research papers Acta Crystallographica Section C
Structural Chemistry ISSN 2053-2296
A new tetragonal structure type for Li2B2C Volodymyr Pavlyuk,a,b* Viktoriya Milashys,a Grygoriy Dmytriva and Helmut Ehrenbergc a
Department of Inorganic Chemistry, Ivan Franko Lviv National University, Kyryla and Mefodiya Street 6, 79005 Lviv, Ukraine, bInstitute of Chemistry, Environment Protection and Biotechnology, Jan Dlugosz University, al. Armii Krajowej 13/15, 42-200 Czestochowa, Poland, and cKarlsruhe Institute of Technology (KIT), Institute for Applied Materials (IAM), Hermann-von-Helmholtz-Platz 1, D-76344 EggensteinLeopoldshafen, Germany Correspondence e-mail: [email protected] Received 2 November 2014 Accepted 21 November 2014
The ternary dilithium diboron carbide, Li2B2C (tetragonal, space group P4m2, tP10), crystallizes as a new structure type and consists of structural fragments which are typical for structures of elemental lithium and boron or binary borocarbide B13C2. The symmetries of the occupied sites are .m. and 2mm. for the B and C atoms, and 4m2 and 2mm. for the Li atoms. The coordination polyhedra around the Li atoms are cuboctahedra and 15-vertex distorted pseudo-Frank–Kasper polyhedra. The environment of the B atom is a ten-vertex polyhedron. The nearest neighbours of the C atom are two B atoms, and this group is surrounded by a deformed cuboctahedron with one centred lateral facet. Electronic structure calculations using the TB–LMTO–ASA method reveal strong B C and B B interactions. Keywords: crystal structure; dilithium diboron carbide; binary borocarbide; TB–LMTO–ASA method; ternary structure; electron localization function (ELF) mapping; Li–B–C phases; intermetallic compounds; structural materials.
aspect of interest for Li–B–C compounds is as possible structural materials due to their ultralight weight. The first ternary Li–B–C compound LiBC (space group ˚ ) represents a totally interP63/mmc, a = 2.7523, c = 7.058 A calated heterographite and was described by Wo¨rle et al. (1995). This layered lithium borocarbide is isovalent with and structurally similar to the superconductor MgB2 (Rosner et al., 2002). Polycrystalline samples of LixBC samples were synthesized by a flux method for a wide range of flux compositions (x = 0.5–2.4), and a single phase was observed for the starting flux composition of Li1.25BC (Souptel et al., 2003). However, compared with graphite, the LiBC heterographite shows poor performance for both electrochemical Li insertion and extraction (Langer et al., 2012). In recent years, several new Li–B–C compounds have been reported: LiB13C2 ˚ ) and (space group Imma, a = 5.6677, b = 10.820, c = 8.039 A ˚ Li2B12C2 (space group Amm2, a = 4.706, b = 9.010, c = 5.652 A (Vojteer & Hillebrecht, 2006), Li1.43–1.68B38.82–38.76C6 (space ˚ ; Vojteer, group R3m, a = 5.6031–5.6154, c = 12.366–12.256 A 2008), Li0.4–0.56BC (space group P63/mmc, a = 2.520–2.4809, c = ˚ ) and Li0.83–1BC (space group P63/mmc, a = 7.333–7.4568 A ˚ ; Fogg et al., 2006). We 7.0533–7.04798, c = 46.025–46.092 A now present a new tetragonal structure type for Li2B2C.
2. Experimental 2.1. Synthesis and crystallization
The Li–B–C samples were prepared from the following reactants: lithium (rod, cut into small pieces of 1 mm3, 99.9 at%), boron (powder, 99.99 at%) and carbon (graphite powder, 99.99 at%). Appropriate amounts of all components were mixed according to the intended stoichiometry of the product and pressed into a tablet at a pressure of 6 bar (1 bar = 100 000 Pa). The tablet was closed inside a tantalum crucible in a glove-box under an argon atmosphere. The crucible was sealed by arc melting under a dry argon atmosphere. The reaction between the elements was initiated in an induction furnace at 1473 K. After 15 min, the sample was cooled rapidly to room temperature by removing the crucible from the furnace into ambient conditions. The reaction product was
1. Introduction Lithium intermetallides containing nonmetallic and p elements, such as B, Al, C, Si, Ge, Sn, Pb and Sb (Pavlyuk & Bodak, 1995; Po¨ttgen et al., 2010; Scrosati & Garche, 2010; Zhang, 2011; Langer et al., 2012), and metallic elements such as copper (Choi et al., 2004; Pavlyuk et al., 2008, 2011; Dmytriv et al., 2010), silver (Dmytriv et al., 2005; Pavlyuk et al., 2005, 2007; Sreeraj et al., 2006; Lacroix-Orio et al., 2008; Chumak et al., 2013), gold (Sreeraj et al., 2006; Dmytriv et al., 2011), palladium (Pavlyuk et al., 1989, 1995) and zinc (Alca´ntara et al., 2002; Dmytriv et al., 2007; Chumak et al., 2010; Pavlyuk et al., 2012, 2014) have been studied intensively as model systems for electrode materials in lithium-ion batteries. Another Acta Cryst. (2015). C71
Figure 1 A clinographic projection of the Li2B2C unit-cell contents and the coordination polyhedra of the atoms.
doi:10.1107/S2053229614025510
# 2015 International Union of Crystallography
1 of 5
research papers Table 1 Experimental details. Crystal data Chemical formula Mr Crystal system, space group Temperature (K) ˚) a, c (A ˚ 3) V (A Z Radiation type (mm 1) Crystal size (mm)
Li2B2C 47.51 Tetragonal, P4m2 293 4.1389 (4), 7.1055 (11) 121.72 (3) 2 Mo K 0.05 0.07 0.05 0.01
Data collection Diffractometer Absorption correction Tmin, Tmax No. of measured, independent and observed [I > 2(I)] reflections Rint ˚ 1) (sin /)max (A Refinement R[F 2 > 2(F 2)], wR(F 2), S No. of reflections No. of parameters ˚ 3) max, min (e A
Oxford Xcalibur3 CCD area-detector diffractometer Analytical (CrysAlis RED; Oxford Diffraction, 2008) 0.891, 0.998 1356, 182, 178 0.026 0.645
0.017, 0.057, 1.44 182 19 0.22, 0.19
Stadi-P (Mo K 1 radiation) diffractometer in Debye–Scherrer mode (2 from 5 to 45 in steps of 0.02 , linear positionsensitive detector with a 6 aperture). A laminar-like single crystal of the title compound, metallic dark grey in colour, was isolated from the Li60B30C10 alloy by mechanical fragmentation. This single crystal was protected from the air during X-ray data collection in a sealed thinwalled glass capillary (Hilgenberg, No. 10). 2.2. Refinement
Crystal data, data collection and structure refinement details are summarized in Table 1. The analysis of systematic extinctions yielded the noncentrosymmetric space group P4m2, and was confirmed by the subsequent structure refinement. Also, a statistical test of the distribution of the E values using the program E-STATS from the WinGX system (Farrugia, 2012) suggested that the structure is noncentrosymmetric. The structure was solved after applying an analytical absorption correction in the space group P4, and after extra symmetry or pseudosymmetry testing was transformed
Computer programs: CrysAlis CCD (Oxford Diffraction, 2008), CrysAlis RED (Oxford Diffraction, 2008), SHELXS2014 (Sheldrick, 2008), SHELXL2014 (Sheldrick, 2008) and DIAMOND (Brandenburg, 2006).
powdered in an agate mortar, added to a capillary of 0.3 mm diameter and sealed for X-ray diffraction (XRD) on a Stoe
Figure 3 Figure 2 The relationship between the Li, B, B13C2 and Li2B2C structures.
2 of 5
Pavlyuk et al.
Li2B2C
(a) The borocarbon and (b) the lithium atomic networks in the Li2B2C structure. Acta Cryst. (2015). C71
research papers
Figure 4 The boron or borocarbon atomic networks in some related compounds.
to the space group P4m2. In the first stage of the refinement, the positions of all atoms were obtained correctly by direct methods. Initial refinement of the atomic parameters showed that the 1c, 1d and 2g positions were occupied by Li atoms. One 2g and one 4k position were occupied by C and B atoms, respectively. In the final refinement cycles, all atoms were refined successfully with anisotropic displacement parameters. The crystal of the title compound contains no atom heavier than C and the data were collected with Mo radiation, so the absolute structure could not be determined. Acta Cryst. (2015). C71
3. Results and discussion The existence of a new tetragonal structure of Li2B2C was revealed by X-ray powder diffraction patterns, differing from the powder patterns of all known Li–B–C phases. Therefore, a full structure analysis was performed using single-crystal X-ray diffraction. The obtained single-crystal data show that the title compound crystallizes with a new tetragonal structure type (space group P4m2). The unit-cell contents and the coordination polyhedra of the atoms are shown in Fig. 1. The Pavlyuk et al.
Li2B2C
3 of 5
research papers
Figure 5
Figure 6
(a) ELF mapping and (b) isosurfaces of the ELF around the atoms in the Li2B2C structure.
(a) Total and partial DOS and (b) –COHP curves for Li2B2C from TB– LMTO–ASA calculations.
number of neighbouring atoms correlates well with the sizes of the central atoms. The coordination polyhedra around Li3 and Li4, on 1d and 1c sites, respectively, are cuboctahedra, viz. [Li3Li4C4Li4] and [Li4Li4C4Li4]. Atoms Li5 on a 2g site are at the centres of 15-vertex distorted pseudo-Frank–Kasper polyhedra, viz. [Li5B6C5Li4]. The coordination polyhedra around the B atoms are ten-vertex polyhedra, viz. [BB4C3Li3]. The nearest neighbours of the C atom are two B atoms, and this [–B–C–B–] group is surrounded by a 13-vertex cuboctahedron with one centred lateral facet. A detailed crystal chemical analysis shows (Fig. 2) that the title structure consists of intergrown B13C2 and Li (W-type) structural fragments alternating along the c axis. The [–B4C2–] structural fragment of borocarbide B13C2 (Kirfel et al., 1979) is similar to the elemental boron structural fragment [–B6–] and can be generated by the substitution of B atoms by C atoms. Another way of describing this structure type is to analyse the network perpendicular to the longest unit-cell axis. The B and C atoms form a corrugated network, which accommodates the majority of the isolated square B4 groups, each of which is connected by means of a C atom to the same four groups of atoms, forming 12-membered rings (Fig. 3a). This corrugated
network has the symbol 12241. The Li atoms also form a corrugated network, as shown in Fig. 3(b). Networks of B4 or substituted B2C2 squares are usually connected to eight-membered rings in borides and borocarbides. Such networks are compared in Fig. 4 for the known binary borides LiB3 (Mair et al., 1999), CrB4 (Andersson et al., 1968) and ThB4 (Zalkin & Templeton, 1950), and the ternary borocarbides CeB2C2 (van Duijn et al., 2000) and YB2C2 (Bauer & Nowotny, 1971), with the different connectivity scheme of the title compound Li2B2C. The electronic structure of the title compound was calculated using the tight-binding linear muffin-tin orbital method in the atomic spheres approximation (TB-LMTO-ASA; Andersen, 1975; Andersen & Jepsen, 1984; Andersen et al., 1985, 1986), using the experimental crystallographic data presented here. The exchange and correlation were interpreted in the local density approximation (von Barth & Hedin, 1972). The chemical bonding in the Li2B2C intermetallic compound is visualized by means of electron localization function (ELF) mapping, which is shown in Fig. 5(a). The isosurfaces of the ELF around the atoms of the title compound
4 of 5
Pavlyuk et al.
Li2B2C
Acta Cryst. (2015). C71
research papers are shown in Fig. 5(b), and the total and partial densities of states (DOS) are shown in Fig. 6(b). The Fermi level (EF) lies in a continuous DOS region, indicating a metallic character for the title compound. The DOS is low over the entire energy range near the Fermi level and confirms its relative stability. The chemical bonding [integrated crystal orbital Hamilton populations (iCOHP) curve] exhibits strong B C (d = ˚ and iCOHP = 7.773 eV) interactions between 7 1.5654 A and 4 eV (Fig. 6b). A slightly weaker interaction is observed ˚ and iCOHP = 5.286 eV. between B atoms, with d = 1.6667 A ˚ and iCOHP = The Li B interaction has d = 2.102 A 0.355 eV, so is much weaker. The weakest interaction is that ˚ and iCOHP = 0.073 eV). between Li atoms (d = 2.920 A Financial support from the Deutsche Forschungsgemeinschaft (DFG, grant No. EH183/7), the Ministry of Education and Science of Ukraine (grant No. M/206-2009) and the Bundesministerium fu¨r Bildung und Forschung (grant No. WTZ UKR 08/024) is gratefully acknowledged.
References Alca´ntara, R., Tillard-Charbonnel, M., Spina, L., Belin, C. & Tirado, J. L. (2002). Electrochim. Acta, 47, 1115–1120. Andersen, O. K. (1975). Phys. Rev. B, 12, 3060–3083. Andersen, O. K. & Jepsen, O. (1984). Phys. Rev. Lett. 53, 2571–2574. Andersen, O. K., Jepsen, O. & Glo¨tzel, D. (1985). In Highlights of Condensed Matter Theory, edited by F. Bassani, F. Fumi & M. P. Tosi. New York: NorthHolland. Andersen, O. K., Pawlowska, Z. & Jepsen, O. (1986). Phys. Rev. B, 34, 5253– 5269. Andersson, S., Lundstro¨m, T., Andresen, A. F. & Pearson, W. B. (1968). Acta Chem. Scand. 22, 3103–3110. Barth, U. von & Hedin, L. (1972). J. Phys. C, 5, 1629–1642. Bauer, J. & Nowotny, H. (1971). Monatsh. Chem. 102, 1129–1145. Brandenburg, K. (2006). DIAMOND. Crystal Impact GbR, Bonn, Germany. Choi, W., Lee, J. Y. & Lim, H. S. (2004). Electrochem. Commun. 6, 816– 820. Chumak, I., Dmytriv, G., Pavlyuk, V., Oswald, S., Eckert, J., Trill, H., Eckert, H., Pauly, H. & Ehrenberg, H. (2010). J. Mater. Res. 25, 1492–1499. Chumak, I., Pavlyuk, V., Dmytriv, G., Pauly, H. & Ehrenberg, H. (2013). J. Solid State Chem. 197, 248–253. Dmytriv, G., Pauly, H., Ehrenberg, H., Pavlyuk, V. & Vollmar, E. (2005). J. Solid State Chem. 178, 2825–2831. Dmytriv, G., Pavlyuk, V., Pauly, H., Eckert, J. & Ehrenberg, H. (2011). J. Solid State Chem. 184, 1328–1332.
Acta Cryst. (2015). C71
Dmytriv, G., Pavlyuk, V., Tarasiuk, I., Ehrenberg, H., Chumak, I. & Pauly, H. (2010). Acta Cryst. A66, s150–s151. Dmytriv, G., Pavlyuk, V., Tarasiuk, I., Pauly, H., Ehrenberg, H., Marciniak, B., Prochwicz, W. & Schroeder, G. (2007). Visn. Lviv. Univ. Ser. Khim. 48, 172– 178. Duijn, J. van, Suzuki, K. & Attfield, J. P. (2000). Angew. Chem. Int. Ed. 39, 365– 366. Farrugia, L. J. (2012). J. Appl. Cryst. 45, 849–854. Fogg, A. M., Meldrum, J., Darling, G. R., Claridge, J. B. & Rosseinsky, M. J. (2006). J. Am. Chem. Soc. 128, 10043–10053. Kirfel, A., Gupta, A. & Will, G. (1979). Acta Cryst. B35, 1052–1059. Lacroix-Orio, L., Tillard, M. & Belin, C. (2008). Solid State Sci. 10, 5–11. Langer, T., Dupke, S., Dippel, C., Eckert, H. & Pottgen, R. (2012). Z. Naturforsch. Teil B, 67, 1212–1220. Mair, G., von Schnering, H. G., Wo¨rle, M. & Nesper, R. (1999). Z. Anorg. Allg. Chem. 625, 1207–1211. Oxford Diffraction (2008). CrysAlis CCD and CrysAlis RED. Oxford Diffraction Ltd, Abingdon, Oxfordshire, England. Pavlyuk, V. V. & Bodak, O. I. (1995). Ternary Alloys – Evaluated Constitutional Data, Phase Diagrams, Crystal Structures and Applications of Lithium Alloy Systems, edited by G. Effenberg, F. Aldinger & A. Prince, Vol. 15. Weinheim: VCH. Pavlyuk, V., Chumak, I., Akselrud, L., Lidin, S. & Ehrenberg, H. (2014). Acta Cryst. B70, 212–217. Pavlyuk, V., Chumak, I. & Ehrenberg, H. (2012). Acta Cryst. B68, 34–39. Pavlyuk, V., Dmytriv, G., Chumak, I., Ehrenberg, H. & Pauly, H. (2005). J. Solid State Chem. 178, 3303–3307. Pavlyuk, V., Dmytriv, G., Tarasiuk, I., Chumak, I. & Ehrenberg, H. (2011). Acta Cryst. C67, i59–i62. Pavlyuk, V., Dmytriv, G., Tarasiuk, I., Pauly, H. & Ehrenberg, H. (2007). Intermetallics, 15, 1409–1415. Pavlyuk, V., Dmytriv, G., Tarasiuk, I., Pauly, H. & Ehrenberg, H. (2008). Acta Cryst. C64, i15–i17. Pavlyuk, V. V., Kevorkov, D. G., Bodak, O. I. & Pecharskii, V. K. (1995). Kristallografiya, 40, 183–184. Pavlyuk, V. V., Pecharskii, V. K. & Bodak, O. I. (1989). Kristallografiya, 34, 306–309. Po¨ttgen, R., Dinges, T., Eckert, H., Sreeraj, P. & Wiemho¨fer, H.-D. (2010). Z. Phys. Chem. 224, 1475–1504. Rosner, H., Kitaigorodsky, A. & Pickett, W. E. (2002). Phys. Rev. Lett. 88, 127001. Scrosati, B. & Garche, J. (2010). J. Power Sources, 195, 2419–2430. Sheldrick, G. M. (2008). Acta Cryst. A64, 112–122. Souptel, D., Hossain, Z., Behr, G., Lo¨ser, W. & Geibel, C. (2003). Solid State Commun. 125, 17–21. Sreeraj, P., Wiemho¨fer, H.-D., Hoffmann, R.-D., Walter, J., Kirfel, A. & Po¨ttgen, R. (2006). Solid State Sci. 8, 843–848. Vojteer, N. (2008). Dissertation, Universita¨t Freiburg/Breisgau, Germany. Vojteer, N. & Hillebrecht, H. (2006). Angew. Chem. Int. Ed. 45, 165–168. Wo¨rle, M., Nesper, R., Mair, G., Schwarz, M. & Von Schnering, H. G. (1995). Z. Anorg. Allg. Chem. 621, 1153–1159. Zalkin, A. & Templeton, D. H. (1950). J. Chem. Phys. 18, 391–392. Zhang, W.-J. (2011). J. Power Sources, 196, 13–24.
Pavlyuk et al.
Li2B2C
5 of 5
supporting information
supporting information Acta Cryst. (2015). C71
[doi:10.1107/S2053229614025510]
A new tetragonal structure type for Li2B2C Volodymyr Pavlyuk, Viktoriya Milashys, Grygoriy Dmytriv and Helmut Ehrenberg Computing details Data collection: CrysAlis CCD (Oxford Diffraction, 2008); cell refinement: CrysAlis CCD (Oxford Diffraction, 2008); data reduction: CrysAlis RED (Oxford Diffraction, 2008); program(s) used to solve structure: SHELXS2014 (Sheldrick, 2008); program(s) used to refine structure: SHELXL2014 (Sheldrick, 2008); molecular graphics: DIAMOND (Brandenburg, 2006); software used to prepare material for publication: SHELXL2014 (Sheldrick, 2008). dilithium diboron carbide Crystal data Li2B2C Mr = 47.51 Tetragonal, P4m2 a = 4.1389 (4) Å c = 7.1055 (11) Å V = 121.72 (3) Å3 Z=2 F(000) = 44
Dx = 1.296 Mg m−3 Mo Kα radiation, λ = 0.71073 Å Cell parameters from 182 reflections θ = 2.9–27.3° µ = 0.05 mm−1 T = 293 K Plate, metallic dark grey 0.07 × 0.05 × 0.01 mm
Data collection Oxford Xcalibur3 CCD area-detector diffractometer Radiation source: fine-focus sealed tube Graphite monochromator Detector resolution: 0 pixels mm-1 ω scans Absorption correction: analytical (CrysAlis RED; Oxford Diffraction, 2008) Tmin = 0.891, Tmax = 0.998
1356 measured reflections 182 independent reflections 178 reflections with I > 2σ(I) Rint = 0.026 θmax = 27.3°, θmin = 2.9° h = −5→5 k = −5→5 l = −9→9
Refinement Refinement on F2 Least-squares matrix: full R[F2 > 2σ(F2)] = 0.017 wR(F2) = 0.057 S = 1.44 182 reflections 19 parameters 0 restraints
Acta Cryst. (2015). C71
Primary atom site location: structure-invariant direct methods Secondary atom site location: difference Fourier map w = 1/[σ2(Fo2) + (0.0091P)2 + 0.0124P] where P = (Fo2 + 2Fc2)/3 (Δ/σ)max < 0.001 Δρmax = 0.22 e Å−3 Δρmin = −0.19 e Å−3
sup-1
supporting information Special details Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes. Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2)
C1 B2 Li3 Li4 Li5
x
y
z
Uiso*/Ueq
0.0000 0.2424 0.0000 0.5000 0.5000
0.5000 0.5000 0.0000 0.5000 0.0000
0.2184 (2) 0.0501 (2) 0.5000 0.5000 0.2113 (4)
0.0060 (4) 0.0059 (3) 0.0045 (9) 0.0039 (8) 0.0069 (6)
Atomic displacement parameters (Å2)
C1 B2 Li3 Li4 Li5
U11
U22
U33
U12
U13
U23
0.0049 (11) 0.0053 (7) 0.0038 (11) 0.0034 (11) 0.0072 (19)
0.0054 (11) 0.0054 (6) 0.0038 (11) 0.0034 (11) 0.0064 (19)
0.0076 (8) 0.0069 (6) 0.0059 (19) 0.0048 (19) 0.0071 (14)
0.000 0.000 0.000 0.000 0.000
0.000 −0.0003 (5) 0.000 0.000 0.000
0.000 0.000 0.000 0.000 0.000
Geometric parameters (Å, º) C1—B2 C1—B2i B2—B2ii
1.5614 (17) 1.5614 (17) 1.6671 (13)
B2—B2iii B2—B2i B2—B2iv
1.6671 (13) 2.0067 (2) 2.1322 (2)
B2—C1—B2i C1—B2—B2ii C1—B2—B2iii B2ii—B2—B2iii C1—B2—B2i B2ii—B2—B2i
79.98 (10) 137.55 (8) 137.55 (8) 79.51 (7) 50.01 (5) 129.75 (4)
B2iii—B2—B2i C1—B2—B2iv B2ii—B2—B2iv B2iii—B2—B2iv B2i—B2—B2iv
129.75 (4) 129.99 (5) 50.25 (4) 50.25 (4) 180.0
Symmetry codes: (i) −x, −y+1, z; (ii) y, −x+1, −z; (iii) −y+1, x, −z; (iv) −x+1, −y+1, z.
Acta Cryst. (2015). C71
sup-2
Structural Chemistry ISSN 2053-2296
A new tetragonal structure type for Li2B2C Volodymyr Pavlyuk,a,b* Viktoriya Milashys,a Grygoriy Dmytriva and Helmut Ehrenbergc a
Department of Inorganic Chemistry, Ivan Franko Lviv National University, Kyryla and Mefodiya Street 6, 79005 Lviv, Ukraine, bInstitute of Chemistry, Environment Protection and Biotechnology, Jan Dlugosz University, al. Armii Krajowej 13/15, 42-200 Czestochowa, Poland, and cKarlsruhe Institute of Technology (KIT), Institute for Applied Materials (IAM), Hermann-von-Helmholtz-Platz 1, D-76344 EggensteinLeopoldshafen, Germany Correspondence e-mail: [email protected] Received 2 November 2014 Accepted 21 November 2014
The ternary dilithium diboron carbide, Li2B2C (tetragonal, space group P4m2, tP10), crystallizes as a new structure type and consists of structural fragments which are typical for structures of elemental lithium and boron or binary borocarbide B13C2. The symmetries of the occupied sites are .m. and 2mm. for the B and C atoms, and 4m2 and 2mm. for the Li atoms. The coordination polyhedra around the Li atoms are cuboctahedra and 15-vertex distorted pseudo-Frank–Kasper polyhedra. The environment of the B atom is a ten-vertex polyhedron. The nearest neighbours of the C atom are two B atoms, and this group is surrounded by a deformed cuboctahedron with one centred lateral facet. Electronic structure calculations using the TB–LMTO–ASA method reveal strong B C and B B interactions. Keywords: crystal structure; dilithium diboron carbide; binary borocarbide; TB–LMTO–ASA method; ternary structure; electron localization function (ELF) mapping; Li–B–C phases; intermetallic compounds; structural materials.
aspect of interest for Li–B–C compounds is as possible structural materials due to their ultralight weight. The first ternary Li–B–C compound LiBC (space group ˚ ) represents a totally interP63/mmc, a = 2.7523, c = 7.058 A calated heterographite and was described by Wo¨rle et al. (1995). This layered lithium borocarbide is isovalent with and structurally similar to the superconductor MgB2 (Rosner et al., 2002). Polycrystalline samples of LixBC samples were synthesized by a flux method for a wide range of flux compositions (x = 0.5–2.4), and a single phase was observed for the starting flux composition of Li1.25BC (Souptel et al., 2003). However, compared with graphite, the LiBC heterographite shows poor performance for both electrochemical Li insertion and extraction (Langer et al., 2012). In recent years, several new Li–B–C compounds have been reported: LiB13C2 ˚ ) and (space group Imma, a = 5.6677, b = 10.820, c = 8.039 A ˚ Li2B12C2 (space group Amm2, a = 4.706, b = 9.010, c = 5.652 A (Vojteer & Hillebrecht, 2006), Li1.43–1.68B38.82–38.76C6 (space ˚ ; Vojteer, group R3m, a = 5.6031–5.6154, c = 12.366–12.256 A 2008), Li0.4–0.56BC (space group P63/mmc, a = 2.520–2.4809, c = ˚ ) and Li0.83–1BC (space group P63/mmc, a = 7.333–7.4568 A ˚ ; Fogg et al., 2006). We 7.0533–7.04798, c = 46.025–46.092 A now present a new tetragonal structure type for Li2B2C.
2. Experimental 2.1. Synthesis and crystallization
The Li–B–C samples were prepared from the following reactants: lithium (rod, cut into small pieces of 1 mm3, 99.9 at%), boron (powder, 99.99 at%) and carbon (graphite powder, 99.99 at%). Appropriate amounts of all components were mixed according to the intended stoichiometry of the product and pressed into a tablet at a pressure of 6 bar (1 bar = 100 000 Pa). The tablet was closed inside a tantalum crucible in a glove-box under an argon atmosphere. The crucible was sealed by arc melting under a dry argon atmosphere. The reaction between the elements was initiated in an induction furnace at 1473 K. After 15 min, the sample was cooled rapidly to room temperature by removing the crucible from the furnace into ambient conditions. The reaction product was
1. Introduction Lithium intermetallides containing nonmetallic and p elements, such as B, Al, C, Si, Ge, Sn, Pb and Sb (Pavlyuk & Bodak, 1995; Po¨ttgen et al., 2010; Scrosati & Garche, 2010; Zhang, 2011; Langer et al., 2012), and metallic elements such as copper (Choi et al., 2004; Pavlyuk et al., 2008, 2011; Dmytriv et al., 2010), silver (Dmytriv et al., 2005; Pavlyuk et al., 2005, 2007; Sreeraj et al., 2006; Lacroix-Orio et al., 2008; Chumak et al., 2013), gold (Sreeraj et al., 2006; Dmytriv et al., 2011), palladium (Pavlyuk et al., 1989, 1995) and zinc (Alca´ntara et al., 2002; Dmytriv et al., 2007; Chumak et al., 2010; Pavlyuk et al., 2012, 2014) have been studied intensively as model systems for electrode materials in lithium-ion batteries. Another Acta Cryst. (2015). C71
Figure 1 A clinographic projection of the Li2B2C unit-cell contents and the coordination polyhedra of the atoms.
doi:10.1107/S2053229614025510
# 2015 International Union of Crystallography
1 of 5
research papers Table 1 Experimental details. Crystal data Chemical formula Mr Crystal system, space group Temperature (K) ˚) a, c (A ˚ 3) V (A Z Radiation type (mm 1) Crystal size (mm)
Li2B2C 47.51 Tetragonal, P4m2 293 4.1389 (4), 7.1055 (11) 121.72 (3) 2 Mo K 0.05 0.07 0.05 0.01
Data collection Diffractometer Absorption correction Tmin, Tmax No. of measured, independent and observed [I > 2(I)] reflections Rint ˚ 1) (sin /)max (A Refinement R[F 2 > 2(F 2)], wR(F 2), S No. of reflections No. of parameters ˚ 3) max, min (e A
Oxford Xcalibur3 CCD area-detector diffractometer Analytical (CrysAlis RED; Oxford Diffraction, 2008) 0.891, 0.998 1356, 182, 178 0.026 0.645
0.017, 0.057, 1.44 182 19 0.22, 0.19
Stadi-P (Mo K 1 radiation) diffractometer in Debye–Scherrer mode (2 from 5 to 45 in steps of 0.02 , linear positionsensitive detector with a 6 aperture). A laminar-like single crystal of the title compound, metallic dark grey in colour, was isolated from the Li60B30C10 alloy by mechanical fragmentation. This single crystal was protected from the air during X-ray data collection in a sealed thinwalled glass capillary (Hilgenberg, No. 10). 2.2. Refinement
Crystal data, data collection and structure refinement details are summarized in Table 1. The analysis of systematic extinctions yielded the noncentrosymmetric space group P4m2, and was confirmed by the subsequent structure refinement. Also, a statistical test of the distribution of the E values using the program E-STATS from the WinGX system (Farrugia, 2012) suggested that the structure is noncentrosymmetric. The structure was solved after applying an analytical absorption correction in the space group P4, and after extra symmetry or pseudosymmetry testing was transformed
Computer programs: CrysAlis CCD (Oxford Diffraction, 2008), CrysAlis RED (Oxford Diffraction, 2008), SHELXS2014 (Sheldrick, 2008), SHELXL2014 (Sheldrick, 2008) and DIAMOND (Brandenburg, 2006).
powdered in an agate mortar, added to a capillary of 0.3 mm diameter and sealed for X-ray diffraction (XRD) on a Stoe
Figure 3 Figure 2 The relationship between the Li, B, B13C2 and Li2B2C structures.
2 of 5
Pavlyuk et al.
Li2B2C
(a) The borocarbon and (b) the lithium atomic networks in the Li2B2C structure. Acta Cryst. (2015). C71
research papers
Figure 4 The boron or borocarbon atomic networks in some related compounds.
to the space group P4m2. In the first stage of the refinement, the positions of all atoms were obtained correctly by direct methods. Initial refinement of the atomic parameters showed that the 1c, 1d and 2g positions were occupied by Li atoms. One 2g and one 4k position were occupied by C and B atoms, respectively. In the final refinement cycles, all atoms were refined successfully with anisotropic displacement parameters. The crystal of the title compound contains no atom heavier than C and the data were collected with Mo radiation, so the absolute structure could not be determined. Acta Cryst. (2015). C71
3. Results and discussion The existence of a new tetragonal structure of Li2B2C was revealed by X-ray powder diffraction patterns, differing from the powder patterns of all known Li–B–C phases. Therefore, a full structure analysis was performed using single-crystal X-ray diffraction. The obtained single-crystal data show that the title compound crystallizes with a new tetragonal structure type (space group P4m2). The unit-cell contents and the coordination polyhedra of the atoms are shown in Fig. 1. The Pavlyuk et al.
Li2B2C
3 of 5
research papers
Figure 5
Figure 6
(a) ELF mapping and (b) isosurfaces of the ELF around the atoms in the Li2B2C structure.
(a) Total and partial DOS and (b) –COHP curves for Li2B2C from TB– LMTO–ASA calculations.
number of neighbouring atoms correlates well with the sizes of the central atoms. The coordination polyhedra around Li3 and Li4, on 1d and 1c sites, respectively, are cuboctahedra, viz. [Li3Li4C4Li4] and [Li4Li4C4Li4]. Atoms Li5 on a 2g site are at the centres of 15-vertex distorted pseudo-Frank–Kasper polyhedra, viz. [Li5B6C5Li4]. The coordination polyhedra around the B atoms are ten-vertex polyhedra, viz. [BB4C3Li3]. The nearest neighbours of the C atom are two B atoms, and this [–B–C–B–] group is surrounded by a 13-vertex cuboctahedron with one centred lateral facet. A detailed crystal chemical analysis shows (Fig. 2) that the title structure consists of intergrown B13C2 and Li (W-type) structural fragments alternating along the c axis. The [–B4C2–] structural fragment of borocarbide B13C2 (Kirfel et al., 1979) is similar to the elemental boron structural fragment [–B6–] and can be generated by the substitution of B atoms by C atoms. Another way of describing this structure type is to analyse the network perpendicular to the longest unit-cell axis. The B and C atoms form a corrugated network, which accommodates the majority of the isolated square B4 groups, each of which is connected by means of a C atom to the same four groups of atoms, forming 12-membered rings (Fig. 3a). This corrugated
network has the symbol 12241. The Li atoms also form a corrugated network, as shown in Fig. 3(b). Networks of B4 or substituted B2C2 squares are usually connected to eight-membered rings in borides and borocarbides. Such networks are compared in Fig. 4 for the known binary borides LiB3 (Mair et al., 1999), CrB4 (Andersson et al., 1968) and ThB4 (Zalkin & Templeton, 1950), and the ternary borocarbides CeB2C2 (van Duijn et al., 2000) and YB2C2 (Bauer & Nowotny, 1971), with the different connectivity scheme of the title compound Li2B2C. The electronic structure of the title compound was calculated using the tight-binding linear muffin-tin orbital method in the atomic spheres approximation (TB-LMTO-ASA; Andersen, 1975; Andersen & Jepsen, 1984; Andersen et al., 1985, 1986), using the experimental crystallographic data presented here. The exchange and correlation were interpreted in the local density approximation (von Barth & Hedin, 1972). The chemical bonding in the Li2B2C intermetallic compound is visualized by means of electron localization function (ELF) mapping, which is shown in Fig. 5(a). The isosurfaces of the ELF around the atoms of the title compound
4 of 5
Pavlyuk et al.
Li2B2C
Acta Cryst. (2015). C71
research papers are shown in Fig. 5(b), and the total and partial densities of states (DOS) are shown in Fig. 6(b). The Fermi level (EF) lies in a continuous DOS region, indicating a metallic character for the title compound. The DOS is low over the entire energy range near the Fermi level and confirms its relative stability. The chemical bonding [integrated crystal orbital Hamilton populations (iCOHP) curve] exhibits strong B C (d = ˚ and iCOHP = 7.773 eV) interactions between 7 1.5654 A and 4 eV (Fig. 6b). A slightly weaker interaction is observed ˚ and iCOHP = 5.286 eV. between B atoms, with d = 1.6667 A ˚ and iCOHP = The Li B interaction has d = 2.102 A 0.355 eV, so is much weaker. The weakest interaction is that ˚ and iCOHP = 0.073 eV). between Li atoms (d = 2.920 A Financial support from the Deutsche Forschungsgemeinschaft (DFG, grant No. EH183/7), the Ministry of Education and Science of Ukraine (grant No. M/206-2009) and the Bundesministerium fu¨r Bildung und Forschung (grant No. WTZ UKR 08/024) is gratefully acknowledged.
References Alca´ntara, R., Tillard-Charbonnel, M., Spina, L., Belin, C. & Tirado, J. L. (2002). Electrochim. Acta, 47, 1115–1120. Andersen, O. K. (1975). Phys. Rev. B, 12, 3060–3083. Andersen, O. K. & Jepsen, O. (1984). Phys. Rev. Lett. 53, 2571–2574. Andersen, O. K., Jepsen, O. & Glo¨tzel, D. (1985). In Highlights of Condensed Matter Theory, edited by F. Bassani, F. Fumi & M. P. Tosi. New York: NorthHolland. Andersen, O. K., Pawlowska, Z. & Jepsen, O. (1986). Phys. Rev. B, 34, 5253– 5269. Andersson, S., Lundstro¨m, T., Andresen, A. F. & Pearson, W. B. (1968). Acta Chem. Scand. 22, 3103–3110. Barth, U. von & Hedin, L. (1972). J. Phys. C, 5, 1629–1642. Bauer, J. & Nowotny, H. (1971). Monatsh. Chem. 102, 1129–1145. Brandenburg, K. (2006). DIAMOND. Crystal Impact GbR, Bonn, Germany. Choi, W., Lee, J. Y. & Lim, H. S. (2004). Electrochem. Commun. 6, 816– 820. Chumak, I., Dmytriv, G., Pavlyuk, V., Oswald, S., Eckert, J., Trill, H., Eckert, H., Pauly, H. & Ehrenberg, H. (2010). J. Mater. Res. 25, 1492–1499. Chumak, I., Pavlyuk, V., Dmytriv, G., Pauly, H. & Ehrenberg, H. (2013). J. Solid State Chem. 197, 248–253. Dmytriv, G., Pauly, H., Ehrenberg, H., Pavlyuk, V. & Vollmar, E. (2005). J. Solid State Chem. 178, 2825–2831. Dmytriv, G., Pavlyuk, V., Pauly, H., Eckert, J. & Ehrenberg, H. (2011). J. Solid State Chem. 184, 1328–1332.
Acta Cryst. (2015). C71
Dmytriv, G., Pavlyuk, V., Tarasiuk, I., Ehrenberg, H., Chumak, I. & Pauly, H. (2010). Acta Cryst. A66, s150–s151. Dmytriv, G., Pavlyuk, V., Tarasiuk, I., Pauly, H., Ehrenberg, H., Marciniak, B., Prochwicz, W. & Schroeder, G. (2007). Visn. Lviv. Univ. Ser. Khim. 48, 172– 178. Duijn, J. van, Suzuki, K. & Attfield, J. P. (2000). Angew. Chem. Int. Ed. 39, 365– 366. Farrugia, L. J. (2012). J. Appl. Cryst. 45, 849–854. Fogg, A. M., Meldrum, J., Darling, G. R., Claridge, J. B. & Rosseinsky, M. J. (2006). J. Am. Chem. Soc. 128, 10043–10053. Kirfel, A., Gupta, A. & Will, G. (1979). Acta Cryst. B35, 1052–1059. Lacroix-Orio, L., Tillard, M. & Belin, C. (2008). Solid State Sci. 10, 5–11. Langer, T., Dupke, S., Dippel, C., Eckert, H. & Pottgen, R. (2012). Z. Naturforsch. Teil B, 67, 1212–1220. Mair, G., von Schnering, H. G., Wo¨rle, M. & Nesper, R. (1999). Z. Anorg. Allg. Chem. 625, 1207–1211. Oxford Diffraction (2008). CrysAlis CCD and CrysAlis RED. Oxford Diffraction Ltd, Abingdon, Oxfordshire, England. Pavlyuk, V. V. & Bodak, O. I. (1995). Ternary Alloys – Evaluated Constitutional Data, Phase Diagrams, Crystal Structures and Applications of Lithium Alloy Systems, edited by G. Effenberg, F. Aldinger & A. Prince, Vol. 15. Weinheim: VCH. Pavlyuk, V., Chumak, I., Akselrud, L., Lidin, S. & Ehrenberg, H. (2014). Acta Cryst. B70, 212–217. Pavlyuk, V., Chumak, I. & Ehrenberg, H. (2012). Acta Cryst. B68, 34–39. Pavlyuk, V., Dmytriv, G., Chumak, I., Ehrenberg, H. & Pauly, H. (2005). J. Solid State Chem. 178, 3303–3307. Pavlyuk, V., Dmytriv, G., Tarasiuk, I., Chumak, I. & Ehrenberg, H. (2011). Acta Cryst. C67, i59–i62. Pavlyuk, V., Dmytriv, G., Tarasiuk, I., Pauly, H. & Ehrenberg, H. (2007). Intermetallics, 15, 1409–1415. Pavlyuk, V., Dmytriv, G., Tarasiuk, I., Pauly, H. & Ehrenberg, H. (2008). Acta Cryst. C64, i15–i17. Pavlyuk, V. V., Kevorkov, D. G., Bodak, O. I. & Pecharskii, V. K. (1995). Kristallografiya, 40, 183–184. Pavlyuk, V. V., Pecharskii, V. K. & Bodak, O. I. (1989). Kristallografiya, 34, 306–309. Po¨ttgen, R., Dinges, T., Eckert, H., Sreeraj, P. & Wiemho¨fer, H.-D. (2010). Z. Phys. Chem. 224, 1475–1504. Rosner, H., Kitaigorodsky, A. & Pickett, W. E. (2002). Phys. Rev. Lett. 88, 127001. Scrosati, B. & Garche, J. (2010). J. Power Sources, 195, 2419–2430. Sheldrick, G. M. (2008). Acta Cryst. A64, 112–122. Souptel, D., Hossain, Z., Behr, G., Lo¨ser, W. & Geibel, C. (2003). Solid State Commun. 125, 17–21. Sreeraj, P., Wiemho¨fer, H.-D., Hoffmann, R.-D., Walter, J., Kirfel, A. & Po¨ttgen, R. (2006). Solid State Sci. 8, 843–848. Vojteer, N. (2008). Dissertation, Universita¨t Freiburg/Breisgau, Germany. Vojteer, N. & Hillebrecht, H. (2006). Angew. Chem. Int. Ed. 45, 165–168. Wo¨rle, M., Nesper, R., Mair, G., Schwarz, M. & Von Schnering, H. G. (1995). Z. Anorg. Allg. Chem. 621, 1153–1159. Zalkin, A. & Templeton, D. H. (1950). J. Chem. Phys. 18, 391–392. Zhang, W.-J. (2011). J. Power Sources, 196, 13–24.
Pavlyuk et al.
Li2B2C
5 of 5
supporting information
supporting information Acta Cryst. (2015). C71
[doi:10.1107/S2053229614025510]
A new tetragonal structure type for Li2B2C Volodymyr Pavlyuk, Viktoriya Milashys, Grygoriy Dmytriv and Helmut Ehrenberg Computing details Data collection: CrysAlis CCD (Oxford Diffraction, 2008); cell refinement: CrysAlis CCD (Oxford Diffraction, 2008); data reduction: CrysAlis RED (Oxford Diffraction, 2008); program(s) used to solve structure: SHELXS2014 (Sheldrick, 2008); program(s) used to refine structure: SHELXL2014 (Sheldrick, 2008); molecular graphics: DIAMOND (Brandenburg, 2006); software used to prepare material for publication: SHELXL2014 (Sheldrick, 2008). dilithium diboron carbide Crystal data Li2B2C Mr = 47.51 Tetragonal, P4m2 a = 4.1389 (4) Å c = 7.1055 (11) Å V = 121.72 (3) Å3 Z=2 F(000) = 44
Dx = 1.296 Mg m−3 Mo Kα radiation, λ = 0.71073 Å Cell parameters from 182 reflections θ = 2.9–27.3° µ = 0.05 mm−1 T = 293 K Plate, metallic dark grey 0.07 × 0.05 × 0.01 mm
Data collection Oxford Xcalibur3 CCD area-detector diffractometer Radiation source: fine-focus sealed tube Graphite monochromator Detector resolution: 0 pixels mm-1 ω scans Absorption correction: analytical (CrysAlis RED; Oxford Diffraction, 2008) Tmin = 0.891, Tmax = 0.998
1356 measured reflections 182 independent reflections 178 reflections with I > 2σ(I) Rint = 0.026 θmax = 27.3°, θmin = 2.9° h = −5→5 k = −5→5 l = −9→9
Refinement Refinement on F2 Least-squares matrix: full R[F2 > 2σ(F2)] = 0.017 wR(F2) = 0.057 S = 1.44 182 reflections 19 parameters 0 restraints
Acta Cryst. (2015). C71
Primary atom site location: structure-invariant direct methods Secondary atom site location: difference Fourier map w = 1/[σ2(Fo2) + (0.0091P)2 + 0.0124P] where P = (Fo2 + 2Fc2)/3 (Δ/σ)max < 0.001 Δρmax = 0.22 e Å−3 Δρmin = −0.19 e Å−3
sup-1
supporting information Special details Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes. Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2)
C1 B2 Li3 Li4 Li5
x
y
z
Uiso*/Ueq
0.0000 0.2424 0.0000 0.5000 0.5000
0.5000 0.5000 0.0000 0.5000 0.0000
0.2184 (2) 0.0501 (2) 0.5000 0.5000 0.2113 (4)
0.0060 (4) 0.0059 (3) 0.0045 (9) 0.0039 (8) 0.0069 (6)
Atomic displacement parameters (Å2)
C1 B2 Li3 Li4 Li5
U11
U22
U33
U12
U13
U23
0.0049 (11) 0.0053 (7) 0.0038 (11) 0.0034 (11) 0.0072 (19)
0.0054 (11) 0.0054 (6) 0.0038 (11) 0.0034 (11) 0.0064 (19)
0.0076 (8) 0.0069 (6) 0.0059 (19) 0.0048 (19) 0.0071 (14)
0.000 0.000 0.000 0.000 0.000
0.000 −0.0003 (5) 0.000 0.000 0.000
0.000 0.000 0.000 0.000 0.000
Geometric parameters (Å, º) C1—B2 C1—B2i B2—B2ii
1.5614 (17) 1.5614 (17) 1.6671 (13)
B2—B2iii B2—B2i B2—B2iv
1.6671 (13) 2.0067 (2) 2.1322 (2)
B2—C1—B2i C1—B2—B2ii C1—B2—B2iii B2ii—B2—B2iii C1—B2—B2i B2ii—B2—B2i
79.98 (10) 137.55 (8) 137.55 (8) 79.51 (7) 50.01 (5) 129.75 (4)
B2iii—B2—B2i C1—B2—B2iv B2ii—B2—B2iv B2iii—B2—B2iv B2i—B2—B2iv
129.75 (4) 129.99 (5) 50.25 (4) 50.25 (4) 180.0
Symmetry codes: (i) −x, −y+1, z; (ii) y, −x+1, −z; (iii) −y+1, x, −z; (iv) −x+1, −y+1, z.
Acta Cryst. (2015). C71
sup-2
