From discrete anions to extended solids [Elektronische Ressource] : new uranium thiophosphates / Christine Gieck

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From discrete anions to extended solids: new uranium thiophosphates Dissertation zur Erlangung des Grades „Doktor der Naturwissenschaften“ am Fachbereich Chemie und Pharmazie der Johannes-Gutenberg-Universität Mainz Christine Gieck geboren in Groß-Umstadt Mainz, 2003 1 Die experimentellen Untersuchungen zu der vorliegenden Arbeit wurden am Institut für Anorganische Chemie und Analytische Chemie der Johannes-Gutenberg-Universität in Mainz in der Zeit von November 1997 bis Mai 2002 unter der Leitung von Prof. Dr. W. Tremel durchgeführt.

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From discrete anions to extended solids:
new uranium thiophosphates







Dissertation
zur Erlangung des Grades
„Doktor der Naturwissenschaften“
am Fachbereich Chemie und Pharmazie
der Johannes-Gutenberg-Universität Mainz









Christine Gieck
geboren in Groß-Umstadt



Mainz, 2003
1 Die experimentellen Untersuchungen zu der vorliegenden Arbeit wurden
am Institut für Anorganische Chemie und Analytische Chemie der
Johannes-Gutenberg-Universität in Mainz in der Zeit von November 1997
bis Mai 2002 unter der Leitung von Prof. Dr. W. Tremel durchgeführt.
2





Für meine Mutter















The most important phrase in science,
the one which heralds new results
is not “Eureka” but “That’s funny…”

Isaac Asimov

3 Table of Contents

1 Introduction 1
2 Comprehensive uranium thiophosphate chemistry:
Framework compounds based on pseudotetrahedrally
coordinated metal centers 5
Introduction 5
Experimental section 6
Physical measurements 10
Results and discussion 12
Crystal structures 12
Discussion 18
Vibrational spectroscopy 26
Magnetic behavior 30
3 Synthesis and characterization of Rb U(PS ) , CsU (PS )5 4 3 2 4 3
and Na U(PS ) 34 2 4 2
Introduction34
Experimental section 35
Physical measurements 36
Results and discussion 38
4 Interlocking inorganic screw helices: Synthesis, structure
and magnetism of the novel framework uranium ortho-
thiophosphates A U (PS ) (A = K, Rb) 46 11 7 4 13
Introduction 46
Experimental section 48
Physical measurements 49
Results and discussion 51
Conclusion59
5 CsLiU(PS ) , a zeotype uranium thiophosphate obtained 4 2
from high temperature reactions in salt melts 61
Introduction 61
Experimental section 62
4 Crystal structure determination 63
Results and discussion 64
6 Cs UP S , a coordination polymer based on an open 3 2 8
tetrahedral network containing the unprecedented
U=S thiouranyl unit 70
Introduction 70
Experimental section 70
Physical measurements 71
Results and discussion 72
Conclusion77
7 An unprecedented M=S unit in the structure of the
novel thiophosphates Li Rb M (S)S (PS ) (M = Th, U) 79 3 6 3 2 4 5
Introduction 79
Experimental section 80
Crystal structure determination 81
Results and discussion 82
8 Summary86

Appendix91
References 123





5 1 Introduction

The preparation and characterization of micro- and mesoporous
oxide-based materials has been an important issue during the last
decades. The most important class of microporous inorganic compounds
are the zeolites, crystalline materials with porous network structures.
-Zeolite frameworks consist of corner-sharing SiO and AlO tetrahedra. 4 4
The negative charge of the porous 3D alumosilicate framework is coun-
terbalanced by templating alkali metal cations residing in the cavities.
Zeolites are generally prepared by hydrothermal synthesis techniques,
where the size of the cavities can be “fine tuned” by choosing suitable
countercations. The introduction of surfactant liquid crystals serving as
templates in the reaction mixture resulted in the formation of meso-
porous silicate and alumosilicate frameworks with pore sizes ranging from
[1]15 to 100 Å.
-The substitution of either SiO or AlO with different tetrahedral oxidic 4 4
units yielded a class of so-called “zeotype” materials, whose properties
-resemble the parent compounds. For example, the substitution of AlO 4
[2] [3] [4]yielded zeotype silicates of boron, gallium, iron and titanium, while
the introduction of orthophosphate units into the framework resulted in
[5-7]the formation of porous aluminium- and galliumphosphates.
The properties of the corresponding porous non-oxidic chalcogenides
were investigated only recently. The most important difference between
oxygen and the heavier chalcogen atoms is the preference of the latter
[8]elements to form stable infinite Q chains instead of Q-Q double bonds. n
This ability of the chalcogens leads to the formation of a multitude of
possible connectivity patterns.
Most of these non-oxidic zeotype compounds are air- and moisture-
sensitive and cannot be precipitated from aqueous solutions. The vast
majority was obtained from high-temperature reactions in a polychalco-
genide or alkali metal halide flux. New synthetic routes include the self-
4-assembly of suitable anionic precursors like Ge Q (Q = S, Se) in 4 10
1 [9-15]solutions containing organic templates. The properties of the reaction
products are determined by the polarity of the solvent and the structure
of the templating surfactant molecule aggregates.
The most successful candidates for the formation of porous or low-
dimensional network structures are the thio- and selenophosphates of
transition metals. Their easy accessibility by solid-state reactions, the
large variety of possible connectivity patterns and the comparative sta-
bility of the precursors resulted in the synthesis and characterization of an
intriguing variety of transition metal chalcogenophosphates.
The arrangement of the different building blocks in the crystal struc-
tures of these compounds depends on the preferred coordination
z-environment for the metal centers and the structure of the P Q (Q = S, x y
Se) ligands. For example, the combination of the tetrahedral PQ ligand, 4
which acts as a twofold bidentate connector between two metal
centers, with a MQ octahedron results in a triangular connectivity for the 6
[16]metal atom. The combination of a MQ polyhedron with four bi-8
dentate PQ ligands leads to the formation of a pseudotetrahedral 4
[17]environment for the central metal atom. The high and variable
coordination numbers of transition metal atoms combined with the
condensation equilibria of chalcophosphates may lead to structural
arrangements of astounding complexity.
The most important class of ternary metal chalcogenophosphates are
the hexathiodiphosphates of divalent transition metals. This so-called
[18]MPS structure type is adopted for M = Cr, Mn, Fe, Ni, Cd and Zn. These 3
compounds contain the MS octahedron coordinated by six S atoms 6
4-belonging to three ethane-like P S groups. The resulting crystal structure 2 6
can be derived form the CdCl structure type by replacing the Cl atoms 2
with sulfur and 1/3 of the metal cations with P dumbbells. The corres-2
ponding selenophosphates, MPSe , crystallize in most cases in a similar 3
[19]structure type based on the atom arrangement found in CdI . Both 2
MPS and MPSe consist of 2D layers separated by van der Waals gaps. 3 3
The presence of these gaps, as well as the ability of the metal centers to
2 [20]act as electron acceptors, leads to a multitude of intercalation
products.
[20,21]Lithium metal hexadithiophosphates can be prepared either by
electrochemical intercalation of lithium between the layers or by ion
exchange reactions. For example, the compound Li Ni PS is used as a x 1-x 3
[22]cathode material in room-temperature lithium batteries.
Recent research interests include the preparation of nanocomposites
with the 2D MPS system acting as the host layer system and planar 3
[23]organic molecules or polymers as the intercalated guest species.
Transparent thin films of MnPS and CdPS , which were prepared by ex-3 3
[24]foliation, are useful host matrices for nonlinear optical chromophores
[25] in optical devices.
The replacement of the divalent metal atoms in the crystal structure of
+ 3+MPQ with 1/2 M and 1/2 M cations leads to the formation of a 3
[26,27]number of heterocharge substitution products, M’ M’’’ PQ . The 0.5 0.5 3
structure of the resulting cation sublattice can be correlated to the ratio
[26d]of the metal-chalcogen distances. For r’/r’’’ ≈ 1, M’ and M’’’ form
distinct triangular sublattices, whereas for r’/r’’’ > 1, an ordered arrange-
ment of the cations in separate zigzag chains can be observed. The
existence of these low-dimensional sublattices leads to interesting
physical properties, for example Ag V PS shows 1D magnetic beha-0.5 0.5 3
[26b]viour as the result of the existence of one-dimensional vanadium
chains in the structure. In the compounds Cu In PS and Cu Cr PS , 0.5 0.5 3 0.5 0.5 3
where the triangular Cu’ sublattice is distorted due to the presence of an
[27c]off-centering Jahn-Teller effect, ferroelectricity can be observed.
[28]While the crystal structures of Hg P S and the rhombohedral modi-2 2 6
[19a]fication of Sn P S are closely related to the parent MPS structure 2 2 6 3
[29] [30] [31]type and the compounds SnP S , V PS and In (P S ) crystallize 2 6 0.78 3 4 2 6 3
in MPS defect variants, a completely new atom arrangement can be 3
observed for the hexathiodiphosphates of the tetravalent metal cations
Ti, Zr, Hf, Th and U.
3 [32]The orthorhombic TiP S structure contains the metal cations in an 2 6
octahedral environment, whereas the tetragonal ZrP S structure type 2 6
4+ [33] [34]consists of M (M = Zr, Th, U ) coordinated by eight S atoms in a
square-antiprismatic fashion. Interestingly, the TiP S structure is also 2 6
[35]adopted for HfP S , the result was interpreted as a clue for the 2 6
existence of high-temperature and low-temperature modifications in the
IVM P S system. 2 6
The investigation of the group 5 metal/thiophosphate system resulted
in a multitude of new compounds, many of them crystallizing in low-
dimensional structure types with interesting optical properties. For
[36]example, V PS forms infinite one-dimensional chains while 2D-2 10
[37] [38] [39] [30] [40] [41]NbP S , Nb PS , Nb P S , V PS , VPS and V P S 2 8 2 10 4 2 21 0.78 3 5 10 2 4 13
[42] [43] [44]contain parallel slabs. 3D-NbP S , Ta P S and TaPS consist of 2 8 2 2 11 6
[45]three-dimensional networks. The tantalum thiophosphates Ta P S and 4 4 29
[46]TaPS Se are formal intercalation compounds of TaPS with one-dimen-6 6
sional chalcogenide chains residing in the pores of the host lattice.
A reduction of these frameworks can be achieved by adding alkali
metal chalcogenides to the reactive flux. In many cases, the structure of
the resulting anionic unit can be derived from a ternary compound with
[47]a higher-dimensional network. For example, in the case of K Pd(PS ) , 4 4 2
4-the anion can be obtained by formal excision of the [Pd(PS ) ] unit from 4 2
[48] 6-the layered structure of Pd (PS ) . The Zintl anion [Cr (PS ) ] , which is 3 4 2 2 4 4
[49]found in K Cr (PS ) , can be interpreted as a reduced fragment of the 6 2 4 4
[50]infinite 1D anionic chain found in K Cr (PS ) . 3 2 4 3
The aim of this thesis was the preparation and characterization of new
uranium thiophosphates, which were, until recently, not investiga-
[17b,34]ted. In these compounds, uranium is coordinated by eight ligands,
as most anionic units donate two S atoms, a pseudotetrahedral coordi-
nation was expected resulting in open 3D networks with large pore sizes.
In these cavities, the alkali metal countercations should be able to move
freely, resulting in ionic conductivity and ion exchange properties of the
compounds.
4 2 Comprehensive uranium thiophosphate chemistry:
Framework compounds based on pseudotetrahedrally
coordinated metal centers

Introduction

Actinide chalcogenides, especially those of uranium and thorium
have been investigated for a long time. The first crystal structures were
[1]already described by Zachariasen more than fifty years ago. One of
the intriguing topics in the solid state chemistry of the uranium chalco-
genides is the valence state of uranium. The “reduced” compounds (the
4+term “reduced” refers to the oxidation state U ) such as the mono-
[2] [3] [4] [5]chalcogenides UQ (Q = S, Se, Te), U S , U Te , or UTe bridge the 3 5 7 12 2
gap between localized and itinerant systems due to relative positioning
of the 5 f and 7 s states and the associated localization/delocalization of
[6]the 5 f electrons. The chalcogen-rich compounds such as UTe , U Te , 2 2 3
[7] [8]UQ (Q = Se, Te) or UTe on the other hand have attracted attention 3 5
because they are close to the metal-insulator boundary and thus may
exhibit low-dimensionality, magnetism or charge density wave behavior.
In accordance with the general trends observed for transition elements,
high oxidation states of uranium are not achieved in sulfides, selenides,
or tellurides. Still, in the chalcogen-rich systems the chalcogen’s ability to
catenate has led to formal oxidation state assignments beyond 4+ in
5+ 3- 2- 2- [9]Rb U P Se = Rb (U )(PSe ) P(Se ) (Se ) which are still open to 5 4 4 26 4 4 4 4 2 4 2
[10]debate.
Whereas binary uranium chalcogenides and quaternary uranium
[11]chalcophosphates A U P Q , many of which are accessible from a x y z
reactive polychalcogenide fluxes, are reasonably well characterized,
the information concerning the corresponding ternary chalcogenophos-
[12]phates U P Q is scarce. By using standard solid-state reaction x y z
techniques, four new compounds from the U-P-S system were obtained.
Their crystal structures and physical properties were investigated.
5