Energy dispersive exafs studies on homogeneous metal catalysts
Energy dispersive exafs studies on homogeneous metal catalysts
Extended X-ray Absorption Fine Structure (EXAFS), Quick EXAFS (QuEXAFS) and Energy Dispersive EXAFS (EDE) data have been analysed for the nickel β-diketonate catalysts, Ni(dpm)2 and Ni(dpm)2(PPh3)2, and palladium diimine catalysts, Pd(phen)Cl2, Pd(bipy)Cl2 and Pd(tmeda)Cl2, using curved wave theory with ab initio phaseshifts. The derived parameters for metal compounds were in good agreement between all methods, within experimental error of 0.02-0.05 Å for the bond distances. QuEXAFS studies on Ni(dpm)2/AlEt2(OEt)/-hexene of different rations (1:1:20 and 1:2:20) were acquired using Si(220) monochromator at sub-ambient temperature (-20°C and 0°C) monitored the formation of Ni(dpm)C2H5(R), R=alkyl, and Ni(dpm)(C2H5)(PPh3) on the addition of PPh3. The derived structural parameters from QuEXAFS gave averaged distances of Ni-O 1.86 Å, Ni-C 2.00 Å and Ni-P 2.20 Å. A stopped flow system was used for in situ time-resolved EDE and UV-visible kinetic studies on the nickel systems at room temperature. EDE measurements using a new rectangular Si(111) monochomator and Hamamatsu S4874 photodiode array at Station 9.3, Daresbury Laboratory has yielded consecutive spectra taken at 1-1000 accumulations with 2-30 ms integration time to follow the changes during initiation of the catalytic reaction. The Ni(dpm)2:AlEt2(OEt):1-hexene of ratio of 1:6:20 were acquired within 16 s, and Ni(dpm)2:PPh3:AlEt2(OEt):1-hexene of 1:2:4:20 were acquired within 0.24 s for each spectrum. The growth of a pre-edge feature and change at the top of the edge can be clearly seen to show the reaction reached completion in less than 6 s indicates averaged distances of 3 Ni-O/C 2.00 Å and 1 Ni-P 2.11 Å.gif>. Using the stronger reagent of AlEt3, EDE was able to follow the reaction within 31 ms (15 ms dead-time). The bond lengths in the palladium complexes in solid state were refined at 2 Pd-N 2.12 Å and 2 Pd-Cl 2.33 Å. Addition of AgBF4 to one of the palladium complexes gives the cationic complex, Pd(tmeda)(NCMe)22+.
University of Southampton
Abdul Rahman, Mohd Basyaruddin
1999
Abdul Rahman, Mohd Basyaruddin
Abdul Rahman, Mohd Basyaruddin
(1999)
Energy dispersive exafs studies on homogeneous metal catalysts.
University of Southampton, Doctoral Thesis.
Record type:
Thesis
(Doctoral)
Abstract
Extended X-ray Absorption Fine Structure (EXAFS), Quick EXAFS (QuEXAFS) and Energy Dispersive EXAFS (EDE) data have been analysed for the nickel β-diketonate catalysts, Ni(dpm)2 and Ni(dpm)2(PPh3)2, and palladium diimine catalysts, Pd(phen)Cl2, Pd(bipy)Cl2 and Pd(tmeda)Cl2, using curved wave theory with ab initio phaseshifts. The derived parameters for metal compounds were in good agreement between all methods, within experimental error of 0.02-0.05 Å for the bond distances. QuEXAFS studies on Ni(dpm)2/AlEt2(OEt)/-hexene of different rations (1:1:20 and 1:2:20) were acquired using Si(220) monochromator at sub-ambient temperature (-20°C and 0°C) monitored the formation of Ni(dpm)C2H5(R), R=alkyl, and Ni(dpm)(C2H5)(PPh3) on the addition of PPh3. The derived structural parameters from QuEXAFS gave averaged distances of Ni-O 1.86 Å, Ni-C 2.00 Å and Ni-P 2.20 Å. A stopped flow system was used for in situ time-resolved EDE and UV-visible kinetic studies on the nickel systems at room temperature. EDE measurements using a new rectangular Si(111) monochomator and Hamamatsu S4874 photodiode array at Station 9.3, Daresbury Laboratory has yielded consecutive spectra taken at 1-1000 accumulations with 2-30 ms integration time to follow the changes during initiation of the catalytic reaction. The Ni(dpm)2:AlEt2(OEt):1-hexene of ratio of 1:6:20 were acquired within 16 s, and Ni(dpm)2:PPh3:AlEt2(OEt):1-hexene of 1:2:4:20 were acquired within 0.24 s for each spectrum. The growth of a pre-edge feature and change at the top of the edge can be clearly seen to show the reaction reached completion in less than 6 s indicates averaged distances of 3 Ni-O/C 2.00 Å and 1 Ni-P 2.11 Å.gif>. Using the stronger reagent of AlEt3, EDE was able to follow the reaction within 31 ms (15 ms dead-time). The bond lengths in the palladium complexes in solid state were refined at 2 Pd-N 2.12 Å and 2 Pd-Cl 2.33 Å. Addition of AgBF4 to one of the palladium complexes gives the cationic complex, Pd(tmeda)(NCMe)22+.
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Published date: 1999
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Local EPrints ID: 463598
URI: http://eprints.soton.ac.uk/id/eprint/463598
PURE UUID: 5726cacf-e5a7-43fd-94d2-241e2e3b54a5
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Date deposited: 04 Jul 2022 20:54
Last modified: 04 Jul 2022 20:54
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Author:
Mohd Basyaruddin Abdul Rahman
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