Halide polynuclear

Niobium and Ta also form a number of polynuclear halides in which the metal has non-integral oxidation states (see text). 

The oxide (p. 1209), chalcogenides (p. 1210) and halides (p. 1211) have already been described. Of them, the only ionic compound is HgF2 but other compounds in which there is appreciable charge separation are the hydrated salts of strong oxoacids, e.g. the nitrate, perchlorate, and sulfate. In aqueous solution such salts are extensively hydrolysed (HgO is only very weakly basic) and they require acidification to prevent the formation of polynuclear hydroxo-bridged species or the precipitation of basic salts such as Hg(OH)(N03) which contains infinite zigzag chains ... 

The first communications about the synthesis [9,49] and structure [9,70,101] of polynuclear technetium halides appeared in 1982-83. These studies demonstrated the superior capacity of technetium to form polynuclear... 

Deliberate and stepwise increase of the nuclearity of polynuclear complexes is possible by condensation reactions between silyl-substituted heteronuclear complexes [Ln(R3Si)M]xM L m and metal halides. Two such examples are shown in Scheme 3 (reaction of MeCp(CO)2(MePh2Si)Mn-HgPh with PhHgCl, and reaction of [MeCp(CO)2(MePh2Si)Mn]2Hg with HgBr2) [18]. 

An important and convenient method274 to synthesize triphenylgermanium halides, useful for the preparation of polynuclear clusters, is the reaction of PhMgBr with GeCLj in toluene ... 

Numerous d cobalt(III) complexes are known and have been studied extensively. Most of these complexes are octahedral in shape. Tetrahedral, planar and square antiprismatic complexes of cobalt(lII) are also known, but there are very few. The most common ligands are ammonia, ethylenediamine and water. Halide ions, nitro (NO2) groups, hydroxide (OH ), cyanide (CN ), and isothiocyanate (NCS ) ions also form Co(lII) complexes readily. Numerous complexes have been synthesized with several other ions and neutral molecular hgands, including carbonate, oxalate, trifluoroacetate and neutral ligands, such as pyridine, acetylacetone, ethylenediaminetetraacetic acid (EDTA), dimethylformamide, tetrahydrofuran, and trialkyl or arylphosphines. Also, several polynuclear bridging complexes of amido (NHO, imido (NH ), hydroxo (OH ), and peroxo (02 ) functional groups are known. Some typical Co(lll) complexes are tabulated below ... 

Complexes of adenine (10 Ade) have been isolated by mixing the ligand in 2-methoxy-ethanol with chromium(II) halides in butanol. The low magnetic moments (Table 16)104 indicate dinuclear species [Cr2X2(Ade)4+] (Section 35.3.5.5), or polynuclear structures with bidentate adenine. 

Metal cluster compounds can be conveniently grouped into two classes (I) polynuclear carbonyls, nitrosyls. and related compounds and (II) halide and oxide complexes. The former group was included m Chapter 15. The second class will be discussed in this section.146... 

Olefin and acetylene complexes of Au(I) can be prepared by direct interaction of the unsaturated compounds with a Au(I) halide (190,191). The resulting products, however, are not very stable and decompose at low temperatures. Reaction with Au(III) halides leads to halogenation of the unsaturated compound and formation of Au(I) complexes or polynuclear complexes with gold in mixed oxidation states. 

By the stepwise thermal decomposition of the tris chelate, mono adducts of the type [NiX2(N—N)] (X = halides, NCS) were obtained.852-854 These complexes are polynuclear six-coordinate with bridging anions. In the thiocyanato derivative the nickel atoms are ferromagnetically coupled. 

The bis complexes [NiXzU] (L = Ph3PO, Ph3AsO,1807,1808 Me3PO, Me3AsO 1809 X = halides) are pseudotetrahedral in the case of the bulky triphenyl-substituted ligands and polynuclear six-coordinated in the case of the trimethyl-substituted ligands. 

---