2-Amino-5-methyl-1,3,4-thiadiazole and 2-amino-5-ethyl-1,3,4-thiadiazole

The structures of 2-amino-5-methyl-1,3,4-thia­diazo­le, C₃H₅N₃S, and 2-amino-5-ethyl-1,3,4-thia­diazo­le, C₄H₇N₃S, have been determined for comparison with unsubstituted 2-amino-1,3,4-thia­diazo­le. Despite their different space groups (P2₁/n and Pbca, respectively), the packing modes of the methyl and ethyl derivatives are similar, with comparable three-dimensional hydrogen-bonding associations. This is in contrast to the hydrogen-bonding network in 2-amino-1,3,4-thia­diazo­le, which is one-dimensional and has denser packing. It is shown that both packing forms are different polymorphs of a specific subunit of each array.

S1. Comment

In terms of hydrogen-bonding potential, 2-amino-1,3,4-thiadiazole has two donor elements, the 2-amino H atoms, and two acceptors, N3 and N4 in the thiadiazole ring. The structure of this compound is known (Khusenov et al., 1997) and shows a hydrogen-bonding network comprising two associated molecules linked via N—H···N interactions, graph set R₂²(8), which in turn associate with another molecular pair via N—H···N hydrogen bonds, graph set R₄⁴(10). The overall pattern produces a flat ribbon array (see deposited Fig.). In this network, the 5-position does not appear to affect the overall lattice packing, so the author postulated as to whether or not substitution at this point influenced the parent hydrogen-bonding network. The structures of several 5-substituted analogues are known, yet of the small substituents, such as NH₂ (Senda & Maruha, 1987), SH (Downie et al., 1972) and SO₂NH₂ (Pedregosa et al., 1993), each is itself involved in hydrogen-bonding interactions, thus significantly altering the resultant arrays. Similarly, in the structures of the HBr (Antolini et al., 1993) and HCl.hydrate salts of 2-amino-5-methyl-1,3,4-thiadiazole (Pilz et al., 1998), the halides are involved in the hydrogen-bonding network. Larger substituents, such as those containing phenyl rings (Foresti et al., 1985; Molina et al., 1988; Leung et al., 1992; Anders et al., 1999), affect the molecular packing by their very size. Thus, the structures of 2-amino-1,3,4-thiadiazoles with simple non-hydrogen-bonding substituents, namely, 2-amino-5-methyl-1,3,4-thiadiazole, (I), and 2-amino-5-ethyl-1,3,4-thiadiazole, (II), have been investigated to elucidate the influence of these substituents on the molecular packing observed in the parent thiadiazole. \sch

Interestingly, crystals of (I) (Fig. 1) and (II) (Fig. 2) could not be obtained from simple organic solvent solutions, yet crystals of both compounds abounded when attempts were made to form adducts of these materials with aromatic carboxylic acids, such as those used by Lynch et al. (1998, 1999). For (I) and (II), the specific crystals used for data collection were separated as unreacted starting materials following the attempted formation of co-crystals of (I) with 2-aminobenzoic acid, and of (II) with N-methylpyrrole-2-carboxylic acid. The only successfully characterized co-crystal of either (I) or (II) was that of (II) with indole-2-carboxylic acid (see deposited Fig.), yet the inherent disorder in this structure, even in data collected at 150 K, yields an R value of 0.11 (Lynch et al., 1998, 1999). As expected for these types of complexes, the carboxylate groups associate across the N3/N21 sites, thus creating R₂²(8) graph-set dimers.

An overview of the data for (I) and (II) shows that they crystallize in monoclinic and orthorhombic space groups, respectively, yet the resultant molecular packing is quite similar. Figs. 3 and 4 display the packing for both molecules, while hydrogen-bonding geometries are listed in Tables 1 and 2, respectively. Short contact distances not listed in the tables, yet worthy of note, are for (I), S1···S1(2 - x, -y, 1 - z) 3.628 (2) Å, and for (II), S1···N4(1/2 - x, y - 1/2, z) 3.517 (2) Å.

Figs. 3 and 4 show an interesting three-dimensional hydrogen-bonded polymeric network that essentially consists of repeating ring systems made up of six associated molecules [graph set R₆⁶(20)]. As expected, both (I) and (II) form dimers via the N21—H···N3 interaction, but the main difference in packing between these two and the parent 2-amino-1,3,4-thiadiazole arises via the N21—H···N4 interaction. In 2-amino-1,3,4-thiadiazole, the dimers formed by the N21—H···N3 interaction form further dimers (via the N21—H···N4 interaction) with similarly associated molecules. In (I) and (II), the N21—H···N4 interactions from one molecular pair then link different sets of dimers. These hydrogen-bonding networks [i.e. those of (I) and (II) versus that of the parent] are essentially two different arrangements of the same dimer association, but the packing in the parent (see deposited Fig) is more dense (ρ 1.609 Mg m^-3) than that shown in Figs. 3 and 4 (ρ 1.416 and 1.418 Mg m^-3, respectively). It would now be interesting to elucidate the structures of both 5-propyl and 5-halo substituted 2-amino-1,3,4-thiadiazoles to determine what effect, if any, they have on the overall hydrogen-bonding networks and to determine if other packing forms are possible.

S2. Experimental

Crystals of (I) and (II) were separated as unreacted starting materials following the total evaporation of ethanol solutions containing equimolar amounts (2 mmol) of (I) with 2-aminobenzoic acid, and of (II) with N-methylpyrrole-2-carboxylic acid.

S3. Refinement

The 5-methyl and 5-ethyl H atoms were included in the refinement at calculated positions, and refined as riding models with C—H = 0.98 (CH₃) or 0.99 Å (CH₂). The 2-amino H atoms were located from difference syntheses and refined freely. Two packing diagrams, of the parent 2-amino-1,3,4-thiadiazole and of the co-crystal of (II) with indole-2-carboxylic acid, are available as deposited data.

Computing details

For both compounds, data collection: DENZO (Otwinowski & Minor, 1997) and COLLECT (Nonius, 1998); cell refinement: DENZO and COLLECT; data reduction: DENZO and COLLECT; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: PLUTON94 (Spek, 1994) and PLATON97 (Spek, 1997); software used to prepare material for publication: SHELXL97.

Figures

Fig. 1. The molecular configuration and atomic numbering scheme for (I), showing 50% probability displacement ellipsoids. H atoms are drawn as small spheres of arbitrary radii. Fig. 2. The molecular configuration and atomic numbering scheme for (II), showing 50% probability displacement ellipsoids. H atoms are drawn as small spheres of arbitrary radii. Fig. 3. The molecular packing for (I). Hydrogen bonds are indicated by dotted lines [symmetry codes: (i) 1 - x, 1 - y, 1 - z; (ii) 1/2 + x, 1/2 - y, 1/2 + z]. Fig. 4. The molecular packing for (II). Hydrogen bonds are indicated by dotted lines [symmetry codes: (i) 1 - x, -y, -z; (ii) 1/2 - x, 1/2 + y, z]. # Deposition Figures # Fig. 5. Molecular packing of 2-amino-1,3,4-thiadiazole. H-bonding # associations are indicated by dotted lines. # Fig. 6. Molecular packing for the 1:1 organic salt of (II) with # indole-2-carboxylic acid. H-bonding associations are indicated by dotted # lines.

(I) 2-amino-5-methyl-1,3,4-thiadiazole

Crystal data

C3H5N3S	Dx = 1.416 Mg m^−3
Mr = 115.16	Melting point: 497-499 K K
Monoclinic, P21/n	Mo Kα radiation, λ = 0.71073 Å
a = 8.5116 (17) Å	Cell parameters from 9981 reflections
b = 6.5690 (13) Å	θ = 2.9–30.5°
c = 10.243 (2) Å	µ = 0.47 mm^−1
β = 109.36 (3)°	T = 150 K
V = 540.34 (18) Å^3	Block, colourless
Z = 4	0.25 × 0.15 × 0.10 mm
F(000) = 240

Data collection

Nonius KappaCCD area-detector diffractometer	1235 independent reflections
Radiation source: Enraf Nonius FR591 rotating anode	982 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.055
Detector resolution: 9.091 pixels mm^-1	θmax = 27.5°, θmin = 3.8°
ϕ and ω scans	h = −11→11
Absorption correction: multi-scan (SORTAV; Blessing, 1995)	k = −7→8
Tmin = 0.893, Tmax = 0.955	l = −13→12
7274 measured reflections

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.036	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.105	H atoms treated by a mixture of independent and constrained refinement
S = 0.82	w = 1/[σ^2(Fo^2) + (0.0755P)^2 + 0.3034P] where P = (Fo^2 + 2Fc^2)/3
1235 reflections	(Δ/σ)max < 0.001
73 parameters	Δρmax = 0.25 e Å^−3
0 restraints	Δρmin = −0.26 e Å^−3

Special details

Experimental. PLEASE NOTE cell_measurement_ fields are not relevant to area detector data, the entire data set is used to refine the cell, which is indexed from all observed reflections in a 10 degree phi range.

Geometry. Mean plane data ex SHELXL97 for molecule (I) ############################################

Least-squares planes (x,y,z in crystal coordinates) and deviations from them (* indicates atom used to define plane)

5.6810 (0.0046) x + 3.1622 (0.0051) y - 7.7562 (0.0067) z = 0.6583 (0.0039)

* 0.0001 (0.0007) S1 * -0.0023 (0.0010) C2 * 0.0039 (0.0011) N3 * -0.0039 (0.0010) N4 * 0.0022 (0.0009) C5 0.0021 (0.0032) N21 0.0203 (0.0032) C51

Rms deviation of fitted atoms = 0.0028

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

	x	y	z	Uiso*/Ueq
S1	0.82071 (5)	0.07524 (7)	0.54690 (4)	0.0323 (2)
C2	0.6881 (2)	0.2817 (3)	0.53423 (17)	0.0310 (4)
N21	0.7260 (2)	0.4356 (3)	0.62420 (19)	0.0499 (5)
H21	0.662 (3)	0.520 (4)	0.621 (2)	0.048 (7)*
H22	0.820 (3)	0.428 (3)	0.698 (2)	0.041 (6)*
N3	0.55033 (17)	0.2699 (2)	0.42772 (15)	0.0308 (4)
N4	0.54338 (17)	0.0939 (2)	0.35191 (15)	0.0284 (3)
C5	0.6724 (2)	−0.0212 (3)	0.39867 (18)	0.0301 (4)
C51	0.6949 (3)	−0.2161 (3)	0.3334 (2)	0.0432 (5)
H51	0.5944	−0.2459	0.2548	0.054*
H52	0.7146	−0.3263	0.4014	0.054*
H53	0.7906	−0.2048	0.3008	0.054*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
S1	0.0236 (3)	0.0409 (3)	0.0271 (3)	0.00910 (16)	0.00120 (19)	−0.00123 (17)
C2	0.0238 (8)	0.0392 (10)	0.0258 (9)	0.0066 (7)	0.0025 (7)	−0.0003 (7)
N21	0.0334 (9)	0.0593 (12)	0.0389 (10)	0.0204 (8)	−0.0123 (8)	−0.0223 (8)
N3	0.0238 (7)	0.0352 (8)	0.0263 (7)	0.0036 (6)	−0.0015 (6)	−0.0033 (6)
N4	0.0240 (7)	0.0330 (8)	0.0248 (7)	−0.0009 (5)	0.0036 (6)	−0.0014 (6)
C5	0.0282 (8)	0.0342 (9)	0.0265 (9)	−0.0009 (7)	0.0074 (7)	0.0014 (7)
C51	0.0423 (11)	0.0376 (11)	0.0460 (11)	0.0017 (8)	0.0095 (9)	−0.0090 (9)

Geometric parameters (Å, º)

S1—C2	1.7418 (17)	N3—N4	1.383 (2)
S1—C5	1.7407 (18)	N4—C5	1.288 (2)
C2—N3	1.312 (2)	C5—C51	1.486 (3)
C2—N21	1.334 (2)	C51—H51	0.98
N21—H21	0.77 (3)	C51—H52	0.98
N21—H22	0.90 (2)	C51—H53	0.98
C2—S1—C5	87.34 (8)	N4—C5—C51	124.04 (17)
N3—C2—N21	124.35 (16)	N4—C5—S1	113.15 (14)
N3—C2—S1	113.21 (13)	C51—C5—S1	122.80 (14)
N21—C2—S1	122.44 (13)	C5—C51—H51	109.5
C2—N21—H21	120.4 (18)	C5—C51—H52	109.5
C2—N21—H22	118.9 (13)	H51—C51—H52	109.5
H21—N21—H22	120 (2)	C5—C51—H53	109.5
C2—N3—N4	112.12 (14)	H51—C51—H53	109.5
C5—N4—N3	114.17 (15)	H52—C51—H53	109.5
C5—S1—C2—N3	−0.26 (14)	N3—N4—C5—C51	−178.86 (17)
C5—S1—C2—N21	−179.65 (19)	N3—N4—C5—S1	0.67 (19)
N21—C2—N3—N4	−179.95 (18)	C2—S1—C5—N4	−0.24 (14)
S1—C2—N3—N4	0.66 (19)	C2—S1—C5—C51	179.29 (17)
C2—N3—N4—C5	−0.9 (2)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N21—H21···N3^i	0.77 (3)	2.20 (3)	2.954 (2)	169 (2)
N21—H22···N4^ii	0.90 (2)	2.03 (2)	2.933 (3)	174 (2)

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

(II) 2-amino-5-ethyl-1,3,4-thiadiazole

Crystal data

C4H7N3S	Dx = 1.418 Mg m^−3
Mr = 129.19	Melting point: 473-476 K K
Orthorhombic, Pbca	Mo Kα radiation, λ = 0.71073 Å
a = 7.2752 (3) Å	Cell parameters from 6797 reflections
b = 10.7294 (4) Å	θ = 2.9–45.3°
c = 15.4991 (7) Å	µ = 0.42 mm^−1
V = 1209.84 (9) Å^3	T = 150 K
Z = 8	Block, colourless
F(000) = 544	0.35 × 0.18 × 0.07 mm

Data collection

Nonius KappaCCD area-detector diffractometer	1385 independent reflections
Radiation source: Enraf Nonius FR591 rotating anode	1125 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.041
Detector resolution: 9.091 pixels mm^-1	θmax = 27.5°, θmin = 3.6°
ϕ and ω scans	h = −9→8
Absorption correction: multi-scan (SORTAV; Blessing, 1995)	k = −12→13
Tmin = 0.866, Tmax = 0.971	l = −19→20
7813 measured reflections

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.036	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.092	H atoms treated by a mixture of independent and constrained refinement
S = 1.05	w = 1/[σ^2(Fo^2) + (0.0438P)^2 + 0.4846P] where P = (Fo^2 + 2Fc^2)/3
1385 reflections	(Δ/σ)max < 0.001
82 parameters	Δρmax = 0.26 e Å^−3
0 restraints	Δρmin = −0.33 e Å^−3

Special details

Experimental. PLEASE NOTE cell_measurement_ fields are not relevant to area detector data, the entire data set is used to refine the cell, which is indexed from all observed reflections in a 10 degree phi range.

Geometry. Mean plane data ex SHELXL97 for molecule (II) #############################################

Least-squares planes (x,y,z in crystal coordinates) and deviations from them (* indicates atom used to define plane)

3.3710 (0.0049) x - 2.1629 (0.0058) y + 13.3748 (0.0054) z = 1.7776 (0.0009)

* -0.0042 (0.0007) S1 * 0.0048 (0.0009) C2 * -0.0031 (0.0010) N3 * -0.0014 (0.0010) N4 * 0.0039 (0.0009) C5 0.0331 (0.0027) N21 0.0545 (0.0031) C51 0.0237 (0.0035) C52

Rms deviation of fitted atoms = 0.0037

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

	x	y	z	Uiso*/Ueq
S1	0.11939 (6)	0.16283 (4)	0.12883 (3)	0.02593 (17)
C2	0.3003 (2)	0.09453 (14)	0.07287 (10)	0.0237 (3)
N21	0.4472 (2)	0.16103 (14)	0.04870 (11)	0.0327 (4)
H21	0.531 (3)	0.126 (2)	0.0179 (14)	0.047 (6)*
H22	0.448 (3)	0.240 (2)	0.0578 (13)	0.041 (5)*
N3	0.27772 (18)	−0.02507 (12)	0.05862 (9)	0.0266 (3)
N4	0.11361 (18)	−0.06880 (13)	0.09304 (9)	0.0265 (3)
C5	0.0180 (2)	0.01614 (15)	0.13126 (10)	0.0251 (4)
C51	−0.1606 (3)	−0.00415 (18)	0.17678 (14)	0.0378 (4)
H51	−0.2535	0.0529	0.1520	0.047*
H52	−0.1451	0.0182	0.2383	0.047*
C52	−0.2327 (3)	−0.13618 (19)	0.17130 (13)	0.0382 (4)
H53	−0.3459	−0.1432	0.2052	0.048*
H54	−0.1404	−0.1939	0.1942	0.048*
H55	−0.2584	−0.1570	0.1109	0.048*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
S1	0.0278 (2)	0.0184 (3)	0.0316 (3)	0.00372 (15)	0.00348 (15)	−0.00314 (15)
C2	0.0255 (8)	0.0198 (8)	0.0260 (8)	0.0035 (6)	−0.0003 (6)	−0.0003 (6)
N21	0.0328 (8)	0.0188 (8)	0.0466 (10)	−0.0026 (6)	0.0123 (7)	−0.0052 (6)
N3	0.0258 (7)	0.0187 (7)	0.0354 (8)	−0.0007 (5)	0.0065 (6)	−0.0030 (5)
N4	0.0258 (7)	0.0215 (7)	0.0322 (8)	−0.0009 (5)	0.0041 (6)	−0.0011 (6)
C5	0.0260 (8)	0.0208 (8)	0.0287 (9)	0.0014 (6)	−0.0002 (6)	−0.0012 (6)
C51	0.0321 (9)	0.0362 (10)	0.0450 (11)	0.0011 (8)	0.0120 (8)	−0.0054 (8)
C52	0.0327 (9)	0.0446 (11)	0.0372 (10)	−0.0108 (8)	0.0074 (8)	−0.0028 (9)

Geometric parameters (Å, º)

S1—C2	1.7380 (16)	C5—C51	1.494 (2)
S1—C5	1.7385 (16)	C51—C52	1.513 (3)
C2—N3	1.312 (2)	C51—H51	0.99
C2—N21	1.339 (2)	C51—H52	0.99
N21—H21	0.86 (2)	C52—H53	0.98
N21—H22	0.85 (2)	C52—H54	0.98
N3—N4	1.3893 (18)	C52—H55	0.98
N4—C5	1.290 (2)
C2—S1—C5	87.15 (8)	C5—C51—C52	114.29 (15)
N3—C2—N21	125.01 (15)	C5—C51—H51	108.7
N3—C2—S1	113.68 (12)	C52—C51—H51	108.7
N21—C2—S1	121.30 (12)	C5—C51—H52	108.7
C2—N21—H21	118.9 (14)	C52—C51—H52	108.7
C2—N21—H22	118.9 (14)	H51—C51—H52	107.6
H21—N21—H22	122 (2)	C51—C52—H53	109.5
C2—N3—N4	111.90 (13)	C51—C52—H54	109.5
C5—N4—N3	113.63 (13)	H53—C52—H54	109.5
N4—C5—C51	125.62 (15)	C51—C52—H55	109.5
N4—C5—S1	113.63 (13)	H53—C52—H55	109.5
C51—C5—S1	120.73 (13)	H54—C52—H55	109.5
C5—S1—C2—N3	0.76 (13)	N3—N4—C5—S1	0.42 (18)
C5—S1—C2—N21	−178.51 (15)	C2—S1—C5—N4	−0.66 (13)
N21—C2—N3—N4	178.55 (16)	C2—S1—C5—C51	177.61 (15)
S1—C2—N3—N4	−0.69 (17)	N4—C5—C51—C52	−3.3 (3)
C2—N3—N4—C5	0.2 (2)	S1—C5—C51—C52	178.69 (14)
N3—N4—C5—C51	−177.75 (16)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N21—H21···N3^i	0.86 (2)	2.12 (2)	2.983 (2)	175 (2)
N21—H22···N4^ii	0.85 (2)	2.17 (2)	3.012 (2)	167 (2)

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