper(II) Coordination Polyhedron: Empirical Force Field Model with Distorsion Coordinate Potential

In order to reproduce the geometry of tetracoordinated copper (II) chelates with a »distorted« coordination polyhedron (planar/ /tetrahedral), two new empirical functions for the calculation of the conformational potential were introduced. The first depends on the distorsion coordinate (1, defined as an angle between bisectors of two valence angles around the central atom. The second function is a two-well valence angle bend ing potential for valence angles around copper, with minima at 90" and 109.47°. The new functions were tested on bis-(N,N-dimethylvalinato)copper(II). A consistent force field (CFF) calculation with the new functions yielded the correct geometry of copper coordination, i. e. a distorted tetrahedron. The valence angles around copper (N-Cu-N, O-Cu-N and O-Cu-O) were reproduced fairly well with root-mean square deviation with respect to the crystal structure of 3.20° and 3.73° for the model with a two-well and the model with a quadratic valence angle bending potential, respectively. The measured diastereoselectivity (Gibbs energy difference between CU(L-ligand12 and Cuu=ligand) (o-ligand)) was reproduced within 3 kJ mol-i.