Group IV

Group IV. C-Donor ligands. Treatment of salts of Pt (Pd, Rh, Ir) with 1-benzoyl -iminopyridinium (L) gives the complexes [PtCl(L - H)L] (see p. 398).103 Dicyano-methanide complexes of Pt (Pd, Rh, Ir) have been prepared, e.g. equation (38) (see p. 398) 101 Tricyanomethanide complexes of Pt have been synthesized by oxidative 

A safe synthesis of a number of metal fulminato-complexes, including [Pt(R3E)2-(CNO)J (E = P, As or Sb) and [PtX(CNO)(PPh3)2], (X = H, H, Me, CN or NCO) by reaction of AsPh4CNO with the appropriate Pt substrate has been reported. The thermally very stable complex [Pt(CNO)2(PPh3)2] was shown to isomerize to the isocyahato-complex under mild conditions, and to be reduced by phosphines to the cyanide [Pt(CN)2(PPh3)2].99 Other fulminato-complexes have been synthesized (equation 39) (R = Ph, Me or Et), and again i.r. evidence also shows isomerization 

Formation of sulphur ylide complexes of Pt(Pd) of type [PtX2(R2S)Sy] (X = Cl, Br or I R = Me, Et Sy = Me(Ph)SCHC(0)C6H4Cl-p) has been reported.105 The v(CO) band of the metal complexes occurs at higher frequencies than in the free ylide, and in addition spin-spin coupling between the ylide methine proton and the 195Pt nucleus is observed, which is indicative of the Pt—C bond (47). 

Three double complex salts [Pt(CNR)4][Pt(CN)4](R = Me, Et or Bu ) exhibit low-energy electronic absorption bands in the solids which are absent in solution spectra of the anion or cation complexes with simple counter-ions.171 These bands, which are responsible for the intense colour of the solids, are ascribed to M - L charge transfer which has been red-shifted by Davydov interaction between anion and cation. Cation-anion association was also observed in MeCN solution and association constants were measured. 

The gaseous molecule PtC2 has been observed in a high-temperature mass spectrometer and its atomization energy determined.172 

In this group the outer quantum level has a full s level and two electrons in the corresponding p level. As the size of the atom increases the ionisation energy changes (see Table 8.1) and these changes are reflected in the gradual change from a typical non-metallic element, carbon, to the weakly metallic element, lead. Hence the oxides of carbon and silicon are acidic whilst those of tin and lead are amphoteric. 

Only the carbon atom can gain four electrons this only happens when it is combined with extremely electropositive elements and this state may be regarded as exceptional. Bonding in carbides is almost invariably predominantly covalent. 

The oxidation state +4 involves both the s and p electrons. The oxidation state +2, involving only the p electrons, becomes increasingly important with increasing atomic size, and the two 

The concept of oxidation states is best applied only to germanium, tin and lead, for the chemistry of carbon and silicon is almost wholly defined in terms of covalency with the carbon and silicon atoms sharing all their four outer quantum level electrons. These are often tetrahedrally arranged around the central atom. There are compounds of carbon in which the valency appears to be less than 

Silicon, germanium, tin and lead can make use of unfilled d orbitals to expand their covalency beyond four and each of these elements is able (but only with a few ligands) to increase its covalency to six. Hence silicon in oxidation state -f-4 forms the octahedral hexafluorosilicate complex ion [SiFg] (but not [SiCl] ). Tin and lead in oxidation state -1-4 form the hexahydroxo complex ions, hexahydroxostannate(IV). [Sn(OH) ] and hexahydroxoplum-bate(IV) respectively when excess alkali is added to an aqueous solution containing hydrated tin(IV) and lead(IV) ions. 

A good deal of mechanistic work for the Group IV elements can generally be described as organometallic, and is reviewed elsewhere. Only a limited number of papers are dealt with below. 

Carbon.— The use of isotopes in studies of the mechanisms of reactions of carbon dioxide or carbonates has been reviewed. Measurements using and give a rate constant of 1141 mol s for the exchange reaction between carbon dioxide and carbonate ion at 25 °C the same techniques have been applied to the bovine carbonic anhydrase-catalysed exchange between carbon dioxide, its related species, and water.The decomposition rates of the alkyl monocarbonates in aqueous alkali and the effect of polyelectrolytes on the conversion of ammonium cyanate into urea have been reported. The application of calculations originally used for 5 b2 processes to the classical Sn2 halide ion-alkyl halide exchange reaction accounts quantitatively for the relative reactivities in terms of steric effects alone it is not necessary to invoke polar effects. Some further evidence for ion-pair intermediates in Sn2 substitutions has been obtained.  

Carbon.— In the first volume of this Specialist Periodical Report we mentioned the novel suggestion that the two fundamental mechanisms of nucleophilic substitution, 5k1 and 5n2, might combine into one mechanism in which ion-pairing between the leaving group and the remaining organic 

Carbon dioxide is often considered an inorganic compound, so it is relevant to mention that the kinetics of exchange between carbon dioxide and water have been investigated, under both homogeneous and heterogeneous conditions. The rate law and appropriate rate constants have been determined for the reaction of carbon dioxide with aqueous alkali in the presence of [As(OH)aO] as catalyst.  

General.—A particularly extensive study has been made of the kinetics of reaction with iodine of compounds containing Group IV element to Group IV element bonds, RJM —M R, where R may or may not be the same as R and likewise M and M  

In all cases second-order kinetics, first-order in each reactant, were observed. Some of the kinetic results are reproduced in Tables 2 and 3. The range of rate constants is illustrated by the values in Table 2 reaction with bromine instead of iodine was too fast to follow. Table 3 contains all the activation parameters reported. The kinetic results have been discussed in terms of 

Gerster, Internat. J. Appl. Radiation Isotopes, 1971, 22, 339 Chem. Abs., 1971, 75, 53 812w). 

Carbon. A stability constant for [(CN)3] has been measured there is a rapid formation of this species from [CN] + (CN)2, followed by a slower decomposition to organic products. The oxidation of cyanide ion by ozone in aqueous solution has been reported.  

Ab initio MO-LCAO-SCF methods have been applied to the formation of the bicarbonate ion from carbon dioxide and hydroxide ion. It is concluded that in the gas phase there should be no barrier to reaction, and that in solution solvation of the hydroxide ion reduces reactivity. The authors speculate that the high activity of carbonic anhydrase may be due to an unsolvated hydroxide in Zn—OH in a hydrophobic environment. 

The selection of molecules and of depth of coverage appropriate in a discussion of the inorganic chemistry of carbon is a debatable issue. The present review takes the middle ground, with C—H and C—C bonds usually being inadmissible. 

Reduction of CO by the hydrated electron might be expected to yield CO or HCO. However, by the use of pulse radiolysis Raef and Swallow demonstrated that the first detectable species is HC(OH)2 (250). Presumably CO- undergoes very rapid hydrolysis. It is difficult to estimate accurately the energetics of the CO/CO couple, but the CO/HCO couple is more easily discussed. The JANAF tables indicate a value of AfG° = 28.3 + 8 kj/mol for HCO in the gas phase. By neglecting the hydration free energy a value of —1.54 V is calculated for E° for the CO/HCO couple. The chemistry of HC(OH)2 is beyond the scope of this review. 

There is an intriguing report that C03 can be oxidized to C03 by triplet-state duroquinone in micellar solutions (264). From Benson s data we calculate A(G° = -171 16 kJ/mol for C03 in the gas phase (43). By applying a correction of 10 kJ/mol for hydration of C03 we obtain 0 = 2.3 + 0.2 VfortheC03/C03 couple, which shows that C03 is indeed a viable intermediate in the triplet duroquinone system. 

CC13 is generated by reduction of CC14 (191, 202). The NBS tables do not supply a value of AfG° for CC13, but the JANAF tables cite 92 8 kJ/mol for this species. With the same approximations as above for the CF3 systems, we calculate E° = —0.23 V for the CC14/(CC13, Cl ) couple. Despite the apparent ease of reduction of CC14, Roster and Asmus reported that it was not reduced by C02 (191). 

In a pulse radiolysis study of CS2 Roebke and co-workers identified several derivative species (258). SC(OH)S, its conjugate base, and the pKa (4.4) that relates them were determined from the reaction of CS2 with OH. SCSH and its pKa (1.6) were determined by the reactions of eaq and H with CS2. The redox characteristics of these species remain unexplored. A subsequent pulse radiolysis study has not contributed any additional thermochemical information (56a). 

Gregory, G. Kohnstam, M. Paddon-Row, and A. Queen, Chem. Comm., 1970, 1032. 

Carbon.— The suggestion that the mechanisms of nucleophilic substitution at carbon, 5n1 and 5 n2, might merge into an ion-pair mechanism has been further 

Matsuzawa and K. Saito, Bull. Chem. Soc. Japan, 1973, 46, Till. 

Carbon.—The approach to equilibrium between CO3 and [HCO3]- has been followed by the stopped-flow indicator technique, and the catalytic coefficient for 

Discussion of the borderline region between the Sn1 and 5n2 mechanisms of substitution continues. The case for an ion-pair mechanism is considered to be not proven. A kinetic study of the solvolyses of a range of secondary tosylates in a range of solvents has been interpreted as showing a range of nucleophilic solvent assistance with a spectrum of 5n1/ S n2 character. 

The decomposition of tetronitromethane has been examined. In aqueous solution it involves hetCTolytic cleavage of the C—N bond  

In less polar solvents homolytic cleavage takes place, followed by hydrogen abstraction from the solvent. A study of the photolysis of C(N02)4 has also appeared. Finally we note that the decomposition of peroxodicarbonates in aqueous acid proceeds through [HCaOsl and [HC04] as intermediates.  

Carbon.—Two further papers on the kinetics of hydration of carbon dioxide have been published. A kinetic study of the reaction of carbon disulphide with the disulphide anion indicates that the initial step is the bimolecular 

From the published rate constants at 0, 10, and 20 °C one can calculate an activation energy of 20.5 0.4 kcal mol for this reaction. Rate constants for decomposition of the trithiocarbonate anion, CS, and its protonated derivatives, in aqueous solution have been estimated.  

The kinetics of the acid hydrolysis of cyanide ion were studied several decades ago. The kinetics of base hydrolysis of cyanide ion have only recently been investigated, though the reaction products were established as formate ion and ammonia many years ago. Rates of alkaline hydrolysis are first-order in cyanide ion, zero-order in hydroxide. The rate-determining step cannot therefore be attack of hydroxide at cyanide ion. However, both water attack at cyanide or hydroxide attack at hydrocyanic acid are consistent with the reported rate law. The overall kinetic pattern for the reaction, including the 

Mal kova and V. D. Ovchinnikova, Trudy Ivanovsk. khim.-tekhnol. Inst., 1970, 59 Chem. Abs., 1972, 77, 52 788x). 

Kremer and L. A. Zatuchnaya, Kontrol Tekhnol. Protsessov Obogashch. Poles. Iskop., 1971, 132 (Chem. Abs., 1973, 78, 48 522j). 

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Landolt-Bornstein "Zahlenwerte und Funktionen aus Naturwissenschaft und Technik," New. Ser. Group IV, Vol. Ill, Springer Verlag, Berlin, 1975. Also Part 4c (Solubility of Gases in Liquids), 1976. 

There are hundreds of semiconductor materials, but silicon alone accounts for tire overwhelming majority of tire applications world-wide today. The families of semiconductor materials include tetraliedrally coordinated and mostly covalent solids such as group IV elemental semiconductors and III-V, II-VI and I-VII compounds, and tlieir ternary and quaternary alloys, as well as more exotic materials such as tire adamantine, non-adamantine and organic semiconductors. Only tire key features of some of tliese materials will be mentioned here. For a more complete description, tire reader is referred to specialized publications [6, 7, 8 and 9]. 

The group IV semiconductor materials are fourfold coordinated covalent solids from elements in column IV of tire periodic table. The elemental semiconductors are diamond, silicon and gennanium. They crystallize in tire diamond lattice. 

Figure 2.5 shows the boiling points of the hydrides in elements of Groups IV. V, VI and VII. Clearly there is an attractive force between the molecules of the hydrides of fluorine, oxygen and nitrogen... 

What are the principal differences in physical and chemical properties between any one metal from Group I and any one metal from Group IV and any one transition metal How far can you explain these differences in terms of their different atomic structures ... 

The most important trend to be noted in the covalent hydrides is the change in acid-base behaviour as we cross a period from Group IV to Group VII. In Period 1, we have... 

The tendency of elements of higher atomic number to retain the s electrons as an inert pair is also encountered in Group IV, and in this case it is found that for lead the most stable oxidation state is + 2, achieved by loss of two p electrons. 

Figure S.l. Mean thermochemical bond energies Jor represenlaiive bonds in Group IV...

Tin slowly dissolves in dilute hydrochloric, nitric and sulphuric acids, and is in fact the only Group IV element to do so. The reactions with more concentrated acid are rapid. With hydrochloric acid. 

All Group IV elements form both a monoxide, MO, and a dioxide, MO2. The stability of the monoxide increases with atomic weight of the Group IV elements from silicon to lead, and lead(II) oxide, PbO, is the most stable oxide of lead. The monoxide becomes more basic as the atomic mass of the Group IV elements increases, but no oxide in this Group is truly basic and even lead(II) oxide is amphoteric. Carbon monoxide has unusual properties and emphasises the different properties of the group head element and its compounds. 

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