Silver(I) nitrate adducts with bidentate 2-, 3- and 4-pyridyl phosphines.: Solution 31P and [31P-109Ag] NMR studies of 1:2 complexes and crystal structure of dimeric [{Ag(d2pype)(μ-d2pype)}2]-[NO3]2•2CH2Cl2 [d2pype = 1,2-bis(di-2-pyridylphosphino)ethane]

The 1 : 2 complexes of silver(I) nitrate with 1,2-bis(di-n-pyridylphosphino)ethane (dnpype) for n = 2, 3 and 4 have been synthesized and solution properties characterized by NMR spectroscopy, including variable-temperature one-dimensional P-31-{H-1}, two-dimensional [P-31-P-31] COSY and [P-31-Ag-109] HMQC NMR experiments. The 3-pyridyl (d3pype) and 4-pyridyl (d4pype) complexes exist as bis-chelated monomeric [Ag(d3pype)(2)](+) and [Ag(d4pype)(2)](+) while the 2-pyridyl (d2pype) complex forms an equilibrium mixture of monomeric [Ag(d2pype)(2)](+), dimeric [{Ag(d2pype)(2)}(2)](2+) and trimeric [{Ag(d2pype)(2)}(3)](3+) species in which the d2pype ligands co-ordinate in both bridging and chelated modes via the phosphorus atoms, The relative percentages of the species present are dependent on both temperature and solvent, Crystals of the 2-pyridyl complex obtained from CH2Cl2-Et2O solution have been shown by crystal structure determination to be the dimer [{Ag(d2pype)(mu-d2pype)}(2)]-[NO3](2) .2CH(2)Cl(2). Each silver ion is co-ordinated by one chelated and two bridging d2pype ligands forming a ten-membered ring in a double boat conformation. The pyridyl nitrogen atoms do not co-ordinate to the silver. The differences in solution behaviour of the three systems and the potential significance of these complexes to th antitumour properties of chelated 1:2 silver(I) diphosphine complexes are discussed.