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 Ca0.3 39Cu2(BO3)(2), which are isostructural with SrCu2(BO3)(2), have been r efined from single-crystal Xray diffraction data. The structures consi st of slightly puckered layers with the composition [CuBO3](-) stacked along the c axes, with Sr, Ba or Ca atoms eight-coordinated between t he layers. The interlayer separation is directly affected by the subst itution of smaller Ca or larger Ba atoms in place of Sr. In both struc tures, 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 f rom D-3h to C-2v symmetry.