Anion structures

The adsorption of anions on metal electrodes has been one of the major topics in surface electrochemistry. Specific adsorption of anions occurs when the anion loses aU or part of its solvation shell and forms a direct chemical bond with the substrate. In this situation the surface coverage by anions can be high and the adlayer tends to form a close-packed structure that depends critically on the surface atomic geometry of the underlying substrate and the balance between the anion-metal and anion-anion interaction energies. The structures of halide anions adsorbed onto Au(Jtkl), Ag(hkl), and Pt(hkl) low-index surfaces have been the most widely studied systems by SXS, and a comprehensive review of ordered anion adlayers on metal electrodes is given by Magnussen [57]. 

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Xanthine anions structure, 5, 509 Xanthine-8-carboxylic acid synthesis, 3, 308, 322 Xanthine oxidase... 

B10H14 undergoes numerous cluster-addition reactions in which B or other atoms become incorporated in an expanded cluster. Thus in a reaction which differs from that on p. 175 BEU" adds to B10H14 with elimination of H2 to form initially the /<7o-BiiHi4 anion (structure 41, p. 178) and then the closo-B 2B 2 ... 

Angeli s salt Na2N203 has been shown by vibration spectroscopy to contain the trioxodinitrate(II) anion structure (2). Its decomposition and reactions in aqueous solutions have been extensively studied by nmr spectroscopy and other techniques. 

Figure 13.13 Schematic representation of the anion structure in M2IAS2F10OJ.H2O.

Se3Bri3- < > SeCls , TeClj-, TeCle ", etc.< > The anion structures are much as expected with the Se species featuring square planar (pseudo-octahedral) units, and the trinuclear Se " anions as in the tellurium analogue above. See also p. 776. There are, in addition, a fascinating series of bromoselenate(II) dianions based on fused planar SeBr4 units, e.g. Se3Brg ", Se4Bri4 ,... 

The following discussion concerns the thermal liquidus ranges available in different ionic liquids, as functions of cation and anion structure and composition. In particular, those structural features of cation and anion that promote these properties (while providing other desirable, and sometimes conflicting characteristics of the liquid, such as low viscosity, chemical stability, etc.) and variations in liquidus ranges and stabilities are the focus of this chapter. 

In this younger field of chemistry, some examples of anions may be still missing. One possible candidate is the [BN4] ion with a tetrahedral coordination of boron as in cubic BN, others may be adopted from oxoborates. Another interesting feature is the existence of structures with condensed nitridoborate anions derived from portions of BN structures. Until now the only example with a condensed anion structure is U(BN), containing kinked B-B bonded chains of (BN)x with B-B distances near 188 pm, slightly longer than in [B2N4] . ... 

The validity (or lack thereof) of the classical Zind formahsm as applied to less polar intermetallics, involving metals along the Zind border, is nicely probed by electron-poof trelides. Seminal work by Corbett [44] and Belin [48] recognized the proclivity of trelides (Ga, In, H) to form cluster-based anion structures. The apparent electron deficiency in the chemical bonding of these cluster com-... 

State, as shown in Fig. 10.8 [65]. The "trefoil bonding state, previously proposed and predicted to exist in aromatic hydrocarbon annulene molecules, is finally encountered, albeit in an extended intermetallic network [65]. This also highlights the important role of interactions between incompletely filled lone pairs in the stabilization of low-dimensional anion structures. 

The niobium-arseitic compounds described here, with novel anionic structures, clearly demonstrate the many possibilities for stractural motifs in this system. Similarly high potential for diverse structures and properties should be expected for the heavier pitictides when combined with other transition metals and the alkali-metal group. 

Examples of the anionic structures in polyphosphides, polyarsenides and poly antimonides. For comparison, recall the structures of red and black phosphorus and of arsenic (pp. 108, 109 and 110). Stereo image for NaPs... 

In the case of anionic systems, following the ideas of Diinitz [6], crystal structure (C) is a good model of an intermediate in which a nucleophile attacks a silicon atom included in a pentacoordinated anionic structure. Such an intermediate occurs during the nucleophilic displacement illustrated in Scheme 3. 

The TS for anionic SN2 reactions involves loose ion pairs as in a charge delocalized (soft) anion. On the another hand, the GS could involve a neutral electrophile and either tight or loose ion pairs depending on the anion structure (hard or soft) (Eq. 32). 

The slight steric differences between the alkyl groups of the cations lead to quite different far-orders of their polyiodide anion structures. In solid tBu2iPrPSeI7 [Figure 16(c)], one iodide anion bridges two of the iPr3PSeI+ cations and is in further contact with three I2 molecules the other I anion is in contact with five I2 molecules.59... 

Metallocenium Salts of Transition Metal Bisdichalcogenate Anions Structure and Magnetic Properties... 

In case of [M(edt)2] based salts, the size of the small anion is similar to the size of the CsMes ligand of the cation and only type I structural motives (D+ A D+ A-chains) were observed. For the intermediate size anionic complexes, [M(tdx)2], [M(mnt)2] and [Ni(a-tpdt)2], the most common structural motive obtained in salts based on those anions is also of type I. For the larger anionic complexes, [M(bdx)2] and [M(dmix)2], types III and IV chain arrangements were observed. In both cases anion molecules (type IV) or face-to-face pair of anions (type III) alternate with side-by-side pairs of cations. The complexes [M(mnt)2] and [M(dmix)2] (M = Ni, Pd and Pt) frequently present dimerization in the solid state [19], and they are the only anions where the chain arrangements present face-to-face pairs of anions (structural motives II and III). The variety of structural... 

Comparing the Raman spectra of silicate melts with various NBO/Si and NBO/T ratios with the Raman spectra of crystals of the same chemical composition, the above authors subdivided the anion structure of silicate melts into three compositional ranges ... 

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