A Semiconductive Nature of Bis(dithiolato)nickelate Radical Salt Exhibiting Broadband Photoconduction

The fractional oxidation state [M(dmit)2] (dmit(2)= 2-thioxo-1, 3-dithiole-4, 5-dithiolate) salts have long attracted attention in the molecular metal area owing to high conductivity and even superconductivity. In this study, we achieved a mixedvalence salt (1) of [Ni(dmit)2](0.5-) with monovalent 1,3-N,N-dimethyl-imidazolium (DiMIm(+)) by a solvent evaporation approach under ambient conditions. The mixed valence of [Ni(dmit)(2)](0.5-) has been characterized by an analysis of the IR spectrum and crystal structure. In the crystal structure of 1, two [Ni(dmit)(2)](0.5-) anions overlap in an eclipsed mode to form a [Ni(dmit)(2)](2)(1-) dimer, featuring a radical bearing an S = 1/2 spin; the dimeric radicals stack into a column along the b axis, and the adjacent columns connect together via the lateral-to-lateral S center dot center dot center dot S contacts along the a axis, and through the head-to-head S center dot center dot center dot S contacts along the [101] direction. Salt 1 shows the magnetic behavior of an S = 1/2 Heisenberg antiferromagnetic uniform linear chain with J/k(B) = -47.5(4) K and a semiconducting feature with sigma = 2.52 x 10(-3) S cm(-1) at 293 K, 2.32 x 10(-2) S cm(-1) at 373 K, and E-a = 0.22 eV, as well as broadband photoconductivity under irradiation of green and white lights. This study suggests the possibility of designing new photoconductors based on the mixed-valence [Ni(dmit)2]0.5- salt.