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 Tc2(O2CCH3)4Cl2 with HCl­(g) at 300 °C have been characterized by extended X-ray absorption fine structure (EXAFS) spectroscopy. For the [Tc2X8]3– anions, the Tc–Tc separations found by EXAFS spectroscopy (2.12(2) Å for both X = Cl and Br) are in excellent agreement with those found by single-crystal X-ray diffraction (SCXRD) measurements (2.117[4] Å for X = Cl and 2.1265(1) Å 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) Å 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 Tc2(O2CCH3)4Cl2 with HCl­(g) at 300 °C indicates the presence of amorphous α-TcCl3. The Tc–Tc separation (i.e., 2.46(2) Å) measured in this compound is consistent with the presence of TcTc double bonds in the [Tc3]9+ core.