Dimer anion

Sodium Perborate Hydrates. Peroxyborates are commonly known as perborates, written as if the perborate anion were BO . X-ray crystal stmcture has shown that they contain the dimeric anion [(H0)2B(02)2B(0H)2] (7) (92). Three sodium perborate hydrates, NaBO XH2O (x = 1, 3, and 4), are known. Only the mono- and tetrahydrate are of commercial importance, primarily as bleaching agents (qv) in laundry products. 

Figure 13.14 Schematic representation of the structure of (a) the trimeric anion [Sb.iFi203l, and (b) the dimeric anion fAs2F

Figure 15.52 Structures of various S-N oxoanions (a) hydroxylamine-A-sulfonate, (b) A-nitrosohydroxylamine A-sulfonate and (c) the dimeric anion in Fremy s salt K2[0N(S03)2])2.

Recently Noble s group (Haub et al., 1992) showed that sulfidomolybdenum dimer anion complexes react with arenediazonium ions and form complexes (Mo)2S — N2 — Ar. Synthesis and (homolytic) dediazoniation reflect characteristics of arene-diazosulfide anions (see Zollinger, 1995, Sec. 10.1). 

Substituted 2-naphthols, as azo coupling components 356ff., 362 Sulfanilic acid 14, 71 Sulfidomolybdenum dimer anion, complex with diazonium ions 117 Surface-enhanced Raman spectroscopy 280... 

Breaking Br from varied monomeric 78) and dimeric antimonates 19) requires an effort of about 1 eV more for dimeric anions as than for monomeric anions (see Fig. 10). 

This corresponds to a decreased nucleophilicity of the complexed anions. The energetic effort depends on the bromine content in the sphere of ligands. The higher the bromine content, compared to the chlorine content, the easier an halide ion can be splitted from the dimeric anion. 

Another type of interaction is the association of radical ions with the parent compounds. Recently (118), a theoretical study was reported on the interaction of butadiene ions with butadiene. Assuming a sandwich structure for the complex, the potential curve based on an extended Hiickel calculation for two approaching butadienes (B + B) revealed only repulsion, as expected, while the curves for B + and B + B" interactions exhibit shallow minima (.068 and. 048 eV) at an interplanar distance of about 3.4 A. From CNDO/2 calculations, adopting the parameter set of Wiberg (161), the dimer cation radical, BJ, appears to be. 132 eV more stable than the separate B and B species, whereas the separate B and B species are favored by. 116eV over the dimer anion radical, BJ. This finding is consistent with experimental results formation of the dimer cation radical was proved in a convincing manner (162) while the attempts to detect the dimer anion radical have been unsuccessful. With other hydrocarbons, the reported formation of benzene dimer anion radical (163) represents an exceptional case, while the dimeric cation radical was observed... 

The crystal structure of [Fe(Cp)2]2[Ni(mnt)2]2[Fe(Cp)2] is composed by segregated stacks of pairs of cations, [Fe(Cp)2]+, and zig-zag dimerized anions stacks, with a neutral [Fe(Cp)2] molecule laying beside each anionic dimer [65]. In the case of [Co(Cp)2][Ni(dmit)2], the crystal structure consists of layers composed by two types of chains formed by the [Ni(dmit)2] anions, through short S—S contacts. Cation pairs are located between the anionic stacks [68], In the crystal structure of [Co(Cp)2][Ni(dmit)2]3 2MeCN, the partially oxidized anions form... 

Dimeric anions such as [Mo207]2 does not occur in aqueous solution... 

An ab initio study on the structure and splitting of the uracil dimer anion-radical (see Scheme 3.72, R = H) gives preference to the one-step mechanism (Voityuk and Roesch 1997). Anion-radical anions of the pyrimidine dimers cleave with rate constants in excess of 10 s ... 

Hence, in toluene, no dimer anion-radicals are observed. Encounters between anion-radicals and neutral molecules result in electron transfer instead. Charge transfer from the solute anion-radicals to toluene is unlikely, since toluene is a poor electron acceptor. Consistent with this fact, no differences were observed in the anion-radical ESR-coupling constants in toluene when compared to those in -hexane (Werst 1993). Charge (not electron) transfer from the toluene molecules to the... 

Electron photodetachment upon laser excitation of the solvent anion above 1.76 eV was observed (Fig. 2a,c) [18]. The cross section of photodetachment linearly increases between 1.76 and 3 eV (Fig. 2b). Under the same physical conditions, the photodetachment and absorption spectra of the solvent anion are identical (Fig. 2b) [20], suggesting a bound-to-CB transition the quantum yield of the photodetachment is close to unity. The photodetachment spectrum is similar to the photoelectron spectra of (C02) 9 clusters observed by Tsukuda et al. [24] in the gas phase it is distinctly different from the electron photodetachment spectra of CO2 in hydrocarbon liquids [27]. This suggests that a C-C bound, 7)2, symmetric dimer anion constitutes the core of the solvent radical anion [18,19]. 

To the best of our knowledge, pulse radiolysis transient absorption studies of neat CS2 have not been reported. CS2 anion in 0.1 M cyclohexane and 0.1 M THF solutions appears as a single 275-nm peak [35] there is no charge-resonance band that can be attributed to the dimer anion, at early (< 10 nsec) or later times. 

The studies carried out in the gas phase and low-temperature matrices suggest that (CS2) anions have somewhat different structure from the (C02) anions discussed in the previous section [24]. Similar to the ( 2) anions, the CS2 monomer and C-C bound C2S4 dimer anions switch as the core of the (CS2) anion [36]. However, unlike the two core anions in the (C02) anions, CS2 and C2S4 anions coexist in the clusters of all sizes ( = 2-6) with the monomer core being statistically prevalent [36]. The dimer core is... 

Below, we consider a polar, negative-EAg liquid—acetonitrile—in which the dimer anion formation (because of the electron accessing low-lying ir orbitals) competes with... 

Na4[(VO)2 ( + )-ffcreo-mmt (-)-[Pg.519]

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