Bis(dihydro­nium) naphthalene-1,5-disulfonate

The title compound is a salt, 2H₅O₂⁺·C₁₀H₆O₆S₂²⁻, in which the anion lies across an inversion centre in the space group C2/­c, while the cation contains a short but noncentred O—H...O hydrogen bond. The ionic components are linked by charge-assisted O—H...O hydrogen bonds into a three-dimensional framework structure.

S1. Comment

In solid hydrates of strong acids, the H atom has been found to be hydrated to form a series of cations which have been characterized as H₃O⁺, H₅O₂⁺, H₇O₃⁺ and H₉O₄⁺ depending upon the degree of hydration. A search of the Cambridge Structural Database (Version 5.28; Allen, 2002) for structures containing the 1,5-naphthalenedisulfonate anion yielded only seven examples, all salts of the metals of groups 1 and 2 (Cai et al., 2001). The structure of 1,5-naphthalenedisulfonic acid itself is not known. We report here the crystal structure of 1,5-naphthalenedisulfonic acid tetrahydrate, in which the H atoms of the SO₃H groups are transferred to the water molecules to form the salt 2H₅O₂⁺·C₁₀H₆(SO₃)₂]^2-, (I).

The anion in (I) lies across a centre of inversion so that the asymmetric unit of (I) consists of one-half of a naphthalene-1,5-disulfonate(2-) anion and an H₅O₂⁺ cation (Fig. 1). The naphthalene ring of the anion is essentially planar [the greatest deviations of the C atoms from the weighted mean ring plane are smaller than 0.010 (2) Å], but its bond distances exhibit significant differences from those of naphthalene itself (Brock & Dunitz, 1982; Oddershede & Larsen, 2001). The C2—C3, C3—C4 and C3—C3ⁱ bonds [symmetry code: (i) -x + 1, -y, -z + 1; Table 1] are significantly longer than the other C—C bonds within the ring. The distortions are the result of the substitution effect of the SO₃ groups joined to the ring at the 1,5-positions. The ab-initio gas-phase geometry calculated for an isolated anion shows quite good correlation between the C—C bonds and C—C—C angles within the ring (Fig. 2). Thus the distortions arise mainly from the electronic structure and to a lesser degree from the molecular interaction as well as from the crystal packing forces. The S—O bonds of the SO₃^- group are all intermediate in length between double S═O and single bonds (Allen et al., 1987), indicating charge delocalization onto all O atoms of this group.

The C—S bond length in the crystal structure is shorter than that calculated for the gas-phase structure (1.841 Å), owing to the interactions of negatively charged SO₃^- groups with the π-aromatic ring. In the crystal structure, this interaction decreases as a result of the hydrogen-bonding system, which reduces the charge on the SO₃^- groups. The small differences between the experimental S—O bond lengths result from the strengths of the hydrogen bonds in which the O atoms are involved (Table 2).

The acidic H atom is dihydrated such that pairs of water molecules are joined together via a short O—H···O hydrogen bond to form a discrete H₅O₂⁺ ion. However, the acidic H atom is not located at the centre between the O atoms, but closer to one of the two water molecules (Table 2). This is in contrast to the results of molecular orbital (MO) calculations performed for an isolated H₅O₂⁺ cation, which is predicted to be symmetric (O···O = 2.417 Å, O—H = 1.210 Å and O—H—O = 176.6°), although in the crystal structure the cation is nonsymmetrical. Ab initio MO calculations indicate that substantial energy is involved in the hydration of the hydronium ion (e.g. H₃O⁺ + H₂O = H₅O₂⁺, 37 kcal mol^-1). The H₅O₂⁺ ion has a gauche conformation, with a dihedral angle of 99.5° as defined by the dihedral angle between the two planes defined by atoms O4, H41 and H42 and atoms O5, H51 and H52. Thus the bonding arrangement together with the lone-pair of electrons around each O atom in H₅O₂⁺ is tetrahedral. However, because of the hydrogen-bonding system and, especially, to the lone-pair of electrons on both O atoms, the tetrahedron is significantly distorted, since the lone-pair of electrons afford a wider region than the bonding pair, as predicted by the valence-shell electron pair repulsion model (Gillespie, 1963, 1992).

The molecular arrangement in the crystal structure of (I) is mainly determined by relatively strong and directional hydrogen bonds (Table 2), and to a lesser degree by a π–π interaction between the naphthalene ring systems, where the interplanar spacing is ca 3.53 Å (Fig. 3). This value is comparable to the sum of the C atom van der Waals radii of the π-ring system (Pauling, 1967). However, as a result of the mutual shift of the rings, the π–π interaction is not fully effective. The π–π overlaping between the rings takes place only via the outermost C—C bonds (C1—C5ⁱ and C5—C1ⁱ). The 1,5-naphthalenedisulfate anions are stacked in the crystal structure along the b axis at z = 0 and z = 1/2, and they make an angle of 17.7° with the (010) plane, so forming sheets parallel to (001). The H₅O₂⁺ cations are located between these sheets and join together via O—H···O hydrogen bonds into a three-dimensional network. Each H₅O₂⁺ cation links four anions. Atom O1 of the SO₃^_ group is involved in two hydrogen bonds while the other two O atoms of SO₃^_ are each involved in one hydrogen bond (Table 2).

Related literature

For related literature, see: Allen (2002); Allen et al. (1987); Cai et al. (2001); Frisch et al. (1998); Gillespie (1963, 1992); Oddershede & Larsen (2001); Pauling (1967).

S2. Experimental

Suitable crystals of (I) were obtained by slow evaporation of an aqueous solution of 1,5-naphthalenedisulfonic acid. MO calculations were performed using GAUSSIAN98 (Frisch et al., 1998).

S3. Refinement

H atoms bonded to C atom were treated as riding atom in geometrically idealized positions, with C—H distances of 0.93 Å and U_iso(H) = 1.2U_eq(C). H atoms bonded to O atoms were located in difference maps and their coordinates were refined with U_iso(H) = 1.5U_eq(O), giving a range of O—H distances of 0.80 (4)–0.86 (4) Å for the terminal H atoms and 1.02 (4) and 1.42 (4) Å for the bridging H atom.

Computing details

Data collection: CrysAlis CCD (Oxford Diffraction, 2005); cell refinement: CrysAlis CCD (Oxford Diffraction, 2005); data reduction: CrysAlis RED (Oxford Diffraction, 2005); program(s) used to solve structure: SHELXS97 (Sheldrick, 1990a); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: SHELXTL (Sheldrick, 1990b); software used to prepare material for publication: SHELXL97 (Sheldrick, 1997).

Figures

	Fig. 1. A view of (I), showing displacement ellipsoids at the 50% probability level and H atoms as spheres of arbitrary radii. Hydrogen bonds are drawn as dashed lines.
	Fig. 2. Results of the optimized molecular orbital calculations (B3LYP/6–31+G*) for the naphthalene-1,5-disulfonate(2-) anion (Å, °).
	Fig. 3. A View of the crystal packing in (I), showing the three-dimensional hydrogen-bonded network. H atoms have been omitted for clarity.

Bis(dihydronium) naphthalene-1,5-disulfonate

Crystal data

2H5O2^+·C10H6O6S2^2^−	F(000) = 752
Mr = 360.37	Dx = 1.616 Mg m^−3 Dm = 1.61 Mg m^−3 Dm measured by floatation
Monoclinic, C2/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -C 2yc	Cell parameters from 1082 reflections
a = 9.1183 (18) Å	θ = 3.6–28.9°
b = 7.1051 (14) Å	µ = 0.41 mm^−1
c = 22.954 (4) Å	T = 295 K
β = 95.08 (1)°	Plate, colourless
V = 1481.3 (5) Å^3	0.32 × 0.28 × 0.11 mm
Z = 4

Data collection

Kuma KM-4 diffractometer with CCD area detector	1835 independent reflections
Radiation source: fine-focus sealed tube	1575 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.017
Detector resolution: 1024x1024 with blocks 2x2 pixels mm^-1	θmax = 28.9°, θmin = 3.6°
ω–scan	h = −11→12
Absorption correction: analytical face-indexed, SHELXTL (Sheldrick, 1990b)	k = −9→9
Tmin = 0.884, Tmax = 0.961	l = −31→28
9288 measured reflections

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)] = 0.030	H atoms treated by a mixture of independent and constrained refinement
wR(F^2) = 0.077	w = 1/[σ^2(Fo^2) + (0.0381P)^2 + 0.9846P] where P = (Fo^2 + 2Fc^2)/3
S = 1.06	(Δ/σ)max = 0.001
1835 reflections	Δρmax = 0.28 e Å^−3
116 parameters	Δρmin = −0.28 e Å^−3
0 restraints	Extinction correction: SHELXL97, Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.0378 (15)

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 of F² against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F², conventional R-factors R are based on F, with F set to zero for negative F². The threshold expression of F² > σ(F²) is used only for calculating R-factors(gt) 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
S1	0.43372 (4)	0.15337 (5)	0.636456 (13)	0.03117 (14)
O1	0.51167 (12)	0.00295 (15)	0.67039 (4)	0.0380 (3)
O2	0.29174 (12)	0.19037 (17)	0.65773 (4)	0.0417 (3)
O3	0.52443 (14)	0.31903 (15)	0.63376 (5)	0.0460 (3)
C1	0.25634 (16)	0.0434 (2)	0.54291 (6)	0.0339 (3)
H1	0.1809	0.0663	0.5667	0.041*
C2	0.39923 (15)	0.06717 (19)	0.56418 (5)	0.0281 (3)
C3	0.51847 (15)	0.03049 (18)	0.52944 (5)	0.0269 (3)
C4	0.66794 (16)	0.0504 (2)	0.55032 (6)	0.0325 (3)
H4	0.6921	0.0876	0.5888	0.039*
C5	0.77700 (16)	0.0160 (2)	0.51518 (6)	0.0363 (3)
H5	0.8747	0.0319	0.5297	0.044*
O4	0.75030 (15)	0.0361 (2)	0.74097 (5)	0.0461 (3)
H41	0.664 (3)	0.028 (3)	0.7222 (11)	0.069*
H42	0.736 (2)	0.103 (4)	0.7690 (11)	0.069*
O5	0.9387 (2)	0.1384 (2)	0.68043 (10)	0.0664 (7)
H51	0.962 (4)	0.060 (6)	0.6578 (15)	0.099*
H52	0.960 (4)	0.254 (6)	0.6733 (16)	0.099*
H2	0.836 (4)	0.094 (4)	0.7213 (13)	0.069*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
S1	0.0441 (2)	0.0285 (2)	0.02254 (18)	0.00090 (14)	0.01200 (13)	−0.00211 (12)
O1	0.0476 (6)	0.0383 (6)	0.0279 (5)	0.0014 (5)	0.0028 (4)	0.0012 (4)
O2	0.0488 (6)	0.0502 (7)	0.0285 (5)	0.0094 (5)	0.0162 (4)	−0.0016 (5)
O3	0.0657 (7)	0.0324 (6)	0.0427 (6)	−0.0084 (5)	0.0205 (5)	−0.0095 (5)
C1	0.0356 (7)	0.0376 (7)	0.0304 (7)	0.0026 (6)	0.0128 (5)	0.0006 (6)
C2	0.0383 (7)	0.0256 (6)	0.0215 (6)	0.0023 (5)	0.0094 (5)	0.0008 (5)
C3	0.0360 (7)	0.0230 (6)	0.0228 (6)	0.0019 (5)	0.0083 (5)	0.0015 (5)
C4	0.0397 (7)	0.0341 (7)	0.0242 (6)	0.0006 (6)	0.0050 (5)	−0.0017 (5)
C5	0.0340 (7)	0.0414 (8)	0.0338 (7)	−0.0011 (6)	0.0055 (6)	−0.0003 (6)
O4	0.0442 (6)	0.0575 (8)	0.0373 (6)	−0.0024 (6)	0.0082 (5)	−0.0120 (5)
O5	0.0756 (13)	0.0470 (7)	0.0898 (16)	−0.0114 (8)	0.0442 (12)	−0.0162 (8)

Geometric parameters (Å, º)

S1—O3	1.4431 (12)	C4—C5	1.357 (2)
S1—O2	1.4475 (11)	C4—H4	0.9300
S1—O1	1.4683 (11)	C5—C1^i	1.406 (2)
S1—C2	1.7703 (13)	C5—H5	0.9300
C1—C2	1.361 (2)	O4—H41	0.86 (3)
C1—C5^i	1.406 (2)	O4—H42	0.82 (3)
C1—H1	0.9300	O4—H2	1.02 (4)
C2—C3	1.4281 (18)	O5—H51	0.80 (4)
C3—C4	1.411 (2)	O5—H52	0.86 (4)
C3—C3^i	1.431 (2)
O3—S1—O2	113.54 (7)	C4—C3—C3^i	119.38 (15)
O3—S1—O1	111.35 (7)	C2—C3—C3^i	117.10 (15)
O2—S1—O1	111.02 (7)	C5—C4—C3	121.11 (13)
O3—S1—C2	107.27 (7)	C5—C4—H4	119.4
O2—S1—C2	106.80 (7)	C3—C4—H4	119.4
O1—S1—C2	106.42 (6)	C4—C5—C1^i	120.63 (14)
C2—C1—C5^i	119.82 (13)	C4—C5—H5	119.7
C2—C1—H1	120.1	C1^i—C5—H5	119.7
C5^i—C1—H1	120.1	H41—O4—H42	103 (2)
C1—C2—C3	121.94 (12)	H41—O4—H2	120 (2)
C1—C2—S1	117.66 (10)	H42—O4—H2	107 (2)
C3—C2—S1	120.37 (10)	H51—O5—H52	118 (4)
C4—C3—C2	123.52 (12)

Symmetry code: (i) −x+1, −y, −z+1.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O4—H2···O5	1.02 (4)	1.42 (4)	2.416 (2)	163 (3)
O4—H41···O1	0.86 (3)	1.76 (3)	2.6059 (19)	167 (2)
O4—H42···O2^ii	0.82 (3)	1.83 (3)	2.6294 (17)	164 (2)
O5—H51···O3^iii	0.80 (4)	1.90 (4)	2.6562 (19)	156 (4)
O5—H52···O1^iv	0.86 (4)	1.83 (4)	2.6891 (19)	171 (4)

Symmetry codes: (ii) −x+1, y, −z+3/2; (iii) x+1/2, y−1/2, z; (iv) x+1/2, y+1/2, z.