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Crystal structure of the R3Ag1−δSiS7 (R = La, Ce, Pr, Nd, Sm, δ = 0.10–0.23) compounds
Journal of Alloys and Compounds 460 (2008) 201–205
Crystal structure of the R3Ag1−δSiS7 (R = La, Ce, Pr, Nd, Sm, δ = 0.10–0.23) compounds M. Daszkiewicz a,∗ , L.D. Gulay a,b , O.S. Lychmanyuk b , A. Pietraszko a a
W. Trzebiatowski Institute of Low Temperature and Structure Research, Polish Academy of Sciences, Ok´olna Street 2, P.O. Box 1410, Wrocław 50-950, Poland b Department of General and Inorganic Chemistry, Volyn State University, Voli Avenue 13, Lutsk 43009, Ukraine Received 26 April 2007; received in revised form 16 May 2007; accepted 17 May 2007 Available online 21 May 2007
Abstract The crystal structure of the R3 Ag1−δ SiS7 (R = La, Ce, Pr, Nd, Sm, δ = 0.10–0.23, space group P63 , Pearson symbol hP23.80 − 23.54) compounds were determined by means of X-ray single crystal diffraction (a = 1.04168(8) nm, c = 0.57825(4) nm, R1 = 0.0116 for La3 Ag0.90 SiS7 ; a = 1.0312(1) nm, c = 0.57395(7) nm, R1 = 0.0152 for Ce3 Ag0.82 SiS7 ; a = 1.0248(1) nm, c = 0.57223(5) nm, R1 = 0.0105 for Pr3 Ag0.85 SiS7 ; a = 1.0192(1) nm, c = 0.57020(6) nm, R1 = 0.0292 for Nd3 Ag0.81 SiS7 , a = 1.0100(1) nm, c = 0.56643(6) nm, R1 = 0.0208 for Sm3 Ag0.77 SiS7 . Gradual decrease of the silver amount in the series of chalcogenides was found. © 2007 Elsevier B.V. All rights reserved. Keywords: Chalcogenides; Rare-earth compounds; Ag compounds; Crystal structure; X-ray single crystal diffraction
1. Introduction The rare-earth chalcogenides are being intensively studied during last years due to their specific thermal, electrical and optical properties which, e.g., make them prospective materials in the field of infrared and non-linear optics [1,2]. The investigation of the crystal structures of new compounds is an important step in this research. Especially, systematic investigation on the specific chalcogenides systems can be helpful in the “crystal structure ↔ properties” relationship. The existence of quaternary R3 AgSiS7 (R = La, Ce, Pr, Nd and Sm) compounds (La3 CuSiS7 structure type, space group P63 ) has been demonstrated in Ref. [3]. Lattice parameters for these compounds have been determined. The crystal structure of the La3 AgSiS7 compound has been reinvestigated recently in Ref. [4] by means of X-ray single crystal diffraction. These compounds are members of a large family of the compounds with the general formula R3 MTX7 (space group P63 ), where R—lanthanide element, M—mono-valent element (Cu, Ag), T—Si, Ge, Sn and X—S, Se. This paper presents a part of our systematic investigations of rare-earth chalcogenides with transition metals. The crys∗
Corresponding author. Tel.: +48 71 343 50 21. E-mail address: [email protected] (M. Daszkiewicz).
0925-8388/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2007.05.067
tal structure of the R3 Ag1−δ SiS7 (R = La, Ce, Pr, Nd, Sm, δ = 0.10–0.23) compounds investigated by means of X-ray single crystal diffraction are given and discussed. 2. Experimental details The samples with the compositions R3 AgSiS7 (R = La, Ce, Pr, Nd, Sm) were prepared by fusion of the high purity elements (the purity of the ingredients was better than 99.9 wt.%) in evacuated silica ampoules in a tube furnace. The ampoules were heated with a heating rate of 30 K/h to the maximal temperature, 1420 K. Then, they were kept at this temperature for 3 h. Afterwards they were cooled slowly (10 K/h) to 870 K and annealed at this temperature for 240 h. After annealing the ampoules were quenched in cold water. Diffraction-quality single crystals for the crystal structure determination were selected from the obtained samples. X-ray intensity data were collected on a KUMA Diffraction KM-4 four-circle single crystal diffractometer equipped with a CCD detector using graphite-monochromatized Mo K␣ radiation (λ = 0.071073 nm). The raw data were treated with the CrysAlis Data Reduction Program [5] taking into account correction on absorption. The intensities of the reflections were corrected for Lorentz and Polarization factors. The crystal structures were solved by Patterson methods [6] and refined by full matrix least squares method using SHELXL-97 program [7].
3. Results and discussion The existence of quaternary compounds of approximate compositions R3 AgSiS7 (R = La, Ce, Pr, Nd and Sm) was established. The crystal structures of all compounds were investigated
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Table 1 Crystal data and structure refinement details of the R3 Ag1−δ SiS7 (R = La, Ce, Pr, Nd, Sm, δ = 0.10–0.23) compounds
Volume (nm3 ) Number of formula units per unit cell Calculated density (g/cm3 ) Absorption coefficient (mm−1 ) F(000) Crystal size Θ range for data collection Index ranges
Reflections collected Independent reflections Refinement method Absolute structure parameter Data/restraints/parameters Goodness-of-fit on F2 Final R indices [I > 2σ(I)] R indices (all data) Extinction coefficient Largest diff. peak and hole × 10−3
La3 Ag1−␦ SiS7 (δ = 0.10) 766.32 P63 (No. 173) a = 1.04168(8) nm, c = 0.57825(6) nm 0.54339(7) 2
Ce3 Ag1−δ SiS7 (δ = 0.18) 761.86 P63 (no. 173) a = 1.0312(1) nm, c = 0.57395(7) nm 0.5286(1) 2
Pr3 Ag1−δ SiS7 (δ = 0.15) 779.04 P63 (no. 173) a = 1.0248(1) nm, c = 0.57223(5) nm 0.5204(1) 2
Nd3 Ag1−δ SiS7 (δ = 0.19) 787.90 P63 (no. 173) a = 1.0192(1) nm, c = 0.57020(6) nm 0.5130(1) 2
Sm3 Ag1−δ SiS7 (δ = 0.23) 805.11 P63 (no. 173) a = 1.0100(1) nm, c = 0.56643(6) nm 0.5004(1) 2
4.684 14.545
4.786 15.611
4.971 17.080
5.100 18.258
5.343 20.750
679 0.12 mm × 0.15 mm × 0.17 mm 4.19–26.35 −12 ≤ h ≤ 13 −13 ≤ k ≤ 13 −7 ≤ l ≤ 7 6905 748 [R(int.) = 0.0333] Full-matrix least-square on F2 −0.01(1) 739/1/41 1.139 R1 = 0.0116, wR2 = 0.0282 R1 = 0.0117, wR2 = 0.0282 0.0054(1) 0.517 and −0.366 e/nm3
678 0.08 mm × 0.13 mm × 0.16 mm 3.95–24.27 −11 ≤ h ≤ 10 −11 ≤ k ≤ 11 −6 ≤ l ≤ 6 5288 574 [R(int.) = 0.0487] Full-matrix least-square on F2 0.00(2) 574/1/43 1.005 R1 = 0.0152, wR2 = 0.0240 R1 = 0.0157, wR2 = 0.0241 0.0094(3) 0.590 and −0.406 e/nm3
696 0.10 mm × 0.12 mm × 0.15 mm 4.24–26.32 −12 ≤ h ≤ 12 −12 ≤ k ≤ 9 −7 ≤ l ≤ 7 6037 700 [R(int.) = 0.0287] Full-matrix least-square on F2 −0.02(2) 700/1/43 1.045 R1 = 0.0105, wR2 = 0.0235 R1 = 0.0108, wR2 = 0.0236 0.0082(3) 0.535 and −0.564 e/nm3
701 0.08 mm × 0.09 mm × 0.13 mm 4.00–26.35 −12 ≤ h ≤ 12 −11 ≤ k ≤ 12 −7 ≤ l ≤ 7 6129 704 [R(int.) = 0.0543] Full-matrix least-square on F2 −0.01(4) 704/1/43 1.273 R1 = 0.0292, wR2 = 0.0542 R1 = 0.0305, wR2 = 0.0545 0.0116(6) 1.241 and −1.897 e/nm3
712 0.12 × 0.13 × 0.14 mm 4.03–26.35 −12 ≤ h ≤ 12 −12 ≤ k ≤ 12 −7 ≤ l ≤ 7 6434 681 [R(int.) = 0.0749] Full-matrix least-square on F2 −0.02(3) 681/1/43 1.094 R1 = 0.0208, wR2 = 0.0481 R1 = 0.0211, wR2 = 0.0483 0.0068(4) 1.525 and −1.143 e/nm3
M. Daszkiewicz et al. / Journal of Alloys and Compounds 460 (2008) 201–205
Empirical formula Formula weight Space group Unit cell dimensions
Table 2 Atomic coordinates and temperature factors for the R3 Ag1−δ SiS7 (R = La, Ce, Pr, Nd, Sm, δ = 0.10–0.23) compounds Atom
Position
U11
U22
1 0.85 0.05 1 1 1 1
0.00853(5) 0.0278(2) 0.030(2) 0.0080(3) 0.0108(3) 0.0118(1) 0.0098(1)
0.00925(8) 0.0107(1) 0.006(2) 0.0084(4) 0.0135(4) 0.0105(3) 0.0101(4)
0.00793(8) 0.0107(1) 0.006(2) 0.0084(4) 0.0135(4) 0.0153(3) 0.0086(3)
0.2438(1) 0.1819(5) 0.968(4) 0.3287(4) 0.9658(4) 0.7298(4) 0.9726(2)
1 0.756(7) 0.069(7) 1 1 1 1
0.0106(1) 0.058(2) 0.011(6) 0.0093(7) 0.0135(6) 0.0152(3) 0.0110(3)
0.0110(1) 0.0106(5) 0.015(4) 0.011(1) 0.014(1) 0.0133(7) 0.0123(9)
0.64099(1) 0 0 2/3 2/3 0.73544(9) 0.4757(1)
0.23872(8) 0.1717(5) 0.967(3) 0.3257(3) 0.9596(3) 0.7253(2) 0.9694(1)
1 0.749(7) 0.105(7) 1 1 1 1
0.00902(7) 0.044(1) 0.034(6) 0.0083(3) 0.0107(3) 0.0131(1) 0.0096(1)
0.87665(4) 0 0 1/3 1/3 0.9099(2) 0.5895(3)
0.64112(4) 0 0 2/3 2/3 0.7349(2) 0.4763(3)
0.2422(2) 0.169(1) 0.961(4) 0.3286(8) 0.9627(7) 0.7273(5) 0.9742(4)
1 0.70(1) 0.11(1) 1 1 1 1
0.87554(3) 0 0 1/3 1/3 0.9083(1) 0.5881(1)
0.64113(3) 0 0 2/3 2/3 0.7354(1) 0.4767(1)
0.2422(1) 0.163(3) 0.973(5) 0.3291(6) 0.9596(5) 0.7255(3) 0.9765(3)
1 0.62(2) 0.15(2) 1 1 1 1
y/b
z/c
La3 Ag1−δ SiS7 (δ = 0.10) La 6c Ag1 2a Ag2 2a Si1 2b S1 2b S2 6c S3 6c
0.87860(1) 0 0 1/3 1/3 0.91276(8) 0.59234(9)
0.64075(1) 0 0 2/3 2/3 0.73662(8) 0.47444(9)
0.22994(5) 0.1775(1) 0.970(3) 0.3157(3) 0.9532(3) 0.7181(1) 0.9568(1)
Ce3 Ag1−δ SiS7 (δ = 0.18) Ce 6c Ag1 2a Ag2 2a Si 2b S1 2b S2 6c S3 6c
0.87783(3) 0 0 1/3 1/3 0.9120(1) 0.5910(1)
0.64106(3) 0 0 2/3 2/3 0.7373(1) 0.4751(1)
Pr3 Ag1−δ SiS7 (δ = 0.15) Pr 6c Ag1 2a Ag2 2a Si 2b S1 2b S2 6c S3 6c
0.87713(1) 0 0 1/3 1/3 0.91058(9) 0.5902(1)
Nd3 Ag1−δ SiS7 (δ = 0.19) Nd 6c Ag1 2a Ag2 2a Si 2b S1 2b S2 6c S3 6c Sm3 Ag1−δ SiS7 (δ = 0.23) Sm 6c Ag1 2a Ag2 2a Si 2b S1 2b S2 6c S3 6c
U33
U23
U13
U12
0.00865(8) 0.0620(7) 0.077(9) 0.0071(6) 0.0054(6) 0.0093(3) 0.0109(4)
−0.0008(1) 0 0 0 0 −0.0007(4) 0.0009(3)
−0.0009(1) 0 0 0 0 0.0001(3) 0.0011(3)
0.00447(6) 0.00536(8) 0.003(1) 0.0042(2) 0.0068(2) 0.0062(3) 0.0047(3)
0.0099(1) 0.0106(5) 0.015(4) 0.011(1) 0.014(1) 0.0230(7) 0.0101(8)
0.0108(1) 0.152(7) 0.00(1) 0.004(1) 0.011(1) 0.0097(8) 0.0108(7)
−0.0007(3) 0 0 0 0 −0.001(1) 0.0018(6)
−0.0010(3) 0 0 0 0 0.0013(8) 0.0018(6)
0.0052(1) 0.0053(3) 0.008(2) 0.0058(5) 0.0074(5) 0.0094(6) 0.0059(7)
0.0095(1) 0.0099(3) 0.014(1) 0.0094(5) 0.0130(5) 0.0105(3) 0.0104(4)
0.0085(10) 0.0099(3) 0.014(1) 0.0094(5) 0.0130(5) 0.0175(4) 0.0088(4)
0.0091(1) 0.114(4) 0.07(1) 0.0061(7) 0.0061(7) 0.0111(4) 0.0098(4)
−0.0009(1) 0 0 0 0 −0.0009(5) 0.0007(4)
−0.0008(1) 0 0 0 0 0.0010(4) 0.0007(4)
0.00468(7) 0.0049(1) 0.007(1) 0.0047(2) 0.0065(2) 0.0067(3) 0.0050(4)
0.0114(1) 0.054(4) 0.024(8) 0.0100(9) 0.0123(8) 0.0151(4) 0.0117(5)
0.0121(2) 0.0107(9) 0.019(5) 0.010(1) 0.014(1) 0.0127(9) 0.012(1)
0.0112(2) 0.0107(9) 0.019(5) 0.010(1) 0.014(1) 0.020(1) 0.011(1)
0.0112(2) 0.14(1) 0.03(2) 0.008(1) 0.008(1) 0.011(1) 0.0113(9)
−0.0007(3) 0 0 0 0 0.000(1) 0.0007(9)
−0.0010(4) 0 0 0 0 0.000(1) 0.001(1)
0.0060(1) 0.0054(4) 0.009(2) 0.0054(6) 0.0070(6) 0.0077(8) 0.0060(9)
0.0120(1) 0.074(6) 0.031(6) 0.0108(6) 0.0129(6) 0.0166(3) 0.0125(3)
0.0114(1) 0.0109(7) 0.013(2) 0.0109(8) 0.0138(8) 0.0132(6) 0.0126(7)
0.0106(1) 0.0109(7) 0.013(2) 0.0109(8) 0.0138(8) 0.0225(7) 0.0118(7)
0.0142(2) 0.19(1) 0.06(1) 0.010(1) 0.011(1) 0.0144(8) 0.0139(7)
−0.0009(1) 0 0 0 0 −0.002(1) 0.0005(6)
−0.0009(2) 0 0 0 0 0.0002(8) 0.0009(6)
0.0055(1) 0.0055(4) 0.006(1) 0.0054(4) 0.0069(4) 0.0091(5) 0.0068(6)
M. Daszkiewicz et al. / Journal of Alloys and Compounds 460 (2008) 201–205
Ueq. × 102 , nm2
x/a
Ueq. is defined as one third of the trace of the orthogonalized Uij tensor. The anisotropic temperature factor exponent takes the form: −2π2 [h2 a2 U11 + · · · + 2hkabU12 ].
203
204
M. Daszkiewicz et al. / Journal of Alloys and Compounds 460 (2008) 201–205
because the Ag2–Ag1 distance is ∼0.17 nm. The occupation of the Ag1 position decreases and the occupation of the Ag2 position increases when going from La to Sm in the series (Fig. 1). One additional position of the Ag atom exists for the investigated in present paper R3 Ag1−δ SiS7 compounds when compared with La3 CuSiS7 [9] type of structure for the R3 AgSiS7 (R = La, Ce, Pr, Nd and Sm) compounds reported in Ref. [3,4]. Relevant interatomic distances (δ, nm) and coordination numbers (C.N.) of the R, Ag and Si atoms in the structure of Fig. 1. The occupation factors of the Ag1 and Ag2 positions in the structure of the R3 Ag1−δ SiS7 (R = La, Ce, Pr, Nd, Sm, δ = 0.10−0.23) compounds.
using X-ray single crystal diffraction. The extinctions observed were found to be consistent with the space group P63 that was applied for the crystal structure solution and refinement. One position of R, one position of Ag, one position of Si and three positions of S were determined at the first stage. High values of anisotropic parameters for Ag atom and residual electron density near this atom were observed. Since these extra sites were situated in triangular antiprismatic interstices formed by S atoms additional Ag atoms (Ag2) were located there at the second stage. Reasonable values of anisotropic parameters for Ag atoms were finally obtained. The final values of R1 factors were also significantly improved. The crystal data and refinement information are summarized in Table 1, whereas the final atomic coordinates and anisotropic parameters are given in Table 2. Similarly to the Ce3 Ag0.81 SnS7 and La3 Ag0.82 SnS7 crystal structures [8] reduced content of silver for R3 Ag1−δ SiS7 (R = La, Ce, Pr, Nd, Sm, δ = 0.10–0.23) was observed when compared with initial compositions. In these non-stoichiometric compounds the charge neutrality can be realized assuming Ag2+ ions existence in the structure. It is noteworthy that two different positions of the silver atom imply Ag deficiency. Assuming that in one unit cell silver atom occupies Ag2 position, the next cell must be occupied in the same manner or remain unoccupied,
Fig. 2. The unit cell and the coordination polyhedra of the Sm (a), Ag1 (b), Ag2 (c), Si (d), S1 (e), S2 (f) and S3 (g) atoms in the structure of the Sm3 Ag1−δ SiS7 (δ = 0.23) compound.
Table 3 Interatomic distances (δ, nm) and coordination numbers (C.N.) of the atoms R3 Ag1−δ SiS7 (R = La, Ce, Pr, Nd, Sm, δ = 0.10–0.23) compounds Atoms
δ (nm)
C.N.
La3 Ag1−δ SiS7 (δ = 0.10)
Ce3 Ag1−δ SiS7 (δ = 0.18)
Pr3 Ag1−δ SiS7 (δ = 0.15)
Nd3 Ag1−δ SiS7 (δ = 0.19)
Sm3 Ag1−δ SiS7 (δ = 0.23)
−1S3 −1S2 −1S2 −1S2 −1S3 −1S3 −1S2 −1S1
0.29118(9) 0.29412(8) 0.2956(1) 0.29761(8) 0.30365(9) 0.30737(9) 0.3086(1) 0.31187(7)
0.2883(1) 0.2910(1) 0.2922(2) 0.2937(1) 0.3006(1) 0.3047(1) 0.3076(2) 0.3086(1)
0.28638(9) 0.28985(9) 0.2911(1) 0.29203(9) 0.2984(1) 0.3032(1) 0.3058(1) 0.30644(8)
0.2849(2) 0.2884(2) 0.2891(3) 0.2903(2) 0.2968(2) 0.3018(2) 0.3054(3) 0.3047(1)
0.2820(1) 0.2862(2) 0.2862(1) 0.2865(1) 0.2937(1) 0.2999(1) 0.3045(2) 0.3012(1)
−3S2
0.24321(8)
0.2403(1)
0.24084(9)
0.2403(2)
0.2377(3)
−3S2 −3S2
0.2815(9) 0.2824(9)
0.275(1) 0.282(1)
0.276(1) 0.280(1)
0.272(1) 0.282(1)
0.273(1) 0.275(1)
−1S1 −3S3
0.2096(2) 0.2136(1)
0.2083(4) 0.2137(1)
0.2095(2) 0.2135(1)
0.2086(6) 0.2139(3)
0.2093(4) 0.2139(2)
R 8
Ag1 3 Ag2 6 Si 4
M. Daszkiewicz et al. / Journal of Alloys and Compounds 460 (2008) 201–205
205
Fig. 3. The packing of the [SmS11 S24 S33 ] trigonal prisms [Ag1S23 ], triangles [Ag2S26 ], octahedra and [SiS11 S33 ] tetrahedra in the structure of the Sm3 Ag1−δ SiS7 (δ = 0.23) compound.
the compounds are given in Table 3. All interatomic distances (except the Ag1–Ag2 distances) agree well with the sum of the respective ionic radii [10]. Since the Ag1 and Ag2 sites are partially occupied, not more than one of two adjacent positions will be occupied. Thus, the close contact between the Ag1 and Ag2 atoms does not really exist. The unit cell and the coordination polyhedra of the Sm (a), Ag1 (b), Ag2 (c), Si (d), S1 (e), S2 (f) and S3 (g) atoms in the structure of the Sm3 Ag1−δ SiS7 (δ = 0.23) compound are shown in Fig. 2. The Sm atom is eight coordinated to one S1, four S2 and three S3 atoms. Its coordination polyhedron may be described as a bi-capped trigonal prism. The Ag1 atom is three coordinated to three S2 atoms. These S2 atoms form triangle and the Ag1 atom is situated close to the plane of triangle. The Ag2 atom is located practically in the centre of trigonal antiprism of six S2 atoms. The Si atom is located on a 31 screw axis and its surroundings (one S1 atom and three S3 atoms) form a compressed tetrahedron which can be ideally described in C3v point group symmetry. The S1 and S3 atoms are located in [S1SiSm3 ] and [S3SiSm3 ]
tetrahedra, respectively. The S2 atom has six neighbours which create [S3Ag22 Sm4 ] distorted octahedron. The packing of the [SmS11 S24 S33 ] trigonal prisms [Ag1S23 ], triangles [Ag2S26 ], trigonal antiprisms and [SiS11 S33 ] tetrahedra in the structure of the Sm3 Ag1−δ SiS7 (δ = 0.23) compound is shown in Fig. 3. Three [SmS11 S24 S33 ] trigonal prisms are connected to each other by corners around the 63 screw axis. Their S2 atoms simultaneously form triangular and trigonal antiprismatic surroundings around the Ag1 and Ag2 atoms, respectively. These triangles and trigonal antiprisms create column directed along c-axis with Ag situated on a principal axis of the column. Three different [SmS11 S24 S33 ] trigonal prisms are connected to the [SiS11 S33 ] tetrahedra by corners. The dependence of the lattice parameters (a and c) and unit cell volume (V) of the R3 Ag1−δ SiS7 (R = La, Ce, Pr, Nd, Sm, δ = 0.10–0.23) compounds on the ionic radii of the rare-earth elements are shown in Fig. 4 reflecting the well known lanthanide contraction when going from La to Sm. The lattice parameter a decreases significantly, whereas parameter c decreases slightly with the decrease of the ionic radii of rare-earth element. References
Fig. 4. The dependence of the lattice parameters (a and c) and unit cell volume (V) of the R3 Ag1−δ SiS7 (R = La, Ce, Pr, Nd, Sm, δ = 0.10−0.23) compounds on the ionic radii of the rare-earth elements.
[1] A.A. Eliseev, G.M. Kuzmichyeva, Handbook on the Physics and Chemistry of Rare Earths, vol. 13, Elsevier Science Publishers B.V., 1990 (Chapter 89, pp. 191–281). [2] V.A. Starodub, Uspehi Khimii (in Russian) 68 (10) (1999) 883. [3] M. Guittard, M. Julien-Pouzol, Bull. Soc. Chim. France 7 (1970) 2467. [4] L.-B. Wu, F.-Q. Huang, Z. Kristallogr, New Cryst. St. 220 (2005) 307. [5] M. Mayer, CrysAlis Data Reduction Program, Version 1.171.30 3, Oxford Diffraction Ltd., 2006. [6] G.M. Sheldrick, Program for the Solution of Crystal Structures, University of G¨ottingem, Germany, 1985. [7] G.M. Sheldrick, Program for Crystal Structures Refinement, University of G¨ottingem, Germany, 1997. [8] M. Daszkiewicz, L.D. Gulay, A. Pietraszko, V.Ya. Shemet, J. Solid State Chem. 180 (2007) 2053. [9] G. Collin, P. Laruelle, Bull. Soc. Fr. Mineral. Cr. 94 (1971) 175. [10] N. Wiberg, Lehrbuch der Anorganischen Chemie, Walter de Gruyter, Berlin, 1995, p. 1838.
Crystal structure of the R3Ag1−δSiS7 (R = La, Ce, Pr, Nd, Sm, δ = 0.10–0.23) compounds M. Daszkiewicz a,∗ , L.D. Gulay a,b , O.S. Lychmanyuk b , A. Pietraszko a a
W. Trzebiatowski Institute of Low Temperature and Structure Research, Polish Academy of Sciences, Ok´olna Street 2, P.O. Box 1410, Wrocław 50-950, Poland b Department of General and Inorganic Chemistry, Volyn State University, Voli Avenue 13, Lutsk 43009, Ukraine Received 26 April 2007; received in revised form 16 May 2007; accepted 17 May 2007 Available online 21 May 2007
Abstract The crystal structure of the R3 Ag1−δ SiS7 (R = La, Ce, Pr, Nd, Sm, δ = 0.10–0.23, space group P63 , Pearson symbol hP23.80 − 23.54) compounds were determined by means of X-ray single crystal diffraction (a = 1.04168(8) nm, c = 0.57825(4) nm, R1 = 0.0116 for La3 Ag0.90 SiS7 ; a = 1.0312(1) nm, c = 0.57395(7) nm, R1 = 0.0152 for Ce3 Ag0.82 SiS7 ; a = 1.0248(1) nm, c = 0.57223(5) nm, R1 = 0.0105 for Pr3 Ag0.85 SiS7 ; a = 1.0192(1) nm, c = 0.57020(6) nm, R1 = 0.0292 for Nd3 Ag0.81 SiS7 , a = 1.0100(1) nm, c = 0.56643(6) nm, R1 = 0.0208 for Sm3 Ag0.77 SiS7 . Gradual decrease of the silver amount in the series of chalcogenides was found. © 2007 Elsevier B.V. All rights reserved. Keywords: Chalcogenides; Rare-earth compounds; Ag compounds; Crystal structure; X-ray single crystal diffraction
1. Introduction The rare-earth chalcogenides are being intensively studied during last years due to their specific thermal, electrical and optical properties which, e.g., make them prospective materials in the field of infrared and non-linear optics [1,2]. The investigation of the crystal structures of new compounds is an important step in this research. Especially, systematic investigation on the specific chalcogenides systems can be helpful in the “crystal structure ↔ properties” relationship. The existence of quaternary R3 AgSiS7 (R = La, Ce, Pr, Nd and Sm) compounds (La3 CuSiS7 structure type, space group P63 ) has been demonstrated in Ref. [3]. Lattice parameters for these compounds have been determined. The crystal structure of the La3 AgSiS7 compound has been reinvestigated recently in Ref. [4] by means of X-ray single crystal diffraction. These compounds are members of a large family of the compounds with the general formula R3 MTX7 (space group P63 ), where R—lanthanide element, M—mono-valent element (Cu, Ag), T—Si, Ge, Sn and X—S, Se. This paper presents a part of our systematic investigations of rare-earth chalcogenides with transition metals. The crys∗
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tal structure of the R3 Ag1−δ SiS7 (R = La, Ce, Pr, Nd, Sm, δ = 0.10–0.23) compounds investigated by means of X-ray single crystal diffraction are given and discussed. 2. Experimental details The samples with the compositions R3 AgSiS7 (R = La, Ce, Pr, Nd, Sm) were prepared by fusion of the high purity elements (the purity of the ingredients was better than 99.9 wt.%) in evacuated silica ampoules in a tube furnace. The ampoules were heated with a heating rate of 30 K/h to the maximal temperature, 1420 K. Then, they were kept at this temperature for 3 h. Afterwards they were cooled slowly (10 K/h) to 870 K and annealed at this temperature for 240 h. After annealing the ampoules were quenched in cold water. Diffraction-quality single crystals for the crystal structure determination were selected from the obtained samples. X-ray intensity data were collected on a KUMA Diffraction KM-4 four-circle single crystal diffractometer equipped with a CCD detector using graphite-monochromatized Mo K␣ radiation (λ = 0.071073 nm). The raw data were treated with the CrysAlis Data Reduction Program [5] taking into account correction on absorption. The intensities of the reflections were corrected for Lorentz and Polarization factors. The crystal structures were solved by Patterson methods [6] and refined by full matrix least squares method using SHELXL-97 program [7].
3. Results and discussion The existence of quaternary compounds of approximate compositions R3 AgSiS7 (R = La, Ce, Pr, Nd and Sm) was established. The crystal structures of all compounds were investigated
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Table 1 Crystal data and structure refinement details of the R3 Ag1−δ SiS7 (R = La, Ce, Pr, Nd, Sm, δ = 0.10–0.23) compounds
Volume (nm3 ) Number of formula units per unit cell Calculated density (g/cm3 ) Absorption coefficient (mm−1 ) F(000) Crystal size Θ range for data collection Index ranges
Reflections collected Independent reflections Refinement method Absolute structure parameter Data/restraints/parameters Goodness-of-fit on F2 Final R indices [I > 2σ(I)] R indices (all data) Extinction coefficient Largest diff. peak and hole × 10−3
La3 Ag1−␦ SiS7 (δ = 0.10) 766.32 P63 (No. 173) a = 1.04168(8) nm, c = 0.57825(6) nm 0.54339(7) 2
Ce3 Ag1−δ SiS7 (δ = 0.18) 761.86 P63 (no. 173) a = 1.0312(1) nm, c = 0.57395(7) nm 0.5286(1) 2
Pr3 Ag1−δ SiS7 (δ = 0.15) 779.04 P63 (no. 173) a = 1.0248(1) nm, c = 0.57223(5) nm 0.5204(1) 2
Nd3 Ag1−δ SiS7 (δ = 0.19) 787.90 P63 (no. 173) a = 1.0192(1) nm, c = 0.57020(6) nm 0.5130(1) 2
Sm3 Ag1−δ SiS7 (δ = 0.23) 805.11 P63 (no. 173) a = 1.0100(1) nm, c = 0.56643(6) nm 0.5004(1) 2
4.684 14.545
4.786 15.611
4.971 17.080
5.100 18.258
5.343 20.750
679 0.12 mm × 0.15 mm × 0.17 mm 4.19–26.35 −12 ≤ h ≤ 13 −13 ≤ k ≤ 13 −7 ≤ l ≤ 7 6905 748 [R(int.) = 0.0333] Full-matrix least-square on F2 −0.01(1) 739/1/41 1.139 R1 = 0.0116, wR2 = 0.0282 R1 = 0.0117, wR2 = 0.0282 0.0054(1) 0.517 and −0.366 e/nm3
678 0.08 mm × 0.13 mm × 0.16 mm 3.95–24.27 −11 ≤ h ≤ 10 −11 ≤ k ≤ 11 −6 ≤ l ≤ 6 5288 574 [R(int.) = 0.0487] Full-matrix least-square on F2 0.00(2) 574/1/43 1.005 R1 = 0.0152, wR2 = 0.0240 R1 = 0.0157, wR2 = 0.0241 0.0094(3) 0.590 and −0.406 e/nm3
696 0.10 mm × 0.12 mm × 0.15 mm 4.24–26.32 −12 ≤ h ≤ 12 −12 ≤ k ≤ 9 −7 ≤ l ≤ 7 6037 700 [R(int.) = 0.0287] Full-matrix least-square on F2 −0.02(2) 700/1/43 1.045 R1 = 0.0105, wR2 = 0.0235 R1 = 0.0108, wR2 = 0.0236 0.0082(3) 0.535 and −0.564 e/nm3
701 0.08 mm × 0.09 mm × 0.13 mm 4.00–26.35 −12 ≤ h ≤ 12 −11 ≤ k ≤ 12 −7 ≤ l ≤ 7 6129 704 [R(int.) = 0.0543] Full-matrix least-square on F2 −0.01(4) 704/1/43 1.273 R1 = 0.0292, wR2 = 0.0542 R1 = 0.0305, wR2 = 0.0545 0.0116(6) 1.241 and −1.897 e/nm3
712 0.12 × 0.13 × 0.14 mm 4.03–26.35 −12 ≤ h ≤ 12 −12 ≤ k ≤ 12 −7 ≤ l ≤ 7 6434 681 [R(int.) = 0.0749] Full-matrix least-square on F2 −0.02(3) 681/1/43 1.094 R1 = 0.0208, wR2 = 0.0481 R1 = 0.0211, wR2 = 0.0483 0.0068(4) 1.525 and −1.143 e/nm3
M. Daszkiewicz et al. / Journal of Alloys and Compounds 460 (2008) 201–205
Empirical formula Formula weight Space group Unit cell dimensions
Table 2 Atomic coordinates and temperature factors for the R3 Ag1−δ SiS7 (R = La, Ce, Pr, Nd, Sm, δ = 0.10–0.23) compounds Atom
Position
U11
U22
1 0.85 0.05 1 1 1 1
0.00853(5) 0.0278(2) 0.030(2) 0.0080(3) 0.0108(3) 0.0118(1) 0.0098(1)
0.00925(8) 0.0107(1) 0.006(2) 0.0084(4) 0.0135(4) 0.0105(3) 0.0101(4)
0.00793(8) 0.0107(1) 0.006(2) 0.0084(4) 0.0135(4) 0.0153(3) 0.0086(3)
0.2438(1) 0.1819(5) 0.968(4) 0.3287(4) 0.9658(4) 0.7298(4) 0.9726(2)
1 0.756(7) 0.069(7) 1 1 1 1
0.0106(1) 0.058(2) 0.011(6) 0.0093(7) 0.0135(6) 0.0152(3) 0.0110(3)
0.0110(1) 0.0106(5) 0.015(4) 0.011(1) 0.014(1) 0.0133(7) 0.0123(9)
0.64099(1) 0 0 2/3 2/3 0.73544(9) 0.4757(1)
0.23872(8) 0.1717(5) 0.967(3) 0.3257(3) 0.9596(3) 0.7253(2) 0.9694(1)
1 0.749(7) 0.105(7) 1 1 1 1
0.00902(7) 0.044(1) 0.034(6) 0.0083(3) 0.0107(3) 0.0131(1) 0.0096(1)
0.87665(4) 0 0 1/3 1/3 0.9099(2) 0.5895(3)
0.64112(4) 0 0 2/3 2/3 0.7349(2) 0.4763(3)
0.2422(2) 0.169(1) 0.961(4) 0.3286(8) 0.9627(7) 0.7273(5) 0.9742(4)
1 0.70(1) 0.11(1) 1 1 1 1
0.87554(3) 0 0 1/3 1/3 0.9083(1) 0.5881(1)
0.64113(3) 0 0 2/3 2/3 0.7354(1) 0.4767(1)
0.2422(1) 0.163(3) 0.973(5) 0.3291(6) 0.9596(5) 0.7255(3) 0.9765(3)
1 0.62(2) 0.15(2) 1 1 1 1
y/b
z/c
La3 Ag1−δ SiS7 (δ = 0.10) La 6c Ag1 2a Ag2 2a Si1 2b S1 2b S2 6c S3 6c
0.87860(1) 0 0 1/3 1/3 0.91276(8) 0.59234(9)
0.64075(1) 0 0 2/3 2/3 0.73662(8) 0.47444(9)
0.22994(5) 0.1775(1) 0.970(3) 0.3157(3) 0.9532(3) 0.7181(1) 0.9568(1)
Ce3 Ag1−δ SiS7 (δ = 0.18) Ce 6c Ag1 2a Ag2 2a Si 2b S1 2b S2 6c S3 6c
0.87783(3) 0 0 1/3 1/3 0.9120(1) 0.5910(1)
0.64106(3) 0 0 2/3 2/3 0.7373(1) 0.4751(1)
Pr3 Ag1−δ SiS7 (δ = 0.15) Pr 6c Ag1 2a Ag2 2a Si 2b S1 2b S2 6c S3 6c
0.87713(1) 0 0 1/3 1/3 0.91058(9) 0.5902(1)
Nd3 Ag1−δ SiS7 (δ = 0.19) Nd 6c Ag1 2a Ag2 2a Si 2b S1 2b S2 6c S3 6c Sm3 Ag1−δ SiS7 (δ = 0.23) Sm 6c Ag1 2a Ag2 2a Si 2b S1 2b S2 6c S3 6c
U33
U23
U13
U12
0.00865(8) 0.0620(7) 0.077(9) 0.0071(6) 0.0054(6) 0.0093(3) 0.0109(4)
−0.0008(1) 0 0 0 0 −0.0007(4) 0.0009(3)
−0.0009(1) 0 0 0 0 0.0001(3) 0.0011(3)
0.00447(6) 0.00536(8) 0.003(1) 0.0042(2) 0.0068(2) 0.0062(3) 0.0047(3)
0.0099(1) 0.0106(5) 0.015(4) 0.011(1) 0.014(1) 0.0230(7) 0.0101(8)
0.0108(1) 0.152(7) 0.00(1) 0.004(1) 0.011(1) 0.0097(8) 0.0108(7)
−0.0007(3) 0 0 0 0 −0.001(1) 0.0018(6)
−0.0010(3) 0 0 0 0 0.0013(8) 0.0018(6)
0.0052(1) 0.0053(3) 0.008(2) 0.0058(5) 0.0074(5) 0.0094(6) 0.0059(7)
0.0095(1) 0.0099(3) 0.014(1) 0.0094(5) 0.0130(5) 0.0105(3) 0.0104(4)
0.0085(10) 0.0099(3) 0.014(1) 0.0094(5) 0.0130(5) 0.0175(4) 0.0088(4)
0.0091(1) 0.114(4) 0.07(1) 0.0061(7) 0.0061(7) 0.0111(4) 0.0098(4)
−0.0009(1) 0 0 0 0 −0.0009(5) 0.0007(4)
−0.0008(1) 0 0 0 0 0.0010(4) 0.0007(4)
0.00468(7) 0.0049(1) 0.007(1) 0.0047(2) 0.0065(2) 0.0067(3) 0.0050(4)
0.0114(1) 0.054(4) 0.024(8) 0.0100(9) 0.0123(8) 0.0151(4) 0.0117(5)
0.0121(2) 0.0107(9) 0.019(5) 0.010(1) 0.014(1) 0.0127(9) 0.012(1)
0.0112(2) 0.0107(9) 0.019(5) 0.010(1) 0.014(1) 0.020(1) 0.011(1)
0.0112(2) 0.14(1) 0.03(2) 0.008(1) 0.008(1) 0.011(1) 0.0113(9)
−0.0007(3) 0 0 0 0 0.000(1) 0.0007(9)
−0.0010(4) 0 0 0 0 0.000(1) 0.001(1)
0.0060(1) 0.0054(4) 0.009(2) 0.0054(6) 0.0070(6) 0.0077(8) 0.0060(9)
0.0120(1) 0.074(6) 0.031(6) 0.0108(6) 0.0129(6) 0.0166(3) 0.0125(3)
0.0114(1) 0.0109(7) 0.013(2) 0.0109(8) 0.0138(8) 0.0132(6) 0.0126(7)
0.0106(1) 0.0109(7) 0.013(2) 0.0109(8) 0.0138(8) 0.0225(7) 0.0118(7)
0.0142(2) 0.19(1) 0.06(1) 0.010(1) 0.011(1) 0.0144(8) 0.0139(7)
−0.0009(1) 0 0 0 0 −0.002(1) 0.0005(6)
−0.0009(2) 0 0 0 0 0.0002(8) 0.0009(6)
0.0055(1) 0.0055(4) 0.006(1) 0.0054(4) 0.0069(4) 0.0091(5) 0.0068(6)
M. Daszkiewicz et al. / Journal of Alloys and Compounds 460 (2008) 201–205
Ueq. × 102 , nm2
x/a
Ueq. is defined as one third of the trace of the orthogonalized Uij tensor. The anisotropic temperature factor exponent takes the form: −2π2 [h2 a2 U11 + · · · + 2hkabU12 ].
203
204
M. Daszkiewicz et al. / Journal of Alloys and Compounds 460 (2008) 201–205
because the Ag2–Ag1 distance is ∼0.17 nm. The occupation of the Ag1 position decreases and the occupation of the Ag2 position increases when going from La to Sm in the series (Fig. 1). One additional position of the Ag atom exists for the investigated in present paper R3 Ag1−δ SiS7 compounds when compared with La3 CuSiS7 [9] type of structure for the R3 AgSiS7 (R = La, Ce, Pr, Nd and Sm) compounds reported in Ref. [3,4]. Relevant interatomic distances (δ, nm) and coordination numbers (C.N.) of the R, Ag and Si atoms in the structure of Fig. 1. The occupation factors of the Ag1 and Ag2 positions in the structure of the R3 Ag1−δ SiS7 (R = La, Ce, Pr, Nd, Sm, δ = 0.10−0.23) compounds.
using X-ray single crystal diffraction. The extinctions observed were found to be consistent with the space group P63 that was applied for the crystal structure solution and refinement. One position of R, one position of Ag, one position of Si and three positions of S were determined at the first stage. High values of anisotropic parameters for Ag atom and residual electron density near this atom were observed. Since these extra sites were situated in triangular antiprismatic interstices formed by S atoms additional Ag atoms (Ag2) were located there at the second stage. Reasonable values of anisotropic parameters for Ag atoms were finally obtained. The final values of R1 factors were also significantly improved. The crystal data and refinement information are summarized in Table 1, whereas the final atomic coordinates and anisotropic parameters are given in Table 2. Similarly to the Ce3 Ag0.81 SnS7 and La3 Ag0.82 SnS7 crystal structures [8] reduced content of silver for R3 Ag1−δ SiS7 (R = La, Ce, Pr, Nd, Sm, δ = 0.10–0.23) was observed when compared with initial compositions. In these non-stoichiometric compounds the charge neutrality can be realized assuming Ag2+ ions existence in the structure. It is noteworthy that two different positions of the silver atom imply Ag deficiency. Assuming that in one unit cell silver atom occupies Ag2 position, the next cell must be occupied in the same manner or remain unoccupied,
Fig. 2. The unit cell and the coordination polyhedra of the Sm (a), Ag1 (b), Ag2 (c), Si (d), S1 (e), S2 (f) and S3 (g) atoms in the structure of the Sm3 Ag1−δ SiS7 (δ = 0.23) compound.
Table 3 Interatomic distances (δ, nm) and coordination numbers (C.N.) of the atoms R3 Ag1−δ SiS7 (R = La, Ce, Pr, Nd, Sm, δ = 0.10–0.23) compounds Atoms
δ (nm)
C.N.
La3 Ag1−δ SiS7 (δ = 0.10)
Ce3 Ag1−δ SiS7 (δ = 0.18)
Pr3 Ag1−δ SiS7 (δ = 0.15)
Nd3 Ag1−δ SiS7 (δ = 0.19)
Sm3 Ag1−δ SiS7 (δ = 0.23)
−1S3 −1S2 −1S2 −1S2 −1S3 −1S3 −1S2 −1S1
0.29118(9) 0.29412(8) 0.2956(1) 0.29761(8) 0.30365(9) 0.30737(9) 0.3086(1) 0.31187(7)
0.2883(1) 0.2910(1) 0.2922(2) 0.2937(1) 0.3006(1) 0.3047(1) 0.3076(2) 0.3086(1)
0.28638(9) 0.28985(9) 0.2911(1) 0.29203(9) 0.2984(1) 0.3032(1) 0.3058(1) 0.30644(8)
0.2849(2) 0.2884(2) 0.2891(3) 0.2903(2) 0.2968(2) 0.3018(2) 0.3054(3) 0.3047(1)
0.2820(1) 0.2862(2) 0.2862(1) 0.2865(1) 0.2937(1) 0.2999(1) 0.3045(2) 0.3012(1)
−3S2
0.24321(8)
0.2403(1)
0.24084(9)
0.2403(2)
0.2377(3)
−3S2 −3S2
0.2815(9) 0.2824(9)
0.275(1) 0.282(1)
0.276(1) 0.280(1)
0.272(1) 0.282(1)
0.273(1) 0.275(1)
−1S1 −3S3
0.2096(2) 0.2136(1)
0.2083(4) 0.2137(1)
0.2095(2) 0.2135(1)
0.2086(6) 0.2139(3)
0.2093(4) 0.2139(2)
R 8
Ag1 3 Ag2 6 Si 4
M. Daszkiewicz et al. / Journal of Alloys and Compounds 460 (2008) 201–205
205
Fig. 3. The packing of the [SmS11 S24 S33 ] trigonal prisms [Ag1S23 ], triangles [Ag2S26 ], octahedra and [SiS11 S33 ] tetrahedra in the structure of the Sm3 Ag1−δ SiS7 (δ = 0.23) compound.
the compounds are given in Table 3. All interatomic distances (except the Ag1–Ag2 distances) agree well with the sum of the respective ionic radii [10]. Since the Ag1 and Ag2 sites are partially occupied, not more than one of two adjacent positions will be occupied. Thus, the close contact between the Ag1 and Ag2 atoms does not really exist. The unit cell and the coordination polyhedra of the Sm (a), Ag1 (b), Ag2 (c), Si (d), S1 (e), S2 (f) and S3 (g) atoms in the structure of the Sm3 Ag1−δ SiS7 (δ = 0.23) compound are shown in Fig. 2. The Sm atom is eight coordinated to one S1, four S2 and three S3 atoms. Its coordination polyhedron may be described as a bi-capped trigonal prism. The Ag1 atom is three coordinated to three S2 atoms. These S2 atoms form triangle and the Ag1 atom is situated close to the plane of triangle. The Ag2 atom is located practically in the centre of trigonal antiprism of six S2 atoms. The Si atom is located on a 31 screw axis and its surroundings (one S1 atom and three S3 atoms) form a compressed tetrahedron which can be ideally described in C3v point group symmetry. The S1 and S3 atoms are located in [S1SiSm3 ] and [S3SiSm3 ]
tetrahedra, respectively. The S2 atom has six neighbours which create [S3Ag22 Sm4 ] distorted octahedron. The packing of the [SmS11 S24 S33 ] trigonal prisms [Ag1S23 ], triangles [Ag2S26 ], trigonal antiprisms and [SiS11 S33 ] tetrahedra in the structure of the Sm3 Ag1−δ SiS7 (δ = 0.23) compound is shown in Fig. 3. Three [SmS11 S24 S33 ] trigonal prisms are connected to each other by corners around the 63 screw axis. Their S2 atoms simultaneously form triangular and trigonal antiprismatic surroundings around the Ag1 and Ag2 atoms, respectively. These triangles and trigonal antiprisms create column directed along c-axis with Ag situated on a principal axis of the column. Three different [SmS11 S24 S33 ] trigonal prisms are connected to the [SiS11 S33 ] tetrahedra by corners. The dependence of the lattice parameters (a and c) and unit cell volume (V) of the R3 Ag1−δ SiS7 (R = La, Ce, Pr, Nd, Sm, δ = 0.10–0.23) compounds on the ionic radii of the rare-earth elements are shown in Fig. 4 reflecting the well known lanthanide contraction when going from La to Sm. The lattice parameter a decreases significantly, whereas parameter c decreases slightly with the decrease of the ionic radii of rare-earth element. References
Fig. 4. The dependence of the lattice parameters (a and c) and unit cell volume (V) of the R3 Ag1−δ SiS7 (R = La, Ce, Pr, Nd, Sm, δ = 0.10−0.23) compounds on the ionic radii of the rare-earth elements.
[1] A.A. Eliseev, G.M. Kuzmichyeva, Handbook on the Physics and Chemistry of Rare Earths, vol. 13, Elsevier Science Publishers B.V., 1990 (Chapter 89, pp. 191–281). [2] V.A. Starodub, Uspehi Khimii (in Russian) 68 (10) (1999) 883. [3] M. Guittard, M. Julien-Pouzol, Bull. Soc. Chim. France 7 (1970) 2467. [4] L.-B. Wu, F.-Q. Huang, Z. Kristallogr, New Cryst. St. 220 (2005) 307. [5] M. Mayer, CrysAlis Data Reduction Program, Version 1.171.30 3, Oxford Diffraction Ltd., 2006. [6] G.M. Sheldrick, Program for the Solution of Crystal Structures, University of G¨ottingem, Germany, 1985. [7] G.M. Sheldrick, Program for Crystal Structures Refinement, University of G¨ottingem, Germany, 1997. [8] M. Daszkiewicz, L.D. Gulay, A. Pietraszko, V.Ya. Shemet, J. Solid State Chem. 180 (2007) 2053. [9] G. Collin, P. Laruelle, Bull. Soc. Fr. Mineral. Cr. 94 (1971) 175. [10] N. Wiberg, Lehrbuch der Anorganischen Chemie, Walter de Gruyter, Berlin, 1995, p. 1838.