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A photoacoustic calorimetric characterization of the reaction enthalpy and volume for the preparation of a reactive intermediate from CpMn(CO)3

Paper ID Volume ID Publish Year Pages File Format Full-Text
28029 44056 2008 7 PDF Available
Title
A photoacoustic calorimetric characterization of the reaction enthalpy and volume for the preparation of a reactive intermediate from CpMn(CO)3
Abstract

Photoacoustic calorimetry (PAC) allows measurement of the energetics of reactive intermediates. Here, we report the examination of the metal carbonyl η5-CpMn(CO)3 (Cp, cyclopentadiene) via time-independent PAC, in a homologous series of solvents. The measured heat releases allow one to determine simultaneously the enthalpy and volume change resulting from the photodissociation of CpMn(CO)3. While the photoacoustic signal results from both of these processes, it has often been assumed that the volume change contribution to the observed photoacoustic signal is negligible for small molecules undergoing photodissociation. The current study tests the assumption of a negligible reaction volume by using a more complete treatment. The reaction of an equimolar number of photons and CpMn(CO)3 molecules, the subsequent photodissociation of the Mn–CO bond, and the ligation of a solvent molecule in an alkane solvent yields ΔHobs = 32.7 ± 0.7 kcal/mol and ΔVchem = 11.0 ± 1.3 mL/mol, both of which are independent of the quantum yield of photodissociation. A detailed analysis of the quantum yield is included (using both previously reported measurements, and new data from this work), from which we determine Φdiss = 0.635. This quantum yield allows us to determine ΔHrxn = 51.6 kcal/mol and ΔVrxn = 17.3 mL/mol. These results demonstrate that if the contribution of the reaction volume change to the photoacoustic signal is ignored, the reaction enthalpy derived would underestimate the true value by 7%. We also estimate the BDE{Cp(CO)2Mn–CO} to be 59.4 kcal/mol.

Keywords
Photoacoustic calorimetry; Photodissociation; Bond enthalpy; Thermodynamics; Metal carbonyl
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A photoacoustic calorimetric characterization of the reaction enthalpy and volume for the preparation of a reactive intermediate from CpMn(CO)3
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Publisher
Database: Elsevier - ScienceDirect
Journal: Journal of Photochemistry and Photobiology A: Chemistry - Volume 197, Issues 2–3, 25 June 2008, Pages 335–341
Authors
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Subjects
Physical Sciences and Engineering Chemical Engineering Bioengineering
Get Full-Text Now
Don't Miss Today's Special Offer
Price was $35.95
You save - $31
Price after discount Only $4.95
100% Money Back Guarantee
Full-text PDF Download
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