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

Single crystals of Sn(H 2 O) 3 [B 10 H 10 ] · 3 H 2 O and Sn(H 2 O) 3 [B 12 H 12 ] · 4 H 2 O are easily accessible by reactions of aqueous solutions of the acids (H 3 O) 2 [B 10 H 10 ] and (H 3 O) 2 [B 12 H 12 ] 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 P 1 ¯ and Z = 2. The crystallographic main features are electroneutral ∞ 1 { Sn(H 2 O) 3/1 [B 10 H 10 ] 3/3 } and ∞ 1 { Sn(H 2 O) 3/1 [B 12 H 12 ] 3/3 } double chains running along the a -axes. Each Sn 2+ cation is coordinated by three water molecules of hydration ( d (Sn–O) = 221–225 pm for the B 10 and d (Sn–O) = 222–227 pm for the B 12 compound) and additionally by hydridic hydrogen atoms of the three nearest boron clusters ( d (Sn–H) = 281–322 pm for the B 10 and d (Sn–H) = 278–291 pm for the B 12 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 [B n H n ] 2− (n = 10 and 12) clusters and the crystal water molecules pursuant to B–H δ− ⋯ δ+ H–O interactions often called dihydrogen bonds.