Crystal structures of M-2[B10H10] (M = Na, K, Rb) via real-space simulated annealing powder techniques

Alkali metal decahydro-closo-decaborates M-2[B10H10] (M = Na, K, Rb) were synthesised by ion-exchange and characterised via infrared and B-11-NMR spectroscopy. The crystal structures of Na-2[B10H10,], K-2[B10H10], and Rb-2[B10H10] were determined from X-ray powder diffraction data using real-space techniques. The compounds crystallise in the monoclinic space group P2(1)/n (no. 14) with the lattice constants: Na2[B10H10]: a = 1028.28(6) pm, b = 1302.18(5) pm, c = 667.34(3) pm, beta = 93.754(3)degrees; K-2[B10H10]: a = 1285.54(8) pm, b = 1117.84(7) pm, c = 682.27(4) pm, beta = 93.357(3)degrees; Rb-2[B10H10]: a = 1320.04(7) pm, b = 1136.88(6) pm, c = 704.23(4) pm, P = 94.158(3)degrees. The hydroborate anions are arranged almost hexagonally with alkali metal cations in the tetrahedral interstices.