Synthesis and Electrochemistry of (µ-Oxo) technetium Complexes with Bipyridine and Halide Ligands. Crystal Structures of (µ-O)[X(bpy)2Tc]2X2bpy (X = Cl, Br) and (µ-O)[Cl(phen)2Tcl2Cl2 (original) (raw)

Dinuclear p-oxo complexes of technetium, in which the two Tc atoms are in intimate electronic communication, have been synthesized and structurally characterized. (p-O)[X(bpy)2Tc]2Xz*bpy, where X = C1 (I) and Br (II), are isomorphic and crystallize in the orthorhombic space group Pbcn with the following unit cell parameters: a = 18.29 (1) A, b = 9.763 (2) A, c = 25.99 (2) A, 2 = 4, and R = 0.071, for X = C1, and u = 18.584 (6) A, b = 9.9602 (8) A, c = 26.131 (2) A, 2 = 4, and R = 0.032 for X = Br. The compound (p-O)[Cl(phen)2Tc]C12.4H20 (111) also crystallized in Pbcn with the following unit cell parameters: a = 17.31 (2) A, b = 10.61 (2) A, c = 25.77 (2) A, 2 = 4, and R = 0.075. In each structure, the geometry is distorted octahedral around each Tc, with the equatorial ligands on the opposite metal atoms being staggered relative to one another. The bridging oxygen atom sits on a 2-fold symmetry element which bisects the angle formed by the staggered Tc-X bonds. The molecules are bent along theTc-0-Tcaxes by 171.9 , 173.0(3), and 171.6(9)O, and theTc-Obondlengthsare 1.824(2), 1.8278(6), and 1.819(3) A for I, 11, and 111, respectively. The average equatorial T o N bond distance for the three structures is 2.1 l(2) A, and the average Tc-N trans to the bridging oxygen is 2.135(22) A. The Tc-X bond distances are 2.418(4), 2.5665(7), and 2.408(6) A, for I, 11, and 111, respectively. Infrared Tc-0 stretching frequencies are in the range 723-730 cm-I. Halides are easily dissociated from the phenanthroline complexes and an analog, (p-Experimental Section Caution! All syntheses were performed with 99Tc, which isaj3-emitting isotope with a half-life of 2.15 X lo5 years. (Only milligram quantities should be handled with the minimum shielding present under normal laboratory conditions.) Synthesis. The starting materials, [(n-Bu),N] [TcOXs], were prepared from (NH4)TcOd (Oak Ridge) by the method of Cotton (X = C1)8 and by a modification of the method of Preetz (X = Br).9.'0 The compound, (pO)[Br(bpy)2Tc]2Br2.bpyI was prepared by dispersing 200 mg of [(n-Bu)4N][TcOBr4] with 600 mg of 2,2'-bipyridine in 5 mL of DMF. After the mixture was refluxed for 6-8 h, purple crystals were collected by filtration, washed with acetone and diethyl ether, and dried in a vacuum desiccator. Yield: 80%. Anal. Calcd for H~~C S O N I O O B~~T C~: C, 45.69; H, 3.07; N, 10.66. Found: C, 44.60; H, Clarke, M. J.; Podbielski, L. Coord. Chem. Reo. 1987, 78, 253-331. 3.04; N, 10.44. IR in KBr pellet (cm-I): y~~-o .~~ = 730 (s); 1660 (s). Davison, A.; Jones, A. G. Int.