Synthesis and Properties of a Fifteen‐Coordinate Complex: The Thorium Aminodiboranate [Th(H3BNMe2BH3)4]

Daly, Scott R.; Piccoli, Paula M. B.; Schultz, Arthur J.; Todorova, Tanya K.; Gagliardi, Laura; Girolami, Gregory S.

doi:10.1002/ange.200905797

Cited by 24 publications

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References 42 publications

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“…A literature survey provided only a few diamagnetic hydride complexes: the thorium systems 1-3 shown in Scheme 2 [9] and a few borohydride complexes of Th IV and UO 2 2+ . [10] The hydride shifts in 1-3 are in the high-frequency range, comparable to the abovementioned Ta complex (only some protons involved in low-barrier hydrogen bonds feature similar shifts; for example, in hydrogen maleate, d =+ 20.3 ppm), [11] thus defining the upper limits of currently known 1 H shifts of diamagnetic compounds. The experimental value of 3 (d =+ 0.9 ppm) [9d] was most likely misassigned, as the analogous Zr complex exhibits a hydride shift of d =+ 9.6 ppm.…”

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confidence: 80%

Giant Spin‐Orbit Effects on NMR Shifts in Diamagnetic Actinide Complexes: Guiding the Search of Uranium(VI) Hydride Complexes in the Correct Spectral Range

et al. 2012

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Transition-and inner-transition metal hydride complexes are crucial reagents in a great variety of stoichiometric and catalytic transformations, including CÀH bond activation. [1] As hydrogen atoms near heavy-metal centers are difficult to locate by X-ray diffraction, often their prime characterization is by 1 H NMR spectroscopy, sometimes augmented by IR spectroscopy. A significant part of the utility of 1 H NMR spectroscopy in this field arises from the fact that the chemical shifts of metal-bound protons are characteristic and occupy extreme positions in the proton shift range, even for diamagnetic compounds. For instance, complexes with d 6 or d 8 metal configuration exhibit shifts below d = 0 ppm, in record cases down to below d = À50 ppm for iridium hydride complexes. [2,3] While this phenomenon was explained as early as the 1960s by Buckingham and Stephens as being due to offcenter paramagnetic ring currents [4] (see Ref.[5] for the earliest DFT results), we have recently shown that the largest low-frequency shifts of this kind are, to an appreciable part, caused by relativistic spin-orbit (SO) effects. [2] These heavyatom induced SO effects are mediated through the Fermi contact mechanism to which proton shifts are particularly susceptible, owing to the large hydrogen 1 s-orbital contributions to bonding (the transfer of SO-induced spin polarization to the NMR nucleus is decisive in this situation). [6] In contrast, d 10 metal hydride complexes of mercury or gold exhibit large high-frequency shifts up to d =+ 17 ppm, again predominantly because of SO coupling. [2] Some d 0 metal hydrides have been studied by 1 H NMR spectroscopy as well. Similarly to d 10 systems they often also exhibit shifts in the very highfrequency range (Scheme 1). [7] As shown in Scheme 1, SO effects again play a very important role in these NMR shift values, increasingly so moving down a group in the periodic table (cf. 1 H NMR shifts within the [H 2 MCp* 2 ] series, M = Ti, Zr, Hf, Cp* = h-C 5 Me 5 ). Probably the largest known shift value of such a d 0 complex is the d =+ 18.9 ppm of the tantalum complex in Scheme 1.We note in passing, that deshielding SO shifts are generally related to high-lying occupied orbitals with ssymmetry relative to the bond between the SO center and NMR atom (e.g. for the abovementioned d 10 and d 0 metal hydride complexes), whereas p-type occupied orbitals provide shielding SO contributions (e.g. in the d 6 and d 8 hydride complexes or for heavy halogen substituents). [8] In view of these observations, we wondered about the magnitude of hydride shifts when the d 0 transition-metal center is replaced by an actinide ion to form the corresponding f 0 species, as SO effects should be particularly large in this case. A literature survey provided only a few diamagnetic hydride complexes: the thorium systems 1-3 shown in Scheme 2 [9] and a few borohydride complexes of Th IV and UO 2 2+ . [10] The hydride shifts in 1-3 are in the high-frequency range, comparable to the abovementioned Ta complex (only some prot...

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confidence: 80%

Giant Spin‐Orbit Effects on NMR Shifts in Diamagnetic Actinide Complexes: Guiding the Search of Uranium(VI) Hydride Complexes in the Correct Spectral Range

et al. 2012

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“…[56] Unrestricted DFT calculations on the thorium aminodiboranate complex [Th(H 3 BNMe 2 BH 3 ) 4 ] provide a 16-coodinate structure; however single-crystal X-ray and neutron diffraction studies indicate that the ligands distort and the Th center becomes 15-coordinate when placed within a nonsymmetric crystal environment. [57] If periodic boundary conditions are imposed based on the experimental cell dimensions, DFT calculations reproduce the 15-coordinate structure. In a classic example Figure 5.…”

Section: Assessing the Effect Of Crystal Packing Forcesmentioning

confidence: 99%

Evaluating f‐Element Bonding from Structure and Thermodynamics

Minasian

Krinsky

Arnold

2011

Chemistry A European J

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The practical goal to measure and understand the thermodynamic properties of molecules and materials containing f-elements is often achieved through indirect methods. Of the characterization tools available to inorganic chemists, few are more powerful than X-ray crystallography. Yet for lanthanides and actinides, interpretation of a bond length is a challenging undertaking that involves a complex interplay of steric and electronic forces. In this Concept article, we perform an analysis of selected examples in which structural criteria alone have been used to draw qualitative conclusions about chemical bonding. In other instances for which such an analysis is not valid, thermodynamic information is evaluated side by side with structural data to provide reasonable interpretations of a covalent/ionic mode of bonding. A geometric variation larger than 3σ is not necessarily correlated to a change in bonding, nor is an increase in bond energy related to a bond with more covalent character. However, careful consideration of thermodynamic information can lead to reasonable interpretations of electronic structure, and may provide a more reliable benchmark for the theoretical methods which can describe f-elements.

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“…The record for the actinide elements stood at 14 for many years (in U(BH 4 ) 4 ), but is now 15, established experimentally by Daly et al. for Th(H 3 BNMe 2 BH 3 ) 4 , 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.…”

Section: Figurementioning

confidence: 99%

Seventeen‐Coordinate Actinide Helium Complexes

Kaltsoyannis

2017

Angew Chem Int Ed

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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 AcHe , ThHe , and PaHe are all found to be true geometric minima, with the He atoms clearly located in the first shell around the actinide. Analysis of AcHe (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 >0.95) are found between QTAIM metrics (bond critical point electron densities and delocalization indices) and the average Ac-He distances, and also with the incremental He binding energies.

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Synthesis and Properties of a Fifteen‐Coordinate Complex: The Thorium Aminodiboranate [Th(H₃BNMe₂BH₃)₄]

Cited by 24 publications

References 42 publications

Giant Spin‐Orbit Effects on NMR Shifts in Diamagnetic Actinide Complexes: Guiding the Search of Uranium(VI) Hydride Complexes in the Correct Spectral Range

Giant Spin‐Orbit Effects on NMR Shifts in Diamagnetic Actinide Complexes: Guiding the Search of Uranium(VI) Hydride Complexes in the Correct Spectral Range

Evaluating f‐Element Bonding from Structure and Thermodynamics

Seventeen‐Coordinate Actinide Helium Complexes

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