SR0.735BA0.265CU2(BO3)(2) AND SR-0.661CA0.339CU2(BO3)(2)

The crystal structures of Sr0.735Ba0.265Cu2(BO3)(2) and Sr-0.661 Ca0.339Cu2(BO3)(2), which are isostructural with SrCu2(BO3)(2), have been refined from single-crystal Xray diffraction data. The structures consist of slightly puckered layers with the composition [CuBO3](-) stacked along the c axes, with Sr, Ba or Ca atoms eight-coordinated between the layers. The interlayer separation is directly affected by the substitution of smaller Ca or larger Ba atoms in place of Sr. In both structures, each Cu atom is coordinated by four O atoms with Cu-O distances ranging from 1.91 to 1.94 Angstrom. The berate groups are distorted from D-3h to C-2v symmetry.