Probing the Presence of Multiple Metal-Metal Bonds in Technetium Chlorides by X-ray Absorption Spectroscopy: Implications for Synthetic Chemistry

The cesium salts of Tc(2)X(8)](3-) (X = Cl, Br), the reduction product of (n-Bu(4)N)TcOCl(4)] with (n-Bu(4)N)BH(4) in THF, and the product obtained from reaction of Tc(2)(O(2)CCH(3))(4)Cl(2) with HCl(g) at 300 °C have been characterized by extended X-ray absorption fine structure (EXAFS) spectroscopy. For the Tc(2)X(8)](3-) anions, the Tc-Tc separations found by EXAFS spectroscopy (2.12(2) ? for both X = Cl and Br) are in excellent agreement with those found by single-crystal X-ray diffraction (SCXRD) measurements (2.1174] ? for X = Cl and 2.1265(1) ? for X = Br). The Tc-Tc separation found by EXAFS in these anions is slightly shorter than those found in the Tc(2)X(8)](2-) anions (2.16(2) ? for X = Cl and Br). Spectroscopic and SCXRD characterization of the reduction product of (n-Bu(4)N)TcOCl(4)] with (n-Bu(4)N)BH(4) are consistent with the presence of dinuclear species that are related to the Tc(2)Cl(8)](n-) (n = 2, 3) anions. From these results, a new preparation of (n-Bu(4)N)(2)Tc(2)Cl(8)] was developed. Finally, EXAFS characterization of the product obtained from reaction of Tc(2)(O(2)CCH(3))(4)Cl(2) with HCl(g) at 300 °C indicates the presence of amorphous α-TcCl(3). The Tc-Tc separation (i.e., 2.46(2) ?) measured in this compound is consistent with the presence of Tc═Tc double bonds in the Tc(3)](9+) core.