Abstract
Single crystals and polycrystalline samples of a synthetic analogue of saranchinaite, Na 2 Cu(SO 4) 2 , have been prepared by two different methods. The structural analysis revealed unusual heptahedral CuO 7 coordination [4 + 1 + 2] of Cu 2+ cations in its crystal structure. The title compound crystallizes in the noncentrosymmetric space group P2 1 and exhibits the averaged nonlinear coefficient ⟨d⟩ = 1.4[d 14 (SiO 2)] ≈ 0.5 pm/V. Electrochemical tests showed a limited electrochemical performance and low mobility of Na ions in the structure. The magnetic properties of Na 2 Cu(SO 4) 2 reflect its crystal structure with half of copper cations as mainly paramagnetic and the other half as strongly engaged in antiferromagnetic dimer interactions. Analysis of the synthesis methods for preparation of the other Na-containing anhydrous sulfates is reported. Dehydration of the Na 2 M(SO 4) 2 (H 2 O) x (x = 0−6) phases, various structure types, and the structural complexity of Na 2 M(SO 4) 2 (M = Mn, Co, Ni, Cu, Zn, Cd) compounds are also discussed.