Reduced Zirconium Halide Clusters in Aqueous Solution

Abstract

Reduced hexazirconium halide cluster compounds have good solubility and stability in strongly acidic and/or halide-rich aqueous solutions. Cyclic voltammetric (CV) measurements in aqueous media established that [(Zr6BCl12)(H2O)6]2+/+ and [(Zr6BBr12)(H2O)6]2+/+ exhibited positive half-wave potentials (E1/2 = 0.059V and 0.160 V, respectively) vs the SHE, indicating that these clusters are only modestly reducing. Several new crystalline cluster compounds have been isolated from cold 12 M HCl solutions; the structures of each contain extended hydrogen-bonding water networks. Crystallographic data for these compounds are reported as follows: [Rb0.44(H3O)4.56][(Zr6BCl12)Cl6].19.44H2O (3), cubic, Im3m, a = 13.8962(3) A, Z = 2; (H3O)5[(Zr6BeCl12)Cl6].19H2O (4), cubic, Im3m, a = 13.8956(4) A, Z = 2; (H3O)5[(Zr6MnCl12)Cl6].19H2O (5), cubic, Im3m, a = 14.029(3) A, Z = 2; (H3O)4[(Zr6BCl12)Cl6].12.97H2O (6), tetragonal, P4(2)/mnm, a = 11.5373(2) A, c = 15.7169(4) A, Z = 2; (H3O)4[(Zr6BCl2)Br6].13.13H2O (7), tetragonal, P4(2)/mnm, a = 11.7288(6) A, c = 15.931(1) A, Z = 2.

Excision of Zirconium Iodide Clusters from Highly Cross-Linked Solids

“…Because the steric congestion around zirconium atoms is greatest in the iodide clusters (they have the most acute trans X i −Zr−X i angles), the hexazirconium metal cores in the iodides are least accessible to nucleophiles, and therefore, they show the greatest kinetic “stability” in aqueous solution. Clusters with larger interstitial atoms (Be, Fe, or Mn) are more reactive than the C- and B-centered clusters in water, presumably by virtue of the greater steric accessibility of their Zr atoms …”

“…or ionic liquids (AlCl 3 /1-ethyl-3-methylimidazolium chloride, AlCl 3 /ImCl). − However, no solution chemistry of iodide-supported hexazirconium clusters had been investigated. Recently, we have demonstrated that the deoxygenated water is a useful solvent for dissolution of some hexazirconium cluster compounds and demonstrated the surprising kinetic stability of clusters obtained thereby in aqueous media. − …”

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“…15 Some reduced halide clusters have considerable stability in strongly acidic or halide rich solutions. 16 Half-wave potentials of 0.059 and 0. 17 A refinement 18 of the structure of K 2 [TiF 6 ] shows octahedral co-ordination of Ti (Ti-F 1.8605 Å).…”

A DFT Study of the Interstitial Chemical Shifts in Main Group Element Centered Hexazirconium Halide Clusters

“…NMR spectroscopy has proven to be an invaluable analytical tool for characterizing centered hexanuclear zirconium halide clusters (Figure ), [(Zr 6 ZX 12 )L 6 ] m - (X = Cl, Br, I; Z = H, Be, B, C, N, Mn, and Co; L = various ligands), as species in solution − and as building blocks in the solid state . NMR spectroscopy serves a more central and comprehensive analytical role in the study of [(Zr 6 ZX 12 )L 6 ] m - based clusters than is possible for any other polynuclear metal clusters.…”