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

The cesium salts of [Tc2X8](3-) (X = Cl, Br), the reduction product of (n-Bu4N)[TcOCl4] with (n-Bu4N)BH4 in THF, and the product obtained from reaction of Tc-2(O2CCH3)(4)Cl-2 with HCl(g) at 300 degrees C have been characterized by extended X-ray absorption fine structure (EXAFS) spectroscopy. For the [TcX8](3-) anions, the Tc-Tc separations found by EXAFS spectroscopy (2.12(2) angstrom for both X = Cl and Br) are in excellent agreement with those found by single-crystal X-ray diffraction (SCXRD) measurements (2.117[4] angstrom for X = Cl and 2.1265(1) angstrom for X = Br). The Tc-Tc separation found by EXAFS in these anions is slightly shorter than those found in the [Tc2X8](2-) anions (2.16(2) angstrom for X = Cl and Br). Spectroscopic and SCXRD characterization of the reduction product of (n-Bu4N)[TcOCl4] with (n-Bu4N)BH4 are consistent with the presence of dinuclear species that are related to the [Tc2Cl8](n-) (n = 2, 3) anions. From these results, a new preparation of (n-Bu4N)(2)[Tc2Cl8] was developed. Finally, EXAFS characterization of the product obtained from reaction of Tc-2(O2CCH3)(4)Cl-2 with HCl(g) at 300 degrees C indicates the presence of amorphous alpha-TcCl3. The Tc-Tc separation (i.e., 2.46(2) angstrom) measured in this compound is consistent with the presence of Tc=Tc double bonds in the [Tc-3](9+) core.