Magneto-structural Correlations in Ni(2+)–Halide···Halide–Ni(2+) Chains

[Image: see text] We present the magnetic properties of a new family of S = 1 molecule-based magnets, NiF(2)(3,5-lut)(4)·2H(2)O and NiX(2)(3,5-lut)(4), where X = HF(2), Cl, Br, or I (lut = lutidine C(7)H(9)N). Upon creation of isolated Ni–X···X–Ni and Ni–F–H–F···F–H–F–Ni chains separated by bulky and nonbridging lutidine ligands, the effect that halogen substitution has on the magnetic properties of transition-metal-ion complexes can be investigated directly and in isolation from competing processes such as Jahn–Teller distortions. We find that substitution of the larger halide ions turns on increasingly strong antiferromagnetic interactions between adjacent Ni(2+) ions via a novel through-space two-halide exchange. In this process, the X···X bond lengths in the Br and I materials are more than double the van der Waals radius of X yet can still mediate significant magnetic interactions. We also find that a simple model based on elongation/compression of the Ni(2+) octahedra cannot explain the observed single-ion anisotropy in mixed-ligand compounds. We offer an alternative that takes into account the difference in the electronegativity of axial and equatorial ligands.