Other ligand-bridged compounds

The remarkable sulphur-bridged dinuclear complex [ -S,S (TcO)2(SCH2CH2S)3 ]° was obtained by reaction of [TcOCU] with ethanedithiol in mclhanolic solution. 

The intramolecular Tc-Tc distance is 7.175(4) A, and the distance between the oxo ligands 0(1)-0(1) 3.96(2) A. The Tc=0 stretch was observed at 962 cm. [AsPh4]2 [Tc202(H2ema)4 decomposes immediately in aqueous basic solution to give two equivalents of [AsPh4][TcO(ema)] [247]. 

6-Tetrakis(2-pyridyl)pyrazine (tppz) reacts with [TcOCUj in ethanol to give a dark green precipitate of [/i-tppz TcOCl2(OEt))2] which is soluble in CH2CI2. acetonitrile, DMF, and nitromethanc. As indicated by the presence of two distinct Tc=0 stretching vibrations at 938 and 916 cm the two Tc(V) centers are reported to experience different coordination environments, one Tc atom is deduced to be seven-coordinate and the other six-coordinatc [248]. 

Some structural data of dinuclear 0x0 complexes are reviewed in Table 12.8. A. 

In contrast to the well characterized nitridohalogeno complexes [TcNCU] and [TcNBr4] of Tc(Vl), the existence of the corresponding complexes of Tc(V), [TcNX4], could not yet be proved. Only spectroelectrochemical studies at -60 C showed a reversible one-electron reduction of [Tc NX4], but the reduced species have not been isolated [249). 

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Other ligands that react to form these Hg(I) complexes are 1,2- and 1,4-diaminoben-zene, 1,10-phenanthroline , and the bridged ring compound ... 

It appears that a modified mechanism operates when tr .s-(o-tolyl)phosphine is used as the ligand,133 and this phosphine has been found to form a palladacycle. Much more stable than noncyclic Pd(0) complexes, this compound is also more reactive toward oxidative addition. As with the other mechanisms, various halide adducts or halide-bridged compounds may enter into the overall mechanism. 

Fig. 5. Ten types of different structures identified by X-ray diffraction, where the abbreviated N-0 is used to express each bridging amidate ligand and X denotes axial donors such as OH2, N03, N02 (nitro), Cl, and Br. For the compounds involving axial ligands (X), the total complex charge is given assuming that X is a monoanion. Note that, in some cases, amine ligand in cis-Pt(NH3)2 will be replaced with other ligands, such as in Pt(en), cis-Pt(NH3)Cl, cis-PtCl2, and Pt(bpy).

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