Experimental and theoretical investigations of magnetic properties for two low-dimensional spin systems based on bis(2-thioxo-1,3-dithiole-4,5-dithiolato) nickelate monoanion building blocks

Two complexes of [Ni(dmit)₂]^- (dmit^2- = 2-thioxo-1,3-dithiole-4,5-dithiolate) with nonmagnetic Schiff base cations, 1-(4-bromobenzylideneamino)pyridinium (4-BrBz-1-APy⁺; 1) and 1-(3-nitrobenzylideneamino)pyridinium (3-NO₂Bz-1-APy⁺; 2), have been characterized structurally. Their striking structural feature is the deviation of the [Ni(dmit)₂]^- anion from the square-planar environment around the Ni atom with 11.42° and 6.57° dihedral angles (between the mean molecular planes of two dmit^2- ligands) in 1 and 2, respectively. These twists arise from the molecular packing interactions between the superimposed anion and cation. In 1, the magnetic [Ni(dmit) ₂]^- anions are arranged into a wave-shaped regular spin chain, whose magnetism was well fitted by one-dimensional (1D) Heisenberg uniform linear antiferromagnetic chain with |J/k_B| = 66 K. In 2, 1D ladder-shape [Ni(dmit)₂]^- chains are formed through lateral-to-lateral S⋯S contacts between the adjacent anions, which are further aligned into a two-dimensional (2D) anion layer via van der Waals forces. Complex 2 shows Curie-Weiss-type paramagnetic behavior with Curie constant C = 0.421 emu K mol^-1 and Weiss constant θ = -1.279 K. The broken-symmetry DFT approach was utilized to evaluate the magnetic coupling nature for 1 and 2, the theoretical analyses performed at ubpw91/lanl2dz level and concerned the so-called "weak bonding" regime approaches qualitatively explained the magnetic behaviors of 1 and 2.