Ligand influences on the structures of molybdenum oxide networks

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(x)MoO₃(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(x)MoO₃(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(x)MoO₃(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(x)MoO₃(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.