research papers
X-ray diffraction patterns of [N(CH)][CdCl], tetramethylammonium trichlorocadmate(II), have been investigated in the temperature range 80-293 K, which includes two phase transitions at 118 and 104 K, respectively. The main interest in this compound is to establish the mechanism of the structural phase transitions common to other members of the isostructural family [(CH)N][MX]. It is supposed to be related to the ordering of the organic part together with some small distortion of the inorganic chains. The origin of the order-disorder mechanism would be the orientationally disordered distribution of the tetramethylammonium tetrahedra at room temperature. Maximum Entropy Methods suggest that the most probable distribution of the organic groups can be described through the so-called two-well model, in which one threefold axis of the tetramethylammonium tetrahedron coincides with the crystallographic threefold axis of the structure. Below 118 K the reflections are split. However, the splitting cannot be fully explained by the ferroelastic domains expected to appear after the phase transitions. Recent NMR results [Mulla-Osman et al. (1998). J. Phys. Condensed Matter, 10, 2465-2476] corroborate the existence of more domains than expected from symmetry considerations. A model of ferroelastic domains which is in agreement with both X-ray diffraction diagram and NMR measurements is proposed.
Supporting information
Crystallographic Information File (CIF) https://doi.org/10.1107/S0108768199013622/na0098sup1.cif | |
Structure factor file (CIF format) https://doi.org/10.1107/S0108768199013622/na0098Isup2.hkl |
CCDC reference: 1272242
Computing details top
Data collection: CAD4VPC; cell refinement: CAD4VPC; data reduction: xtal_DIFDAT_ABSORB_ADDREF_SORTRF; program(s) used to solve structure: Xtal; program(s) used to refine structure: xtal_CRYLSQ; molecular graphics: Xtal; software used to prepare material for publication: xtal_BONDLA_CIFIO.
(tmcc) top
Crystal data top
C4CdCl3H12N | Dx = 2.008 Mg m−3 |
Mr = 292.62 | Mo Kα radiation, λ = 0.71073 Å |
Hexagonal, P63/m | Cell parameters from 25 reflections |
Hall symbol: -P_6c | θ = 4–25° |
a = 9.126 (5) Å | µ = 2.99 mm−1 |
c = 6.718 (2) Å | T = 293 K |
V = 484.5 (6) Å3 | Hexagonal prism, colourless |
Z = 2 | 0.29 × 0.12 × 0.09 mm |
F(000) = 284 |
Data collection top
CAD4 diffractometer | 791 reflections with F____ > _.000_σ(F___) |
Radiation source: xray_tube | Rint = 0.021 |
Graphite monochromator | θmax = 44.9°, θmin = 4.0° |
θ/2θ scans | h = 0→15 |
Absorption correction: analytical (Alcock, 1974) | k = 0→15 |
Tmin = 0.709, Tmax = 0.788 | l = −13→13 |
2979 measured reflections | 3 standard reflections every 60 min |
1406 independent reflections | intensity decay: 3% |
Refinement top
Refinement on F | 0 restraints |
Least-squares matrix: full | 0 constraints |
R[F2 > 2σ(F2)] = 0.045 | H-atom parameters not defined |
wR(F2) = 0.032 | Weighting scheme based on measured s.u.'s |
S = 0.67 | (Δ/σ)max = 0.363 |
791 reflections | Δρmax = 1.51 e Å−3 |
29 parameters | Δρmin = −4.81 e Å−3 |
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
x | y | z | Uiso*/Ueq | ||
Cd | 0.00000 | 0.00000 | 0.00000 | 0.0319 (2) | |
Cl | 0.1006 (1) | −0.1552 (1) | 0.25000 | 0.0388 (5) | |
N | 0.33330 | 0.66660 | −0.25000 | 0.035 (2) | |
C1 | 0.532 (2) | 0.153 (2) | 0.212 (3) | 0.075 (9) | |
C2 | 0.578 (3) | 0.219 (2) | 0.415 (2) | 0.19 (3) |
Atomic displacement parameters (Å2) top
U11 | U22 | U33 | U12 | U13 | U23 | |
Cd | 0.0387 (2) | 0.0387 (2) | 0.0183 (2) | 0.01934 (9) | 0.00000 | 0.00000 |
Cl | 0.0505 (7) | 0.0460 (6) | 0.0304 (5) | 0.0319 (6) | 0.00000 | 0.00000 |
N | 0.034 (2) | 0.034 (2) | 0.036 (3) | 0.017 (1) | 0.00000 | 0.00000 |
C1 | 0.086 (8) | 0.035 (5) | 0.06 (2) | −0.006 (5) | −0.04 (1) | −0.006 (7) |
C2 | 0.28 (5) | 0.25 (3) | 0.13 (2) | 0.21 (3) | 0.15 (2) | 0.17 (2) |
Geometric parameters (Å, º) top
Ni—C1 | 1.50 (1) | Ni—C1iv | 1.50 (1) |
Ni—C2ii | 1.46 (2) | Ni—C2v | 1.46 (2) |
Ni—C1iii | 1.50 (2) | Ni—C1vi | 1.50 (2) |
Ni—C2 | 1.46 (3) | Ni—C2iv | 1.46 (3) |
Ni—C1ii | 1.50 (3) | Ni—C1v | 1.50 (3) |
Ni—C2iii | 1.46 (4) | Ni—C2vi | 1.46 (4) |
C1—Ni—C2ii | 118 (1) | C2—Ni—C2v | 142 (2) |
C1—Ni—C1iii | 117 (1) | C2—Ni—C1vi | 102 (1) |
C1—Ni—C2 | 59 (1) | C2—Ni—C2iv | 99 (2) |
C1—Ni—C1ii | 117 (1) | C2—Ni—C1v | 100 (2) |
C1—Ni—C2iii | 115 (1) | C2—Ni—C2vi | 142 (3) |
C1—Ni—C1iv | 20 (1) | C1ii—Ni—C2iii | 118 (2) |
C1—Ni—C2v | 102 (1) | C1ii—Ni—C1iv | 121 (1) |
C1—Ni—C1vi | 121 (1) | C1ii—Ni—C2v | 40 (1) |
C1—Ni—C2iv | 40 (1) | C1ii—Ni—C1vi | 121 (2) |
C1—Ni—C1v | 121 (1) | C1ii—Ni—C2iv | 100 (2) |
C1—Ni—C2vi | 100 (1) | C1ii—Ni—C1v | 20 (1) |
C2ii—Ni—C1iii | 115 (1) | C1ii—Ni—C2vi | 102 (2) |
C2ii—Ni—C2 | 68 (2) | C2iii—Ni—C1iv | 100 (1) |
C2ii—Ni—C1ii | 59 (1) | C2iii—Ni—C2v | 142 (1) |
C2ii—Ni—C2iii | 68 (2) | C2iii—Ni—C1vi | 40 (2) |
C2ii—Ni—C1iv | 102 (1) | C2iii—Ni—C2iv | 142 (3) |
C2ii—Ni—C2v | 99 (1) | C2iii—Ni—C1v | 102 (2) |
C2ii—Ni—C1vi | 100 (1) | C2iii—Ni—C2vi | 99 (2) |
C2ii—Ni—C2iv | 142 (2) | C1iv—Ni—C2v | 118 (1) |
C2ii—Ni—C1v | 40 (1) | C1iv—Ni—C1vi | 117 (1) |
C2ii—Ni—C2vi | 142 (1) | C1iv—Ni—C2iv | 59 (1) |
C1iii—Ni—C2 | 118 (2) | C1iv—Ni—C1v | 117 (1) |
C1iii—Ni—C1ii | 117 (2) | C1iv—Ni—C2vi | 115 (1) |
C1iii—Ni—C2iii | 59 (2) | C2v—Ni—C1vi | 115 (1) |
C1iii—Ni—C1iv | 121 (1) | C2v—Ni—C2iv | 68 (2) |
C1iii—Ni—C2v | 100 (1) | C2v—Ni—C1v | 59 (1) |
C1iii—Ni—C1vi | 20 (1) | C2v—Ni—C2vi | 68 (2) |
C1iii—Ni—C2iv | 102 (1) | C1vi—Ni—C2iv | 118 (2) |
C1iii—Ni—C1v | 121 (2) | C1vi—Ni—C1v | 117 (2) |
C1iii—Ni—C2vi | 40 (2) | C1vi—Ni—C2vi | 59 (2) |
C2—Ni—C1ii | 115 (2) | C2iv—Ni—C1v | 115 (2) |
C2—Ni—C2iii | 68 (1) | C2iv—Ni—C2vi | 68 (1) |
C2—Ni—C1iv | 40 (1) | C1v—Ni—C2vi | 118 (2) |
Symmetry codes: (i) −x+1, −y+1, z+1/2; (ii) −x+y+1, −x+1, z; (iii) −y+1, x−y, z; (iv) x, y, −z+1/2; (v) −x+y+1, −x+1, −z+1/2; (vi) −y+1, x−y, −z+1/2. |