Oxotris(oxalate)niobate(V): An oxalate delivery agent in the design of building blocks

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.

Keywords:

• Copper(II)
• iron(III)
• niobium(V)
• oxalate
• cyanide
• heterobimetallic compounds
• magnetic properties

Notes

We dedicate this paper to Professor Juan Faus in honor of his career as an inspiring scientist for several generations of inorganic chemists.