Structure and Dynamics of ND3BF3 in the Solid and Gas Phases: A Combined NMR, Neutron Diffraction, and Ab Initio Study

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TypeArticle
Journal titleInorganic Chemistry
ISSN00201669
Volume41
Issue26
Pages70647071; # of pages: 8
AbstractThe decrease in DA bond lengths, previously reported for some Lewis acid/base complexes, in going from the gas to the solid phases is investigated by obtaining an accurate crystal structure of solid ND3BF3 by powder neutron diffraction. The B-N internuclear distance is 1.554(3) ?, 0.118 ? shorter than the most recent gas-phase microwave value and 0.121 ? shorter than the single molecule geometry optimized (1.672 ?, CISD/6-311++G(d,p)) bond length. The crystal structure also shows N-D???F-B hydrogen bonds. The effects of this change in structure and of intermolecular hydrogen-bonding on nuclear magnetic shielding (i.e., chemical shifts) and the nuclear quadrupolar coupling constants (QCC) are investigated by ab initio molecular orbital and density functional theory calculations. These calculations show that the nitrogen (15N and 14N) and boron (11B and 10B) chemical shifts should be rather insensitive to changes in rBN and that the concomitant changes in molecular structure. Calculations on hydrogen-bonded clusters, based on the crystal structure, indicate that H-bonding should also have very little effect on the chemical shifts. On the other hand, the 11B and 14N QCCs show large changes because of both effects. An analysis of the 10B{19F} line shape in solid ND310BF3 yields a 11B QCC of ?0.130 MHz. This is reasonably close an earlier value of ?0.080 MHz and the value of ?0.050 MHz calculated for a [NH3BF3]4 cluster. The gas-phase value is 1.20 MHz. Temperature-dependent deuterium T1 measurements yield an activation energy for rotation of the ND3 group in solid ND3BF3 of 9.5 ? 0.1 kJ/mol. Simulations of the temperature-dependent T1 anisotropy gave an Ea of 9.5 ? 0.2 kJ/mol and a preexponential factor, A, of 3.0 ? 0.1 ? 1012 s-1. Our calculated value for a [NH3BF3]4 cluster is 16.4 kJ/mol. Both are much higher than the previous value of 3.9 kJ/mol, from solid-state proton T1 measurements.
Publication date
Linkhttp://pubs3.acs.org/acs/journals/doilookup?in_doi=10.1021/ic0203771
AffiliationNational Research Council Canada; NRC Canadian Neutron Beam Centre
Peer reviewedNo
Identifier10007817
NPARC number12327320
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Record identifier3b866b1c-a42c-45a1-8e4f-e309cd7617fd
Record created2009-09-10
Record modified2016-05-09
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