Singlyanti-anti Carboxylate-Bridged Zig-Zag Chain Complexes from a Carboxylate-Containing Tridentate Schiff Base Ligand and M(hfac)2 [M = MnII, NiII, and CuII]: Synthesis, Crystal Structure, and Magnetic Properties

Abstract

The reaction of M(hfac)2 with the tridentate Schiff base H2L (where H2L stands for the 1:1 condensation product of 2-imidazolecarboxaldehyde with β-alanine) leads to the complexes [M(HL)(hfac)]n [M = MnII, NiII, and CuII; hfac = hexafluoroacetylacetonate anion] (1–3). The structures of the complexes 1 and 3 have been solved by X-ray crystallographic methods. The structures are very similar and consist of infinite zig-zag chains, running parallel to the b axis, in which the metal ions are bridged sequentially by anti-anti carboxylate groups with intrachain metal–metal distances of 6.134 Å for 1 and 6.239 Å for 3. Each monodeprotonated HL ligand acts as a tridentate one to a metal(II) ion and as a monodentate one to a neighbouring metal(II) centre. Metal atoms exhibit distorted octahedral coordination spheres comprised of two oxygen atoms from the hexafluoroacetylacetonate ligand, three donor atoms from the HL ligand and the oxygen atom belonging to the carboxylate group of an adjacent molecule. The complexes 1–3 have been confirmed to be isomorphous and isostructural on the basis of X-ray powder diffraction and IR spectra. The magnetic properties of the three compounds were studied by susceptibility measurements as a function of the temperature and successfully analyzed in terms of the isotropic spin Hamiltonian for one-dimensional infinite chain systems to give the coupling parameters J = –0.91 cm−1, g = 2.03 (1); J = –13.2 cm−1, g = 2.24 (2); and J = 0.40 cm−1, g = 2.11 (3). The magnetic behaviour for all three complexes can be satisfactorily explained in terms of the conformation of the bridge and the interaction between the d orbitals of the metal centre and the bridge.