Synthesis and structural characterization of three new compounds containing [Nb6Cl12]2+ units as hydrated hydroxides

Abstract

Conditions have been established for the preparation of three different hydrated chloroniobium cluster hydroxide compounds from alkaline solutions: triclinic [Nb₆Cl₁₂(OH)₂(H₂O)₄]·4H₂O 1 and two cubic compounds whose structures are uncertain with regard to the co-ordination of OH^– ions, Nb₆Cl₁₂(OH)₂(H₂O)₁₄2 and Nb₆Cl₁₂(H₂O)₁₄(OMe)₂3. Based upon structural data 2 and 3 may contain either the cation [Nb₆Cl₁₂(H₂O)₆]²⁺ or the neutral cluster [Nb₆Cl₁₂(OH)₂(H₂O)₄] containing hydroxo ligands. In 1 distinct distances of 2.147(5) for Nb–OH, and 2.250(5) and 2.289(5)Å for Nb–OH₂ were found. In 2 and 3 only distances of 2.19(1) and 2.193(7)Å, respectively, were found for the Nb–O bonds of co-ordinated water (or hydroxide-water averaged). Compound 1 is triclinic, space group P1, a= 8.930(3), b= 9.195(2), c= 9.118(1)Å, α= 104.37(2), β= 99.51(2) and γ= 116.99(2)°, U= 611.9(3)ų, Z= 1, R= 1, R= 0.036. Compound 2 is cubic, space group Fm3m, a= 14.59(2)Å, U= 3105.7(1)ų, Z= 4, R= 0.028. Compound 3 is also cubic, space group Fm3m, a= 14.627(1)Å, U= 3129.3(1)ų, Z= 4, R= 0.031. IR spectra of 1 show strong O–H and Nb–O stretching bands that reflect the presence of co-ordinated OH^– groups. In 2 and 3 the IR spectra are less definitive about possible co-ordination of hydroxide.