Iron(<scp>iii</scp>) complexes of 2-methyl-6-(pyrimidin-2-yl-hydrazonomethyl)-phenol as spin-crossover molecular materials

Abstract

Four new mononuclear Fe(iii) complexes 1-4 of 2-methyl-6-(pyrimidin-2-yl-hydrazonomethyl)-phenol (H₂L) have been synthesized and characterized by magnetic susceptibility measurements and single-crystal X-ray diffraction analysis. Complexes 1-3 are ionic compounds with the formula [Fe(HL)₂]X·nsolvent (X = ClO₄^- (1), BF₄^- (2) and Cl^- (3)), while complex 4 ([Fe(HL)(L)]) is neutral. The central Fe(iii) ion in complexes 1-4 is coordinated by four nitrogen and two oxygen atoms of two Schiff base ligands HL^- or L^2-, and the coordination geometries of Fe^III are all distorted octahedral. Magnetic measurements indicate that complex 1 shows an abrupt spin transition with a thermal hysteresis of 32 K (T_1/2↓ = 158 K and T_1/2↑ = 190 K), and complex 4 exhibits a gradual incomplete spin transition. Complexes 2 and 3 are high spin with a room-temperature χ_mT value of 4.32 cm³ K mol^-1 and 4.39 cm³ K mol^-1, respectively.