AN ANALYSIS OF THE SHAPE OF THE COORDINATION POLYHEDRON OF PENTACOORDINATED COPPER(II) CHELATES WITH N-ALKYLATED AMINO-ACIDS

An analysis of eight pentacoordinated (aqua) copper(II) chelates with N-alkylated amino acids revealed that they could be separated in two g roups with respect to the shape of their coordination polyhedra. Group I, consisting of N,N-dimethylated derivatives, can be described as di storted square pyramids with a pseudo C-4 nu symmetry. Group II, consi sting of other N-alkylated and N,N-dialkylated derivatives, can be des cribed as square pyramids distorted towards the trigonal pyramid along the axis O-Cu-O' = 180 degrees. The apical bond length (Cu-OH2) corre lates extremely well on the N-Cu-N' angle (r = 0.9996) for the group I molecules and substantially less well for group II (r = 0.954). Multi ple regression of experimental apical lengths on the N-Cu-N' angle and the absolute difference \N-Cu-N' - O-Cu-O'\ yields \R\ = 0.981 for N = 8. By applying the different measures of distortion of the copper(II ) coordination polyhedron, it was possible to predict the apical bond length from the structures obtained by molecular mechanics calculation s with the minimum Value for the root-mean-square deviation between ex periment and theory 0.083 Angstrom (group I), 0.032 Angstrom (group II ) and 0.068 Angstrom (both groups).