Solvent-dependent access to mono- and dinuclear copper(II) assemblies based on a flexible imidazole ligand

Abstract

Seven copper(ii) complexes with the less bulky (compared to bis-phenyl-substituted imidazoles used in our previous studies) monodentate 2-phenylimidazole (LH) ligand have been prepared from the general CuII/X-/LH (X- = NO3-, ClO4-, BF4-, SO42-, Cl-) reaction system and were structurally characterized by X-ray diffraction. Interestingly, the choice of reaction/crystallization solvent provides two distinct groups of complexes: methanolic solutions favour mostly the formation of dinuclear products {i.e. [Cu2(OMe)2(NO3)2(LH)4]·2MeOH (1a·2MeOH), [Cu2(OMe)2(LH)4](ClO4)2 (2a), [Cu2(OMe)2(LH)4]SiF6 (3), [Cu2(SO4)2(LH)4] (4)}, whereas in the presence of acetonitrile, mononuclear cationic complexes were isolated {i.e. [Cu(LH)4](NO3)2 (1b) and [Cu(LH)4](ClO4)2 (2b)}. A notable exception is the mononuclear complex [CuCl2(LH)2] (5) isolated from methanol. The roles of the solvent and inorganic anions on the complex stoichiometry and molecular structure are critically discussed. The complexes' self-assembly is firmly directed by robust N-H⋯X (X = O, Cl or F) motifs, leading to varying dimensionalities and packing arrangements depending on the coordinated/counter inorganic ions: 1D tapes (for NO3- in 1b), layers (for ClO4- in 2a and 2b, SiF62- in 3 and Cl- in 5) and 3D networks (for NO3- in 1a and SO42- in 4). Intramolecular π⋯π contacts enhance the rigidity of certain complexes, and additional weak intermolecular C-H⋯Y (Y = O, Cl or F), C-H⋯π and π⋯π interactions complement the stability of the packing towards 3D assemblies. Lastly, comparisons of the molecular and supramolecular chemistry of the Cu(ii)/LH complexes with previously characterized Cu(ii) complexes with the bulkier 4,5-diphenylimidazole ligand reveal similarities and differences, which are discussed. © 2016 The Royal Society of Chemistry.