CRYSTAL-STRUCTURE OF RB2BA4O71

The crystal structure of Rb2B4O7 is described, the first structure det ermined for anhydrous rubidium borates. It belongs to the triclinic sy stem, sp. gr. <P(1)over bar>; a = 9.860(4), b = 10.653(6), c = 6.649(4 ) Angstrom; alpha = 103.4(1), beta = 101.4(1), gamma = 89.1(1)degrees; V = 665.5 Angstrom(3); Z = 4; d(calc) = 3.26 g/cm(3). The atomic coor dinates of atoms of the isostructural K2B4O7 compound were used in the anisothropic approximation, R = 0.053. The structure consists of a th ree-dimensional skeleton formed by three kinds of mixed anions: [(BO1. 5)-O-III](0) triangles; [(B2BO5.5)-B-IV-O-III](2-) simple rings consis ting of two tetrahedra and a triangle; and [(B2B2O7)-B-IV-O-III](2-) d ouble rings formed by [(B2BO5.5)-B-IV-O-III](2-) simple rings of two s hared tetrahedra.