Electronic energy levels and stereochemistry of the cis-distorted octahedral complex nitritobis-(2,2′-bipyridyl)copper(II) nitrate

Abstract

The polarised single-crystal electronic and e.s.r. spectra of [Cu bipy₂(ONO)]NO₃(bipy = 2,2′-bipyridyl) have been determined and related to the cis-distorted octahedral molecular structure of this complex. The single-crystal e.s.r. spectra establish the short Cu–N bond as the z axis, and the x and y axes as bisecting the in-plane copper–ligand bonds. The polarised electronic spectra are interpreted in C_2ν symmetry with the principle C₂ axis lying along the x axis of the magnetic co-ordinates. Crystal-field calculations and the e.s.r. spectra establish a d_z² orbital as the ground state; the polarisation data then suggests the partial one-electron orbital energy sequence d_z² > d_xy > d_z²–y² > d_xz. The position of the d_yz orbital is uncertain but is probably close to that of the d_xz orbital. The g-value expressions for this environment are calculated.

The stereochemistry of [Cu bipy₂(ONO)]NO₃ is compared with those of [Cu bipy₂l]l and Cu dmp Cl₂,H₂O (dmp = 2,9-dimethyl-1,10-phenanthroline), and the description of the first complex as cis-distorted octahedral is justified. The relationship between regular cis-octahedral, trigonal bipyramidal and square-based pyramidal configurations is examined and a correlation diagram between the one-electron energy levels involved, is suggested.