The ephemeral dihydrate of sulfanilic acid

Evaporation of an aqueous solution of sulfanilic acid (systematic name: 4-amino­benzene-1-sulfonic acid) at 273 K affords a crystalline dihydrate, C₆H₇NO₃S·2H₂O. The organic mol­ecule exists as a zwitterion; two zwitterions are aligned in an anti­parallel fashion about a crystallographic centre of inversion. They inter­act directly via two N—H...O hydrogen bonds between the ammonium group of one zwitterion and the sulfonate group of its symmetry-related counterpart, and their aromatic rings are π-stacked, with an inter­planar distance of 3.533 (3) Å. One of the cocrystallized water mol­ecules connects the resulting pairs into layers and the second crosslinks the layers into a three-dimensional network. All H atoms connected to N or O atoms find acceptors in suitable geometries. In the resulting crystal, polar and hydrogen-bond-dominated slabs alternate with stacks of organic arene rings. Although the new dihydrate shows efficient space filling, with a packing coefficient of 75.7%, it is unstable and undergoes fast desolvation at room temperature. In this process, the ortho­rhom­bic ansolvate forms as a pure phase.

Computing details

Data collection: SMART (Bruker, 2001); cell refinement: SAINT-Plus (Bruker, 2009); data reduction: SAINT-Plus (Bruker, 2009); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL2017 (Sheldrick, 2015); molecular graphics: PLATON (Spek, 2009); software used to prepare material for publication: SHELXL2017 (Sheldrick, 2015).

4-Aminobenzene-1-sulfonic acid dihydrate

Crystal data

C6H7NO3S·2H2O	F(000) = 440
Mr = 209.22	Dx = 1.632 Mg m^−3
Monoclinic, P21/n	Mo Kα radiation, λ = 0.71073 Å
a = 11.3338 (6) Å	Cell parameters from 5814 reflections
b = 5.7650 (3) Å	θ = 5.7–62.7°
c = 13.9048 (8) Å	µ = 0.37 mm^−1
β = 110.3710 (11)°	T = 100 K
V = 851.71 (8) Å^3	Transparent platelet, colourless
Z = 4	0.20 × 0.12 × 0.02 mm

Data collection

Bruker D8 gonimeter with an APEX CCD detector diffractometer	3264 independent reflections
Radiation source: Incoatec microsource	2834 reflections with I > 2σ(I)
Multilayer optics monochromator	Rint = 0.060
ω scans	θmax = 33.3°, θmin = 2.9°
Absorption correction: multi-scan (SADABS; Bruker, 2008)	h = −17→17
Tmin = 0.898, Tmax = 1.000	k = −8→8
28058 measured reflections	l = −21→21

Refinement

Refinement on F^2	0 restraints
Least-squares matrix: full	Hydrogen site location: mixed
R[F^2 > 2σ(F^2)] = 0.036	H atoms treated by a mixture of independent and constrained refinement
wR(F^2) = 0.093	w = 1/[σ^2(Fo^2) + (0.040P)^2 + 0.670P] where P = (Fo^2 + 2Fc^2)/3
S = 1.01	(Δ/σ)max = 0.004
3264 reflections	Δρmax = 0.64 e Å^−3
146 parameters	Δρmin = −0.47 e Å^−3

Special details

Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.

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

	x	y	z	Uiso*/Ueq
S1	0.44658 (2)	1.06435 (5)	0.21108 (2)	0.00910 (8)
O1	0.50583 (8)	1.03106 (16)	0.32230 (6)	0.01236 (16)
O2	0.34514 (8)	0.89939 (16)	0.16541 (7)	0.01307 (17)
O3	0.41028 (8)	1.30458 (15)	0.18416 (7)	0.01308 (17)
N1	0.82843 (9)	0.86847 (18)	0.01350 (8)	0.01115 (18)
H1A	0.8316 (17)	0.716 (3)	−0.0011 (13)	0.018 (4)*
H1B	0.904 (2)	0.922 (4)	0.0529 (17)	0.031 (5)*
H1C	0.8032 (18)	0.945 (3)	−0.0484 (15)	0.020 (5)*
C1	0.56405 (10)	0.9992 (2)	0.15760 (8)	0.00969 (19)
C2	0.56254 (11)	0.7856 (2)	0.11052 (9)	0.0112 (2)
H2	0.501644	0.671824	0.109839	0.013*
C3	0.65147 (11)	0.7406 (2)	0.06433 (9)	0.0113 (2)
H3	0.651525	0.595896	0.031647	0.014*
C4	0.73980 (10)	0.9090 (2)	0.06655 (8)	0.00986 (19)
C5	0.74390 (11)	1.1202 (2)	0.11611 (9)	0.0114 (2)
H5	0.806388	1.232035	0.118439	0.014*
C6	0.65530 (11)	1.1652 (2)	0.16215 (9)	0.0113 (2)
H6	0.656920	1.308275	0.196510	0.014*
O4	0.15086 (9)	0.58774 (16)	0.05400 (7)	0.01464 (17)
H4A	0.104 (2)	0.580 (4)	0.0877 (18)	0.039 (6)*
H4B	0.216 (2)	0.643 (4)	0.0974 (18)	0.039 (6)*
O5	0.44760 (9)	1.56610 (16)	0.36443 (7)	0.01373 (17)
H5A	0.426 (2)	1.499 (4)	0.3081 (18)	0.031 (5)*
H5B	0.458 (2)	1.706 (4)	0.3501 (16)	0.034 (6)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
S1	0.00924 (12)	0.00977 (13)	0.00848 (12)	0.00031 (9)	0.00332 (9)	0.00032 (9)
O1	0.0131 (4)	0.0148 (4)	0.0090 (3)	0.0007 (3)	0.0036 (3)	0.0010 (3)
O2	0.0101 (3)	0.0150 (4)	0.0139 (4)	−0.0025 (3)	0.0038 (3)	−0.0015 (3)
O3	0.0154 (4)	0.0114 (4)	0.0134 (4)	0.0031 (3)	0.0064 (3)	0.0017 (3)
N1	0.0113 (4)	0.0115 (4)	0.0116 (4)	0.0007 (3)	0.0052 (3)	−0.0001 (3)
C1	0.0096 (4)	0.0106 (5)	0.0088 (4)	0.0006 (4)	0.0032 (3)	0.0007 (4)
C2	0.0118 (4)	0.0102 (5)	0.0117 (5)	−0.0013 (4)	0.0042 (4)	−0.0007 (4)
C3	0.0131 (5)	0.0097 (5)	0.0115 (5)	−0.0005 (4)	0.0049 (4)	−0.0012 (4)
C4	0.0096 (4)	0.0115 (5)	0.0090 (4)	0.0010 (4)	0.0038 (4)	0.0008 (4)
C5	0.0116 (4)	0.0109 (5)	0.0120 (5)	−0.0012 (4)	0.0043 (4)	−0.0006 (4)
C6	0.0118 (4)	0.0099 (5)	0.0119 (5)	−0.0006 (4)	0.0038 (4)	−0.0011 (4)
O4	0.0150 (4)	0.0155 (4)	0.0141 (4)	−0.0021 (3)	0.0060 (3)	−0.0027 (3)
O5	0.0166 (4)	0.0122 (4)	0.0128 (4)	0.0004 (3)	0.0057 (3)	0.0011 (3)

Geometric parameters (Å, º)

S1—O3	1.4560 (9)	C2—H2	0.9500
S1—O2	1.4564 (9)	C3—C4	1.3870 (16)
S1—O1	1.4685 (9)	C3—H3	0.9500
S1—C1	1.7765 (11)	C4—C5	1.3919 (16)
N1—C4	1.4572 (14)	C5—C6	1.3905 (16)
N1—H1A	0.90 (2)	C5—H5	0.9500
N1—H1B	0.90 (2)	C6—H6	0.9500
N1—H1C	0.92 (2)	O4—H4A	0.83 (2)
C1—C2	1.3916 (16)	O4—H4B	0.84 (2)
C1—C6	1.3943 (16)	O5—H5A	0.83 (2)
C2—C3	1.3952 (15)	O5—H5B	0.85 (2)
O3—S1—O2	113.54 (5)	C1—C2—H2	120.4
O3—S1—O1	112.32 (5)	C3—C2—H2	120.4
O2—S1—O1	112.09 (5)	C4—C3—C2	119.40 (11)
O3—S1—C1	106.22 (5)	C4—C3—H3	120.3
O2—S1—C1	105.80 (5)	C2—C3—H3	120.3
O1—S1—C1	106.18 (5)	C3—C4—C5	121.51 (10)
C4—N1—H1A	110.9 (11)	C3—C4—N1	119.74 (10)
C4—N1—H1B	108.5 (14)	C5—C4—N1	118.73 (10)
H1A—N1—H1B	111.4 (18)	C6—C5—C4	119.10 (11)
C4—N1—H1C	110.6 (12)	C6—C5—H5	120.4
H1A—N1—H1C	106.3 (16)	C4—C5—H5	120.4
H1B—N1—H1C	109.0 (18)	C5—C6—C1	119.60 (11)
C2—C1—C6	121.07 (10)	C5—C6—H6	120.2
C2—C1—S1	119.71 (9)	C1—C6—H6	120.2
C6—C1—S1	119.20 (9)	H4A—O4—H4B	101 (2)
C1—C2—C3	119.25 (10)	H5A—O5—H5B	104 (2)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N1—H1A···O4^i	0.90 (2)	1.94 (2)	2.8296 (14)	168.6 (16)
N1—H1B···O5^ii	0.90 (2)	1.87 (2)	2.7610 (14)	173 (2)
N1—H1C···S1^iii	0.92 (2)	2.945 (19)	3.5833 (11)	127.7 (14)
N1—H1C···O2^iii	0.92 (2)	2.09 (2)	2.9056 (14)	146.8 (16)
N1—H1C···O5^iv	0.92 (2)	2.352 (19)	2.8657 (13)	115.0 (14)
C5—H5···O1^v	0.95	2.64	3.5636 (15)	165
O4—H4A···O1^vi	0.83 (2)	2.06 (2)	2.8888 (13)	174 (2)
O4—H4B···O2	0.84 (2)	2.06 (2)	2.8463 (13)	156 (2)
O5—H5A···S1	0.83 (2)	2.89 (2)	3.5912 (10)	143.0 (19)
O5—H5A···O3	0.83 (2)	2.01 (2)	2.8279 (13)	168 (2)
O5—H5B···S1^vii	0.85 (2)	2.80 (2)	3.5750 (10)	152.4 (19)
O5—H5B···O1^vii	0.85 (2)	2.02 (2)	2.8693 (13)	173 (2)

Symmetry codes: (i) −x+1, −y+1, −z; (ii) −x+3/2, y−1/2, −z+1/2; (iii) −x+1, −y+2, −z; (iv) x+1/2, −y+5/2, z−1/2; (v) −x+3/2, y+1/2, −z+1/2; (vi) −x+1/2, y−1/2, −z+1/2; (vii) x, y+1, z.