Supramolecular motifs and solvatomorphism within the compounds [M(bpy)3]2[NbO(C2O4)3]Cl·nH2O (M = Fe2+, Co2+, Ni2+, Cu2+ and Zn2+; n = 11, 12). Syntheses, structures and magnetic properties

Abstract

Solvatomorphism has been found between two series of complexes of the composition [M(bpy)₃]₂[NbO(C₂O₄)₃]Cl·nH₂O [M = Fe²⁺ (1, 2), Co²⁺ (3, 4), Ni²⁺ (5, 6), Cu²⁺ (7) and Zn²⁺ (8, 9); bpy = 2,2′-bipyridine)], crystallizing in the monoclinic space groupP2₁/c [3, 5, 8 (n = 11)] or in the orthorhombic space groupP2₁2₁2₁ [2, 4, 6, 7 (n = 12)]. All the structures contain two symmetry independent [M(bpy)₃]²⁺ cations, one [NbO(C₂O₄)₃]³⁻ anion, one Cl⁻ anion, and crystal water molecules. The cations possess a trigonally distorted octahedral geometry, with an additional tetragonal distortion in 7. Analysis of crystal packing reveals a specific type of supramolecular contact comprising four bipyridine ligands from two neighbouring [M(bpy)₃]²⁺ cations—quadruple aryl embrace (QAE) contact. The contact is realized by the alignment of two molecular two-fold rotation axes, preserving the parallel orientation of the molecular three-fold rotation axes. The resulting two-dimensional honeycomb lattices of [M(bpy)₃]²⁺ cations are placed between the hydrogen bonding layers made of [NbO(C₂O₄)₃]³⁻ and Cl⁻ anions and the majority of the crystal water molecules. The temperature-dependent magnetic susceptibility measurements (1.8–300 K) show a significant orbital angular momentum contribution for 3 and 4 (high-spin Co²⁺), the influence of zero-field splitting for 5 and 6 (Ni²⁺) and a substantially paramagnetic Curie behaviour for the Cu²⁺ compound (7).