Structural, Electronic, and Magnetic Consequences of O-Carbonyl vs O-Alkoxy Ester Coordination in New Dicopper Complexes Containing the Cu2(μ-Cl)2 Core

The complexes [Cu2(μ-Cl)2(Cl)2(L)2] (L = dialkylpyridine-2,6-dicarboxylate; R = Et, L = depc, 1; R = i-Pr, L = dppc, 2) have been prepared and their magnetic properties studied. The crystal structures of complexes 1 and 2 have been solved. Compound 1 belongs to the P1̄ space group with Z = 2, a = 8.3020(10) Å, b = 9.2050(10) Å, c = 10.065(2) Å, α = 99.040(10)°, β = 100.810(10)°, and γ = 106.502(10)° whereas 2 belongs to the C2/c space group with Z = 8, a = 11.6360(10) Å, b = 25.906(3) Å, c = 11.76579(10) Å, and β = 107.900(10)°. The different alkyl ester substitutes produce substantial structural and electronic differences. The Cu2Cl2 core geometry is planar for 1 whereas it adopts a butterfly shape in the case of 2. Furthermore, in 2 the dppc ligand coordinates only by the carbonyl oxygen atoms whereas in 1 the depc ligand coordinates through carbonyl and alkoxy oxygen atoms. Magnetic susceptibility data show a ferromagnetic coupling between the two Cu(II) centers in both cases (J = 39.9(6) cm-1 for 1, and J = 51.3(5) cm-1 for 2) with very weak antiferromagnetic interactions (J ‘ = −0.59 cm-1 and −0.57 cm-1 for 1 and 2, respectively). Theoretical calculations at the extended Hückel level have also been carried out to further understand the electronic nature of complexes 1 and 2.