Quantum mechanical exchange in a transition metal hydride complex: NMR data for [cp(PPh3)IrH3]+ fitted by a two-dimensional model

Scheurer, Ch.; Wiedenbruch, R.; Meyer, Rolf; Ernst, R. R.; Heinekey, D. Michael

doi:10.1063/1.474112

Cited by 54 publications

(17 citation statements)

References 27 publications

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“…Although in the theoretical study we could not simulate the influence of each different added ligand or of the several solvents that have been used, we will show how sensitive the calculated J is to the nature of the complex and how several experimental trends are well described by the dynamic study. Since the dynamic study used here is different from that of Lluch and Lledos et al,12a we have presented its essential aspects. The dynamic study is focused on OsH 3 X(PH 3 ) 2 (X = Cl, I) and OsH 3 Cl(PH 3 ) 3 .…”

Section: Resultssupporting

confidence: 88%

“…The discovery of unusually large splittings in the energy levels of multiple (>2) chemically-inequivalent hydrogen nuclei, measurable by 1 H NMR spectroscopy, has sparked much activity to experimentally characterize and theoretically model the phenomenon which is now called quantum exchange coupling (QEC). − The associated 1 H NMR spectra follow exactly the rules of “traditional” NMR energy states and selection rules 4 but with larger than normal (sometimes immensely larger) coupling constants, J . These J values do not arise from Fermi contact or other traditional “magnetic” mechanisms, and, indeed, they have nothing to do with shared electron density, s orbital character, or structural parameters such as interbond angle.…”

Section: Introductionmentioning

confidence: 99%

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Quantum Exchange Coupling: A Hypersensitive Indicator of Weak Interactions

et al. 1997

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Os(H) 3 ClL 2 (L ) P i Pr 3 ) forms a 1:1 adduct with L′ ) PEt 3 , NH 3 , MeCN, acetone, methanol, and THF. The case L′ ) PEt 3 permits the clearest identification of adduct structure as pentagonal bipyramidal. For NH 3 and MeCN, the respective kinetics of L′ loss are measured as ∆H q ) 20.7(3) and 17.6(3) kcal/mol and ∆S q ) 16(1) and 14.7(9) cal/(mol K). For acetone, methanol, and THF, the following respective ∆H°and ∆S°values for L′ binding are measured: ∆H°) -10.4(1), -6.66(8), and -5.8(2) kcal/mol; ∆S°) -41.8(5), -25.5(3), and -33(1) cal/(mol K). Decoalesced 1 H NMR spectra are reported for several of these Os(H) 3 ClL 2 L′ species, and they show a variety of examples of quantum exchange coupling among the hydride ligands. The values of J ex are higher when L′ is a more weakly-binding ligand. The quantum exchange coupling constants of Os(H) 3 XL 2 (X ) Cl, Br, I, OCH 2 CF 3 , OCH(CF 3 ) 2 ) in CD 2 Cl 2 , in toluene, and in methylcyclohexane show an unprecedented decrease of J with increasing temperature, which is attributed to weak formation of Os(H) 3 Cl(solvent)L 2 adducts at low temperature. For L′ ) CO, adduct formation leads to liberation of coordinated H 2 . Excess L′ ) MeCN or NH 3 slowly leads to formation of [Os(H) 3 L′ 2 L 2 ]Cl; the X-ray structure for L′ ) NH 3 is reported. Crystal data (-171°C): a ) 11.561(4) Å, b ) 14.215(5) Å, c ) 8.851(3) Å, R ) 97.51(2)°, ) 107.73(2)°, γ ) 104.47(2)°, with Z ) 2 in space group P1 h. The potential energy was calculated for exchange of 2H of OsH 3 X(PH 3 ) 2 L (X ) Cl with L ) no ligand and PH 3 , X ) I with L ) no ligand) using effective core potential ab initio methods at the MP2 level. The site exchange is found to be energetically easier for Cl than for I, in agreement with experiment. The hydride site exchange in the sevencoordinate species OsH 3 Cl(PH 3 ) 3 (a model for coordination of either ligand or solvent to Os) is found to be easier than that in the 16-electron species. No dihydrogen ligand is located on the reaction path for site exchange. The current theory which relates quantum exchange to a tunneling effect was used for calculating J ex as a function of temperature. The dynamic study was done using several sets of coordinates, in particular the rotation angle φ and the internuclear distance r between the exchanging H. The vibrational levels have been calculated and the symmetry of each level assigned within the permutation group in order to determine the nature of the nuclear spin function associated with each level. It is found that the rotation, φ, gives rise to the largest tunneling effect but that r cannot be neglected. The influence of the temperature, J ex (T), was included by a Boltzmann distribution. The results are in qualitative agreement with experiment in that quantum exchange coupling is larger in the case of Cl than in the case of I. Additional ligand L increases the value of the quantum exchange coupling mostly by lowering the activation energy for pairwise exchange.

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Section: Resultssupporting

confidence: 88%

Section: Introductionmentioning

confidence: 99%

Quantum Exchange Coupling: A Hypersensitive Indicator of Weak Interactions

et al. 1997

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“…Recently it was realized that the AlexanderÈBinsch formalism can also be employed to describe the simultaneous presence of coherent and incoherent exchange processes14 in transition metal hydrides, modeling the complete nuclear motion via two phenomenological constants, a rate constant k describing the incoherent exchange and the coherent exchange splitting A l t . theoretical interpretation of these rate constants has been given by Szymanski36,37 and Scheurer et al 32,38 In the following we want to brieÑy summarize the NMR line shape theory of a system of two deuterons bound in a twofold potential and subject to coherent and incoherent exchange. A detailed discussion of this formalism can be found in ref.…”

Section: Nmr Line Shape Theorymentioning

confidence: 99%

Coherent D2 rotational tunneling and incoherent D2 dynamics in a solid non-classical RuD2 complex studied by 2H solid state NMR spectroscopy

Wehrmann¹,

Fong²,

Morris³

et al. 1999

Phys. Chem. Chem. Phys.

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The 2H solid state NMR spectra and relaxation data of a transition metal g2-dideuterium complex, namely T 1 have been measured in the temperature regime from 5.4 to 320 K. trans-[Ru(D 2)Cl(PPh 2 CH 2 CH 2 PPh 2) 2 ]PF 6 , In the sample, coherent and incoherent exchange processes on the time scale of the quadrupolar RuÈD 2 interaction have been found, leading at low temperatures to a tunnel splitting of the 2H NMR spectrum. With increasing temperature a slight increase of the tunnel splitting is observed, in conjunction with a strong increase of the incoherent exchange process, which Ðnally, at temperatures above 20 K, destroys the tunnel splitting and determines the spectral line shape. For the description of the experimental spectra a Liouville formulation of the AlexanderÈBinsch NMR line shape theory, adapted for exchanging deuterons, is employed. It is shown that the whole evaluation of the 2H magnetization takes place in four 2D and two 4D subspaces of the 81D Liouville space, leading to a drastic simpliÐcation of the numerical e †orts in the simulation of the spectral line shapes. The height of the tunnel barrier calculated from the value of the tunnel splitting is 270 meV (6.22 kcal mol~1). The incoherent exchange rates extracted from the spectra and from relaxation data T 1 are analyzed in terms of a Bell tunneling model, with a temperature dependent e †ective potential.

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“…To solve the one-dimensional nuclear Schrödinger equation (eq ), the discrete variable representation (DVR) was used. − This method has already been successfully applied in several chemical studies. − The energy eigenstates for small intercalated ions along the C 3 v axis of the quantum dot were resolved within the DVR. Some questions naturally arise as to the proper description of the electronic potential when treating the nuclear degrees of freedom nonclassically.…”

Section: Methodsmentioning

confidence: 99%

Classical or Quantum? A Computational Study of Small Ion Diffusion in II–VI Semiconductor Quantum Dots

et al. 2016

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Ion diffusion in semiconductor nanocrystals, or quantum dots (QDs), has gained recognition in recent years as a crucial process for advancing both energy storage and, more generally, the postsynthetic p-type doping chemistry of these materials. In this report, we present first an energetic analysis of group I cations (H+, Li+, and Na+) diffusion in (MX)84 – QDs, with M = Zn, Cd and X = S, Se. The bound solutions to the corresponding one-dimensional nuclear Schrödinger equation were solved for these systems, relying on the discrete variable representation method. From this vantage, the quantum nature of the intercalating ion can be revealed. Evidence for the importance of including quantum effects in the treatment of these diffusion processes is presented, both with the density of energy eigenstates of the intercalating ion and from a comparison of the standard deviation in the population distribution of the intercalating ion to the lattice spacings of its host material. Results suggest that the use of classical mechanics for simulations of the ion diffusion processes in these and other related materials can be a questionable practice for the smallest group I cations. Trends devised herein can be useful to help guide the development of new experimental approaches to postsynthetic doping of semiconductor nanocrystals, and in designing electrode materials for next generation electrochemical energy storage devices.

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Quantum mechanical exchange in a transition metal hydride complex: NMR data for [cp(PPh3)IrH3]+ fitted by a two-dimensional model

Cited by 54 publications

References 27 publications

Quantum Exchange Coupling: A Hypersensitive Indicator of Weak Interactions

Quantum Exchange Coupling: A Hypersensitive Indicator of Weak Interactions

Coherent D2 rotational tunneling and incoherent D2 dynamics in a solid non-classical RuD2 complex studied by 2H solid state NMR spectroscopy

Classical or Quantum? A Computational Study of Small Ion Diffusion in II–VI Semiconductor Quantum Dots

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