Supramolecular features in the engineering of 3d metal complexes with phenyl-substituted imidazoles as ligands: the case of copper(II)

With the aim of recording and assessing the role and impact of various non-covalent interactions activated during the self-assembly process of 3d metal complexes with organic ligands, the synthesis and X-ray characterization of a series of eleven Cu(II) complexes with two phenyl-substituted imidazoles [1-methyl-4,5- diphenylimidazole (L) and 4,5-diphenylimidazole (HL')] as ligands have been carried out. A variety of parameters and conditions have been probed using the general CuII/X-/L or HL' (X- = Cl-, Br-, I-, NO3 -, NO2- or ClO4-) reaction system. In structures with the ligand L (1-7), lacking any group capable of establishing strong intermolecular H-bonding contacts, the burden of the supramolecular organization is undertaken by weak, yet productive, C-H center dot center dot center dot X and C-H center dot center dot center dot pi interactions, while the metal ions keep their preferred coordination geometries (square planar and square pyramidal). In compounds with the ligand HL' (8-11), however, robust and recurring N-H center dot center dot center dot X (X = Cl or O) motifs have the leading role towards effectively directing the self-assembly; flexible water molecules contribute actively, when needed {[Cu.HL')(4)].ClO4)(2) center dot EtOH center dot CH2Cl2 center dot H2O}, to maximize the number of these motifs. At a second level of organization, additional subordinate C-H center dot center dot center dot Cl or O and C-H center dot center dot center dot p interactions complement the rigidity of the structures. The distortion of the coordination environment (seesaw) of Cu-II centres in compounds [CuCl2(HL')(2)]center dot Me2CO center dot 0.25H(2)O and [CuCl.HL')(3)] Cl center dot 0.6H(2)O appears to reflect the balance of forces within the crystallization system to facilitate the necessary orientation of the tectons so as to form the hierarchically prevailing N-H center dot center dot center dot X synthons. Moreover, the small number of intermolecular pi center dot center dot center dot pi contacts observed, despite the abundance of aromatic rings, indicates their weakness to form at the expense of stronger interactions. Lastly, comparison with previously structurally characterized analogous Co(II)), Ni (II) and Zn (II) complexes (vide infra) corroborates and adds confidence to the conclusions deduced herein.