Octahedral {TaI} Clusters.

Ta powder reacts with I at 650 °C with the formation of TaI, which belongs to the family of {M(μ-X)} clusters. It undergoes aquation with the formation of the intensely colored [TaI(HO)]. The crystal structure was determined for [TaI(HO)](BPh)·HO (Ta-Ta 2.9322(6) Å, Ta-I 2.8104(7) Å, Ta-O 2.3430(5) Å). With DMF, [TaI(DMF)]I·DMF was isolated (Ta-Ta 2.9500(2) Å, Ta-I 2.8310(4) Å, Ta-O 2.2880(7) Å). Cyclic voltammetry of [TaI(HO)] shows two consecutive quasi-reversible one-electron oxidations ( 0.61 and 0.92 V vs Ag/AgCl). Reaction of TaI with BuNCN yields (BuN)[TaI(CN)]·CHCN (Ta-Ta 2.9777(4) Å, Ta-I 2.8165(6) Å, Ta-C 2.2730(7) Å). Quantum chemical calculations reproduce well the experimental geometry of the aqua complex and show the essentially Ta-centered nature of both the HOMO and LUMO. The long-term stability of [TaI(HO)] solutions can be greatly enhanced in the presence of polystyrenesulfonate (PSS), which forms nanoparticle associates with the aqua complex in water (ca. 1 cluster per 3 PSS monomeric units).