METAL-METAL MULTIPLY-BONDED COMPLEXES OF TECHNETIUM .2. PREPARATION AND CHARACTERIZATION OF THE FULLY SOLVATED DITECHNETIUM CATION [TC-2(CH3CN)(10)](4+)

Acidification of Tc2Cl4(PR(3))(4) with HBF4 . Et(2)O in a mixture of acetonitrile and methylene chloride results in the formation of the metal-metal triply-bonded solvated complex [Tc-2(CH3CN)(10)][BF4](4) (1) in 80% yield. This compound may also be prepared through reduction of [Bu(4)N](2)[TcCl6] with either Bu(3)SnH or finely divided Zn followed by treatment with HBF4 . Et(2)O, but in lower yields (approximately 50%). The quadruply bonded species Tc2Cl82- also reacts with HBF4 . Et(2)O in a mixture of acetonitrile and diethyl ether under mild heating to produce small amounts of blue [Tc-2(CH3CN)10][BF4](4) (yield 14%). In addition to the formation of 1, yellow crystals that proved to be the mononuclear Tc(III) species [TcCl2(CH3CN)(4)][BF4] (2) were isolated in 34% yield from the reaction solution. The dinuclear cation [Tc-2(CH3CN)(10)](4+) was crystallized as the mixed salt [Tc-2(CH3CN)(8)(CF3-SO3)(2)](BF4)(2) . CH3CN (1a . CH3CN) by addition of 8 equivs of Tl(CF3SO3) to a CH3CN solution of 1 followed by slow diffusion of a mixture of Et(2)O and hexanes. Compound 1a . CH3CN crystallized in the tetragonal space group P4(1)2(1)2 with a = 12.181(2) Angstrom, c = 27.385(3) Angstrom, V = 4063(1) Angstrom(3) and Z = 4. The molecular structure of 1a entails a staggered M(2)L(8) conformation with approximate D-4d symmetry. The two axial positions of the dinuclear cation are occupied by CF3SO3- anions. The BF4- anions occupy general positions within the unit cell. The Tc=Tc bond distance is 2.122(1) Angstrom, consistent with a Tc-Tc multiple bond. Single crystal X-ray analysis of [TcCl2(CH3CN)(4)][BF4] revealed a trans:disposition of chloride ligands with approximate D-4h symmetry about the Tc atom. Crystal data for 2: orthorhombic space group Ibam, with a = 6.250(1) Angstrom, b = 12.189(2) Angstrom, c = 20.880(5) Angstrom, V = 1590.7(5) Angstrom(3) and Z = 4. Nitrile complexes 1 and 2 have been fully characterized by a variety of physical and spectroscopic techniques including H-1 NMR, UV-vis and IR spectroscopies and cyclic voltammetry.