Synthesis, crystal structures and magnetism of triclinic hydrogen selenite chlorides ACu(HSeO₃)Cl₂ (A = Rb, Cs)

Single crystals of ACu(HSeO3)Cl2 (A = Rb, Cs) were prepared through hydrothermal reactions. They crystallized in the triclinic P-1 space group with similar lattice parameters: a = 6.6955(2) angstrom, b = 7.3492(2) angstrom, c = 7.4457(2) angstrom, alpha = 109.368(2)o, beta = 109.919(2)o, and gamma = 97.496(2)o for RbCu(HSeO3)Cl2 and a = 6.9183(2) angstrom, b = 7.4541 (2) angstrom, c = 7.5723(2) angstrom, alpha = 108.329(2)o, beta = 110.006(2)o, and gamma = 98.024(2)o for CsCu(HSeO3)Cl2. The crystal structures of these isomorphic compounds consisted of unusual [Cu(HSeO3)Cl2] chains, where the elongated apical Cu-Cl distances in an elongated CuO4Cl2 octahedron, stabilized by the Jahn-Teller effect, constrained the symmetry, as well as the size of the alkali cations. The magnetic characterization of ACu(HSeO3)Cl2 revealed weak ferromagnetic interactions along the chains of CuO2Cl4 octahedra.