During the reaction of an aqueous solution of (H3O)2[B12H12] with Tl2CO3 anhydrous thallium(I) dodecahydro-closo-dodecaborate Tl2[B12H12] is obtained as colorless, spherical single crystals. It crystallizes in the cubic system with the centrosymmetric space group Fm (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 (6s2lone 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]·3H2O can be isolated. This compound crystallizes orthorhombically with the non-centrosymmetric space group Pna21 (a = 1839.08(9), b = 1166.52(6), c = 717.27(4) pm, Z = 4). The crystal structure of Pb(H2O)3[B12H12]·3H2O 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–Oδ–···+δH–O- and unconventional B–Hδ–···+δH–O hydrogen bonds play a significant role in the stabilization of the entire crystal structure.