Supporting information
Crystallographic Information File (CIF) https://doi.org/10.1107/S0108768101006607/js0110sup1.cif | |
Structure factor file (CIF format) https://doi.org/10.1107/S0108768101006607/js0110sup2.hkl | |
Structure factor file (CIF format) https://doi.org/10.1107/S0108768101006607/js0110sup3.hkl | |
Portable Document Format (PDF) file https://doi.org/10.1107/S0108768101006607/js0110sup4.pdf |
Sc_{2}B54/49C157/49 | The structural model can be described based on a trigonal cell with lattice constants A=B=23.710(9), C=6.703(2). In the present refinement, the structure is treated as an interpenetration of two layered subsystem structures, and refined in a five-dimensional formalism based on the superspace-group approach for composite crystals. New basis selected are a=a1=A/7, b=b1=B/7, c=C, as the strong reflections could be indexed using two sets of hexagonal axis with different a and common c: a1=b1=A/7=3.387 and c=6.703; a2=b2=A/9=2.634 and c=6.703. Each reflection is expressed by ha1*+kb1*+lc*+ma2*+nb2*. The new cell constants are a=b=a1=b1=3.387(1), c=6.703(2), sigma1=(9/7 0 0), sigma2=(0 9/7 0). The possible superspace group can be derived from the possible space groups of two subsystems. If the space groups of the two parts are assumed to be both P-3m1, the symmetry operations of the probable superspace group are listed as equivalent positions in xyzx4x5 as follows. |
M_{r} = 140.43 | D_{x} = 3.501 Mg m^{−}^{3} |
Trigonal, P3m1(p00)(0p0)0m0† | Mo Kα radiation, λ = 0.70930 Å |
q_{1} = 1.286a*; q_{2} = 1.286b*‡ | µ = 4.79 mm^{−}^{1} |
a = 3.387 (1) Å | T = 293 K |
c = 6.703 (2) Å | Platelike, silver metallic |
V = 66.59 (1) Å^{3} | 0.20 × 0.10 × 0.06 mm |
Z = 1 |
† Symmetry operations: (1) x, y, z, x_{4}, x_{5}; (2) −y, x−y, z, −x_{5}, x_{4}−x_{5}; (3) −x+y, −x, z, −x_{4}+x_{5}, −x_{4}; (4) y, x, −z, x_{5}, x_{4}; (5) x−y, −y, −z, x_{4}−x_{5}, −x_{5}; (6) −x, −x+y, −z, −x_{4}, −x_{4}+x_{5}; (7) −x, −y, −z, −x_{4}, −x_{5}; (8) y, −x+y, −z, x_{5}, −x_{4}+x_{5}; (9) x−y, x, −z, x_{4}−x_{5}, x_{4}; (10) −y, −x, z, −x_{5}, −x_{4}; (11) y−x, y, z, x_{5}−x_{4}, x_{5}; (12) x, x−y, z, x_{4}, x_{4}−x_{5}. ‡ ; |
Enraf-Nonius CAD4 diffractometer | 1795 reflections with I > 2σ(I) |
Radiation source: xray tube | R_{int} = 0.050 |
Graphite monochromator | θ_{max} = 37.5°, θ_{min} = 1.7° |
ω–2θ scans | h = ?→? |
Absorption correction: gaussian ? | k = ?→? |
T_{min} = ?, T_{max} = ? | l = ?→? |
8284 measured reflections | 3 standard reflections |
8284 independent reflections | intensity decay: none |
Refinement on F | 43 parameters |
Least-squares matrix: full | 0 restraints |
R[F^{2} > 2σ(F^{2})] = 0.053 | Calculated w = 1 |
wR(F^{2}) = .048 | |
1795 reflections |
Sc_{2}B54/49C157/49 | V = 66.59 (1) Å^{3} |
M_{r} = 140.43 | Z = 1 |
Trigonal, P3m1(p00)(0p0)0m0† | Mo Kα radiation |
q_{1} = 1.286a*; q_{2} = 1.286b*‡ | µ = 4.79 mm^{−}^{1} |
a = 3.387 (1) Å | T = 293 K |
c = 6.703 (2) Å | 0.20 × 0.10 × 0.06 mm |
† Symmetry operations: (1) x, y, z, x_{4}, x_{5}; (2) −y, x−y, z, −x_{5}, x_{4}−x_{5}; (3) −x+y, −x, z, −x_{4}+x_{5}, −x_{4}; (4) y, x, −z, x_{5}, x_{4}; (5) x−y, −y, −z, x_{4}−x_{5}, −x_{5}; (6) −x, −x+y, −z, −x_{4}, −x_{4}+x_{5}; (7) −x, −y, −z, −x_{4}, −x_{5}; (8) y, −x+y, −z, x_{5}, −x_{4}+x_{5}; (9) x−y, x, −z, x_{4}−x_{5}, x_{4}; (10) −y, −x, z, −x_{5}, −x_{4}; (11) y−x, y, z, x_{5}−x_{4}, x_{5}; (12) x, x−y, z, x_{4}, x_{4}−x_{5}. ‡ ; |
Enraf-Nonius CAD4 diffractometer | 1795 reflections with I > 2σ(I) |
Absorption correction: gaussian ? | R_{int} = 0.050 |
T_{min} = ?, T_{max} = ? | 3 standard reflections |
8284 measured reflections | intensity decay: none |
8284 independent reflections |
R[F^{2} > 2σ(F^{2})] = 0.053 | 43 parameters |
wR(F^{2}) = .048 | 0 restraints |
1795 reflections |
Refinement. The crystal is composed of two layered subsystem structures, i.e. Sc—C—Sc sandwiches (a1=b1=3.387 and c=6.703) and graphite-like layers of the composition B1/3 C2/3 (a2=b2=2.634 and c=6.703). The structure refinement was performed in a five-dimensional formalism based on the trigonal superspace group P-3m1(p 0 0)(0 p 0)0m0 through FMLSM (Kato, K., Acta Cryst.(1994) A50, 351–357) using the data indexed by five integers, h, k, l, m and n. On account of the commensurate feature of the lattice geometry, the summations instead of integrals in the structure-factor formula were used with summation points 49 (subsystem1) and 81 (subsystem2). In the model, all atoms are located at special positions, that is Sc in (1/3 2/3 z) and C in (0 0 1/2) of the first subsystem and B1/3 C2/3 in (1/3 2/3 z) of the second system. Besides one scaling factor and one parameter for extinction correction, atomic coordinates and thermal parameters, the Fourier amplitudes of the modulation functions were considered as structural parameters. For Sc in subsystem 1, displacive modulations up to the third order and modulations in anisotropic thermal parameters up to the first order were adopted. For C in subsystem 1, displacive modulations up to the first order were adopted. For B and C in subsystem2, random distribution of B and C were assumed and displacive modulations of B1/3 C2/3 up to the first order were adopted. Isotropic and unmodulated thermal parameters were adopted for C in subsystem 1 and B1/3 C2/3 in subsystem 2. |
x | y | z | U_{iso}*/U_{eq} | Occ. (<1) | |
Sc | 0.333333 | 0.666667 | 0.32221 (6) | 0.00775 (7) | |
C | 0.00 | 0.00 | 0.500000 | 0.0089 (4) | 0.500000 |
B1/3C2/3 | 0.333333 | 0.666667 | −0.0004 (3) | 0.0093 (3) |
U^{11} | U^{22} | U^{33} | U^{12} | U^{13} | U^{23} | |
Sc | 0.0074 (1) | 0.0074 | 0.0084 (2) | 0.0037 | 0.00 | 0.00 |
Experimental details
Crystal data | |
Chemical formula | Sc_{2}B54/49C157/49 |
M_{r} | 140.43 |
Crystal system, space group | Trigonal, P3m1(p00)(0p0)0m0† |
Temperature (K) | 293 |
Wave vectors | q_{1} = 1.286a*; q_{2} = 1.286b*‡ |
a, c (Å) | 3.387 (1), 6.703 (2) |
V (Å^{3}) | 66.59 (1) |
Z | 1 |
Radiation type | Mo Kα |
µ (mm^{−}^{1}) | 4.79 |
Crystal size (mm) | 0.20 × 0.10 × 0.06 |
Data collection | |
Diffractometer | Enraf-Nonius CAD4 diffractometer |
Absorption correction | Gaussian |
No. of measured, independent and observed [I > 2σ(I)] reflections | 8284, 8284, 1795 |
R_{int} | 0.050 |
(sin θ/λ)_{max} (Å^{−}^{1}) | 0.857 |
Refinement | |
R[F^{2} > 2σ(F^{2})], wR(F^{2}), S | 0.053, .048, ? |
No. of reflections | 1795 |
No. of parameters | 43 |
Δρ_{max}, Δρ_{min} (e Å^{−}^{3}) | ?, ? |
† Symmetry operations: (1) x, y, z, x_{4}, x_{5}; (2) −y, x−y, z, −x_{5}, x_{4}−x_{5}; (3) −x+y, −x, z, −x_{4}+x_{5}, −x_{4}; (4) y, x, −z, x_{5}, x_{4}; (5) x−y, −y, −z, x_{4}−x_{5}, −x_{5}; (6) −x, −x+y, −z, −x_{4}, −x_{4}+x_{5}; (7) −x, −y, −z, −x_{4}, −x_{5}; (8) y, −x+y, −z, x_{5}, −x_{4}+x_{5}; (9) x−y, x, −z, x_{4}−x_{5}, x_{4}; (10) −y, −x, z, −x_{5}, −x_{4}; (11) y−x, y, z, x_{5}−x_{4}, x_{5}; (12) x, x−y, z, x_{4}, x_{4}−x_{5}.
‡ ;
Computer programs: FMLSM (Kato, 1994).