Synthesis and structural studies of N-heterocyclic carbene Ag(I) and Hg(II) complexes and recognition of dihydrogen phosphate anion.

Bis-benzimidazolium salt (S)-2,2'-bis[2″-(N-Et-benzimidazoliumyl)ethoxy]-1,1'-binaphthyl hexafluorophosphate [(S)-L(1)H(2)]·(PF(6))(2) and bis-imidazolium salts (S)-2,2'-bis[2″-(N-R-imidazoliumyl)ethoxy]-1,1'-binaphthyl hexafluorophosphate [(S)-L(2)H(2)]·(PF(6))(2) and [(S)-L(3)H(2)]·(PF(6))(2) (R = ethyl or benzyl), as well as their five N-heterocyclic carbene Hg(II) and Ag(I) complexes such as [(S)-L(1)Hg(HgBr(4))] (1), [(S)-L(2)Hg(HgBr(4))] (2), [(S)-L(2)Hg(HgI(4))] (3), {[(S)-L(2)Ag](PF(6))}(n) (4) and [(S)-L(3)Ag](PF(6)) (5) have been prepared and characterized. Each of complexes 1-3 consists of two rings (one 6-membered ring and one 11-membered ring), in which the oxygen atom in the ligand participates in coordination with Hg(II) ion. In complex 4, 1D helical polymeric chain is formed via biscarbene ligand (S)-L(2) and Ag(I) ion. A 15-membered macrometallocycle is constructed through a ligand (S)-L(3) and a Ag(I) ion in complex 5. Additionally, the selective recognition of H(2)PO(4)(-) using complex 5 as a receptor was investigated on the basis of fluorescence and UV/vis spectroscopic titrations. The results indicate that complex 5 can distinguish effectively H(2)PO(4)(-) from other anions.