Formation enthalpies halides

Alternative negative ion-based methods for measuring carbene and diradical enthalpies of formation have been developed, which can give BDEs indirectly. A common approach for this involves the use of halide affinity measurements. The relationship between enthalpy of formation and halide affinity is illustrated by Eq. 5.14. 

Fig. 8. Correlation between Pearson s hardness parameter (7P) derived from gas-phase enthalpies of formation of halide compounds of Lewis acids (19), and the hardness parameter in aqueous solution (/A), derived from formation constants of fluoride and hydroxide complexes in aqueous solution (17). The Lewis acids are segregated by charge into separate correlations for monopositive ( ), dipositive (O), and tripositive ( ) cations, with a single tetrapositive ion (Zr4+, ). The /P value for Tl3+ was not reported, but the point is included in parentheses to show the relative ionicity of Tl(III) to ligand bonds. 

TABLE 2.1 Formation Enthalpy of Schottky Defects in Some Alkali Halide Compounds of Formula MX"... 

Table 3.3 The formation enthalpy of Schottky defects, AHs, in some alkali halide compounds of formula MX...

Formation enthalpy of the oxides, sulfides, and halides in qnestion... 

For the alkah and lead halides, a simple empirical relation exists between the formation enthalpy of Schottky defects and the melting temperature Tnj, i.e.,... 

For the formation of the hydrogen halides by the direct combination of the elements, the enthalpies of formation are ... 

The above Born-Haber cycle represents the enthalpy changes in the formation of an alkali metal halide MX from an alkali metal (Li. Na, K, Rb. Cs) and a halogen (Fj. CI2. Br2 or I2). 

ENTHALPY DATA FOR HALIDE ION FORMATION IN AOLEOL S SOLI DON... 

Figure 4,4 Standard enthalpies of formation (A// and lattice energies (plotted as —t/O for alkali metal halides and hydrides.

In the course of this study, the authors determined /Lvalues for dibenzyl, methyl phenyl, methyl p-nitrophenyl, di-p-tolyl, di-isopropyl and tetramethylene sulphoxides and for diethyl, dipropyl and dibutyl sulphites. The /Lscales are applied to the various reactions or the spectral measurements. The /Lscales have been divided into either family-dependent (FD) types, which means two or more compounds can share the same /Lscale, family-independent (FI) types. Consequently, a variety of /Lscales are now available for various families of the bases, including 29 aldehydes and ketones, 17 carboxylic amides and ureas, 14 carboxylic acids esters, 4 acyl halides, 5 nitriles, 10 ethers, 16 phosphine oxides, 12 sulphinyl compounds, 15 pyridines and pyrimidines, 16 sp3 hybridized amines and 10 alcohols. The enthalpies of formation of the hydrogen bond of 4-fluorophenol with both sulphoxides and phosphine oxides and related derivatives fit the empirical equation 18, where the standard deviation is y = 0.983. Several averaged scales are shown in Table 1588. 

Complex chlorides of plutonium (34, 41) do not present such a wide range of formulae as the complex fTuorides but we have at hand thermodynamic information on two important species which have also been characterized with other actinides. In table II we have disregarded the complex halides for which no thermodynamic data are available. The enthalpy of formation of Cs2NaPuClg(c) (55) and Cs2PuClg(c) (56) have been obtained from enthalpy of solution measurements."The selected (8) values are AHf(Cs2NaPuCl6,c) =... 

Enthalpy of formation, solution, and dehydration, halides and halo-... 

Considering that the standard enthalpies of formation of various oxides, sulfides, and halides of As, Sb, and Bi are very close to each other, the similarity between this value and the standard enthalpy for the surface formation of As(OH)3, A//f = —680 + 20 kJ/mol, was taken as an indication that, indeed, the As redox process on Pt(l 11) involves the formation of hydroxide species [Blais et al., 2001]. For comparison with A/7 for the surface formation of Bi(OH)2, the strategy followed... 

An alternate positive ion approach, similar to that in Eq. 5.4a is to obtain a carbon-halogen BDE, R X, from which it is possible to obtain the enthalpy of formation of the radical from which the hydrocarbon BDE can be derived. The advantage of this approach is that it is easier to measure the R appearance energy from RX than it is from RH because of the weaker RX bond. However, a limitation of the approach is that the enthalpies of formation of organic halides, required to determine the enthalpies of formation of the cations, are generally not known as accurately as those for hydrocarbons. 

A variation of the halide affinity approach was used by Riveros et al. in the investigation of the enthalpy of formation of o-benzyne. Reaction of bromo- or iodobenzene with base in an ICR leads predominantly to the formation the expected M-1 anion, but also leads to the formation of solvated halide ions (Eq. 5.15). By using substrates with known halide affinities, it was possible to assign limits to the enthalpy of formation of the benzyne product. Ultimately, the experiment is comparable to that outlined in Eq. 5.14, although the acidity and halide affinity measurements are made in a single step. 

Enthalpies of formation for the singlet and triplet states of methylene were obtained from the photodissociation of ketene.131 The data for CH2 (3Bi) were recently confirmed by methods which do not rely on ketene.132,133 In a widely applicable procedure, threshold collision energies for the loss of halide ion from RR C-X- were combined with gas phase acidities of RR CH-Cl to give AHf (RR C ) (Eq. 11).134 Similarly, gas phase acidities of the radicals RR CH were combined with ionization energies of the radical anions RR C -, or electron affinities of the carbenes RR C (Eq. 12).135136... 

Some values for the enthalpy of formation of Schottky defects in alkali halides of formula MX that adopt the sodium chloride structure are given in Table 2.1. The experimental determination of these values (obtained mostly from diffusion or ionic conductivity data (Chapters 5 and 6) is not easy, and there is a large scatter of values in the literature. The most reliable data are for the easily purified alkali halides. Currently, values for defect formation energies are more often obtained from calculations (Section 2.10). 

TABLE 5.3 Approximate Enthalpy Values for Formation and Movement of Vacancies in Alkali Halide Crystals... 

Figure 7.4 Thermodynamic data needed in evaluation of the enthalpy of formation of MX(s). (a) Lattice enthalpy of sodium halides (b) lattice enthalpy of alkali iodides (c) electron gain and dissociation enthalpies of halides (d) ionization and atomization enthalpies of alkali metals.

Larger differences are observed when comparing the enthalpy of formation of the different halides of a given alkali metal. The enthalpy of formation of gaseous halide ions is exothermic since the exothermic electron gain enthalpy in absolute value is larger than the endothermic dissociation enthalpy. Furthermore, the enthalpy of formation of gaseous halide ions becomes less favourable with... 

Extension of the method to nonisostructural metal halides, some of which yield erroneous AHf values via Bom-Haber cycles, is shown in Fig. 1. All curves are nonlinear with the bow increasing in the expected order T1(I) < Pb(II) < Bi(III) < Ag(I). For the first transition metal dihalides, however, straight lines can be drawn within the limits of enthalpy errors except for Zn(II) or Mn(II) salts. Thus heats of formation of the fluorides can be extrapolated linearly from the other three halides to a first approximation. 

Table 12a. Standard enthalpy of formation, A/ff(g), enthalpy of disruption, AHjy, and metal-halogen bond enthalpy contribution, (M-X), in metal carbonyl halides (kJ mol-1)...

The enthalpy AHN2 for ester (halide) formation is given by... 

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