Abstract
This work concerns the oxalate delivery process that occurs when using (NH4)3[NbO(C2O4)3]·6H2O as a suitable oxalate source in the synthesis of two compounds, [Cu(dmphen)(C2O4)(H2O)] (1) and [{Cu(dmphen)(CH3OH)}2(μ-C2O4)](ClO4)2 (2) (dmphen = 2,9-dimethyl-1,10-phenanthroline). {[Fe{HB(pz)3}(CN)2(μ-CN)]2[{Cu(dmphen)}2(μ-C2O4)]}∙xCH3OH (3) (2.0 ≤ x ≤ 2.4) was obtained by reacting 2 and PPh4[Fe{HB(pz)3}(CN)3]∙H2O [ = tetraphenylphosphonium and = tris(pyrazolyl)borate]. Crystal structures of 1–3 have been determined by single-crystal X-ray diffraction experiments: 1 is a mononuclear trigonal bipyramidal copper(II) species, 2 is a centrosymmetric oxalato-bridged dicopper(II) complex, and 3 consists of centrosymmetric tetranuclear units with intramolecular iron–copper and copper–copper distances around 5.010(1) and 5.1833(9) Å, respectively. Variable-temperature magnetic measurements of 2 and 3 were carried out from 50 to 350 (1) and 1.9 to 300 K (3). A strong antiferromagnetic interaction between copper(II) ions occurs in 2 (J = −340 cm−1, the spin Hamiltonian being defined as ). Analysis of the magnetic data of 3 shows magnetic interactions across the oxalate (J1 = −341 cm−1) and single cyanide (J2 = +12.9 cm−1) … (J2 = +12.9 cm−1) bridges . Simple symmetry considerations of the interacting magnetic orbitals in 2 and 3 provide a clear picture of the exchange pathways involved in these complexes.
Notes
We dedicate this paper to Professor Juan Faus in honor of his career as an inspiring scientist for several generations of inorganic chemists.