Distinct structures of inorganic-organic supramolecular assemblies based on discrete metallocyclic complexes incorporating flexible imidazole ligands: Syntheses, crystal structures and properties

Three new interesting discrete dinuclear metallocyclic complexes, namely, {[Pd2(1)4](NO3)4·2DMSO·2H2O}n (4), [Pd2(2)2Br4]n (5), and {[Pd2(3)2Cl4]·4DMSO}n (6) have been successfully synthesized by the reaction of flexible exo-bidentate imidazole-containing ligands 1,3-bis(imidazol-1-ylmethyl)benzene (1), 1,3-bis(imidazol-1-ylmethyl)-5-methylbenzene (2), and 2,6-bis(imidazol-1-ylmethyl)-4-tert-butylphenol (3) with corresponding palladium salts. All these complexes were characterized by NMR spectroscopy in combination with elemental analysis, powder X-ray diffraction (PXRD), single-crystal X-ray diffraction, and thermal gravimetric analysis (TGA), respectively. Though all three complexes involve the similar supramolecular building blocks [2+2] metallocyclic units, under the inducement effect of the organic ligands, compounds 4-6 exhibit delicate geometric diversification of the resulting high-dimensional inorganic-organic supramolecular assemblies (e.g., [4+2] lantern-like cage structure, 1D channel, and 2D undulating framework, respectively). Furthermore, these results demonstrate that the secondary interactions such as intermolecular π⋯π stacking interactions and hydrogen bonds could play important roles in the aspect of linking low-dimensional entities into high-dimensional supramolecular frameworks.