Relation between structure and spectra of pseudo-tetrahedral copper(II) complexes. Crystal structure of bis(di-2-pyridylamido)copper(II)

Abstract

The copper(II) complex of the deprotonated form of di-2-pyridylamine has been prepared by treating the ligand with freshly prepared copper(II) hydroxide, and the crystal structure determined. Crystal data: Monoclinic, space group C2/c, a= 14.691(6), b= 12.256(9), c= 11.945(2)Å, β= 124.24(3)°, and Z= 4. The final R value was 0.039 for 1 052 independent, observed reflections. The copper atom environment is pseudo-tetrahedral with a dihedral angle of 58.8° between the two CuN₂ ligand planes. It is demonstrated that the observed molecular structure and the ligand field spectra in the literature are in good agreement. The extent of distortion from pure tetrahedral geometry in a series of related copper bis(bidentate ligand) complexes, as estimated from ligand-field spectra, correlates very well with the observed crystallographic dihedral angle values. This structural result is now available for calibration of the electronic and e.s.r. spectral data for small-molecule pseudo-tetrahedral copper(II) complexes and the presumed four-co-ordinated Type I ‘blue’ copper protein sites.