Cation Exchange in Small ZnS and CdS Molecular Analogues

Abstract

The simplest means of altering the chemistry and electronic structure of any material, from molecular clusters to single crystals, is by the introduction of chemical impurities. We present a systematic study of the cation exchange reaction involving Co(2+) ions with metal benzenethiolate clusters, [M4(SPh)10](2-) (M = Zn, Cd), yielding diluted magnetic clusters having the general formula [(M1-xCox)4(SPh)10](2-). This method allows high concentrations of doping at the molecular level without forming concentrated magnetic clusters such as [Co4(SPh)10](2-). Changes in the electronic structure of the molecular species containing on average <1 Co(2+) per cluster were observed and characterized by a variety of analytical (high-resolution electrospray mass spectrometry) and spectroscopic techniques (electronic absorption including stopped-flow kinetics, luminescence, and paramagnetic (1)H NMR). The mass spectrometry results strongly suggest that the cation exchange reaction with Co(2+) is thermodynamically favored for the [Zn4(SPh)10](2-) cluster compared to the [Cd4(SPh)10](2-) clusters at room temperature. The rate of the cation exchange is orders of magnitude faster for the [Cd4(SPh)10](2-) cluster than for [Zn4(SPh)10](2-) and is governed by ligand interconversion processes. This simple room temperature cation exchange into molecular clusters is a model reaction that provides important structural information regarding the effect of Co(2+) doping on the cluster stability.