Mononuclear and binuclear copper(II) complexes with bis(2-imidazolyl) (bis(methoxycarbonyl)methylmethane) (BIBM), a tripodal bis(imidazole) based ligand. Synthesis, crystal structure and magnetic Characterization of [Cu(BIBM)_2](ClO_4)_2 and [{Cu(BIBM)(H _2O)}_2(μ_(1,2,3,4)-C_2O 4](C4O4)·6H2O

摘要

Two new Cu(II) complexes with bis(2-imidazolyl) (bis(methoxycarbonyl) methylmethane) (BIBM), a tridentate bis(imidazole) based ligand with the formula [Cu(BIBM)_2](ClO_4)_2 (1) and [{Cu(BIBM)(H _2O)}_2(μ_(1,2,3,4)-C_2O _4)](C_4O_4)·6H_2O (2) have been synthesized and characterized. Compound 1 shows mononuclear cationic [Cu(BIBM)_2]~(2+) units and perchlorate ions. The coordination around the Cu(II) ion shows a tetragonally-elongated octahedral geometry. The BIBM ligand acts as a k~3-N,N',O tripodal ligand, through two imidazole N atoms and a weak Cu-O(carboxymethyl) axial interaction. In the crystal structure cations and anions connect through H-bonds generating linear chains. Linear chains assemble forming molecular layers through imidazole rings aromatic-aromatic interactions. The structure of compound 2 consists on centrosymmetric oxalate-bridged binuclear [Cu_2(BIBM) _2(OH_2)_2(μ_(1,2,3,4)-C _2O_4)]~(2+) units, squarate dianions and water molecules in a 1:1:6 relation. The geometry around copper ions could be described as tetragonally elongated octahedrons of the 4+1+1′ type. In the structure, molecular building blocks (MBBs) are packed together by multiple-path H-bonding and π-π stacking interactions, giving rise to the supramolecular 3D network. The molecular EPR spectra is indicative of an essentially d_(x2-y2) ground state for copper(II) ions in both compounds. Magnetic susceptibility measurements of compound 2 show strong antiferromagnetic exchange between the copper(II) ions (J = -325 cm ~(-1)). The magnitude of the exchange interaction is discussed in relation to the structural features and compared with published magneto-structural data on similar oxalato-bridged copper(II) compounds.