The Spin Gap Transition around 180 K Observed in a New Molecular Magnet based on the [Ni(mnt) 2 ] – Monoanion and Substituted Benzylpyridinium

A new molecular magnet, [NO 2 BrBzPyCH 3 ][Ni(mnt) 2 ] ( 1 ) ([NO 2 BrBzPyCH 3 ] + = 1‐(2′‐bromo‐4′‐nitrobenzyl)‐2‐methylpyridinium, and mnt 2– = maleonitriledithiolate), has been prepared and characterized by single crystal X‐ray diffraction and magnetic measurements. The Ni(III) ions of 1 form a quasi‐one‐dimensional alternating zig‐zag magnetic chain within a Ni(mnt) 2 – column by intermolecular Ni···S, Ni···Ni or π···π interactions, and the [NO 2 BrBzPyCH 3 ] + cations stack into a column via weak Br···O interaction, p···π stacking interactions and C‐H···O hydrogen bonds between the cations. Magnetic susceptibility measurements in the temperature range 1.8‐300 K show that 1 exhibits a spin‐gap transition around 180 K, and an antiferromagnetic interaction in the high‐temperature phase (HT) and spin gap behavior in the low‐temperature phase (LT). The transition for 1 is a second‐order phase transition as determined by DSC analyses.