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

Tetradentate NS 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 NS 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 NS coordination platform to assemble a series of first-row transition metal complexes, we have designed a novel tetradentate NS ligand containing a central dipyrrin donor functionalized with two thioether-substituted aryl units. Interestingly, complexation of the NS 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 NiCl readily forms two chloride-bridged centrosymmetric dinickel complexes in which the nickel centers are hexacoordinated by an NSCl coordination environment in distorted octahedron geometry. In contrast, metalation of the ligand with CuCl gives a mononuclear copper complex consisting of a pentacoordinated copper center in a trigonal bipyramidal geometry with an NSCl coordination sphere. Unexpectedly, the complexation of the ligand with ZnCl forms a homoleptic zinc complex in which the zinc center is surrounded by an N 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 NS coordination platform with geometric flexibility.