The crystal structures of two hydro-closo-borates with divalent tin in comparison : Sn(H2O)3[B10H10] · 3 H2O and Sn(H2O)3[B12H12] · 4 H2O

Abstract

Single crystals of Sn(H2O)3[B10H10] · 3 H2O and Sn(H2O)3[B12H12] · 4 H2O are easily accessible by reactions of aqueous solutions of the acids (H3O)2[B10H10] and (H3O)2[B12H12] with an excess of tin metal powder after isothermal evaporation of the clear brines. Both compounds crystallize with similar structures in the triclinic system with space group P1¯ and Z = 2. The crystallographic main features are electroneutral 1∞{Sn(H2O)3/1[B10H10]3/3} and 1∞{ Sn(H2O)3/1[B12H12]3/3} double chains running along the a-axes. Each Sn2+ cation is coordinated by three water molecules of hydration (d(Sn-O) = 221-225 pm for the B10 and d(Sn-O) = 222-227 pm for the B12 compound) and additionally by hydridic hydrogen atoms of the three nearest boron clusters (d(Sn-H) = 281-322 pm for the B10 and d(Sn-H) = 278-291 pm for the B12 compound), which complete the coordination sphere. Between these tin(II)-bonded water and the three or four interstitial crystal water molecules, classical bridging hydrogen bonds are found, connecting the double chains to each other. Furthermore, there is also non-classical hydrogen bonding between the anionic [BnHn]2- (n = 10 and 12) clusters and the crystal water molecules pursuant to B-Hδ-⋯δ+H-O interactions often called dihydrogen bonds.