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 group s with respect to the shape of their coordination polyhedra. Group I, consisting of N,N-dimethylated derivatives, can be described as distorted square pyramids with a pseudo C4v symmetry. Group II, consisting of other N-alkylated and N,N-dialkylated derivatives, can be described as square pyramids distorted towards the trigonal pyramid along the axis O-Cu-O' = 180°. The apical bond length (Cu-OH2) correlates extremely well on the NCu-N' angle tr = 0.9996) for the group I molecules and sub stantially less well for group II (r = 0.954). Multiple regression of experimental apical lengths on the N-Cu-N' angle and the absolute difference IN-Cu-N' O-Cu-O'I yields IRI= 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 calculations with the minimum value for the root-mean-square deviation between experiment and the ory 0.083 A (group I), 0.032 A (group II) and 0.068 A (both groups).