The crystal structures of dieuropium penta siliconoctanitride, Eu2Si5N8, and europium ytterbium tetrasiliconheptanitride, EuYbSi4N7, are based on three-dimensional networks of corner-sharing SiN4 tetrahedra. Eu2Si5N8 is isotypic with the previously reported Sr and Ba analogues; EuYbSi4N7 is isotypic with SrYbSi4N7 and BaYbSi4N7

Huppertz, Hubert

Schnick, Wolfgang

English

Open Access LMU

NATHALIE AUDEBRAND et al. 1751 Guillou, N., Auffrrdic, J. P., Lourr, M. & Lourr, D. (1993). J. Solid State Chem. 106, 295-300. Johnson, C. K. (1976). ORTEPII. Report ORNL-5138. Oak Ridge National Laboratory, Tennessee, USA. Leclaire, A. (1979). J. Solid State Chem. 28, 235-244. Manek, E. & Meyer, G. (1993). Z. Anorg. Allg. Chem. 619, 761-765. Meyer, P., Rimsky, A. & Chevalier, R. (1976). Acta Cryst. B32, 1143- 1146. North, A. C. T., Phillips, D. C. & Mathews, F. S. (1968). Acta Cryst. A24, 351-359. Pearson, W. B. (1966). A Handbook of Lattice Spacings and Structures of Metals and Alloys, Vol II, p. 80. Oxford: Pergamon Press. Sheldrick, G. M. (1990). Acta Cryst. A46, 467-473. Sheldrick, G. M. (1993). SHELXL93. Program for the Refinement ofCrystal Structures. University of G6ttingen, Germany. Wartchow, R. & Ludwig, W. (1995). Z, Kristallogr. 210, 879. Acta Cryst. (1997). C53, 1751-1753 Eu2SisNs and EuYbSi4N7. The First Nitridosilicates with a Divalent Rare Earth Metal HUBERT HUPPERTZ AND WOLFGANG SCHNICK Laboratorium fiir Anorganische Chemie, Universitiitsstrasse 30, D-95440 Bayreuth, Germany. E-mail: wolfgang. schnick @ uni-bayreuth, de(Received I May 1997; accepted 13 June 1997) Abstract The crystal structures of dieuropium pentasilicon- octanitride, Eu2SisN8, and europium ytterbium tetra- siliconheptanitride, EuYbSi4N7, are based on three- dimensional networks of corner-sharing SiN4 tetrahedra. Eu2SisN8 is isotypic with the previously reported Sr and Ba analogues; EuYbSiaN7 is isotypic with SrYbSinN7 and BaYbSiaN7. Comment Recently, we developed a novel synthetic approach to multinary nitridosilicates by reacting alkaline earth or rare earth metals with silicon diimide in a specially developed high-frequency furnace (Huppertz & Schnick, 1997b). These reactions may be interpreted as the dissolution of an electropositive metal in a nitrido- analogous polymeric acid accompanied by the evolution of hydrogen. SiO4 and SiN4 tetrahedra re characteristic structural elements in oxo- and nitridosilicates, respectively. These tetrahedra are commonly connected through corner shar- ing to give network structures. Additionally, in nitrido- silicates, edge sharing has been observed (BasSi2N6; Yamane & DiSalvo, 1996) as well as vertex sharing to- gether with edge sharing of SiN4 tetrahedra (BaSi7Ni0; Huppertz & Schnick, 1997a). In contrast o oxygen in oxosilicates, nitrogen in nitridosilicates shows a greater flexibility. Whereas the structural chemistry of oxosili- cates is limited to terminal O atoms and simple bridg- ing O I21 atoms, the nitridosilicates extend this range, exhibiting terminal N Ill atoms, and N TM, N TM and N [41 atoms, connected to two, three and even four neighbour- ing Si tetrahedral centres, respectively. These structural variabilities in nitridosilicates provide a significant ex- tension of the conventional silicate chemistry. Until now nitridosilicates have only been obtained in combination with divalent alkaline earth metals (e.g. Ca2SisN8; Schlieper & Schnick, 1995), diva- lent transition metals (e.g. MnSiN2; Maunaye, March- and, Guyader, Laurent & Lang, 1971), or trivalent lanthanides (e.g. Ce3Si6Nll, BaYbSi4N7; Huppertz & Schnick, 1996a,b). The title compounds Eu2SisN8 and EuYbSi4N7 represent the first nitridosilicates containing a divalent rare earth metal. The structure of Eu2SisN8 is based on a network of corner-sharing SiN4 tetrahedra nd is isotypic with Sr2SisN8 and Ba2SisN8 (Schlieper, Milius & Schnick, 1995). In this network half of the N atoms connect two, and the other half three, Si atoms. The N TM atoms are arranged in corrugated sheets perpendicular to [ 100] (Fig. 1). The Eu 2÷ ions, which are mainly coordinated by N TM atoms (EumN: 2.60-3.25 A), are situated in channels along [100] formed by Si6N6 rings. The Si-N network structure in EuYbSiaN7 is built up from star-shaped [N(SiN3)4] building blocks (Fig. 2), Fig. 1. Crystal structure of Eu2SisNs, viewed along [100]. © 1997 International Union of Crystallography Printed in Great Britain - all rights reserved Acta Crystallographica Section C ISSN 0108-2701 © 199~" 1752 Eu2Si5N8 AND EuYbSi4N7 where the central N atoms simultaneously bridge four Si tetrahedral centres. By connecting these groups through common N TM atoms, a stacking variant of the wurtzite- analogous aluminium nitride structure is formed. Sys- tematic elimination of tetrahedra from this arrangement along [100] leads to the formation of Si6N6-ring chan- nels, containing Eu 2÷ and Yb 3+ ions. The Eu 2+ and Yb 3+ ions show anticuboctahedral nd octahedral co- ordination, respectively, by N atoms of the Si4N7 net- work. The Eu- -N  and Yb- -N  contact distances (2.93- 3.06 and 2.27-2.28 ,~, respectively) approximately cor- respond to the sum of the ionic radii (Baur, 1987). The bond lengths to the N [4] atoms are significantly longer (S i - -N:  1.87-1.94 A) than those to the N [2] atoms (S i -  N: 1.69-1.72 A). Exper imenta l  For the synthesis of Eu2Si5N8, metallic europium (136.8 mg, 0.90mmol) and silicon diimide (l16.2mg, 2mmol) were mixed thoroughly under argon in a glove box and transferred to a tungsten crucible positioned in a high-frequency furnace. The reaction mixture was heated to 923 K and directly to 1923 K within 2 h, maintained at that temperature for 3 h, and then quenched to room temperature. This process led to the formation of Eu2SisNs as a single-phase coarsely crystalline red solid. For EuYbSi4N7, the metals Eu and Yb (1 mmol) were mixed with Si(NH)2 (2 mmol) under inert gas atmosphere and transferred in a tungsten crucible to the high-frequency reactor. Under nitrogen atmosphere the reaction mixture was slowly heated up to 1923 K, maintained at that temperature for 48 h, and then quenched to room temperature. Eu2SisNs Crystal data Eu2SisN8 Mo Ka radiation Mr = 556.45 A = 0.71073 ,~ Orthorhombic Cell parameters from 33 Pmn2 ~ reflections a = 5.7094(4) ,4, 0 = 5.14-17.44 ° b = 6.8207 (4) ,~, # = 17.896 mm -I c = 9.3291 (6) A T = 293 (2) K V - 363.29 (4) ,~3 Prism Z = 2 0.10 x 0.08 x 0.08 mm Dx = 5.087 Mg m -3 Red D,, not measured Fig. 2. Crystal structure of EuYbSi4N7, viewed along [100]. The Eu 2+ ions are shown as grey and the Yb 3÷ ions as black spheres. The reaction of pure metals with sil icon diimide [Si(NH)2] provides a straightforward preparative route to nitridosilicates. These compounds possess highly con- densed network structures howing outstanding chem- ical, thermal and mechanical stabilities, which are a direct consequence of the high stability of the chemi- cal bonding between the constituent elements. Data collection Siemens P4 diffractometer t~¢ scans  Absorption correction: empirical via ~b scans [XSCANS (Siemens, 1994) and SHELXTL (Sheldrick, 1994)] Tmi, = 0.218, Tmax = 0.278 1811 measured reflections 1727 independent reflections 1609 reflections with I > 2o-(/) Rint = 0.0101 0m~ = 34.99 °h= -949  k = -11 ---* 11 l - -15  ~ 15 3 standard reflections every 97 reflections intensity decay: 0.89% Refinement Refinement on F 2 R[F 2 > 2o.(F2)] = 0.024 wR(F 2) = 0.047 S = 1.122 1727 reflections 83 parameters w = l/[o.2(F 2) + (0.0168P) 2 + 1.8337P] where e = (F 2 ÷ 2F2)/3 ( /~/o . )max = O.OO1 Apmax = 1.16 e ,~-3 Apmin  = - -  1.11 e ,~,-3 Extinction correction: SHELXTL (Sheldrick, 1994) Extinction coefficient: 0.0293 (7) Scattering factors from International Tables for Crystallography (Vol. C) Absolute configuration: Flack (1983) parameter = 0.17 (3) Table 1. Selected geometric parameters (,4, o ) fo r  Eu2SisNs Eu I - -N  1 i 2.529 (8) S i I - -N6  iv 1.768 (6) Eu ! - -N3  ii 2.724 (5) Si i - -N4  iii 1.769 (4) Eu I - -N2  2.8931 (14) S i2- -N I i 1.710(10) HUBERT HUPPERTZ AND WOLFGANG SCHNICK 1753 Eu l - -N4  iii 2.975 (4) Si2--N2 TM 1.718 (9) Eu I - -N3  "i 3.158 (6) Si2--N3 viii 1.719 (4) Eu l - -N6  i~ 3.246 (6) Si3--N2 1.668 (8) Eu2--N2 ii 2.554 (9) Si3--N5 ix 1.735 (6) Eu2--N3 ii 2.589 (5) Si3--N4 1.765 (4) Eu2--NI  i~ 2.8902 (12) Si4---N3 1.682 (3) Eu2--N5 ~ 2.902 (6) Si4---N5 1.752 (3) Eu2--N4 ~i 3.235 (4) S i4~N6 1.759 (4) Si I - -N  I 1.672 (8) Si4---N4 1.782 (4) Si3--N4---Si l  x 126.2 (3) S i4- -N5--S i4  xii 110.4 (3) S i3- -N4- -S i4  116.5 (2) Si4---N6---Si4 TM 107.2 (3) SilX--N4---Si4 117.3 (2) Si4---N6---Sil xi'' 117.5 (2) Si3Xi--N5--Si4 124.0 (2) Symmetry codes: (i) x,y - 1, z; (ii) ~ - x, -y ,  z - 4" (iii) x - l,y, z; (iv) ~ -x ,  1 -y , z -  4;(v) x -  1 ,y ,z -  1;(vi) x -  4,1 -y , z -  4" (vii) ~ -x ,  -y ,  4 +z; (viii) 3 -x ,  y, z; (ix) 7 -x ,  1 -y ,  z -  ½; (x) ! +x, y, z; (xi) 7_x , i  -y ,  ½+z:(xii) 4 -x ,y ,z ; (x i i i )  ~ -x , i  -y ,  ½ +z. EuYbSi4N7 Crystal data EuYbSi4N7 Mo Ka  radiation Mr = 535.43 A = 0.71073 Hexagonal Cell parameters from 62 P63mc reflections a = 5.9822 (3) ,4, 0 = 5.74-17.48 ° c = 9.7455 (4) ,~, # = 26.406 ram-m V = 302.03 (2) A 3 T = 293 (2) K Z = 2 Prism Dx = 5.887 Mg m -3 0.20 × 0.10 × 0.10 mm Dm not measured Brown Data collection Siemens P4 diffractometer scans Absorption correction: empirical via ~b scans [XSCANS (Siemens, 1994) and SHELXTL (Sheldrick, 1994)] Tmin = 0 .56 ,  Tmax = 0.71 4996 measured reflections 1378 independent reflections 1250 reflections with I > 2or(/) Rint = 0.0439 0max ---- 52.48 ° h = -12  ~ 12 k = -13  ---, 13 l = -21  ---+ 21 3 standard reflections every 97 reflections intensity decay: 1.36% Refinement Refinement on F 2 R[F 2 > 2cr(Fe)] = 0.021 wR(F 2) = 0.049 S = 1.068 1378 reflections 32 parameters w = l/[tre(Fo 2) + (0.0251P) 2+ 0.1496P] where P = (Fo 2 + 2F,2)/3 (z~/O)max = 0.002 Apmax = 1.69 e ~-3  Apmin = -4 .21  e ,~-3 Extinction correction: SHELXTL (Sheldrick, 1994) Extinction coefficient: 0.0436 (13) Scattering factors from International Tables for Crystallography (Vol. C) Absolute configuration: Flack (1983) parameter = -0 .013  (11) Tab le  2. Selected geometr ic parameters  (,~, o ) fo r  EuYbSi4N7 Ybl--N 1 2.267 (3) Si I--N2 1,694 (3) Yb I--N2' 2.280 (3) Si I--N3 '' 1.865 (4) EuI--NI 2.925 (3) Si2--N2' 1.713 (3) EuI--N2 ~' 2.9947 (2) Si2--N1 1.7189 (15) EuI--N I'" 3.058 (3) Si2--N3 1.941 (2) Si2Vi--N I--Si2 113.0(2) Si I vi'l--N3--Si2 112.07(11) SiI--N2--Si2 TM 116.9 (2) Si2--N3--Si2 'x 106.75 (12) Symmetry codes: (i) x, I + y, z; (ii) x - y, x, 4 + z; (iii) y, -x  + y, 4 + z; (iv) I +x,y,z ; (v)  1 -x , -Y ,  4 +z;(vi)  1 -y ,  1 +x-y ,z ; (v i i )  1 - x, -y ,  z - ½ ; (viii) x - 1, y, z; (ix) -y ,  x - y, z. The directions of the polar axes were determined usin_g reflections of the sign ranges hkl for Eu2SisN8 and hkl for EuYbSinN7 together with all corresponding Friedel pairs /~/~l and /~k[ for Eu2SisN8 and EuYbSi4N7, respectively. The complete spheres implied by the index ranges in the tables were not recorded. The origins were fixed by the method of Flack & Schwarzenbach (1988). Our experience in crystal structure determination of rare earth compounds indicates that a significant residual electron density may occur despite an absorption correction. Accord- ingly, the appreciable residual electron density located in the neighbourhood of some heavy atoms in EuYbSinN7 is not un- usual. The displacement factors for N2 in both compounds are strongly anisotropic. This might be caused by disorder, resid- ual absorption errors or actual marked anisotropy. However, in the absence of other evidence we cannot distinguish these pos- sibilities. The l ight-atom U values are necessarily imprecise in the presence of heavy atoms. For both compounds,  data collection: XSCANS (Siemens, 1994); cell refinement: XSCANS; data reduction: SHELXTL (Sheldrick, 1994); program(s) used to solve structures: SHELXTL; program(s) used to refine structures: SHELXTL; molecular graphics: KPLOT (Hundt, 1979); software used to prepare material for publication: SHELXTL. F inanc ia l  suppor t  by the Deutsche  Forschungsgemein -  schaf t  (pro ject  SCHN 377/6 -1 ,  377/6 -2  and  Got t f r ied  Wi lhe lm Le ibn iz  p rogram)  and the Fonds  der  Chem-  i schen  Indust r ie  is g ra te fu l ly  acknowledged.  Supplementary data for this paper are available from the IUCr electronic archives (Reference: JZ1226). Services for accessing these data are described at the back of the journal. References  Baur, W. H. (1987). Crystallogr. Rev. 1, 59-80. Rack, H. D. (1983). Acta Cryst. A39, 876-881. Flack, H. D. & Schwarzenbach, D. (1988). Acta Cryst. A44, 499-506. Hundt, R. (1979). KPLOT. A Structure Visualizing Program. Univer- sity of Bonn, Germany. Huppertz, H. & Schnick, W. (1996a). Angew. Chem. Int. Ed. Engl. 35, 1983-1984. Huppertz, H. & Schnick, W. (1996b). Z. Anorg. Allg. Chem. 623, 212-217. Huppertz, H. & Schnick, W. (1997a). Chem. Eur. J. 3, 249-252. Huppertz, H. & Schnick, W. (1997b). Chem. Eur. J. 3, 679-683. Maunaye, M., Marchand, R., Guyader, J., Laurent, Y. & Lang, J. (1971). Bull. Soc. Fr. Mineral. Cristallogr. 94, 561-564. Schlieper, T., Milius, W. & Schnick, W. (1995). Z. Anorg. Allg. Chem. 621, 1380-1384. Schlieper, T. & Schnick, W. (1995). Z. Anorg. Allg. Chem. 621, 1037- 1041. Sheldrick, G. M. (1994). SHELXTL. Release 5.03. Siemens Analytical X-ray Instruments Inc., Madison, Wisconsin, USA. Siemens (1994). XSCANS User's Manual. Version 2.1. Siemens Analytical X-ray Instruments Inc., Madison, Wisconsin, USA. Yamane, H. & DiSalvo, F. J. (1996). J. Alloy. Compd. 240, 33-36. 

KPLOT. A Structure Visualizing Program.

XSCANS User's Manual. Version 2.1. Siemens Analytical X-ray Instruments Inc.,

Eu2Si5N8 and EuYbSi4N7

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Eu2Si5N8 and EuYbSi4N7

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