Problem 28
Suggest likely products for the following reactions, with the stoichiometries stated: (a) \(\mathrm{B}_{5} \mathrm{H}_{9}+\mathrm{Br}_{2} \stackrel{298 \mathrm{K}}{ }\) (b) \(\mathrm{B}_{4} \mathrm{H}_{10}+\mathrm{PF}_{3} \rightarrow\) (c) \(1-\mathrm{BrB}_{5} \mathrm{H}_{8} \stackrel{\mathrm{KH}, 195 \mathrm{K}}{\longrightarrow}\) (d) \(2-\mathrm{MeB}_{5} \mathrm{H}_{8} \stackrel{\mathrm{ROH}}{ }\)
Problem 29
Crystalline \(\mathrm{Ag}_{2}\left[\mathrm{B}_{12} \mathrm{Cl}_{12}\right]\) may be described as having a structure based on an anti-fluorite-type arrangement. By approximating each \(\left[\mathrm{B}_{12} \mathrm{Cl}_{12}\right]^{2-}\) ion to a sphere, draw a diagram to represent a unit cell of \(\mathrm{Ag}_{2}\left[\mathrm{B}_{12} \mathrm{Cl}_{12}\right] .\) What type of interstitial hole does each \(\mathrm{Ag}^{+}\) ion occupy in this idealized structure?
Problem 32
(a) \(\mathrm{NMR}\) spectroscopic data for \(\left[\mathrm{HAl}\left(\mathrm{BH}_{4}\right)_{2}\right]_{n}\) are consistent with the compound existing in two forms in solution. One form is probably a dimer and the other, a higher oligomer. Each species possesses one boron environment, and in the \(^{11} \mathrm{B}\) NMR spectrum, each species exhibits a binomial quintet. The chemical shift of the signal for each species in the \(^{27} \mathrm{Al}\) NMR spectrum suggests an octahedral environment for the Al atom. Suggest a structure for the dimer \(\left[\mathrm{HAl}\left(\mathrm{BH}_{4}\right)_{2}\right]_{2}\) which is consistent with these observations and comment on whether the data indicate a static or dynamic molecule. (b) The elemental analysis for an adduct \(\mathbf{A}\) is \(15.2 \%\) B \(75.0 \%\) Cl, \(4.2 \%\) C and \(5.6 \%\) O. The \(^{11}\) B NMR spectrum of A contains two singlets \((\delta-20.7\) and \(+68.9 \mathrm{ppm}\) ) with relative integrals \(1: 3 ;\) the signal at \(\delta-20.7\) ppm is characteristic of a \(\mathrm{B}\) atom in a tetrahedral environment, while that at \(\delta+68.9\) ppm is consistent with trigonal planar boron. In the IR spectrum, there is a characteristic absorption at \(2176 \mathrm{cm}^{-1} .\) Suggest an identity for \(\mathbf{A}\) and draw its structure.
