Kinetic behaviour investigations and crystal structure of nitric acid dihydrate

X-ray powder diffraction experiments are performed to prove the possible crystallization of nitric acid dihydrate (HNO₃·2H₂O, further denoted NAD) and to determine the best thermal conditions for growing a single crystal. It is shown that the kinetic behaviour of NAD strongly depends on the preliminary thermal treatment. One good single crystal obtained by an in situ adapted Bridgman method procedure enabled determination of the crystal structure. The intensities of diffracted lines with h odd are all very weak. The H atom of nitric acid is delocalized to one water molecule leading to an association of equimolar nitrate (NO₃^-) and an H₅O₂⁺ ionic group. The asymmetric unit contains two such molecules. These two molecules are related by a pseudo a/2 translation (with a 0.3 Å mean atomic distance difference), except for one H atom of the water molecules (0.86 Å) because of their different orientations in the two molecules. The two molecules, linked by very strong hydrogen bonds, are arranged in layers. Two layers which are linked by weaker hydrogen bonds are approximately oriented along the c axis. The structure may be described by translations of this set of two layers along the c axis without hydrogen bonds leading to a two-dimensional hydrogen-bond network. The structures of the monohydrate (NAM) and trihydrate (NAT) are re-determined for comparisons. These structures may be described by one- and three-dimensional hydrogen-bond networks, respectively.

Computing details

Data collection: Philips PW1100 software; cell refinement: Philips PW1100 software; data reduction: Philips PW1100 software; program(s) used to solve structure: SHELXS86 (Sheldrix, 1990); program(s) used to refine structure: SHELXL93 (Sheldrick, 1993); molecular graphics: ORTEP-III (Burnett and Johnson, 1996).

Figures

(I)

Crystal data

HNO3·2(H2O)	F(000) = 416
Mr = 99.04	Dx = 1.654 Mg m^−3
Monoclinic, P21/n	Mo Kα radiation, λ = 0.71069 Å
a = 17.509 (3) Å	Cell parameters from 25 reflections
b = 7.619 (4) Å	θ = 5.5–25°
c = 6.253 (3) Å	µ = 0.19 mm^−1
β = 107.5 (3)°	T = 200 K
V = 796 (2) Å^3	Cylindrical, colourless
Z = 8	0.5 mm (radius)

Data collection

Philips PW1100 diffractometer	Rint = 0.042
Radiation source: fine-focus sealed tube	θmax = 26.0°, θmin = 2.4°
Graphite monochromator	h = −21→20
ω–2θ scans	k = −9→9
3665 measured reflections	l = −3→7
1567 independent reflections	3 standard reflections every 60 min
1315 reflections with > σ(I)	intensity decay: 1%

Refinement

Refinement on F^2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F^2 > 2σ(F^2)] = 0.032	Only H-atom displacement parameters refined
wR(F^2) = 0.092	w = 1/[σ^2(Fo^2) + (0.0375P)^2], P = (Fo^2 + 2Fc^2)/3
S = 1.34	(Δ/σ)max = 0.003
1567 reflections	Δρmax = 0.3 e Å^−3
150 parameters	Δρmin = −0.2 e Å^−3
0 restraints	Extinction correction: SHELXL, Fc^*=kFc[1+0.001xFc^2l^3/sin(2q)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.040 (4)

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.

Refinement. Refinement on F² for ALL reflections except for 0 with very negative F² or flagged by the user for potential systematic errors. Weighted R-factors wR and all goodnesses of fit S are based on F², conventional R-factors R are based on F, with F set to zero for negative F². The observed criterion of F² > σ(F²) is used only for calculating the R factor etc. and is not relevant to the choice of reflections for refinement. R-factors based on F² are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
NA	0.10177 (7)	0.14924 (18)	0.8655 (2)	0.0251 (3)
O1A	0.04054 (6)	0.04734 (14)	0.8034 (2)	0.0321 (3)
O2A	0.09168 (6)	0.30802 (15)	0.8536 (2)	0.0346 (3)
O3A	0.16836 (6)	0.07946 (16)	0.9337 (2)	0.0387 (3)
NB	0.38750 (7)	−0.15648 (18)	1.1057 (2)	0.0244 (3)
O1B	0.44779 (6)	−0.05405 (14)	1.1747 (2)	0.0332 (3)
O2B	0.39614 (7)	−0.31434 (14)	1.1393 (2)	0.0347 (3)
O3B	0.32115 (6)	−0.08980 (15)	1.0037 (2)	0.0328 (3)
O4A	0.07134 (7)	−0.27208 (16)	0.9186 (2)	0.0260 (3)
H1A	0.0632 (15)	−0.143 (4)	0.884 (5)	0.086 (9)*
H2A	0.1196 (14)	−0.309 (3)	0.902 (4)	0.054 (6)*
H3A	0.0366 (13)	−0.338 (3)	0.847 (4)	0.054 (7)*
O4B	0.41388 (7)	0.27453 (16)	1.0743 (2)	0.0271 (3)
H1B	0.4267 (14)	0.158 (4)	1.102 (4)	0.066 (8)*
H2B	0.3660 (15)	0.300 (3)	1.095 (4)	0.067 (7)*
H3B	0.4497 (13)	0.345 (3)	1.150 (4)	0.047 (6)*
O5A	0.20905 (6)	−0.36788 (17)	0.8978 (2)	0.0305 (3)
H4A	0.2401 (16)	−0.275 (3)	0.914 (5)	0.065 (7)*
H5A	0.2093 (15)	−0.419 (3)	0.780 (5)	0.077 (9)*
O5B	0.28264 (7)	0.32933 (18)	1.1298 (2)	0.0351 (4)
H4B	0.2453 (18)	0.238 (4)	1.044 (5)	0.101 (10)*
H5B	0.2622 (13)	0.419 (3)	1.085 (4)	0.057 (8)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
NA	0.0201 (5)	0.0215 (7)	0.0331 (7)	−0.0002 (5)	0.0070 (5)	0.0024 (6)
O1A	0.0192 (5)	0.0210 (5)	0.0522 (8)	−0.0019 (4)	0.0045 (5)	0.0013 (6)
O2A	0.0314 (6)	0.0190 (6)	0.0517 (8)	−0.0006 (5)	0.0097 (5)	0.0022 (6)
O3A	0.0188 (5)	0.0327 (7)	0.0593 (9)	0.0036 (5)	0.0039 (5)	0.0031 (7)
NB	0.0201 (6)	0.0217 (6)	0.0315 (7)	0.0015 (5)	0.0081 (5)	0.0021 (6)
O1B	0.0208 (5)	0.0198 (6)	0.0538 (8)	−0.0021 (4)	0.0031 (5)	0.0002 (6)
O2B	0.0325 (6)	0.0168 (5)	0.0493 (8)	0.0006 (5)	0.0041 (5)	0.0034 (6)
O3B	0.0188 (5)	0.0296 (7)	0.0478 (7)	0.0045 (4)	0.0067 (5)	0.0084 (6)
O4A	0.0204 (6)	0.0228 (6)	0.0324 (7)	−0.0012 (5)	0.0041 (5)	0.0012 (5)
O4B	0.0249 (6)	0.0210 (6)	0.0323 (7)	−0.0028 (5)	0.0040 (5)	−0.0003 (5)
O5A	0.0232 (5)	0.0263 (6)	0.0389 (7)	0.0008 (5)	0.0045 (5)	−0.0024 (6)
O5B	0.0248 (6)	0.0311 (7)	0.0460 (8)	0.0009 (5)	0.0054 (5)	−0.0021 (7)

Geometric parameters (Å, º)

NA—O1A	1.286 (2)	NB—O1B	1.279 (2)
NA—O2A	1.222 (2)	NB—O2B	1.223 (2)
NA—O3A	1.235 (2)	NB—O3B	1.253 (2)
O4A—H1A	0.99 (3)	O4B—H1B	0.92 (3)
O4A—H2A	0.93 (2)	O4B—H2B	0.91 (3)
O4A—H3A	0.81 (3)	O4B—H3B	0.85 (2)
O5A—H4A	0.88 (3)	O5B—H4B	0.99 (3)
O5A—H5A	0.83 (3)	O5B—H5B	0.78 (2)
O2A—NA—O3A	123.5 (1)	H3A—O4A—H1A	117 (2)
O2A—NA—O1A	119.2 (1)	H2A—O4A—H1A	111 (2)
O3A—NA—O1A	117.4 (1)	H3B—O4B—H2B	110 (2)
O2B—NB—O3B	122.3 (1)	H3B—O4B—H1B	114 (2)
O2B—NB—O1B	119.7 (1)	H2B—O4B—H1B	111 (2)
O3B—NB—O1B	118.0 (1)	H4A—O5A—H5A	108 (3)
H3A—O4A—H2A	108 (2)	H5B—O5B—H4B	105 (2)