Magnetic anisotropy and slow magnetic relaxation processes of cobalt(ii)-pseudohalide complexes

Abstract

Three mononuclear six-coordinate Co(II)-pseudohalide complexes [Co(L)X₂] with two N-donor pseudohalido coligands occupying the cis-positions (X = NCS⁻ (1), NCSe⁻ (2) or N(CN)₂⁻ (3)), and a five-coordinate complex [Co(L)(NCO)][B(C₆H₅)₄] (4) [L = 1,4,7,10-tetramethyl-1,4,7,10-tetraazacyclododecane (12-TMC)] have been prepared and structurally characterized. Easy-plane magnetic anisotropy for 1–3 and easy-axis anisotropy for 4 were revealed via the analyses of the direct-current magnetic data, high-frequency and -field EPR (HFEPR) spectra and ab initio theoretical calculations. They display slow magnetic relaxations under an external applied dc field. Typically, two slow relaxation processes were found in 1 and 2 while only one relaxation process occurs in 3 and 4. The Raman-like mechanism is found to be dominant in the studied temperature range in 1. For 2–4, the Raman process is dominant in the low temperature region, while the Orbach mechanism dominates in the high temperature range.