Ammonium 2-mercapto­pyridine-3-carboxyl­ate hydrate

The crystal structure of ammonium 2-mercapto­pyridine-3-carboxyl­ate hydrate, NH₄⁺·C₆H₄NO₂S^-·H₂O, contains a zwitterionic anion with the pyridine-N atom protonated. All potential donor and acceptor atoms are involved in hydrogen-bonding, resulting in a three-dimensional network structure.

Key indicators

• Single-crystal X-ray study
• T = 296 K
• Mean [sigma](C-C) = 0.004 Å
• R factor = 0.040
• wR factor = 0.174
• Data-to-parameter ratio = 17.8

checkCIF results

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 Alert Level C:



PLAT_353  Alert C Long    N-H Bond (0.87A)   N(11)  -   H(12)  =       1.01 Ang.


 0 Alert Level A = Potentially serious problem

 0 Alert Level B = Potential problem

 1 Alert Level C = Please check

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S1. Comment

2-Mercapto-substituted alcohols and acids have considerable utility as bidentate ligands in coordination chemistry (Harris & Livingstone, 1964; McAuliffe, 1986). These ligands may act as either mono- or di-anionic species and with bismuth(III) often give octahedral complexes (Agoes et al., 1997; Sagatys et al., 2003). The ammonium tris(2-mercaptobenzoato-O,S)bismuth(III) dihydrate complex (Sagatys et al., 2003) is readily formed, while the complex with the analogous ligand thionicotinic acid (2-mercaptopyridine-3-carboxylic acid) is less so. The structure of the ionic species formed from the latter acid under aqueous ammoniacal conditions was therefore determined in an attempt to explain this anomoly.

The crystal structure of ammonium 2-mercaptopyridine-3-carboxylate hydrate, (I), confirms the presence of a zwitterionic anion species with protonation at the pyridine-N atom and deprotonation as the carboxylate and thiolate residues (Fig. 1). The plane of the carboxylate group at C3 is anticlinally related to that of the pyridine ring [torsion angle C2—C3—C7—O71 = 75.1 (4)°]. The formation of the stable zwitterion probably accounts for the different behaviour of thionicotinic acid compared to thiosalicylic acid as a complexing agent.

The crystal packing of (I) shows that all ammonium H atoms, together with the zwitterionic pyridinium H atom, are involved in hydrogen-bonding interactions to carboxylate and water O atoms, as well as to a thiol-S atom [N11—H14···S2 = 3.350 (3) Å] (Fig. 2 and Table 1). The water molecule is also hydrogen bonded to two carboxylate O atoms, giving a three-dimensional network structure.

S2. Experimental

The title compound, (I), was prepared by dissolving 5.0 g (3.2 mmol) of thionicotinic acid (2-mercaptopyridine-3-carboxylic acid) in 150 ml of 28% ammonia solution at room temperature and allowing the filtered solution to evaporate to dryness at room temperature over a period of ca 3 weeks.

S3. Refinement

H atoms involved in hydrogen-bonding interactions (i.e. H1, H11, H12, H13, H14, H21 and H22) were located by difference methods, and both positional and displacement parameters were refined. Other H atoms were included in the riding-model approximation.

Computing details

Data collection: MSC/AFC Diffractometer Control Software (Molecular Structure Corporation, 1999); cell refinement: MSC/AFC Diffractometer Control Software; data reduction: TEXSAN for Windows (Molecular Structure Corporation, 1999); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: PLATON for Windows (Spek, 1999).

Figures

	Fig. 1. The molecular configuration and atom-naming scheme for (I). Ellipsoids are shown at the 30% probability level.
	Fig. 2. The packing of (I) in the unit cell, viewed down a, showing hydrogen-bonding interactions as broken lines.

ammonium 2-mercaptopyridine-3-carboxylate hydrate

Crystal data

H4N^+·C6H4NO2S^−·H2O	F(000) = 400
Mr = 190.22	Dx = 1.424 Mg m^−3
Monoclinic, P21/n	Mo Kα radiation, λ = 0.71069 Å
Hall symbol: -P 2yn	Cell parameters from 25 reflections
a = 6.8327 (4) Å	θ = 11.8–18.9°
b = 10.8017 (12) Å	µ = 0.34 mm^−1
c = 12.2436 (5) Å	T = 296 K
β = 100.854 (5)°	Plate, colourless
V = 887.47 (12) Å^3	0.35 × 0.35 × 0.12 mm
Z = 4

Data collection

Rigaku AFC-7R diffractometer	Rint = 0.041
Radiation source: Rigaku rotating anode	θmax = 29.5°, θmin = 2.5°
Graphite monochromator	h = 0→8
ω–2θ scans	k = 0→13
2631 measured reflections	l = −15→15
2451 independent reflections	3 standard reflections every 150 reflections
1113 reflections with I > 2σ(I)	intensity decay: 0.5%

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)] = 0.040	H atoms treated by a mixture of independent and constrained refinement
wR(F^2) = 0.174	w = 1/[σ^2(Fo^2) + (0.1032P)^2 + 0.154P] where P = (Fo^2 + 2Fc^2)/3
S = 1.00	(Δ/σ)max < 0.001
2451 reflections	Δρmax = 0.33 e Å^−3
138 parameters	Δρmin = −0.24 e Å^−3
Primary atom site location: structure-invariant direct methods

Special details

Geometry. Bond distances, angles etc. have been calculated using the rounded fractional coordinates. All e.s.d.'s are estimated from the variances of the (full) variance-covariance matrix. The cell e.s.d.'s are taken into account in the estimation of distances, angles and torsion angles

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
S2	0.16986 (13)	0.37274 (8)	0.37160 (7)	0.0356 (3)
O71	0.2178 (3)	0.1737 (2)	0.16045 (17)	0.0381 (8)
O72	−0.0904 (3)	0.1222 (2)	0.17581 (17)	0.0369 (7)
N1	0.2715 (4)	0.1932 (3)	0.5196 (2)	0.0340 (9)
C2	0.2008 (4)	0.2221 (3)	0.4105 (2)	0.0274 (9)
C3	0.1579 (4)	0.1187 (3)	0.3383 (2)	0.0261 (9)
C4	0.1793 (5)	−0.0004 (3)	0.3796 (3)	0.0357 (10)
C5	0.2488 (5)	−0.0213 (3)	0.4930 (3)	0.0393 (11)
C6	0.2945 (5)	0.0767 (4)	0.5616 (3)	0.0409 (11)
C7	0.0906 (5)	0.1411 (3)	0.2149 (2)	0.0270 (9)
N11	0.2151 (4)	0.1086 (3)	−0.0645 (2)	0.0386 (9)
O2	0.6010 (4)	0.2069 (3)	0.2788 (2)	0.0601 (10)
H1	0.316 (5)	0.261 (4)	0.570 (3)	0.047 (11)*
H4	0.150800	−0.068400	0.331400	0.0430*
H5	0.264800	−0.101200	0.522700	0.0480*
H6	0.344400	0.068900	0.638000	0.0500*
H11	0.147 (8)	0.034 (6)	−0.092 (5)	0.080 (16)*
H12	0.194 (7)	0.127 (6)	0.013 (5)	0.079 (15)*
H13	0.136 (7)	0.157 (5)	−0.116 (4)	0.069 (15)*
H14	0.346 (6)	0.116 (5)	−0.067 (5)	0.075 (14)*
H21	0.475 (6)	0.189 (6)	0.237 (6)	0.066 (15)*
H22	0.702 (7)	0.179 (6)	0.258 (6)	0.070 (15)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
S2	0.0459 (5)	0.0313 (4)	0.0300 (4)	−0.0004 (4)	0.0079 (3)	−0.0025 (4)
O71	0.0400 (14)	0.0517 (15)	0.0239 (11)	−0.0036 (12)	0.0097 (9)	−0.0009 (10)
O72	0.0325 (13)	0.0464 (14)	0.0281 (11)	0.0001 (11)	−0.0039 (9)	−0.0002 (11)
N1	0.0356 (16)	0.0439 (17)	0.0207 (12)	−0.0019 (14)	0.0005 (11)	−0.0052 (12)
C2	0.0242 (16)	0.0354 (18)	0.0222 (14)	−0.0004 (13)	0.0030 (11)	−0.0007 (12)
C3	0.0250 (15)	0.0323 (17)	0.0208 (12)	0.0005 (13)	0.0037 (10)	−0.0012 (12)
C4	0.042 (2)	0.0314 (17)	0.0335 (17)	0.0011 (15)	0.0066 (14)	−0.0007 (14)
C5	0.048 (2)	0.037 (2)	0.0326 (17)	0.0069 (16)	0.0070 (14)	0.0131 (14)
C6	0.044 (2)	0.054 (2)	0.0229 (15)	0.0070 (18)	0.0016 (14)	0.0103 (16)
C7	0.0322 (17)	0.0257 (15)	0.0218 (13)	0.0039 (13)	0.0021 (11)	−0.0022 (12)
N11	0.0437 (17)	0.0412 (18)	0.0298 (14)	0.0062 (14)	0.0040 (12)	0.0003 (12)
O2	0.0365 (15)	0.091 (2)	0.0523 (17)	−0.0042 (15)	0.0074 (12)	−0.0295 (16)

Geometric parameters (Å, º)

S2—C2	1.697 (3)	N11—H12	1.01 (6)
O71—C7	1.242 (4)	N11—H14	0.90 (4)
O72—C7	1.256 (4)	C2—C3	1.420 (4)
O2—H21	0.94 (5)	C3—C4	1.380 (5)
O2—H22	0.84 (5)	C3—C7	1.514 (3)
N1—C6	1.357 (5)	C4—C5	1.399 (5)
N1—C2	1.368 (3)	C5—C6	1.351 (5)
N1—H1	0.97 (4)	C4—H4	0.9394
N11—H13	0.91 (5)	C5—H5	0.9349
N11—H11	0.96 (6)	C6—H6	0.9371
H21—O2—H22	119 (6)	C2—C3—C4	120.7 (3)
C2—N1—C6	125.2 (3)	C4—C3—C7	120.4 (3)
C6—N1—H1	117 (2)	C3—C4—C5	120.5 (3)
C2—N1—H1	117 (2)	C4—C5—C6	119.1 (3)
H11—N11—H14	119 (5)	N1—C6—C5	119.6 (3)
H12—N11—H13	112 (5)	O71—C7—C3	118.0 (3)
H12—N11—H14	109 (5)	O72—C7—C3	116.5 (3)
H13—N11—H14	113 (5)	O71—C7—O72	125.5 (2)
H11—N11—H13	93 (5)	C3—C4—H4	120.24
H11—N11—H12	111 (5)	C5—C4—H4	119.27
S2—C2—C3	125.4 (2)	C4—C5—H5	121.88
S2—C2—N1	119.7 (2)	C6—C5—H5	119.02
N1—C2—C3	114.9 (3)	N1—C6—H6	117.12
C2—C3—C7	118.9 (3)	C5—C6—H6	123.25
C6—N1—C2—S2	177.0 (3)	C2—C3—C7—O71	75.1 (4)
C6—N1—C2—C3	−2.6 (4)	C2—C3—C7—O72	−106.5 (3)
C2—N1—C6—C5	1.1 (5)	C7—C3—C4—C5	177.5 (3)
N1—C2—C3—C4	2.9 (4)	C4—C3—C7—O72	74.3 (4)
N1—C2—C3—C7	−176.4 (3)	C4—C3—C7—O71	−104.2 (4)
S2—C2—C3—C4	−176.8 (2)	C3—C4—C5—C6	0.1 (5)
S2—C2—C3—C7	4.0 (4)	C4—C5—C6—N1	0.3 (6)
C2—C3—C4—C5	−1.7 (5)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N1—H1···O72^i	0.97 (4)	1.83 (4)	2.801 (4)	174 (4)
N11—H11···O72^ii	0.96 (6)	1.97 (6)	2.892 (4)	159 (5)
N11—H12···O71	1.01 (6)	1.85 (6)	2.839 (3)	166 (4)
N11—H13···O2^iii	0.91 (5)	1.94 (5)	2.774 (4)	151 (4)
N11—H14···S2^iv	0.90 (4)	2.47 (4)	3.350 (3)	164 (5)
O2—H21···O71	0.94 (5)	1.84 (5)	2.767 (3)	173 (6)
O2—H22···O72^v	0.84 (5)	1.98 (6)	2.806 (3)	167 (7)

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