Two Dodecahydro-closo-Dodecaborates with Lone-Pair Cations of the 6th Period in Comparison: Tl2[B12H12] and Pb(H2O)3[B12H12]•3H2O

During the reaction of an aqueous solution of (H3O)(2)[B12H12] with Tl2CO3 anhydrous thallium(I) dodecahydrocloso- dodecaborate Tl2[B12H12] is obtained as colorless, spherical single crystals. It crystallizes in the cubic system with the centrosymmetric space group Fm (3) over bar (a = 1074.23(8) pm, Z = 4) in an anti-CaF2 type structure. Four quasi-icosahedral [B12H12](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 (H3O)(2)[B12H12] with PbCO3 and after isothermic evaporation colorless, plate-like single crystals of lead(II) dodecahydro-closo-dodecaborate hexahydrate Pb(H2O)(3)[B12H12]center dot 3H(2)O can be isolated. This compound crystallizes orthorhombically with the non-centrosymmetric space group Pna2(1) (a = 1839.08(9), b = 1166.52(6), c = 717.27(4) pm, Z = 4). The crystal structure of Pb(H2O)(3)[B12H12]center dot 3H(2)O is characterized as a layer-like arrangement. The Pb2+ 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 [B12H12](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 Pb2+ 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 Pb2+ cation. Since additional intercalating water of hydration is present as well, both classical H-O-delta center dot center dot center dot H+delta-O-and unconventional B-H-delta center dot center dot center dot H+delta-O hydrogen bonds play a significant role in the stabilization of the entire crystal structure.