An x-ray, spectroscopic, and magnetic study of the structure of nickel squarate dihydrate, NiC4O4 · 2H2O

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Abstract
The structure of nickel squarate dihydrate, NiC4O4 · 2H2O, has been investigated by initial susceptibility measurements, infrared spectroscopy, and single crystal x‐ray diffraction techniques. The results indicate that the structure consists of Ni ions situated at the centers of the edges of a cube, with squarate ions in the cube faces. Each nickel is roughly octahedrally coordinated by four squarate oxygens, and by two water oxygens. The lattice constants were found to be a = b = c =8.0685A, with α = β = γ = 90° within experimental accuracy. The structure was found to be noncubic. A spin‐orbit coupling parameter of −280 (30) cm−1, which is 86% of the free ion value, is obtained from the magnetic and spectroscopic results. The structure of this compound, which is isostructural with the Mn(II), Fe(II), and CO(II) squarates, is different than that proposed by two other sets of workers. All crystals investigated were found to be macroscopically twinned, and a reason for such twinning is proposed.

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