Ligand influences on copper molybdate networks: The structures and magnetism of [Cu(3,4′-bpy)MoO₄], [Cu(3,3′-bpy)_0.5MoO₄], and [Cu(4,4′-bpy)_0.5 MoO₄]·1.5H₂O

The reactions of a Cu(II) salt, MoO₃, and the appropriate bipyridine ligand yield a series of bimetallic oxides, [Cu(3,4′-bpy)MoO₄] (1), [Cu(3,3′-bpy)_0.5MoO₄] (2), and [Cu(4,4′-bpy)_0.5MoO₄]·1.5H₂O (3·1.5H₂O). The structures of 1-3 exhibit three-dimensional covalent frameworks, constructed from bimetallic oxide layers tethered by the dipodal organoimine ligands. However, the {CuMoO₄} networks are quite distinct. For structure 1, the layer consists of corner-sharing {MoO₄} tetrahedra and {CuN₂O₃} square pyramids, while the layer of 2 is constructed from {MoO₄} tetrehedra and binuclear {Cu₂O₆N₂} units of edge-sharing copper square pyramids. The oxide substructure of 3 consists of {MoO₄} tetrahedra corner-sharing with tetranuclear clusters of edge-sharing {CuO₅N} octahedra. Crystal data: C₁₀H₈N₂O₄CuMo (1), orthorhombic Pbca, a = 12.4823(6) Å, b = 9.1699(4) Å, c = 19.5647(9) Å, V = 2239.4(1) ų, Z = 8; C₅H₄NO₄CUMO (2), triclinic P1, a = 5.439(1) Å, b = 6.814(1) Å, c = 10.727(2) Å, α = 73.909(4)°, β = 78.839(4)°; γ = 70.389(4)°; V = 357.6(1) ų, Z = 2; C₁₀H₈N₂O₈Cu ₂Mo₂·1.5H₂O, triclinic P1, a = 7.4273(7) Å, b = 9.2314(8) Å, c = 13.880(1) Å, α = 71.411(2)°, β= 88.528(2)°, γ = 73.650(2)°, V = 863.4(1) ų, Z = 2. The magnetic properties of 1-3 arise solely from the presence of the Cu(ll) sites, but reflect the structural differences within the bimetallic oxide layers. Compound 1 exhibits magnetic behavior consistent with ferromagnetic chains which couple antiferromagnetically at low temperature. Compound 2 exhibits strong antiferromagnetic dimeric interactions, with the magnetic susceptibility data consistent with the Bleaney-Bowers equation. Similarly, the magnetic susceptibility of 3 is dominated by antiferromagnetic interactions, which may be modeled as a linear S = 1/2 Heisenberg tetramer.