Three New Polynuclear Copper(II) Complexes with the Symmetric [Cu(μ_1,1-N₃)₂Cu]²⁺ Core and Pyridine Derivatives: Syntheses, Structure, and Magnetic Behavior

Three new polynuclear copper(II) complexes, derived from the end-on azido bridging ligand and pyridine derivatives, have been synthesized, and their crystal structures have been determined by X-ray diffraction methods; they are the dinuclear compounds [Cu2(μ1,1-N3)2(4-Etpy)4(μ-NO3)2] (1), and [Cu2(μ1,1-N3)2(3-ampy)4(μ-NO3)2]·C2H5OH (2), and the trinuclear [Cu3(μ1,1-N3)4(N3)2(Meinic)2(DMF)2] (3). 4-Etpy is 4-ethylpyridine, 3-ampy is 3-aminopyridine, and Meinic is methylisonicotinate. Compound 1, C28H36Cu2N12O6, crystallized in the monoclinic system, space group P21/n, with a = 12.355(9) Å, b = 12.474(4) Å, c = 12.854(6) Å, β = 117.68(4)°, and Z = 2. Compound 2, C22H30Cu2N16O7, crystallized in the triclinic system, space group P̄1, with a = 9.695(2) Å, b = 10.895(2) Å, c = 7.909(2) Å, α = 96.81(3)°, β = 96.40(3)°, γ = 96.56(3)° and Z = 1. Compound 3, C20H28Cu3N22O6, crystallized in the monoclinic system, space group P21/n, with a = 7.755(2) Å, b = 14.680(5) Å, c = 15.810(5) Å, β = 102.81(2)°, and Z = 2. 1−3 have the symmetric [Cu(μ1,1-N3)2Cu]2+ core and structural parameters outside the previously reported range. Magnetic susceptibility data, measured from 2 to 300 K, show strong ferromagnetic coupling for the dinuclear end-on compounds 1 and 2 and bulk moderate ferromagnetic coupling for the trinuclear compound 3. These data were fitted to the appropriate equations derived from the Hamiltonian H = −JS1S2 for 1 and 2 and from the Hamiltonian H = −J1(SA1SB + SA2SB) − J2SA1·SA2 for 3, giving the parameters J = 230.1(1) cm-1, g = 2.17(0.01) for 1, J = 223.2(2) cm-1, g = 2.16(0.01) for 2, and J1 = 47.3(2) cm-1, J2 = −22.5(1) cm-1, gA = 2.26(0.02), gB = 2.07(0.03) for 3. The magnetic susceptibility data can be correlated with the structural parameters.