Solvent-dependent access to mono- and dinuclear copperIJII) assemblies based on a flexible imidazole ligand†

Seven copperIJII) 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 Cu/ X−/LH (X− = NO3 −, ClO4 −, BF4 −, SO4 2−, 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, SiF6 2− in 3 and Cl− in 5) and 3D networks (for NO3 − in 1a and SO4 2− 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.