STRONG HYDROGEN BOND-MEDIATED COMPLEXATION OF H2PO4- BY NEUTRAL BIS-THIOUREA HOSTS

Highly preorganized bis-thiourea receptors based on a xanthene spacer selectively (H2PO4- > CH3COO- > Cl-) bind dihydrogenphosphate via mult itopic hydrogen bonding, giving stronger complexes with H2PO4- than an y synthetic neutral receptor known so far. The high complexation stren gths are rationalized by the hydrogen bond donor strength of the thiou rea groups and by host preorganization. The hydrogen bond acceptor str engths of the guest anions and, for small ions, guest solvation explai n the observed selectivity of complexation in dimethyl sulfoxide(DMSO) . (C) 1997, Elsevier Science Ltd.