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The Structure Chemistry of Boron-Rich Solids of the Alkali Metals

“…It states that for molecular B n closo-cages, the electronic demand necessary to stabilise the polyhedral arrangement is 2n ϩ 2, according to the traditional counting scheme (RudolphϪWilliamsϪWade rules [58Ϫ60] ). Even if we have to remind ourselves that there exist other concepts to describe boron-rich compounds (for example Mingos' rules [61] ) and of known exceptions from Lipscomb's predictions (for example B 9 Br 9 [62] and Li 1.8 B 14…”

Multidimensional potential of boron-containing molecules in functional materials

“…X = H, n = 8). 43,44 Several theoretical studies have appeared later for species with X = H 45,46 and the attention was also extended to perhalide compounds (X = Hal, n = 6, 8, 9, 10), [47][48][49][50][51][52][53][54][55][56] to peralkylated species such as [B 12 Me 12 ] •-, 57 and to related OR substituted derivatives (R = CH 2 Ph, H). [58][59][60] The substituted 'hypercloso' compounds, typically generated by one-electron oxidation from dianionic closo precursors, are stabilized with electronegative substituents because neither Hal + nor R + or RO + are good leaving groups such as H + .…”

“…[58][59][60] The substituted 'hypercloso' compounds, typically generated by one-electron oxidation from dianionic closo precursors, are stabilized with electronegative substituents because neither Hal + nor R + or RO + are good leaving groups such as H + . Our focus here will be on the more symmetrical cases, on the compound series [B 6 Hal 6 ] •-(Hal = Cl, Br, I), on well studied [53][54][55][56] [B 9 Br 9 ] •-and on the systems [B 12 X 12 ] •-. In most cases, the number of boron nuclei and the resulting extensive hyperfine splitting precludes the observation of resolved EPR spectra, however, the g factor (hν = gβH) and its anisotropy can also provide valuable information on the electronic structure.…”

“…The tricapped trigonal prismatic closo cluster system [B 9 Br 9 ] k-, k = 0-2, has been well-characterised experimentally and theoretically, its chemical and electrochemical two-step electron transfer reactivity with a [B 9 Br 9 ] •-intermediate has been described [53][54][55] as well as the effects of protonation. 56 The lower symmetry in comparison to [B 6 X 6 ] •-and [B 12 X 12 ] •-results in a non-degenerate redox active MO (HOMO of [B 9 X 9 ] 2-) which is responsible for less pronounced g factor anisotropy 55 for [B 9 Br 9 ] •-(g > 2, g 1 -g 3 = 0⋅05) in relation to [B 6 Br 6 ] •-(g < 2, g 1 -g 3 = 0⋅20).…”

“…Structural changes during the electron transfer are rather small, the overall tricapped trigonal prismatic cluster arrangement being maintained. 55 This obviously low reorganisation energy probably contributes to the stability of the radical intermediate in that redox system. 54,55…”