Assembly of supermolecular complexes with tripodal ligand titmb and tib: a 2D rhombic grid network assembled from 2-connected tib

Abstract

A 2D rhombic grid network complex [Cu₄(tib)₈](CH₃COO)₈·32H₂O (6) has been prepared by reaction of the tripodal ligand 1,3,5-tris(imidazol-1-ylmethyl)benzene (tib) with Cu(CH₃COO)₂ in aqueous solution and characterized by single crystal X-ray diffraction. In the solid state, the tripodal ligand tib acts as a 2-connected ditopic bridging ligand. Studies about the influences that control the supramolecular assembly and crystal packing process of complexes (1–6), which are assembled from tripodal ligands titmb and tib with metal atoms, not only illustrate that hydrogen bonds play a very important role in the construction of supramolecular complexes, but also that the reaction conditions together with the metal atoms co-affect inorganic supramolecular formation. Results show that the formation of N⋯H–OH hydrogen bonds between the hydrogen atoms of the solvent water molecules and the imidazole coordinative nitrogen atoms of the third arm of tib makes the tripodal ligand tib act as a 2-connected bridging ligand when it coordinates with copper(II) atoms. It is found that the conformations of the tripodal ligands tib and titmb (titmb = 1,3,5-tris(imidazol-1-ylmethyl)-2,4,6-trimethylbenzene) are obviously controlled by the reaction conditions. When reacted in organic solvents, both of the titmb and tib are in the same W-form; when water is present in the solvent, the conformations of the two tripodal ligands will change from the W-form to the Y-form; when reacted in water, tripodal ligand tib is in a novel Y-form. Results also show that the coordination geometry of the metal atoms also plays an important role in the construction of supramolecular complexes. In 2D/3D complexes 1, 2, 5 and 6, the involved transitional metal atom is the same – all are copper(II) atoms – and the coordination geometry of copper is square-planar N₄ or square-based pyramid N₅ or N₄O₁, while in the discrete cage complexes 3 and 4, the involved transitional metal atoms are the zinc(II) and silver(I) atoms, and the coordination geometries of zinc and silver are tetrahedral N₂O₂ or linear N₂, respectively. These studies show that the hydrogen bonds play a very important role in the crystal packing process of this infinite 2D rhombic grid network complex 6. There are no large channels formed in the 2D complexes 1 and 2, but large channels are formed by the columnar packing of the 2D (4,4) rhombic grid layers of complex 6 along the a axis, and in which the cubic O₈ chains are accommodated.