Solvation Effects on Geometry and Chemical Shifts. An Ab Initio/IGLO Reconciliation of Apparent Experimental Inconsistencies on H<sub>3</sub>B · NH<sub>3</sub>

Bühl, Michæl; Steinke, Thomas; Schleyer, Paul von Ragué; Boese, Roland

doi:10.1002/anie.199111601

Cited by 95 publications

(44 citation statements)

References 28 publications

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“…The same has been surmised in other cases, for instance for d( 11 B) in aqueous BH 3 ÀNH 3 . [44] To be on the safe side, however, point charges were included in the subsequent chemical-shift evaluations in water.…”

Section: Resultsmentioning

confidence: 99%

Medium Effects on51V NMR Chemical Shifts: A Density Functional Study

2001

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Car-Parrinello molecular dynamics simulations were performed for [H2VO4], [VO2(OH2)4]+, and [VO(O2)2(OH2)]- in periodic boxes with 30, 28, and 29 water molecules, respectively, employing the BLYP density functional. On the timescale of the simulations, up to 2 ps, well-structured first solvation spheres are discernible for [H2VO4]- and [VO(O2)2(OH2)]- containing, on average, eight and ten water molecules, respectively. One of the four water molecules directly attached to the metal in [VO2(OH2)4]+ is only loosely bound, and the average coordination number of vanadium in aqueous VO2+ is between five and six. 51V chemical shifts were evaluated at the B3LYP level for representative snapshots along the trajectories, including the water molecules of the solvent by means of point charges. The resulting averaged delta(51V) values are proposed to model the combined effects of temperature (dynamic averaging) and solvent (charge polarization). Both effects are shown to be rather small, of the order of a few dozen ppm. The observed shielding of 51V in the bis(peroxo) complex with respect to the vanadate species is not reproduced computationally.

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Section: Resultsmentioning

confidence: 99%

Medium Effects on51V NMR Chemical Shifts: A Density Functional Study

2001

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“…[52] More often, however, such direct effects are small and can be superseded by "indirect" effects, that is, by changes in the molecular geometry on solvation. [53] These latter effects (which could be modeled by optimizing the geometry in the presence of a continuum) are expected to be small for 1, given the slight sensitivity of the computed d( 11 B) values toward the details of the geometrical parameters (see above). Thus, a single-point PCM calculation was performed for the gas-phase BP86/AE1 geometry.…”

Section: B: When Comparing the D(mentioning

confidence: 99%

Computational Study of Structures and Properties of Metallaboranes: Cobalt Bis(dicarbollide)

Bühl

Hnyk

Macháček

2005

Chemistry A European J

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A density functional study at the BP86/AE1 level is presented for the cobalt bis(dicarbollide) ion [3-Co-(1,2-C2B9H11)2]- (1) and selected isomers and rotamers thereof. Rotation of the two dicarbollide moieties with respect to each other is facile, as judged by the small energetic separation of the three rotamers located (within 11 kJ mol(-1)) and by the low barriers for their interconversion (at most 41 kJ mol(-1)). Among the isomers differing in carbon atom positions that contain two equivalent dicarbollide ligands, the 1,7 ("carbon apart") form [2-Co-(1,7-C2B9H11)2]- is the most stable, 121 kJ mol(-1) below 1. The electronic structure of 1 is characterized in terms of molecular orbitals, population analysis, and excitation energies from time-dependent density functional theory, relevant to UV/Vis spectroscopy. Experimental 11B NMR chemical shifts of 1 are reproduced to better than 5 ppm at the GIAO-B3LYP/II' level, and the computed delta(11B) values are only little affected by rotational averaging or the presence of a polarizable continuum. Larger such effects are found for the as-yet unknown 59Co chemical shift, for which a value in the range between -1800 and -2400 ppm is predicted. Even though the accuracy achieved for the theoretical delta(11B) values is somewhat lower than that for heteroboranes at conventional ab initio levels, the level of density functional employed can afford qualitatively reliable chemical shifts, which can be useful in assignments and structural refinements of heteroboranes containing transition metal.

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“…The observed B1 N1 distance can be compared well with the value of 1.565Å in ammonia-borane [15], 1.564Å in hydrazine-borane [23], and 1.600Å in ethylenediamine-bis(borane) [24]. From a CSD (Cambridge Structural Database) [25] search, it has been found that this distance is longer for the complexes with secondary amines (in the range 1.61-1.62Å) and tertiary amines (in the range 1.61-1.66Å), in spite of the increasing gas-phase basicity in the series N 2 H 4 < NH 3 < NH 2 R < NHR 2 < NR 3 .…”

Section: X-ray Analysismentioning

confidence: 77%

“…Except for the longer distance B N (1.658Å), the calculated structural parameters for 1a in the gas phase are close to those determined by X-ray structural analysis in the solid state (see Table 2). In the case of the ammoniaborane adduct H 3 N BH 3 , the B3LYP/6-311++G calculated distance B N (1.671Å) is also longer than the distance experimentally determined (1.565Å [15]). The Gaussian 98 implementation of the gaugeindependent atomic orbital (GIAO) method for calculating nuclear magnetic shielding tensors at both HF and DFT levels [16] was successfully employed (vide infra).…”

Section: Infrared Spectrum and Computational Partmentioning

confidence: 78%