A square planar [NiCl ₄ ] (super 2-) ion in the layered double hydroxide Al ₂ Li(OH) ₆ [NiCl ₄ ] (sub 1/2)

Tokyo Institute of Technology, Department of Inorganic Materials, Tokyo, Japan

The layered double hydroxide (LDH) Al ₂ Li(OH) ₆ [NiCl ₄ ] (sub 1/2) was synthesized by anion exchange of Al ₂ Li(OH) ₆ (NO ₃ ) and the coordination structure of [NiCl ₄ ] (super 2-) in the interlayers was investigated. The LDH had a hexagonal cell with a = 5.06 and c = 23.06 Aa. Since the basal spacing of one layer was 7.7 Aa, the interlayer distance was calculated to be 2.9 Aa and was too narrow for the usual tetrahedral NiCl ₄ structure. From extended X-ray absorption fine structure (EXAFS) measurements, the first neighbour Ni-Cl distances in the LDH were 2.10 Aa which was compatible with four-fold coordination. Since the electron spin resonance (ESR) spectrum of the LDH showed no absorption, the [NiCl ₄ ] (super 2-) structure was considered to be square planar, rather than the usual tetrahedral structure in the interlayers of LDH.

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