Dinuclear and polynuclear complexes

The change in oxidation state Tc to Tc, so enhances the rr and n bonding that a substantial contraction in the Tc-Tc distance occurs. Furthermore, the staggered rotational orientation of the chlorine atoms may allow an additional small reduction in the Tc-Tc bond distance [561], 

Some ditcchnctium(II) chloro phosphine complexes were synthesized by reduction of the corresponding TeCU phosphine compounds in benzene or THF with finely divided metallic Zn  

When the ditechnctiumfll) phosphine chloro complexes [Tc2Cl4(PR3)4]° are acidified with the strong acid HBF4-Kt20 in a mixture of CH.-iCN and CH2CI2 the blue complex salt Tc2(CH3CN)io][BF4]4 is formed  

Polynuclear complexes of low valent technetium have been extensively studied by Russian researchers. Halogeno complexes are selectively compiled in table 12.18.A. The compounds were prepared by reduction of HTCO4 in cone, hydrogen halide solutions with molecular hydrogen under a pressure of 3-5 MPa at 140-220 C [567j. 

Complex Tc cluster geometry Tc-Tc multiple bond di.vlancc [AJ References  

---

Dinuclear and polynuclear complexes with azomethine ligands and tneir magnetic properties. V. A. Kogan, V. V. Zelentsov, O. A. Osipov and A. S. Burlov, Russ. Chem. Rev. (Engl. Transl.), 1979, 48,645-656 (112). 

Since monocyclopentadienyl rare-earth complexes require four to six a-donor ligands to reach the stable coordination numbers 7 to 9, monomeric complexes must bind several neutral donor molecules. Generally, some of these donor molecules are easily lost, and dinuclear and polynuclear complexes are formed. This accounts for the fact that monocyclopentadienyl rare-earth complexes exhibit rich structural complexity. Figure 18.4.4 shows the structure of CpErCl2(THF)3. 

In related work, Vicic and Jones have achieved a remarkably mild HDS of DBT on nickel -a widely used promoter metal in industrial catalysts- according to the set of reactions summarized in Fig. 4.9 [45-48]. Although the starting material is dinuclear, most of the relevant reactions in this system occur on mononuclear fragments and thus the inclusion of this chemistry in this Section, rather than in the following one devoted to dinuclear and polynuclear complexes, seems justified. 

There are few photochemical studies on dinuclear and polynuclear gold (I) and (III) complexes in the literature. The [ n+ l)pa, nda ] excited states of [Au2(dppm)2] are powerful reductants, with an E° value of—1.6(1) V vs. SSCE (saturated sodium chloride calomel electrode) [3, 4a, 9] however [Au2(diphosphine)2] systems do not... 

This section excludes the quite extensive dinuclear and polynuclear Os/CO cluster chemistry, which will only be referred to where it overlaps with classical coordination chemistry. The general classes of Os dimers that are often encountered are Os2n+ in = 4-8) complexes with Os—Os bonds, with or without bridging ligands Os(II) dimers,... 

Diphenyl ditellurium and bis[cyclopentadicnyltricarbonyl molybdenum] formed cyclopen-tadienyltricarbonyl(benzenetellurolato)molybdenum in benzene at 25" when irradiated with light from a 250 W infrared lamp. At higher temperatures, dinuclear and polynuclear benzentellurolato bridged complexes were produced3. 

Mononuclear, dinuclear, and polynuclear palladium complexes with arenetellurolates as ligands were prepared. 

Several studies were carried out in the last decade to test the catalytic activity of mononuclear pyrazole complexes as well as dinuclear and polynuclear species containing bridging pyrazolate groups. Particularly investigated were the pyrazolate complexes in which the M( -pz ) M (Type A) or the M(/x-pz )(ft-X)M" (Type B) framework is present. 

Transition metal complexes can be classified into mononuclear and dinuclear (or polynuclear) complexes. Depending on the effective atomic number of the metal and the kind of ligands, the complexes can be mononuclear like Fe(CO)s or dinuclear like Co2(CO)g. The characteristic feature of dinuclear metal complexes is that they have a metal-metal bond in their structure. The metal-metal bond is cleaved oxidatively by the reaction with some covalent molecules to form a-bonded complexes. This reaction is regarded as a one-electron oxidation. This is another way of forming o-bonded complexes and is useful for organic synthesis. 

The names of dinuclear and polynuclear chain compounds containing metal-metal bonds are formed analogously to the mononuclear complexes, treating the metal from the farther group in the Periodic Chart with its attached groups as a ligand, the name of which terminates in -io. 

Figure 2 Bridging modes observed in dinuclear and polynuclear rare earth carboxylates. (Reproduced with permission from from R. Wang and Z. Zheng, Rare Earth Complexes with Carboxylic Acids, Polyaminopolycarboxyhc Acids and Amino Acids in Chim-Hui Huang, Rare Earth Coordination Chemistry Fundamentals and Applications. John Whey Sons (Asia) Pte Ltd, 2010.)...

---