Synthesis, Crystal Structure, and Magnetic Properties of Oxalato−Copper(II) Complexes with 3,3-Bis(2-imidazolyl)propionic Acid, an Imidazole−Carboxylate Polyfunctional Ligand: From Mononuclear Entities to Ladder-Like Chains

The synthesis of five new Cu(II) compounds of formula [Cu(HBIP)(C2O4)]·H2O (1), [Cu(HBIP)(C2O4)(OH2)]·2H2O (2), [{Cu(HBIP)Cl}2(μ-C2O4)]·2H2O (3), [{Cu(BIP)}2(μ-C2O4)]·2H2O (4) and [{Cu(BIP)}2(μ-C2O4)]·6H2O (5), together with their spectral and magnetic characterization, is reported. Crystal structures of compounds 2, 3 and 5 have been solved. All these compounds crystallize in the triclinic system, space group P1̄, with a = 7.3322(3) Å, b = 10.014(1) Å, c = 11.541(1) Å, α = 113.22(1)°, β = 91.37(1)°, γ = 94.51(1)°, Z = 2 for compound 2; a = 7.444(2) Å, b = 8.518(2) Å, c = 11.231(2) Å, α = 97.45(2)°, β = 98.99(2)°, γ = 97.95(2)°, Z = 1 for compound 3; and a = 7.977(1) Å, b = 8.656(1) Å, c = 11.807(1) Å, α = 69.06(1)°, β = 86.07(1)°, γ = 67.36(1)°, Z = 1 for compound 5. In compound 2 the asymmetric unit consists of one isolated neutral [Cu(HBIP)(C2O4)(OH2)] molecule and two noncoordinated water molecules. The Cu(II) ion is five-coordinated (4+1 coordination mode) with HBIP and oxalato entities acting as bidentate ligands and the water molecule as the fifth ligand. The structure of compound 3 is made up of centrosymmetric binuclear [{Cu(HBIP)(Cl)}2(μ-C2O4)] units and noncoordinated water molecules. The two copper atoms are linked through a bis-bidentate oxalato group leading to a metal−metal separation of 5.28(3) Å. The coordination stereochemistry of the CuN2O2Cl chromophore is approximately SP. Compound 5 exhibits a structure built of ladder-like chains. In these chains the rungs are constituted by the neutral dinuclear centrosymmetric [(BIP)Cu(C2O4)Cu(BIP)] entities. The oxalato group bridges two copper atoms in a bis-bidentate fashion, whereas the BIP acts as a tridentate ligand, connecting through their carboxylate groups these dimeric units along the a axis. The copper atom is involved in a five-coordinated CuN2O2O‘ chromophore, with a coordination geometry intermediate between SP and TBP. The magnetic properties of all complexes have been investigated. Compound 1 and 2 follow a Curie−Weiss law with very low values of θ. The other three compounds exhibit an antiferromagnetic coupling, with 2 J = −265 cm-1 for 3, 2 J = −108 cm-1 for 4, and 2 J = −5.7 cm-1 for 5. The strength of the exchange interaction is discussed on the basis of the structural features and correlated with published magneto-structural data on similar oxalato-bridged copper(II) compounds.