Spin-crossover phenomena of the mononuclear MnIII complex tuned by metal dithiolene counteranions

Abstract

Three ion-pair complexes based on spin-crossover [Mn(5-Br-sal-N-1,5,8,12)]ClO₄ with TBA₂[Ni(mnt)₂], TBA₂[Pt(mnt)₂] (mnt = maleonitriledithiolate) and TBA[Ni(dmit)₂] respectively (dmit = 2-thioxo-1,3-dithiole-4,5-dithiolato) have been synthesized and structurally characterized. Complexes 1 [Mn(5-Br-sal-N-1,5,8,12)]₂[Ni(mnt)₂] and 2 [Mn(5-Br-sal-N-1,5,8,12)]₂[Pt(mnt)₂] are isomorphic and show the axial compression of the octahedral coordination environment of Mn^III ions. With the temperature increasing the equatorial metal–ligand bond lengths show significant elongation, but the axial bond lengths remain unchanged. Complex 3 [Mn(5-Br-sal-N-1,5,8,12)][Ni(dmit)₂]·CH₃CN contains π–π, p–π and H-bonds weak interactions. Magnetic investigation shows the spin-crossover phenomena for 1 and 2, and T_1/2 has been increased by 230 K comparing with the reactant complex. However, no spin-crossover was observed in complex 3, and theoretical calculations show that there are weak antiferromagnetic couplings mediated through π–π interactions.