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)-(LH2)-H-1]-(PF6)(2) and bis-imidazolium salts (S)-2,2'-bis[2"-(N-R-imidazoliumyl) ethoxy]-1,1'-binaphthyl hexafluorophosphate [(S)-(LH2)-H-2]center dot(PF6)(2) and [(S)-(LH2)-H-3]center dot(PF6)(2) (R = ethyl or benzyl), as well as their five N-heterocyclic carbene Hg(II) and Ag(I) complexes such as [(S)-(LHg)-Hg-1(HgBr4)] (1), [(S)-(LHg)-Hg-2(HgBr4)] (2), [(S)-(LHg)-Hg-2(HgI4)] (3), {[(S)-(LAg)-Ag-2](PF6)}(n) (4) and [(S)-(LAg)-Ag-3](PF6) (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 H2PO4 - 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 H2PO4 - from other anions.