Cs[H2NB2(C6F5)6] Featuring an Unequivocal 16-Coordinate Cation

Pollak, David; Goddard, Richard; Pörschke, Klaus‐Richard

doi:10.1021/jacs.6b02590

Cited by 23 publications

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“…This has been seen very recently in the experimental work of Pollak et al, [2] who found 16 Cs···F contacts in Cs[H2NB2(C6F5)6], and that by Popov et al in CoB16 -, [3] and has also been predicted theoretically by Gu et al [4] for M@Li16 (M = Ca, Sr, Ba, Ti, Zr and Hf). The record for the actinide elements stood at 14 for many years (in U(BH4)4), [5] but is now 15, established experimentally by Daly et al for Th(H3BNMe2BH3)4, [6] although the same authors used density functional theory (DFT) to predict that in the gas phase the number of Th···H contacts could rise to 16. All of these contributions make reference to the work of Hermann et al [7] who, in 2007, published in this journal a DFT survey of the geometric structures of Pb 2+ coordinated by He atoms.…”

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confidence: 60%

Seventeen‐Coordinate Actinide Helium Complexes

Kaltsoyannis

2017

Angewandte Chemie

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Abstract:The geometries and electronic structures of molecular ions featuring He atoms complexed to actinide cations are explored computationally using density functional and coupled cluster theories. A new record coordination number is established, as AcHe17 3+ , ThHe17 4+ and PaHe17 4+ are all found to be true geometric minima, with the He atoms clearly located in the first shell around the actinide. Analysis of AcHen 3+ (n = 1-17) using the Quantum Theory of Atoms in Molecules (QTAIM) confirms these systems as having closed shell, charge-induced dipole bonding. Excellent correlations (R 2 > 0.95) are found between QTAIM metrics (bond critical point electron densities and delocalisation indices) and the average Ac-He distances, and also with the incremental He binding energies.

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confidence: 60%

Seventeen‐Coordinate Actinide Helium Complexes

Kaltsoyannis

2017

Angewandte Chemie

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“…Regardless of any scheme or table, cesium appears an outlier—one that binds through the outer core, with a free electron to boot. It recently broke the record for highest coordination number, 16, in a confined tetracosahedral arrangement of F atoms . And we sense it will feature in many new interesting molecules and materials.…”

Section: Figurementioning

confidence: 95%

Cesium's Off‐the‐Map Valence Orbital

et al. 2017

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The Td‐symmetric [CsO4]+ ion, featuring Cs in an oxidation state of 9, is computed to be a minimum. Cs uses outer core 5s and 5p orbitals to bind the oxygen atoms. The valence Cs 6s orbital lies too high to be involved in bonding, and contributes to Rydberg levels only. From a molecular orbital perspective, the bonding scheme is reminiscent of XeO4: an octet of electrons to bind electronegative ligands, and no low‐lying acceptor orbitals on the central atom. In this sense, Cs+ resembles hypervalent Xe.

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“…It recently broke the record for highest coordination number,1 6, in ac onfined tetracosahedral arrangement of Fa toms. [22] And we sense it will feature in many new interesting molecules and materials.…”

Section: This Additional Electron With Respect To [Cso 4 ]mentioning

confidence: 99%

Cesium's Off‐the‐Map Valence Orbital

et al. 2017

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The T d -symmetric [CsO 4 ]+ ion, featuring Cs in an oxidation state of 9, is computed to be am inimum. Cs uses outer core 5s and 5p orbitals to bind the oxygen atoms.T he valence Cs 6s orbital lies too high to be involved in bonding, and contributes to Rydberg levels only.F romamolecular orbital perspective,the bonding scheme is reminiscent of XeO 4 : an octet of electrons to bind electronegative ligands,a nd no low-lying acceptor orbitals on the central atom. In this sense, Cs + resembles hypervalent Xe.Even if we realize that for some heavier elements the border between valence and core orbitals fades, [1] it could still be argued that hard-line distinction is only partially wrong at most;c ome what may,r eactivity would feature the formal valence orbitals in some sort of role.B ut is that unfailingly true?I ti st he first question in this work, in which we theoretically explore [CsO 4 ] + ,amolecule shown in Figure 1.Electrons in core orbitals are often thought of as frozen. Whereas this helps reducing the cost of quantum-chemical calculations,there are cases in which these electrons play as ignificant role in electronic structure and bonding.There exists aprofusion of recent literature on high-pressure effects in elemental solids.S odium, lithium, and aluminum, under high pressures,a ll have their core orbitals overlap.[2] And this happens even for osmium, the most incompressible element. [3] In particular settings,s uch core overlap may push valence electrons to lattice interstitials,s tripping the metal of conductivity,and forming what is referred to as an electride. [4] Direct effects on bonding occur, too:p ressure was shown to turn cesium into ap block element, and mercury into ad 8 transition metal.[5]Cesium fascinates further. In am olecule,i td oes not require extreme conditions to use core orbitals for bonding. Hoffmann and co-workers showed that its occupied 5p orbitals contribute to holding CsF 5 together.[ À ,have received attention too.B ut the literature on these systems reports two distinct oxygen molecules that coordinate to the alkali metal, rather than amolecule of T d symmetry. [9] We start by assessing the thermodynamic and kinetic stability of T d [CsO 4 ] + .C omputation was carried out at ZORA-PBE0/TZ2P,w ith the ADF program.[10] TheP BE0 functional, with inclusion of relativistic effects by ZORA, has been shown to give accurate results for cesium complexes. [11] Calculations predict that T d [CsO 4 ] + is al ocal-minimum equilibrium structure,w ith all Hessian eigenvalues positive. Square-planar D 4h [CsO 4 ] + exists as at ransition state between, and 53.7 kcal mol À1 above,t wo tetrahedral minima with mutually inverted structures. T d [CsO 4 ] + prefers asinglet state-the nearest triplet lies more than 43 kcal mol À1 higher in energy.Itfeatures alarge HOMO-LUMO gap,4.68 eV,as computed at our level of theory.Our minimum of interest is thermodynamically,h ighly unstable towards dissociation, as shown in Figure 2

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Cs[H₂NB₂(C₆F₅)₆] Featuring an Unequivocal 16-Coordinate Cation

Cited by 23 publications

References 72 publications

Seventeen‐Coordinate Actinide Helium Complexes

Seventeen‐Coordinate Actinide Helium Complexes

Cesium's Off‐the‐Map Valence Orbital

Cesium's Off‐the‐Map Valence Orbital

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