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The crystal structure determinations of picolinamidium squarate, C
6H
7N
2O
+·C
4O
4−, (I), and di-
p-toluidinium squarate dihydrate, 2C
7H
10N
+·C
4O
42−·2H
2O, (II), are reported. While salt formation occurs by donation of one H atom from squaric acid to the picolinamide molecule in (I), in compound (II), each squaric acid molecule donates one H atom to the
p-toluidine N atom of two
trans p-toluidine molecules. In (I), the pyridine ring is coplanar with the squarate monoanion through imposed crystallographic mirror symmetry; in (II), the dihedral angle between the
p-toluidine moiety and the squarate dianion is 70.71 (1)°. In (I), a three-dimensional structure is formed
via van der Waals interactions between parallel planes of molecules, with hydrogen-bond interactions (N—H
O and O—H
O) acting within the planes; hydrogen bonds form a three-dimensional network in (II).
Supporting information
CCDC references: 248167; 248168
Compound (I) was prepared by mixing squaric acid and picolinamide in a 1:1 molar ratio in a mixed solution of methanol and water (1:1, 50 ml) with stirring at 333 K for 3 h. Crystals of (I) were obtained by slow evaporation of the solvent. The crystals were filtered off, washed in water and methanol, and dried in vacuo. Compound (II) was prepared by mixing squaric acid and p-toluidine in a 1:2 molar ratio in a mixed solution of methanol and water (1:1, 50 ml) with stirring at 333 K for 3 h. Crystals of (I) were obtained by slow evaporation of the solvent. The crystals were filtered off, washed in water and methanol, and dried in vacuo.
All H atoms of (I), except atom H5 (on N1), were placed at calculated positions (C—H = 0.93 Å, N—H = 0.86 Å and O—H 0.82 Å) and were allowed to ride on the parent atom [Uiso(H)= 1.2U(C) and Uiso(H)=1.5U(O)]. Atom H5 atom in (I) was located in a difference Fourier map and refined with the N—H distance restrained to 0.87 (3) Å. In (II), H atoms of the p-toluidine moiety (H2, H3, H5 and H6, and H7A–H7C) were located at calculated positions (C—H = 0.93 Å and C—H = 0.96 Å, respectively) and were allowed to ride on the parent atom [Uiso(H)= 1.2U(C)]. All other H atoms were refined with isotropic displacement parameters. The H atoms on atom N1 were positioned from a difference map and refined with the N—H distance restrained to 0.87 (3) Å.
For both compounds, data collection: X-AREA (Stoe & Cie, 2001); cell refinement: X-AREA; data reduction: X-RED32 (Stoe & Cie, 2001). Program(s) used to solve structure: SHELXS97 (Sheldrick, 1997) for (I); SIR97 (Altomare et al., 1999) for (II). For both compounds, program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEPIII (Burnett & Johnson, 1996); software used to prepare material for publication: WinGX (Farrugia, 1999).
Crystal data top
C6H7N2O+·C4HO4− | F(000) = 488 |
Mr = 236.18 | Dx = 1.565 Mg m−3 |
Orthorhombic, Ima2 | Mo Kα radiation, λ = 0.71069 Å |
Hall symbol: I2 -2a | Cell parameters from 5873 reflections |
a = 6.302 (5) Å | θ = 2.3–28.8° |
b = 9.076 (5) Å | µ = 0.13 mm−1 |
c = 17.531 (5) Å | T = 293 K |
V = 1002.7 (10) Å3 | Prism, yellow |
Z = 4 | 0.4 × 0.3 × 0.2 mm |
Data collection top
STOE IPDS-II diffractometer | 728 independent reflections |
Radiation source: fine-focus sealed tube | 589 reflections with I > 2σ(I) |
Graphite monochromator | Rint = 0.022 |
Detector resolution: 6.67 pixels mm-1 | θmax = 28.8°, θmin = 2.3° |
rotation method scans | h = −8→0 |
Absorption correction: integration (X-RED32; Stoe & Cie, 2002) | k = −12→12 |
Tmin = 0.965, Tmax = 0.984 | l = −23→21 |
2316 measured reflections | |
Refinement top
Refinement on F2 | Secondary atom site location: difference Fourier map |
Least-squares matrix: full | Hydrogen site location: inferred from neighbouring sites |
R[F2 > 2σ(F2)] = 0.031 | H atoms treated by a mixture of independent and constrained refinement |
wR(F2) = 0.085 | w = 1/[σ2(Fo2) + (0.0611P)2] where P = (Fo2 + 2Fc2)/3 |
S = 1.04 | (Δ/σ)max < 0.001 |
728 reflections | Δρmax = 0.17 e Å−3 |
107 parameters | Δρmin = −0.16 e Å−3 |
2 restraints | Extinction correction: SHELXL97, Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4 |
Primary atom site location: structure-invariant direct methods | Extinction coefficient: 0.061 (12) |
Crystal data top
C6H7N2O+·C4HO4− | V = 1002.7 (10) Å3 |
Mr = 236.18 | Z = 4 |
Orthorhombic, Ima2 | Mo Kα radiation |
a = 6.302 (5) Å | µ = 0.13 mm−1 |
b = 9.076 (5) Å | T = 293 K |
c = 17.531 (5) Å | 0.4 × 0.3 × 0.2 mm |
Data collection top
STOE IPDS-II diffractometer | 728 independent reflections |
Absorption correction: integration (X-RED32; Stoe & Cie, 2002) | 589 reflections with I > 2σ(I) |
Tmin = 0.965, Tmax = 0.984 | Rint = 0.022 |
2316 measured reflections | |
Refinement top
R[F2 > 2σ(F2)] = 0.031 | 2 restraints |
wR(F2) = 0.085 | H atoms treated by a mixture of independent and constrained refinement |
S = 1.04 | Δρmax = 0.17 e Å−3 |
728 reflections | Δρmin = −0.16 e Å−3 |
107 parameters | |
Special details top
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 (Å2) top | x | y | z | Uiso*/Ueq | |
C1 | 0.2500 | 0.3447 (3) | 0.34376 (17) | 0.0540 (8) | |
H1 | 0.2500 | 0.3791 | 0.3937 | 0.065* | |
C2 | 0.2500 | 0.4429 (3) | 0.28301 (19) | 0.0565 (8) | |
H2 | 0.2500 | 0.5438 | 0.2922 | 0.068* | |
C3 | 0.2500 | 0.3916 (3) | 0.2096 (2) | 0.0601 (8) | |
H3 | 0.2500 | 0.4567 | 0.1686 | 0.072* | |
C4 | 0.2500 | 0.2418 (4) | 0.19766 (18) | 0.0570 (7) | |
H4 | 0.2500 | 0.2048 | 0.1482 | 0.068* | |
C5 | 0.2500 | 0.1958 (3) | 0.32885 (16) | 0.0481 (6) | |
C6 | 0.2500 | 0.0754 (3) | 0.38762 (18) | 0.0555 (7) | |
C7 | 0.2500 | −0.1674 (3) | −0.00328 (16) | 0.0477 (7) | |
C8 | 0.2500 | −0.2654 (4) | 0.0606 (2) | 0.0565 (7) | |
C9 | 0.2500 | −0.1340 (3) | 0.11224 (17) | 0.0483 (7) | |
C10 | 0.2500 | −0.0388 (3) | 0.04258 (16) | 0.0453 (6) | |
N1 | 0.2500 | 0.1502 (3) | 0.25642 (13) | 0.0499 (7) | |
N2 | 0.2500 | 0.1144 (3) | 0.45934 (17) | 0.0689 (9) | |
H2A | 0.2500 | 0.0483 | 0.4945 | 0.083* | |
H2B | 0.2500 | 0.2063 | 0.4714 | 0.083* | |
O1 | 0.2500 | −0.1833 (2) | −0.07767 (13) | 0.0626 (6) | |
H6 | 0.2500 | −0.2713 | −0.0883 | 0.094* | |
O2 | 0.2500 | 0.0964 (2) | 0.03153 (13) | 0.0564 (6) | |
O3 | 0.2500 | −0.1170 (3) | 0.18110 (14) | 0.0689 (7) | |
O4 | 0.2500 | −0.3996 (3) | 0.07001 (15) | 0.0979 (12) | |
O5 | 0.2500 | −0.0535 (2) | 0.36337 (14) | 0.0674 (7) | |
H5 | 0.2500 | 0.055 (3) | 0.246 (3) | 0.089 (15)* | |
Atomic displacement parameters (Å2) top | U11 | U22 | U33 | U12 | U13 | U23 |
C1 | 0.089 (2) | 0.0372 (13) | 0.0361 (15) | 0.000 | 0.000 | −0.0038 (10) |
C2 | 0.090 (2) | 0.0354 (12) | 0.0445 (16) | 0.000 | 0.000 | 0.0047 (11) |
C3 | 0.094 (2) | 0.0464 (16) | 0.0399 (17) | 0.000 | 0.000 | 0.0069 (12) |
C4 | 0.0869 (19) | 0.0504 (14) | 0.0336 (15) | 0.000 | 0.000 | 0.0020 (13) |
C5 | 0.0742 (17) | 0.0362 (10) | 0.0339 (14) | 0.000 | 0.000 | 0.0009 (10) |
C6 | 0.0930 (19) | 0.0362 (13) | 0.0373 (14) | 0.000 | 0.000 | 0.0030 (10) |
C7 | 0.0717 (18) | 0.0375 (12) | 0.0341 (14) | 0.000 | 0.000 | −0.0010 (9) |
C8 | 0.096 (2) | 0.0376 (15) | 0.0358 (15) | 0.000 | 0.000 | 0.0000 (11) |
C9 | 0.0760 (17) | 0.0345 (13) | 0.0345 (14) | 0.000 | 0.000 | −0.0009 (10) |
C10 | 0.0610 (14) | 0.0330 (12) | 0.0418 (16) | 0.000 | 0.000 | −0.0005 (9) |
N1 | 0.0773 (17) | 0.0359 (11) | 0.0364 (13) | 0.000 | 0.000 | −0.0051 (9) |
N2 | 0.136 (3) | 0.0357 (11) | 0.0347 (14) | 0.000 | 0.000 | 0.0047 (11) |
O1 | 0.1175 (16) | 0.0353 (9) | 0.0350 (11) | 0.000 | 0.000 | 0.0015 (8) |
O2 | 0.0911 (14) | 0.0336 (9) | 0.0445 (11) | 0.000 | 0.000 | 0.0021 (9) |
O3 | 0.1219 (19) | 0.0451 (11) | 0.0398 (12) | 0.000 | 0.000 | −0.0052 (11) |
O4 | 0.220 (4) | 0.0361 (11) | 0.0374 (13) | 0.000 | 0.000 | 0.0016 (9) |
O5 | 0.128 (2) | 0.0344 (10) | 0.0396 (12) | 0.000 | 0.000 | 0.0011 (8) |
Geometric parameters (Å, º) top
C1—C5 | 1.377 (4) | C7—O1 | 1.312 (4) |
C1—C2 | 1.388 (4) | C7—C10 | 1.417 (4) |
C1—H1 | 0.9300 | C7—C8 | 1.429 (4) |
C2—C3 | 1.368 (5) | C8—O4 | 1.229 (4) |
C2—H2 | 0.9300 | C8—C9 | 1.498 (4) |
C3—C4 | 1.376 (5) | C9—O3 | 1.217 (4) |
C3—H3 | 0.9300 | C9—C10 | 1.496 (4) |
C4—N1 | 1.324 (4) | C10—O2 | 1.243 (3) |
C4—H4 | 0.9300 | N1—H5 | 0.88 (3) |
C5—N1 | 1.336 (4) | N2—H2A | 0.8600 |
C5—C6 | 1.502 (4) | N2—H2B | 0.8600 |
C6—O5 | 1.245 (4) | O1—H6 | 0.8200 |
C6—N2 | 1.306 (4) | | |
| | | |
C5—C1—C2 | 119.0 (3) | O1—C7—C8 | 135.2 (3) |
C5—C1—H1 | 120.5 | C10—C7—C8 | 93.9 (2) |
C2—C1—H1 | 120.5 | O4—C8—C7 | 136.2 (3) |
C3—C2—C1 | 120.2 (3) | O4—C8—C9 | 135.0 (3) |
C3—C2—H2 | 119.9 | C7—C8—C9 | 88.8 (2) |
C1—C2—H2 | 119.9 | O3—C9—C10 | 137.5 (3) |
C2—C3—C4 | 118.6 (3) | O3—C9—C8 | 134.5 (3) |
C2—C3—H3 | 120.7 | C10—C9—C8 | 88.0 (2) |
C4—C3—H3 | 120.7 | O2—C10—C7 | 136.5 (3) |
N1—C4—C3 | 120.1 (3) | O2—C10—C9 | 134.2 (3) |
N1—C4—H4 | 119.9 | C7—C10—C9 | 89.3 (2) |
C3—C4—H4 | 119.9 | C4—N1—C5 | 123.0 (3) |
N1—C5—C1 | 119.0 (3) | C4—N1—H5 | 117 (4) |
N1—C5—C6 | 115.2 (3) | C5—N1—H5 | 120 (4) |
C1—C5—C6 | 125.8 (3) | C6—N2—H2A | 120.0 |
O5—C6—N2 | 125.7 (3) | C6—N2—H2B | 120.0 |
O5—C6—C5 | 116.7 (3) | H2A—N2—H2B | 120.0 |
N2—C6—C5 | 117.6 (3) | C7—O1—H6 | 109.5 |
O1—C7—C10 | 130.9 (3) | | |
| | | |
C5—C1—C2—C3 | 0.0 | C7—C8—C9—O3 | 180.0 |
C1—C2—C3—C4 | 0.0 | O4—C8—C9—C10 | 180.0 |
C2—C3—C4—N1 | 0.0 | C7—C8—C9—C10 | 0.0 |
C2—C1—C5—N1 | 0.0 | O1—C7—C10—O2 | 0.0 |
C2—C1—C5—C6 | 180.0 | C8—C7—C10—O2 | 180.0 |
N1—C5—C6—O5 | 0.0 | O1—C7—C10—C9 | 180.0 |
C1—C5—C6—O5 | 180.0 | C8—C7—C10—C9 | 0.0 |
N1—C5—C6—N2 | 180.0 | O3—C9—C10—O2 | 0.0 |
C1—C5—C6—N2 | 0.0 | C8—C9—C10—O2 | 180.0 |
O1—C7—C8—O4 | 0.0 | O3—C9—C10—C7 | 180.0 |
C10—C7—C8—O4 | 180.0 | C8—C9—C10—C7 | 0.0 |
O1—C7—C8—C9 | 180.0 | C3—C4—N1—C5 | 0.0 |
C10—C7—C8—C9 | 0.0 | C1—C5—N1—C4 | 0.0 |
O4—C8—C9—O3 | 0.0 | C6—C5—N1—C4 | 180.0 |
Hydrogen-bond geometry (Å, º) top
D—H···A | D—H | H···A | D···A | D—H···A |
N2—H2A···O4i | 0.86 | 1.89 | 2.751 (4) | 179 |
N2—H2B···O2ii | 0.86 | 2.08 | 2.913 (4) | 164 |
O1—H6···O5iii | 0.82 | 1.80 | 2.602 (3) | 165 |
N1—H5···O3 | 0.88 (3) | 1.93 (3) | 2.761 (4) | 156 (5) |
N1—H5···O5 | 0.88 (3) | 2.28 (6) | 2.633 (4) | 104 (4) |
Symmetry codes: (i) −x+1/2, −y−1/2, z+1/2; (ii) −x+1/2, −y+1/2, z+1/2; (iii) −x+1/2, −y−1/2, z−1/2. |
Crystal data top
2C7H10N+·C4O42−·2H2O | F(000) = 776 |
Mr = 364.40 | Dx = 1.310 Mg m−3 |
Orthorhombic, Pbca | Mo Kα radiation, λ = 0.71069 Å |
Hall symbol: -P 2ac 2ab | Cell parameters from 7934 reflections |
a = 7.761 (5) Å | θ = 1.8–27.7° |
b = 22.288 (5) Å | µ = 0.10 mm−1 |
c = 10.684 (5) Å | T = 293 K |
V = 1848.1 (15) Å3 | Prism, colorless |
Z = 4 | 0.4 × 0.3 × 0.2 mm |
Data collection top
STOE IPDS-II diffractometer | 1219 reflections with I > 2σ(I) |
Radiation source: fine-focus sealed tube | Rint = 0.085 |
Graphite monochromator | θmax = 28.0°, θmin = 1.8° |
Detector resolution: 6.67 pixels mm-1 | h = −10→9 |
rotation method scans | k = −29→29 |
21375 measured reflections | l = −14→13 |
2208 independent reflections | |
Refinement top
Refinement on F2 | Secondary atom site location: difference Fourier map |
Least-squares matrix: full | Hydrogen site location: inferred from neighbouring sites |
R[F2 > 2σ(F2)] = 0.037 | H atoms treated by a mixture of independent and constrained refinement |
wR(F2) = 0.094 | w = 1/[σ2(Fo2) + (0.0604P)2] where P = (Fo2 + 2Fc2)/3 |
S = 0.84 | (Δ/σ)max < 0.001 |
2208 reflections | Δρmax = 0.14 e Å−3 |
140 parameters | Δρmin = −0.12 e Å−3 |
3 restraints | Extinction correction: SHELXL97, Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4 |
Primary atom site location: structure-invariant direct methods | Extinction coefficient: 0.026 (3) |
Crystal data top
2C7H10N+·C4O42−·2H2O | V = 1848.1 (15) Å3 |
Mr = 364.40 | Z = 4 |
Orthorhombic, Pbca | Mo Kα radiation |
a = 7.761 (5) Å | µ = 0.10 mm−1 |
b = 22.288 (5) Å | T = 293 K |
c = 10.684 (5) Å | 0.4 × 0.3 × 0.2 mm |
Data collection top
STOE IPDS-II diffractometer | 1219 reflections with I > 2σ(I) |
21375 measured reflections | Rint = 0.085 |
2208 independent reflections | |
Refinement top
R[F2 > 2σ(F2)] = 0.037 | 3 restraints |
wR(F2) = 0.094 | H atoms treated by a mixture of independent and constrained refinement |
S = 0.84 | Δρmax = 0.14 e Å−3 |
2208 reflections | Δρmin = −0.12 e Å−3 |
140 parameters | |
Special details top
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 (Å2) top | x | y | z | Uiso*/Ueq | |
C1 | 0.0389 (3) | 0.34699 (9) | 0.3770 (2) | 0.0380 (5) | |
C2 | 0.1282 (3) | 0.32098 (11) | 0.4737 (2) | 0.0479 (6) | |
H4 | 0.1736 | 0.3445 | 0.5375 | 0.057* | |
C3 | 0.1498 (3) | 0.25933 (12) | 0.4752 (2) | 0.0529 (7) | |
H5 | 0.2106 | 0.2417 | 0.5405 | 0.063* | |
C4 | 0.0830 (3) | 0.22355 (11) | 0.3816 (2) | 0.0483 (6) | |
C5 | −0.0058 (3) | 0.25104 (11) | 0.2862 (2) | 0.0500 (6) | |
H6 | −0.0521 | 0.2276 | 0.2225 | 0.060* | |
C6 | −0.0283 (3) | 0.31262 (10) | 0.2821 (2) | 0.0441 (6) | |
H7 | −0.0878 | 0.3304 | 0.2163 | 0.053* | |
C7 | 0.1082 (5) | 0.15625 (12) | 0.3849 (3) | 0.0775 (10) | |
H7A | 0.0355 | 0.1378 | 0.3232 | 0.116* | |
H7B | 0.0786 | 0.1413 | 0.4664 | 0.116* | |
H7C | 0.2265 | 0.1469 | 0.3672 | 0.116* | |
C8 | 0.4382 (3) | 0.47482 (9) | 0.4336 (2) | 0.0362 (5) | |
C9 | 0.4110 (3) | 0.48656 (10) | 0.5661 (2) | 0.0391 (5) | |
N1 | 0.0236 (3) | 0.41212 (9) | 0.3740 (2) | 0.0422 (5) | |
O1 | 0.3630 (2) | 0.44339 (7) | 0.35207 (14) | 0.0472 (5) | |
O2 | 0.3047 (2) | 0.46975 (9) | 0.64676 (15) | 0.0606 (6) | |
O3 | −0.0431 (3) | 0.45026 (9) | 0.61773 (18) | 0.0594 (5) | |
H1 | 0.138 (4) | 0.4292 (13) | 0.367 (2) | 0.068 (9)* | |
H2 | −0.026 (4) | 0.4258 (13) | 0.447 (3) | 0.074 (9)* | |
H3 | −0.036 (4) | 0.4245 (11) | 0.300 (3) | 0.061 (8)* | |
H8 | −0.108 (5) | 0.4577 (14) | 0.695 (4) | 0.093 (11)* | |
H9 | 0.068 (5) | 0.4566 (15) | 0.634 (3) | 0.091 (12)* | |
Atomic displacement parameters (Å2) top | U11 | U22 | U33 | U12 | U13 | U23 |
C1 | 0.0376 (12) | 0.0403 (12) | 0.0360 (12) | −0.0027 (9) | 0.0025 (10) | 0.0008 (9) |
C2 | 0.0543 (16) | 0.0506 (14) | 0.0387 (13) | −0.0024 (12) | −0.0083 (11) | −0.0020 (11) |
C3 | 0.0555 (16) | 0.0546 (16) | 0.0486 (15) | 0.0037 (12) | −0.0066 (13) | 0.0103 (12) |
C4 | 0.0453 (14) | 0.0437 (13) | 0.0559 (15) | −0.0007 (10) | 0.0054 (12) | 0.0014 (11) |
C5 | 0.0499 (14) | 0.0491 (13) | 0.0509 (15) | −0.0054 (11) | −0.0013 (13) | −0.0097 (12) |
C6 | 0.0449 (13) | 0.0485 (13) | 0.0388 (13) | −0.0011 (11) | −0.0066 (11) | −0.0019 (10) |
C7 | 0.080 (2) | 0.0491 (17) | 0.104 (3) | 0.0042 (15) | 0.003 (2) | 0.0042 (16) |
C8 | 0.0378 (12) | 0.0357 (11) | 0.0350 (11) | 0.0012 (9) | −0.0037 (10) | −0.0034 (9) |
C9 | 0.0397 (12) | 0.0453 (12) | 0.0324 (12) | −0.0006 (10) | −0.0001 (10) | 0.0004 (10) |
N1 | 0.0458 (13) | 0.0422 (11) | 0.0386 (12) | −0.0025 (9) | −0.0002 (11) | −0.0012 (9) |
O1 | 0.0474 (10) | 0.0537 (10) | 0.0405 (9) | −0.0071 (8) | −0.0023 (8) | −0.0125 (8) |
O2 | 0.0488 (11) | 0.0954 (14) | 0.0377 (9) | −0.0184 (10) | 0.0039 (8) | 0.0033 (9) |
O3 | 0.0525 (12) | 0.0812 (13) | 0.0447 (11) | −0.0077 (11) | 0.0034 (9) | −0.0134 (9) |
Geometric parameters (Å, º) top
C1—C2 | 1.372 (3) | C7—H7A | 0.9600 |
C1—C6 | 1.374 (3) | C7—H7B | 0.9600 |
C1—N1 | 1.457 (3) | C7—H7C | 0.9600 |
C2—C3 | 1.384 (4) | C8—O1 | 1.261 (3) |
C2—H4 | 0.9300 | C8—C9 | 1.455 (3) |
C3—C4 | 1.379 (4) | C9—O2 | 1.251 (3) |
C3—H5 | 0.9300 | N1—H1 | 0.97 (3) |
C4—C5 | 1.375 (3) | N1—H2 | 0.92 (3) |
C4—C7 | 1.513 (4) | N1—H3 | 0.96 (3) |
C5—H6 | 0.9300 | O3—H8 | 0.98 (4) |
C6—H7 | 0.9300 | O3—H9 | 0.89 (4) |
| | | |
C2—C1—C6 | 120.8 (2) | C5—C6—H7 | 120.6 |
C2—C1—N1 | 118.6 (2) | C4—C7—H7A | 109.5 |
C6—C1—N1 | 120.5 (2) | C4—C7—H7B | 109.5 |
C1—C2—C3 | 119.3 (2) | H7A—C7—H7B | 109.5 |
C1—C2—H4 | 120.3 | C4—C7—H7C | 109.5 |
C3—C2—H4 | 120.3 | H7A—C7—H7C | 109.5 |
C4—C3—C2 | 121.3 (2) | H7B—C7—H7C | 109.5 |
C4—C3—H5 | 119.3 | O1—C8—C9 | 134.8 (2) |
C2—C3—H5 | 119.3 | O2—C9—C8 | 135.4 (2) |
C5—C4—C3 | 117.9 (2) | C1—N1—H1 | 108.6 (17) |
C5—C4—C7 | 121.6 (2) | C1—N1—H2 | 110.2 (19) |
C3—C4—C7 | 120.5 (3) | H1—N1—H2 | 108 (2) |
C4—C5—C6 | 121.9 (2) | C1—N1—H3 | 110.1 (15) |
C4—C5—H6 | 119.1 | H1—N1—H3 | 106 (2) |
C6—C5—H6 | 119.1 | H2—N1—H3 | 114 (3) |
C1—C6—C5 | 118.8 (2) | H8—O3—H9 | 108 (3) |
C1—C6—H7 | 120.6 | | |
| | | |
C6—C1—C2—C3 | −0.2 (4) | C7—C4—C5—C6 | −179.5 (3) |
N1—C1—C2—C3 | −177.4 (2) | C2—C1—C6—C5 | 0.6 (4) |
C1—C2—C3—C4 | −0.2 (4) | N1—C1—C6—C5 | 177.8 (2) |
C2—C3—C4—C5 | 0.2 (4) | C4—C5—C6—C1 | −0.6 (4) |
C2—C3—C4—C7 | 180.0 (3) | O1—C8—C9—O2 | 0.4 (5) |
C3—C4—C5—C6 | 0.3 (4) | | |
Hydrogen-bond geometry (Å, º) top
D—H···A | D—H | H···A | D···A | D—H···A |
N1—H1···O1 | 0.97 (3) | 1.78 (3) | 2.735 (3) | 167 (3) |
N1—H2···O3 | 0.92 (3) | 1.91 (3) | 2.788 (3) | 159 (3) |
N1—H3···O1i | 0.96 (3) | 1.85 (3) | 2.806 (3) | 174 (2) |
O3—H8···O2ii | 0.98 (4) | 1.85 (4) | 2.813 (3) | 170 (3) |
O3—H9···O2 | 0.89 (4) | 1.86 (4) | 2.751 (3) | 173 (3) |
Symmetry codes: (i) x−1/2, y, −z+1/2; (ii) x−1/2, y, −z+3/2. |
Experimental details
| (I) | (II) |
Crystal data |
Chemical formula | C6H7N2O+·C4HO4− | 2C7H10N+·C4O42−·2H2O |
Mr | 236.18 | 364.40 |
Crystal system, space group | Orthorhombic, Ima2 | Orthorhombic, Pbca |
Temperature (K) | 293 | 293 |
a, b, c (Å) | 6.302 (5), 9.076 (5), 17.531 (5) | 7.761 (5), 22.288 (5), 10.684 (5) |
V (Å3) | 1002.7 (10) | 1848.1 (15) |
Z | 4 | 4 |
Radiation type | Mo Kα | Mo Kα |
µ (mm−1) | 0.13 | 0.10 |
Crystal size (mm) | 0.4 × 0.3 × 0.2 | 0.4 × 0.3 × 0.2 |
|
Data collection |
Diffractometer | STOE IPDS-II diffractometer | STOE IPDS-II diffractometer |
Absorption correction | Integration (X-RED32; Stoe & Cie, 2002) | – |
Tmin, Tmax | 0.965, 0.984 | – |
No. of measured, independent and observed [I > 2σ(I)] reflections | 2316, 728, 589 | 21375, 2208, 1219 |
Rint | 0.022 | 0.085 |
(sin θ/λ)max (Å−1) | 0.677 | 0.659 |
|
Refinement |
R[F2 > 2σ(F2)], wR(F2), S | 0.031, 0.085, 1.04 | 0.037, 0.094, 0.84 |
No. of reflections | 728 | 2208 |
No. of parameters | 107 | 140 |
No. of restraints | 2 | 3 |
H-atom treatment | H atoms treated by a mixture of independent and constrained refinement | H atoms treated by a mixture of independent and constrained refinement |
Δρmax, Δρmin (e Å−3) | 0.17, −0.16 | 0.14, −0.12 |
Selected geometric parameters (Å, º) for (I) topC1—C2 | 1.388 (4) | C7—C8 | 1.429 (4) |
C4—N1 | 1.324 (4) | C8—O4 | 1.229 (4) |
C5—N1 | 1.336 (4) | C8—C9 | 1.498 (4) |
C6—N2 | 1.306 (4) | C9—O3 | 1.217 (4) |
C7—O1 | 1.312 (4) | C9—C10 | 1.496 (4) |
C7—C10 | 1.417 (4) | C10—O2 | 1.243 (3) |
| | | |
N1—C4—C3 | 120.1 (3) | C7—C10—C9 | 89.3 (2) |
O4—C8—C9 | 135.0 (3) | | |
Hydrogen-bond geometry (Å, º) for (I) top
D—H···A | D—H | H···A | D···A | D—H···A |
N2—H2A···O4i | 0.86 | 1.89 | 2.751 (4) | 179 |
N2—H2B···O2ii | 0.86 | 2.08 | 2.913 (4) | 164 |
O1—H6···O5iii | 0.82 | 1.80 | 2.602 (3) | 165 |
N1—H5···O3 | 0.88 (3) | 1.93 (3) | 2.761 (4) | 156 (5) |
N1—H5···O5 | 0.88 (3) | 2.28 (6) | 2.633 (4) | 104 (4) |
Symmetry codes: (i) −x+1/2, −y−1/2, z+1/2; (ii) −x+1/2, −y+1/2, z+1/2; (iii) −x+1/2, −y−1/2, z−1/2. |
Selected geometric parameters (Å, º) for (II) topC1—N1 | 1.457 (3) | C8—C9 | 1.455 (3) |
C8—O1 | 1.261 (3) | C9—O2 | 1.251 (3) |
| | | |
C3—C4—C7 | 120.5 (3) | O2—C9—C8 | 135.4 (2) |
| | | |
C1—C2—C3—C4 | −0.2 (4) | O1—C8—C9—O2 | 0.4 (5) |
Hydrogen-bond geometry (Å, º) for (II) top
D—H···A | D—H | H···A | D···A | D—H···A |
N1—H1···O1 | 0.97 (3) | 1.78 (3) | 2.735 (3) | 167 (3) |
N1—H2···O3 | 0.92 (3) | 1.91 (3) | 2.788 (3) | 159 (3) |
N1—H3···O1i | 0.96 (3) | 1.85 (3) | 2.806 (3) | 174 (2) |
O3—H8···O2ii | 0.98 (4) | 1.85 (4) | 2.813 (3) | 170 (3) |
O3—H9···O2 | 0.89 (4) | 1.86 (4) | 2.751 (3) | 173 (3) |
Symmetry codes: (i) x−1/2, y, −z+1/2; (ii) x−1/2, y, −z+3/2. |
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Hydrogen bonding is one of the principal intermolecular interactions that frequently play key roles in molecular recognition and self-assembly (Lehn, 1995; Goswami & Glosh, 1997) as well as in crystal engineering research (Goswami et al., 1998; Desiraju, 2003; Anthony et al., 1998). By choosing an appropriate H-atom acceptor and donor, stable intermolecular hydrogen bonds can be formed, thereby providing novel organic systems with unique chemical and physical (optical, magnetic and electronic) properties (Lehn, 1990; Desiraju, 1995; MacDonald & Whitesides, 1994). Hydrogen bonding has been used effectively to predict and design supramolecular assemblies in one, two and three dimensions (Konar et al., 2003; Tao et al., 2003; Felloni et al., 2002). In particular, the combination of different molecules with acid/base properties may make an important contribution to the predictability of the recognition process (Russel et al., 1994; Burchell et al., 2001). Hydrogen-bonded systems generated from organic cations and anions are of special interest because they would be expected to show stronger hydrogen bonds than neutral molecules (Reetz et al., 1994; Bertolasi et al., 2001; Mathew et al., 2002; Bulut et al., 2003). In the present work, we selected the potentially interesting squaric acid and its anions since they are flat and rigid systems.
Squaric acid can be found in three forms (see scheme), viz. (a) as uncharged H2SQ, (b) as the HSQ− mono-anion and (c) as SQ2− di-anions on deprotonation by amines. These forms have been observed to crystallize with various types of hydrogen bonding, as summarized by Bertolasi et al. (2001). In this context, we have synthesized the title compounds, (I) and (II), in which the mono- and di-anion forms of squaric acid are observed, and we report the structures of these compounds here. Pyridine-2-carboxamide (picolinamide) and p-toluidine, like other organic bases, are protonated in acidic solutions. This bonding of the H atom to the N atoms in (I) and (II) supplies the cationic character. The structures of (I) and (II) are shown in Figs. 1 and 3, respectively, and Tables 1–4 list the bond and hydrogen-bonding geometries.
Compound (I) contains one protonated picolinamide cation and one squarate monoanion (HSQ−), all atoms lying in a crystallographic symmetry-imposed plane (Fig. 1). Each squaric acid molecule donates one H atom to the pyridine N atom of a picolinamide base, forming the picolinamidium squarate salt. As seen in Fig. 2, each squarate monoanion links three picolinamide cations in the same plane. In picolinamide (Takano et al., 1966), the pyridine ring is almost planar and the angle between the plane of pyridine ring and that of the amine group is about 19°. The difference observed in our study can be attributed to the effect of strong hydrogen bonding. The HSQ− ion has one C—O bond (C7—O1) that is longer than a normal single C—O bond, and two intermediate C—O bonds (C8—O4 and C10—O2), while the C9—O3 bond is typical of a C=O double bond? (Table 1). These lengths indicate a degree of delocalization in the HSQ− ion, as has been observed in previous studies (Mathew et al., 2002; Bertolasi et al., 2001).
The crystal packing of (I) is three-dimensional, constructed from van der Vaals interactions between parallel associations of hydrogen-bonded sheets held together by N—H···O and O—H···O interactions (Table 2). The O1—H6···O5 and N2—H2A···O4 (Table 2) intermolecular hydrogen bonds connect the squarate mono-anion to the picolinamide cation, forming a nine-membered ring (Fig. 2). The other O atoms of the HSQ− anion also form hydrogen-bonding interactions with two picolinamide molecules (Fig. 2). The N2···O4 [2.751 (4) Å] bond is shorter than the N1···O3 distance [2.761 (4) Å], in spite of the facts that the formal positive charge resides on the N1+H group and that positively charged hydrogen bonds are normally stronger (Gilli & Gilli, 2000). A similar situation has also been observed in 2-aminopyrimidinium hydrogen squarate (Bertolasi et al., 2001), where such behaviour was attributed to the resonance structure of the HSQ− mono-anion (as noted above), with the negative charge not residing on O3 but being shared between atoms O2 and O4. Here, however, there is also a weak intramolecular contact between atoms H5 and O5. The N2+—H2A···O41/2- interaction is the most energetically favoured as a result of the resonance structure of the carboxyl amide group. It can be seen from the N2—C6 bond length [1.306 (4) Å], which is approximately equal to the length of a previously reported C═N double bond (Shanmuga et al., 2000). The formal positive charge residing on the N1+H group does not appear to affect the resonance structure of the pyridine ring, ?which is similar to? that in the crystal structure of picolinamide (Takano et al., 1966).
In (II), each squaric acid molecule donates one H atom to the p-toluidine N atom of two trans p-toluidine molecules, forming the di-p-toluidinium squarate monohydrate salt. The asymmetric unit of (II) contains one protonated p-toluidinium cation and one-half of a centrosymmetric squarate dianion, SQ2−, together with an uncoordinated water molecule. A view of (II) and its numbering scheme is shown in Fig. 3. Both the SQ2− and the p-toluidine moiety is essentially planar, with maximum deviations from these planes being 0.001 (1) Å for atoms C8 and C9, and 0.004 (2) Å for atom C6, while the dihedral angle between the N1/C6/C1/C2 and O1/C8/C9/O2 planes is 70.71 (1)°. The C—O and C—C bond distances in SQ2− are of equal length (Table 3), indicating aromaticity (Mathew et al., 2002). All the O atoms of the SQ2− ion, the uncoordinated water molecule and the N atom of p-toluidine make a contribution to the crystal packing (Table 4). The uncoordinated water molecule links the p-toluidine and SQ2− moieties by hydrogen-bonding interactions, thus forming an infinite three-dimensional lattice, as shown in Fig. 4.