A new bis(thioether)-dipyrrin N2S2 ligand and its coordination behaviors to nickel, copper and zinc.

Abstract

Tetradentate N2S2 coordination platforms are widespread in biological systems and have endowed metalloenzymes and metalloproteins with abundant reactivities and functions. However, there are only three types of N2S2 scaffolds respectively based on the bipyridine, aryl and alkyl amine derivatives, which are significantly underdeveloped for coordination chemistry. With the objective of developing a new N2S2 coordination platform to assemble a series of first-row transition metal complexes, we have designed a novel tetradentate N2S2 ligand containing a central dipyrrin donor functionalized with two thioether-substituted aryl units. Interestingly, complexation of the N2S2 ligand with the chloride salts of Ni(II), Cu(II) and Zn(II) yields various geometries with various coordination numbers. The reaction between the ligand and NiCl2 readily forms two chloride-bridged centrosymmetric dinickel complexes in which the nickel centers are hexacoordinated by an N2S2Cl2 coordination environment in distorted octahedron geometry. In contrast, metalation of the ligand with CuCl2 gives a mononuclear copper complex consisting of a pentacoordinated copper center in a trigonal bipyramidal geometry with an N2S2Cl coordination sphere. Unexpectedly, the complexation of the ligand with ZnCl2 forms a homoleptic zinc complex in which the zinc center is surrounded by an N4 coordination sphere from two dipyrrin units in a non-planar pseudo-tetrahedral geometry despite the steric hindrance of two bulk thioether-substituted aryl units. These various geometries illustrate the potential structural flexibility of this new ligand. In addition, the optical properties of these compounds were also examined. This work thus provides a new N2S2 coordination platform with geometric flexibility.