Binding polyprotic small molecules with second-sphere hydrogen bonds

Abstract

Second-sphere hydrogen bonds are known for playing significant roles in homogeneous catalysis and in biological processes with metal-containing molecules. In this work, we highlight a tetradentate asymmetric ether-sulfonamidate ligand that facilitates second-sphere hydrogen bonding in transition metal complexes. We explored its ability to bind mono-, di-, tri-, and tetra-protic ligands when supporting a cobalt(II) ion. The structures of three such cobalt complexes containing bound water, ammonia, and hydrazine are presented. Additionally, spectroscopic analysis of a strongly bound hydroxide ion complex is presented. A hydrogen-bonding configuration, not yet observed in crystal structures of this type, resulted in a bridging hydrazine complex with the two cobalt ions separated by a distance of 5 Å.