Take a sneak peek at the new NIST.gov and let us know what you think!
(Please note: some content may not be complete on the beta site.).
NIST Authors in Bold
|Author(s):||William E. Wallace; Lewandowski Hans; Meier J. Robert;|
|Title:||Reactive MALDI Mass Spectrometry of Saturated Hydrocarbons: A Theoretical Study|
|Published:||May 01, 2010|
|Abstract:||Recently it has been shown that the cobaltocenium cation, prepared by the laser ablation of a CoCp(CO)2/fullerene matrix, may react with alkanes and polyethylenes in the gas phase via a dehydrogenation reaction to produce [Co(Cp)2(alkadiene)]+ ions without chain scission (W.E. Wallace, Chem. Commun. 2007, 4525-4527). To better understand these experimental observations density functional calculations were used to obtain the gas-phase binding energies and molecular structures of cobaltocenium, Co(Cp)2+, with 1,3-butadiene, 2,4 hexadiene and 2,3-hexadiene. Calculations were conducted for both cis and trans molecular configurations, in both singlet and triplet electronic states, and with a variety of cyclopentadienyl hapticities. For 1,3 butadiene the 18 electron rule would predict a [Co(η3 Cp)2(η4 1,3 butadiene)]+, however, the lowest energy structure, [Co(η5 Cp)2(η4 1,3 butadiene)]+, has a higher than expected cyclopentadienyl hapticity. In this structure a distance of nearly 0.5 nm between the metal core and the butadiene ligand leads to very little electron sharing. In turn, the lack of orbital overlap leads to a low enthalpy giving the cis butadiene complex a -3.1 kcal/mol binding energy and the trans-butadiene binding a -0.9 kcal/mol binding energy. These low binding energies lead to low levels of charged alkanes in the reactive MALDI process compromising the sensitivity of the method in agreement with experimental observations.|
|Citation:||International Journal of Mass Spectrometry|
|Pages:||pp. 32 - 37|
|Keywords:||alkane, cobaltocene, dehydrogenation, density-functional theory, hydrocarbon, polymer|
|Research Areas:||Characterization, Polymers, Materials Science|
|PDF version:||Click here to retrieve PDF version of paper (353KB)|