Structure and dynamics in metal tetrahydroborates. I. Nuclear magnetic resonance studies of zirconium and hafnium tetrakis(tetrahydroborates)

Tobin J Marks, Lawrence A. Shimp

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Abstract

The identical temperature dependence of the pmr spectra of Zr(BH4)4 and Hf(BH4)4 is due to the variable rate of 10B and 11B quadrupolar spin-lattice relaxation. Intramolecular rearrangement processes are still rapid at -80°. Quantitative analysis of the spectra as a function of solution viscosity yields results at least partially in accord with the hydrodynamic model for molecular reorientation, though inertial effects are also probably operative. Within experimental error, both molecules have the same nuclear quadrupole coupling constants, which are estimated to be: 10B, 3.5 ± 0.6 MHz; 11B, 1.7 ± 0.3 MHz, and the same activation energies for molecular reorientation, 3.1 ± 0.1 kcal/mol.

Original languageEnglish
Pages (from-to)1542-1550
Number of pages9
JournalJournal of the American Chemical Society
Volume94
Issue number5
Publication statusPublished - 1972

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Hafnium
Molecular Models
Spin-lattice relaxation
Hydrodynamics
Zirconium
Viscosity
Spectrum Analysis
Magnetic Resonance Spectroscopy
Activation energy
Metals
Nuclear magnetic resonance
Molecules
Temperature
Chemical analysis
hafnium tetrahydroborate

ASJC Scopus subject areas

  • Chemistry(all)

Cite this

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abstract = "The identical temperature dependence of the pmr spectra of Zr(BH4)4 and Hf(BH4)4 is due to the variable rate of 10B and 11B quadrupolar spin-lattice relaxation. Intramolecular rearrangement processes are still rapid at -80°. Quantitative analysis of the spectra as a function of solution viscosity yields results at least partially in accord with the hydrodynamic model for molecular reorientation, though inertial effects are also probably operative. Within experimental error, both molecules have the same nuclear quadrupole coupling constants, which are estimated to be: 10B, 3.5 ± 0.6 MHz; 11B, 1.7 ± 0.3 MHz, and the same activation energies for molecular reorientation, 3.1 ± 0.1 kcal/mol.",
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AU - Shimp, Lawrence A.

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N2 - The identical temperature dependence of the pmr spectra of Zr(BH4)4 and Hf(BH4)4 is due to the variable rate of 10B and 11B quadrupolar spin-lattice relaxation. Intramolecular rearrangement processes are still rapid at -80°. Quantitative analysis of the spectra as a function of solution viscosity yields results at least partially in accord with the hydrodynamic model for molecular reorientation, though inertial effects are also probably operative. Within experimental error, both molecules have the same nuclear quadrupole coupling constants, which are estimated to be: 10B, 3.5 ± 0.6 MHz; 11B, 1.7 ± 0.3 MHz, and the same activation energies for molecular reorientation, 3.1 ± 0.1 kcal/mol.

AB - The identical temperature dependence of the pmr spectra of Zr(BH4)4 and Hf(BH4)4 is due to the variable rate of 10B and 11B quadrupolar spin-lattice relaxation. Intramolecular rearrangement processes are still rapid at -80°. Quantitative analysis of the spectra as a function of solution viscosity yields results at least partially in accord with the hydrodynamic model for molecular reorientation, though inertial effects are also probably operative. Within experimental error, both molecules have the same nuclear quadrupole coupling constants, which are estimated to be: 10B, 3.5 ± 0.6 MHz; 11B, 1.7 ± 0.3 MHz, and the same activation energies for molecular reorientation, 3.1 ± 0.1 kcal/mol.

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