Halogen substitution effects on crystal structures and magnetic properties in nickel dithiolate molecular crystals

Abstract

A series of nickel dithiolene molecular crystals [Et₃N(CH₂)₃X][Ni(mnt)₂] (1: X = H, 2: X = Cl, 3: X = Br and 4: X = I and Br; mnt²⁻ = maleonitriledithiolate) were prepared by introducing triethylpropylammonium derivatives (X–CH₂CH₂CH₂–NEt₃⁺) into [Ni(mnt)₂]⁻ building blocks. 1 crystallizes in a monoclinic system with the space group P2₁/n at 293 K, and the cations and anions in 1 are arranged in columnar segregated stacks along the a-axis direction. Crystals 2 and 3 also belong to monoclinic systems with space groups P2₁/n and P2₁/c, but 4 crystallizes in a triclinic system with the space group P. Interactions between [Ni(mnt)₂]⁻ ions in all crystals are antiferromagnetic, and the magnitudes of the interactions are qualitatively consistent with the strength of intermolecular interactions estimated from transfer integrals, where interactions between [Ni(mnt)₂]⁻ ions are greater than the others in all crystals. The magnetic measurement data demonstrate that antiferromagnetic behavior was observed in 1 and can be fitted well through the 1D alternating linear chain model. Crystal 2 shows spin dimer magnetic behavior, and the magnetic susceptibilities of 3 and 4 show Curie–Weiss-type paramagnetic character in the whole temperature regions. This study showed that halogen substitution on the cations has significant effects on the arrangement and magnetic behavior of [Ni(mnt)₂]⁻.