The molecular structure of the tris(2-mercapto-1-tolylimidazolyl)hydroborato zinc(2-mercapto-1-tolylimidazole) complex, {[Tmp-Tol]Zn(mimp-Tol)}[ClO4]: intermolecular N–H⋯OClO3versus intramolecular N–H⋯S hydrogen bonding interactions of the mercaptoimidazole ligand

Abstract

The molecular structure of the tris(2-mercapto-1-tolylimidazolyl)hydroborato complex {[Tm^p-Tol]Zn(mim^p-Tol)}[ClO₄]·3MeCN has been determined by X-ray diffraction, thereby demonstrating that the mim^p-Tol ligand exhibits a N–H⋯O hydrogen bond with the [ClO₄]⁻ counterion, {[Tm^p-Tol]Zn(mim^p-Tol)⋯(OClO₃)}, rather than hydrogen bond with a sulfur of the [Tm^p-Tol] ligand. DFT calculations on a series of related complexes, namely {[Tm^Me]Zn(mim^Me)}⁺, {[Tm^Me]Zn(mim^Me)}⋯(OClO₃)}, {[Tm^Me]Zn(mim^Me)}⋯[O(H)Me]}⁺, and {[Tm^Me]Zn(mim^Me)}⋯(NCMe)}⁺ demonstrate that an intramolecular N–H⋯S hydrogen bond within {[Tm^Me]Zn(mim^Me)}⁺ is also less favored than the corresponding hydrogen bonding interactions with MeCN, MeOH, and [ClO₄]⁻. The inability of the sulfur atoms of [Tm^R] ligand to act as an effective hydrogen bond acceptor is in marked contrast to the ability of sulfur atoms in thiolate ligands to participate in the formation of N–H⋯S hydrogen bonds, an observation that reflects the “thione” versus “thiolate” nature of the [Tm^R] ligand.