Li4Ca3Si2N6 and Li4Sr3Si2N6 - Quaternary Lithium Nitridosilicates with Isolated [Si2N6]10- Ions

Transcription

1 LiCaSiN and LiSrSiN - Quaternary Lithium Nitridosilicates with Isolated [SiN]0- Ions Sandro Pagano, Saskia Lupart, Sebastian Schmiechen, Wolfgang Schnick To cite this version: Sandro Pagano, Saskia Lupart, Sebastian Schmiechen, Wolfgang Schnick. LiCaSiN and LiSrSiN - Quaternary Lithium Nitridosilicates with Isolated [SiN]0- Ions. Zeitschrift für Anorganische und Allgemeine Chemie, 00, (), pp.0. <0.00/zaac.0000>. <hal- 00> HAL Id: hal-00 Submitted on Jan 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 LiCaSiN and LiSrSiN - Quaternary Lithium Nitridosilicates with Isolated [SiN]0- Ions Journal: Zeitschrift für Anorganische und Allgemeine Chemie Manuscript ID: zaac.0000.r Wiley - Manuscript type: Communication Date Submitted by the Author: -May-00 Complete List of Authors: Pagano, Sandro; LMU Munich, Chemistry Lupart, Saskia; LMU Munich, Chemistry Schmiechen, Sebastian; LMU Munich, Chemistry Schnick, Wolfgang; LMU Munich, Chemistry Keywords: Lithium, Fluxing agent, Strontium, Nitridosilicate, X-ray diffraction

3 Page of ZAAC Li Ca Si N and Li Sr Si N - Quaternary Lithium Nitridosilicates with Isolated [Si N ] 0- Ions Sandro Pagano, [a] Saskia Lupart, [a] Sebastian Schmiechen, [a] and Wolfgang Schnick [a]* Department Chemie der Ludwig-Maximilians-Universität München Prof. Dr. W. Schnick Department Chemie Lehrstuhl für Anorganische Festkörperchemie Ludwig Maximilians Universität München Butenandtstraße (D) D München, Germany Fax: + (0) 0 0 E mail: wolfgang.schnick@uni muenchen.de

4 ZAAC Page of Abstract The isotypic nitridosilicates Li Ca Si N and Li Sr Si N were synthesized by reaction of Sr or Ca with Si(NH) and additional excess of Li N in weld shut tantalum ampoules. The crystal structure, which has been solved by single-crystal X-ray diffraction (Li Sr Si N : C/m, Z =, a =.(), b =.(), c =.00() Å, β = 0.(), wr = 0.00) is made up from isolated [Si N ] 0- ions and is isotypic to Li Sr Ge N. The bonding angels and distances within the edge-sharing [Si N ] 0- double-tetrahedra are strongly dependent on the lewis acidity of the counter ions. This finding is discussed in relation to the compounds Ca Si N and Ba Si N which also exhibit isolated [Si N ] 0- ions. Keywords Lithium; Fluxing Agent; Strontium; Nitridosilicates; X-Ray diffraction Introduction Recently, we have reported on the utilization of liquid lithium for the synthesis of quaternary lithium nitridosilicates. The ability of liquid lithium to dissolve a variety of metals, silicon and nitrogen allows for a controlled synthesis of group-type silicates, chain-like anions up to frameworks by simply adjusting the Li N content, the nitrogen pressure (LiN ) and the reaction temperature. [] By adding an excess of Li N to the reaction mixture higher condensation of the [SiN ]-tetrahedra network is suppressed and the lowest degree of condensation for nitridosilicates is observed. Orthosilicate-like isolated [SiN ] - tetrahedra, which might occur in the compound Li SiN are not yet structurally verified. [,] Consequently, up to now group-type silicates made up from edge-sharing [Si N ] 0- doubletetrahedra represent nitridosilicates with the lowest degree of condensation characterized by single-crystal X-ray diffractometry so far. Identical building blocks have already been reported for Ba Si N synthesized by DiSalvo et al. in a sodium flux and Ca Si N obtained via solid-state reaction of Ca N and Si. [,] In this contribution we report on synthesis and structural features of Li Ca Si N and on the isotypic Sr-phase. Results and discussion

5 Page of ZAAC Li Ca Si N and Li Sr Si N were synthesized from the corresponding metals, Si(NH) and an excess of Li N in weld shut tantalum ampoules at 00 C. Addition of Li metal as a fluxing agent was not essential for the synthesis of suitable single crystals. This might be due to Li N acting as a flux as it melts above C under autogenous nitrogen pressure in closed systems. [] The title compounds are not stable against air and moisture and were handled under inert gas atmosphere. The approximate atomic ratio of heavy elements (Ca/Sr and Si) was determined by energy dispersive X-ray microanalysis. Li Ca Si N and Li Sr Si N crystallize in the monoclinic space group C/m with two formula units per unit cell (for details see Table ). The unit cell and coordination spheres of Li Sr Si N are depicted in Figure and Figure, respectively. The asymmetric unit consist of two Sr and N sites, one Si and Li site named according to Figure. The structure is built up from isolated [Si N ] 0- ions and is isotypic to that of the nitridogermanate Li Sr Ge N. [] Group-like [Si N ] 0- ions have already been reported for Ca Si N and Ba Si N. [,] Due to the edge-sharing of [SiN ] tetrahedra, the tetrahedra angels are distorted to values of - (N-Si-N) for all compounds (cf. Table ). The corresponding Si-N bonds are elongated from. Å to.. Å, resulting in quite short Si-Si distances ranging from.0() Å in Ca Si N to.() Å in Ba Si N. [,] The Si-Si distances of Li Ca Si N and Li Sr Si N are ranging in between these values (cf. Table ). Regarding the series of isolated [Si N ] 0- ions one could assume that the distortion of the square built up from Si and N is dependent on the lewis acidity of the surrounding metal ions. The smaller ionic radius of Ca + compared to Sr + and Ba + leads to shorter N-metal distances and the higher lewis acidity results in a displacement of N from the ideal square built up from Si and N. Consequently, the angels Si-N-Si are increasing from.() in Ba Si N,.() in Li Sr Si N to.() in Ca Si N. [,] Presumably, this effect is responsible for the decrease of the distances Si-Si in the sequence Ba +, Sr + to Ca + (Table ). The distances N-EA (EA = alkaline earth) in Li Ca Si N and Li Sr Si N are in the typical range for alkaline earth nitrides. [] In Li Ca Si N both metal sites are coordinated by six N-atoms, whereas in Li Sr Si N Sr exhibits a + coordination. The coordination spheres (cf. Figure ) were assigned by lattice energy calculations (MAPLE; Madelung part of lattice energie). [,0] In both compounds Li is coordinated by four N-atoms in distorted tetrahedral fashion (0- ) with typical distances Li-N (values within the sum of the ionic radii). [,] The smaller lattice parameters of Li Ca Si N also lead to significantly shorter Li-N distances (Li-N:.(),.0(),.() Å, Li-N:.() Å). Edgesharing of [LiN ]-polyhedra along [00] causes chains of Li + -ions with quite short Li-Li

6 ZAAC Page of distances (Li Ca Si N :.(),.()Å; Li Sr Si N :.(),.()Å). The Li-ion conductor Li SiN exhibits comparable chains of [LiN x ]-polyhedra with analogoues Li-Li distances. [] It may be noted that the addition of % of Eu to the reaction mixture yielded red single crystals, which, however showed no fluorescence under UV light at room temperature. Conclusion In this contribution, we demonstrate that addition of an excess of Li N to the reaction mixture of Ca/Sr and Si(NH) suppresses the higher condensation of [SiN ]-tetrahedra and a low degree of condensation for nitridosilicates is achieved. The isotypic compounds Li Ca Si N and Li Sr Si N are the third and fourth example of nitridosilicates containing isolated [Si N ] 0- ions, respectively. Presumably, the lengths of the distances Si-Si within the [Si N ] 0- ions is dependent on the lewis acidity of the counter ions. It may be noted that the presence of [LiN ]-polyhedra chains along [00] might be an interesting feature for lithium ion conductivity. Experimental Section All manipulations were performed with rigorous exclusion of oxygen and moisture in flamedried Schlenk-type glassware on a Schlenk line interfaced to a vacuum (0 - mbar) line or in an argon-filled glove box (Unilab, MBraun, Garching, O < 0. ppm, H O < 0. ppm). Li N was purchased from Alfa Aesar (. %), Ca and Sr from Sigma-Aldrich (. %) and Si(NH) was synthesized according to the literature. [] For the reactions, tantalum crucibles (wall thickness 0. mm, internal diameter 0 mm, length 00 mm) were cleaned in a mixture of HNO (conc.) and HF (0 %). They were arc-welded under a pressure of bar purified argon. The crucible holder was water cooled in order to avoid decomposition reactions during welding. Single crystals of Li Ca Si N and Li Sr Si N were synthesized from 0 mg Li N (. mmol), 0 mg Si(NH) (0. mmol) and mg Ca (0. mmol) / mg Sr (0. mmol) in closed tantalum crucibles placed in silica tubes. The silica tube (under argon) was placed in the middle of a tube furnace. The temperature was raised to 00 C (rate 0 C h - ), maintained for h, subsequently cooled to 00 C (rate C h - ) and finally quenched to room temperature by switching off the furnace.

7 Page of ZAAC X-ray diffraction: By inspection under a microscope integrated in a glove box, colorless single crystals of the title compounds were isolated from residual Li N and enclosed in glass capillaries. Single-crystal X-ray diffraction data were collected on a Stoe IPDS I for Li Ca Si N and on an Oxford Diffraction XCalibur for Li Sr Si N (Mo Kα radiation). The program package SHELX was used for structure solution and refinement. [] Further details of the crystal structure investigations can be obtained from the Fachinformationszentrum Karlsruhe, Eggenstein-Leopoldshafen, Germany (fax: (+)-0-; crysdata@fiz-karlsruhe.de) on quoting the depository number CSD-0 (Li Ca Si N ) and CSD- (Li Sr Si N ), the names of the authors and citation of the publication. Microanalysis: EDX spectra of selected crystals were obtained using a JSM 00F scanning electron microscope (JEOL) equipped with an EDX detector (Oxford Instruments). The approximate molar ratio of the elements Ca : Si was found to be () : () (average from independent measurements) for Li Ca Si N and Sr : Si was found to be () : () (average from independent measurements) for Li Sr Si N. Acknowledgments We thank Dr. Peter Mayer, Thomas Miller (single-crystal X-ray diffractometry) and Christian Minke (X-ray microanalysis). The authors gratefully acknowledge financial support from the Fonds der Chemischen Industrie (FCI) and the Deutsche Forschungsgemeinschaft (DFG), project SCHN / -.

8 ZAAC Page of Table. Crystallographic data of Li Ca Si N and Li Sr Si N. Formula Li Ca Si N Li Sr Si N Formula mass / g mol Crystal system monoclinic Space group C/m (no. ) a =.() a =.() b =.0() b =.() Cell parameters / Å, c =.() c =.00() β = 0.() β = 0.() Cell volume / 0 pm V =.() V =.() Formula units / cell Crystal size / mm ρ calcd. / g cm -.. µ / mm -.. F(000) Oxford Diffractometer Stoe IPDS I Diffraction XCalibur Temperature / K () 00() Radiation, Mo-K monochromator α, (λ =.0 pm), graphite Absorption correction multi-scan numerical min. /max. transmission 0. / / 0. θ range / Measured reflections Independent reflections 0 Observed reflections 0 Refined parameters GoF.. R indices (F o σ (F o )) R = 0.0 R = 0.00 R indices (all data) wr = 0.0 [a] wr = 0.0 [b] Max. / min. residual electron density/ eå - 0. / -0.. / -. [a] w= [σ (F o ) +(0.0 P) P] where P= (F o + F c ) / R = 0.0 R = 0.0 wr = 0.0 wr = 0.00 [b] w= [σ (F o ) +(0.0 P) P] where P= (F o + F c ) /

9 Page of ZAAC Table. Comparison of compounds exhibiting isolated [Si N ] 0- ions. Ba Si N [] Ca Si N [] Li M Si N Ca Synthesis Na-Flux solid-state Li-Flux Li-Flux Space group P C/c C/m C/m X-ray T /K 00 Si-Si /Å.().0().().0() Si-N /Å.() [a].() [a].() [a].() [a] Si-N /Å.() [a].() [a].().() Si-N-Si /.() [a].() [a].().() [a] Averaged values because of more than one set of symmetry independent bonds/angles. Sr

10 ZAAC Page of Figure. Two unit cells of Li Sr Si N along [00-]. Ellipsoids at 0 % probability level. [SiN ] units are depicted as closed gray tetrahedra, N atoms black, Sr ions white/black and Li ions gray. Figure. Coordination spheres in Li Sr Si N. N atoms black, Sr ions white and Li ions gray.

11 Page of ZAAC References [] S. Pagano, S. Lupart, M. Zeuner, W. Schnick, Angew. Chem. 00,, -; Angew. Chem., Int. Ed. 00,, -. [] J. Lang, J.-P. Charlot, Rev. Chim. Miner. 0,, -. [] H. Yamane, S. Kikkawa, M. Koizumi, Solid State Ionics,, -. [] F. Ottinger, R. Nesper, Z. Anorg. Allg. Chem. 00,, -0. [] H. Yamane, F. J. DiSalvo, J. Alloys Compd., 0, -. [] R. P. Elliot, Constitution of Binary Alloys, McGraw-Hill Book Company, New York,. [] D. G. Park, Z. A. Gál, F. J. DiSalvo, J. Solid State Chem. 00,, -0. [] P. Hoehn, S. Hoffmann, J. Hunger, S. Leoni, F. Nitsche, W. Schnelle, R. Kniep, Chem. Eur. J. 00,, -. [] R. D. Shannon, Acta Crystallogr., Sect. A: Cryst. Found. Crystallogr.,, -. [0] R. Hübbenthal, Programm zur Berechnung des Madelunganteils der Gitterenergie, Vers. ; Universität Gießen. [] H. Baur, Crystallogr. Rev.,, -. [] S. Pagano, M. Zeuner, S. Hug, W. Schnick, Eur. J. Inorg. Chem. 00, -. [] H. Lange, G. Wötting, G. Winter, Angew. Chem., 0, 0-; Angew. Chem., Int. Ed. Engl., 0, -. [] G. M. Sheldrick, Acta Crystallogr., Sect. A: Found. Crystallogr. 00,, -.

12 ZAAC Page 0 of Figure x0mm (00 x 00 DPI)

13 Figure Page of ZAAC