The Many Faces of Rare Earth Carbodiimide Compounds

Transcription

1 The Many Faces of Rare Earth Carbodiimide Compounds Hans-Juergen Meyer To cite this version: Hans-Juergen Meyer. The Many Faces of Rare Earth Carbodiimide Compounds. Zeitschrift für Anorganische und Allgemeine Chemie, 00, (), pp.. <.0/zaac.0000>. <hal-000> HAL Id: hal Submitted on Sep 0 HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

2 ZAAC The Many Faces of Rare Earth Carbodiimide Compounds Journal: Zeitschrift für Anorganische und Allgemeine Chemie Manuscript ID: zaac.0000.r Wiley - Manuscript type: Article Date Submitted by the Author: -May-00 Complete List of Authors: Meyer, Hans-Juergen Keywords: Rare earth, Carbodiimide, Fluoride, Metathesis

3 Page of ZAAC The Many Faces of Rare Earth Carbodiimide Compounds Leonid Unverfehrt, Markus Ströbele, Jochen Glaser, and H.-Jürgen Meyer* Dedicated to Professor Martin Jansen on the Occasion of his 0th Birthday Keywords: Rare earth; Fluoride; Carbodiimide; Metathesis Abstract. Solid state metathesis reactions have been established as a successful tool in syntheses of rare earth carbodiimide compounds. Current results evidence the new compounds LiRE(CN ) with RE = La, Ce and the carbodiimide nitride Ce (CN ) N. LiRE(CN ) compounds were synthesized by solid state metathesis reactions between REF and Li (CN ) in : molar ratio. Ce (CN ) N was obtained via thermal conversion of LiCe(CN ). Crystal structures of LiLa(CN ) and Ce (CN ) N were determined from X-ray single crystal data (LiLa(CN ) : P /m, a =.() pm, b =.() pm, c =.0() pm, β =.() ; Ce (CN ) N: P, a =.() pm, b = 0.() pm, c =.() pm) and LiCe(CN ) was assigned from indexed X-ray powder diffraction data (LiCe(CN ) : a =.() pm, b =.0() pm, c = 0.() pm, β =.() ). The crystal structure of LiLa(CN ) represents a layer-like arrangement of ions as typical for this type of compounds. The crystal structure of Ce (CN ) N reveals chains of [NCe ] tetrahedra running parallel to each other, and trigonal prismatic to trigonal antiprismatic arrangements of six distinctly interconnected [Ce -NCN-Ce ] units. Both structures contain (CN ) - ions deviating from their ideal D h symmetry, with C N distances ranging between and pm and N C N angles near 0. * Prof. Dr. H.-J. Meyer juergen.meyer@uni-tuebingen.de [a] Abteilung für Festkörperchemie und Theoretische Anorganische Chemie Institut für Anorganische Chemie Ob dem Himmelreich Eberhard-Karls-Universität Tübingen D-0 Tübingen, Germany

4 ZAAC Page of Introduction Rare earth (RE) carbodiimides are an emerging and rapidly growing group of compounds. Dioxide monocarbodiimides were reported in presumably synthesized under fortuitous conditions with the aid of a graphite container serving as a carbon source for the carbodiimide ion of La O (CN ) []. Two distinct structures are reported for RE O (CN ). Tetragonal La O (CN ) is reported to contain axially-parallel disordered [N=C=N] - ions, whereas in trigonal RE O (CN ) with RE = Ce Gd, Dy, Ho, Er, Tm, Yb [,] the alignment of [N=C=N] - ions follows the threefold axis. A great deal of rare earth carbodiimide or infrequently cyanamide compounds was synthesized following solid state metathesis reactions between rare earth trihalides and lithium carbodiimide. Upon heating these mixtures, solid state metathesis reactions reveal their characteristics, with an ignition coming about in a temperature regime around 0 to 0 C when double exchange of ions is being completed. A flux can be used in reactions to lower the reaction temperature and to improve the crystal growth of products. A series of quasi-binary carbodiimides RE (CN ) [-] with trivalent rare earth ions (RE = Y Lu, except Pm, La) has been established by this route as well as some families of multinary carbodiimides (or in some cases cyanamides) represented by the formulas REX(CN ) (X = Cl, F) [,], RE X(CN )N (X = Cl, Br, I) [,], ARE X (CN ) (A = Li, X = F), and two more compositions being reported in this work. Carbodiimides or cyanamides containing divalent europium ions were obtained for Eu(CN ) [] through high temperature reactions, and through halide-based flux reactions for a number of multinary europium compounds []. The synthesis of new rare earth compounds containing nitrides or carbodiimides has received considerable attention due to the luminescence properties of doped compounds and their potential in solid state lightning, but also for other perspectives. The luminescence behaviour of lanthanide-doped carbodiimide compounds has been studied for RE O (CN ):Ln [] and Y O (CN ):Eu [] in relation to the well-known red light emitter Y O S:Eu. For compounds Gd (CN ) :Ln with Ln = Ce, Tb a broad yellow emission has been obtained. Furthermore, the dimorphic character of structures has been demonstrated for Y O (CN ) and by pressure induced phase transition for Tm (CN ) []. Still there are some homologous examples of RE compounds missing in carbodiimide containing families. Some of them can be assumed isotypic and others have just not been attempted to make. A challenging example may be the missing compound La (CN ) []. The rational approach of solid state metathesis reactions has been successfully used as a conceptual tool for the discovery of some novel [] compounds and turns out to be a promising endeavour in solid state synthesis.

5 Page of ZAAC Experimental Section Synthesis of Li (CN ) Li (CN ) was prepared via reaction of 00 mg (ca. 0 mmol) Li N (Alfa Aesar,. %) with an excess of 00 mg (ca. mmol) melamine (Fluka, > %, purum) [] following the reaction equation: Li N + C N (NH ) Li (CN ) + NH The reaction mixture was carefully homogenized in an agate mortar under argon atmosphere (glove box) and placed into a silver boat. An argon flooded transfer shuttle was used to replace the silver boat from the glove box into a silica tube, being inserted into the silica tube under nitrogen counter current. The reaction mixture was heated up (ca. C/min) in a silica tube under nitrogen flow (ca. 00 ml/min) to 0 C and remained at this temperature for about ten minutes before it was further heated up very slowly ( C/min.) to 0 C. From 0 C the temperature was further raised ( C/min.) to 00 C to remove the excess of melamine from the product. Afterwards the reaction was allowed to cool down to room temperature and the crystalline powder was inspected by XRD. The beginning of the reaction was obtained at 0 C, as indicated by the development of NH at the exhaust pipe of the silica tube. Note that faster heating-up rates may generate a strongly exothermic reaction when reaching temperatures near 0 00 C, thereby expelling material from the reaction vessel. If Li NH was present in the product, the mixture was carefully ground with ca. 0 mg melamine and heated ( C/min.) to 00 C. Preparations of Li (CN ) proceeded quantitatively and yielded a single phase product according to powder XRD. Synthesis of LiLa(CN ) and LiCe(CN ) Rare earth trifluorides (REF ) were synthesized as previously reported []. Solid state metathesis reactions were performed between REX (X = F, Cl) and Li (CN ). Reactions of LaCl (ABCR,. %) were carried out in flame sealed silica ampoules and reactions with trifluorides in copper ampoules ( cm long pieces, inner diameter ca. mm, thickness of the wall ca. mm, cleaned with HCl). Copper tubes were sealed first from one side by arcmelting, loaded with starting materials under argon (glove box) and than sealed from the other side, before they were flame sealed into silica tubing. Reaction containers were charged with : molar mixtures of REX (RE = La, Ce; X = F, Cl) and Li (CN ) under dry argon atmosphere inside a glove box. The reaction vessels were placed into a tube furnace and reacted at 0 0 C for two days before they were allowed to cool down to room temperature. The course of reactions can be specified by the following equation:

6 ZAAC Page of REX + Li (CN ) LiRE(CN ) + LiX Reactions departing from REF yielded colourless powders of LiLa(CN ) and yellow powders of LiCe(CN ) at 00 C besides coproduced LiF. Reactions with LaCl and Li (CN ) yielded LiLa(CN ) in the temperature range 0 0 C. Product treatments of LiCe(CN ) and LiF above 0 C gave rise to the decomposition into a crystalline product containing the new compound Ce (CN ) N. All compounds behave moderately stable in air and against hydrolysis. Reaction products were washed in water, dried with acetone, and inspected by powder XRD. X-Ray Powder Diffraction The XRPD patterns of the reaction products were collected with a Stadi-P (Stoe, Darmstadt) powder diffractometer using Cu-K α radiation (germanium monochromator). No significant reflections of any side phase could be identified after indexing the patterns of LiLa(CN ) and LiCe(CN ) by using the program system WinXPow []. The patterns were indexed monoclinically with a =.() pm, b =.() pm, c =.() pm, β =.() yielding V = 0.() Å based on 0 single indexed lines for LiLa(CN ) ; and a =.() pm, b =.0() pm, c = 0.() pm, β =.() yielding V = 00.() Å based on single indexed lines for LiCe(CN ). X-Ray Single-Crystal Diffraction Colourless needle shaped single-crystals of LiLa(CN ) and orange crystals of Ce (CN ) N were selected and mounted on the tips of glass fibers for single-crystal X-ray diffraction measurements (Stoe, IPDS I diffractometer, graphite monochromated Mo-K α radiation, λ(mo- K α ) =.0 pm) performed at () K for LiLa(CN ) and at room temperature for Ce (CN ) N (Table ). Intensities were corrected for Lorentz factors, polarization and absorption effects by the IPDS software X-Red/X-Shape. The crystal structure solutions and anisotropic refinements of all atoms of LiLa(CN ) and Ce (CN ) N were obtained with the program SHELX- package []. Crystallographic data are given in Table, atom positions are listed in Table, and selected bond lengths are displayed in Table. Further details on the crystal structure investigations can be obtained from Fachinformationszentrum Karlsruhe, Eggenstein-Leopoldshafen, Germany (fax: (+)-0-; crysdata@fiz-karlsruhe.de on quoting the CSD number 00 of LiLa(CN ) and CSD number 00 of Ce (CN ) N. Results and Discussion During the past, the synthesis of Li (CN ) has been accomplished in several ways, i.e. through ammonolysis of Li (CO ) [0, ], from Li C and Li N [], or by reaction of Li(NH ) or

7 Page of ZAAC Li N with melamine []. According to our experiments, the synthesis from Li N and melamine described by Becker and Jansen is a useful and time efficient route for the preparation of Li (CN ). A selective choice of starting materials, i.e. pure rare earth trihalide and Li (CN ) is of course crucial in order to drive solid state metathesis reactions towards desired products. The employment of various compositions of these starting materials has been successfully applied to synthesize various compositions of rare earth carbodiimide compounds such as RE (CN ), REX(CN ) (X = Cl, F), ARE X (CN ) (A = Li, X = F), and RE X(CN )N (X = Cl, Br, I), now being attributed by the new composition ARE(CN ) (A = Li; RE = La, Ce). This composition was indeed expected to exist, not only with lithium but also with other monovalent cations. On the other hand, the carbodiimide nitride RE (CN ) N was obtained unintentionally from thermal decomposition of LiCe(CN ). Corresponding rare earth nitridoborate nitrides, e.g. Ce +x (B N )N x with x =,, where synthesized under multilateral solid state metathesis conditions departing from appropriate amounts of RECl, Li (BN ), Li N and Li as reducing agent []. Many carbodiimide compounds appear to be thermally labile at temperatures above 00 C. This is of course one reason that these compounds can hardly be obtained from high temperature reactions of elements but there are some exceptions [, ]. LaCl(CN ) was previously shown to transform into La Cl(CN )N on heating up to temperatures above 0 C. A direct synthesis of RE X(CN )N (X = Cl, Br, I) compounds was accomplished by using multilateral metathesis reactions departing from REX, Li (CN ), and Li N, or from other combinations of compounds []. A similar decomposition as for LaCl(CN ) is obtained for LiCe(CN ) after being heated at temperatures around 0 C. As noted from the previous example, a decomposition of only a portion of (CN ) - ions is the result of the reaction to yield crystalline powder and single-crystals of Ce (CN ) N. A feasible solid state metathesis synthesis for this type of rare earth carbodiimide nitride compounds is at hand. Most rare earth carbodiimide compounds known to date can be considered to contain nearly linear and nearly symmetrical [N=C=N] - ions, but there can be deviations from the ideal D h symmetry in structures, frequently due to non-equivalent environments of the two terminal nitrogen atoms. Departing from the two non-equivalent bond lengths within the cyanamide molecule H C C N of roughly pm and pm we note less distinct or sometimes equivalent C N distances within [NCN] - ions of rare earth carbodiimide compounds, typically around pm as present in the structure of lithium carbodiimide. A pronounced difference was found in the [NCN] - ion of LaCl(CN ) with C N bond lengths of 0.() and.() pm, pointing out that it is difficult to make up a fixed borderline for the notation as a carbodiimide or cyanamide ion.

8 ZAAC Page of The crystal structure of LiLa(CN ) resembles layers of La + ions and two differently aligned (CN ) - ions, as displayed in Figure. A similar difference in C N bond lengths as in LaCl(CN ) is obtained in one of the two crystallographically distinct [NCN] - ions contained in the structure of LiLa(CN ), of which one set of N() C() N() bond lengths is.0() and.() pm and the second set N() C() N() being 0.() and.() pm. In addition, the N C N bond angles of both ions are refined near being close to 0 which is regarded for a carbodiimide ion (Table ). Lithium ions are situated in a slightly distorted tetrahedral environment of nitrogen atoms having Li N distances within the interval of 0 pm. The lanthanum ion is surrounded by eight nitrogen atoms forming a bicapped trigonal prism, shown in Figure, having La N distances of pm. Ce (CN ) N is the first example of a rare earth carbodiimide nitride. In the light of more RE (CN ) N compounds having this composition, the structure of this compound will be presented here only briefly. The crystal structure of Ce (CN ) N was refined in the noncentrosymmetric space group P, being rare in solid state chemistry. The unit cell of Ce (CN ) N contains eight formula units, accommodating six crystallographically independent cerium ions, six independent carbodiimide anions, and two independent nitride ions (Figure ). The two nitride ions (N() and N()) are surrounded tetrahedrally by cerium ions with Ce N distances between.() and.() pm. These tetrahedra are interconnected in an alternating fashion by shared corners and edges to form chains parallel to the crystallographic y direction. The six [NCN] - ions exhibit C N distances ranging from to pm, being almost linear with N C N angles around (Table ). Environments of [NCN] - ions compromise more or less distorted trigonal prismatic or trigonal antiprismatic surroundings with cerium ions, all displayed in Figure. The six crystallographically distinct cerium ions are shown in Figure, with coordination numbers between seven and eight with N atoms of both types, N - and [NCN] -. Displayed Ce N distances with nitrogen atoms of [NCN] - ions range from 0.() to 0.() pm, but there are also short contacts with carbon atoms in the order of 00 pm. Only one cerium ion (Ce()) remains without a contact to a nitride ion. Acknowledgement. Support of this research by the Deutsche Forschungsgemeinschaft (Bonn) through the project Nitridocarbonate is gratefully acknowledged.

9 Page of ZAAC References [] Y. Hashimoto, M. Takahashi, S. Kikkawa, F. Kanamaru, J. Solid State Chem.,, ; Y. Hashimoto, M. Takahashi, S. Kikkawa, F. Kanamaru, Chem. Soc. Japan, Chem. Letters,,. [] Y. Hashimoto, M. Takahashi, S. Kikkawa, F. Kanamaru, J. Solid State Chem.,,. [] M. Li, W. Yuan, J. Wang, C. Gu, H. Zhao, Powder Diffract. 00,,. [] M. Neukirch, S. Tragl, H.-J. Meyer, Inorg. Chem. 00,,. [] O. Reckeweg, T. Schleid, F.J. DiSalvo, Z. Naturforsch. 00, b,. [] J. Glaser, L. Unverfehrt, H. Bettentrup, G. Heymann, H. Huppertz, T. Jüstel, H.-J. Meyer, Inorg. Chem. 00,,. [] R. Srinivasan, J. Glaser, S. Tragl, H.-J. Meyer, Z. Anorg. Allg. Chem. 00,,. [] L. Unverfehrt, J. Glaser, M. Ströbele, S. Tragl, K. Gibson, H.-J. Meyer, Z. Anorg. Allg. Chem. 00,,. [] R. Srinivasan, M. Ströbele, H.-J. Meyer, Inorg. Chem. 00,, 0. [] R. Srinivasan, Dissertation, Univ. Tübingen, 00. [] O. Reckeweg, F.J. DiSalvo, Z. Anorg. Allg. Chem. 00,,. [] W. Liao, U. Englert, R. Dronskowski, European J. Inorg. Chem. 00,, ; W. Liao, R Dronskowski, Z. Anorg. Allg. Chem. 00,, ; W. Liao, R. Dronskowski, Z. Anorg. Allg. Chem. 00,, ; W. Liao, C. Hu, R. Kremer, R. Dronskowski, Inorg. Chem. 00,,. [] E. Säilynoja, M. Lastusaari, J. Hölsä, P. Porcher, J. Luminescence,, ; J. Hölsä, R.-J. Lamminmäki, M. Lastusaari, E. Säilynoja, P. Porcher, Spectrochim. Acta A,, 0; M. Takahashi, Y. Hashimoto, S. Kikkawa, H. Kobayashi, Zairyo 000,, 0. [] J. Sindlinger, J. Glaser, H. Bettentrup, T. Jüstel, H.-J. Meyer, Z. Anorg. Allg. Chem. 00,,. [] H. Hartmann, W. Eckelmann, Z. Anorg. Allg. Chem.,,. [] J. Glaser, H.-J. Meyer, Angew. Chem. 00, 0, ; Angew. Chem. Engl. Ed. 00,,. [] M. Becker, M. Jansen, Z. Allg. Anorg. Chem.,,. [] WinXPow, Version.: Diffractometer Software, Stoe & Cie GmbH, Darmstadt, Germany, 00. [] Sheldrick, G. M. SHELX-: Program Package for Crystal Structure Determination, University of Göttingen, Göttingen, Germany,. [0] A. Perret, Bl. Soc. Ind. Mulhouse,,.

10 ZAAC Page of [] M.G. Down, M.J. Haley, P. Hubberstey, R.J. Pulham, A.E. Thunder, J. Chem. Soc., Dalton Trans., 0. [] B. Blaschkowski, H. Jing, H.-J. Meyer, Angew. Chem. 00,, ; Angew. Chem. Int. Ed. Engl. 00,,. [] J.K. Bendyna, P. Höhn, W. Schnelle, R. Kniep, Sci Techn. Adv. Mat. 00,,.

11 Page of ZAAC Table Single-crystal data from structure refinements of LiLa(CN ) and Ce (CN ) N. Empirical formula LiLa(CN ) Ce (CN ) N Formula weight / g/mol.. Crystal system monoclinic orthorhombic Space group P /m (No. ) P (No. ) Unit cell dimensions /pm a =.() b =.() c =.0() a =.() b = 0.() c =.() Angle/ β =.() Volume / pm 0.().() Z Temperature /K () () Density (calculated) / g cm -.. Absorption coefficient /mm -.. F(000) 00 Crystal description colourless needle orange-red needle Crystal size /mm 0. x 0.0 x x 0.0 x 0.0 Θ range for data collection /. to..0 to. Index range - h ; - k ; - l - h, - k, -0 l 0 Reflections collected Independent reflections 0 R int Data / Parameters / 0 / Goodness-of-fit on F. 0. R indices [I > σ(i)] R = 0.0, wr = 0.0 R = 0.0, wr = 0.00 R indices (all data) R = 0.0, wr = 0.0 R = 0.0, wr = 0.0 Largest diff. peak and hole e Å -.0 and and -0. CSD-Number 00 00

12 ZAAC Page of Table Atom positions and isotropic displacement parameters (Å ) of LiLa(CN ) and Ce (CN ) N. x y z U eq LiLa(CN ) La() 0.() ¼ 0.() 0.0() N() 0.0() -¼ 0.() 0.0() C() 0.() -¼ 0.() 0.0() N() 0.0() ¼ -0.0() 0.0() N() 0.() ¼ 0.0() 0.0() C() 0.0() -¼ 0.() 0.0() N() 0.0() -¼ 0.() 0.0() Li() 0.() -¼ 0.() 0.00() Ce (CN ) N Ce() 0.() 0.0() 0.() 0.0() Ce() 0.() 0.() 0.() 0.0() Ce() 0.0() -0.0() 0.() 0.0() Ce() 0.() 0.() 0.() 0.0() Ce() 0.() 0.0() 0.() 0.0() Ce() 0.() 0.() 0.0() 0.0() N() 0.() 0.0() 0.0() 0.0() C() -0.() 0.0() 0.0() 0.0() N() -0.0() 0.0() 0.0() 0.0() N() 0.() 0.0() -0.0() 0.0() C() 0.() 0.() 0.00() 0.0() N() 0.() 0.() 0.00() 0.0() N() 0.() -0.0() 0.() 0.0() C() 0.0() -0.0() 0.() 0.0() N() 0.0() -0.00() 0.0() 0.0() N() 0.0() 0.() 0.() 0.0() C() 0.() 0.() 0.00() 0.0() N() 0.() 0.() 0.() 0.0() N() -0.0() 0.() 0.0() 0.0() C() -0.() 0.0() 0.0() 0.0() N() -0.() 0.() 0.() 0.0() N() 0.() 0.0() 0.() 0.0() C() 0.0() 0.0() 0.0() 0.0() N() 0.0() -0.0() 0.() 0.0() N() 0.() 0.() 0.() 0.0() N() 0.() 0.00() 0.00() 0.0()

13 Page of ZAAC Table Selected bond lengths (in pm), angles (, in ), and multiplicities in LiLa(CN ) and Ce (CN ) N. LiLa(CN ) La() N().() x La() N().() x,.() x La() N().() La() N() 0.() x Li() N() () Li() N().() x Li() N() 0() N() C() N().0(),.() N() C() N().() N() C() N() 0.(),.() N() C() N().() Ce (CN ) N Ce() N().0() Ce() N().() Ce() N().() Ce() N().() Ce() N().0() Ce() N().() Ce() N().() Ce() N().() Ce N (NCN) 0.() 0.() N() C() N() (), () N() C() N() () N() C() N() (), () N() C() N().() N() C() N() (), () N() C() N() () N() C() N() (), () N() C() N().() N() C() N() (), () N() C() N() () N() C() N() (), () N() C() N() ()

14 ZAAC Page of Figure. Monoclinic crystal structure of LiLa(CN ). Figure. Environment of the lanthanum ion in LiLa(CN ).

15 Page of ZAAC Figure. Orthorhombic crystal structure of Ce(CN)N. Figure. Environments of the six independent carbodiimide ions in Ce(CN)N.

16 ZAAC Page of Figure. Environments of the six independent cerium ions in Ce (CN ) N.