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 Cu^II/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.