Observation of Magnetic Bistability in Polymorphs of the [Ni(dmit)2]− Complexes

Abstract

Four ion-pair complexes of [Ni(dmit)(2)](-) with [NO(2)bzql](+) have been obtained, which belong to two kinds of polymorph forms, [NO(2)bzql][Ni(dmit)(2)] (1alpha and 1beta) and [NO(2)bzql][Ni(dmit)(2)].CH(3)COCH(3) (2alpha and 2beta) (where dmit = 2-thioxo-1,3-dithiole-4,5-dithiolate and [NO(2)bzql](+) = 1-(4-nitrobenzyl)quinolinium). Though 1alpha, 2alpha, and 2beta all show anionic dimerization structures at room temperature, they have different anionic and cationic arrangement fashions, which give rise to different magnetic behaviors for these polymorphs or pseudo-polymorphs. Compounds 1alpha, 1beta, and 2alpha exhibit magnetic bistabilities. In particular, 1alpha has a hysteretic loop at approximately 55 K, while 2beta does not display a spin transition in the 2-300 K range. On the basis of the crystal structure data of 2alpha in high- and low-temperature phases, the magnetic coupling feature within the [Ni(dmit)(2)](-) spin dimer was explored with the broken-symmetry approach at the UBPW91/LANL2DZ level; combined with the experimental data and theoretical analyses, the relationship between the magnetic coupling nature and the stacking pattern of [Ni(dmit)(2)](-) anions as well as the origin of the phase interconversion are discussed.