A multi-edge EXAFS study of nickel halide phosphine and arsine complexes
A multi-edge EXAFS study of nickel halide phosphine and arsine complexes
Arsenic, bromine, chlorine, nickel and phosphorus K-edge EXAFS (Extended X-ray Absorption Fine Structure) studies were used to investigate
the structure of nickel halide phosphine and arsine complexes.
Analysis at the ligand edges as well as at the nickel centre, not only helped to substantiate the nickel-ligand distances derived, but also helped to elucidate the stereochemistries of the complexes studied. By investigating the errors associated with information derived from the different edges, selective cross-referencing enabled us to develop three-dimensional models of the compounds.
f Nickel K-edge analysis of nickel-ligand distances gave errors of ca ± 0.02 X. Larger errors were experienced for chlorophosphine complexes where EXAFS analysis was unable to differentiate phosphorus and chlorine atoms. The presence of non-bonded carbons on the backbone of the bidentate phosphincs could be determined with surprisingly small associated errors, ca ± 0.03 X.
Arsenic and bromine K-edge EXAFS studies also gave ligand-nickel distances with an average error of ca ± 0.02 A. Analysis often showed other shells beyond the bonded distances, frequently indicating the stereochemistry of the complexes. The errors associated with these non-bonded distances were significantly large ca. ± 0.07 X.
EXAFS analysis in the soft X-ray region is in its infancy and this study at phosphorus and chlorine K-cdges indicates that although the quality of the results derived do not mirror those from the other nickel, arsenic and bromine K-edges, they can provide useful information. The bonded distances derived at the phosphorus K-edge appeared to be systematically smaller than the expected values, and correcting factors of + 0.11 X and + 0.07 X were employed for P-C and P-Ni distances respectively.
Attempts to calculate bond angles by triangulation of the distances derived was in many cases successful indicating the stereochemistry of the ligands about the nickel atom centre; errors in the derived distances appeared to cancel out.
Attempts were made throughout to quantify errors and to observe trends so that the magnitude of the errors associated with particular distances could be anticipated. The study helped to illustrate that an emphasis on error analysis with known structures is essential so that these can be quantified with unknown structures, especially for the longer less precisely defined non-bonded distances.
University of Southampton
1990
Leach, Harriet
(1990)
A multi-edge EXAFS study of nickel halide phosphine and arsine complexes.
University of Southampton, Doctoral Thesis.
Record type:
Thesis
(Doctoral)
Abstract
Arsenic, bromine, chlorine, nickel and phosphorus K-edge EXAFS (Extended X-ray Absorption Fine Structure) studies were used to investigate
the structure of nickel halide phosphine and arsine complexes.
Analysis at the ligand edges as well as at the nickel centre, not only helped to substantiate the nickel-ligand distances derived, but also helped to elucidate the stereochemistries of the complexes studied. By investigating the errors associated with information derived from the different edges, selective cross-referencing enabled us to develop three-dimensional models of the compounds.
f Nickel K-edge analysis of nickel-ligand distances gave errors of ca ± 0.02 X. Larger errors were experienced for chlorophosphine complexes where EXAFS analysis was unable to differentiate phosphorus and chlorine atoms. The presence of non-bonded carbons on the backbone of the bidentate phosphincs could be determined with surprisingly small associated errors, ca ± 0.03 X.
Arsenic and bromine K-edge EXAFS studies also gave ligand-nickel distances with an average error of ca ± 0.02 A. Analysis often showed other shells beyond the bonded distances, frequently indicating the stereochemistry of the complexes. The errors associated with these non-bonded distances were significantly large ca. ± 0.07 X.
EXAFS analysis in the soft X-ray region is in its infancy and this study at phosphorus and chlorine K-cdges indicates that although the quality of the results derived do not mirror those from the other nickel, arsenic and bromine K-edges, they can provide useful information. The bonded distances derived at the phosphorus K-edge appeared to be systematically smaller than the expected values, and correcting factors of + 0.11 X and + 0.07 X were employed for P-C and P-Ni distances respectively.
Attempts to calculate bond angles by triangulation of the distances derived was in many cases successful indicating the stereochemistry of the ligands about the nickel atom centre; errors in the derived distances appeared to cancel out.
Attempts were made throughout to quantify errors and to observe trends so that the magnitude of the errors associated with particular distances could be anticipated. The study helped to illustrate that an emphasis on error analysis with known structures is essential so that these can be quantified with unknown structures, especially for the longer less precisely defined non-bonded distances.
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Published date: 1990
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Local EPrints ID: 460380
URI: http://eprints.soton.ac.uk/id/eprint/460380
PURE UUID: d015fa9f-7790-45bc-bc28-bf02bb97fd13
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Date deposited: 04 Jul 2022 18:20
Last modified: 04 Jul 2022 18:20
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Author:
Harriet Leach
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