Highly preorganized bis-thiourea receptors based on a xanthene spacer selectively (H2PO4- > CH3COO- > Cl-) bind dihydrogenphosphate via multitopic hydrogen bonding, giving stronger complexes with H2PO4- than any synthetic neutral receptor known so far. The high complexation strengths are rationalized by the hydrogen bond donor strength of the thiourea groups and by host preorganization. The hydrogen bond acceptor strengths of the guest anions and, for small ions, guest solvation explain the observed selectivity of complexation in dimethyl sulfoxide (DMSO).
Bibliographical noteFunding Information:
We are indebted to Dr. M. Sasaki for assistancei n mass spectroscopy and S. Amemiya for various interestingd iscussions. This work was supportedb y the Ministry of Education, Science and Culture, Japan, the TokuyamaS cienceF oundationa nd a SasakawaS cientific ResearchG rant from the Japan Science Society.