Supporting information
Crystallographic Information File (CIF) https://doi.org/10.1107/S0108270100013834/av1051sup1.cif | |
Structure factor file (CIF format) https://doi.org/10.1107/S0108270100013834/av1051C6ADAsup2.hkl | |
Structure factor file (CIF format) https://doi.org/10.1107/S0108270100013834/av1051C8ADAsup3.hkl |
CCDC references: 158229; 158230
Crystallization of the n-alkylamine and H3AsO4 in methanol solutions (Kroupa & Fuith, 1994). Crystals which appeared single-domained under the polarization microscope were selected for a diffractometer measurement.
The structures are superstructures and ferroelastic structures as well. They can be related to the prototypic space group P 2/b 21/n 21/a. Therefore the crystals were expected to be twinned though the samples were chosen which seemed to be single-domained when viewed in the polarization microscope.
The domain proportion f was a refined parameter which converged to the value to -0.006 (4) and 0.026 (4) for C6ADA and C8ADA, respectively. (Therefore in case of C6ADA the domain proportion was set to 0.0 and this parameter was not refined.)
The domain proportion was also determined from well separated diffractions. In case of C6ADA there were used 19 pairs of the diffraction 004 measured at various azimuthal angles. The determined values of the domain proportion was 0.007 (3). In case of C8ADA there were used 31 pairs of different diffractions, among them also the reflections of the type 004. The values of the domain proportion determined in this way resulted in 0.009 (3).
All hydrogen atoms could be found in the difference Fourier maps. Most of them were refined to tolerable positions, nevertheless they all were restrained during refinement in order to prevent the H atoms to be misplaced.
The bond distances as well as the angles in which the H atoms were involved were restrained. The O—H, N—H and C—H bond lengths were restrained to 0.85, 0.90 and 0.95 Å, respectively.
For both compounds, data collection: Enraf-Nonius Software (Enraf-Nonius, 1989); cell refinement: Enraf-Nonius Software; data reduction: JANA2000 (Petříček & Dušek, 2000); program(s) used to solve structure: JANA2000; program(s) used to refine structure: JANA2000; molecular graphics: ORTEPIII (Burnett & Johnson, 1996). Software used to prepare material for publication: JANA98 (Petříček & Dušek, 1998) for C6ADA; JANA98 (Petříček & Dušek, 2000) for C8ADA.
(C6H13NH3)[As(O)2(OH)2] | F(000) = 1008 |
Mr = 243.13 | Dx = 1.555 Mg m−3 |
Monoclinic, P21/n | Mo Kα radiation, λ = 0.71073 Å |
a = 9.3105 (7) Å | Cell parameters from 25 reflections |
b = 29.929 (2) Å | θ = 12.6–13.9° |
c = 7.453 (6) Å | µ = 3.26 mm−1 |
β = 90.64 (7)° | T = 292 K |
V = 2077 (2) Å3 | Plate, colourless |
Z = 8 | 0.43 × 0.20 × 0.09 mm |
Enraf-Nonius CAD-4-MACHIII-PC diffractometer | Rint = 0.038 |
ω–2θ scans | θmax = 26.5° |
Absorption correction: gaussian (Templeton & Templeton, 1978) | h = −11→11 |
Tmin = 0.482, Tmax = 0.749 | k = 0→37 |
4613 measured reflections | l = 0→9 |
4290 independent reflections | 3 standard reflections every 3600 min |
2505 reflections with I > 3σ(I) | intensity decay: 7.0% |
Refinement on F | 0 constraints |
Least-squares matrix: full with fixed elements per cycle | H-atom parameters constrained |
R[F2 > 2σ(F2)] = 0.036 | Weighting scheme based on measured s.u.'s w = [σ2(Fo) + 0.0001(Fo)2]-1 |
wR(F2) = 0.047 | (Δ/σ)max = 0.001 |
S = 1.89 | Δρmax = 1.86 e Å−3 |
4290 reflections | Δρmin = −2.43 e Å−3 |
362 parameters | Extinction correction: Becker & Coppens, 1974, type I, Lorentz. iso. |
58 restraints | Extinction coefficient: 0.000029 (2) |
(C6H13NH3)[As(O)2(OH)2] | V = 2077 (2) Å3 |
Mr = 243.13 | Z = 8 |
Monoclinic, P21/n | Mo Kα radiation |
a = 9.3105 (7) Å | µ = 3.26 mm−1 |
b = 29.929 (2) Å | T = 292 K |
c = 7.453 (6) Å | 0.43 × 0.20 × 0.09 mm |
β = 90.64 (7)° |
Enraf-Nonius CAD-4-MACHIII-PC diffractometer | 2505 reflections with I > 3σ(I) |
Absorption correction: gaussian (Templeton & Templeton, 1978) | Rint = 0.038 |
Tmin = 0.482, Tmax = 0.749 | 3 standard reflections every 3600 min |
4613 measured reflections | intensity decay: 7.0% |
4290 independent reflections |
R[F2 > 2σ(F2)] = 0.036 | 58 restraints |
wR(F2) = 0.047 | H-atom parameters constrained |
S = 1.89 | Δρmax = 1.86 e Å−3 |
4290 reflections | Δρmin = −2.43 e Å−3 |
362 parameters |
Experimental. All the samples contained domains which could be reproducibly moved if the stress was exerted. In contrast to the crystals of C6ADA and C8ADA the domains could be called forth by stress not as easily as in C7ADA. |
Refinement. The structure was refined as a twin. domain fraction f: calculated from the refinement: 0.026 (4) calculated from 31 pairs of measured intensities of well separated refelctions icluding the reflections 004 which were measured at different azimuthal angles: 0.009 (3) The twinning matrix is given in _diffrn_reflns_transf_matrix_ items The H atoms except of those which are bonded to the O atoms were restrained by the distfix and anglefix functions of JANA2000: The values for distfix were 0.85(0.022) A ng. for O—H distances. The values for distfix were 0.90(0.022) A ng. for N—H distances. The values for distfix were 0.95(0.03) A ng. for methyl-H distances. The values for distfix were 0.95(0.013) A ng. for methylene-H distances. The values for anglefix were 109.47(1.00) °. |
x | y | z | Uiso*/Ueq | ||
As1 | 0.08376 (3) | 0.30239 (1) | 0.25269 (4) | 0.0232 (1) | |
O11 | −0.0423 (3) | 0.34309 (9) | 0.2279 (4) | 0.0414 (9) | |
O21 | 0.1177 (2) | 0.29244 (8) | 0.4672 (2) | 0.0351 (8) | |
O31 | 0.2201 (2) | 0.31701 (8) | 0.1270 (3) | 0.0341 (7) | |
O41 | 0.0102 (2) | 0.25386 (8) | 0.1756 (3) | 0.0367 (8) | |
As2 | 0.57995 (3) | 0.30006 (1) | 0.26243 (4) | 0.0237 (1) | |
O12 | 0.4614 (3) | 0.34303 (9) | 0.2641 (3) | 0.0410 (9) | |
O22 | 0.6188 (3) | 0.29041 (9) | 0.0427 (3) | 0.0388 (9) | |
O32 | 0.7232 (2) | 0.31610 (9) | 0.3762 (3) | 0.0372 (8) | |
O42 | 0.5067 (2) | 0.25360 (8) | 0.3410 (2) | 0.0325 (7) | |
N1 | 0.1936 (3) | 0.6915 (1) | 0.2670 (3) | 0.030 (1) | |
C11 | 0.1091 (4) | 0.6498 (1) | 0.2468 (5) | 0.033 (1) | |
C21 | 0.2039 (4) | 0.6089 (1) | 0.2545 (5) | 0.038 (1) | |
C31 | 0.1159 (4) | 0.5662 (1) | 0.2491 (5) | 0.042 (1) | |
C41 | 0.2055 (4) | 0.5238 (1) | 0.2531 (5) | 0.043 (1) | |
C51 | 0.1164 (5) | 0.4815 (2) | 0.2506 (6) | 0.052 (2) | |
C61 | 0.2062 (7) | 0.4390 (2) | 0.2550 (7) | 0.068 (2) | |
N2 | 0.7013 (3) | 0.69112 (9) | 0.2308 (4) | 0.030 (1) | |
C12 | 0.6139 (4) | 0.6498 (1) | 0.2494 (5) | 0.033 (1) | |
C22 | 0.7070 (4) | 0.6088 (1) | 0.2443 (5) | 0.037 (1) | |
C32 | 0.6168 (4) | 0.5661 (1) | 0.2501 (5) | 0.042 (1) | |
C42 | 0.7049 (4) | 0.5235 (1) | 0.2466 (5) | 0.043 (1) | |
C52 | 0.6152 (5) | 0.4812 (2) | 0.2495 (6) | 0.052 (2) | |
C62 | 0.7047 (6) | 0.4389 (2) | 0.2480 (7) | 0.067 (2) | |
H1N1 | 0.234 (2) | 0.6945 (9) | 0.377 (2) | 0.04 (1)* | |
H2N1 | 0.133 (3) | 0.7145 (8) | 0.246 (3) | 0.08 (2)* | |
H3N1 | 0.262 (2) | 0.6915 (9) | 0.185 (3) | 0.04 (1)* | |
H1C11 | 0.043 (2) | 0.650 (1) | 0.342 (2) | 0.05 (1)* | |
H2C11 | 0.059 (2) | 0.652 (1) | 0.136 (2) | 0.06 (1)* | |
H1C21 | 0.266 (2) | 0.610 (1) | 0.155 (2) | 0.05 (1)* | |
H2C21 | 0.259 (2) | 0.608 (1) | 0.362 (2) | 0.04 (1)* | |
H1C31 | 0.055 (2) | 0.564 (1) | 0.350 (2) | 0.05 (1)* | |
H2C31 | 0.059 (2) | 0.564 (1) | 0.142 (2) | 0.06 (1)* | |
H1C41 | 0.267 (2) | 0.524 (1) | 0.152 (2) | 0.06 (1)* | |
H2C41 | 0.262 (2) | 0.525 (1) | 0.361 (2) | 0.05 (1)* | |
H1C51 | 0.058 (3) | 0.480 (1) | 0.145 (2) | 0.08 (2)* | |
H2C51 | 0.056 (3) | 0.483 (1) | 0.352 (2) | 0.06 (1)* | |
H1C61 | 0.137 (4) | 0.416 (1) | 0.245 (5) | 0.12 (2)* | |
H2C61 | 0.261 (3) | 0.435 (1) | 0.362 (3) | 0.12 (2)* | |
H3C61 | 0.269 (3) | 0.438 (1) | 0.153 (4) | 0.08 (2)* | |
H1N2 | 0.764 (2) | 0.6937 (9) | 0.318 (2) | 0.04 (1)* | |
H2N2 | 0.638 (3) | 0.7138 (8) | 0.236 (3) | 0.07 (1)* | |
H3N2 | 0.747 (2) | 0.6917 (9) | 0.126 (2) | 0.05 (1)* | |
H1C12 | 0.562 (2) | 0.653 (1) | 0.358 (2) | 0.04 (1)* | |
H2C12 | 0.548 (2) | 0.650 (1) | 0.151 (2) | 0.032 (9)* | |
H1C22 | 0.756 (2) | 0.610 (1) | 0.133 (2) | 0.05 (1)* | |
H2C22 | 0.775 (2) | 0.607 (1) | 0.340 (2) | 0.05 (1)* | |
H1C32 | 0.559 (2) | 0.568 (1) | 0.354 (2) | 0.05 (1)* | |
H2C32 | 0.556 (2) | 0.563 (1) | 0.148 (2) | 0.05 (1)* | |
H1C42 | 0.757 (2) | 0.526 (1) | 0.138 (2) | 0.06 (1)* | |
H2C42 | 0.770 (2) | 0.524 (1) | 0.347 (2) | 0.04 (1)* | |
H1C52 | 0.554 (2) | 0.483 (1) | 0.147 (2) | 0.06 (1)* | |
H2C52 | 0.559 (3) | 0.483 (1) | 0.354 (2) | 0.06 (1)* | |
H1C62 | 0.768 (3) | 0.439 (1) | 0.348 (4) | 0.13 (3)* | |
H2C62 | 0.643 (3) | 0.414 (1) | 0.257 (4) | 0.09 (2)* | |
H3C62 | 0.758 (3) | 0.436 (1) | 0.141 (4) | 0.10 (2)* | |
HO11 | −0.116 (3) | 0.336 (1) | 0.282 (5) | 0.07 (1)* | |
HO41 | 0.007 (4) | 0.252 (1) | 0.059 (2) | 0.07 (1)* | |
HO12 | 0.382 (3) | 0.335 (2) | 0.224 (6) | 0.11 (2)* | |
HO22 | 0.613 (4) | 0.2626 (6) | 0.015 (4) | 0.05 (1)* |
U11 | U22 | U33 | U12 | U13 | U23 | |
As1 | 0.0206 (2) | 0.0292 (2) | 0.0197 (2) | −0.0019 (2) | 0.0002 (1) | 0.0035 (1) |
O11 | 0.025 (1) | 0.038 (2) | 0.061 (2) | 0.004 (1) | 0.005 (1) | 0.015 (1) |
O21 | 0.048 (1) | 0.039 (2) | 0.018 (1) | −0.006 (1) | −0.0037 (9) | 0.002 (1) |
O31 | 0.022 (1) | 0.057 (2) | 0.023 (1) | −0.010 (1) | 0.0018 (9) | 0.000 (1) |
O41 | 0.046 (1) | 0.043 (2) | 0.021 (1) | −0.019 (1) | −0.001 (1) | −0.002 (1) |
As2 | 0.0204 (2) | 0.0304 (2) | 0.0201 (2) | −0.0024 (2) | −0.0026 (1) | −0.0019 (1) |
O12 | 0.023 (1) | 0.038 (2) | 0.061 (2) | 0.005 (1) | −0.008 (1) | −0.010 (1) |
O22 | 0.058 (2) | 0.036 (2) | 0.022 (1) | −0.009 (1) | 0.006 (1) | −0.004 (1) |
O32 | 0.020 (1) | 0.060 (2) | 0.031 (1) | −0.009 (1) | −0.0078 (9) | 0.004 (1) |
O42 | 0.044 (1) | 0.034 (1) | 0.020 (1) | −0.014 (1) | −0.0045 (9) | 0.0014 (9) |
N1 | 0.030 (2) | 0.031 (2) | 0.028 (1) | 0.002 (1) | −0.001 (1) | 0.000 (1) |
C11 | 0.031 (2) | 0.034 (2) | 0.032 (2) | 0.002 (2) | −0.007 (2) | −0.001 (2) |
C21 | 0.037 (2) | 0.033 (2) | 0.043 (2) | 0.004 (2) | −0.004 (2) | −0.005 (2) |
C31 | 0.039 (2) | 0.038 (3) | 0.048 (2) | −0.002 (2) | −0.002 (2) | 0.000 (2) |
C41 | 0.048 (3) | 0.035 (3) | 0.046 (2) | −0.003 (2) | −0.001 (2) | −0.002 (2) |
C51 | 0.057 (3) | 0.042 (3) | 0.055 (3) | −0.009 (2) | 0.000 (2) | −0.002 (2) |
C61 | 0.104 (4) | 0.039 (3) | 0.062 (3) | −0.004 (3) | −0.001 (3) | −0.001 (2) |
N2 | 0.031 (2) | 0.029 (2) | 0.031 (1) | 0.005 (1) | −0.001 (1) | 0.000 (1) |
C12 | 0.028 (2) | 0.035 (2) | 0.035 (2) | 0.000 (2) | 0.000 (2) | 0.000 (2) |
C22 | 0.033 (2) | 0.038 (3) | 0.040 (2) | −0.002 (2) | −0.003 (2) | 0.002 (2) |
C32 | 0.037 (2) | 0.040 (3) | 0.049 (2) | −0.004 (2) | −0.002 (2) | −0.002 (2) |
C42 | 0.051 (3) | 0.034 (3) | 0.043 (2) | −0.006 (2) | 0.001 (2) | 0.002 (2) |
C52 | 0.060 (3) | 0.040 (3) | 0.055 (3) | −0.011 (2) | −0.003 (3) | 0.003 (2) |
C62 | 0.102 (4) | 0.036 (3) | 0.064 (3) | −0.004 (3) | 0.005 (3) | 0.003 (2) |
As1—O11 | 1.700 (3) | C41—H1C41 | 0.95 (2) |
As1—O21 | 1.653 (2) | C41—H2C41 | 0.95 (2) |
As1—O31 | 1.645 (2) | C51—H1C51 | 0.95 (2) |
As1—O41 | 1.703 (2) | C51—H2C51 | 0.95 (2) |
As2—O12 | 1.695 (3) | C61—H1C61 | 0.94 (3) |
As2—O22 | 1.706 (2) | C61—H2C61 | 0.95 (3) |
As2—O32 | 1.645 (2) | C61—H3C61 | 0.97 (3) |
As2—O42 | 1.658 (2) | N2—H1N2 | 0.87 (2) |
N1—C11 | 1.484 (5) | N2—H2N2 | 0.90 (3) |
C11—C21 | 1.510 (5) | N2—H3N2 | 0.89 (2) |
C21—C31 | 1.518 (6) | C12—H1C12 | 0.95 (2) |
C31—C41 | 1.519 (6) | C12—H2C12 | 0.95 (2) |
C41—C51 | 1.514 (6) | C22—H1C22 | 0.95 (2) |
C51—C61 | 1.522 (7) | C22—H2C22 | 0.95 (2) |
N2—C12 | 1.488 (5) | C32—H1C32 | 0.95 (2) |
C12—C22 | 1.502 (5) | C32—H2C32 | 0.95 (2) |
C22—C32 | 1.531 (6) | C42—H1C42 | 0.95 (2) |
C32—C42 | 1.517 (6) | C42—H2C42 | 0.96 (2) |
C42—C52 | 1.517 (6) | C52—H1C52 | 0.95 (2) |
C52—C62 | 1.515 (7) | C52—H2C52 | 0.94 (2) |
O11—HO11 | 0.83 (3) | C62—H1C62 | 0.95 (3) |
O41—HO41 | 0.87 (2) | C62—H2C62 | 0.94 (3) |
O12—HO12 | 0.83 (3) | C62—H3C62 | 0.95 (3) |
O22—HO22 | 0.86 (2) | O11—O32i | 2.588 (3) |
N1—H1N1 | 0.90 (2) | O21—O22ii | 2.543 (3) |
N1—H2N1 | 0.90 (3) | O31—O12 | 2.579 (3) |
N1—H3N1 | 0.89 (2) | O41—O42iii | 2.504 (3) |
C11—H1C11 | 0.94 (2) | N1—O22iv | 2.960 (4) |
C11—H2C11 | 0.95 (2) | N1—O32v | 2.771 (3) |
C21—H1C21 | 0.95 (2) | N1—O42vi | 2.747 (4) |
C21—H2C21 | 0.95 (2) | N2—O21v | 2.841 (3) |
C31—H1C31 | 0.95 (2) | N2—O31iv | 2.784 (3) |
C31—H2C31 | 0.95 (2) | N2—O41vi | 2.814 (4) |
O11—As1—O21 | 111.0 (1) | O12—As2—O22 | 106.3 (1) |
O11—As1—O31 | 106.5 (1) | O12—As2—O32 | 107.4 (1) |
O11—As1—O41 | 107.5 (1) | O12—As2—O42 | 111.3 (1) |
O21—As1—O31 | 117.3 (1) | O22—As2—O32 | 111.4 (1) |
O21—As1—O41 | 104.2 (1) | O22—As2—O42 | 106.8 (1) |
O31—As1—O41 | 110.2 (1) | O32—As2—O42 | 113.4 (1) |
Symmetry codes: (i) x−1, y, z; (ii) x−1/2, −y+1/2, z+1/2; (iii) x−1/2, −y+1/2, z−1/2; (iv) −x+1, −y+1, −z; (v) −x+1, −y+1, −z+1; (vi) −x+1/2, y+1/2, −z+1/2. |
D—H···A | D—H | D···A | D—H···A |
O11—HO11···O32i | 0.83 (3) | 2.588 (3) | 174 (4) |
O41—HO41···O42iii | 0.87 (2) | 2.504 (3) | 178 (4) |
O12—HO12···O31 | 0.83 (3) | 2.579 (3) | 176 (4) |
O22—HO22···O21vii | 0.86 (2) | 2.543 (3) | 175 (3) |
N1—H3N1···O22iv | 0.89 (2) | 2.960 (4) | 160 (2) |
N1—H1N1···O32v | 0.90 (2) | 2.771 (3) | 160 (2) |
N1—H2N1···O42vi | 0.90 (3) | 2.747 (4) | 167 (2) |
N2—H1N2···O21v | 0.87 (2) | 2.841 (3) | 170 (2) |
N2—H3N2···O31iv | 0.89 (2) | 2.785 (3) | 159 (2) |
N2—H2N2···O41vi | 0.90 (3) | 2.814 (4) | 161 (2) |
Symmetry codes: (i) x−1, y, z; (iii) x−1/2, −y+1/2, z−1/2; (iv) −x+1, −y+1, −z; (v) −x+1, −y+1, −z+1; (vi) −x+1/2, y+1/2, −z+1/2; (vii) x+1/2, −y+1/2, z−1/2. |
(C8H17NH3)[As(O)2(OH)2] | F(000) = 1136 |
Mr = 271.19 | Dx = 1.479 Mg m−3 |
Monoclinic, P21/n | Mo Kα radiation, λ = 0.71073 Å |
a = 9.307 (1) Å | Cell parameters from 25 reflections |
b = 34.936 (4) Å | θ = 11–14° |
c = 7.488 (1) Å | µ = 2.79 mm−1 |
β = 90.58 (1)° | T = 292 K |
V = 2434.6 (5) Å3 | Plate, colourless |
Z = 8 | 0.41 × 0.26 × 0.12 mm |
Enraf-Nonius CAD-4-MACHIII-PC diffractometer | Rint = 0.015 |
ω–2θ scans | θmax = 26° |
Absorption correction: gaussian (Templeton & Templeton, 1978) | h = −11→11 |
Tmin = 0.348, Tmax = 0.717 | k = 0→42 |
5743 measured reflections | l = 0→9 |
4771 independent reflections | 3 standard reflections every 3600 min |
3125 reflections with I > 3σ(I) | intensity decay: 5.0% |
Refinement on F | 0 constraints |
Least-squares matrix: full with fixed elements per cycle | H-atom parameters constrained |
R[F2 > 2σ(F2)] = 0.043 | Weighting scheme based on measured s.u.'s w = [σ2(Fo) + 0.0001(Fo)2]-1 |
wR(F2) = 0.070 | (Δ/σ)max = 0.001 |
S = 3.19 | Δρmax = 1.36 e Å−3 |
4771 reflections | Δρmin = −1.07 e Å−3 |
431 parameters | Extinction correction: Becker & Coppens, 1974, type I, Lorentz. iso. |
70 restraints | Extinction coefficient: 0.000069 (3) |
(C8H17NH3)[As(O)2(OH)2] | V = 2434.6 (5) Å3 |
Mr = 271.19 | Z = 8 |
Monoclinic, P21/n | Mo Kα radiation |
a = 9.307 (1) Å | µ = 2.79 mm−1 |
b = 34.936 (4) Å | T = 292 K |
c = 7.488 (1) Å | 0.41 × 0.26 × 0.12 mm |
β = 90.58 (1)° |
Enraf-Nonius CAD-4-MACHIII-PC diffractometer | 3125 reflections with I > 3σ(I) |
Absorption correction: gaussian (Templeton & Templeton, 1978) | Rint = 0.015 |
Tmin = 0.348, Tmax = 0.717 | 3 standard reflections every 3600 min |
5743 measured reflections | intensity decay: 5.0% |
4771 independent reflections |
R[F2 > 2σ(F2)] = 0.043 | 70 restraints |
wR(F2) = 0.070 | H-atom parameters constrained |
S = 3.19 | Δρmax = 1.36 e Å−3 |
4771 reflections | Δρmin = −1.07 e Å−3 |
431 parameters |
Refinement. The structure was refined as a twin. domain fraction f: calculated from the refinement: 0.026 (4) calculated from 31 pairs of measured intensities of well separated reflections including the reflections 004 which were measured at different azimuthal angles: 0.01 (1) The twinning matrix is given in _diffrn_reflns_transf_matrix_ items The H atoms except of those which are bonded to the O atoms were restrained by the distfix and anglefix functions of JANA2000: The values for distfix were 0.85(0.022) A ng. for O—H distances. The values for distfix were 0.90(0.022) A ng. for N—H distances. The values for distfix were 0.95(0.03) A ng. for methyl-H distances. The values for distfix were 0.95(0.013) A ng. for methylene-H distances. The values for anglefix were 109.47(1.00) °. |
x | y | z | Uiso*/Ueq | ||
As1 | 0.08370 (3) | 0.294625 (9) | 0.25268 (4) | 0.0233 (1) | |
O11 | −0.0431 (2) | 0.32941 (7) | 0.2281 (3) | 0.0429 (9) | |
O21 | 0.1175 (2) | 0.28668 (6) | 0.4665 (3) | 0.0361 (7) | |
O31 | 0.2207 (2) | 0.30771 (7) | 0.1290 (3) | 0.0346 (7) | |
O41 | 0.0103 (2) | 0.25285 (7) | 0.1759 (3) | 0.0395 (8) | |
As2 | 0.57989 (3) | 0.292651 (9) | 0.26326 (4) | 0.0238 (1) | |
O12 | 0.4614 (2) | 0.32965 (7) | 0.2659 (3) | 0.0403 (9) | |
O22 | 0.6182 (3) | 0.28446 (8) | 0.0442 (3) | 0.0414 (9) | |
O32 | 0.7228 (2) | 0.30587 (7) | 0.3759 (3) | 0.0358 (7) | |
O42 | 0.5069 (2) | 0.25254 (6) | 0.3412 (2) | 0.0296 (7) | |
N1 | 0.1942 (3) | 0.70009 (7) | 0.2668 (3) | 0.0285 (9) | |
C11 | 0.1113 (3) | 0.6641 (1) | 0.2480 (4) | 0.032 (1) | |
C21 | 0.2053 (3) | 0.6291 (1) | 0.2551 (5) | 0.036 (1) | |
C31 | 0.1166 (4) | 0.5927 (1) | 0.2482 (5) | 0.038 (1) | |
C41 | 0.2066 (4) | 0.5563 (1) | 0.2528 (5) | 0.039 (1) | |
C51 | 0.1187 (4) | 0.5199 (1) | 0.2499 (5) | 0.040 (1) | |
C61 | 0.2067 (4) | 0.4835 (1) | 0.2526 (5) | 0.039 (1) | |
C71 | 0.1180 (4) | 0.4472 (1) | 0.2504 (6) | 0.050 (1) | |
C81 | 0.2051 (6) | 0.4108 (1) | 0.2530 (7) | 0.064 (2) | |
N2 | 0.7031 (3) | 0.69985 (8) | 0.2305 (3) | 0.0296 (9) | |
C12 | 0.6156 (3) | 0.6644 (1) | 0.2494 (4) | 0.032 (1) | |
C22 | 0.7080 (3) | 0.6290 (1) | 0.2435 (5) | 0.033 (1) | |
C32 | 0.6179 (4) | 0.5926 (1) | 0.2486 (5) | 0.040 (1) | |
C42 | 0.7069 (4) | 0.5563 (1) | 0.2482 (5) | 0.038 (1) | |
C52 | 0.6181 (4) | 0.5198 (1) | 0.2490 (5) | 0.041 (1) | |
C62 | 0.7053 (4) | 0.4834 (1) | 0.2466 (5) | 0.038 (1) | |
C72 | 0.6183 (4) | 0.4470 (1) | 0.2485 (6) | 0.049 (1) | |
C82 | 0.7049 (5) | 0.4108 (1) | 0.2476 (6) | 0.061 (2) | |
H2N1 | 0.132 (2) | 0.7197 (6) | 0.253 (3) | 0.06 (1)* | |
H1N1 | 0.235 (2) | 0.7012 (7) | 0.376 (2) | 0.034 (9)* | |
H3N1 | 0.262 (2) | 0.7017 (7) | 0.184 (2) | 0.019 (8)* | |
H1C1 | 0.044 (2) | 0.6669 (9) | 0.342 (2) | 0.035 (9)* | |
H2C1 | 0.061 (2) | 0.6630 (9) | 0.137 (2) | 0.04 (1)* | |
H1C2 | 0.268 (2) | 0.634 (1) | 0.159 (2) | 0.06 (1)* | |
H2C2 | 0.259 (2) | 0.6279 (8) | 0.363 (2) | 0.026 (8)* | |
H1C31 | 0.052 (2) | 0.591 (1) | 0.345 (2) | 0.05 (1)* | |
H2C31 | 0.064 (2) | 0.5906 (8) | 0.139 (2) | 0.022 (8)* | |
H1C41 | 0.263 (3) | 0.556 (1) | 0.153 (4) | 0.05 (1)* | |
H2C41 | 0.266 (2) | 0.5574 (9) | 0.357 (2) | 0.035 (9)* | |
H1C51 | 0.060 (3) | 0.5186 (9) | 0.139 (4) | 0.05 (1)* | |
H2C51 | 0.057 (2) | 0.5226 (9) | 0.350 (2) | 0.037 (9)* | |
H1C61 | 0.267 (3) | 0.4832 (9) | 0.144 (4) | 0.04 (1)* | |
H2C61 | 0.266 (2) | 0.486 (1) | 0.356 (2) | 0.07 (1)* | |
H1C71 | 0.057 (4) | 0.445 (1) | 0.145 (5) | 0.09 (2)* | |
H2C71 | 0.060 (2) | 0.448 (1) | 0.354 (2) | 0.06 (1)* | |
H1C81 | 0.265 (3) | 0.411 (1) | 0.357 (3) | 0.09 (2)* | |
H2C81 | 0.147 (3) | 0.3886 (8) | 0.253 (4) | 0.09 (2)* | |
H3C81 | 0.264 (3) | 0.411 (1) | 0.148 (3) | 0.11 (2)* | |
H1N2 | 0.765 (2) | 0.7002 (9) | 0.322 (2) | 0.06 (1)* | |
H2N2 | 0.641 (3) | 0.7193 (6) | 0.241 (3) | 0.06 (1)* | |
H3N2 | 0.751 (2) | 0.7022 (7) | 0.128 (2) | 0.031 (9)* | |
H1C12 | 0.565 (2) | 0.6694 (9) | 0.356 (2) | 0.04 (1)* | |
H2C12 | 0.550 (2) | 0.6633 (8) | 0.152 (2) | 0.031 (9)* | |
H1C22 | 0.767 (2) | 0.634 (1) | 0.143 (2) | 0.07 (1)* | |
H2C22 | 0.767 (2) | 0.6261 (7) | 0.347 (2) | 0.015 (7)* | |
H1C32 | 0.560 (2) | 0.594 (1) | 0.352 (2) | 0.07 (1)* | |
H2C32 | 0.558 (2) | 0.5920 (8) | 0.145 (2) | 0.026 (9)* | |
H1C42 | 0.763 (2) | 0.5557 (9) | 0.143 (2) | 0.05 (1)* | |
H2C42 | 0.772 (3) | 0.5565 (9) | 0.356 (4) | 0.04 (1)* | |
H1C52 | 0.558 (2) | 0.519 (1) | 0.145 (2) | 0.05 (1)* | |
H2C52 | 0.562 (3) | 0.5223 (9) | 0.348 (4) | 0.05 (1)* | |
H1C62 | 0.764 (2) | 0.4844 (9) | 0.144 (2) | 0.033 (9)* | |
H2C62 | 0.763 (2) | 0.486 (1) | 0.351 (2) | 0.06 (1)* | |
H1C72 | 0.555 (3) | 0.446 (1) | 0.147 (4) | 0.05 (1)* | |
H2C72 | 0.563 (2) | 0.4490 (9) | 0.354 (2) | 0.04 (1)* | |
H1C82 | 0.768 (3) | 0.412 (1) | 0.348 (3) | 0.12 (2)* | |
H2C82 | 0.645 (3) | 0.3889 (8) | 0.256 (4) | 0.09 (2)* | |
H3C82 | 0.760 (3) | 0.409 (1) | 0.142 (3) | 0.08 (2)* | |
HO11 | −0.118 (3) | 0.320 (1) | 0.274 (5) | 0.10 (2)* | |
HO41 | 0.009 (3) | 0.2552 (9) | 0.061 (2) | 0.04 (1)* | |
HO12 | 0.389 (2) | 0.3195 (9) | 0.220 (4) | 0.03 (1)* | |
HO22 | 0.603 (4) | 0.2621 (5) | 0.008 (4) | 0.06 (1)* |
U11 | U22 | U33 | U12 | U13 | U23 | |
As1 | 0.0215 (2) | 0.0273 (2) | 0.0211 (2) | −0.0022 (1) | 0.0013 (1) | 0.0030 (1) |
O11 | 0.024 (1) | 0.041 (2) | 0.064 (2) | 0.003 (1) | 0.002 (1) | 0.015 (1) |
O21 | 0.046 (1) | 0.039 (1) | 0.024 (1) | −0.006 (1) | −0.002 (1) | −0.001 (1) |
O31 | 0.025 (1) | 0.052 (2) | 0.027 (1) | −0.010 (1) | 0.0027 (9) | 0.006 (1) |
O41 | 0.045 (1) | 0.052 (2) | 0.021 (1) | −0.017 (1) | 0.000 (1) | −0.005 (1) |
As2 | 0.0223 (2) | 0.0275 (2) | 0.0216 (2) | −0.0021 (1) | −0.0016 (1) | −0.0008 (1) |
O12 | 0.025 (1) | 0.030 (1) | 0.065 (2) | 0.003 (1) | −0.009 (1) | −0.006 (1) |
O22 | 0.064 (2) | 0.037 (2) | 0.023 (1) | −0.008 (1) | 0.007 (1) | −0.002 (1) |
O32 | 0.025 (1) | 0.047 (1) | 0.036 (1) | −0.008 (1) | −0.0077 (9) | 0.012 (1) |
O42 | 0.047 (1) | 0.020 (1) | 0.022 (1) | −0.010 (1) | −0.0017 (9) | 0.0003 (9) |
N1 | 0.031 (1) | 0.026 (2) | 0.028 (1) | 0.003 (1) | 0.000 (1) | −0.001 (1) |
C11 | 0.033 (2) | 0.028 (2) | 0.034 (2) | −0.001 (2) | −0.005 (2) | −0.004 (2) |
C21 | 0.034 (2) | 0.030 (2) | 0.044 (2) | 0.006 (2) | −0.003 (2) | −0.008 (2) |
C31 | 0.040 (2) | 0.026 (2) | 0.049 (2) | −0.002 (2) | 0.002 (2) | −0.004 (2) |
C41 | 0.037 (2) | 0.034 (2) | 0.045 (2) | 0.000 (2) | −0.001 (2) | −0.003 (2) |
C51 | 0.044 (2) | 0.030 (2) | 0.046 (2) | −0.001 (2) | 0.001 (2) | −0.004 (2) |
C61 | 0.048 (2) | 0.029 (2) | 0.040 (2) | −0.002 (2) | −0.003 (2) | −0.002 (2) |
C71 | 0.059 (3) | 0.031 (2) | 0.060 (3) | −0.007 (2) | 0.003 (2) | 0.000 (2) |
C81 | 0.094 (4) | 0.032 (3) | 0.067 (3) | −0.001 (3) | −0.005 (3) | 0.004 (2) |
N2 | 0.029 (1) | 0.030 (2) | 0.031 (1) | 0.002 (1) | 0.003 (1) | −0.003 (1) |
C12 | 0.028 (2) | 0.029 (2) | 0.038 (2) | −0.001 (2) | 0.000 (2) | −0.002 (2) |
C22 | 0.031 (2) | 0.028 (2) | 0.040 (2) | 0.000 (2) | −0.003 (2) | −0.005 (2) |
C32 | 0.036 (2) | 0.032 (2) | 0.051 (2) | 0.001 (2) | −0.003 (2) | −0.004 (2) |
C42 | 0.041 (2) | 0.028 (2) | 0.043 (2) | −0.001 (2) | 0.003 (2) | 0.001 (2) |
C52 | 0.047 (2) | 0.031 (2) | 0.045 (2) | −0.001 (2) | −0.002 (2) | 0.001 (2) |
C62 | 0.048 (2) | 0.028 (2) | 0.039 (2) | −0.002 (2) | 0.002 (2) | 0.001 (2) |
C72 | 0.060 (3) | 0.034 (3) | 0.052 (3) | −0.005 (2) | 0.001 (2) | 0.003 (2) |
C82 | 0.093 (4) | 0.026 (3) | 0.064 (3) | −0.002 (2) | 0.005 (3) | 0.001 (2) |
As1—O11 | 1.703 (2) | C51—H1C51 | 0.99 (3) |
As1—O21 | 1.652 (2) | C51—H2C51 | 0.95 (2) |
As1—O31 | 1.648 (2) | C61—H1C61 | 0.99 (3) |
As1—O41 | 1.709 (2) | C61—H2C61 | 0.95 (2) |
As2—O12 | 1.699 (2) | C71—H1C71 | 0.97 (4) |
As2—O22 | 1.707 (2) | C71—H2C71 | 0.95 (2) |
As2—O32 | 1.634 (2) | C81—H3C81 | 0.96 (3) |
As2—O42 | 1.666 (2) | C81—H1C81 | 0.95 (2) |
N1—C11 | 1.480 (4) | C81—H2C81 | 0.94 (3) |
C11—C21 | 1.506 (5) | N2—H1N2 | 0.89 (2) |
C21—C31 | 1.517 (5) | N2—H2N2 | 0.89 (2) |
C31—C41 | 1.523 (5) | N2—H3N2 | 0.89 (2) |
C41—C51 | 1.512 (5) | C12—H1C12 | 0.95 (2) |
C51—C61 | 1.510 (5) | C12—H2C12 | 0.95 (2) |
C61—C71 | 1.515 (6) | C22—H1C22 | 0.95 (2) |
C71—C81 | 1.507 (6) | C22—H2C22 | 0.95 (2) |
N2—C12 | 1.490 (4) | C32—H1C32 | 0.95 (2) |
C12—C22 | 1.508 (5) | C32—H2C32 | 0.95 (2) |
C22—C32 | 1.524 (5) | C42—H1C42 | 0.95 (2) |
C32—C42 | 1.512 (5) | C42—H2C42 | 1.01 (3) |
C42—C52 | 1.521 (5) | C52—H1C52 | 0.95 (2) |
C52—C62 | 1.508 (5) | C52—H2C52 | 0.92 (3) |
C62—C72 | 1.509 (5) | C62—H1C62 | 0.95 (2) |
C72—C82 | 1.500 (6) | C62—H2C62 | 0.95 (2) |
O11—HO11 | 0.84 (3) | C72—H1C72 | 0.95 (3) |
O41—HO41 | 0.87 (1) | C72—H2C72 | 0.95 (2) |
O12—HO12 | 0.83 (2) | C82—H1C82 | 0.95 (3) |
O22—HO22 | 0.84 (2) | C82—H2C82 | 0.95 (3) |
N1—H2N1 | 0.90 (2) | C82—H3C82 | 0.95 (2) |
N1—H1N1 | 0.90 (1) | O11—O32i | 2.588 (3) |
N1—H3N1 | 0.89 (2) | O21—O22ii | 2.552 (3) |
C11—H1C11 | 0.95 (2) | O31—O12 | 2.571 (3) |
C11—H2C11 | 0.95 (1) | O41—O42iii | 2.513 (3) |
C21—H1C21 | 0.95 (2) | N1—O22iv | 2.974 (4) |
C21—H2C21 | 0.95 (2) | N1—O32v | 2.785 (3) |
C31—H1C31 | 0.95 (2) | N1—O42vi | 2.735 (3) |
C31—H2C31 | 0.95 (1) | N2—O21v | 2.843 (3) |
C41—H1C41 | 0.92 (3) | N2—O31iv | 2.803 (3) |
C41—H2C41 | 0.95 (2) | N2—O41vi | 2.809 (4) |
O11—As1—O21 | 110.5 (1) | O12—As2—O22 | 106.3 (1) |
O11—As1—O31 | 106.3 (1) | O12—As2—O32 | 107.7 (1) |
O11—As1—O41 | 107.4 (1) | O12—As2—O42 | 111.6 (1) |
O21—As1—O31 | 116.8 (1) | O22—As2—O32 | 111.5 (1) |
O21—As1—O41 | 104.7 (1) | O22—As2—O42 | 106.6 (1) |
O31—As1—O41 | 110.9 (1) | O32—As2—O42 | 112.9 (1) |
Symmetry codes: (i) x−1, y, z; (ii) x−1/2, −y+1/2, z+1/2; (iii) x−1/2, −y+1/2, z−1/2; (iv) −x+1, −y+1, −z; (v) −x+1, −y+1, −z+1; (vi) −x+1/2, y+1/2, −z+1/2. |
D—H···A | D—H | D···A | D—H···A |
O11—HO11···O32i | 0.84 (3) | 2.588 (3) | 174 (5) |
O41—HO41···O42iii | 0.87 (2) | 2.513 (3) | 165 (3) |
O12—HO12···O31 | 0.83 (3) | 2.571 (3) | 168 (3) |
O22—HO22···O21vii | 0.84 (2) | 2.552 (3) | 163 (3) |
N1—H3N1···O22iv | 0.89 (2) | 2.975 (4) | 165 (2) |
N1—H1N1···O32v | 0.90 (2) | 2.785 (3) | 164 (2) |
N1—H2N1···O42vi | 0.90 (3) | 2.735 (3) | 162 (2) |
N2—H1N2···O21v | 0.89 (2) | 2.843 (3) | 166 (3) |
N2—H3N2···O31iv | 0.89 (2) | 2.803 (3) | 153 (2) |
N2—H2N2···O41vi | 0.89 (3) | 2.809 (4) | 163 (2) |
Symmetry codes: (i) x−1, y, z; (iii) x−1/2, −y+1/2, z−1/2; (iv) −x+1, −y+1, −z; (v) −x+1, −y+1, −z+1; (vi) −x+1/2, y+1/2, −z+1/2; (vii) x+1/2, −y+1/2, z−1/2. |
Experimental details
(C6ADA) | (C8ADA) | |
Crystal data | ||
Chemical formula | (C6H13NH3)[As(O)2(OH)2] | (C8H17NH3)[As(O)2(OH)2] |
Mr | 243.13 | 271.19 |
Crystal system, space group | Monoclinic, P21/n | Monoclinic, P21/n |
Temperature (K) | 292 | 292 |
a, b, c (Å) | 9.3105 (7), 29.929 (2), 7.453 (6) | 9.307 (1), 34.936 (4), 7.488 (1) |
β (°) | 90.64 (7) | 90.58 (1) |
V (Å3) | 2077 (2) | 2434.6 (5) |
Z | 8 | 8 |
Radiation type | Mo Kα | Mo Kα |
µ (mm−1) | 3.26 | 2.79 |
Crystal size (mm) | 0.43 × 0.20 × 0.09 | 0.41 × 0.26 × 0.12 |
Data collection | ||
Diffractometer | Enraf-Nonius CAD-4-MACHIII-PC diffractometer | Enraf-Nonius CAD-4-MACHIII-PC diffractometer |
Absorption correction | Gaussian (Templeton & Templeton, 1978) | Gaussian (Templeton & Templeton, 1978) |
Tmin, Tmax | 0.482, 0.749 | 0.348, 0.717 |
No. of measured, independent and observed [I > 3σ(I)] reflections | 4613, 4290, 2505 | 5743, 4771, 3125 |
Rint | 0.038 | 0.015 |
(sin θ/λ)max (Å−1) | 0.628 | 0.617 |
Refinement | ||
R[F2 > 2σ(F2)], wR(F2), S | 0.036, 0.047, 1.89 | 0.043, 0.070, 3.19 |
No. of reflections | 4290 | 4771 |
No. of parameters | 362 | 431 |
No. of restraints | 58 | 70 |
H-atom treatment | H-atom parameters constrained | H-atom parameters constrained |
Δρmax, Δρmin (e Å−3) | 1.86, −2.43 | 1.36, −1.07 |
Computer programs: Enraf-Nonius Software (Enraf-Nonius, 1989), Enraf-Nonius Software, JANA2000 (Petříček & Dušek, 2000), JANA2000, ORTEPIII (Burnett & Johnson, 1996), JANA98 (Petříček & Dušek, 1998), JANA98 (Petříček & Dušek, 2000).
As1—O11 | 1.700 (3) | As2—O22 | 1.706 (2) |
As1—O21 | 1.653 (2) | As2—O32 | 1.645 (2) |
As1—O31 | 1.645 (2) | As2—O42 | 1.658 (2) |
As1—O41 | 1.703 (2) | N1—C11 | 1.484 (5) |
As2—O12 | 1.695 (3) | N2—C12 | 1.488 (5) |
As1—O11 | 1.703 (2) | As2—O22 | 1.707 (2) |
As1—O21 | 1.652 (2) | As2—O32 | 1.634 (2) |
As1—O31 | 1.648 (2) | As2—O42 | 1.666 (2) |
As1—O41 | 1.709 (2) | N1—C11 | 1.480 (4) |
As2—O12 | 1.699 (2) | N2—C12 | 1.490 (4) |
C3ADP | C4ADP | C5ADP | C6ADP | C7ADP | C8ADP | C9ADP | C6ADA | C8ADA | |
N1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 |
C1 | 2 | 2 | 2 | 2 | 2 | 2 | 2 | 2 | 2 |
C2 | 4 | 4 | 4 | 4 | 4 | 4 | 4 | 4 | 4 |
C3 | 5 | 4 | 6 | 4 | 6 | 4 | 6 | 4 | 4 |
C4 | 6 | 8 | 8 | 8 | 8 | 8 | 8 | 8 | |
C5 | 7 | 4 | 8 | 4 | 8 | 4 | 4 | ||
C6 | 7 | 8 | 8 | 8 | 7 | 8 | |||
C7 | 7 | 4 | 8 | 4 | |||||
C8 | 7 | 8 | 7 | ||||||
C9 | 7 |
%T Ferroelasticity and complicated phase transition sequences were discovered in the series of the related dihydrogenphosphates C1ADP-C12ADP by Kroupa \& Fuith (1993, 1994). The phase transition in C3ADP was also investigated by Iwata et al. (1996). Regarding the phase transitions, the compounds C$n$ADP can be divided into three groups: a) C1ADP-C4ADP b) the compounds with $n$$>$5 and $n$ even and c) $n$$γeq$5 and $n$ odd.
Each of the compounds of group a) undergoes a continuous ferroelastic phase transition. In contrast to group a) each of the compounds in groups b) and c) undergoes a discontinuos ferroelastic phase transition. In addition, the compounds of the latter two groups b) and c) undergo other phase transitions when they are heated from the room temperature phase up to the ferroelastic phase transition. The hysteresis effects are common. (In the case of C9ADP, the original room-temperature phase does not even recover after cooling, Kroupa \& Fuith, 1993.) The compounds in group c) undergo more complicated phase transitions. The differences between the phase transition sequences of the first-time and at least once heated crystals are more prominent in group c) than in group b).
The ferroelastic phase transitions in the dihydrogenarsenates occur at considerably higher temperatures (by tens of K) than in the corresponding dihydrogenphosphates. C6ADA undergoes a ferroelastic phase transition at $σim$378 K, C7ADA at $σim$364 K and C8ADA melts at $σim$380 K before a phase transition takes place (Kroupa \& Fuith, 1994).
Until now, the structural studies were performed only in the series of the dihydrogenphosphates C2ADP-C10ADP. C2ADP, C3ADP and C4ADP were studied by Kasatani et al. (1998), C3ADP by Fábry, Císa\v rová \& Kroupa et al. (2000a), C4ADP by Fábry, Císa\v rová \& Kroupa et al. (2000b), C5ADP and C6ADP by Kasatani et al. (1999), C5ADP, C6ADP, C9ADP by Fábry et al. (2000), C7ADP and C8ADP by Fábry et al. (1997), and C10ADP by Oliver et al. (1998). The reasons for different packing of $n$-alkylammonium chains were explained by Fábry, Pet\v r\'ι\v cek, C\'ι sa\v rová \& Kroupa et al. (2000) by dominancy of the hydrogen-bonding of the ammonium groups to the double layers of the dihydrogenphosphates. Until now, however, no structure determination of any of the dihydrogenarsenates was performed. σch
The aim of this study was a structure determination of C6ADA and C8ADA in order to find out structural differences between these compounds and the corresponding dihydrogenphosphates, and to find out the reason for differences in the phase transitions.
The twinning matrix which relates the diffractions $h$$_{1}$$k$$_{1}$$l$$_{1}$ and $h$$_{2}$$k$$_{2}$$l$$_{2}$ from the dominant and minor domains, respectively, is analogous to that in the dihydrogenphosphates. The diffractions $h$$_{1}$$k$$_{1}$$l$$_{1}$ and $h$$_{2}$$k$$_{2}$$l$$_{2}$ are expressed in the reciprocal space basis of the first domain and a, c, $βeta$ mean the lattice parameters.
$$πmatrix{h_{2} & k_{2} & l_{2} χr} = πmatrix{h_{1} & k_{1} & l_{1} χr} πmatrix{-1 & 0 & 0 χr 0 & -1 & 0 χr 2 {a οver c}χosβeta & 0 & 1 χr} $$
The structures are similar to C6ADP and C8ADP which are depicted elsewhere. Figs. 1 and 2 depict the closest C$χdots$C intermolecular contacts in C6ADA. The refined values of the minor domain proportion are in good accordance with the values which were calculated from the intensities of well separated pertinent diffractions from the minor and the prevailing domains. The differences are due to imprecision in the reading of the crystal shape, and consequently in absorption correction, as well as in shielding of the domains which may be unevenly distributed within the specimen. The interatomic distances are normal - Tables 1 and 2 - Allen \& Kennard, 1993. The hydrogen-bond distances and angles regarding the double layers of dihydrogenarsenates are comparable to those in the dihydrogenphosphates C6ADP and C8ADP (Table 3). The hydrogen bonds N$χdots$O are shorter by $σim$0.033 AA in the dihydrogenarsenates than in the dihydrogenphosphates. The N$χdots$O distances are more evenly distributed in C6ADA and C8ADA than in the corresponding dihydrogenphosphates. The absolute values of the atomic displacement vectors - a measure of the distorsion of a structure from a prototypic phase (Abrahams \& Keve, 1971) - for the non-hydrogen atoms are in the range 0.01-0.14 AA.
The differences in the phase-transition sequences between the members of the family C$n$ADP with $n$$λeq$4 and with $n$$γeq$5 (which depend also on the parity of $n$) and in C$n$ADA are affected by the number of the C$χdots$C and C$χdots$N contacts and their distances. As it was already pointed out by Fábry et al. (1997) the closest C$χdots$C distances correspond well to the van der Waals contacts (Weast \& Astle, 1980). However, in C5ADP, C7ADP and C9ADP the closest C$χdots$C distances are as short as 3.7 AA in contrast to those in the dihydrogenphosphates with $n$ even which are about 3.8 AA long (in C4ADP 3.9 AA). It should be noted that C5ADP, C7ADP and C9ADP are the compounds where hysteresis effects are the most prominent as it was pointed in the Introduction. On the other hand, in C$n$ADP with $n$$λeq$4, the chains are so short that sufficient number of carbons can not get into interaction.
The larger dihydrogenarsenates would cause the $n$-alkylammonium chains in the dihydrogenarsenates to be more distant from each other than in the pertinent dihydrogenphosphates (Table 4). The average difference between the corresponding C$χdots$C distances in C6ADA - C6ADP and C8ADA - C8ADP are 0.065 and 0.062 AA, respectively.
The phase transition phenomena observed in these compounds can be explained at least qualitatively by the distances between the atoms in the neighbouring chains as well as by the number of these contacts. The closer the $n$-alkylammonium chains are, the more complicated phase transitions are observed. Not surprisingly, the phase transitions in the dihydrogenarsenates take place at higher temperatures than in the analogous dihydrogenphosphates. It is because the molecules in the dihydrogenarsenates have more space and thermal agitation must be more intensive to bring about these molecules into interaction which would provoke a phase transition.
From this point of view, on the phase transitions it may also be predicted that not only in C9ADP (Kroupa \& Fuith, 1993), but also in other C$n$ADP with $n$ odd and $n$$γeq$11, the room-temperature phase would not recover after the crystals were heated and cooled. It is because the longer chains would be less able to restore the original low-temperature arrangement.
As in the dihydrogenphosphates, the ferroelastic switching in C6ADA and C8ADA is concomitant to hopping of the hydrogens HO41 and HO22 from the donor (O41, O22, respectively) to the acceptor oxygens (O42, O21, respectively) - Tab. 3.