Trinuclear supramolecular Zn(II) complexes derived from N′-(pyridine carbonyl) hydrazine carboperthioates: Synthesis, structural characterization, luminescent properties and metalloaromaticity

Abstract

Novel trinuclear Zn(II) complexes [Zn3(μ-4-pchcp)2(py)4] (1) and [Zn3(μ-3-pchcp)2(py)4] (2) have been isolated containing N′-(pyridine-4-carbonyl) and (N′-pyridine-3-carbonyl) hydrazine carboperthioate ligands which have been generated from potassium N′-(pyridine-4-carbonyl) and (N′-pyridine-3-carbonyl) hydrazine carbodithioates by in situ S–S coupling. In both complexes, the middle Zn(II) center has four coordinate tetrahedral arrangement bonded through two hydrazinic nitrogens and two sulfur atoms from two perthio ligands. This center mimic structurally a model compound for the zinc finger protein in which zinc is coordinated by two nitrogen atoms of the histidine and two sulfur atoms of the cysteine of the amino acid residue arranged in a tetrahedral fashion. Both terminal Zn(II) centers have five coordination with τ=0.57, characteristic of a geometry close to trigonal bipyramidal coordinated by one carbonyl oxygen, one hydrazinic nitrogen, one sulfur from perthio ligand and two nitrogens of pyridine which act as secondary ligand. In both complexes, ortho-CH bonds from the pyridine or pyridyl part of the ligand produce CH⋯π interactions with the metal chelate rings. The molecular geometry of complexes is symmetrical, which is a consequence of the four CH⋯π (chelate ring) interactions working cooperatively. We report here the self-assembly of two supramolecular structures based on similar trimeric Zn(II) units that are built from 4 and 3-substituted pyridyl ligands coordinated to Zn(II) ions. In the solid state, the supramolecular structures can be controlled by the pyridyl substituent via intermolecular interaction such as CH⋯S, π⋯π stacking and CH⋯π interactions. Complex 1 is a fluorescent material with maximum emission at 470nm at an excitation wavelength of 347nm.