Stereochemical nonrigidity in solid zirconium and hafnium tetrakistetrahydroborates. Evidence for two dynamic intramolecular rearrangement processes in covalent tridentate tetrahydroborates

I. Ssuer Chuang, Tobin J Marks, William J. Kennelly, John R. Kolb

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Abstract

Proton nuclear magnetic resonance studies of stereochemical dynamics in Zr(BH 4) 4 and Hf(BH 4) 4 have been carried out in the solid state. Variable temperature investigations were conducted in both continuous wave and pulsed modes. Two intramolecular motional processes were identified for each complex and the nature of these processes was interpreted on the basis of effective second moment calculations in both diffusive and positional jump regimes. The higher temperature process is assigned to rapid intramolecular bridge-terminal hydrogen exchange, E a(Zr) = 5.2 ± 0.3 (ΔG = 8.1 at 214 K) 1; E a(Hf) = 8.4 ± 0.3 (ΔG = 7.3 at 200 K) kcal/mol. The lower temperature motion is suggested to involve rapid threefold rotation about the ligand M-B-H (terminal) axis with E a(Zr) = 5.4 ±0.2 (ΔG = 4.3 at 124 K) 1; E a(Hf) = 4.6 ±0.2 (ΔG = 4.4 at 133 K) kcal/mol.

Original languageEnglish
Pages (from-to)7539-7545
Number of pages7
JournalJournal of the American Chemical Society
Volume99
Issue number23
Publication statusPublished - 1977

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Hafnium
Zirconium
Temperature
Nuclear magnetic resonance
Protons
Hydrogen
Magnetic Resonance Spectroscopy
Ligands

ASJC Scopus subject areas

  • Chemistry(all)

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title = "Stereochemical nonrigidity in solid zirconium and hafnium tetrakistetrahydroborates. Evidence for two dynamic intramolecular rearrangement processes in covalent tridentate tetrahydroborates",
abstract = "Proton nuclear magnetic resonance studies of stereochemical dynamics in Zr(BH 4) 4 and Hf(BH 4) 4 have been carried out in the solid state. Variable temperature investigations were conducted in both continuous wave and pulsed modes. Two intramolecular motional processes were identified for each complex and the nature of these processes was interpreted on the basis of effective second moment calculations in both diffusive and positional jump regimes. The higher temperature process is assigned to rapid intramolecular bridge-terminal hydrogen exchange, E a(Zr) = 5.2 ± 0.3 (ΔG ≠ = 8.1 at 214 K) 1; E a(Hf) = 8.4 ± 0.3 (ΔG ≠ = 7.3 at 200 K) kcal/mol. The lower temperature motion is suggested to involve rapid threefold rotation about the ligand M-B-H (terminal) axis with E a(Zr) = 5.4 ±0.2 (ΔG ≠ = 4.3 at 124 K) 1; E a(Hf) = 4.6 ±0.2 (ΔG ≠ = 4.4 at 133 K) kcal/mol.",
author = "Chuang, {I. Ssuer} and Marks, {Tobin J} and Kennelly, {William J.} and Kolb, {John R.}",
year = "1977",
language = "English",
volume = "99",
pages = "7539--7545",
journal = "Journal of the American Chemical Society",
issn = "0002-7863",
publisher = "American Chemical Society",
number = "23",

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TY - JOUR

T1 - Stereochemical nonrigidity in solid zirconium and hafnium tetrakistetrahydroborates. Evidence for two dynamic intramolecular rearrangement processes in covalent tridentate tetrahydroborates

AU - Chuang, I. Ssuer

AU - Marks, Tobin J

AU - Kennelly, William J.

AU - Kolb, John R.

PY - 1977

Y1 - 1977

N2 - Proton nuclear magnetic resonance studies of stereochemical dynamics in Zr(BH 4) 4 and Hf(BH 4) 4 have been carried out in the solid state. Variable temperature investigations were conducted in both continuous wave and pulsed modes. Two intramolecular motional processes were identified for each complex and the nature of these processes was interpreted on the basis of effective second moment calculations in both diffusive and positional jump regimes. The higher temperature process is assigned to rapid intramolecular bridge-terminal hydrogen exchange, E a(Zr) = 5.2 ± 0.3 (ΔG ≠ = 8.1 at 214 K) 1; E a(Hf) = 8.4 ± 0.3 (ΔG ≠ = 7.3 at 200 K) kcal/mol. The lower temperature motion is suggested to involve rapid threefold rotation about the ligand M-B-H (terminal) axis with E a(Zr) = 5.4 ±0.2 (ΔG ≠ = 4.3 at 124 K) 1; E a(Hf) = 4.6 ±0.2 (ΔG ≠ = 4.4 at 133 K) kcal/mol.

AB - Proton nuclear magnetic resonance studies of stereochemical dynamics in Zr(BH 4) 4 and Hf(BH 4) 4 have been carried out in the solid state. Variable temperature investigations were conducted in both continuous wave and pulsed modes. Two intramolecular motional processes were identified for each complex and the nature of these processes was interpreted on the basis of effective second moment calculations in both diffusive and positional jump regimes. The higher temperature process is assigned to rapid intramolecular bridge-terminal hydrogen exchange, E a(Zr) = 5.2 ± 0.3 (ΔG ≠ = 8.1 at 214 K) 1; E a(Hf) = 8.4 ± 0.3 (ΔG ≠ = 7.3 at 200 K) kcal/mol. The lower temperature motion is suggested to involve rapid threefold rotation about the ligand M-B-H (terminal) axis with E a(Zr) = 5.4 ±0.2 (ΔG ≠ = 4.3 at 124 K) 1; E a(Hf) = 4.6 ±0.2 (ΔG ≠ = 4.4 at 133 K) kcal/mol.

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