Novel structural variation of silver(I)-pyridine complexes in nitromethane as studied by X-ray absorption spectroscopy

The XAFS spectra were measured at around the Ag K-edge of the Ag(I) ion in nitromethane (NM) with a variety of concentrations of pyridine (PY). In NM without PY, the Ag(I) ion is tetrahedrally solvated by four NM molecules similar to those in most solvents. The Ag-O bond length in NM solvent is longer than that in aqueous solution, indicating the low donating ability of NM. The mono-, bis-, tris-, and tetrakis-pyridine complexes are formed in NM by the addition of PY. The EXAFS analyses reveal that the structure of the formed PY complex in NM is linear for Ag(py)(nm)(+), linear for Ag(py)(2)(+), triangular for Ag(py)(3)(+), and tetrahedral for Ag(py)(4)(+). The longer Ag-O bond length for Ag(py)(nm)(+) than that for Ag(nm)(4)(+) and the release of bound NM molecules at the formation of Ag(py)(nm)(+) are interpreted to be due to the strong sigma donating property of PY. The Ag-N bond length (220 pm) for Ag(py)(3)(+) is intermediate between 216 pm for Ag(py)(2)(+) and 228 pm for Ag(py)(4)(+). The formation equilibria of Ag(py)(3)(+) and Ag(py)(4)(+) are analyzed on the basis of the changeover of EXAFS spectra as a function of the total concentrations of Ag+ and PY in NM. (C) 2011 Elsevier B.V. All rights reserved.