Trihalides thermochemical data

Boron trihalides, BX3, are trigonal planar molecules which are sp2 hybridized. The X—B—X angles are 120°. Important physical and thermochemical data are presented in Table 1 (8—14). Additional thermodynamic and spectroscopic data may be found in the literature (1—5). 

Boron subhalides are binary compounds of boron and the halogens, where the atomic ratio of halogen to boron is less than 3. The boron monohalides, BC1, [20583-55-5], bromoborane(l) [19961-29-6], BBr, and iodoborane(l) [13842-56-3], BI, are unstable species that have been observed spectroscopically when the respective trihalides were subjected to a discharge (5). Boron dihalide radicals have been studied, and structural and thermochemical data for these species ( BX2) have been deduced (5). 

The determination of thermodynamic properties for the trihalides has been a particularly active area of investigation and the availability of data has been greatly enhanced. Several compilations of thermochemical data are available. Available experimental data and estimated values are found in the early reference works of Wicks and Block (1963) and Feber (1965). Since data are still unavailable for many halides, the value of these compilations has remained. Thermodynamic data are reviewed by Novikov and Baev (1964) and the thermodynamic and magnetic properties are extensively reviewed by Westrum... 

A substantial amount of thermochemical data have been reported for the dichlorides, but as with the trihalides, only estimated values are available for many dihalides (Wicks and Block, 1963 Feber, 1965 Johnson, 1969). A limited amount of data is reported for the condensed and gaseous dihalides (Schumm et al., 1973) and estimated values for a large number of gaseous dihalides are available (Krasnov and Danivola, 1969). 

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