Group 16 elements cationic compounds

Formulas of compounds consisting of the monatomic ions of main-group elements can be predicted by assuming that cations have lost all their valence electrons and anions have gained electrons in their valence shells until each ion has an octet of electrons, ora duplet in the case of FI, Li, and Be. 

The number of known polycationic compounds of main group elements is far less than that of polyanionic compounds. Examples include the chalcogen cations S]+, S]+, Se]o and Teg that are obtained when the elements react with Lewis acids under oxidizing conditions. The ions S]1, Sc]1 and Te] have a square structure that can be assumed to have a 6n electron system. 

Zintl phases remarks on their definition. We have seen that the Zintl phases may be considered as a group of compounds formed by an electropositive (cationic) component (alkali, alkaline earth metal, lanthanide) and an anionic component (for instance a main group element of moderate electronegativity). The anionic part of the structure may be described in terms of normal valence combination. 

In introductory chemistry courses, much emphasis is necessarily placed on the concept of stoichiometry, that is, the fact that elements combine in certain definite proportions by weight, proportions that reflect their valences and atomic masses. For much of the chemistry of the main group elements and organic compounds, this concept works extremely well, but in transition metal chemistry in particular it is common for ions of more than one oxidation state to form with comparable ease, and sometimes to occur together in the same ionic solid. The presence of more highly oxidized cations... 

The number of known polycationic compounds of main group elements is far less than that of polyanionic compounds. Examples include the chalcogen cations S4 , S , Se" ... 

Now we can work out the formula of an ionic compound formed between the monatomic ions of two main-group elements, one a metal and the other a nonmetal. Unless a lower oxidation number is specified (as for the p-block metals), the metal atom loses all its valence electrons, and the nonmetal atom gains enough electrons to complete its valence shell. Then we adjust the numbers of cations and anions so that the resulting compound is electrically neutral. A simple example is calcium chloride. The calcium atoms ([Ar]4s2) each lose two electrons, to form... 

H. Bock and B. G. Ramsey, Angew. Chem., 85, 773 (1973) Angew. Chem., Int. Ed. Engl., 12, 734 (1973), report on the interpretation of the PE spectra of main group element compounds by comparison of equivalent radical cation states of chemically related molecules, based on MO perturbation arguments. 

The selective Bock Oxidation using AICI3/CH2Q2 in the meantime has formed widespread application for main group element compounds the prediction of one-electron oxidizability based on first ionization energies IEJ < 8 eV is valid also for numerous other classes of compounds. For examples of ESR/ENDOR-detected radical cations or their rearrangement products, see BN heterocycles H. Noth, W. Winterstein, W. Kaim and H. Bock, Chem. Ber., 112, 2494 (1979) tetra-teri-butyltetrahedrane H. Bock, R. Roth and G. Maier, Chem. Ber., 117, 172 (1984) tetrakis(dimethylamino)-p-benzoquinone H. Bock, P. Hanel and U. Lechner-Knoblauch, Tetrahedron Lett., 26, 5155 (1985) 1,2-dithiolane H. Bock, B. I. Chenards, P. Rittmeyer and U. Stein, Z. Naturforsch. B, 43, 177 (1988), and references cited therein. 

Thus it is evident that in compounds with early transition-element cations (Group IV, V and VI) the less tightly-bound d electrons often prefer to be collective and their structures therefore are less easily predictable. 

Sometimes dx x is long, sometimes it is short. In Table 1 are shown two series of compounds studied by Mewis.38 In these the cation is kept constant, and so is the main group element P. Only the metal varies. 

An unusual system involves the incorporation of a main group element, that is, germanium, within the macrocycle side chain. This is shown in Figure 17. The compounds were prepared in order to assess alkali metal cation transport. This was done but the results proved equivocal <2001JOM108>. 

In addition to such divalent species, the elements form compounds in formal oxidation states IV and VI with four, five, or six bonds tellurium may give an 8-coordinate ion TeFg". Some examples of compounds of Group 16 elements and their stereochemistries are listed in Table 12-2. They also form cyclic and polycyclic cations (e.g., S2+, Te +) under special conditions. 

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