Polynuclear Bismuth‐Oxo Clusters: Insight into the Formation Process of a Metal Oxide

Abstract

The reaction of the bismuth silanolates [Bi(OSiR₂R′)₃] (R = R′ = Me, Et, iPr; R = Me, R′ = tBu) with water has been studied. Partial hydrolysis gave polynuclear bismuth-oxo clusters whereas amorphous bismuth-oxo(hydroxy) silanolates were obtained when an excess of water was used in the hydrolysis reaction. The metathesis reaction of BiCl₃ with NaOSiMe₃ provided mixtures of heterobimetallic silanolates. The molecular structures of [Bi₁₈Na₄O₂₀(OSiMe₃)₁₈] (2), [Bi₃₃NaO₃₈(OSiMe₃)₂₄]⋅3 C₇H₈ (3⋅3 C₇H₈), [Bi₅₀Na₂O₆₄(OH)₂(OSiMe₃)₂₂]⋅2 C₇H₈⋅2 H₂O (4⋅2 C₇H₈⋅2 H₂O), [Bi₄O₂(OSiEt₃)₈] (5), [Bi₉O₇(OSiMe₃)₁₃]⋅0.5 C₇H₈ (6⋅0.5 C₇H₈), [Bi₁₈O₁₈(OSiMe₃)₁₈]⋅2 C₇H₈ (7⋅2 C₇H₈) and [Bi₂₀O₁₈(OSiMe₃)₂₄]⋅3 C₇H₈ (8⋅3 C₇H₈) are presented and compared with the solid-state structures of [Bi₂₂O₂₆(OSiMe₂tBu)₁₄] (9) and β-Bi₂O₃. Compound 2 crystallises in the triclinic space group P with the lattice constants a = 17.0337(9), b = 19.5750(14), c = 26.6799(16) Å, α = 72.691(4), β = 73.113(4) and γ = 70.985(4)°; compound 3⋅3 C₇H₈ crystallises in the monoclinic space group P2₁/n with the lattice constants a = 20.488(4), b = 22.539(5), c = 26.154(5) Å and β = 100.79(3)°; compound 4⋅2 C₇H₈⋅2 H₂O crystallises in the monoclinic space group P2₁/n with the lattice constants a = 20.0518(12), b = 24.1010(15), c = 27.4976(14) Å and β = 103.973(3)°; compound 5 crystallises in the monoclinic space group P2₁/c with the lattice constants a = 25.256(5), b = 15.372(3), c = 21.306(4) Å and β = 113.96(3)°; compound 6⋅0.5 C₇H₈ crystallises in the triclinic space group P with the lattice constants a = 15.1916(9), b = 15.2439(13), c = 22.487(5) Å, α = 79.686(3), β = 74.540(5) and γ = 66.020(4)°; compound 7⋅2 C₇H₈ crystallises in the triclinic space group P with the lattice constants a = 14.8295(12), b = 16.1523(13), c = 18.4166(17) Å, α = 75.960(4), β = 79.112(4) and γ = 63.789(4)°; and compound 8⋅3 C₇H₈ crystallises in the triclinic space group P with the lattice constants a = 17.2915(14), b = 18.383(2), c = 18.4014(18) Å, α = 95.120(5), β = 115.995(5) and γ = 106.813(5)°. The molecular structures of the bismuth-rich compounds are related to the CaF₂-type structure. Formally, the hexanuclear [Bi₆O₈]²⁺ fragment might be described as the central building unit, which is composed of bismuth atoms placed at the vertices of an octahedron and oxygen atoms capping the trigonal faces. Depending on the reaction conditions and the identity of R, the thermal decomposition of the hydrolysis products [Bi_nO_l(OH)_m(OSiR₃)_{3n−(2l−m)}] gives α-Bi₂O₃, β-Bi₂O₃, Bi₁₂SiO₂₀ or Bi₄Si₃O₁₂.