Self-assembled macrocyclic tetranuclear molecular square [Ni(HL)]44+ and molecular rectangle [Cu2Cl2L]2 {H2L = bis[phenyl(2-pyridyl)methanone] thiocarbazone}

Abstract

The conformationally rigid, nickel(II)-based cationic molecular square [Ni(HL)]₄⁴⁺ and copper(II)-based neutral molecular rectangle [Cu₂Cl₂L]₂ were achieved via self-assembly from novel rigid pentadentate N₄S ligand bis[phenyl(2-pyridyl)methanone] thiocarbazone (H₂L). Crystal structure analyses show that the tetranuclear nickel(II) cation [Ni(HL)]₄⁴⁺ is located at the inversion center with four nickel atoms in the corners of a square with edge length Ni⋯Ni ca. 4.8 Å, each metal center being octahedrally coordinated by sulfur atoms, pyridine nitrogen and carbazone nitrogen atoms from two perpendicular HL⁻ ligands. Relative to the square of metal cations the sulfur atoms are midway between the edges of the square, each being connected to two nickel atoms with the angles Ni–S–Ni ca. 163°. The tetranuclear copper(II) complex [Cu₂Cl₂L]₂ is also located in the inversion center with four copper atoms in the corners of a rectangle. Two edges of the rectangle are Cu–S–Cu bridges with edge length Cu⋯Cu of 4.51 Å, the other two edges are double Cu–Cl–Cu bridges with Cu⋯Cu distance of 3.41 Å. Each metal center is coordinated in a tetragonal-pyramid with the sulfur atom, pyridine nitrogen atom, carbazone nitrogen atom and one chlorine atom comprising the basal plane, whereas the other chlorine atom of the symmetry-related half of the molecule occupies the apical position. The crystal structure of the free ligand is also reported for comparison.