Metal-bonded anions

Table 1. Metal-molten salt systems in which solid, sub-valent compounds with metal-metal bonds have been synthesized by symproportionation or similar reactions. The many sub-halides of gallium and indium have been omitted. These compounds contain either sub-valent monoatomic cations e.Lj. (Ga )(GaCl4 )l > and (In )(Cl )] " and/or ligand-stabilized metal-metal bonded anions (Ga+)2(Ga2X6- ), X = Br, For a review of the sub-valent chemistry of the group...

The most common oxidation state of niobium is +5, although many anhydrous compounds have been made with lower oxidation states, notably +4 and +3, and Nb can be reduced in aqueous solution to Nb by zinc. The aqueous chemistry primarily involves halo- and organic acid anionic complexes. Virtually no cationic chemistry exists because of the irreversible hydrolysis of the cation in dilute solutions. Metal—metal bonding is common. Extensive polymeric anions form. Niobium resembles tantalum and titanium in its chemistry, and separation from these elements is difficult. In the soHd state, niobium has the same atomic radius as tantalum and essentially the same ionic radius as well, ie, Nb Ta = 68 pm. This is the same size as Ti ... 

Bimetallic Complexes. There are two types of bimetaUic organometaUic thorium complexes those with, and those without, metal—metal interactions. Examples of species containing metal—metal bonds are complexes with Ee or Ru carbonyl fragments. Cp ThX(CpRu(CO)2), where X = Cl or 1, and Cp7Th(CpM(CO)2), where M = Ee or Ru, have both been prepared by interaction of CP2TI1X2 or Cp ThCl [62156-90-5] respectively, with the anionic metal carbonyl fragment. These complexes contain very polar metal—metal bonds that can be cleaved by alcohols. 

In anionic polymerization, as in carbonium ion polymerization, termination does not involve bimolecular reaction between two growing chains. Neither can recombination of ions lead to termination, since a carbon-metal bond is highly polar, in the case of alkali metals frequently completely ionized, and in every case very reactive. The termination step leading to the formation of a terminal C=C double bond is not too probable. This reaction involves the formation of a metal hydride, and this does not contribute greatly to the driving force. Consequently, such a termination is observed at higher temperatures only and it is probably more common in coordination polymerization where the metals involved are less electropositive. 

Similar reactions with the corresponding acetamidinate anion gave only the monomeric [MeC(NCy)2]2V(THF)2 and [MeC(NCy)2]2VCl, respectively (Scheme 108). Removal of THF from [MeC(NCy)2]2V(TFlF)2 or reduction of [MeC (NCy)2]2VCl led to formation of the homoleptic V(III) complex [MeC(NCy)2]3V instead of a metal-metal-bonded dimer. ° °... 

Group IB-Transition- and Inner Transition-Metal Bonds 8.3.2.1. by Coupling Carbonyl Anions with Group-IB Monohalides... 

Whereas Cu and Ag form complexes with derivatives of transition-metal carbonyls in which the Cu or Ag are 4 coordinated in both the reactant and in the final product, many analogous Au complexes exhibit only 2 coordination. For example, the simple Au complex Ph3PAuCI reacts with transition-metal carbonyl anions in THF to give complexes with transition-metal to Au bonds, e.g. ... 

Anionic complexes also can be prepared from (THT)Au(C6F5) which reacts with carbonyl anions in CH2CI2 to give compounds with Au to transition-metal bonds ... 

It has been noted (Section II,B,1) that reactions between transition metal carbonyl anions and silicon halides often fail to produce species containing silicon-transition metal bonds, and that such failure has been ascribed to nucleophilic attack by carbonyl oxygen. It is therefore interesting that compounds containing Si—O—C—transition metal linkages have recently been isolated from such reactions [Eqs. (105) (R = Me, Ph) 183) and (106)... 

Opinions differ on the nature of the metal-adsorbed anion bond for specific adsorption. In all probability, a covalent bond similar to that formed in salts of the given ion with the cation of the electrode metal is not formed. The behaviour of sulphide ions on an ideal polarized mercury electrode provides evidence for this conclusion. Sulphide ions are adsorbed far more strongly than halide ions. The electrocapillary quantities (interfacial tension, differential capacity) change discontinuously at the potential at which HgS is formed. Thus, the bond of specifically adsorbed sulphide to mercury is different in nature from that in the HgS salt. Some authors have suggested that specific adsorption is a result of partial charge transfer between the adsorbed ions and the electrode. 

Therefore, metal NPs in ILs are probably stabilized by protective layers via the loosely bond anionic moieties of the IL, oxide layer, and/or NHC transient species. 

---