Structure correlation study of four-coordinate copper(I) and (II) complexes

The geometries of four-coordinate Cu I and Cu II complexes in the Cambridge Structural Database (CSD) have been analysed systematically and compared u sing symmetry-deformation coordinates and principal component analysis. The observed stereochemistries have been rationalized in terms of the d-electr on configurations, interligand repulsion and pi-bonding effects. The result s confirm that the majority of four-coordinate copper(I) complexes in the C SD adopt tetrahedral geometries and deviations from tetrahedral symmetry ar e caused by the presence of chelating ligands or by the incorporation of co pper centres into dimeric or polymeric structures. Four-coordinate copper(I I) complexes generally adopt geometries close to square planar; this is par ticularly evident for bis(chelate) complexes where pi-bonding is important. Distortions towards tetrahedral geometries are attributable to steric inte ractions of bulky substituents in the bidentate ligands.