A LITHOSILICATE WITH COLUMNAR UNITS - RBLI5(LI[SIO4])2

In order to prepare RbLi3[SiO4] single crystals of RbLi5{Li[SiO4]}2 have been obtained for the first time by heating of a well ground mixture of the binary oxides RbO0.68, LiO0.5 and SiO2 [Rb:Li:Si = 1.1:3.0:1.0; 600-degrees-C; 21 d] in tightly closed Ni tubes. The new "lithosilicate" crystallizes monoclinic (space group C2/m with a = 1563.1(2) pm, b = 635.4(1) pm, c = 776.3(1) pm, beta = 90.53(1)-degrees, Guinier-Simon powder data). The crystal structure was determined by four-cycle diffractometer data [Philips PW 1100, 1237 from 1609 I(o) (hkl), Z = 4, R = 9.2%, R(W) = 8.3%], parameters see text. The Madelung Part of Lattice Energy, MAPLE, and Effective Coordination Numbers, ECoN, these via Mean Fictive Ionic Radii, MEFIR, have been calculated.