Strontium nickel and barium nickel selenites: Synthesis and X-ray diffraction parameters

A new strontium nickel selenite, Sr₂Ni(SeO₃)₃, was prepared and structurally characterized. The compound crystallizes in triclinic system (space group P \(\bar 1\), a = 7.2860(10) Å, b = 7.581(2) Å, c = 8.722(2) Å, α = 103.02(2)°, β = 105.580(10)°, γ = 95.260(10)°, Z = 2) and is isostructural to cobalt and copper analogues. The structure of Sr₂Ni(SeO₃)₃ is a three-dimensional framework built of eight-vertex polyhedra SrO₈] and distorted octahedra NiO₆] sharing edges and vertices. The framework channels accommodate selenium atoms bonded to the framework oxygen atoms. The selenite groups SeO₃ are pyramidal, which is indicative of high stereochemical activity of the Se(IV) lone pair. The possibility of replacement of some Ni atoms by Cu in Sr₂Ni(SeO₃)₃ was studied. The search for analogous barium phases did not reveal such compounds, but BaM(SeO₃)₂ phases were found, where M = Co, Ni, or Cu. The unit cell parameters of the new selenite BaM(SeO3)2 were determined: space group Pnma, a = 14.989(5) Å, b = 5.439(2) Å, c = 7.161(3) Å, Z = 4.