The isomers 3,3'-(1,2-ethynediyl)bis(2-pyridone), (I), and 6,6'-(1,2-ethynediyl)bis(2-pyridone), (II), were designed to form a hydrogen-bonded pair through alignment of their complementary cyclic lactam moieties. Instead, an equimolar mixture of (I) and (II) dissolved in methanol produced crystals of 3,3'-(1,2-ethynediyl)bis(2-pyridone)-6,6'-(1,2-ethynediyl)bis(2-pyridone)-methanol (1/2/2), 0.5C12H8N2O2·C12H8N2O2·CH4O, in which one molecule of (I), situated at a center of symmetry, is hydrogen bonded to two molecules of (II) and to two molecules of methanol.
Supporting information
CCDC reference: 162565
Dipyridone (II) was prepared according to the method outlined in Ducharme &
Wuest (1988), whereas the synthesis of (I) required more steps. In a strategy
similar to the synthesis of asymmetric dipyridone (III) described in the same
paper, dipyridone (I) was prepared by brominating commercially available
2-pyridone to give 3-bromo-2-pyridone, protecting the keto group by
benzylation to give 2-(benzyloxy)-3-bromopyridine, and coupling the latter
with (trimethylsilyl)-acetylene under conditions described by Takahashi et
al. (1980). Desilylation and coupling of the resulting alkyne with
2-(benzyloxy)-3-bromopyridine, and debenzylation with trifluoroacetic acid
gave (I).
The symmetric dipyridones (I) and (II) had very poor solubility in nonpolar
solvents such as CDCl3. Crystals were prepared by vapor diffusion of diethyl
ether into an equimolar solution of (I) and (II) in methanol.
The structure was solved in the space group P1. The center of symmetry was
readily located, and refinement continued in P1. Three reflections
(210, 200, and -211) were omitted from the refinement because their
intensities were too strong to be measured precisely. Hydrogen atoms were
constrained geometrically with bond distances C—H 0.93–0.96, N—H 0.86,
and O—H 0.82 Å, and Uiso equal to 1.2 times Ueq of the
attached atom. For methanol, the torsion angles determining the conformations
of the methyl and hydroxyl groups were refined.
Data collection: COLLECT (UCLA, 1984); cell refinement: LEAST (UCLA, 1984); data reduction: REDUCE (UCLA, 1984); program(s) used to solve structure: SHELXS86 (Sheldrick, 1990); program(s) used to refine structure: SHELXL93 (Sheldrick, 1993); molecular graphics: SHELXTL (Sheldrick, 1995); software used to prepare material for publication: SHELXTL.
3,3'-(1,2-Ethynediyl)bis-2(1
H)-pyridinone (I) and
6,6'-(1,2-Ethynediyl)bis-2(1
H)-pyridinone
top
Crystal data top
0.5C12H8N2O2·C12H8N2O2·CH4O | Z = 2 |
Mr = 350.35 | F(000) = 366 |
Triclinic, P1 | Dx = 1.407 Mg m−3 |
a = 7.334 (4) Å | Mo Kα radiation, λ = 0.71070 Å |
b = 10.791 (6) Å | Cell parameters from 25 reflections |
c = 11.543 (7) Å | θ = 4.9–10.3° |
α = 69.70 (2)° | µ = 0.10 mm−1 |
β = 75.01 (2)° | T = 156 K |
γ = 86.653 (15)° | Parallelepiped, colorless |
V = 827.2 (8) Å3 | 0.50 × 0.30 × 0.30 mm |
Data collection top
Picker Diffractometer (Crystal Logic) | Rint = 0.000 |
Radiation source: fine-focus sealed tube | θmax = 30.0°, θmin = 2.0° |
Graphite monochromator | h = −10→0 |
profile data from θ/2θ scans | k = −15→14 |
4819 measured reflections | l = −16→15 |
4819 independent reflections | 3 standard reflections every 97 reflections |
2561 reflections with I > 2σ(I) | intensity decay: 1.5% |
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)] = 0.051 | Hydrogen site location: inferred from neighbouring sites |
wR(F2) = 0.176 | H-atom parameters constrained |
S = 1.08 | Calculated w = 1/[σ2(Fo2) + (0.054P)2 + 0.4326P] where P = (Fo2 + 2Fc2)/3 |
4816 reflections | (Δ/σ)max = −0.002 |
237 parameters | Δρmax = 0.33 e Å−3 |
0 restraints | Δρmin = −0.35 e Å−3 |
Crystal data top
0.5C12H8N2O2·C12H8N2O2·CH4O | γ = 86.653 (15)° |
Mr = 350.35 | V = 827.2 (8) Å3 |
Triclinic, P1 | Z = 2 |
a = 7.334 (4) Å | Mo Kα radiation |
b = 10.791 (6) Å | µ = 0.10 mm−1 |
c = 11.543 (7) Å | T = 156 K |
α = 69.70 (2)° | 0.50 × 0.30 × 0.30 mm |
β = 75.01 (2)° | |
Data collection top
Picker Diffractometer (Crystal Logic) | Rint = 0.000 |
4819 measured reflections | 3 standard reflections every 97 reflections |
4819 independent reflections | intensity decay: 1.5% |
2561 reflections with I > 2σ(I) | |
Refinement top
R[F2 > 2σ(F2)] = 0.051 | 0 restraints |
wR(F2) = 0.176 | H-atom parameters constrained |
S = 1.08 | Δρmax = 0.33 e Å−3 |
4816 reflections | Δρmin = −0.35 e Å−3 |
237 parameters | |
Special details top
Experimental. Cell was reindexed after data collection to obtain a reduced triclinic cell.
Standard reflections with final (reported) indices are: 2 1 0 - 1 2 2 0 - 1 3 |
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 on F2 for ALL reflections except for 3 (2 1 0, 2 0 0, -2 1
1) removed by the user because they were too strong for the detector. Weighted
R-factors wR and all goodnesses of fit S are based on
F2, conventional R-factors R are based on F,
with F set to zero for negative F2. The observed criterion of
F2 > σ(F2) is used only for calculating
_refine_ls_R_factor_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 | |
N1 | 0.7799 (3) | 0.7109 (2) | 0.8448 (2) | 0.0215 (4) | |
H1 | 0.7465 | 0.6792 | 0.7943 | 0.026* | |
C2 | 0.8058 (3) | 0.6242 (2) | 0.9579 (2) | 0.0228 (5) | |
C3 | 0.8608 (3) | 0.6825 (2) | 1.0385 (2) | 0.0240 (5) | |
H3 | 0.8823 | 0.6282 | 1.1159 | 0.029* | |
C4 | 0.8819 (3) | 0.8154 (2) | 1.0040 (2) | 0.0246 (5) | |
H4 | 0.9154 | 0.8511 | 1.0584 | 0.029* | |
C5 | 0.8534 (3) | 0.9000 (2) | 0.8861 (2) | 0.0229 (5) | |
H5 | 0.8680 | 0.9912 | 0.8625 | 0.027* | |
C6 | 0.8042 (3) | 0.8459 (2) | 0.8072 (2) | 0.0200 (4) | |
C7 | 0.7800 (3) | 0.9242 (2) | 0.6844 (2) | 0.0224 (5) | |
C8 | 0.7656 (3) | 0.9941 (2) | 0.5815 (2) | 0.0230 (5) | |
C9 | 0.7469 (3) | 1.0806 (2) | 0.4597 (2) | 0.0222 (5) | |
N10 | 0.7288 (3) | 1.0229 (2) | 0.3739 (2) | 0.0221 (4) | |
H10 | 0.7300 | 0.9381 | 0.3971 | 0.026* | |
C11 | 0.7087 (3) | 1.0930 (2) | 0.2528 (2) | 0.0236 (5) | |
C12 | 0.7054 (3) | 1.2337 (2) | 0.2217 (2) | 0.0256 (5) | |
H12 | 0.6892 | 1.2866 | 0.1423 | 0.031* | |
C13 | 0.7254 (4) | 1.2914 (2) | 0.3051 (2) | 0.0276 (5) | |
H13 | 0.7240 | 1.3830 | 0.2817 | 0.033* | |
C14 | 0.7483 (4) | 1.2145 (2) | 0.4273 (2) | 0.0266 (5) | |
H14 | 0.7639 | 1.2544 | 0.4840 | 0.032* | |
O15 | 0.7798 (3) | 0.5029 (2) | 0.9856 (2) | 0.0315 (4) | |
O16 | 0.6982 (3) | 1.0338 (2) | 0.1796 (2) | 0.0315 (4) | |
N17 | 0.3268 (3) | 0.6248 (2) | 0.1530 (2) | 0.0227 (4) | |
H17 | 0.2811 | 0.5887 | 0.1104 | 0.027* | |
C18 | 0.3562 (3) | 0.5448 (2) | 0.2675 (2) | 0.0204 (4) | |
C19 | 0.4418 (3) | 0.6097 (2) | 0.3321 (2) | 0.0206 (4) | |
C20 | 0.4822 (3) | 0.7439 (2) | 0.2789 (2) | 0.0212 (4) | |
H20 | 0.5378 | 0.7849 | 0.3206 | 0.025* | |
C21 | 0.4411 (3) | 0.8196 (2) | 0.1632 (2) | 0.0228 (5) | |
H21 | 0.4655 | 0.9105 | 0.1291 | 0.027* | |
C22 | 0.3647 (3) | 0.7573 (2) | 0.1018 (2) | 0.0231 (5) | |
H22 | 0.3382 | 0.8056 | 0.0243 | 0.028* | |
C23 | 0.4822 (3) | 0.5314 (2) | 0.4503 (2) | 0.0213 (4) | |
O24 | 0.3095 (3) | 0.42417 (15) | 0.30880 (15) | 0.0262 (4) | |
O1S | 0.7867 (3) | 0.7530 (2) | 0.4500 (2) | 0.0318 (4) | |
H1S | 0.7465 | 0.6996 | 0.5222 | 0.038* | |
C2S | 0.9279 (4) | 0.6948 (3) | 0.3785 (3) | 0.0394 (6) | |
H2S1 | 1.0062 | 0.7629 | 0.3083 | 0.047* | |
H2S2 | 0.8698 | 0.6407 | 0.3463 | 0.047* | |
H2S3 | 1.0038 | 0.6412 | 0.4322 | 0.047* | |
Atomic displacement parameters (Å2) top | U11 | U22 | U33 | U12 | U13 | U23 |
N1 | 0.0307 (11) | 0.0162 (8) | 0.0198 (9) | −0.0014 (7) | −0.0111 (8) | −0.0052 (7) |
C2 | 0.0313 (13) | 0.0161 (10) | 0.0216 (11) | −0.0003 (9) | −0.0108 (9) | −0.0039 (8) |
C3 | 0.0325 (13) | 0.0228 (11) | 0.0196 (10) | 0.0006 (9) | −0.0105 (9) | −0.0081 (9) |
C4 | 0.0317 (13) | 0.0238 (11) | 0.0229 (11) | 0.0013 (9) | −0.0119 (9) | −0.0104 (9) |
C5 | 0.0294 (12) | 0.0152 (10) | 0.0248 (11) | 0.0003 (9) | −0.0085 (9) | −0.0066 (8) |
C6 | 0.0231 (11) | 0.0147 (10) | 0.0202 (10) | 0.0002 (8) | −0.0053 (8) | −0.0036 (8) |
C7 | 0.0262 (12) | 0.0178 (10) | 0.0236 (11) | −0.0002 (9) | −0.0073 (9) | −0.0070 (8) |
C8 | 0.0274 (12) | 0.0192 (10) | 0.0224 (11) | −0.0013 (9) | −0.0071 (9) | −0.0061 (8) |
C9 | 0.0257 (12) | 0.0203 (10) | 0.0190 (10) | −0.0004 (9) | −0.0056 (9) | −0.0046 (8) |
N10 | 0.0288 (10) | 0.0147 (8) | 0.0219 (9) | −0.0036 (7) | −0.0086 (8) | −0.0031 (7) |
C11 | 0.0264 (12) | 0.0215 (11) | 0.0208 (11) | −0.0043 (9) | −0.0071 (9) | −0.0031 (8) |
C12 | 0.0309 (13) | 0.0206 (11) | 0.0213 (11) | −0.0005 (9) | −0.0104 (9) | 0.0005 (9) |
C13 | 0.0374 (14) | 0.0158 (10) | 0.0256 (12) | 0.0030 (9) | −0.0064 (10) | −0.0035 (9) |
C14 | 0.0385 (14) | 0.0184 (10) | 0.0220 (11) | 0.0012 (10) | −0.0075 (10) | −0.0060 (9) |
O15 | 0.0527 (12) | 0.0169 (8) | 0.0284 (9) | −0.0033 (7) | −0.0209 (8) | −0.0036 (7) |
O16 | 0.0460 (11) | 0.0259 (9) | 0.0254 (9) | −0.0088 (8) | −0.0147 (8) | −0.0063 (7) |
N17 | 0.0344 (11) | 0.0168 (9) | 0.0192 (9) | −0.0019 (8) | −0.0120 (8) | −0.0049 (7) |
C18 | 0.0285 (12) | 0.0149 (9) | 0.0192 (10) | 0.0007 (8) | −0.0075 (9) | −0.0065 (8) |
C19 | 0.0259 (12) | 0.0173 (10) | 0.0201 (10) | 0.0003 (8) | −0.0088 (9) | −0.0059 (8) |
C20 | 0.0279 (12) | 0.0172 (10) | 0.0200 (10) | −0.0009 (8) | −0.0082 (9) | −0.0067 (8) |
C21 | 0.0296 (12) | 0.0166 (10) | 0.0222 (11) | −0.0006 (9) | −0.0095 (9) | −0.0044 (8) |
C22 | 0.0302 (12) | 0.0178 (10) | 0.0200 (10) | −0.0006 (9) | −0.0103 (9) | −0.0018 (8) |
C23 | 0.0288 (12) | 0.0159 (10) | 0.0226 (10) | −0.0015 (8) | −0.0101 (9) | −0.0078 (8) |
O24 | 0.0428 (10) | 0.0155 (7) | 0.0227 (8) | −0.0041 (7) | −0.0141 (7) | −0.0045 (6) |
O1S | 0.0493 (12) | 0.0183 (8) | 0.0237 (8) | −0.0024 (8) | −0.0071 (8) | −0.0032 (6) |
C2S | 0.037 (2) | 0.040 (2) | 0.0390 (15) | −0.0027 (12) | −0.0059 (12) | −0.0131 (12) |
Geometric parameters (Å, º) top
N1—C2 | 1.370 (3) | C13—C14 | 1.414 (3) |
N1—C6 | 1.375 (3) | C13—H13 | 0.93 |
N1—H1 | 0.86 | C14—H14 | 0.93 |
C2—O15 | 1.249 (3) | N17—C22 | 1.358 (3) |
C2—C3 | 1.433 (3) | N17—C18 | 1.369 (3) |
C3—C4 | 1.355 (3) | N17—H17 | 0.86 |
C3—H3 | 0.93 | C18—O24 | 1.256 (3) |
C4—C5 | 1.411 (3) | C18—C19 | 1.448 (3) |
C4—H4 | 0.93 | C19—C20 | 1.378 (3) |
C5—C6 | 1.365 (3) | C19—C23 | 1.430 (3) |
C5—H5 | 0.93 | C20—C21 | 1.402 (3) |
C6—C7 | 1.427 (3) | C20—H20 | 0.93 |
C7—C8 | 1.194 (3) | C21—C22 | 1.360 (3) |
C8—C9 | 1.429 (3) | C21—H21 | 0.93 |
C9—C14 | 1.362 (3) | C22—H22 | 0.93 |
C9—N10 | 1.375 (3) | C23—C23i | 1.200 (4) |
N10—C11 | 1.381 (3) | O1S—C2S | 1.411 (3) |
N10—H10 | 0.86 | O1S—H1S | 0.82 |
C11—O16 | 1.242 (3) | C2S—H2S1 | 0.96 |
C11—C12 | 1.434 (3) | C2S—H2S2 | 0.96 |
C12—C13 | 1.355 (3) | C2S—H2S3 | 0.96 |
C12—H12 | 0.93 | | |
| | | |
C2—N1—C6 | 123.8 (2) | C12—C13—C14 | 121.1 (2) |
C2—N1—H1 | 118.1 | C12—C13—H13 | 119.5 |
C6—N1—H1 | 118.1 | C14—C13—H13 | 119.5 |
O15—C2—N1 | 120.0 (2) | C9—C14—C13 | 118.1 (2) |
O15—C2—C3 | 124.2 (2) | C9—C14—H14 | 120.9 |
N1—C2—C3 | 115.8 (2) | C13—C14—H14 | 120.9 |
C4—C3—C2 | 121.1 (2) | C22—N17—C18 | 124.6 (2) |
C4—C3—H3 | 119.4 | C22—N17—H17 | 117.7 |
C2—C3—H3 | 119.4 | C18—N17—H17 | 117.7 |
C3—C4—C5 | 120.6 (2) | O24—C18—N17 | 119.7 (2) |
C3—C4—H4 | 119.7 | O24—C18—C19 | 125.0 (2) |
C5—C4—H4 | 119.7 | N17—C18—C19 | 115.3 (2) |
C6—C5—C4 | 118.9 (2) | C20—C19—C23 | 121.9 (2) |
C6—C5—H5 | 120.5 | C20—C19—C18 | 119.7 (2) |
C4—C5—H5 | 120.5 | C23—C19—C18 | 118.4 (2) |
C5—C6—N1 | 119.7 (2) | C19—C20—C21 | 121.3 (2) |
C5—C6—C7 | 122.4 (2) | C19—C20—H20 | 119.4 |
N1—C6—C7 | 117.9 (2) | C21—C20—H20 | 119.4 |
C8—C7—C6 | 176.9 (2) | C22—C21—C20 | 118.5 (2) |
C7—C8—C9 | 178.4 (2) | C22—C21—H21 | 120.7 |
C14—C9—N10 | 120.5 (2) | C20—C21—H21 | 120.7 |
C14—C9—C8 | 122.5 (2) | N17—C22—C21 | 120.4 (2) |
N10—C9—C8 | 117.0 (2) | N17—C22—H22 | 119.8 |
C9—N10—C11 | 123.9 (2) | C21—C22—H22 | 119.8 |
C9—N10—H10 | 118.0 | C23i—C23—C19 | 178.2 (3) |
C11—N10—H10 | 118.0 | C2S—O1S—H1S | 109.5 |
O16—C11—N10 | 120.1 (2) | O1S—C2S—H2S1 | 109.5 |
O16—C11—C12 | 125.1 (2) | O1S—C2S—H2S2 | 109.5 |
N10—C11—C12 | 114.8 (2) | H2S1—C2S—H2S2 | 109.5 |
C13—C12—C11 | 121.6 (2) | O1S—C2S—H2S3 | 109.5 |
C13—C12—H12 | 119.2 | H2S1—C2S—H2S3 | 109.5 |
C11—C12—H12 | 119.2 | H2S2—C2S—H2S3 | 109.5 |
Symmetry code: (i) −x+1, −y+1, −z+1. |
Hydrogen-bond geometry (Å, º) top
D—H···A | D—H | H···A | D···A | D—H···A |
N1—H1···O24i | 0.86 | 2.01 | 2.864 (3) | 170 |
N17—H17···O15i | 0.86 | 1.86 | 2.715 (3) | 171 |
N10—H10···O1S | 0.86 | 1.93 | 2.776 (3) | 168 |
O1S—H1S···O24i | 0.82 | 1.90 | 2.712 (3) | 172 |
C21—H21···O16 | 0.93 | 2.52 | 3.152 (3) | 126 |
C22—H22···O16ii | 0.93 | 2.46 | 3.379 (3) | 170 |
Symmetry codes: (i) −x+1, −y+1, −z+1; (ii) −x+1, −y+2, −z. |
Experimental details
Crystal data |
Chemical formula | 0.5C12H8N2O2·C12H8N2O2·CH4O |
Mr | 350.35 |
Crystal system, space group | Triclinic, P1 |
Temperature (K) | 156 |
a, b, c (Å) | 7.334 (4), 10.791 (6), 11.543 (7) |
α, β, γ (°) | 69.70 (2), 75.01 (2), 86.653 (15) |
V (Å3) | 827.2 (8) |
Z | 2 |
Radiation type | Mo Kα |
µ (mm−1) | 0.10 |
Crystal size (mm) | 0.50 × 0.30 × 0.30 |
|
Data collection |
Diffractometer | Picker Diffractometer (Crystal Logic) |
Absorption correction | – |
No. of measured, independent and observed [I > 2σ(I)] reflections | 4819, 4819, 2561 |
Rint | 0.000 |
(sin θ/λ)max (Å−1) | 0.704 |
|
Refinement |
R[F2 > 2σ(F2)], wR(F2), S | 0.051, 0.176, 1.08 |
No. of reflections | 4816 |
No. of parameters | 237 |
H-atom treatment | H-atom parameters constrained |
Δρmax, Δρmin (e Å−3) | 0.33, −0.35 |
Hydrogen-bond geometry (Å, º) top
D—H···A | D—H | H···A | D···A | D—H···A |
N1—H1···O24i | 0.86 | 2.01 | 2.864 (3) | 170 |
N17—H17···O15i | 0.86 | 1.86 | 2.715 (3) | 171 |
N10—H10···O1S | 0.86 | 1.93 | 2.776 (3) | 168 |
O1S—H1S···O24i | 0.82 | 1.90 | 2.712 (3) | 172 |
C21—H21···O16 | 0.93 | 2.52 | 3.152 (3) | 126 |
C22—H22···O16ii | 0.93 | 2.46 | 3.379 (3) | 170 |
Symmetry codes: (i) −x+1, −y+1, −z+1; (ii) −x+1, −y+2, −z. |
The symmetric dipyridone (I) was synthesized as part of an ongoing study of substituted pyridones. The dimerization of 2-pyridones through hydrogen bonding has often been observed (for example, see Maverick et al., 1993). In principle, (I) and (II), being complementary in their structures, could associate to form a 'dimer' which might be more soluble in relatively nonpolar solvents than random hydrogen bonded oligomers. The behavior of symmetric dipyridone (II) and asymmetric dipyridone (III) in solution and in the solid state had been investigated by Ducharme & Wuest (1988). They observed that (III) self-associates in solution and in the crystal, as does a similarly asymmetric compound with one pyridone and one carboxylic acid function (Wash et al., 1997). On the other hand, (II) is only about 20% associated in solution, and in the crystal is polymeric. Structural diagrams for (I), (II) and (III) appear in the scheme. \sch
We found (I) and (II) to be insoluble in non-polar solvents. Solutions equimolar in (I) and (II) in dimethylsulfoxide or methanol show no evidence for association. This is not unexpected as both solvents participate (and compete) in hydrogen bonding. We report here that association does take place in the solid state, but it is mediated by methanol, the solvent from which the crystals were grown. In addition, though (II) is found in the conformation shown in the scheme, (I) is centrosymmetric, with each of its pyridone groups hydrogen bonded to one of the pyridones of (II) and to one molecule of methanol. The second lactam nitrogen (N10) of each molecule of (II) is hydrogen bonded to the methanol, connecting (II) with (I) in a N—H···O—H···O═C arrangement, while the lactam oxygen O16 participates in two short C═O···H—C contacts. One of the C═O···H—C interactions and the hydrogen bonds are shown in Fig. 1; the relevant distances and angles are presented in Table 1.
The planes of the centrosymmetrically related six-membered rings in (I) are parallel, but the normals to the two unique ring planes in (II) form an angle of 9.89 (12)°. Thus (II) in the present structure is more nearly planar than (III) in the dimeric complex (interplanar angle 29°; Ducharme & Wuest, 1988).
The hydrogen bonding between the cyclic lactam moieties may be compared to that found in 13 related fragments (Maverick et al., 1993) in which N···O distances across the lactam-lactam motif average 2.82 (5) Å. The corresponding N···O distances of 2.864 (3) and 2.715 (3) Å for N1···O24A and N17···O15A (Fig. 1, Table 1) in the present structure are consistent with the average, even though the methanol is also involved in the intermolecular interaction. The angle between the normals to the planes of the two six-membered rings (N1—C6 and N17A—C22A) is 9.16 (13)°, and the N—H···O bonding angles are nearly linear. Though two of the pyridone rings in the `trimer' are not involved in lactam-lactam hydrogen bonding, the complex may be quite stable. Recently, the strength of a C—H···O `weak hydrogen bond' has been estimated to be as much as half that of a N—H···O═C hydrogen bond (Vargas et al., 2000).
The conformation of (I) with mirror symmetry shown in the scheme was approximated by rotation of one pyridone ring of centrosymmetric (I) by 180° using the program OPEC (Gavezzotti, 1983). The two O atoms in the planar, mirror-symmetric conformation would be about 4.31 Å apart, too close to allow the observed solvation by methanol. This suggests that the observed conformation of (I) predominates in methanol solution. Neither the expected `dimer' of (I) and (II), nor a 'trimer' with the opposite composition, two molecules of mirror-symmetric (I) joined to one molecule of centrosymmetric (II), would be likely to form.