7 Inorganic and Organometallic Chemistry Introduction The activity of the group comprises the synthesis, characterization and reactivity studies of inorganic, organometallic and intermetallic compounds of actinides and lanthanides and ion molecule reactions with the same elements, in order to understand the influence of the electronic configuration and of the size of these elements in the chemical behaviour of their compounds. Due to the type of chemistry we are dealing with, we extended our work to the chemistry of rhenium, with the aim of developing compounds that could be used as intermediates in reactions directed to organic synthesis and that can be models for compounds with 99m Tc to be used as radiopharmaceuticals. These activities are supported by X-ray diffraction analysis for structural studies and thermochemical studies for determination of metal-ligand bond disruption enthalpies. The gas-phase reactions of metallic, intermetallic and oxide ions involving lanthanides and actinides with organic substrates are studied by means of Fourier transform ion cyclotron resonance spectroscopy. The work done during 1996 in the domain of organometallic compounds allowed to accomplish the study of the reactivity of the system UCl 2 (HBpz 3 ) 2 towards several organic substrates. The analogous UCl 2 (Bpz 4 ) 2 system is now under investigation. The introduction of more sterically hindered polypyrazolylborate ligands, such as [HB(3-tBupz) 3 ] and [HB(3- Mespz) 3 ] allowed the synthesis of new systems of U (IV) and Ln(II) and their reactivity is being studied. The synthesis of alkoxides of lanthanides that could be active in some catalytic transformations was also studied. We were trying to get alkoxides of low nuclearity using alcohols with additional ether or amine functions. The compounds were tested in the carboxylation reaction of methanol but probably due to the highly aggregated structures obtained, the compounds did not show to be active in this particular transformation. The only compound which showed to be active in this reaction was the ytterbium:nickel (1:1) alloy. 78% of conversion of methanol to dimethylcarbonate was achieved by reacting the alloy with methanol under CO 2 . The reactivity of oxo-complexes of rhenium towards several neutral substrates was studied as well as the properties of rhenium (V) diolates. Attempts to prepare 99m Tc analogues have been done. The work in the gas-phase included studies of the reactivity of lanthanide and actinide metal and oxide ions with hydrocarbons, alcohols and phenols. Comparative studies with alkaline- earth ions were made due to the similarity of these elements with lanthanides in low oxidation states. The studies undertaken provided further examples confirming the relevance of the accessibility of reactive electronic configurations to the reactivity of lanthanide and actinide ions with organic molecules. Formation of f-d intermetallic ions was achieved and these species may be available for future studies of the influence of the d element in the reactivity with organic molecules. Reactivity of several lanthanide oxide cluster ions with small oxygenated molecules was also studied. Collaborative work has extended the gas-phase research to studies of transition metal ions.
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7
Inorganic and Organometallic Chemistry
Introduction
The activity of the group comprises the synthesis, characterization and reactivity studies of
inorganic, organometallic and intermetallic compounds of actinides and lanthanides and ion
molecule reactions with the same elements, in order to understand the influence of the
electronic configuration and of the size of these elements in the chemical behaviour of their
compounds. Due to the type of chemistry we are dealing with, we extended our work to the
chemistry of rhenium, with the aim of developing compounds that could be used as
intermediates in reactions directed to organic synthesis and that can be models for compounds
with 99m
Tc to be used as radiopharmaceuticals. These activities are supported by X-ray
diffraction analysis for structural studies and thermochemical studies for determination of
metal-ligand bond disruption enthalpies. The gas-phase reactions of metallic, intermetallic and
oxide ions involving lanthanides and actinides with organic substrates are studied by means of
Fourier transform ion cyclotron resonance spectroscopy.
The work done during 1996 in the domain of organometallic compounds allowed to
accomplish the study of the reactivity of the system UCl2(HBpz3)2 towards several organic
substrates. The analogous UCl2(Bpz4)2 system is now under investigation. The introduction of
more sterically hindered polypyrazolylborate ligands, such as [HB(3-tBupz)3] and [HB(3-
Mespz)3] allowed the synthesis of new systems of U (IV) and Ln(II) and their reactivity is
being studied.
The synthesis of alkoxides of lanthanides that could be active in some catalytic
transformations was also studied. We were trying to get alkoxides of low nuclearity using
alcohols with additional ether or amine functions. The compounds were tested in the
carboxylation reaction of methanol but probably due to the highly aggregated structures
obtained, the compounds did not show to be active in this particular transformation. The only
compound which showed to be active in this reaction was the ytterbium:nickel (1:1) alloy.
78% of conversion of methanol to dimethylcarbonate was achieved by reacting the alloy with
methanol under CO2.
The reactivity of oxo-complexes of rhenium towards several neutral substrates was studied as
well as the properties of rhenium (V) diolates. Attempts to prepare 99m
Tc analogues have been
done.
The work in the gas-phase included studies of the reactivity of lanthanide and actinide metal
and oxide ions with hydrocarbons, alcohols and phenols. Comparative studies with alkaline-
earth ions were made due to the similarity of these elements with lanthanides in low oxidation
states. The studies undertaken provided further examples confirming the relevance of the
accessibility of reactive electronic configurations to the reactivity of lanthanide and actinide
ions with organic molecules. Formation of f-d intermetallic ions was achieved and these
species may be available for future studies of the influence of the d element in the reactivity
with organic molecules. Reactivity of several lanthanide oxide cluster ions with small
oxygenated molecules was also studied. Collaborative work has extended the gas-phase
research to studies of transition metal ions.
Inorganic and Organometallic Chemistry ________________________________________________________
8
Research Team
Researchers – 12 * (10 PhD)
Research Students – 4
BSc Last Year Students – 4
Technicians – 2
* 2 Post-doctoral
Publications:
Journals – 7
Special Publ. – 1
Conf. Commun.: 10
Internal Reports: 1
Theses:
PhD – 1
MSc – 1
Lic. – 4
________________________________________________________ Inorganic and Organometallic Chemistry
9
f - Element Chemistry
Hydrocarbyl Derivatives of [UCl2{HB(pz)3}2]: Synthesis, Characterization
and Reactivity Studies Towards Protic Substrates and Ketones
M. Paula C. Campelloa, Maria José Calhorda
c, Ângela Domingos
a, Adelino Galvão
b,
João
Paulo Leala, A.Pires de Matos
a and Isabel Santos
a
aDepartamento de Química, ITN, 2686 Sacavém Codex, Portugal
bDepartamento de Engenharia Química, Instituto Superior Técnico, 1096 Lisboa Codex, Portugal
cI. T. Q. B., R. da Quinta Grande 6, Apt. 127, 2780 Oeiras, Portugal and Faculdade de Ciências,
Edifício C4, Campo Grande, 1700 Lisboa
Abstract
The reaction of [UCl2{HB(pz)3}2] (1) with lithium alkyls LiR (R=Me, CH2SiMe3, C6H4-o-
CH2NMe2) in the 1:1 or 1:2 molar ratio affords the compounds [UClR{HB(pz)3}2] (pz=
Marktscheffel, J.A.; Esser, L. Chem. Rev. 1995, 95, 865; Hubert-Pfalzgraf, L.G. New J. Chem.
1995, 19, 727.
3- Yin, W.W.; Marshall, A.G.; Marçalo, J.; Pires de Matos, A. J. Am. Chem. Soc. 1994, 116,
8666.
4- Breton, S.; PhD Thesis, Université de Nice-Sophia Antipolis, 1995; Azzaro, M.; Breton, S.;
Decouzon, M.; Geribaldi, S. Int. J. Mass Spectrom. Ion Processes 1993, 128, 1; Geribaldi, S.;
Breton, S.; Decouzon, M.; Azzaro, M. New J. Chem. 1995, 19, 887.
Communication to: 9ème
Journée de la Chimie / Provence-Alpes-Côte d’Azur, Nice, France,
March 22, 1996.
________________________________________________________ Inorganic and Organometallic Chemistry
19
Current Work
Reactivity of alkaline earth metal and oxide ions with
pentamethylcyclopentadiene in the gas phase
Joaquim Marçaloa, António Pires de Matos
a and William J. Evans
b
a Departamento de Química, ITN, Estrada Nacional 10, 2686 Sacavém Codex, Portugal
b Department of Chemistry, University of California, Irvine
The gas-phase reactivity of the alkaline earth metal (Ca+, Sr
+ and Ba
+) and oxide (CaO
+, SrO
+
and BaO+) ions with pentamethylcyclopentadiene was studied by FTICR/MS, for comparative
purposes with previous results obtained with lanthanide (Ln = La - Lu) and group 3 (Sc and
Y) metal and metal oxide ions. The alkaline earth metal ions were produced by laser
desorption/ionization of metal hydroxide pellets and the oxide ions by reaction of the metal
ions with N2O introduced through pulsed valves. The organic reagent was admitted to the
instrument through a leak valve, and pulsed-in argon was used for collisional cooling of the
reagent ions. The reactivity of the metal cations was similar to the one observed before for
Sm+, Eu
+, Tm
+ and Yb
+, namely the formation of the fulvenide ion (C5Me4CH2)M
+ as main
primary product and of the metallocene ion (C5Me5)2M+ as main secondary product. These
similarities in the reactivity can be explained by the similar behaviour of the s1 ground states
of the group 2 metal ions and the fns
1 ground states (with large promotion energies to f
n-1d
1s
1
states) of the referred lanthanide ions. In the case of the metal oxide ions MO+, the reactivity
with pentamethylcyclopentadiene, being mainly determined by the strength of the M+ – O
bonds, again showed similarities with EuO+ and YbO
+ (the lanthanide ions with the weakest
M+ – O bonds, similar to the ones present in the alkaline earth oxide ions), with formation of
MOH+ as main primary product and M(C5Me5)
+ as secondary product.
Gas phase reactivity of rare earth ions with alcohols, phenols and other
oxygenated molecules
José Manuel Carretasa, Joaquim Marçalo
a, António Pires de Matos
a, Serge Geribaldi
b, Marc
Pissavinib, Michele Decouzon
b, Maurice Azzaro
b
a Departamento de Química, ITN, Estrada Nacional 10, 2686 Sacavém Codex, Portugal
b Laboratoire de Chimie Physique Organique, Université de Nice-Sophia Antipolis
The gas phase reactions of the rare earth ions Sc+, Y
+ and Ln
+ (Ln = La - Lu) with isopropanol
and phenol were studied by FT-ICR/MS. The metallic ions were produced by laser ionisation
of the corresponding metals and were thermalised by collisions with argon; the reagents were
introduced through leak valves to pressures of (1-5) 10-7
Torr. All the ions except Yb+
reacted exothermically with isopropanol and phenol, with formation of MO+ and MOH
+ ions
as primary products, as well as of MOC6H4+ in the case of phenol, a product resulting from
the simultaneous activation of O-H and aromatic C-H bonds. The primary product ions
participate in subsequent reactions that lead to M(OR)x(HOR)y+ species, where x = 1-2 and y
= 0-3. The detailed study of the mechanisms of the primary reactions, of the reaction
sequences, of the corresponding kinetics and of the energies involved in the various steps,
showed important differences in the relative reactivity of the metallic ions.
Inorganic and Organometallic Chemistry ________________________________________________________
20
Gas phase synthesis of lanthanide and actinide - transition metal
intermetallic ions
Maria da Conceição Vieira, Joaquim Marçalo and António Pires de Matos Departamento de Química, ITN, Estrada Nacional 10, 2686 Sacavém Codex, Portugal
FT-ICR/MS was used to study the formation of intermetallic ions involving metals of the f
and d blocks. In particular, the series of ions LnFe+ (Ln = La - Lu), as well as ThFe
+ and UFe
+,
were synthesized by gas phase reaction of the metal ions, produced by laser ionization of pure
metal pieces, with the volatile carbonyl complex Fe(CO)5, followed by excitation and
collision with argon of the MFe(CO)2+ product ions formed. Advantage was taken from the
potentialities of the FT-ICR/MS technique for performing kinetic studies, which showed that
significant differences in reaction efficiencies existed along the lanthanide series.
Gas phase reactivity of lanthanide oxide cluster ions with small oxygenated
molecules
Joaquim Marçaloa, António Pires de Matos
a, Hans H. Cornehl
b, Christoph Heinemann
b and
Helmut Schwarzb
a Departamento de Química, ITN, Estrada Nacional 10, 2686 Sacavém Codex, Portugal
b Institut für Organische Chemie, Technische Universität Berlin
The reactivity of several lanthanide (Ln = La, Pr, Eu, Tb, Ho, Tm, Lu) oxide cluster cations
LnxOy+ with O2, N2O and H2O in the gas phase was studied by FT-ICR/MS. The cluster ions
were produced by direct laser desorption/ionization of surface oxidized metal pieces or of
metal oxide pellets, and the reagents were admitted to the mass spectrometer through a leak
valve; argon, introduced through pulsed valves, was used for collisional cooling of the reagent
ions. Oxydation reactions with O2 and N2O were observed for some cluster ions, while the
reactivity with water corresponded only to adduct formation. Several effects of the formal
metal valency in the cluster ions as well as of the cluster size on the reactivity and in the
kinetics could be observed.
Characterization and reactivity of transition metal oxide cluster anions in
the gas phase
Maria da Conceição Oliveira*, Maria Alzira Almoster Ferreira
* Joaquim Marçalo
+, Maria da
Conceição Vieira+
* Departamento de Química, FCUL
+ Departamento de Química, ITN, Estrada Nacional 10, 2686 Sacavém Codex, Portugal
Laser desorption/ionization was used in conjunction with FT-ICR/MS to produce and
characterize first-row transition metal oxide anions of the type MxOy-, with M = Mn, Fe, Co,
Ni and Cu. Metal oxide pellets were used as targets and argon, introduced through pulsed
valves, was used for collisional cooling of the reagent ions. Methanol was used to probe the
reactivity of these barely studied anionic species, uncovering important effects of the nature of
the metal and of cluster size in the reaction products formed and in the corresponding kinetic
efficiencies.
________________________________________________________ Inorganic and Organometallic Chemistry
21
Thermochemistry
Alkaline metal alkoxides
João Paulo Leala, P. Nunes
b, M. E. Minas da Piedade
b
aDepartamento de Química, ITN, Estrada Nacional 10, 2686 Sacavém Codex, Portugal
bInstituto Superior Técnico, Av. Rovisco Pais 1096 Lisboa Codex, Portugal
Abstract
In spite of the wide use of alkaline metal alkoxides (MOR, M = Li, Na, K, Rb, Cs) in synthetic
chemistry, thermochemical data for this family of compounds are scarce. The knowledge of
their enthalpies of formation, lattice energies, etc. is of key importance to predict new data and
to discuss the energetics of several reactions involving alkaline metal alkoxides. One example
is the study of the formation and reactivity of the now commonly used super-bases (mixed
aggregates of alkillithium compounds and alkaline metal alkoxides).
In this work, the enthalpies of formation in the crystalline state of a series of MOR (M= K, Cs;
R= Me, Et, n-Bu, t-Bu) compounds were measured by reaction-solution calorimetry. The
corresponding lattice energies, LUº, were also derived, and used to calculate thermochemical
radii, r-, for the alkoxi anions, from the Kapustinskii equation. The estimation of new data for
MOR compounds is discussed using the results obtained in the present work and those
previously published for LiOR and NaOR compounds.
Communication to: Reunião final do Network “Selective Processes and Catalysis Involving
Small Molecules”, ITQB, Oeiras, Portugal, April 1996.
Bond dissociation enthalpies in U-L. What’s the real value?
João Paulo Leala, Noémia Marques
a, J. Takats
b
a Instituto Tecnológico e Nuclear, Dep. Química, Est. Nac. nº 10, P-2686 Sacavém Codex, Portugal
b Department of Chemistry, University of Alberta, Edmonton, Alberta, Canada T6G 2G2
Abstract
Uranium-ligand bond dissociation enthalpies had been widely studied in last years (see a
compilation of existing values in ref. 1). Despite of the considerable quantity of data already
known doubts about their absolute value persist. This is mainly due to the fact that
experimentally differences between two bonds are measured, and than one of them is assumed
(or estimated) and considered as an anchor being all the others related to that one.
On the present work the energetic of the U-O, U-I and U-Cl bonds in compounds of the type
UI2L{HB(dmpz)3} (L=O-tBu, I; dmpz=3,5-dimethylpirazole) and UCl3{HB(dmpz)3} have
been studied by means of oxidative reactions of UI2{HB(dmpz)3}.2thf with appropriate
reagents and using reaction solution calorimetry. The results allow a critical review of
literature data and suggest that a universal scale for uranium-ligand bond dissociation
enthalpies can be achieved.
1) J. P. Leal, J. A. Martinho Simões, J. Chem. Soc. Dalton Trans.1994, 2687.
Communication to: “XV Encontro Nacional da SPQ”, Porto, Portugal, May 1996.
Inorganic and Organometallic Chemistry ________________________________________________________
22
Potassium and Cesium alkoxides energetics
João Paulo Leal,a P. Nunes,
b M. E. Minas da Piedade
b
a Departamento de Química, ITN, Estrada Nacional 10, 2686 Sacavém Codex, Portugal
bInstituto Superior Técnico, Av. Rovisco Pais 1096 Lisboa Codex, Portugal
Abstract
Alkaline metal alkoxides (MOR, M = Li, Na, K, Rb, Cs) had been extensively used in
synthetic chemistry. Despite that thermochemical data for this family of compounds are
scarce. The knowledge of their energetics is crucial to predict new data and to discuss the
energetics of several reactions involving alkaline metal alkoxides [eg.: super-bases (mixed
aggregates of alkillithium compounds and alkaline metal alkoxides)].
In this work, the enthalpies of formation in the crystalline state of a series of MOR (M= K, Cs;
R= Me, Et, n-Bu, t-Bu) compounds were measured by reaction-solution calorimetry. The
corresponding lattice energies were also derived, and used to calculate thermochemical radii,
r-, for the alkoxi anions assuming a ionic lattice structure. This values allow the estimation of
new data for other MOR compounds not yet studied. Critical review of previously published
data for LiOR and NaOR compounds is also made1.
1
(a) J. P. Leal, A. Pires de Matos, J. A. Martinho Simões, J. Organometal. Chem. 1991, 403,
1; (b) J. P. Leal, J. A. Martinho Simões, J. Organometal. Chem. 1993, 460, 131.
Communication to: “XV Encontro Nacional da SPQ”, Porto, Portugal, May 1996.
________________________________________________________ Inorganic and Organometallic Chemistry
23
Surface Studies
Photon stimulated ion desorption of C2H4 adsorbed on graphite
J.M. Coquel1, T. Almeida Gasche
1,2, J. Wilkes
1,3, C. M. Friedrich
4, C.L.A. Lamont
3, M.A.
MacDonald5, R.E. Palmer
1, A.M.C. Moutinho
6
1 Nanoscale Physics Research Laboratory, School of Physiscs and Space Research, University of
Birmingham, Edgbaston, Birmingham B 15 2 TT, U K 2 Instituto Tecnológico e Nuclear, Dep. de Química, Estrada Nacional 10, 2685 Sacavém, Portugal
3 School of Applied Sciences, University of Huddersfield, Huddersfield HD1 3DH, UK
4 Cavendish Laboratory, Univ. of Cambdrige, Cambdrige CB3 OHE, UK
5 CLRC, Daresbury Laboratory, Warrington WA4 4AD, UK
6 GIDS/ CeFITeC, Dep. de Física, FCT, Univ. Nova de Lisboa; 2825 Monte da Caparica, Portugal
Abstract Photon stimulated desorption from C2H4 on highly oriented pyrolitic graphite using VUV synchroton radiation in the energy range 13-40 eV was studied. In contrast with gas phase measurements, only H
+ ions are detected. This is due to the image potential barrier to
desorption from the surface and unequal distribution of kinetic energy amongst the molecular photofragments. The yield of desorbed H
+ ions shows a threshold at 20.5 eV and a resonance
at 24 eV. This behaviour is different from the gas phase and is attributed to selective quenching of excited molecular electronic states on the surface and to chemical reactions between specific molecular dissociated fragments and the substrate.
Communication to: ECOSS 16 (16
th European Conf. on Surface Science), Sept. 1996, Genova,
Italy and also in Física 96, (10 th
Nacional Conf. of Physics), Sept. 1996, Faro, Portugal.
Sample holder for using in surface studies (77-1300 K)
Carlos M.M. Leitão1, Teresa Almeida Gasche
2, Roger Bennet
3, O. M. N. Teodoro
1, G.
Bonfait2, A.M.C. Moutinho
1
1 Centro de Física e Investigação Tecnológica (CeFITeC), Dep. de Física, FCT, Univ. Nova de
Lisboa; 2825 Monte da Caparica, Portugal 2 ITN- Instituto Tecnológico e Nuclear, Dep. de Química, Est. Nac. 10, 2685 Sacavém, Portugal
3 Nanoscale Physics Research Laboratory, School of Physiscs and Space Research, University of
Birmingham, Edgbaston, Birmingham B 15 2 TT, U K
Abstract
The construction of this sample holder have as aim to conceive a system where quick cycles
of cooling and heating would be possible, in the temperature range 77-1300 K. The sample
holder is mounted in a horizontal position. A molybdenum support will be used to mount the
sample. The heating will be done by electronic bombardment. The cooling system is a "cold
finger" type.
The sample holder is going to be used in a surface system in each several surface techniques
are available, e.g. XPS- X-Ray Photoelectron Spectroscopy; AES- Auger Electron
Spectroscopy, ESD- Electron Stimulated Desorption, TDS- thermal Desorption Spectroscopy.
The sample holder will allow not only to work at low temperatures but also to do annealing to
crystals.
Communication to: FÍSICA 96 -10 th
Nacional Conference of Physics, Faro, Portugal,
13-17 September 1996.
Inorganic and Organometallic Chemistry ________________________________________________________
24
Carbon-dioxide adsorbed on graphite: a photon stimulated desorption study
J. M. Coquel1, L. Siller
1, R. E. Palmer
1, R. Carrapa
2, A.M.C. Moutinho
2, J. Wilkes
3, C.L.A.
Lamont3, T. Almeida Gasche
4
1 Nanoscale Physics Research Laboratory, School of Physics and Space Research, University of
Birmingham, Edgbaston, Birmingham B 15 2 TT, U K; 2 Centro de Física e Investigação Tecnológica (CeFITeC), Dep. de Física, FCT, Univ. Nova de
Lisboa; 2825 Monte da Caparica, Portugal; 3 School of Applied Sciences, University of Huddersfield, Huddersfield HD1 3DH, UK;
4 ITN- Instituto Tecnológico e Nuclear, Dep. de Química, Est. Nac. 10, 2685 Sacavém, Portugal
Abstract
Carbon-dioxide physisorbed on graphite at 50 K was studied by photon stimulated desorption
(PSD) graphite using VUV synchrotron radiation in the energy range 13-40 eV 1. Previous
studies showed that the physisorption of CO2 on graphite was not possible for temperatures
below 104 K 2,4. The results obtained in our studies are in contradiction with these
conclusions.
The sample was heated to 900 K. The measurements were done for different dosages of CO2,
in the range of 0.18 to 3.0 L. H+, CO
+ and O2
+ were the ions detected. In the mass
spectrometer, neither negative ions or neutral species were observed. The yield of desorbed
O2+ ions shows a threshold at 15 eV and a resonance at 25 eV. The yield of desorbed CO
+ ions
shows a small resonance at 15 eV and a threshold at 25 eV.