Effect of spacer geometry on oxoanion binding by bis- and tetrakis-thiourea hosts

Hosts with thiourea groups bind anions by formation of multiple hydrogen bonds. This contribution discusses how spacers linking two or four thiourea groups affect the host affinity and selectivity. While most of the bis-thioureas bind H2PO4− preferentially, the extent of selectivity over chloride, acetate, and H2AsO4− is determined by the size of the binding cavity. A tetrakis-thiourea is shown to exhibit a unique H2AsO4− selectivity, and the discrimination of chloride is enhanced by specific solvation in dimethyl sulfoxide.