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Crystals of 2,4,6-triamino-1,3,5-triazine-1,3-dium bis(trifluoroacetate) trihydrate, C3H8N62+·2CF3COO-·3H2O, and 2,4,6-triamino-1,3,5-triazine-1,3-dium bis(trichloroacetate) dihydrate, C3H8N62+·2CCl3COO-·2H2O, both contain doubly protonated melamine rings that lie on crystallographic twofold axes. In the former structure, one water molecule also lies on a twofold axis. While the trifluoroacetate compound crystallizes in a centrosymmetric space group, the trichloroacetate is non-centrosymmetric, so it is useful as a material for non-linear optics. The efficiency of second harmonic generation is about three times greater than that of KDP (KH2PO4). A combination of ionic and donor-acceptor hydrogen-bond interactions link the melaminium(2+) residues with trifluoroacetate or trichloroacetate ions and water molecules to form a three-dimensional network.
Supporting information
CCDC references: 616127; 616128
Melamine was dissolved in 10% aqueous trifluoroacetic or trichloroacetic acid; after several days, colourless single crystals formed, which proved to be suitable for single-crystal X-ray diffraction analysis.
For both compounds, data collection: KM-4 CCD Software (Kuma, 2002); cell refinement: KM-4 CCD Software; data reduction: KM-4 CCD Software; 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.
(I) 2,4,6-triamino-1,3,5-triazin-1,3-dium bis(trifluoroacetate) trihydrate
top
Crystal data top
C3H8N62+·2C2F3O2−·3H2O | F(000) = 416 |
Mr = 408.24 | Dx = 1.707 Mg m−3 Dm = 1.70 Mg m−3 Dm measured by flotation |
Monoclinic, P2/c | Mo Kα radiation, λ = 0.71073 Å |
Hall symbol: -P 2yc | Cell parameters from 1101 reflections |
a = 12.442 (3) Å | θ = 2.9–28.5° |
b = 8.3330 (17) Å | µ = 0.19 mm−1 |
c = 7.6600 (15) Å | T = 295 K |
β = 90.14 (3)° | Parallelepiped, colourless |
V = 794.2 (3) Å3 | 0.32 × 0.18 × 0.14 mm |
Z = 2 | |
Data collection top
KUMA KM-4 diffractometer with CCD detector | 2076 independent reflections |
Radiation source: fine-focus sealed tube | 1101 reflections with I > 2σ(I) |
Graphite monochromator | Rint = 0.023 |
Detector resolution: 33.133 pixels mm-1 | θmax = 29.5°, θmin = 2.9° |
ω scan | h = −16→16 |
Absorption correction: analytical face-indexed (SHELXTL; Sheldrick, 1990b) | k = −11→11 |
Tmin = 0.932, Tmax = 0.981 | l = −9→10 |
9531 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)] = 0.045 | H atoms treated by a mixture of independent and constrained refinement |
wR(F2) = 0.105 | w = 1/[σ2(Fo2) + (0.0462P)2] where P = (Fo2 + 2Fc2)/3 |
S = 1.00 | (Δ/σ)max < 0.001 |
2076 reflections | Δρmax = 0.30 e Å−3 |
136 parameters | Δρmin = −0.20 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: 0.015 (3) |
Crystal data top
C3H8N62+·2C2F3O2−·3H2O | V = 794.2 (3) Å3 |
Mr = 408.24 | Z = 2 |
Monoclinic, P2/c | Mo Kα radiation |
a = 12.442 (3) Å | µ = 0.19 mm−1 |
b = 8.3330 (17) Å | T = 295 K |
c = 7.6600 (15) Å | 0.32 × 0.18 × 0.14 mm |
β = 90.14 (3)° | |
Data collection top
KUMA KM-4 diffractometer with CCD detector | 2076 independent reflections |
Absorption correction: analytical face-indexed (SHELXTL; Sheldrick, 1990b) | 1101 reflections with I > 2σ(I) |
Tmin = 0.932, Tmax = 0.981 | Rint = 0.023 |
9531 measured reflections | |
Refinement top
R[F2 > 2σ(F2)] = 0.045 | 3 restraints |
wR(F2) = 0.105 | H atoms treated by a mixture of independent and constrained refinement |
S = 1.00 | Δρmax = 0.30 e Å−3 |
2076 reflections | Δρmin = −0.20 e Å−3 |
136 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 | |
N3 | 0.0000 | 0.4856 (2) | 0.2500 | 0.0449 (6) | |
H3 | 0.0535 (15) | 0.540 (2) | 0.208 (2) | 0.054* | |
C3 | 0.0000 | 0.3276 (3) | 0.2500 | 0.0369 (6) | |
N1 | 0.08039 (12) | 0.24452 (16) | 0.1730 (2) | 0.0380 (4) | |
H2 | 0.1287 (15) | 0.292 (2) | 0.117 (2) | 0.046* | |
C4 | 0.08051 (13) | 0.07955 (19) | 0.1805 (2) | 0.0344 (4) | |
N2 | 0.0000 | −0.0030 (2) | 0.2500 | 0.0377 (5) | |
N4 | 0.16400 (11) | 0.00395 (16) | 0.11539 (19) | 0.0429 (4) | |
H4A | 0.1665 | −0.0992 | 0.1177 | 0.051* | |
H4B | 0.2161 | 0.0576 | 0.0704 | 0.051* | |
O2 | 0.16287 (10) | 0.65543 (13) | 0.08532 (18) | 0.0559 (4) | |
O1 | 0.23821 (10) | 0.42017 (14) | 0.03021 (19) | 0.0619 (4) | |
C1 | 0.23546 (15) | 0.5683 (2) | 0.0370 (2) | 0.0418 (4) | |
C2 | 0.33896 (16) | 0.6524 (2) | −0.0202 (3) | 0.0570 (5) | |
F1 | 0.40184 (11) | 0.56597 (17) | −0.1193 (2) | 0.0859 (5) | |
F2 | 0.31502 (12) | 0.78282 (17) | −0.1163 (2) | 0.0912 (6) | |
F3 | 0.39624 (12) | 0.6997 (2) | 0.11303 (19) | 0.1099 (7) | |
O3 | 0.36372 (11) | 0.14220 (15) | −0.00606 (17) | 0.0495 (4) | |
H13 | 0.4122 (12) | 0.144 (3) | −0.078 (2) | 0.074* | |
H23 | 0.3543 (17) | 0.2394 (4) | −0.012 (3) | 0.074* | |
O4 | 0.5000 | 0.0095 (2) | 0.2500 | 0.0470 (5) | |
H14 | 0.5361 (13) | 0.0905 (13) | 0.266 (3) | 0.070* | |
Atomic displacement parameters (Å2) top | U11 | U22 | U33 | U12 | U13 | U23 |
N3 | 0.0368 (13) | 0.0256 (11) | 0.0722 (16) | 0.000 | 0.0116 (11) | 0.000 |
C3 | 0.0352 (14) | 0.0277 (13) | 0.0477 (15) | 0.000 | 0.0001 (12) | 0.000 |
N1 | 0.0303 (8) | 0.0287 (8) | 0.0551 (10) | −0.0011 (6) | 0.0064 (7) | 0.0012 (7) |
C4 | 0.0315 (10) | 0.0290 (9) | 0.0426 (10) | 0.0008 (8) | −0.0006 (8) | −0.0048 (8) |
N2 | 0.0331 (11) | 0.0267 (10) | 0.0533 (13) | 0.000 | 0.0012 (10) | 0.000 |
N4 | 0.0374 (9) | 0.0269 (7) | 0.0645 (10) | −0.0006 (6) | 0.0122 (7) | −0.0028 (7) |
O2 | 0.0472 (8) | 0.0318 (7) | 0.0888 (10) | −0.0011 (6) | 0.0256 (7) | 0.0005 (6) |
O1 | 0.0517 (9) | 0.0270 (7) | 0.1072 (11) | −0.0019 (6) | 0.0264 (8) | −0.0023 (7) |
C1 | 0.0412 (11) | 0.0332 (9) | 0.0510 (11) | −0.0016 (9) | 0.0020 (9) | 0.0012 (9) |
C2 | 0.0583 (12) | 0.0427 (10) | 0.0699 (12) | −0.0020 (9) | 0.0156 (10) | 0.0115 (9) |
F1 | 0.0737 (9) | 0.0732 (9) | 0.1113 (13) | −0.0011 (8) | 0.0521 (9) | 0.0116 (9) |
F2 | 0.0885 (11) | 0.0743 (9) | 0.1111 (13) | 0.0054 (8) | 0.0426 (9) | 0.0552 (9) |
F3 | 0.1010 (13) | 0.1393 (17) | 0.0894 (10) | −0.0826 (12) | 0.0037 (9) | 0.0046 (10) |
O3 | 0.0490 (9) | 0.0414 (7) | 0.0584 (8) | 0.0053 (7) | 0.0156 (6) | −0.0020 (7) |
O4 | 0.0455 (12) | 0.0448 (11) | 0.0506 (11) | 0.000 | 0.0048 (9) | 0.000 |
Geometric parameters (Å, º) top
N3—C3 | 1.317 (3) | N4—H4B | 0.8600 |
N3—H3 | 0.868 (18) | O2—C1 | 1.217 (2) |
C3—N1 | 1.3530 (18) | O1—C1 | 1.236 (2) |
C3—N1i | 1.3530 (18) | C1—C2 | 1.531 (3) |
N1—C4 | 1.376 (2) | C2—F3 | 1.304 (2) |
N1—H2 | 0.838 (19) | C2—F1 | 1.308 (2) |
C4—N4 | 1.314 (2) | C2—F2 | 1.346 (2) |
C4—N2 | 1.3278 (18) | O3—H13 | 0.818 (15) |
N2—C4i | 1.3278 (18) | O3—H23 | 0.820 (5) |
N4—H4A | 0.8600 | O4—H14 | 0.820 (13) |
| | | |
C3—N3—H3 | 121.5 (13) | C4—N4—H4B | 120.0 |
N3—C3—N1 | 120.78 (10) | H4A—N4—H4B | 120.0 |
N3—C3—N1i | 120.78 (10) | O2—C1—O1 | 128.97 (17) |
N1—C3—N1i | 118.4 (2) | O2—C1—C2 | 116.08 (15) |
C3—N1—C4 | 119.59 (16) | O1—C1—C2 | 114.93 (16) |
C3—N1—H2 | 120.8 (12) | F3—C2—F1 | 107.12 (17) |
C4—N1—H2 | 119.5 (13) | F3—C2—F2 | 107.66 (17) |
N4—C4—N2 | 120.10 (15) | F1—C2—F2 | 105.01 (16) |
N4—C4—N1 | 117.63 (15) | F3—C2—C1 | 111.90 (16) |
N2—C4—N1 | 122.27 (16) | F1—C2—C1 | 114.77 (15) |
C4—N2—C4i | 117.55 (19) | F2—C2—C1 | 109.92 (16) |
C4—N4—H4A | 120.0 | H13—O3—H23 | 93 (2) |
Symmetry code: (i) −x, y, −z+1/2. |
Hydrogen-bond geometry (Å, º) top
D—H···A | D—H | H···A | D···A | D—H···A |
N3—H3···O2 | 0.868 (18) | 1.915 (18) | 2.7772 (17) | 172.3 (17) |
N1—H2···O1 | 0.838 (19) | 1.86 (2) | 2.684 (2) | 169.4 (17) |
N4—H4A···O2ii | 0.86 | 2.06 | 2.9134 (19) | 171 |
N4—H4B···O3 | 0.86 | 2.05 | 2.895 (2) | 165 |
O3—H13···O4iii | 0.82 (2) | 2.14 (1) | 2.8250 (16) | 141 (2) |
O3—H23···O1 | 0.82 (1) | 2.11 (1) | 2.8078 (18) | 143 (2) |
O4—H14···O3iv | 0.82 (1) | 2.26 (2) | 2.8157 (17) | 126 (2) |
O4—H14···F2v | 0.82 (1) | 2.42 (2) | 3.0581 (17) | 135 (2) |
Symmetry codes: (ii) x, y−1, z; (iii) −x+1, −y, −z; (iv) −x+1, y, −z+1/2; (v) −x+1, −y+1, −z. |
(II) 2,4,6-triamino-1,3,5-triazin-1,3-dium bis(trichloroacetate) dihydrate
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Crystal data top
C3H8N62+·2C2Cl3O2−·2H2O | F(000) = 492 |
Mr = 488.93 | Dx = 1.784 Mg m−3 Dm = 1.78 Mg m−3 Dm measured by flotation |
Monoclinic, C2 | Mo Kα radiation, λ = 0.71073 Å |
Hall symbol: C 2y | Cell parameters from 1456 reflections |
a = 17.865 (3) Å | θ = 3.4–28.5° |
b = 8.465 (2) Å | µ = 0.98 mm−1 |
c = 6.117 (1) Å | T = 295 K |
β = 100.22 (1)° | Paralellepiped, colourless |
V = 910.4 (3) Å3 | 0.32 × 0.27 × 0.21 mm |
Z = 2 | |
Data collection top
KUMA KM-4 diffractometer with CCD detector | 2229 independent reflections |
Radiation source: fine-focus sealed tube | 2109 reflections with I > 2σ(I) |
Graphite monochromator | Rint = 0.028 |
Detector resolution: 33.133 pixels mm-1 | θmax = 28.5°, θmin = 3.4° |
ω scan | h = −23→23 |
Absorption correction: analytical face-indexed, SHELXTL (Sheldrick, 1990b) | k = −11→11 |
Tmin = 0.743, Tmax = 0.814 | l = −8→7 |
6412 measured reflections | |
Refinement top
Refinement on F2 | Hydrogen site location: inferred from neighbouring sites |
Least-squares matrix: full | H atoms treated by a mixture of independent and constrained refinement |
R[F2 > 2σ(F2)] = 0.035 | w = 1/[σ2(Fo2) + (0.0313P)2 + 1.7329P] where P = (Fo2 + 2Fc2)/3 |
wR(F2) = 0.085 | (Δ/σ)max = 0.010 |
S = 1.00 | Δρmax = 0.61 e Å−3 |
2229 reflections | Δρmin = −0.66 e Å−3 |
125 parameters | Extinction correction: SHELXL97, Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4 |
5 restraints | Extinction coefficient: 0.0089 (10) |
Primary atom site location: structure-invariant direct methods | Absolute structure: Flack, 1983, 997 Friedel pairs |
Secondary atom site location: difference Fourier map | Absolute structure parameter: 0.08 (8) |
Crystal data top
C3H8N62+·2C2Cl3O2−·2H2O | V = 910.4 (3) Å3 |
Mr = 488.93 | Z = 2 |
Monoclinic, C2 | Mo Kα radiation |
a = 17.865 (3) Å | µ = 0.98 mm−1 |
b = 8.465 (2) Å | T = 295 K |
c = 6.117 (1) Å | 0.32 × 0.27 × 0.21 mm |
β = 100.22 (1)° | |
Data collection top
KUMA KM-4 diffractometer with CCD detector | 2229 independent reflections |
Absorption correction: analytical face-indexed, SHELXTL (Sheldrick, 1990b) | 2109 reflections with I > 2σ(I) |
Tmin = 0.743, Tmax = 0.814 | Rint = 0.028 |
6412 measured reflections | |
Refinement top
R[F2 > 2σ(F2)] = 0.035 | H atoms treated by a mixture of independent and constrained refinement |
wR(F2) = 0.085 | Δρmax = 0.61 e Å−3 |
S = 1.00 | Δρmin = −0.66 e Å−3 |
2229 reflections | Absolute structure: Flack, 1983, 997 Friedel pairs |
125 parameters | Absolute structure parameter: 0.08 (8) |
5 restraints | |
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 | |
Cl1 | 0.11173 (4) | 0.25144 (9) | 0.83577 (11) | 0.04295 (18) | |
Cl2 | 0.21077 (6) | −0.01624 (11) | 0.90741 (16) | 0.0728 (3) | |
Cl3 | 0.23833 (5) | 0.23057 (13) | 0.60373 (16) | 0.0615 (3) | |
C2 | 0.16740 (15) | 0.1215 (3) | 0.7056 (4) | 0.0332 (5) | |
C1 | 0.11440 (15) | 0.0389 (3) | 0.5062 (4) | 0.0292 (5) | |
O1 | 0.08149 (13) | 0.1281 (2) | 0.3610 (3) | 0.0432 (5) | |
O2 | 0.11062 (15) | −0.1066 (2) | 0.5134 (4) | 0.0502 (6) | |
C3 | 0.0000 | 0.7984 (3) | 0.0000 | 0.0232 (6) | |
N1 | 0.03729 (11) | 0.7166 (2) | 0.1746 (3) | 0.0262 (4) | |
H1 | 0.0619 | 0.7659 | 0.2879 | 0.031* | |
N2 | 0.0000 | 0.4728 (3) | 0.0000 | 0.0262 (5) | |
N3 | 0.0000 | 0.9522 (3) | 0.0000 | 0.0321 (7) | |
H3 | 0.0237 (15) | 1.001 (3) | 0.115 (3) | 0.039* | |
N4 | 0.07323 (13) | 0.4792 (3) | 0.3465 (3) | 0.0368 (5) | |
H41 | 0.0740 | 0.3776 | 0.3490 | 0.044* | |
H42 | 0.0967 | 0.5319 | 0.4582 | 0.044* | |
C4 | 0.03612 (14) | 0.5540 (3) | 0.1719 (4) | 0.0254 (5) | |
O3 | 0.12951 (13) | 0.6302 (2) | 0.7636 (4) | 0.0459 (5) | |
H31 | 0.1363 (17) | 0.7189 (18) | 0.717 (6) | 0.069* | |
H32 | 0.1733 (7) | 0.597 (4) | 0.781 (7) | 0.069* | |
Atomic displacement parameters (Å2) top | U11 | U22 | U33 | U12 | U13 | U23 |
Cl1 | 0.0596 (4) | 0.0338 (3) | 0.0355 (3) | −0.0021 (3) | 0.0086 (3) | −0.0084 (3) |
Cl2 | 0.0929 (6) | 0.0337 (4) | 0.0676 (5) | 0.0040 (4) | −0.0516 (5) | 0.0019 (4) |
Cl3 | 0.0454 (4) | 0.0672 (6) | 0.0734 (5) | −0.0188 (4) | 0.0151 (4) | −0.0133 (5) |
C2 | 0.0391 (13) | 0.0234 (11) | 0.0322 (12) | 0.0001 (10) | −0.0068 (10) | −0.0020 (10) |
C1 | 0.0356 (12) | 0.0253 (10) | 0.0241 (11) | 0.0006 (9) | −0.0017 (9) | −0.0036 (9) |
O1 | 0.0619 (12) | 0.0243 (9) | 0.0346 (9) | 0.0026 (9) | −0.0152 (9) | 0.0004 (8) |
O2 | 0.0765 (15) | 0.0221 (9) | 0.0398 (11) | −0.0029 (9) | −0.0228 (11) | −0.0029 (8) |
C3 | 0.0271 (14) | 0.0177 (13) | 0.0237 (14) | 0.000 | 0.0018 (12) | 0.000 |
N1 | 0.0349 (9) | 0.0175 (9) | 0.0227 (9) | −0.0010 (7) | −0.0040 (7) | −0.0013 (7) |
N2 | 0.0362 (14) | 0.0187 (12) | 0.0211 (12) | 0.000 | −0.0016 (10) | 0.000 |
N3 | 0.0475 (17) | 0.0153 (13) | 0.0289 (15) | 0.000 | −0.0061 (12) | 0.000 |
N4 | 0.0540 (13) | 0.0204 (9) | 0.0297 (10) | 0.0032 (10) | −0.0100 (9) | 0.0035 (9) |
C4 | 0.0321 (11) | 0.0182 (10) | 0.0247 (11) | 0.0005 (8) | 0.0016 (9) | 0.0031 (8) |
O3 | 0.0509 (12) | 0.0324 (10) | 0.0492 (11) | −0.0049 (9) | −0.0050 (10) | 0.0073 (9) |
Geometric parameters (Å, º) top
Cl1—C2 | 1.765 (3) | N1—H1 | 0.8600 |
Cl2—C2 | 1.773 (3) | N2—C4 | 1.324 (3) |
Cl3—C2 | 1.768 (3) | N2—C4i | 1.324 (3) |
C2—C1 | 1.570 (3) | N3—H3 | 0.86 (2) |
C1—O1 | 1.233 (3) | N4—C4 | 1.315 (3) |
C1—O2 | 1.234 (3) | N4—H41 | 0.8600 |
C3—N3 | 1.302 (4) | N4—H42 | 0.8600 |
C3—N1i | 1.346 (2) | O3—H31 | 0.82 (2) |
C3—N1 | 1.346 (2) | O3—H32 | 0.82 (2) |
N1—C4 | 1.377 (3) | | |
| | | |
C1—C2—Cl1 | 108.53 (17) | C3—N1—C4 | 120.0 (2) |
C1—C2—Cl3 | 109.27 (18) | C3—N1—H1 | 120.0 |
Cl1—C2—Cl3 | 109.26 (14) | C4—N1—H1 | 120.0 |
C1—C2—Cl2 | 112.14 (18) | C4—N2—C4i | 117.5 (3) |
Cl1—C2—Cl2 | 107.91 (14) | C3—N3—H3 | 119 (2) |
Cl3—C2—Cl2 | 109.68 (15) | C4—N4—H41 | 120.0 |
O1—C1—O2 | 127.9 (3) | C4—N4—H42 | 120.0 |
O1—C1—C2 | 115.6 (2) | H41—N4—H42 | 120.0 |
O2—C1—C2 | 116.5 (2) | N4—C4—N2 | 120.0 (2) |
N3—C3—N1i | 120.97 (13) | N4—C4—N1 | 117.8 (2) |
N3—C3—N1 | 120.97 (13) | N2—C4—N1 | 122.2 (2) |
N1i—C3—N1 | 118.1 (3) | H31—O3—H32 | 99 (3) |
Symmetry code: (i) −x, y, −z. |
Hydrogen-bond geometry (Å, º) top
D—H···A | D—H | H···A | D···A | D—H···A |
N1—H1···O2ii | 0.86 | 1.84 | 2.700 (3) | 173 |
N3—H3···O1ii | 0.86 (2) | 1.98 (2) | 2.841 (2) | 174 (3) |
N4—H41···O1 | 0.86 | 2.12 | 2.977 (3) | 177 |
N4—H42···O3 | 0.86 | 2.03 | 2.872 (3) | 164 |
O3—H31···O2ii | 0.82 (2) | 1.93 (2) | 2.690 (3) | 153 (4) |
O3—H31···Cl2ii | 0.82 (2) | 2.76 (3) | 3.374 (2) | 133 (3) |
O3—H32···Cl2iii | 0.82 (2) | 2.73 (2) | 3.419 (2) | 143 (4) |
Symmetry codes: (ii) x, y+1, z; (iii) −x+1/2, y+1/2, −z+2. |
Experimental details
| (I) | (II) |
Crystal data |
Chemical formula | C3H8N62+·2C2F3O2−·3H2O | C3H8N62+·2C2Cl3O2−·2H2O |
Mr | 408.24 | 488.93 |
Crystal system, space group | Monoclinic, P2/c | Monoclinic, C2 |
Temperature (K) | 295 | 295 |
a, b, c (Å) | 12.442 (3), 8.3330 (17), 7.6600 (15) | 17.865 (3), 8.465 (2), 6.117 (1) |
β (°) | 90.14 (3) | 100.22 (1) |
V (Å3) | 794.2 (3) | 910.4 (3) |
Z | 2 | 2 |
Radiation type | Mo Kα | Mo Kα |
µ (mm−1) | 0.19 | 0.98 |
Crystal size (mm) | 0.32 × 0.18 × 0.14 | 0.32 × 0.27 × 0.21 |
|
Data collection |
Diffractometer | KUMA KM-4 diffractometer with CCD detector | KUMA KM-4 diffractometer with CCD detector |
Absorption correction | Analytical face-indexed (SHELXTL; Sheldrick, 1990b) | Analytical face-indexed, SHELXTL (Sheldrick, 1990b) |
Tmin, Tmax | 0.932, 0.981 | 0.743, 0.814 |
No. of measured, independent and observed [I > 2σ(I)] reflections | 9531, 2076, 1101 | 6412, 2229, 2109 |
Rint | 0.023 | 0.028 |
(sin θ/λ)max (Å−1) | 0.693 | 0.671 |
|
Refinement |
R[F2 > 2σ(F2)], wR(F2), S | 0.045, 0.105, 1.00 | 0.035, 0.085, 1.00 |
No. of reflections | 2076 | 2229 |
No. of parameters | 136 | 125 |
No. of restraints | 3 | 5 |
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) | 0.30, −0.20 | 0.61, −0.66 |
Absolute structure | ? | Flack, 1983, 997 Friedel pairs |
Absolute structure parameter | ? | 0.08 (8) |
Selected geometric parameters (Å, º) for (I) topN3—C3 | 1.317 (3) | O1—C1 | 1.236 (2) |
C3—N1 | 1.3530 (18) | C1—C2 | 1.531 (3) |
N1—C4 | 1.376 (2) | C2—F3 | 1.304 (2) |
C4—N4 | 1.314 (2) | C2—F1 | 1.308 (2) |
C4—N2 | 1.3278 (18) | C2—F2 | 1.346 (2) |
O2—C1 | 1.217 (2) | | |
| | | |
N1—C3—N1i | 118.4 (2) | C4—N2—C4i | 117.55 (19) |
C3—N1—C4 | 119.59 (16) | O2—C1—O1 | 128.97 (17) |
N2—C4—N1 | 122.27 (16) | | |
Symmetry code: (i) −x, y, −z+1/2. |
Hydrogen-bond geometry (Å, º) for (I) top
D—H···A | D—H | H···A | D···A | D—H···A |
N3—H3···O2 | 0.868 (18) | 1.915 (18) | 2.7772 (17) | 172.3 (17) |
N1—H2···O1 | 0.838 (19) | 1.86 (2) | 2.684 (2) | 169.4 (17) |
N4—H4A···O2ii | 0.86 | 2.06 | 2.9134 (19) | 171.2 |
N4—H4B···O3 | 0.86 | 2.05 | 2.895 (2) | 165.4 |
O3—H13···O4iii | 0.818 (15) | 2.137 (13) | 2.8250 (16) | 141 (2) |
O3—H23···O1 | 0.820 (5) | 2.112 (14) | 2.8078 (18) | 143 (2) |
O4—H14···O3iv | 0.820 (13) | 2.260 (18) | 2.8157 (17) | 125.5 (19) |
O4—H14···F2v | 0.820 (13) | 2.424 (17) | 3.0581 (17) | 135 (2) |
Symmetry codes: (ii) x, y−1, z; (iii) −x+1, −y, −z; (iv) −x+1, y, −z+1/2; (v) −x+1, −y+1, −z. |
Selected geometric parameters (Å, º) for (II) topCl1—C2 | 1.765 (3) | C3—N3 | 1.302 (4) |
Cl2—C2 | 1.773 (3) | C3—N1 | 1.346 (2) |
Cl3—C2 | 1.768 (3) | N1—C4 | 1.377 (3) |
C2—C1 | 1.570 (3) | N2—C4 | 1.324 (3) |
C1—O1 | 1.233 (3) | N4—C4 | 1.315 (3) |
C1—O2 | 1.234 (3) | | |
| | | |
O1—C1—O2 | 127.9 (3) | C4—N2—C4i | 117.5 (3) |
N1i—C3—N1 | 118.1 (3) | N4—C4—N2 | 120.0 (2) |
C3—N1—C4 | 120.0 (2) | | |
Symmetry code: (i) −x, y, −z. |
Hydrogen-bond geometry (Å, º) for (II) top
D—H···A | D—H | H···A | D···A | D—H···A |
N1—H1···O2ii | 0.86 | 1.84 | 2.700 (3) | 173.2 |
N3—H3···O1ii | 0.86 (2) | 1.98 (2) | 2.841 (2) | 174 (3) |
N4—H41···O1 | 0.86 | 2.12 | 2.977 (3) | 177.3 |
N4—H42···O3 | 0.86 | 2.03 | 2.872 (3) | 164.2 |
O3—H31···O2ii | 0.82 (2) | 1.934 (16) | 2.690 (3) | 153 (4) |
O3—H31···Cl2ii | 0.82 (2) | 2.76 (3) | 3.374 (2) | 133 (3) |
O3—H32···Cl2iii | 0.82 (2) | 2.73 (2) | 3.419 (2) | 143 (4) |
Symmetry codes: (ii) x, y+1, z; (iii) −x+1/2, y+1/2, −z+2. |
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The present study is a continuation of our investigations into the characterization of the hydrogen-bonding system formed by melamine in the solid state (Perpétuo & Janczak, 2005). Melamine and its derivatives and organic and inorganic complexes or salts can develop well defined non-covalent supramolecular architectures via multiple hydrogen bonds since they contain complementary arrays of hydrogen-bonding sites (Desiraju, 1990; MacDonald & Whitesides, 1994; Row, 1999; Krische & Lehn, 2000; Sherrington & Taskinen, 2001). In order to expand the understanding of the solid-state physical-organic chemistry of compounds that form multiple N—H···N, N—H···O and O—H···O hydrogen-bonding systems, we present here the solid-state structure of melaminium bis(trifluoroacetate) trihydrate, (I), and melaminium bis(trichloroacetate) dihydrate, (II).
Both crystals contain melamine protonated at two of the three ring N atoms (Figs. 1 and 2); the ring has a crystallographic twofold axis, and thus half of the melaminium(2+) ring is independent. The melaminium ring (C3H8N62+) in both crystals is almost planar, but shows significant distortion from an ideal hexagonal form. The internal C—N—C angle at the non-protonated N atom is significantly smaller than the C—N—C angles at the protonated N atoms (Tables 1 amd 3). The differences between the internal C—N—C angles within the melaminium ring residue correlate with the steric effect of the lone-pair electrons and are fully consistent with the valence-shell electron-pair repulsion therory (VSEPR; Gillespie, 1963, 1992). As a result of the protonation of the melamine ring at two of three ring N atoms, the internal N—C—N angle involving only protonated N atoms is significantly smaller than the N—C—N angles involving both protonated and non-protonated N atoms. The ab initio gas-phase geometry calculated for the isolated doubly protonated melaminium(2+) cation shows quite similar correlation between the internal C—N—C and N—C—N angles within the ring (Drozd & Marchewka, 2005). Thus the ring distortions of the protonated melaminium residue result mainly from the protonation and, to a lesser degree, from the hydrogen-bonding system and the crystal packing. Protonation of the melamine ring also modifies the C—N bonds within the ring when compared with the neutral melamine crystal structure (Varghese et al., 1977). The C—N bonds involving the protonated N atom are slightly longer than the other C—N bonds within the ring. Thus there is evidence for a partially localized double-bond form, in which, for example, the bond order of N2—C4 is greater than that of the other N—C (N1—C4 and N1—C3) bonds. Additionally, protonation of the triazine ring of melamine leads to shortening of the C—NH2 bond in relation to the melamine molecule in the solid state (Varghese et al., 1977) as well as in the gas phase (Drozd & Marchewka, 2005). A search of Cambridge Structural Database (Version 5.27; Allen, 2002) for crystals containing a protonated melaminium residue yields over 30 structures, but only six of them contain doubly protonated melaminium(2+) residues; all of these show melaminium ring distortions quite similar to those found here.
The geometry of the trifluoroacetate ion, CF3COO−, is different from that of the trichloroacetate ion, CCl3COO−. The conformation of the anion in the crystals is well described by the O1—C1—C2—X1 torsion angle [X1 = F2 in (I) and X1 = Cl2 in (II)] and by the C1—C2 bond length. In the trifluoroacetate ion, this torsion angle is −160.0 (1)°, while in the trichloroacetate ion it is −179.0 (1)°, so atoms O1, C1, C2 and Cl2 are almost coplanar. Molecular orbital (MO) calculation using density functional theory and the B3LYP/6–31+G** basis sets (Frisch et al., 1998) performed for the isolated CCl3COO− ion shows a minimum on the potential energy surface (PES) for the conformation observed in the crystal (O1—C1—C2—Cl2 = −179.9°), whereas MO calculation for the CF3COO− ion shows a minimum on the PES for a more rotated conformation (O1—C1—C2—F2 = −175.2°); thus, in the crystal, the rotation of the COO− group in relation to CF3 around the C1—C2 bond results from the hydrogen-bonding interactions. The C1—C2 bond length of 1.531 (3) Å in CF3COO− is shorter than that in CCl3COO− [1.570 (3) Å]. However, this bond in both crystals is longer than that found in typical acetate crystals, for example melaminium acetate (Janczak & Perpétuo, 2001). The differences between the C1—C2 distances, as well as those between the C—F and C—Cl bond lengths, correlate well with the ionic radii of F and Cl (1.31 Å and 1.81 Å, respectively; Shannon, 1976) and their electronegativity (3.98 and 3.16 for F and Cl, respectively; Pauling, 1967). The lengthening of the C1—C2 bond in relation to the typical acetate ion (CH3COO−) results from the repulsion between the negatively charged O atoms and the three Cl or F atoms joined in the α-position in relation to the COO− group. This effect is more pronounced in the gas-phase structures obtained by MO calculations, where C1—C2 equals to 1.588 Å in CF3CCO− and 1.650 Å in CCl3COO− (Frisch et al., 1998). The average C—F and C—Cl bond lengths in the crystal are 1.320 and 1.768 Å, respectively. These values correlate well with the values observed for Csp3—F (1.314–1.332 Å) and for Csp3—Cl (1.761–1.776 Å) (Allen et al., 1987). The C—O bond lengths in the carboxylate group are intermediate between single Csp2—O (1.308–1.320 Å) and double Csp2—O bond values (1.214–1.224 Å; Allen et al. 1987) indicating delocalization of the charge on both O atoms of the COO− group.
An extensive set of hydrogen bonds (Tables 2 and 4) links the components of (I) and (II) into a continuous framework superstructure (Figs. 3 and 4). All H atoms of the doubly protonated melaminium residues in both structures form N—H···O hydrogen bonds. In (I), the melaminum residue acts a donor in eight hydrogen bonds with four symmetrically equivalent CF3COO− ions and two water (O3) molecules forming two-dimensional layers almost parallel to the (101) plane. The two O atoms of the trifluoroacetate ion act as acceptors in two hydrogen bonds; atom O1 interacts with a water molecule and with the H atom of a protonated N atom of the melaminium ring, while atom O2 links two translationally equivalent melaminium residues via the H atoms of amine groups. The two almost parallel N—H···O hydrogen bonding interactions between the melaminium residues and CF3COO− ions are the strongest hydrogen bonds in the structure (Table 2). The water molecules are interconnected via O—H···O hydrogen bonds into chains along the [001] direction. In the chain, the water molecule O4 is surrounded by four water molecules O3, which are related in pairs by the twofold axis upon which atom O4 lies. Each O3 atom is hydrogen bonded to O4 and to another O4 atom related by the inversion center. In conclusion, water molecule O4 has a tetrahedral-like geometry. The chains of water molecules join the melaminium–trifluoroacetate ions into a three-dimensional superstructure (Fig. 3). The melaminium ions are arranged parallel to one another and are separated by ~3.33 Å in the [001] direction.
In (II), each melaminium residue acts as donor in eight N—H···O hydrogen bonds – with four CCl3COO− anions related by the twofold axis and by a unit translation along the b axis, and with two symmetrically equivalent water molecules – to form separate but interacting two-dimensional layers almost parallel to the (−401) plane. These layers are separated by ~3.50 Å. Both O atoms of trichloroacetate act as acceptors in two almost linear bifurcated hydrogen bonds (Table 4). Atom O1 is involved in hydrogen bonds with two amine groups of two symmetry-equivalent melaminium cations, while atom O2 accepts hydrogen bonds from the protonated ring N atom and from one water molecule. This same water molecule also takes part in two hydrogen bonds in which it acts as acceptor for an amine group of the melaminium ion and as a donor to Cl (O3—H32···Cl2ii). In both (I) and (II), the non-protonated ring N atom with the lone pair does not form any hydrogen bonds.
The second harmonic generation (SHG) experiment was carried out using the Kurtz–Perry powder technique (Kurtz & Perry, 1968). The calibrated samples (melaminium trichloroacetate and KDP) were irradiated at 1064 nm by an Nd:YAG laser and the second harmonic beam power diffused by the sample (at 532 nm) was measured as a function of the fundamental beam power. SHG efficiency for melaminium bis(trichloroacetate) dihydrate is about three times greater than for KDP [deff ~3deff(KDP)].