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 σ 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.