Studies of the g factors for the tetragonally elongated and compressed Cu^IIN₆ octahedra in (M^I = K, Rb, Cs; M^II = Ca, Sr, Ba, Pb) crystals

Abstract

The EPR g factors, g _{/ /} and g _⊥, of tetragonally elongated and compressed Cu^IIN₆ octahedral clusters (with the ground states |d_{x ² − y ²} ⟩ and |d _{z ²} ⟩, respectively) in (M^I = K, Rb, Cs; M^II = Ca, Sr, Ba, Pb) crystals were calculated using a two-mechanism model. In the model, the contributions to the g-shifts, Δg_i (= g_i − g_s , where i = // or ⊥; g_s ≈ 2.0023 is the free-ion g value), from both the crystal-field (CF) mechanism related to CF excited states and the charge-transfer (CT) mechanism related to CT excited states, which is neglected in the widely-used CF theory, were considered. For the CF mechanism, two theoretical methods, the perturbation theory method (PTM) and the complete diagonalization (of energy matrix) method (CDM), were applied. The CF parameters used were calculated from the superposition model, in which the structural data for Cu^IIN₆ clusters in crystals were measured exactly by X-ray diffraction. The calculated g factors for both the tetragonally elongated and compressed Cu^IIN₆ octahedra are in reasonable agreement with the experimental values. For the strongly covalent Cu^IIN₆ clusters in crystals with different ground states, both the PTM and CDM can be applied to calculate the g-shifts, , arising from the CF mechanism, but exact and reasonable calculations of g factors should take both CF and CT mechanisms into account.

Keywords:

• crystal field
• electron paramagnetic resonance
• octahedral cluster
• charge transfer