Iñaki Muga

Synthesis, chemical characterization, X-ray crystal structure and magnetic properties of oxalato-bridged copper(II) binuclear complexes with 2,2′-bipyridine and diethylenetriamine as peripheral ligands

Abstract Two new μ-oxalato binuclear copper(II) complexes, [{Cu(NO3)(H2O)(bipy)}2(ox)] (1) and [{Cu(dien)}2(ox)](NO3)2 (2), with ox=oxalate, dien=diethylenetriamine and bipy=2,2′-bipyridine, have been synthesized and their crystal and molecular structures have been determined by single-crystal X-ray diffraction methods. The crystal structure of 1 consists of centrosymmetric neutral dimers where the copper atoms lie in a strongly elongated octahedral environment, surrounded by two nitrogen atoms of a bipy molecule and two oxygen atoms of the bridging oxalato group in the equatorial plane and oxygen atoms of water molecules and nitrate ions in the axial positions. Crystal structure of 2 is made up of non-coordinated nitrate anions and asymmetric binuclear cations in which copper atoms are in a distorted square–pyramidal coordination with three atoms of a diethylenetriamine ligand and an oxygen atom of the asymmetrically coordinated oxalato bridge building the basal plane and the other oxygen atom of the oxalato ligand filling the apical position. Both compounds have been also characterized by Fourier transform infrared (FT-IR) and electron spin resonance (ESR) spectroscopies, thermal analysis and variable temperature magnetic susceptibility measurements. The two compounds exhibit antiferromagnetic exchange with a singlet–triplet separation of −382 and −6.5 cm−1 for 1 and 2, respectively. Magnetic and ESR results are discussed with respect to the crystal structure of the compounds.

Binuclear Ni(II) complexes based on bridging oxalate and tetracyanometallates.: Synthesis, crystal structure and magnetic properties

The trimeric complexes, [{Ni(dien)}2(m-ox){(m-Pd(CN)4)}] (2) and [{Ni(dien)}2(m-ox){(m-Pt(CN)4)}] (3) were synthesised by the reaction of [{Ni(dien)(H2O)}2(m-ox)](PF6)2/2H2O (dien � /dietylenetriamine and ox� /oxalate) with K2Pd(CN)4 and K2Pt(CN)4, respectively. In this reaction, water substitution and molecular reconstruction reactions take place to afford trimer complexes. These compounds are isostructural with the molecular compound [{Ni(dien)}2(m-ox){(m-Ni(CN)4)}] (1). In each complex, the two octahedrally coordinated Ni atoms are oxalate bridged and the sphere of coordination of each Ni is completed by three nitrogen atoms from a diethylenetriamine ligand in fac arrangement and one nitrogen atom from a bridging cyanide ligand, which belongs to the corresponding square-planar complex [M(CN)4] 2� . The three compounds present antiferromagnetic behaviour. The magnetic coupling between the two nickel atoms might occur through both bridges, but the length of the exchange pathway through the bidentate tetracyanometallate ligands is large enough to predict that the magnetic interaction may take place mainly through the

(μ-Oxalato-O1,O2:O1′,O2′)bis[aqua(diethyl­enetri­amine)nickel(II)] bis(hexafluorophosphate) dihydrate

The title compound, [Ni(2)(C(2)O(4))(C(4)H(13)N(3))(2)(H(2)O)(2)](PF(6))(2).2H(2)O, contains a dinuclear oxalato-bridged nickel(II) complex cation. The structure determination reveals the presence of a centrosymmetric binuclear complex where the oxalate ligand is coordinated in a bis-bidentate mode to the Ni atoms. The distorted octahedral environment of each Ni atom is completed by the three N atoms of the diethylenetriamine ligand in a fac arrangement and by one O atom from a water molecule. PF(6)(-) acts as counter-anion. A two-dimensional network of hydrogen bonds links the cations and anions and stabilizes the structure.