The Hexahydro-closo-hexaborate Dianion [B6H6]2– and Its Derivatives

Preetz, W.; Peters, G.

doi:10.1002/(sici)1099-0682(199911)1999:11<1831::aid-ejic1831>3.0.co;2-j

Cited by 63 publications

(21 citation statements)

References 97 publications

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“…For B6 compounds, the agreement with experimental data was within 1-3 ppm except for B 6 H 5 Cl 2-and B 6 H 5 Br 2-, where the calculated data deviated by~5 ppm from the experimental values. However, it is also important to note the relatively large effect (up to 5 ppm for the B 6 H 6 2-molecule) of a counter ion present or solvent used in the experimental NMR setup 7 .…”

Section: Theoretical Calculationsmentioning

confidence: 99%

“…This is further complicated by the fact that Cl 2 or Br 2 can undergo disproportionation in water, yielding HX and HOX (X = Cl, Br) species, which in turn may dissociate and thus acidify the medium. The chemistry of B6 is different in that the cage is easily disrupted in an acidic solution 7 . Thus, halogenation of B6 with elemental Cl 2 or Br 2 proceeds in a strongly basic aqueous solution 45 .…”

Section: The Reaction Mechanism Of the Halogenation Reactions On The mentioning

confidence: 99%

“…observed directive effects of the substituents for further substitution at other sites of the cage have still eluded a mechanistic understanding [6][7][8] .…”

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confidence: 99%

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exo-Substituent effects in halogenated icosahedral (B12H122–) and octahedral (B6H62–) closo-borane skeletons: chemical reactivity studied by experimental and quantum chemical methods

Lepšı́k

Srnec

Hnyk

et al. 2009

Collect. Czech. Chem. Commun.

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Dedicated to the memory of Professor Otto Exner.The exo-substituent effects in halogenated icosahedral B 12 H 12 2-(B12) and octahedral B 6 H 6 2-(B6) closo-borane skeletons were studied both experimentally and theoretically. Firstly, the equilibrium geometries of exo-substituted B12 and B6 clusters were obtained using quantum chemical calculations at the MP2/def2-SVP level. A comparison with the available X-ray crystallographic data revealed a very good agreement between the theoretical and experimental values. Secondly, other descriptors of the molecular structure of these borane compounds -11 B NMR chemical shifts -were experimentally determined and compared with the calculated values obtained by the ab initio/GIAO approach at the MP2/def2-TZVP level. It was shown that the calculated data reproduced the experiment very closely. Thirdly, we investigated experimentally the halogenation reactions of B12 and attempted to explain the observed ratios between the two obtained disubstituted products (meta/ortho~4:1) by calculating their thermodynamic stabilities using the DFT/B3LYP method. These calculations showed the enhanced stability of the meta disubstituted B12 but did not explain why the para product had not been observed in the experiment. We thus turned our attention to the kinetic aspects of exo-substitution reactions by exploring the possible reaction pathways and transition states. In spite of the complexity of the plausible reaction mechanisms, reasonable agreement was obtained between the calculated activation barriers and the experimental observations concerning the halogenation reactions of the B6 and B12 molecules. It also allowed to exclude from considerations certain reaction pathways leading to the mono-and dihalogenated B12 and B6 species.

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Section: Theoretical Calculationsmentioning

confidence: 99%

Section: The Reaction Mechanism Of the Halogenation Reactions On The mentioning

confidence: 99%

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exo-Substituent effects in halogenated icosahedral (B12H122–) and octahedral (B6H62–) closo-borane skeletons: chemical reactivity studied by experimental and quantum chemical methods

Lepšı́k

Srnec

Hnyk

et al. 2009

Collect. Czech. Chem. Commun.

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“…Dies trifft auf die Verbindungsklassen der closo-Borane mit oktaedrischer Gerüststruktur zu, von denen Derivate des Hexaborats [B6H6]2- [1 -5], Boride, Carborane C2B4H6 [6 , 7] und weitere isoelektro nische Borane mit Heteroatomen wie P [8,9], As [ 10] oder Se [ 11 ] bekannt sind. In den letzten Jahren sind das Hexaborat [B6H6]2~ und viele seiner Deri vate röntgenstrukturanalytisch und spektroskopisch charakterisiert worden [1]. Mit Hilfe dieser Daten wurden an einer Reihe der Verbindungen Normalkoordinatenanalysen durchgeführt [2][3][4][5].…”

Section: E Inleitungunclassified

Schwingungsspektren und Normalkoordinatenanalyse der Tetrahalogeno-closo-1,2-diphosphahexaborane P₂B₄X₄, X = Cl, Br / Vibrational Spectra and Normal Coordinate Analysis of the Tetrahalogeno-closo-1,2-diphosphahexaboranes P₂B₄X₄, X = Cl, Br

Lorenzen

Preetz

Keller

et al. 1999

Zeitschrift Für Naturforschung B

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High resolution vibrational spectra of the tetrahalogeno-c/oso-1,2-diphosphahexaboranes P2B4X 4, X = Cl, Br have been measured at low temperatures (20 -60 K). The boron-halogen stretching vibrations are observed below 370 cm-1 while the P-P valence vibrations are found at 414 (Cl) and 372 cm-1 (Br). Due to the presence of the boron isotopes l()B and 11B the P-P stretching vibrations and the cage modes in the region of 550 to 1200 cm-1 are split. Based on the crystallographic data of P2B4C14 normal coordinate analyses have been performed. Using a set of 16 force constants (e.g. fd(PP) = 1.35 (X = Cl) and 1.20 (Br), fd(BB) = 1.30 / 1.65 (Cl) and 1.45 /1.60 (Br), fd(BX) = 4.40 (Cl) and 3.53 (Br) mdyn / Ä) a good agreement of observed and calculated frequencies has been achieved. E inleitung Vergleichende schwingungsspektroskopische Un tersuchungen an unterschiedlich substituierten polyedrischen Boranen erlauben detaillierte Aussagen über die Bindungsverhältnisse in Clusterverbindun gen und ermöglichen Korrelationen zwischen Ver tretern gleichen Aufbaus. Für solche Studien eignen sich besonders Verbindungen mit hoher Symmetrie und einer möglichst kleinen Anzahl an Gerüstato men (Verringerung der Komplexität der Spektren). Dies trifft auf die Verbindungsklassen der closo-Borane mit oktaedrischer Gerüststruktur zu, von denen Derivate des Hexaborats [B6H6]2-[1 -5], Boride, Carborane C2B4H6 [6 , 7] und weitere isoelektro nische Borane mit Heteroatomen wie P [8, 9], As [ 10] oder Se [ 11 ] bekannt sind. In den letzten Jahren sind das Hexaborat [B6H6]2~ und viele seiner Deri vate röntgenstrukturanalytisch und spektroskopisch charakterisiert worden [1]. Mit Hilfe dieser Daten wurden an einer Reihe der Verbindungen Normalkoordinatenanalysen durchgeführt [2-5]. In diesem Zusammenhang ist von besonderem Interesse, denEinfluß der Substitution eines oder mehrerer Bo ratome des Clustergerüsts durch isoelektronische Heteroelemente zu untersuchen. Von oktaedrischen Heteroboranen waren bis vor kurzem nur Deriva te der beiden cis-und trans-Isomere des closoDicarbahexaborans C2B4H6 bekannt. Das 1,6-Isomere wurde IR-und Raman-spektroskopisch unter sucht, und die Schwingungen sind zugeordnet wor den [6 , 7]. Vor kurzem wurde die Co-Pyrolyse von B2C14 mit verschiedenen kovalenten Elementhalo geniden zur Darstellung von perhalogenierten ok taedrischen Heteroboranclustem beschrieben. Die se Methode ermöglicht einen neuartigen Zugang zu den zu [B6X 6]2~ isoelektronischen Heterobo ranen wie z.B. c/-l,2-P2B4X 4 (X = CI, Br) [8,9], Im folgenden wird über die Messung der Schwin gungsspektren von P2B4X 4, X = CI, Br berich tet. Unter Verwendung der Molekülparameter von P2B4C14 [8 ] und der gemessenen Frequenzsätze wird eine Normalkoordinatenanalyse durchgeführt und eine Zuordnung der Schwingungsspektren vor genommen.

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“…18 In contrast, the small members of the hydro-closoborates B n H n 2-(n < 12) are not stable in the gas phase but spontaneously emit one of their excess electrons. 19,20 The smallest hydro-closo-borate that is stable in the gas phase is B 12 H 12 2-.…”

Section: Introductionmentioning

confidence: 99%

Dianionic Tetraborates Do Exist as Stable Entities

2002

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To date, B(6)H(6)(2-) and some of its derivatives are the smallest members of the closo-borates that have been synthesized and analyzed in condensed phases. In contrast, no stable dianionic tetraborate has yet been observed, either in solution or solids or in the gas phase. In this work, the gas-phase stability of dianionic tetraborates B(4)X(4)(2-) (X = H, CN, NC, or BO) is investigated with ab initio methods. For this objective, the geometries of the dianions are optimized, the electronic stability is tested, and various fragmentation channels are studied. In agreement with previous examinations, tetrahedral isomers of all examined tetraborates have been found to represent geometrically stable isomers and to exhibit a triplet electronic ground state. However, these isomers are electronically unstable, i.e., their additional electrons are not bound. Furthermore, new D(2)(d)()-symmetric isomers of B(4)X(4)(2-) (X = H, CN, NC, or BO) have been identified that have a closed-shell singlet ground state and are lower in energy than their tetrahedral counterparts. Moreover, B(4)(CN)(4)(2-) and B(4)(BO)(4)(2-) represent stable gas-phase dianions and are predicted to be observable in suitable experiments. The electronic properties and geometries of these dianions are discussed in detail and explained in terms of the electrostatic repulsion of the excess electrons and the aromaticity of the dianions.

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The Hexahydro-closo-hexaborate Dianion [B6H6]2– and Its Derivatives

Cited by 63 publications

References 97 publications

exo-Substituent effects in halogenated icosahedral (B12H122–) and octahedral (B6H62–) closo-borane skeletons: chemical reactivity studied by experimental and quantum chemical methods

exo-Substituent effects in halogenated icosahedral (B12H122–) and octahedral (B6H62–) closo-borane skeletons: chemical reactivity studied by experimental and quantum chemical methods

Schwingungsspektren und Normalkoordinatenanalyse der Tetrahalogeno-closo-1,2-diphosphahexaborane P₂B₄X₄, X = Cl, Br / Vibrational Spectra and Normal Coordinate Analysis of the Tetrahalogeno-closo-1,2-diphosphahexaboranes P₂B₄X₄, X = Cl, Br

Dianionic Tetraborates Do Exist as Stable Entities

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The Hexahydro-closo-hexaborate Dianion [B6H6]2– and Its Derivatives

Cited by 63 publications

References 97 publications

exo-Substituent effects in halogenated icosahedral (B12H122–) and octahedral (B6H62–) closo-borane skeletons: chemical reactivity studied by experimental and quantum chemical methods

exo-Substituent effects in halogenated icosahedral (B12H122–) and octahedral (B6H62–) closo-borane skeletons: chemical reactivity studied by experimental and quantum chemical methods

Schwingungsspektren und Normalkoordinatenanalyse der Tetrahalogeno-closo-1,2-diphosphahexaborane P2B4X4, X = Cl, Br / Vibrational Spectra and Normal Coordinate Analysis of the Tetrahalogeno-closo-1,2-diphosphahexaboranes P2B4X4, X = Cl, Br

Dianionic Tetraborates Do Exist as Stable Entities

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Schwingungsspektren und Normalkoordinatenanalyse der Tetrahalogeno-closo-1,2-diphosphahexaborane P₂B₄X₄, X = Cl, Br / Vibrational Spectra and Normal Coordinate Analysis of the Tetrahalogeno-closo-1,2-diphosphahexaboranes P₂B₄X₄, X = Cl, Br