The single-crystal electronic and electron spin resonance spectra of bis-(2,2′-bipyridylamine)copper(II) diperchlorate

Abstract

The polarised single-crystal electronic spectra and e.s.r. spectra of bis-(2,2′-bipyridylamine)copper(II) diperchlorate have been determined. The in-plane g-values correlate with copper–nitrogen directions and suggest a d_x²–y² ground state for the compressed tetrahedral CuN₄ chromophore present. The electronic spectra correlate, in the xy-plane with the bisectors of the copper–nitrogen directions; possible reasons for this 45° misalignment of the in-plane g-values and electronic spectral axes are discussed. The electronic spectra are assigned in both C_2v and D₂ symmetries (with a preference for the former) and yield the tentative one-electron orbital sequence d_x²–y² > d_xy > d_xz > d_z² > d_yz. Reasons are given for preferring a tetrahedrally distorted square-coplanar description of the stereochemistry of the CuN₄ chromophore of Cu(bipyam)₂(ClO₄)₂.