Nontransition element compounds

This field has developed at a rapid pace since 1968, and a wide range of heteronuclear complexes of the tri- and tetranuclear variety has been established. It will be convenient to discuss the compounds in the first instance on the basis of nuclearity and, for the tetranuclear species, to subdivide the discussion on the basis of the carbonyl stoichiometry and cluster electron count. We have excluded from the discussion the interaction with nontransition elements, such as Hg, Tl, and Cd, which form a wide range of compounds. 

Heteropoly compounds may be classified according to the ratio of the number of central atoms to the peripheral molybdenum or other such atoms. Compounds with the same number of atoms in the anion usually are isomoiphous and have similar chemical properties. Usually, the heteropolymolybdates and heteropolytungstates containing nontransition elements as central atoms have more structural analogues than those that contain transition elements as central atoms. Table 1 lists all elements... 

An interesting example of oxygen activation by onium salts of nontransition elements has been claimed. Sulfonium salts were found to be especially effective,211 and it was proposed212-214b that dioxygen complexes of sulfonium compounds can initiate autoxidations via hydrogen transfer with hydrocarbons, e.g.,... 

Since the epoxidation step involves no formal change in the oxidation state of the metal catalyst, there is no reason why catalytic activity should be restricted to transition metal complexes. Compounds of nontransition elements which are Lewis acids should also be capable of catalyzing epoxidations. In fact, Se02, which is roughly as acidic as Mo03, catalyzes these reactions.433 It is, however, significantly less active than molybdenum, tungsten, and titanium catalysts. Similarly, boron compounds catalyze these reactions but they are much less effective than molybdenum catalysts 437,438 The low activity of other metal catalysts, such as Th(IV) and Zr(IV) (which are weak oxidants) is attributable to their weak Lewis acidity. 

Redistribution of substituents tends to be especially facile for halides, hydrides, and alkyls of Groups I—III nontransition elements because these compounds are electron-deficient. Bridging groups are present in many of these compounds. Even in the boron trihalides that are not bridged, a bridged transition state making use of the empty valence shell orbitals is possible, so that redistribution can occur with a relatively low activation energy (113) ... 

In comparison with the vast number of known organic compounds, carbon forms few fully three-dimensional cage molecules, some common exceptions being cubane, adamantane, and triptycene. By applying the isostructural principle, chemists have built up an imposing array of adamantanes substituted with a variety of other nontransition elements, but until recently triptycene has strongly resisted most attempts to tinker with its structure in this way. 

The most active elements for the oxygen transfer are the transition metals to the left of the Periodic Table. The order of activity of these is Mo > W > Ti > V > U > Th > Zr, Nb [465]. In addition, several nontransition metal compounds are effective in the reaction, most notably SeO2 and borate esters (See Section 11). The catalytic elements are typically in their highest attainable oxidation state, and have the essential feature of not having a readily accessible lower oxidation state. This is necessary in order not to promote the metal-catalyzed decomposition of the peroxides, which could initiate radical chain reactions. Elements such as Mn, Fe, Co, Rh, Ni, Pt, and Cu are ineffective for this reason. 

In fact, the classification of chemical elements is valuable only in so far as it illustrates chemical behaviour, and it is conventional to use the term transition elements in a mote restricted sense. The elements in the irmer transition series from cerium (58) to lutetium (71) are called the lanthanoids those in the series from thorium (90) to lawrencium (103) are the actl-noids. These two series together make up the /block in the periodic table. It is also common to include scandium, yttrium, and lanthanum with the lanthanoids (because of chemical similarity) and to include actinium with the actinoids. Of the remaining transition elements, it is usual to speak of three main transition series from titanium to copper from zirconium to silver and from hafnium to gold. All these elements have similar chemical properties that result from the presence of unfilled d-orbltals in the element or (in the case of copper, silver, and gold) in the ions. The elements from 104 to 109 and the undiscovered elements 110 and 111 make up a fourth transition series. The elements zinc, cadmium, and mercury have filled d-orbltals both in the elements and in compounds, and are usually regarded as nontransition elements forming group 12 of the periodic table. 

Bokii, N. G., Shklover, V. E., Struchkov, Yu. I., Structural Chemistry of Organic Derivatives of Nontransition Elements. Structural Chemistry of Silicon, Germanium, Tin, and Lead Organic Compounds, Itogi Nauki Tekh. Kristallokhim. 10 [1974] 94/148. 

Maslova, V. A., Rabinovich, I. B., Heat Capacity, Phase Transitions, and Thermodynamic Functions of Alkyl Compounds of Nontransition Elements, Tr. Khim. Khim. Tekhnol. 1974 No. 1, pp. 40/63. 

Colors of ceramics are due to compounds containing the so-called transition (metallic) elements such as iron and copper, as seen above. Some of the colors of such compounds might be familiar to you. Iron oxide can be brown (rust) or red (hematite ore), and maybe you have seen a nice blue copper sulfate crystal. Compounds of other elements (nontransition elements) are rarely colored. What special is there about compounds of transition elements ... 

Chen, N, Y., Chen, R. L., Lu, W. C., Li, C. H. and Villars P. (1999). Regularities of formation of ternary intermetallic compounds Part 4. Ternary intermetallic compounds between two nontransition elements and one transition element. Journal of alloys and compounds, 292, pp. 129-133. 

In all of these compounds, even the tetrahedral ones, a possible starting point for the calculation of properties is an ionic electronic structure with the effects of interatomic matrix elements treated in perturbation theory. As wc liave indiettted, and as will be seen in detail in the next section, it is even possible to treat tlic polar covalent nontransition-metal solids in this way. Thus we should be able to calculate properties of the transition-metal compounds just as we did for the simple ionic compounds. 

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