Hydrogen antimony—oxygen bonds

Of the solvents, aromatic and olefinic hydrocarbons are r-donors ( r-EPD) alcohols, ethers, amines, carboxamides, nitriles, ketones, sulfoxides and N- and P-oxides are n-donors (n-EPD), and haloalkanes are cr-donors (cr-EPD). Boron and antimony triha-lides are acceptor solvents (r-EPA), as are halogens and mixed halogens (c-EPA), and liquid sulfur dioxide (ti-EPA). In principle, all solvents are amphoteric in this respect, i.e. they may act as a donor (nucleophile) and an acceptor (electrophile) simultaneously. For example, water can act as a donor (by means of the oxygen atom) as well as as an acceptor (by forming hydrogen bonds). This is one of the reasons for the exceptional importance of water as a solvent. 

In the first section of this chapter some of the properties of the elements hydrogen, carbon, nitrogen, phosphorus, arsenic, antimony, bismuth, oxygen, sulfur, selenium, tellurium, fluorine, chlorine, bromine, and iodine are described. The following sections are devoted to some of their compounds with one another, especially the single-bonded normal-valence compounds. Compounds of nonmetals with oxygen are discussed in the following chapter. 

The X-ray structure of a representative complex is shown in Figure 2.1. It can be seen that the Sb—O bond of the HCONMea-SbCls complex [22] is much shorter (2.048 A) than the sum of the van der Waals radii (2.2 + 1.4 = 3.6 A) and slightly longer than the sum of the covalent radii (1.41 -1- 0.56 = 1.97 A) of the antimony and oxygen atoms. The Sb—O vector points in the direction of a putative sp lone pair of oxygen (SbOC = 124.5°). The preferred lone pair of oxygen is the less sterically hindered one, on the hydrogen side. 

Despite the fact that sulfonium salts are much more easily prepared than oxonium ones, simple sulfur bases appear to be considerably less basic towards protonic acids, hydrogen bond donors, and most Lewis acids than are their oxygen analogs. The exact values for the freezing point depressions of sulfides in sulfuric acid are controversial (134,136,334) but it is clear that if proper allowance is made for sulfonation, a twofold depression is approached magnifying protonsr tion of the sulfur atom. Evidence for the existence of stable sulfonium salts from the interaction of mercaptans, sulfides and disulfides with hydrogen chloride and antimony pentachloride at low temperatures has recently been described (205). 

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