ANION RECOGNITION BY UREA AND THIOUREA GROUPS - REMARKABLY SIMPLE NEUTRAL RECEPTORS FOR DIHYDROGENPHOSPHATE

A bis-urea and a bis-thiourea host, both derived in only one step from 1,3-bis(aminomethyl)benzene, are shown to bind dihydrogenphosphate selectively over various other anions (H2PO4- > CH3COO- > Cl- > HSO4- > NO3- > ClO4-). The much stronger binding of H2PO4- by the bis-thiourca is rationalized by the stronger H-bond donor strength of the thiourea groups and the binding selectivity is explained in terms of the complex geometry and the basicity of the guest anions. The lack of self-association and the changes in the UV spectrum upon complexation make bis-thiourea hosts a promising new class of neutral receptors for dihydrogenphosphate.