Cationic structures chemistry

Hilgenfeld, R., Saenger, W. Structural Chemistry of Natural and Synthetic Ionophores and their Complexes with Cations, in Topics in Current Chemistry (ed. Boschke, F. L.), p. 8, Berlin—Heidelberg—New York, Springer 1982... 

Structural chemistry of natural and synthetic ionophores and their complexes with cations. R. Hil-genfeld and W. Saenger, Top. Curr. Chem., 1982,101,1-82 (346). 

Trivalent cations are present in most of niobium oxychloride cluster compounds known to date and play an important role in their structural chemistry. The series AxNb6Cli202 (A = K, Rb, Cs, In), on the other hand, represents an example of an oxychloride structure stabilized without a trivalent counter-ion (Fig. 6.12). 

Bachman, R.E. and Schmidbaur, H. (1996) Isolation and Structural Characterization of [P(AuPPh3)5][BF4]2 via Cleavage of a P-P Bond by Cationic Gold Fragments Direct Evidence of the Structure of the Elusive Tetrakis [phosphmeaurio(I)] phosphonium(4-) Cation. Inorganic Chemistry, 35, 1399-1401. 

The present volume deals with the properties of dienes, described in chapters on theory, structural chemistry, conformations, thermochemistry and acidity and in chapters dealing with UV and Raman spectra, with electronic effects and the chemistry of radical cations and cations derived from them. The synthesis of dienes and polyenes, and various reactions that they undergo with radicals, with oxidants, under electrochemical conditions, and their use in synthetic photochemistry are among the topics discussed. Systems such as radialenes, or the reactions of dienes under pressure, comprise special topics of these functional groups. 

Schmittel and Burghart (1997) had published a well-structured review on cation-radical chemistry. The review gave a general picture of the cation-radical nature compiling data of those days. This section scrutinizes data relevant to acid-base reactivity of organic ion-radicals. 

For a general formulation of the Zintl-Klemm concept, consider an intermetallic AmX phase, where A is the more electropositive element, t3 pically an alkali or an alkaline earth metal. Both A and X, viewed as individual atoms, are assumed to follow the octet rule leading to transfer of electrons from A to X, i.e., A AF, X —> X , so that mp = nq. The anionic unit X arising from this electron transfer is considered to be a pseudoatom, which exhibits a structural chemistry closely related to that of the isoelectronic elements [11]. Since bonding also is possible in the cationic units, the numbers of electrons involved in A-A and X-X bonds of various types (caa and exx> respectively) as well as the number of electrons e not involved in localized bonds can be generated from the numbers of valence electrons on A and X, namely and ex, respectively, by the following equations of balance ... 

It is instructive, for example, to compare the structural chemistry of and Zn + which have identical charges and similar sizes. Mg + is hard and rarely occurs in other than six coordination (bonding strength of 0.33 vu), but, because Zn + has a filled d shell which can readily mix with the electrons of the valence shell, it is soft and is found equally often in four- and six-coordination (bonding strength between 0.33 and 0.50, average 0.40 vu, see Section 6.5). A more complete discussion of the behaviour of soft cations is given in Chapter 8. 

There has been particular interest in the chemistry of small organosilicon ions and their neutral counterparts for a number of reasons (i) Small SiCvHv molecules are well suited to draw analogies between the structural chemistry of silicon and carbon—or to state differences, (ii) The chemistry of small silicon compounds is viewed as fundamental in astrophysics and astrochemistry, and a large number of cationic and neutral SiRv molecules have been detected in interstellar and circumstellar matter. 

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