Ligand Influences on the Structures of Molybdenum Oxide Networks

Abstract

The influence of organonitrogen ligands on the network structure of molybdenum oxides was examined by preparing three new molybdenum oxide phases [MoO₃(4,4‘-bpy)_0.5] (MOXI-8), [H_xMoO₃(4,4‘-bpy)_0.5] (MOXI-9), and [MoO₃(triazole)_0.5] (MOXI-32). The structure of [MoO₃(4,4‘-bpy)_0.5] consists of layers of corner-sharing MoO₅N octahedra, buttressed by bridging 4,4‘-bipyridyl ligands into a three-dimensional covalently bonded organic−inorganic composite material. Partial reduction of [MoO₃(4,4‘-bpy)_0.5] yields the mixed-valence material [H_xMoO₃(4,4‘-bpy)_0.5] (x ≈ 0.5). The most apparent structural change upon reduction is found in the Mo−ligand bond lengths of the MoO₅N octahedra, which exhibit the usual (2 + 2 + 2) pattern in [MoO₃(4,4‘-bpy)_0.5] and a more regular (5 + 1) pattern in [H_xMoO₃(4,4‘-bpy)_0.5]. Substitution of triazole for 4,4‘-bipyridine yields [MoO₃(triazole)_0.5], which retains the layer motif of corner-sharing MoO₅N octahedra but with distinct sinusoidal ruffling in contrast to planar layers of [MoO₃(4,4‘-bpy)_0.5] and [H_xMoO₃(4,4‘-bpy)_0.5]. The folding reflects the ligand constraints imposed by the triazole ligand that bridges adjacent Mo sites within a layer. MOXI-8, C₅H₄NMoO₃: monoclinic P2₁/c, a = 7.5727(6) Å, b = 7.3675(7) Å, c = 22.433(3) Å, β = 90.396(8)°, Z = 8. MOXI-9, C₅H_4.5NMoO₃: monoclinic I2/m, a = 5.2644(4) Å, b = 5.2642(4) Å, c = 22.730(2) Å, β = 90.035(1)°, Z = 4. MOXI-32, C₂H₃N₃Mo₂O₆: orthorhombic Pbcm, a = 3.9289(5) Å, b = 13.850(2) Å, c = 13.366(2) Å, Z = 4.