DOKTORI (PH.D.) ÉRTEKEZÉS TÉZISEI Electronic structure and gas phase thermochemistry of organoelement and organometallic compounds Gengeliczki Zsolt témavezető: Sztáray Bálint, Ph.D., egyetemi adjunktus EÖTVÖS LORÁND TUDOMÁNYEGYETEM, KÉMIAI INTÉZET BUDAPEST, 2008. KÉMIA DOKTORI ISKOLA, PROF. DR. INZELT GYÖRGY ELMÉLETI ÉS FIZIKAI KÉMIA, ANYAGSZERKEZETKUTATÁS PROGRAM PROF. DR. SURJÁN PÉTER
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DOKTORI (PH.D.) ÉRTEKEZÉS TÉZISEI
Electronic structure and gas phase thermochemistry
of organoelement and organometallic compounds
Gengeliczki Zsolt
témavezető: Sztáray Bálint, Ph.D., egyetemi adjunktus
EÖTVÖS LORÁND TUDOMÁNYEGYETEM, KÉMIAI INTÉZET
BUDAPEST, 2008.
KÉMIA DOKTORI ISKOLA, PROF. DR. INZELT GYÖRGY
ELMÉLETI ÉS FIZIKAI KÉMIA, ANYAGSZERKEZETKUTATÁS PROGRAM
PROF. DR. SURJÁN PÉTER
1
1 Introduction
The catalytic activity and the often surprisingly high selectivity of transition metal
organometallic catalysts depend on the metal center, the ligands, the reactants, the
products, and the solvent. However, the individual contributions of the different
factors are unknown because accurate data about the electronic structure and
thermochemistry of the transition metal complexes are usually not available.
Ultraviolet photoelectron spectroscopy (UPS) and photoelectron photoion coincidence
spectroscopy (PEPICO) are useful techniques in investigating isolated, solvent free
model compounds in the gas phase in order to study their intrinsic properties, such as
bond energies, not affected by the chemical environment. Both are based on the
photoionization of neutral molecules.
In photoelectron spectroscopy, photoelectrons are analyzed according to their kinetic
energy, from which the vertical ionization energies are determined. Vertical ionization
energies, via Koopmans’ theorem, can be assigned to molecular orbital energies, thus
photoelectron spectroscopy provides direct information on the electronic structure of
the investigated molecules.
Photoelectron photoion coincidence spectroscopy is a form of high precision mass
spectrometry, by which the unimolecular dissociation of energy selected ions can be
studied. Bond dissociation energies, appearance energies of fragment ions and,
indirectly, heats of formation of the gas phase ions and molecules can be derived.
1.1 Overview
In the Results section, six chapters present the achieved results and drawn
conclusions. In the first chapter, a newly developed temperature controlled inlet
system of the PEPICO apparatus is presented. In the second chapter, the application
of Kohn–Sham orbital energies in the assignment of photoelectron spectra of
transition metal complexes is tested. Photoelectron spectroscopy of phosphine
derivatives of cobalt tricarbonyl nitrosyl is discussed in the third chapter. Finally,
chapters from four to six present the photoelectron photoion coincidence studies on
alkylphosphines, as well as phosphine and isocyanide cobalt complexes.
2
1.1.1 Temperature controlled TPEPICO experiments
The development of a new, temperature controlled inlet system for the PEPICO
apparatus became necessary for the study of the dissociation of small, organic ions in
the gas phase. The new inlet system was tested with a study on 1-butyl iodide (n-
C4H9I). Although this project was not crucial in the investigation of organometallic
complexes, it is included in this thesis because it can help understand the details of the
experiment and of the data analysis. One of the major assumptions in the modeling
unimolecular dissociations in the PEPICO apparatus is that the neutral energy
distribution is transposed directly to the ion manifold. The newly developed
temperature controlled inlet allowed this assumption to be tested more rigorously.
1.1.2 Kohn–Sham orbital energies in the assignment of photoelectron
spectra of transition metal complexes
In several studies, Baerends et al. showed that the Kohn–Sham (KS) orbitals are
better approximations of Dyson orbitals than the Hartree–Fock (HF) orbitals, and the
negatives of the orbital energies can be interpreted as vertical ionization energies. The
standard DFT functionals and basis sets, however, underestimate the experimental
ionization potentials by 1–5 eV. Because, from the point of view of a spectroscopist,
an efficient and relatively fast method to reproduce the photoelectron spectra of
transition metal complexes is highly valuable, a scaling method is proposed in this
chapter to compensate the error of the standard functionals and basis sets. The first
vertical ionization energies were computed as the difference in the energy of the
ground state ion and neutral molecule at the equilibrium geometry of the latter. The
negatives of the KS orbital energies were then shifted so the negative of the HOMO
matched with the above calculated ionization potential. This method was tested on a
wide range of transition metal carbonyls, hydrides, halides, sandwich and half
sandwich complexes.
1.1.3 Organoelement and organometallic compounds
The effect of ligand substitution on the electronic structure and bond energies of
organometallic catalysts can be determined by investigating a series of model
compounds. The model compounds chosen in this thesis are the phosphine and
isocyanide derivatives of cobalt tricarbonyl nitrosyl (Co(CO)3NO). Cobalt tricarbonyl
3
nitrosyl plays an important role in synthetic organic chemistry, chemical vapor
deposition and even nanotechnology. In organometallics, it is well known that
phosphine and isocyanide substitution may strongly affect the stability and catalytic
activity of transition metal complexes.
He-I and He-II photoelectron spectra of the substituted complexes revealed that the
highest-lying orbitals, which have a significant metal d-character, can be destabilized
by increasing the electron-donor capability of the phosphine ligands. These findings
are discussed in detail in the third chapter.
In the TPEPICO experiment, upon photoionization, the molecule can dissociate into
fragments, whose heats of formation are well established: