Single-crystal electronic and electron spin resonance spectra of bis-(3-methylpentane-2,4-dionato)copper(II)

Abstract

The polarised single-crystal electronic and e.s.r.spectra of bis-(3-methylpentane-2,4-dionato)copper(II) are reported The e.s.r.spectrum indicates a d_xy ground-state. The electronic spectra have been interpreted in D_2h symmetry by use of a vibronic mechanism and an intensity borrowing mechanism yielding the tentative one-electron orbital sequence: d_xy > d_x²–y² > d_xz > d_z², with the position of the d_yz orbital uncertain but probably close to the d_xz orbital. The combined spin–orbit and orbital reduction parameters are evaluated as r_⊥= 0·74 and r_∥= 0·77 and suggest substantial π bonding, especially out-of-the-plane (contrary to previous suggestions). The high energy of the d_z²→d_xy transition is consistent with the high tetragonal distortion present, with the short in-plane copper–oxygen bonds, and with the description of the complex as being strictly square-coplanar. Data for other bis-chelates of this type are also discussed.