Oxoselenates(IV) of the Trivalent Rare-Earth
Elements and Some Derivatives



Von der Fakultät Chemie der Universität Stuttgart
zur Erlangung der Würde eines Doktors der
Naturwissenschaften (Dr. rer. nat.) genehmigte Abhandlung


vorgelegt von
Joseph Wontcheu
aus Bafang (Kamerun)



Hauptberichter: Prof. Dr. Thomas Schleid
Mitberichter: Dr. Paul Keller
weiterer Prüfer: Dr. Klaus Müller
Prüfungsvorsitzender: Prof. Dr. Gerd Becker


Tag der mündlichen Prüfung: 23. April 2004


Institut für Anorganische Chemie der Universität Stuttgart

2004 Pledge 1
Pledge

I certify that the present dissertation entitled:
"Oxoselenates(IV) of the Trivalent Rare-Earth Elements and Some Derivatives" was carried
out without any unlawful devices. I did not use any other than the described literature sources
or technical devices. This work has never been submitted before in this or similar form to any
other university and has not been used for any examination.


Joseph Wontcheu




















2 Acknowledgements
Acknowledgements

I would like to express my profound gratitude to Prof. Dr. Thomas Schleid for giving me
opportunity to do this work in his laboratory and who, despite his charged work programme,
accepted to supervise this dissertation.
I am also greatly indebted to:
Prof. Dr. Paul Keller
Prof. Dr. Klaus Müller
Prof. Dr. Gerd Becker, for the examination.
I would also like to thank: Christof Schneck for always giving me very new literature data
during the course of this work, Dipl. Chem. Sabine Strobel, Dr. Hagen Grossholz, Dr. Steffen
F. Meier for their continuous encouragements, friendliness, care and company and whose
comments were very helpful.

I also thank Sumati Panicker-Otto for correcting the English language.

My gratitudes also go to Dr. Falk Lissner, Dr. Helge Müller Bunz, Dr. Ingo Hartenbach for
the single crystal measurement.

I also wish to thank Prof. Dr. Emmanuel Ngameni, Dr. Ketcha Joseph Mbadcam, Dr. Paul
Mingo Ghogomu (University of Yaounde I), for their advice and support in my application
for the scholarship.

I appreciate and thank all Doctorates students of our research group, whose long experience in
the laboratory was of great relief for me.

My heart-felt thanks go to my friend Mambe Fotsing Clarisse, whose moral support,
generosity, advice, encouragement and permanent contact contributed emensely to the
realisation of this work.

Finally I’m grateful to Flaubert Mbeunkui who kept me company and with whom I shared
more time in Stuttgart.
Table of contents 3
Table of contents

1 Introduction 7
2 Generalities on the working methods 10
2.1 Use of apparatuses 10
2.1.1 Argon glove-box
2.1.2 Inert gas and vacuum equipment 11
2.2 Structure investigations by means of X-ray diffraction 12
2.2.1 Powder diffractometer 12
2.2.2 Single crystal investigations 13
2.2.2.1 Rotation and oscillation photographs 13
2.2.2.2 The Weissenberg camera 14
2.2.2.3 The IPDS (Image Plate Diffraction System) single crystal diffractometer 15
2.2.2.4 The CCD (Charge Coupled Device) single crys 16
2.2.3 Structure solution and refinement 17
2.3 Synthesis methods 19
2.3.1 Chemicals used
2.3.2 Reaction guidance 20
2.3.3 Devices and computer programs 21
3 Oxoselenates(IV) of the trivalent rare-earth elements 23
3.1 Prefaces and synthesis methods 23
3.2 Structure description of the hexagonal Sc [SeO ] 25 2 33
3.2.1 Structural data for the hexagonal Sc [SeO ] 30 2 33
3.3 Structure description of the orthorhombic Ce [SeO ] 33 2 3 3
3.3.1 Structural data for the orthorhombic Ce [SeO ] 36 2 33
3.4 Structure description of the monoclinic Pr [SeO ] 39 2 33
3.4.1 Structural data for the monoclinic Pr [SeO ] 43 2 33
3.5 Structure description of the triclinic M [SeO ] (M = Y, Sm – Ho, Tm – Lu) 50 2 3 3
3.5.1 Structural data for the triclinic M [SeO ] (M = Y; Sm – Ho, Tm – Lu) 56 2 3 3
4 Oxide oxoselenates(IV) of the trivalent rare-earth elements 73
4.1 Prefaces and synthesis methods 73
4.2 Structure description of M O[SeO ] (M = Sm – Tm) 742 3 24 Table of contents
4.3 Structural data for M O[SeO ] (M = Sm – Tm) 80 2 3 2
5 Oxyhalide oxoselenates(IV) of the trivalent rare-earth elements 87
5.1 Compounds of the formula M O Cl[SeO ] (M = Tb, Dy, Er) 88 3 2 3 2
5.1.1 Synthesis of M O Cl[SeO ] (M = Tb, Dy, Er) 88 3 2 3 2
5.1.2 Structure description of the orthorhombic M O Cl[SeO ] (M = Tb, Dy) 89 3 2 3 2
5.1.3 Structure description of the monoclinic M O Cl[SeO ] (M = Er) 90 3 2 3 2
5.1.4 Structural analogies 91
5.1.5 Structural data for M O Cl[SeO ] (M = Tb, Dy, Er) 97 3 2 3 2
5.2 Compounds of the formula M O Cl [SeO ] 102 4 3 2 3 2
5.2.1 Synthesis of M O Cl [SeO ] (M = Er, Yb) 4 3 2 3 2
5.2.2 Structure description of M O Cl [SeO ] (M = Er, Yb) 103 4 3 2 3 2
5.2.3 Structural data for M O Cl [SeO ] 109 4 3 2 3 2
5.3 Structure of Gd O Br [SeO ] and Tb O Cl [SeO ] 120 5 4 3 3 2 5 4 3 3 2
5.3.1 Synthesis of Gd O Br [SeO ] and Tb O Cl [SeO ] 5 4 3 3 2 5 4 3 3 2
5.3.2 Structure description of Gd O Br [SeO ] and Tb O Cl [SeO ] 120 5 4 3 3 2 5 4 3 3 2
5.3.3 Structural data for Gd O Br [SeO ] and Tb O Cl [SeO ] 125 5 4 3 3 2 5 4 3 3 2
5.4 Structure of M O Br [SeO ] (M = La, Pr) and M O Cl [SeO ] (M = Pr, 9 8 3 3 4 9 8 3 3 4
Nd, Sm, Gd) 130
5.4.1 Synthesis methods
5.4.2 Structure description 131
5.4.3 Structural data 137
6 An alkali metal oxoselenate(IV) of a trivalent rare-earth element:
Li Lu [SeO ] 152 3 5 3 9
6.1 Synthesis of Li Lu [SeO ] 3 5 3 9
6.2 Structure description of Li Lu [SeO ] 152 3 5 3 9
6.3 Structural data for Li Lu [SeO ] 157 3 5 3 9
7 An alkali metal halide oxoselenate(IV) of a trivalent rare-earth element:
CsTmCl [SeO ] 166 2 3
7.1 Synthesis of CsTmCl [SeO ] 2 3
7.2 Structure description of CsTmCl [SeO ] 166 2 3
7.3 Structural data for CsTmCl [SeO ] 171 2 3
8 An alkali metal oxyhalide oxoselenate(IV) of a trivalent rare-earth element: Table of contents 5
CsEu O Cl [SeO ] 174 4 3 3 32
8.1 Synthesis of CsEu O Cl [SeO ] 174 4 3 3 3 2
8.2 Structure description of CsEu O Cl [SeO ] 174 4 3 3 3 2
8.3 Structural data for CsEu O Cl [SeO ] 180 4 3 3 3 2
9 Summary and outlook 185
9.1 Results 185
9.1.1 Oxoselenates(IV) of the trivalent rare-earth elements 186
9.1.1.1 The hexagonal Sc [SeO ] 186 2 3 3
9.1.1.2 The orthorhombic Ce [SeO ] 186 2 3 3
9.1.1.3 The monoclinic Pr [SeO ] 187 2 3 3
9.1.1.4 The triclinic M [SeO ] (M = Y; Sm – Lu) 187 2 3 3
9.1.2 Oxide oxoselenates(IV) of the trivalent rare-earth elements 188
9.1.3 Oxide halide oxoselenates(I 189
9.1.3.1 Compounds of the formula M O Cl[SeO ] (M = Tb, Dy, Er) 190 3 2 3 2
9.1.3.2 O Cl [SeO ] (M = Er, Yb) 190 4 3 2 3 2
9.1.3.3 Structure of Gd O Br [SeO ] and Tb O Cl [SeO ] 191 5 4 3 3 2 5 4 3 3 2
9.1.3.4 Structure of M O Br [SeO ] (M = La, Pr) and M O Cl [SeO ] (M = Pr, Nd, 9 8 3 3 4 9 8 3 3 4
Sm, Gd) 191
9.1.4 An alkali metal oxoselenate(IV) of a trivalent rare-earth-element: Li Lu [SeO ] 192 3 5 3 9
9.1.5 An alkali metal halide oxoselenate(IV) of a trivalent rare-earth-element:
CsTmCl [SeO] 193 2 3
9.1.6 An alkali metal oxide halide oxoselenate(IV) of a trivalent rare-earth-element:
CsEu O Cl [SeO ] 4 3 3 3 2
9.2 Outlook 194
10 Zusammenfassung und Ausblick 195
10.1 Ergebnisse 195
10.1.1 Oxoselenate(IV) der dreiwertigen Selten-Erd-Elemente 196
10.1.1.1 Das hexagonale Sc [SeO ] 196 2 3 3
10.1.1.2 Das orthorhombische Ce [SeO ] 197 2 3 3
10.1.1.3 Das monokline Pr [SeO ] 197 2 3 3
10.1.1.4 Das trikline M [SeO ] (M = Y, Sm – Lu) 198 2 3 3
10.1.2 Oxid-Oxoselenate(IV) der dreiwertigen Selten-Erd-Elemente 199
10.1.3 Oxidhalogenid-Oxoselenate(IV) der dreiwertig 200
10.1.3.1 Verbindungen der Formel M O Cl[SeO ] (M = Tb, Dy, Er) 2003 2 3 26 Table of contents
10.1.3.2 Verbindungen der Formel M O Cl [SeO ] (M = Er, Yb) 201 4 3 2 3 2
10.1.3.3 Struktur von Gd O Br [SeO ] und Tb O Cl [SeO ] 202 5 4 3 3 2 5 4 3 3 2
10.1.3.4 Struktur von M O Br [SeO ] (M = La, Pr) und M O Cl [SeO ] (M = Pr, Nd, 9 8 3 3 4 9 8 3 3 4
Sm, Gd) 203
10.1.4 Ein Alkalimetall-Oxoselenate(IV) mit dreiwertigem Selten-Erd-
Element: Li Lu [SeO ] 204 5 5 3 9
10.1.5 Ein Alkalimetall-Halogenide-Oxoselenate(IV) mit dreiwertigem Selten-Erd-
Element: CsTmCl [SeO] 204 2 3
10.1.6 Ein Alkalimetall-Oxihalogenide-Oxoselenate(IV) mit dreiwertigem Selten-Erd-
Element: CsEu O Cl [SeO ] 205 4 3 3 3 2
10.2 Ausblick 206
11 References 207
Curriculum Vitae 212



















Introduction 7
1 Introduction

Since the discovery of rare-earth oxoselenates(IV) (selenites) by Berzelius in 1818 [1],
considerable efforts have been made to gain and characterize in an aqueous solution new rare-
earth hydrated selenites and hydrogenselenites. Of particular interest was the family of
hydrogenselenites MH[SeO ] ⋅ n HO and unusual corresponding mixed-valence 3 2 2
selenates(IV)/selenates(VI) M[HSeO ][SeO ] ⋅ n H O (M = rare-earth element) which have 3 4 2
been known for some time [2 – 15]. Then again, anhydrous and non-hydrogenselenates of
trivalent lanthanides were synthesized by many authors a few years ago. Namely compounds
with the structural formula M [SeO ] (M = La, Nd, Er) which have been described as 2 3 3
1 2−containing ψ -tetrahedral [SeO ] groups and their structure strongly influenced by the 3
4+steriochemically ''lone pair'' of electron at the Se cations. Since the La compound
crystallized with the orthorhombic system (Pnma) [16, 17], Nd [SeO ] was monoclinic 2 3 3
(P2 /n) [18] whereas Er [SeO ] was triclinic (P 1) [19]. By means of phase diagram 1 2 3 3
supported by thermal analysis (DTA), thermogravimetric (TGA), differential scanning
calorimetric (DSC) and IR spectroscopy, Oppermann and co-workers [20 – 24], Gosponidov
et al. [25 – 28] as well as De Pedro et al. [29, 30] had suggested the presence of similar
M [SeO ] phase obtained as homogeneous powder in the temperature range of 550 – 650°C. 2 3 3
Up to this temperature their decompose losing SeO due to the high stability of the oxidation 2
state IV for the selenium, leading to the formation of phases with the composition M Se O 2 2 7
obtained at the temperature of about 800°C. Details concerning crystals structure of the latter
remind unknown until now despite Giester [31], Jones et al. [32] succeeded in isolating
similar compounds with trivalent transition metals, to be precise Fe Se O and Au Se O 2 2 7 2 2 7
1 2−(according to Fe O[SeO ] and Au O[SeO ] due to the presence of a ψ -tetrahedral [SeO ] 2 3 2 2 3 2 3
units with additional oxygen atoms which are not coordinated to any selenium atom). A phase
with the same situation in the homologous M O /TeO system has also been described very 2 3 2
recently for the oxotellurate(IV) Pr O[TeO ] as adopting the pyrochlore-type crystal 2 3 2
4+structure [33] without stereochemical activity of the lone-pair at Te .
During the last ten years, many works have been done in order to characterize anhydrous
halide oxoselenates(IV) of trivalent lanthanide. In this way Wickleder and co-workers
elucidated the structure of some fluoride oxoselenates for instance M F[SeO ] (M = Nd, Sm, 3 3 4
Gd, Dy) crystallizing with the acentric space group P6 mc [19, 34] as well as LaF[SeO ] 3 3
(monoclinic; P2 /c) [16], these being the first rare-earth halides oxoselenates(IV) although a18 Introduction
chloride oxoselenate of trivalent bismuth BiCl[SeO ] had been pointed out before by 3
Berdonosov et al. [35]. The formation of acentric fluoride oxoselenates(IV) encouraged
corresponding authors to investigate also chlorides. Thus they have successfully synthesized
as single crystals the first rare-earth chloride oxoselenates(IV) explicitely NdCl[SeO ], 3
ErCl[SeO ] and HoCl[SeO ] which crystallized orthorhombically in the space group Pnma 3 3
[36]. These results then came to confirm investigations made by Oppermann et al. which had
reported the presence of three compounds SmClSeO , SmClSe O and SmClSe O from the 3 2 5 3 7
phase diagram of the system SmOCl/SeO [37]. 2
In the crystal chemistry of the above-mentioned oxoselenates(IV), excepted those of
Fe O[SeO ] , Au O[SeO ] and Pr O[TeO ] , descriptions of cations as central atoms and 2 3 2 2 3 2 2 3 2
anions as ligands are given. However, Krivovichev et al. have analyzed very recently some
transition metals oxoselenates(IV) on the basis of anion coordinations. This is particularly
suitable in the description of compounds such as Cu O Cl [SeO ] and Cu O Cl [SeO ] 9 2 6 3 4 5 2 2 3 2
2−which contain ''additional'' oxygen atoms, i.e. atoms not included into the usual [SeO ] 3
complex anions. The ''additional'' oxygen atoms have a tetrahedral coordination environment
6+of metal atoms, therefore being centers in [OCu ] cationic complexes. Relatively high bond 4
strength in oxocentered tetrahedra allows authors to suggest their selection as independent
structural subunits in those compounds [38, 39]. Furthermore, oxocentered [OM ]-tetrahedral 4
units (M = transition metal or rare-earth element) are well known in metal-organic
compounds as polynuclear metal complexes with so-called µ -bridging oxygen atoms. Their 4
structures have been subjected to extensive investigations because of their interesting
magnetic properties due to the metal-metal interaction within the [OM ] tetrahedra [40, 41]. 4
In addition to oxoselenates(IV) and halide oxoselenates(IV) of trivalent lanthanide, oxide
oxoselenates(IV) and oxyhalide oxoselenates(IV) of trivalent or divalent transition metals and
obviously the above-mentioned hydrated and hydrogenselenates, many efforts have been
undertaken in order to synthesize mixed metal phases containing both lanthanides and alkali
or transition metals. But their amount is quite limited to date although Effenberger described a
number of mixed transition metals oxoselenates(IV) with main group elements for example
BaCu[SeO ] and SrCu[SeO ] [42], Sr Cu[SeO ] [43], PbCu [SeO ] [44] and Bi Cu[SeO ] 3 2 3 2 2 3 3 2 3 3 2 3 4
[45]. The presence of both heavier lanthanoids and another metal in anhydrous
oxoselenates(IV) has been studied less extensively, the only compounds stated in the literature
being NaY[SeO ] and NaLa[SeO ] [46], as well as La Cu[SeO ] (isostructural with 3 2 3 2 2 3
Bi Cu[SeO ] ) [47]. In the same approach the combination of magnetic activities of d- and f-2 3 4
metals in the same oxoselenates(IV) compounds has interested Wickleder during the last twoIntroduction 9
years, those compounds are of fundamental interest in solid-state chemistry and materials
science, besides they have the potential for useful physical properties. Novel mixed rare-earth
and transition metals chloride oxoselenates(IV) have afterwards been synthesized and
structurally characterized, to be exact CuGdCl[SeO ] , MnNdCl[SeO ] , CoNd Cl [SeO ] 3 2 3 2 10 8 3 12
and NiNd Cl [SeO ] [48] for these reasons. 10 8 3 12
4+The free non-binding electron pairs (''lone pair'') at the Se cations always observed in those
3+ 3+ 3+compounds, materials containing high coordinated trivalent rare-earth cations (Sc , Y ; La
3+ 3+ 3+ 2−– Nd , Sm – Lu ) in combination with [SeO ] groups and additional oxygen not 3
coordinated to any selenium atom but forming [OM ] tetrahedra (M = rare-earth elements) as 4
well as additional halide anions may be an excellent combination in the search for novel
asymmetric structures. Such materials could have useful non-linear optical properties with
2−potential applications in electro-optical devices. Furthermore, the oxoanion [SeO ] holding a 3
stereochemically active lone pair of electrons may have a tendency for aligning in the solid
state to end up polar structures. This feature increases a number of important physical
properties including second harmonic generation (SHG) and ferroelectric behaviour [49 – 51].
2−On the other hand, [SeO ] anions can provide several advantages in that they could be both 3
better donor ligands for metals (vide infra) and could be thermally very robust. Thus, their
structures seem to be of interest and we are now exploring in our laboratory the solid-state
chemistry of such compounds. It is the aim of this work, which contains three main parts.
While the first one concerns generalities on the working methods, the second offers the
process for single crystals syntheses and therefore the precondition for their structure
determination and description, which the third one extensively deals with.