Spin state transformations of a 3d ion in the pyramidal environment and under latticedistortions

Abstract

Spin state (SS) transitions in metal-containing pyramidal complexesthat originate from crystallographic distortions are the research subjectof this work. The transition elements are considered to be in the3d6 configuration(Fe2+,Co3+), and they display three different SSs: low-spin(LS,S = 0),intermediate-spin (IS,S = 1) and high-spin (HS,S = 2) states. They have been studied in the frame of the crystal field approximation via the effective nuclearcharge Zeff and under oxygen cage distortions. The features of the SS stability have been calculatedwith/without accounting for spin–orbit coupling. Some critical points at which an accidentaldegeneracy of the SSs exist have been revealed. Near the critical points, negligible distortionscan crucially change the SS. It is demonstrated that the ground SS of the pyramidalMeO5 complex is very sensitive to the symmetry and magnitude of its distortions. SS diagrams in theparameter space ‘effective charge’–‘distortion magnitude’ have been established. It is revealed thatthe IS state exists as a ground state for all considered distortions with a corresponding choice ofZeff. Jahn–Teller distortions stabilize the IS state in a wide range ofZeff. The orbital-like reorientation of the electron density distribution was observed for the ISstate at some threshold magnitude of Jahn–Teller distortions.