Strontium–copper selenite–chlorides: Synthesis and structural investigation

Two new complex selenite–chlorides of strontium and copper Sr2Cu(SeO3)2Cl2 (I) and SrCu2(SeO3)2Cl2 (II) were obtained and characterized by X-ray diffraction technique, DTA and IR spectroscopy. Both compounds crystallize in the monoclinic system I: Sp. gr. P21/n, a=5.22996(3) Å, b=6.50528(4) Å, c=12.34518(7) Å, β=91.3643(2)°, Z=2; II: Sp. gr. P21, a=7.1630(14) Å, b=7.2070(14) Å, c=8.0430(16) Å, β=95.92(3)°, Z=2. Comparison of the crystal structure of (I) with the structures of Sr2M(SeO3)2Cl2 (M=Co, Ni) was performed. The substitution of strontium atom in the structure of (I) by Cu2+ ion with a 3d9 Jahn–Teller distorted surrounding leads to the lowering of the structure symmetry and to the appearance of the noncentrosymmetric structure of (II). The noncentrosymmetric character of the structure of (II) was confirmed by SHG signal (1.2 units relative to an α-quartz powder sample).