Salts planar trigonal ions

The crystal structure of Pollard s Salt, (NH UAua.UAg.C1.1. contains dinuclear [AgaCls] anions in which the silver(i) ions exhibit distorted planar trigonal co-ordination (113) the Ag-Cl(terminal) distances, with a mean... 

The salts [CTHejNaOJpgXa]. HjO (X = C1 1, Br 2 or I 3) have been synthesised and characterised by various techniques, including Cl (1), Br (2) and I (3) NQR spectroscopy. Compounds 1 and 2 were iso-structural, but 3 differed. Both 1 and 2 contained trigonal planar HgX3" ions, H-bonded with H2O and cations into 2D sheets parallel to the ac plane. These sheets were connected by double chains of Hg—X interionic bonds along the b direction, resulting in a tbp about Hg with two long... 

Recent results on the chemistry of persistent vinyl cations are summarized. / , / -Disilyl-substituted vinyl cations were synthesized by intramolecular addition of transient silylium ions to alkynes. The vinyl cations are stable at ambient temperature and were isolated in the form of their tetrakispentafluorophenylborate and hexabromocarboranate salts. The vinyl cations were characterized by IR and NMR spectroscopy and by X-ray crystallography. The experimental results for the a-alkyl- and a-aryl-substituted vinyl cations confirm their Y-shape structures, consisting of a linear dicoordinated, formally positively charged a-carbon atom and a trigonal planar coordinated /f-carbon atom. In addition, the spectroscopic data clearly indicate the consequences of, / -silyl hyperconjugation in these vinyl cations. Scope and limitations of the synthetic approach to vinyl cations via addition of silylium ions to C=C triple bonds are discussed. 

Because a carbocation is sp2 hybridized, with trigonal planar geometry and an empty p orbital, this ion has a cycle of three p orbitals. (Remember that it is not the number of orbitals that determines whether a compound is aromatic or not, but rather the number of electrons in the pi MOs.) The cyclopropenyl carbocation has two electrons in its three pi MOs, so it fits Hiickel s rule and should be aromatic. In fact, cyclopropenyl carbocations are significantly more stable than other carbocations, even though they have considerable angle strain. For example, most carbocations react rapidly with water, a weak nucleophile. In contrast, tri-ferf-butyl-cyclopropenyl perchlorate, a carbocation salt, is stable enough to be recrystallized from water. 

Addition of excess iodide to the insoluble Hgl2 results in the formation of soluble mercury iodo complex [Hgl3] , with a trigonal planar structure. The ion is solvated in water and converts to a tetrahedral structure. Further, addition of H leads to tetrahedral [Hg ] ". Reaction of iodide salts with Hg can be used to produce mercury iodo complexes. Other halide and pseudohalides also form [HgXj] and [HgX4] . The tetrahalo anions see Anion) are usually tetrahedral, while the trihalo ions readily add solvent molecules to form distorted tetrahedral or Trigonal Bipyramidal structures. 

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