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The title compounds are proton-transfer compounds of cytosine with nicotinic acid [systematic name: 4-amino-2-oxo-2,3-dihydropyrimidin-1-ium nicotinate monohydrate (cytosinium nicotinate hydrate), C
4H
6N
3O
+·C
6H
4NO
2-·H
2O, (I)] and isonicotinic acid [systematic name: 4-amino-2-oxo-2,3-dihydropyrimidin-1-ium isonicotinate-4-aminopyrimidin-2(1
H)-one-water (1/1/2) (cytosinium isonicotinate cytosine dihydrate), C
4H
6N
3O
+·C
6H
4NO
2-·C
4H
5N
3O·2H
2O, (II)]. In (I), the cation and anion are interlinked by N-H
O hydrogen bonding to form a one-dimensional tape. These tapes are linked through water molecules to form discrete double sheets. In (II), the cytosinium-cytosine base pairs are connected by triple hydrogen bonds, leading to one-dimensional polymeric ribbons. These ribbons are further interconnected
via nicotinate-water and water-water hydrogen bonding, resulting in an overall three-dimensional network.
Supporting information
CCDC references: 790647; 790648
To obtain crystals of (I) suitable for X-ray study, cytosine (0.111 g, 1 mmol)
and nicotinic acid (0.123 g, 1 mmol) were dissolved in water (10 ml) and the
solution was allowed to evaporate slowly. Crystals of (II) were obtained by
slow evaporation of an equimolar solution of cytosine (0.111 g, 1 mmol) and
isonicotinic acid (0.123 g, 1 mmol) in water (25 ml).
All N- and O-bound H atoms were located in a difference Fourier map and their
positions and isotropic displacement parameters were refined. All other H
atoms were located in a difference electron-density map but were positioned
geometrically and included as riding atoms, with C—H = 0.93–0.97 Å and
with Uiso(H) = 1.2Ueq(C).
For both compounds, data collection: SMART (Bruker, 2001); cell refinement: SAINT (Bruker, 2001); data reduction: SAINT (Bruker, 2001); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: DIAMOND (Brandenburg & Putz, 2005); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008).
(I) 4-amino-2-oxo-2,3-dihydropyrimidin-1-ium nicotinate monohydrate
top
Crystal data top
C4H6N3O+·C6H4NO2−·H2O | F(000) = 528 |
Mr = 252.24 | Dx = 1.492 Mg m−3 |
Monoclinic, P21/n | Mo Kα radiation, λ = 0.71073 Å |
Hall symbol: -P 2yn | Cell parameters from 6759 reflections |
a = 7.5314 (5) Å | θ = 2.7–27.9° |
b = 18.2710 (12) Å | µ = 0.12 mm−1 |
c = 8.4249 (6) Å | T = 294 K |
β = 104.374 (1)° | Block, colourless |
V = 1123.03 (13) Å3 | 0.15 × 0.11 × 0.07 mm |
Z = 4 | |
Data collection top
Bruker SMART APEX CCD area-detector diffractometer | 1794 reflections with I > 2σ(I) |
Radiation source: fine-focus sealed tube | Rint = 0.022 |
Graphite monochromator | θmax = 25.0°, θmin = 2.2° |
ω scans | h = −8→8 |
10476 measured reflections | k = −21→21 |
1969 independent reflections | l = −10→10 |
Refinement top
Refinement on F2 | Primary atom site location: structure-invariant direct methods |
Least-squares matrix: full | Secondary atom site location: difference Fourier map |
R[F2 > 2σ(F2)] = 0.037 | Hydrogen site location: inferred from neighbouring sites |
wR(F2) = 0.107 | H atoms treated by a mixture of independent and constrained refinement |
S = 1.06 | w = 1/[σ2(Fo2) + (0.0769P)2 + 0.0889P] where P = (Fo2 + 2Fc2)/3 |
1969 reflections | (Δ/σ)max < 0.001 |
187 parameters | Δρmax = 0.23 e Å−3 |
0 restraints | Δρmin = −0.21 e Å−3 |
Crystal data top
C4H6N3O+·C6H4NO2−·H2O | V = 1123.03 (13) Å3 |
Mr = 252.24 | Z = 4 |
Monoclinic, P21/n | Mo Kα radiation |
a = 7.5314 (5) Å | µ = 0.12 mm−1 |
b = 18.2710 (12) Å | T = 294 K |
c = 8.4249 (6) Å | 0.15 × 0.11 × 0.07 mm |
β = 104.374 (1)° | |
Data collection top
Bruker SMART APEX CCD area-detector diffractometer | 1794 reflections with I > 2σ(I) |
10476 measured reflections | Rint = 0.022 |
1969 independent reflections | |
Refinement top
R[F2 > 2σ(F2)] = 0.037 | 0 restraints |
wR(F2) = 0.107 | H atoms treated by a mixture of independent and constrained refinement |
S = 1.06 | Δρmax = 0.23 e Å−3 |
1969 reflections | Δρmin = −0.21 e Å−3 |
187 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. |
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top | x | y | z | Uiso*/Ueq | |
C2 | 0.42848 (16) | 0.34241 (7) | 0.60189 (15) | 0.0402 (3) | |
C4 | 0.25411 (15) | 0.44944 (7) | 0.49022 (13) | 0.0335 (3) | |
C5 | 0.13659 (17) | 0.40495 (7) | 0.37004 (14) | 0.0402 (3) | |
H5 | 0.0427 | 0.4256 | 0.2895 | 0.048* | |
C6 | 0.16488 (17) | 0.33262 (7) | 0.37604 (15) | 0.0422 (3) | |
H6 | 0.0865 | 0.3027 | 0.3006 | 0.051* | |
O8 | 0.56102 (13) | 0.31600 (5) | 0.69821 (13) | 0.0571 (3) | |
N1 | 0.30523 (15) | 0.30163 (6) | 0.48947 (13) | 0.0435 (3) | |
H1N | 0.317 (2) | 0.2533 (9) | 0.5020 (18) | 0.052 (4)* | |
N3 | 0.39306 (13) | 0.41612 (5) | 0.59947 (12) | 0.0359 (3) | |
H3N | 0.465 (2) | 0.4454 (9) | 0.683 (2) | 0.058 (4)* | |
N7 | 0.23398 (15) | 0.52003 (6) | 0.49988 (13) | 0.0403 (3) | |
H7N | 0.307 (2) | 0.5457 (8) | 0.5842 (19) | 0.048 (4)* | |
H8N | 0.152 (2) | 0.5418 (9) | 0.420 (2) | 0.052 (4)* | |
C11 | 0.58049 (16) | 0.55854 (6) | 0.85746 (13) | 0.0377 (3) | |
C12 | 0.71295 (15) | 0.59760 (7) | 0.99494 (13) | 0.0352 (3) | |
C13 | 0.71106 (18) | 0.67267 (7) | 1.01279 (16) | 0.0452 (3) | |
H13 | 0.6232 | 0.7007 | 0.9415 | 0.054* | |
C14 | 0.84032 (19) | 0.70584 (7) | 1.13708 (16) | 0.0484 (3) | |
H14 | 0.8426 | 0.7564 | 1.1497 | 0.058* | |
C15 | 0.96546 (17) | 0.66225 (7) | 1.24170 (15) | 0.0443 (3) | |
H15 | 1.0527 | 0.6847 | 1.3252 | 0.053* | |
C17 | 0.84512 (17) | 0.55875 (7) | 1.10708 (14) | 0.0390 (3) | |
H17 | 0.8479 | 0.5082 | 1.0960 | 0.047* | |
O9 | 0.61019 (12) | 0.49233 (5) | 0.83824 (10) | 0.0473 (3) | |
O10 | 0.45125 (13) | 0.59542 (5) | 0.77074 (11) | 0.0509 (3) | |
N16 | 0.96848 (14) | 0.58962 (6) | 1.22986 (13) | 0.0431 (3) | |
O1W | 0.79082 (14) | 0.35208 (6) | 1.04537 (14) | 0.0527 (3) | |
H1W | 0.713 (3) | 0.3640 (10) | 1.104 (2) | 0.065 (5)* | |
H2W | 0.749 (3) | 0.3737 (13) | 0.960 (3) | 0.087 (7)* | |
Atomic displacement parameters (Å2) top | U11 | U22 | U33 | U12 | U13 | U23 |
C2 | 0.0415 (6) | 0.0362 (6) | 0.0397 (6) | 0.0028 (5) | 0.0039 (5) | 0.0031 (5) |
C4 | 0.0334 (5) | 0.0352 (6) | 0.0292 (5) | 0.0003 (4) | 0.0029 (4) | 0.0006 (4) |
C5 | 0.0389 (6) | 0.0429 (7) | 0.0327 (6) | −0.0004 (5) | −0.0029 (5) | −0.0017 (5) |
C6 | 0.0431 (7) | 0.0417 (7) | 0.0377 (6) | −0.0063 (5) | 0.0021 (5) | −0.0068 (5) |
O8 | 0.0536 (6) | 0.0424 (5) | 0.0620 (6) | 0.0101 (4) | −0.0107 (5) | 0.0065 (4) |
N1 | 0.0495 (6) | 0.0310 (6) | 0.0463 (6) | 0.0000 (4) | 0.0046 (5) | −0.0021 (4) |
N3 | 0.0347 (5) | 0.0355 (5) | 0.0319 (5) | 0.0007 (4) | −0.0024 (4) | −0.0005 (4) |
N7 | 0.0417 (6) | 0.0343 (6) | 0.0360 (5) | 0.0030 (4) | −0.0073 (5) | −0.0005 (4) |
C11 | 0.0383 (6) | 0.0413 (6) | 0.0292 (6) | −0.0012 (5) | 0.0003 (5) | −0.0017 (5) |
C12 | 0.0370 (6) | 0.0368 (7) | 0.0287 (6) | −0.0020 (4) | 0.0024 (5) | −0.0011 (4) |
C13 | 0.0504 (7) | 0.0362 (7) | 0.0411 (7) | 0.0032 (5) | −0.0040 (5) | 0.0033 (5) |
C14 | 0.0582 (8) | 0.0317 (6) | 0.0504 (7) | −0.0046 (5) | 0.0041 (6) | −0.0046 (5) |
C15 | 0.0433 (7) | 0.0449 (7) | 0.0387 (7) | −0.0092 (5) | −0.0014 (5) | −0.0080 (5) |
C17 | 0.0419 (6) | 0.0336 (6) | 0.0357 (6) | −0.0001 (5) | −0.0012 (5) | −0.0016 (4) |
O9 | 0.0500 (5) | 0.0409 (5) | 0.0413 (5) | −0.0006 (4) | −0.0071 (4) | −0.0090 (4) |
O10 | 0.0490 (5) | 0.0515 (6) | 0.0401 (5) | 0.0059 (4) | −0.0117 (4) | −0.0054 (4) |
N16 | 0.0416 (6) | 0.0420 (6) | 0.0378 (6) | −0.0015 (4) | −0.0054 (4) | −0.0023 (4) |
O1W | 0.0550 (6) | 0.0463 (6) | 0.0507 (6) | 0.0100 (4) | 0.0016 (5) | 0.0014 (4) |
Geometric parameters (Å, º) top
C2—O8 | 1.2189 (15) | C11—O10 | 1.2578 (14) |
C2—N1 | 1.3702 (16) | C11—C12 | 1.5074 (15) |
C2—N3 | 1.3720 (16) | C12—C13 | 1.3802 (18) |
C4—N7 | 1.3036 (16) | C12—C17 | 1.3857 (16) |
C4—N3 | 1.3545 (15) | C13—C14 | 1.3804 (18) |
C4—C5 | 1.4228 (16) | C13—H13 | 0.9300 |
C5—C6 | 1.3375 (18) | C14—C15 | 1.3737 (19) |
C5—H5 | 0.9300 | C14—H14 | 0.9300 |
C6—N1 | 1.3600 (16) | C15—N16 | 1.3315 (17) |
C6—H6 | 0.9300 | C15—H15 | 0.9300 |
N1—H1N | 0.890 (17) | C17—N16 | 1.3320 (16) |
N3—H3N | 0.940 (18) | C17—H17 | 0.9300 |
N7—H7N | 0.912 (17) | O1W—H1W | 0.88 (2) |
N7—H8N | 0.888 (17) | O1W—H2W | 0.81 (3) |
C11—O9 | 1.2481 (15) | | |
| | | |
O8—C2—N1 | 123.17 (12) | O9—C11—O10 | 125.56 (10) |
O8—C2—N3 | 121.51 (11) | O9—C11—C12 | 116.92 (10) |
N1—C2—N3 | 115.32 (10) | O10—C11—C12 | 117.51 (10) |
N7—C4—N3 | 118.98 (10) | C13—C12—C17 | 117.37 (11) |
N7—C4—C5 | 123.25 (11) | C13—C12—C11 | 122.09 (10) |
N3—C4—C5 | 117.77 (11) | C17—C12—C11 | 120.52 (11) |
C6—C5—C4 | 118.20 (11) | C12—C13—C14 | 119.64 (11) |
C6—C5—H5 | 120.9 | C12—C13—H13 | 120.2 |
C4—C5—H5 | 120.9 | C14—C13—H13 | 120.2 |
C5—C6—N1 | 121.78 (11) | C15—C14—C13 | 118.33 (11) |
C5—C6—H6 | 119.1 | C15—C14—H14 | 120.8 |
N1—C6—H6 | 119.1 | C13—C14—H14 | 120.8 |
C6—N1—C2 | 122.29 (11) | N16—C15—C14 | 123.47 (11) |
C6—N1—H1N | 122.2 (10) | N16—C15—H15 | 118.3 |
C2—N1—H1N | 115.3 (10) | C14—C15—H15 | 118.3 |
C4—N3—C2 | 124.46 (10) | N16—C17—C12 | 123.86 (11) |
C4—N3—H3N | 117.1 (10) | N16—C17—H17 | 118.1 |
C2—N3—H3N | 118.3 (10) | C12—C17—H17 | 118.1 |
C4—N7—H7N | 120.1 (10) | C15—N16—C17 | 117.30 (10) |
C4—N7—H8N | 117.8 (10) | H1W—O1W—H2W | 101.9 (19) |
H7N—N7—H8N | 122.0 (15) | | |
| | | |
N7—C4—C5—C6 | −177.03 (12) | O10—C11—C12—C13 | −9.14 (17) |
N3—C4—C5—C6 | 2.85 (16) | O9—C11—C12—C17 | −8.61 (16) |
C4—C5—C6—N1 | −2.22 (18) | O10—C11—C12—C17 | 172.28 (11) |
C5—C6—N1—C2 | −1.52 (19) | C17—C12—C13—C14 | 1.23 (18) |
O8—C2—N1—C6 | −175.66 (12) | C11—C12—C13—C14 | −177.39 (12) |
N3—C2—N1—C6 | 4.34 (17) | C12—C13—C14—C15 | −1.3 (2) |
N7—C4—N3—C2 | −179.95 (11) | C13—C14—C15—N16 | −0.2 (2) |
C5—C4—N3—C2 | 0.17 (16) | C13—C12—C17—N16 | 0.20 (18) |
O8—C2—N3—C4 | 176.34 (11) | C11—C12—C17—N16 | 178.84 (11) |
N1—C2—N3—C4 | −3.66 (16) | C14—C15—N16—C17 | 1.54 (19) |
O9—C11—C12—C13 | 169.96 (12) | C12—C17—N16—C15 | −1.56 (19) |
Hydrogen-bond geometry (Å, º) top
D—H···A | D—H | H···A | D···A | D—H···A |
N1—H1N···O1Wi | 0.89 (2) | 1.98 (2) | 2.854 (2) | 167 (1) |
N3—H3N···O9 | 0.94 (2) | 1.71 (2) | 2.651 (1) | 175 (2) |
N7—H7N···O10 | 0.91 (2) | 1.91 (2) | 2.816 (1) | 176 (1) |
N7—H8N···N16ii | 0.89 (2) | 2.03 (2) | 2.921 (1) | 178 (1) |
O1W—H1W···O10iii | 0.88 (2) | 1.96 (2) | 2.837 (2) | 172 (2) |
O1W—H2W···O9 | 0.81 (3) | 2.51 (2) | 3.207 (1) | 144 (2) |
O1W—H2W···O8 | 0.81 (3) | 2.54 (2) | 3.078 (2) | 125 (2) |
Symmetry codes: (i) x−1/2, −y+1/2, z−1/2; (ii) x−1, y, z−1; (iii) −x+1, −y+1, −z+2. |
(II) 4-amino-2-oxo-2,3-dihydropyrimidin-1-ium
isonicotinate–4-aminopyrimidin-2(1
H)-one–water (1/1/2)
top
Crystal data top
C4H6N3O+·C6H4NO2−·C4H5N3O·2H2O | Z = 2 |
Mr = 381.36 | F(000) = 400 |
Triclinic, P1 | Dx = 1.448 Mg m−3 |
Hall symbol: -P 1 | Mo Kα radiation, λ = 0.71073 Å |
a = 7.1852 (8) Å | Cell parameters from 4610 reflections |
b = 7.3627 (8) Å | θ = 2.3–28.0° |
c = 17.7387 (18) Å | µ = 0.12 mm−1 |
α = 99.831 (2)° | T = 294 K |
β = 92.928 (2)° | Block, colourless |
γ = 107.862 (2)° | 0.18 × 0.15 × 0.12 mm |
V = 874.70 (16) Å3 | |
Data collection top
Bruker SMART APEX CCD area-detector diffractometer | 2751 reflections with I > 2σ(I) |
Radiation source: fine-focus sealed tube | Rint = 0.017 |
Graphite monochromator | θmax = 25.0°, θmin = 1.2° |
ω scans | h = −8→8 |
8483 measured reflections | k = −8→8 |
3083 independent reflections | l = −21→21 |
Refinement top
Refinement on F2 | Primary atom site location: structure-invariant direct methods |
Least-squares matrix: full | Secondary atom site location: difference Fourier map |
R[F2 > 2σ(F2)] = 0.041 | Hydrogen site location: inferred from neighbouring sites |
wR(F2) = 0.130 | H atoms treated by a mixture of independent and constrained refinement |
S = 1.10 | w = 1/[σ2(Fo2) + (0.0807P)2 + 0.1079P] where P = (Fo2 + 2Fc2)/3 |
3083 reflections | (Δ/σ)max < 0.001 |
288 parameters | Δρmax = 0.24 e Å−3 |
0 restraints | Δρmin = −0.35 e Å−3 |
Crystal data top
C4H6N3O+·C6H4NO2−·C4H5N3O·2H2O | γ = 107.862 (2)° |
Mr = 381.36 | V = 874.70 (16) Å3 |
Triclinic, P1 | Z = 2 |
a = 7.1852 (8) Å | Mo Kα radiation |
b = 7.3627 (8) Å | µ = 0.12 mm−1 |
c = 17.7387 (18) Å | T = 294 K |
α = 99.831 (2)° | 0.18 × 0.15 × 0.12 mm |
β = 92.928 (2)° | |
Data collection top
Bruker SMART APEX CCD area-detector diffractometer | 2751 reflections with I > 2σ(I) |
8483 measured reflections | Rint = 0.017 |
3083 independent reflections | |
Refinement top
R[F2 > 2σ(F2)] = 0.041 | 0 restraints |
wR(F2) = 0.130 | H atoms treated by a mixture of independent and constrained refinement |
S = 1.10 | Δρmax = 0.24 e Å−3 |
3083 reflections | Δρmin = −0.35 e Å−3 |
288 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. |
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top | x | y | z | Uiso*/Ueq | |
C2A | 0.6069 (2) | 1.2108 (2) | 0.38576 (8) | 0.0374 (3) | |
C4A | 0.6144 (2) | 0.8963 (2) | 0.38975 (8) | 0.0368 (3) | |
C5A | 0.5315 (2) | 0.8287 (2) | 0.31191 (9) | 0.0436 (4) | |
H5A | 0.5058 | 0.6997 | 0.2877 | 0.052* | |
C6A | 0.4918 (2) | 0.9582 (2) | 0.27464 (9) | 0.0455 (4) | |
H6A | 0.4379 | 0.9190 | 0.2234 | 0.055* | |
N1A | 0.52901 (19) | 1.14623 (18) | 0.31048 (7) | 0.0430 (3) | |
H1A | 0.488 (3) | 1.227 (3) | 0.2820 (12) | 0.062 (5)* | |
N3A | 0.65268 (18) | 1.08314 (16) | 0.42440 (7) | 0.0381 (3) | |
N7A | 0.6549 (2) | 0.7774 (2) | 0.43129 (9) | 0.0464 (3) | |
H7A | 0.630 (3) | 0.654 (3) | 0.4127 (11) | 0.056 (5)* | |
H8A | 0.710 (3) | 0.829 (3) | 0.4807 (12) | 0.056 (5)* | |
O8A | 0.63483 (17) | 1.38231 (15) | 0.41713 (6) | 0.0506 (3) | |
C2B | 0.8936 (2) | 1.1051 (2) | 0.61533 (8) | 0.0366 (3) | |
C4B | 0.8905 (2) | 1.4256 (2) | 0.60700 (8) | 0.0374 (3) | |
C5B | 0.9878 (2) | 1.4965 (2) | 0.68276 (9) | 0.0445 (4) | |
H5B | 1.0222 | 1.6275 | 0.7055 | 0.053* | |
C6B | 1.0286 (2) | 1.3683 (2) | 0.72048 (9) | 0.0449 (4) | |
H6B | 1.0910 | 1.4117 | 0.7705 | 0.054* | |
N1B | 0.98202 (19) | 1.17733 (18) | 0.68825 (7) | 0.0413 (3) | |
H1B | 1.001 (3) | 1.087 (3) | 0.7188 (12) | 0.073 (6)* | |
N3B | 0.85146 (18) | 1.23564 (16) | 0.57567 (7) | 0.0371 (3) | |
H3B | 0.779 (3) | 1.186 (3) | 0.5237 (13) | 0.075 (6)* | |
N7B | 0.8358 (2) | 1.5361 (2) | 0.56600 (8) | 0.0487 (4) | |
H7B | 0.853 (3) | 1.661 (3) | 0.5842 (12) | 0.065 (6)* | |
H8B | 0.768 (3) | 1.478 (3) | 0.5185 (12) | 0.056 (5)* | |
O8B | 0.85081 (17) | 0.93212 (14) | 0.58537 (6) | 0.0485 (3) | |
C11 | 1.1259 (2) | 1.0564 (2) | 0.84675 (9) | 0.0430 (4) | |
C12 | 1.1685 (2) | 0.9584 (2) | 0.91075 (8) | 0.0422 (4) | |
C13 | 1.2473 (2) | 1.0642 (2) | 0.98333 (9) | 0.0467 (4) | |
H13 | 1.2762 | 1.1987 | 0.9942 | 0.056* | |
C14 | 1.2823 (3) | 0.9665 (3) | 1.03958 (10) | 0.0543 (4) | |
H14 | 1.3330 | 1.0389 | 1.0887 | 0.065* | |
C16 | 1.1728 (3) | 0.6753 (3) | 0.95761 (11) | 0.0685 (5) | |
H16 | 1.1482 | 0.5414 | 0.9478 | 0.082* | |
C17 | 1.1297 (3) | 0.7603 (3) | 0.89875 (10) | 0.0614 (5) | |
H17 | 1.0742 | 0.6837 | 0.8508 | 0.074* | |
N15 | 1.2479 (2) | 0.7755 (2) | 1.02790 (9) | 0.0603 (4) | |
O9 | 1.02491 (18) | 0.94678 (16) | 0.78613 (6) | 0.0559 (3) | |
O10 | 1.19248 (19) | 1.23543 (16) | 0.85658 (7) | 0.0599 (4) | |
O1W | 0.3493 (2) | 1.3221 (2) | 0.21982 (8) | 0.0640 (4) | |
H1W | 0.231 (4) | 1.243 (4) | 0.2141 (13) | 0.089 (8)* | |
H2W | 0.358 (3) | 1.399 (4) | 0.1864 (14) | 0.086 (7)* | |
O2W | 0.4076 (3) | 1.5630 (3) | 0.11872 (11) | 0.0930 (6) | |
H3W | 0.525 (4) | 1.618 (4) | 0.1211 (14) | 0.090 (8)* | |
H4W | 0.350 (4) | 1.620 (4) | 0.0942 (16) | 0.103 (9)* | |
Atomic displacement parameters (Å2) top | U11 | U22 | U33 | U12 | U13 | U23 |
C2A | 0.0442 (8) | 0.0295 (7) | 0.0400 (8) | 0.0133 (6) | 0.0009 (6) | 0.0087 (6) |
C4A | 0.0398 (7) | 0.0304 (7) | 0.0420 (8) | 0.0135 (6) | 0.0040 (6) | 0.0075 (6) |
C5A | 0.0509 (8) | 0.0342 (8) | 0.0432 (8) | 0.0144 (6) | 0.0018 (6) | 0.0006 (6) |
C6A | 0.0523 (9) | 0.0461 (9) | 0.0359 (8) | 0.0155 (7) | −0.0006 (6) | 0.0045 (6) |
N1A | 0.0531 (7) | 0.0381 (7) | 0.0403 (7) | 0.0171 (6) | −0.0017 (5) | 0.0115 (5) |
N3A | 0.0473 (7) | 0.0274 (6) | 0.0408 (7) | 0.0147 (5) | −0.0012 (5) | 0.0068 (5) |
N7A | 0.0667 (9) | 0.0271 (7) | 0.0471 (8) | 0.0195 (6) | −0.0033 (6) | 0.0060 (6) |
O8A | 0.0725 (8) | 0.0289 (6) | 0.0515 (6) | 0.0204 (5) | −0.0073 (5) | 0.0078 (5) |
C2B | 0.0421 (7) | 0.0286 (7) | 0.0407 (7) | 0.0135 (6) | 0.0029 (6) | 0.0076 (6) |
C4B | 0.0431 (7) | 0.0284 (7) | 0.0420 (8) | 0.0129 (6) | 0.0046 (6) | 0.0075 (6) |
C5B | 0.0554 (9) | 0.0318 (8) | 0.0417 (8) | 0.0113 (6) | −0.0004 (7) | 0.0014 (6) |
C6B | 0.0560 (9) | 0.0380 (8) | 0.0377 (8) | 0.0142 (7) | −0.0031 (6) | 0.0037 (6) |
N1B | 0.0507 (7) | 0.0357 (7) | 0.0391 (7) | 0.0161 (5) | −0.0005 (5) | 0.0093 (5) |
N3B | 0.0473 (7) | 0.0277 (6) | 0.0380 (7) | 0.0150 (5) | −0.0002 (5) | 0.0072 (5) |
N7B | 0.0710 (9) | 0.0290 (7) | 0.0472 (8) | 0.0210 (6) | −0.0083 (7) | 0.0053 (6) |
O8B | 0.0699 (7) | 0.0269 (6) | 0.0483 (6) | 0.0181 (5) | −0.0080 (5) | 0.0062 (4) |
C11 | 0.0448 (8) | 0.0424 (9) | 0.0417 (8) | 0.0126 (7) | 0.0002 (6) | 0.0114 (6) |
C12 | 0.0434 (8) | 0.0445 (8) | 0.0400 (8) | 0.0152 (6) | 0.0019 (6) | 0.0102 (6) |
C13 | 0.0499 (9) | 0.0475 (9) | 0.0429 (8) | 0.0173 (7) | 0.0019 (7) | 0.0076 (7) |
C14 | 0.0565 (10) | 0.0707 (12) | 0.0376 (8) | 0.0232 (8) | 0.0001 (7) | 0.0120 (8) |
C16 | 0.0960 (15) | 0.0519 (11) | 0.0616 (12) | 0.0276 (10) | −0.0042 (10) | 0.0186 (9) |
C17 | 0.0907 (13) | 0.0455 (10) | 0.0466 (9) | 0.0240 (9) | −0.0080 (9) | 0.0061 (7) |
N15 | 0.0663 (9) | 0.0683 (10) | 0.0552 (9) | 0.0262 (8) | 0.0036 (7) | 0.0282 (8) |
O9 | 0.0707 (8) | 0.0457 (7) | 0.0427 (6) | 0.0071 (5) | −0.0109 (5) | 0.0123 (5) |
O10 | 0.0734 (8) | 0.0412 (7) | 0.0593 (7) | 0.0114 (6) | −0.0146 (6) | 0.0139 (5) |
O1W | 0.0635 (8) | 0.0620 (8) | 0.0665 (8) | 0.0133 (7) | −0.0118 (6) | 0.0312 (7) |
O2W | 0.0721 (11) | 0.0938 (12) | 0.1095 (13) | −0.0005 (9) | −0.0195 (9) | 0.0691 (11) |
Geometric parameters (Å, º) top
C2A—O8A | 1.2399 (17) | C6B—H6B | 0.9300 |
C2A—N3A | 1.3596 (18) | N1B—H1B | 0.96 (2) |
C2A—N1A | 1.3661 (19) | N3B—H3B | 0.99 (2) |
C4A—N7A | 1.3223 (19) | N7B—H7B | 0.89 (2) |
C4A—N3A | 1.3444 (18) | N7B—H8B | 0.92 (2) |
C4A—C5A | 1.417 (2) | C11—O10 | 1.2340 (18) |
C5A—C6A | 1.338 (2) | C11—O9 | 1.2645 (18) |
C5A—H5A | 0.9300 | C11—C12 | 1.511 (2) |
C6A—N1A | 1.359 (2) | C12—C17 | 1.374 (2) |
C6A—H6A | 0.9300 | C12—C13 | 1.377 (2) |
N1A—H1A | 0.94 (2) | C13—C14 | 1.381 (2) |
N7A—H7A | 0.87 (2) | C13—H13 | 0.9300 |
N7A—H8A | 0.91 (2) | C14—N15 | 1.328 (2) |
C2B—O8B | 1.2292 (17) | C14—H14 | 0.9300 |
C2B—N1B | 1.3539 (19) | C16—N15 | 1.328 (3) |
C2B—N3B | 1.3778 (18) | C16—C17 | 1.373 (3) |
C4B—N7B | 1.3092 (19) | C16—H16 | 0.9300 |
C4B—N3B | 1.3498 (18) | C17—H17 | 0.9300 |
C4B—C5B | 1.417 (2) | O1W—H1W | 0.86 (3) |
C5B—C6B | 1.338 (2) | O1W—H2W | 0.88 (3) |
C5B—H5B | 0.9300 | O2W—H3W | 0.81 (3) |
C6B—N1B | 1.3536 (19) | O2W—H4W | 0.83 (3) |
| | | |
O8A—C2A—N3A | 121.62 (13) | C6B—N1B—C2B | 121.89 (12) |
O8A—C2A—N1A | 120.01 (12) | C6B—N1B—H1B | 119.8 (12) |
N3A—C2A—N1A | 118.36 (12) | C2B—N1B—H1B | 118.0 (13) |
N7A—C4A—N3A | 117.50 (13) | C4B—N3B—C2B | 122.94 (12) |
N7A—C4A—C5A | 121.21 (13) | C4B—N3B—H3B | 118.4 (12) |
N3A—C4A—C5A | 121.28 (13) | C2B—N3B—H3B | 118.4 (12) |
C6A—C5A—C4A | 117.20 (13) | C4B—N7B—H7B | 122.3 (13) |
C6A—C5A—H5A | 121.4 | C4B—N7B—H8B | 117.5 (12) |
C4A—C5A—H5A | 121.4 | H7B—N7B—H8B | 120.0 (18) |
C5A—C6A—N1A | 121.03 (14) | O10—C11—O9 | 124.69 (14) |
C5A—C6A—H6A | 119.5 | O10—C11—C12 | 118.49 (13) |
N1A—C6A—H6A | 119.5 | O9—C11—C12 | 116.82 (13) |
C6A—N1A—C2A | 121.74 (13) | C17—C12—C13 | 117.54 (15) |
C6A—N1A—H1A | 116.5 (12) | C17—C12—C11 | 121.24 (14) |
C2A—N1A—H1A | 121.6 (12) | C13—C12—C11 | 121.22 (14) |
C4A—N3A—C2A | 120.33 (12) | C12—C13—C14 | 118.62 (16) |
C4A—N7A—H7A | 122.1 (12) | C12—C13—H13 | 120.7 |
C4A—N7A—H8A | 117.7 (11) | C14—C13—H13 | 120.7 |
H7A—N7A—H8A | 120.1 (17) | N15—C14—C13 | 124.02 (16) |
O8B—C2B—N1B | 122.52 (13) | N15—C14—H14 | 118.0 |
O8B—C2B—N3B | 120.90 (13) | C13—C14—H14 | 118.0 |
N1B—C2B—N3B | 116.57 (12) | N15—C16—C17 | 123.02 (18) |
N7B—C4B—N3B | 118.39 (13) | N15—C16—H16 | 118.5 |
N7B—C4B—C5B | 122.91 (14) | C17—C16—H16 | 118.5 |
N3B—C4B—C5B | 118.69 (13) | C16—C17—C12 | 120.02 (17) |
C6B—C5B—C4B | 117.66 (14) | C16—C17—H17 | 120.0 |
C6B—C5B—H5B | 121.2 | C12—C17—H17 | 120.0 |
C4B—C5B—H5B | 121.2 | C14—N15—C16 | 116.75 (15) |
C5B—C6B—N1B | 122.17 (14) | H1W—O1W—H2W | 108 (2) |
C5B—C6B—H6B | 118.9 | H3W—O2W—H4W | 108 (3) |
N1B—C6B—H6B | 118.9 | | |
| | | |
N7A—C4A—C5A—C6A | 178.76 (14) | N7B—C4B—N3B—C2B | −176.57 (13) |
N3A—C4A—C5A—C6A | −0.5 (2) | C5B—C4B—N3B—C2B | 3.2 (2) |
C4A—C5A—C6A—N1A | −0.3 (2) | O8B—C2B—N3B—C4B | 177.98 (13) |
C5A—C6A—N1A—C2A | −0.4 (2) | N1B—C2B—N3B—C4B | −1.5 (2) |
O8A—C2A—N1A—C6A | −178.38 (14) | O10—C11—C12—C17 | −168.25 (17) |
N3A—C2A—N1A—C6A | 1.9 (2) | O9—C11—C12—C17 | 11.1 (2) |
N7A—C4A—N3A—C2A | −177.30 (13) | O10—C11—C12—C13 | 11.9 (2) |
C5A—C4A—N3A—C2A | 2.0 (2) | O9—C11—C12—C13 | −168.74 (15) |
O8A—C2A—N3A—C4A | 177.65 (13) | C17—C12—C13—C14 | −0.1 (2) |
N1A—C2A—N3A—C4A | −2.6 (2) | C11—C12—C13—C14 | 179.74 (14) |
N7B—C4B—C5B—C6B | 176.98 (15) | C12—C13—C14—N15 | 1.2 (3) |
N3B—C4B—C5B—C6B | −2.8 (2) | N15—C16—C17—C12 | 1.6 (3) |
C4B—C5B—C6B—N1B | 0.8 (2) | C13—C12—C17—C16 | −1.2 (3) |
C5B—C6B—N1B—C2B | 1.0 (2) | C11—C12—C17—C16 | 178.95 (17) |
O8B—C2B—N1B—C6B | 179.91 (14) | C13—C14—N15—C16 | −0.9 (3) |
N3B—C2B—N1B—C6B | −0.6 (2) | C17—C16—N15—C14 | −0.5 (3) |
Hydrogen-bond geometry (Å, º) top
D—H···A | D—H | H···A | D···A | D—H···A |
N1A—H1A···O1W | 0.94 (2) | 1.81 (2) | 2.730 (2) | 164 (2) |
N7A—H7A···O8Ai | 0.87 (2) | 2.02 (2) | 2.835 (2) | 154 (2) |
N7A—H8A···O8B | 0.91 (2) | 1.98 (2) | 2.883 (2) | 175 (2) |
N1B—H1B···O9 | 0.96 (2) | 1.74 (2) | 2.695 (2) | 171 (2) |
N3B—H3B···N3A | 0.99 (2) | 1.86 (2) | 2.846 (2) | 176 (2) |
N7B—H7B···O8Bii | 0.89 (2) | 2.00 (2) | 2.845 (2) | 159 (2) |
N7B—H8B···O8A | 0.92 (2) | 1.90 (2) | 2.816 (2) | 174 (2) |
O1W—H1W···O9iii | 0.86 (3) | 1.94 (3) | 2.792 (2) | 172 (2) |
O1W—H2W···O2W | 0.88 (3) | 1.82 (3) | 2.691 (2) | 173 (2) |
O2W—H3W···O10iv | 0.81 (3) | 1.96 (3) | 2.772 (2) | 171 (2) |
O2W—H4W···N15v | 0.83 (3) | 2.03 (3) | 2.852 (2) | 171 (3) |
Symmetry codes: (i) x, y−1, z; (ii) x, y+1, z; (iii) −x+1, −y+2, −z+1; (iv) −x+2, −y+3, −z+1; (v) x−1, y+1, z−1. |
Experimental details
| (I) | (II) |
Crystal data |
Chemical formula | C4H6N3O+·C6H4NO2−·H2O | C4H6N3O+·C6H4NO2−·C4H5N3O·2H2O |
Mr | 252.24 | 381.36 |
Crystal system, space group | Monoclinic, P21/n | Triclinic, P1 |
Temperature (K) | 294 | 294 |
a, b, c (Å) | 7.5314 (5), 18.2710 (12), 8.4249 (6) | 7.1852 (8), 7.3627 (8), 17.7387 (18) |
α, β, γ (°) | 90, 104.374 (1), 90 | 99.831 (2), 92.928 (2), 107.862 (2) |
V (Å3) | 1123.03 (13) | 874.70 (16) |
Z | 4 | 2 |
Radiation type | Mo Kα | Mo Kα |
µ (mm−1) | 0.12 | 0.12 |
Crystal size (mm) | 0.15 × 0.11 × 0.07 | 0.18 × 0.15 × 0.12 |
|
Data collection |
Diffractometer | Bruker SMART APEX CCD area-detector diffractometer | Bruker SMART APEX CCD area-detector diffractometer |
Absorption correction | – | – |
No. of measured, independent and observed [I > 2σ(I)] reflections | 10476, 1969, 1794 | 8483, 3083, 2751 |
Rint | 0.022 | 0.017 |
(sin θ/λ)max (Å−1) | 0.594 | 0.595 |
|
Refinement |
R[F2 > 2σ(F2)], wR(F2), S | 0.037, 0.107, 1.06 | 0.041, 0.130, 1.10 |
No. of reflections | 1969 | 3083 |
No. of parameters | 187 | 288 |
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) | 0.23, −0.21 | 0.24, −0.35 |
Selected geometric parameters (Å, º) for (I) topC11—O9 | 1.2481 (15) | C11—O10 | 1.2578 (14) |
| | | |
C4—N3—C2 | 124.46 (10) | O9—C11—C12 | 116.92 (10) |
O9—C11—O10 | 125.56 (10) | O10—C11—C12 | 117.51 (10) |
Hydrogen-bond geometry (Å, º) for (I) top
D—H···A | D—H | H···A | D···A | D—H···A |
N1—H1N···O1Wi | 0.89 (2) | 1.98 (2) | 2.854 (2) | 167 (1) |
N3—H3N···O9 | 0.94 (2) | 1.71 (2) | 2.651 (1) | 175 (2) |
N7—H7N···O10 | 0.91 (2) | 1.91 (2) | 2.816 (1) | 176 (1) |
N7—H8N···N16ii | 0.89 (2) | 2.03 (2) | 2.921 (1) | 178 (1) |
O1W—H1W···O10iii | 0.88 (2) | 1.96 (2) | 2.837 (2) | 172 (2) |
O1W—H2W···O9 | 0.81 (3) | 2.51 (2) | 3.207 (1) | 144 (2) |
O1W—H2W···O8 | 0.81 (3) | 2.54 (2) | 3.078 (2) | 125 (2) |
Symmetry codes: (i) x−1/2, −y+1/2, z−1/2; (ii) x−1, y, z−1; (iii) −x+1, −y+1, −z+2. |
Selected geometric parameters (Å, º) for (II) topC11—O10 | 1.2340 (18) | C11—O9 | 1.2645 (18) |
| | | |
C4A—N3A—C2A | 120.33 (12) | O10—C11—C12 | 118.49 (13) |
C4B—N3B—C2B | 122.94 (12) | O9—C11—C12 | 116.82 (13) |
O10—C11—O9 | 124.69 (14) | | |
Hydrogen-bond geometry (Å, º) for (II) top
D—H···A | D—H | H···A | D···A | D—H···A |
N1A—H1A···O1W | 0.94 (2) | 1.81 (2) | 2.730 (2) | 164 (2) |
N7A—H7A···O8Ai | 0.87 (2) | 2.02 (2) | 2.835 (2) | 154 (2) |
N7A—H8A···O8B | 0.91 (2) | 1.98 (2) | 2.883 (2) | 175 (2) |
N1B—H1B···O9 | 0.96 (2) | 1.74 (2) | 2.695 (2) | 171 (2) |
N3B—H3B···N3A | 0.99 (2) | 1.86 (2) | 2.846 (2) | 176 (2) |
N7B—H7B···O8Bii | 0.89 (2) | 2.00 (2) | 2.845 (2) | 159 (2) |
N7B—H8B···O8A | 0.92 (2) | 1.90 (2) | 2.816 (2) | 174 (2) |
O1W—H1W···O9iii | 0.86 (3) | 1.94 (3) | 2.792 (2) | 172 (2) |
O1W—H2W···O2W | 0.88 (3) | 1.82 (3) | 2.691 (2) | 173 (2) |
O2W—H3W···O10iv | 0.81 (3) | 1.96 (3) | 2.772 (2) | 171 (2) |
O2W—H4W···N15v | 0.83 (3) | 2.03 (3) | 2.852 (2) | 171 (3) |
Symmetry codes: (i) x, y−1, z; (ii) x, y+1, z; (iii) −x+1, −y+2, −z+1; (iv) −x+2, −y+3, −z+1; (v) x−1, y+1, z−1. |
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Hydrogen-bonding interactions involving DNA nucleobases play an important role in DNA replication, gene expression and DNA repair. For example, enzymes that replicate or repair DNA often rely on hydrogen-bonding interactions between protein amino acid residues and DNA nucleobases. Understanding hydrogen-bonding interactions between DNA components and other molecules is vital to understanding the properties of DNA polymers and the mechanisms of biological processes. Cytosine is well known for its hydrogen-bonding capabilities in DNA and RNA, and several cytosine derivatives have been reported for use in biological applications (Blackburn & Gait, 1996; Kumar & Leonard, 1988) and in self-assembling triply hydrogen-bonded systems (Sessler & Jayawickramarajah, 2005). Isonicotinic and nicotinic acids play an important role in the metabolism of all living cells and they are positional isomers of pyridinecarboxylic acids. Nicotinic acid, also known as pyridine-3-carboxylic acid, is a member of the B-vitamin family. It is required by human cells for the synthesis of coenzymes and is involved in a wide range of biochemical processes. Nicotinic acid in pharmacological doses is used as an antihyperlipidaemic agent and reduces the level of cholesterol in the blood (Brutts & Lundholm, 1971). Continuing our studies of hydrogen-bond interactions and molecular recognition in the solid state (Sridhar & Ravikumar, 2007a,b, 2008, 2010; Sridhar et al., 2009), we present here the solid-state structures of two salts, namely cytosinium nicotinate hydrate, (I), and cytosinium isonicotinate cytosine dihydrate, (II).
Views of (I) and (II) are shown in Figs. 1 and 2, respectively. In (I), the asymmetric unit contains one cytosinium cation, one nicotinate anion and one water molecule. In (II), one cytosine molecule (suffix A), one cytosinium cation (suffix B), one isonicotinate anion and two water molecules constitute the asymmetric unit. In both structures, the cytosinium cations are protonated at N3, leading to an increase in the internal angles (see angles C2—N3—C4 in Tables 1 and 3) compared with the neutral cytosine molecule (C—N—C = 119.4°; McClure & Craven, 1973).
The C—O bond lengths (Table 1 and 3) of the carboxylic acid groups of both nicotinic and isonicotinic acids are closer to carboxylate bond lengths, where both C—O bond lengths are expected to be 1.255 (10) Å (Allen et al., 1995). In both structures, the carboxylate groups are twisted out of the plane of the benzene ring. Least-squares planes were calculated for the benzene rings and the planes of the respective COO fragments. The dihedral angles are 9.6 (1)° for (I) and 11.8 (1)° for (II).
In (I), N—H···O, N—H···N and O—H···O (Table 2) hydrogen bonds are observed. The water molecule plays a dual role as both donor and acceptor in the hydrogen-bonding interactions. It is involved in four hydrogen bonds, via water–cytosinium and water–anion interactions. The cytosinium cation and nicotinate anion are interlinked by two N—H···O hydrogen bonds and form an R22(8) motif (Etter, 1990; Etter et al., 1990; Bernstein et al., 1995). These cation–anion dimers are further connected by N—H···N hydrogen bonds, thereby generating an infinite one-dimensional tape along the crystallographic a axis (Fig. 3). One of the H atoms (H2W) of the water molecule further links each cation–anion dimer through a three-centred hydrogen bond (Jeffrey & Saenger, 1991) and forms an R22(6)-type motif, while the other H atom (H1W) of the water molecule links to the inversion-related cation–anion dimer, thereby forming a centrosymmetric hexamer which may be described in graph-set notation as R66(20). The R66(20) hexamers are further linked by the water molecules through N1—H1N···O1Wi (symmetry code given in Table 2) hydrogen bonds along the b axis. Thus, the combination of N—H···O, N—H···N and O—H···O hydrogen bonds leads to the formation of a supramolecular two-dimensional hydrogen-bonded network.
The cation–anion tapes of (I) are linked in pairs to form discrete double ribbons. These ribbons lie in the [101] plane but are not hydrogen-bonded together. Pairs of these planes are hydrogen-bonded together to form discrete double planes (Fig. 4), within which aromatic π stacking occurs [centroid-to-centroid separation 3.6353 (7) Å; symmetry code: 1 - x,1 - y,2 - z]. There are no significant interactions between adjacent double planes.
In (II), N—H···O, N—H···N, O—H···O and O—H···N hydrogen bonds (Table 4) are observed. Cytosinium cations are connected to neutral cytosine molecules via triple intramolecular N—H···O and N—H···N hydrogen bonds, to give rings with an R22(8) graph-set motif. This is a reversed Watson–Crick base pairing which occurs via triple hydrogen bonds between the cation protonated at N3 and the neutral cytosine molecule (Fig. 5). Adjacent cytosinium–cytosine base pairs are held together by two N—H···O hydrogen bonds between NH2 and carbonyl groups, leading to one-dimensional supramolecular polymeric ribbons along the crystallographic b axis. Similar triply hydrogen-bonded Watson–Crick base pairs are observed in cytosinium 4-nitrobenzoate cytosine monohydrate (Sridhar & Ravikumar, 2008), cytosine salicylic acid hydrate (2/3/2) complex (Sridhar & Ravikumar, 2010) and cytosine complexes with benzoic and phthalic acids (Perumalla et al., 2005).
In (II), atom N1A of the cytosine molecule forms an N—H···O hydrogen bond with water atom O1W, which in turn links to the second water molecule O2W, while atom N1B of the cytosinium cation links to the anion through an N—H···O hydrogen bond. The two water molecules are involved in five hydrogen bonds via water–cytosine, water–anion and water–water interactions. The water–water (O1W···O2W) chain links the anions into cyclic tetramer and hexamer hydrogen-bonded networks. First, the water molecules O2W form a cyclic tetramer containing an R44(18) motif, which is further linked by the O1W water molecules to form another hexameric [R66(22)] hydrogen-bonded network. Thus, the two water molecules and the anions form alternate hexamers [R66(22)] and tetramers [R44(18)] (Fig. 5).
In (II), the cytosine–cytosinium base pair ribbons along the b axis are connected to adjacent ribbons via a nicotinate–water hydrogen-bonded linkage to form a plane which is tilted by about 20° from the bc plane (Fig. 6). Adjacent layers are all hydrogen-bonded to each other to form a three-dimensional arrangement. This structure exhibits segregation of its molecular components.
By correlating the hydrogen-bonding pattern observed in the 2:1 structure of the present study with two of our previous structures (Sridhar & Ravikumar, 2008, 2010), as well as with structures reported in the literature (Perumalla et al., 2005), the existence of cytosine base-pair self-assembly with triple hydrogen-bonding patterns is predominant.