Thermal and Magnetic Field Switching in a Two‐Step Hysteretic Mn^III Spin Crossover Compound Coupled to Symmetry Breakings

Abstract

A MnIII spin crossover complex with atypical two‐step hysteretic thermal switching at 74 K and 84 K shows rich structural–magnetic interplay and magnetic‐field‐induced spin state switching below 14 T with an onset below 5 T. The spin states, structures, and the nature of the phase transitions are elucidated via X‐ray and magnetization measurements. An unusual intermediate phase containing four individual sites, where 1/4 are in a pure low spin state, is observed. The splitting of equivalent sites in the high temperature phase into four inequivalent sites is due to a structural reorganization involving a primary and a secondary symmetry‐breaking order parameter that induces a crystal system change from orthorhombic→monoclinic and a cell doubling. Further cooling leads to a reconstructive phase transition and a monoclinic low‐temperature phase with two inequivalent low‐spin sites. The coupling between the order parameters is identified in the framework of Landau theory.

Tuning valence tautomerism in a family of dinuclear cobalt complexes incorporating a conjugated bridging bis(dioxolene) ligand with weak communication

“…10,11 Two-step SCO is also observed for mononuclear compounds in which symmetry breaking results in two or more inequivalent SCO centers at an intermediate phase. [12][13][14] Two-step valence tautomerism has only been observed for two dinuclear cobalt complexes bridged by bis (dioxolene) ligands. [15][16][17][18] The first reported example was [{Co(Me 2 tpa)} 2 (spiro)](ClO 4 ) 2 (spiroH 4 = 3,3,3′,3′-tetramethyl-1,1′-spirobi(indan)-5,5′,6,6′-tetraol, Me 2 tpa = bis(6-methyl-2pyridylmethyl)(2-pyridylmethyl)amine).…”