A new heterometallic (Ni2+ and Cr3+) complex – Crystal structure and spectroscopic characterization

A new heterometallic complex, of the composition [Ni(bpy)3]2[Cr(C2O4)3]NO3·10H2O (bpy = 2,2′-bipyridine) (1), was synthesized and characterized by elemental and TG/DTA analyses, IR, UV/vis and EPR spectroscopy and by a single-crystal X-ray diffraction study. The compound crystallizes in the monoclinic P21/c space group, with the unit cell parameters: a = 23.201(7), b = 13.562(4), c = 22.350(7) Å, β = 92.782(5)°, V = 7024(4) Å3 and Z = 4. The molecular structure of 1 consists of two symmetry independent [Ni(bpy)3]2+ cations, one [Cr(C2O4)3]3− anion, one nitrate anion and 10 molecules of water. Due to the rigidity of the didentate ligands, both [Ni(bpy)3]2+ and [Cr(C2O4)3]3− ions possess a trigonally distorted octahedral geometry. Analysis of crystal packing revealed the existence of a specific type of supramolecular contact comprising four bipyridine ligands from two neighbouring [Ni(bpy)3]2+ units – a quadruple aryl embrace (QAE) contact. The electronic spectrum showed superposition of bands characteristic for both nickel(II) and chromium(III) six-coordinated ions. The X-band EPR spectra were recorded on a single crystal and on a powdered sample of 1 in the temperature range 300–5 K. From the obtained spectra, the spin-Hamiltonian parameters for Cr3+ were deduced. Throughout the investigated temperature range, Ni2+ was EPR silent.