AG2CS[B15O24] - AN ANHYDROUS QUATERNARY S ILVER(I)-BORATE WITH A NEW HELICAL BORATE ANION

Single crystals of Ag2Cs[B15O24] were prepared by using a B2O3 flux te chnique with Ag2CO3 and Cs2CO3 in a closed silver tube at 650 degrees C. X-Ray investigations led to a new crystal structure in the space gr oup P 2(1)2(1)2 (Nr. 18) with lattice parameters a = 1778.7 (4); b = 2 219.2 (4); c = 512.2 (1) pm, Z = 4. The silver atoms are part of disto rted AgO4 tetrahedra and planar AgO3 units while the caesium atoms are eightfold coordinated by oxygen. The compound contains an as yet unkn own berate anion [B15O24] with twelve BO3- and three BO4 units per for mula. The BO3 units are connected to eight cords twisted to helices wh ich are combined via BO4 tetrahedra to a three dimensional framework w ith large tunnels occupied by the cations.