The Hydrogen Oxide Bridging Ligand (H₃O₂⁻). 1. Dimerization and Polymerization of Hydrolyzed Trinuclear Metal Cluster Ions

Trinuclear metal cluster ions of molybdenum and tungsten undergo hydrolysis in aqueous solutions. By the addition of various counterions such as Cl⁻, Br⁻, I⁻, and NCS⁻ to this solution several hydrolysis products with different degrees of polymerization have been crystallized. The preparation and X-ray structural characterization of six new compounds are reported; full structural details are presented for two compounds. The two compounds are isomorphous having the formula ([M₃O₂-(O₂CC₂H₅)₆(H₂O)₂]2(H₃O₂)}Br-6H₂O, in compound 1, M = Mo, and in 2, M = W. They crystallized in space group Pl̅ with the following cell dimensions: 1, a = 14.358 (4) Å, b = 12.114 (3) Å,c= 11.402 (2) Å, α = 111.08 (2)°, α = 105.69 (3)°, γ = 66.74 (2)°, V= 1680 (2) ų, and Z = 1; 2, a = 14.316 (3) Å, b = 12.115 (2) Å, c = 11.423 (2) Å, α = 111.14 (2)°, β = 105.59 (2)°, γ = 66.59 (2)°, V = (2) ų, and Z = 1. Dimerization and polymerization occur by formation of a hydrogen oxide ligand (H₃O₂⁻), bridging between two metal atoms of adjacent cluster ions. The H₃O₂− unit appearing in structures 1 and 2 is symmetric with an O-O separation of 2.52 (1) Å and 2.50 (1) Å, respectively.