Crystal structures and magnetic properties of two molecular solids based on bis(maleonitriledithiolate)nickelate monoanion with substituted piperidinium cations

Two new molecular solids, [1-NaMePid][Ni(mnt)2] (1) and [2-NaMePid][Ni(mnt)2] (2) (mnt2− = maleonitriledithiolate, [1-NaMePid]+ = 1-(1′-naphthylmethyl)piperidinium and [2-NaMePid]+ = 1-(2′-naphthylmethyl)piperidinium) have been characterized structurally and magnetically. Both [Ni(mnt)2]− anions and the cations of 1 and 2 form segregated column stacks, and the Ni(III) ions form a 1D zigzig alternating magnetic chain within a [Ni(mnt)2]− column through Ni···S, S···S, Ni···Ni, or π···π interactions. Some conformational features in two isomeric cations and the geometry of the individual [Ni(mnt)2]− anion for 1 and 2 remain similar, while the changes of the space filling properties, the packing requirements and the existence of the water molecule in 2 result in the difference of the stacking mode of the [Ni(mnt)2]− anions. Magnetic susceptibility measurements in the temperature range 2–300 K show that 1 is diamagnetism, while 2 exhibits a novel and interesting spin–gap transition around 16.8 K with antiferromagnetic interaction (J = −4.6 cm−1) in the high-temperature phase (HT) and the spin–gap (Δ/kb = 68.5 K) in the low-temperature phase (LT).