Diborane electron diffraction

Diborane, B H , has the configuration shown in Figure 10-3. This configuration was proposed long ago 74 it has been verified by spectroscopic and other physical evidence.7 The molecular dimensions were obtained by a careful electron-diffraction study.80... 

The last molecule we shall consider in this chapter is diborane, B2H6. Electron diffraction indicates the molecular structure of B2Hg as shown in Figure 7-12. Ha, H, H, and Hg lie in the yz plane, while B2H2 lies in the xz plane. 

Bartell, L.S. and Carroll, B.L. (1965) Electron-diffraction study of diborane and deuter-odiborane. J. Chem. Phys., 42, 1135-1139. 

Diborane, B2Hg. The results of the latest electron diffraction (sector, microphotometer) study of this (diamagnetic) molecule are ... 

Aminoboranes undergo an interesting reaction when heated with di-borane a borane group is absorbed and aminodiboranes are formed (35, 36). The structure of 7V,jV-dimethylaminodiborane has been determined by electron diffraction (70) it (I) is related to the structure of diborane and to the probable structure of dimeric iV,iV-dimethylaminoborane (II).3 It is likely that all aminodiboranes have similar structures. The first member of the group, H2NB2H5, may be prepared by passing diborane over its... 

A) Gas-phase structure of diborane (B2H ) with structural parameters determined by electron diffraction B) representation by Longuet-Higgins and Lipscomb of three-center, two-electron bonds C) molecular orbital description of three-center, two-electron bonding... 

The structure now universally accepted is that shown in Fig. 1, in which the two bridge hydrogen atoms lie on an axis that is perpendicularly bisected by the plane of the other six atoms. There are three mutually perpendicular twofold axes of symmetry (point group D.,), and the dimensions given are those ob-tained from a recent detailed analysis and conflation (192) of electron-diffraction data (13) with the results of high-resolution infrared spectroscopy (193), as listed in Table I (where the electron-diffraction results for deuterodiborane also appear) Even in the absence of microwave data, we can say that the parameters of diborane are now as accurately known as those for almost any other molecule of con arable size. 

Precise molecular parameters for diborane have been obtained from an electron-diffraction study by Bartell and Carroll (13) (Table I), who also give estimates of the mean amplitudes of atomic vibrations. 

Smith and Lipscomb established the crystal structure of the 3 phase of B2H6 [19] after earlier work by Stitt [20,21], Price [22,23] and Hedberg [24] on gas-phase diborane. Jones and Lipscomb [25,26] used structure factors from calculations to explain apparent discrepancies between bond lengths determined from x-ray and electron diffraction experiments. Several recent theoretical studies have considered diborane with correlated, ab initio methods [27-30] and density functionals [31,32]. Trinquier and Malrieu performed a general analysis of bonding in dibridged X2H6 compounds [33]. 

The structure of diborane is found to be as shown (Fig. 3.1) by electron diffraction studies. 

Comparison of Some Investigations,—The best indication of the accuracy in electron-diffraction parameters is probably obtained by comparing with results from various other experimental methods and by comparing parameters from several electron-diffraction investigations on the same compound. Accurate comparison with results obtained by other methods is complicated by the fact that corrections are needed to obtain the same type of parameters. As discussed in Chapter 4, average structures may be obtained both from eiectron-diffraction results and from spectroscopic data. Comparisons of average structures for diborane and for sulphur dioxide are given in Tabie 6. 

The actual chemical structures of boron hydrides remained a mystery for decades. The obvious analogy of the formula of diborane(6), B2H6, to ethane and of tetraborane(lO), B4H10, to butane tempted speculation that the structures were also analogous. In fact, electron diffraction studies appeared to bear this out for B2H6, whieh was incorrectly reported to have the ethane structure. 

Carbon Monoxide- C—B)Borane BH3CO The unstable compound carbon monoxide-(C—B)borane (12), BH3CO, prepared from diborane and carbon monoxide under elevated pressures (20S), has been the subject of intensive spectroscopic investigations. Electron diffraction measurements (204) indicate that the molecule has its B—C—O... 

The diffraction of electrons by gaseous diborane has been studied by Bauer who originally interpreted the data in terms of the ethane model and obtained the following values for the interatomic distances B—B = 1 86 A and B—H = 1 27 A. More recently , however, it has been shown that the data agree equally well with distribution of atoms in the bridge model, the values for the distances being as foUows ... 

---