Two Dodecahydro‐ closo ‐Dodecaborates with Lone‐Pair Cations of the 6th Period in Comparison: Tl 2 [B 12 H 12 ] and Pb(H 2 O) 3 [B 12 H 12 ]·3H 2 O

During the reaction of an aqueous solution of (H 3 O) 2 [B 12 H 12 ] with Tl 2 CO 3 anhydrous thallium(I) dodecahydro‐ closo ‐dodecaborate Tl 2 [B 12 H 12 ] is obtained as colorless, spherical single crystals. It crystallizes in the cubic system with the centrosymmetric space group Fm $\bar{3}$ ( a = 1074.23(8) pm, Z = 4) in an anti ‐CaF 2 type structure. Four quasi ‐icosahedral [B 12 H 12 ] 2– anions ( d (B–B) = 180–181 pm, d (B–H) = 111 pm) exhibit coordinative influence on each Tl + cation and provide a twelvefold coordination in the shape of a cuboctahedron ( d (Tl–H) = 296 pm). There is no observable stereochemical activity of the non ‐bonding electron pairs (6s 2 lone pairs ) at the Tl + cations. By neutralization of an aqueous solution of the acid (H 3 O) 2 [B 12 H 12 ] with PbCO 3 and after isothermic evaporation colorless, plate‐like single crystals of lead(II) dodecahydro‐ closo ‐dodecaborate hexahydrate Pb(H 2 O) 3 [B 12 H 12 ] · 3H 2 O can be isolated. This compound crystallizes orthorhombically with the non ‐centrosymmetric space group Pna 2 1 ( a = 1839.08(9), b = 1166.52(6), c = 717.27(4) pm, Z = 4). The crystal structure of Pb(H 2 O) 3 [B 12 H 12 ] · 3H 2 O is characterized as a layer‐like arrangement. The Pb 2+ cations are coordinated in first sphere by only three oxygen atoms from water molecules ( d (Pb–O) = 247–248 pm). But a coordinative influence of the [B 12 H 12 ] 2– anions ( d (B–B) = 173–181 pm, d (B–H) = 93–122 pm) on lead has to be stated, too, as three hydrogen atoms from three different hydroborate anions are attached to the Pb 2+ cations ( d (Pb–H) = 258–270 pm) completing their first‐sphere coordination number to six. These three oxygen and three hydrogen ligands are arranged as quite irregular polyhedron leaving enough space for a stereochemical lone‐pair activity (6sp) at each Pb 2+ cation. Since additional intercalating water of hydration is present as well, both classical H–O δ – ··· + δ H–O‐ and unconventional B–H δ – ··· + δ H–O hydrogen bonds play a significant role in the stabilization of the entire crystal structure.