Supporting information
Crystallographic Information File (CIF) https://doi.org/10.1107/S0108270101008605/gg1059sup1.cif | |
Structure factor file (CIF format) https://doi.org/10.1107/S0108270101008605/gg1059Isup2.hkl |
CCDC reference: 170211
Under N2, 7-amino-2,4-dimethyl-1,8-naphthyridine (Gorecki & Hawes, 1977) (866 mg, 5.01 mmol) was dissolved in dry toluene (50 ml), tert-butylisocyanate (500 mg, 5.05 mmol) was added, and the mixture was heated to reflux for 2 h. After cooling to room temperature, the solid was filtered off, washed with toluene and dried. Recrystallization from ethanol, toluene/ethanol (10:1) and then toluene gave 1.19 g (87%) of a colourless solid, m. p. 513 K. IR (KBr): cm-1 νσim 3360, 3187, 3119, 3042 (N—H), 2968 (aliphat. C—H), 1682 (C═O), 1601, 1523 (arom.), 1566 (N—H), 1401 (tert-butyl, C—H). 1H-NMR (200 MHz, CDCl3) δ: 1.54 [s, 9H, C(CH3)3], 2.61 (s, 3H, CH3), 2.69 (s, 3H, CH3), 7.05 (s, 1H, ArH), 7.46 (d, J = 8.9 Hz, 1H, ArH), 8.18 (d, J = 8.9 Hz, 1H, ArH), 9.59 (br. s, 1H, NH), 10.08 (br. s, 1H, NH). MS (EI,70 eV): m/z (%) = 272 (3), 257 (16), 200 (57), 173 (100). MS (CI/isobutane): m/z (%) = 273 (100). C17H22N4O (272.4): calculated C 66.15, H 7.40, N 20.57%; found C 66.04, H 7.42, N 20.48%.
All H atoms were located by difference Fourier synthesis and refined with fixed individual displacement parameters [U(H) = 1.5 Ueq(Cmethyl), or U(H) = 1.2 Ueq(C)] using a riding model with C—Haromatic 0.95 and C—Hmethyl 0.98 Å. The methyl groups attached to the aromatic system were allowed to rotate about their local threefold axis. The H atoms bound to N were refined isotropically.
Data collection: SMART (Siemens, 1995); cell refinement: SMART; data reduction: SAINT (Siemens, 1995); program(s) used to solve structure: SHELXS97 (Sheldrick, 1990); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: XP in SHELXTL-Plus (Sheldrick, 1991).
C15H20N4O | Dx = 1.154 Mg m−3 |
Mr = 272.35 | Melting point: 513 K |
Monoclinic, P21/c | Mo Kα radiation, λ = 0.71073 Å |
a = 12.7129 (2) Å | Cell parameters from 5891 reflections |
b = 11.2067 (1) Å | θ = 1–25° |
c = 11.6822 (2) Å | µ = 0.08 mm−1 |
β = 109.578 (1)° | T = 140 K |
V = 1568.14 (4) Å3 | Block, colourless |
Z = 4 | 0.40 × 0.20 × 0.08 mm |
F(000) = 584 |
Siemens CCD three-circle diffractometer | 3174 independent reflections |
Radiation source: fine-focus sealed tube | 2135 reflections with I > 2σ(I) |
Graphite monochromator | Rint = 0.051 |
ω scans | θmax = 26.4°, θmin = 1.7° |
Absorption correction: empirical (SADABS; Sheldrick, 1996) | h = −15→15 |
Tmin = 0.970, Tmax = 0.994 | k = −13→13 |
10199 measured reflections | l = −13→14 |
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)] = 0.050 | H atoms treated by a mixture of independent and constrained refinement |
wR(F2) = 0.136 | w = 1/[σ2(Fo2) + (0.0636P)2 + 0.4824P] where P = (Fo2 + 2Fc2)/3 |
S = 1.02 | (Δ/σ)max < 0.02 |
3174 reflections | Δρmax = 0.29 e Å−3 |
192 parameters | Δρmin = −0.23 e Å−3 |
0 restraints | Extinction correction: SHELXL97, Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4 |
Primary atom site location: structure-invariant direct methods | Extinction coefficient: 0.014 (2) |
C15H20N4O | V = 1568.14 (4) Å3 |
Mr = 272.35 | Z = 4 |
Monoclinic, P21/c | Mo Kα radiation |
a = 12.7129 (2) Å | µ = 0.08 mm−1 |
b = 11.2067 (1) Å | T = 140 K |
c = 11.6822 (2) Å | 0.40 × 0.20 × 0.08 mm |
β = 109.578 (1)° |
Siemens CCD three-circle diffractometer | 3174 independent reflections |
Absorption correction: empirical (SADABS; Sheldrick, 1996) | 2135 reflections with I > 2σ(I) |
Tmin = 0.970, Tmax = 0.994 | Rint = 0.051 |
10199 measured reflections |
R[F2 > 2σ(F2)] = 0.050 | 0 restraints |
wR(F2) = 0.136 | H atoms treated by a mixture of independent and constrained refinement |
S = 1.02 | Δρmax = 0.29 e Å−3 |
3174 reflections | Δρmin = −0.23 e Å−3 |
192 parameters |
Experimental. ; |
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. |
x | y | z | Uiso*/Ueq | ||
N1 | 0.85531 (12) | 0.54915 (14) | 0.48862 (14) | 0.0231 (4) | |
H1 | 0.8923 (16) | 0.4926 (19) | 0.4634 (18) | 0.026 (5)* | |
C2 | 0.92330 (14) | 0.63554 (16) | 0.56465 (15) | 0.0205 (4) | |
O2 | 1.02662 (9) | 0.62078 (11) | 0.59955 (11) | 0.0254 (3) | |
N3 | 0.87183 (13) | 0.72830 (14) | 0.59484 (14) | 0.0249 (4) | |
H3 | 0.7957 (19) | 0.7260 (19) | 0.563 (2) | 0.042 (6)* | |
C4 | 0.92836 (15) | 0.82712 (16) | 0.67685 (17) | 0.0257 (4) | |
C41 | 1.00999 (19) | 0.8910 (2) | 0.6270 (2) | 0.0410 (6) | |
H41A | 0.9697 | 0.9211 | 0.5453 | 0.062* | |
H41B | 1.0679 | 0.8349 | 0.6233 | 0.062* | |
H41C | 1.0447 | 0.9578 | 0.6804 | 0.062* | |
C42 | 0.83422 (17) | 0.91287 (19) | 0.6775 (2) | 0.0416 (6) | |
H42A | 0.7820 | 0.8714 | 0.7093 | 0.062* | |
H42B | 0.7945 | 0.9401 | 0.5945 | 0.062* | |
H42C | 0.8661 | 0.9817 | 0.7292 | 0.062* | |
C43 | 0.98812 (17) | 0.77897 (19) | 0.80489 (18) | 0.0356 (5) | |
H43A | 0.9341 | 0.7383 | 0.8347 | 0.053* | |
H43B | 1.0223 | 0.8453 | 0.8593 | 0.053* | |
H43C | 1.0462 | 0.7224 | 0.8026 | 0.053* | |
C11 | 0.73957 (14) | 0.54333 (16) | 0.43817 (16) | 0.0218 (4) | |
N12 | 0.67811 (12) | 0.62899 (13) | 0.46135 (14) | 0.0239 (4) | |
C13 | 0.56386 (14) | 0.61944 (17) | 0.41554 (17) | 0.0248 (4) | |
N14 | 0.50809 (12) | 0.71130 (15) | 0.44676 (15) | 0.0301 (4) | |
C15 | 0.39668 (15) | 0.70527 (19) | 0.40751 (19) | 0.0341 (5) | |
C15' | 0.33656 (17) | 0.8068 (2) | 0.4442 (2) | 0.0458 (6) | |
H15A | 0.3651 | 0.8158 | 0.5327 | 0.069* | |
H15B | 0.2564 | 0.7896 | 0.4175 | 0.069* | |
H15C | 0.3492 | 0.8808 | 0.4061 | 0.069* | |
C16 | 0.33698 (16) | 0.6101 (2) | 0.3365 (2) | 0.0382 (5) | |
H16 | 0.2577 | 0.6103 | 0.3111 | 0.046* | |
C17 | 0.39086 (16) | 0.5164 (2) | 0.30286 (18) | 0.0352 (5) | |
C17' | 0.32876 (18) | 0.4114 (2) | 0.2298 (2) | 0.0522 (7) | |
H17A | 0.3469 | 0.3391 | 0.2798 | 0.078* | |
H17B | 0.3509 | 0.4008 | 0.1578 | 0.078* | |
H17C | 0.2482 | 0.4263 | 0.2046 | 0.078* | |
C18 | 0.51024 (15) | 0.52085 (18) | 0.34368 (17) | 0.0276 (4) | |
C19 | 0.57963 (15) | 0.43159 (18) | 0.31861 (18) | 0.0298 (5) | |
H19 | 0.5467 | 0.3649 | 0.2695 | 0.036* | |
C20 | 0.69254 (15) | 0.44170 (17) | 0.36482 (17) | 0.0270 (4) | |
H20 | 0.7393 | 0.3825 | 0.3487 | 0.032* |
U11 | U22 | U33 | U12 | U13 | U23 | |
N1 | 0.0187 (8) | 0.0226 (8) | 0.0282 (9) | 0.0039 (6) | 0.0083 (7) | −0.0045 (7) |
C2 | 0.0217 (9) | 0.0218 (10) | 0.0186 (9) | 0.0014 (7) | 0.0075 (7) | 0.0008 (7) |
O2 | 0.0182 (6) | 0.0292 (7) | 0.0269 (7) | 0.0040 (5) | 0.0052 (5) | −0.0043 (6) |
N3 | 0.0188 (8) | 0.0246 (9) | 0.0302 (9) | 0.0008 (6) | 0.0068 (7) | −0.0063 (7) |
C4 | 0.0253 (9) | 0.0225 (10) | 0.0279 (10) | 0.0005 (7) | 0.0071 (8) | −0.0061 (8) |
C41 | 0.0456 (13) | 0.0345 (12) | 0.0447 (13) | −0.0109 (10) | 0.0174 (10) | −0.0029 (10) |
C42 | 0.0351 (12) | 0.0343 (12) | 0.0479 (14) | 0.0079 (9) | 0.0039 (10) | −0.0172 (10) |
C43 | 0.0393 (11) | 0.0377 (12) | 0.0272 (11) | 0.0033 (9) | 0.0075 (9) | −0.0041 (9) |
C11 | 0.0208 (9) | 0.0223 (9) | 0.0239 (10) | 0.0009 (7) | 0.0096 (7) | 0.0016 (7) |
N12 | 0.0204 (8) | 0.0248 (9) | 0.0275 (9) | 0.0017 (6) | 0.0093 (6) | −0.0004 (7) |
C13 | 0.0206 (9) | 0.0291 (10) | 0.0255 (10) | 0.0028 (8) | 0.0089 (8) | 0.0054 (8) |
N14 | 0.0233 (8) | 0.0320 (9) | 0.0372 (10) | 0.0070 (7) | 0.0132 (7) | 0.0059 (8) |
C15 | 0.0255 (10) | 0.0414 (12) | 0.0379 (12) | 0.0086 (9) | 0.0138 (9) | 0.0130 (10) |
C15' | 0.0332 (12) | 0.0485 (14) | 0.0602 (15) | 0.0177 (10) | 0.0215 (11) | 0.0136 (12) |
C16 | 0.0188 (9) | 0.0560 (14) | 0.0398 (12) | 0.0034 (9) | 0.0097 (9) | 0.0110 (11) |
C17 | 0.0250 (10) | 0.0487 (13) | 0.0305 (11) | −0.0038 (9) | 0.0075 (9) | 0.0042 (10) |
C17' | 0.0263 (11) | 0.0716 (18) | 0.0539 (15) | −0.0142 (11) | 0.0070 (11) | −0.0143 (13) |
C18 | 0.0233 (10) | 0.0347 (11) | 0.0255 (10) | −0.0037 (8) | 0.0092 (8) | 0.0027 (9) |
C19 | 0.0286 (10) | 0.0329 (11) | 0.0291 (11) | −0.0072 (8) | 0.0115 (9) | −0.0069 (9) |
C20 | 0.0267 (10) | 0.0276 (10) | 0.0294 (11) | −0.0006 (8) | 0.0127 (8) | −0.0029 (8) |
N1—C11 | 1.391 (2) | N12—C13 | 1.374 (2) |
N1—C2 | 1.400 (2) | C13—N14 | 1.367 (2) |
N1—H1 | 0.90 (2) | C13—C18 | 1.417 (3) |
C2—O2 | 1.249 (2) | N14—C15 | 1.336 (2) |
C2—N3 | 1.337 (2) | C15—C16 | 1.407 (3) |
N3—C4 | 1.483 (2) | C15—C15' | 1.510 (3) |
N3—H3 | 0.91 (2) | C15'—H15A | 0.9800 |
C4—C41 | 1.527 (3) | C15'—H15B | 0.9800 |
C4—C43 | 1.531 (3) | C15'—H15C | 0.9800 |
C4—C42 | 1.537 (3) | C16—C17 | 1.381 (3) |
C41—H41A | 0.9800 | C16—H16 | 0.9500 |
C41—H41B | 0.9800 | C17—C18 | 1.431 (3) |
C41—H41C | 0.9800 | C17—C17' | 1.512 (3) |
C42—H42A | 0.9800 | C17'—H17A | 0.9800 |
C42—H42B | 0.9800 | C17'—H17B | 0.9800 |
C42—H42C | 0.9800 | C17'—H17C | 0.9800 |
C43—H43A | 0.9800 | C18—C19 | 1.427 (3) |
C43—H43B | 0.9800 | C19—C20 | 1.358 (3) |
C43—H43C | 0.9800 | C19—H19 | 0.9500 |
C11—N12 | 1.322 (2) | C20—H20 | 0.9500 |
C11—C20 | 1.430 (3) | ||
C11—N1—C2 | 129.94 (16) | C11—N12—C13 | 118.95 (16) |
C11—N1—H1 | 115.2 (12) | N14—C13—N12 | 114.37 (16) |
C2—N1—H1 | 114.6 (12) | N14—C13—C18 | 123.78 (16) |
O2—C2—N3 | 124.82 (16) | N12—C13—C18 | 121.85 (17) |
O2—C2—N1 | 118.28 (15) | C15—N14—C13 | 117.08 (18) |
N3—C2—N1 | 116.90 (15) | N14—C15—C16 | 122.74 (19) |
C2—N3—C4 | 125.23 (15) | N14—C15—C15' | 116.3 (2) |
C2—N3—H3 | 114.6 (14) | C16—C15—C15' | 120.93 (18) |
C4—N3—H3 | 120.1 (14) | C15—C15'—H15A | 109.5 |
N3—C4—C41 | 110.34 (15) | C15—C15'—H15B | 109.5 |
N3—C4—C43 | 110.01 (16) | H15A—C15'—H15B | 109.5 |
C41—C4—C43 | 111.07 (16) | C15—C15'—H15C | 109.5 |
N3—C4—C42 | 105.11 (14) | H15A—C15'—H15C | 109.5 |
C41—C4—C42 | 109.80 (17) | H15B—C15'—H15C | 109.5 |
C43—C4—C42 | 110.34 (17) | C17—C16—C15 | 121.55 (18) |
C4—C41—H41A | 109.5 | C17—C16—H16 | 119.2 |
C4—C41—H41B | 109.5 | C15—C16—H16 | 119.2 |
H41A—C41—H41B | 109.5 | C16—C17—C18 | 116.79 (19) |
C4—C41—H41C | 109.5 | C16—C17—C17' | 122.51 (18) |
H41A—C41—H41C | 109.5 | C18—C17—C17' | 120.7 (2) |
H41B—C41—H41C | 109.5 | C17—C17'—H17A | 109.5 |
C4—C42—H42A | 109.5 | C17—C17'—H17B | 109.5 |
C4—C42—H42B | 109.5 | H17A—C17'—H17B | 109.5 |
H42A—C42—H42B | 109.5 | C17—C17'—H17C | 109.5 |
C4—C42—H42C | 109.5 | H17A—C17'—H17C | 109.5 |
H42A—C42—H42C | 109.5 | H17B—C17'—H17C | 109.5 |
H42B—C42—H42C | 109.5 | C13—C18—C19 | 117.41 (16) |
C4—C43—H43A | 109.5 | C13—C18—C17 | 118.06 (18) |
C4—C43—H43B | 109.5 | C19—C18—C17 | 124.52 (18) |
H43A—C43—H43B | 109.5 | C20—C19—C18 | 120.22 (18) |
C4—C43—H43C | 109.5 | C20—C19—H19 | 119.9 |
H43A—C43—H43C | 109.5 | C18—C19—H19 | 119.9 |
H43B—C43—H43C | 109.5 | C19—C20—C11 | 118.59 (17) |
N12—C11—N1 | 119.54 (16) | C19—C20—H20 | 120.7 |
N12—C11—C20 | 122.95 (16) | C11—C20—H20 | 120.7 |
N1—C11—C20 | 117.50 (16) | ||
C11—N1—C2—O2 | 179.46 (17) | N14—C15—C16—C17 | 0.0 (3) |
C11—N1—C2—N3 | −0.3 (3) | C15'—C15—C16—C17 | −179.7 (2) |
O2—C2—N3—C4 | −1.6 (3) | C15—C16—C17—C18 | 0.0 (3) |
N1—C2—N3—C4 | 178.18 (16) | C15—C16—C17—C17' | 178.1 (2) |
C2—N3—C4—C41 | 59.2 (2) | N14—C13—C18—C19 | −179.94 (17) |
C2—N3—C4—C43 | −63.7 (2) | N12—C13—C18—C19 | −0.9 (3) |
C2—N3—C4—C42 | 177.53 (18) | N14—C13—C18—C17 | −0.9 (3) |
C2—N1—C11—N12 | −0.2 (3) | N12—C13—C18—C17 | 178.11 (17) |
C2—N1—C11—C20 | −178.79 (17) | C16—C17—C18—C13 | 0.5 (3) |
N1—C11—N12—C13 | −177.06 (16) | C17'—C17—C18—C13 | −177.71 (19) |
C20—C11—N12—C13 | 1.5 (3) | C16—C17—C18—C19 | 179.42 (19) |
C11—N12—C13—N14 | 178.71 (16) | C17'—C17—C18—C19 | 1.2 (3) |
C11—N12—C13—C18 | −0.4 (3) | C13—C18—C19—C20 | 1.2 (3) |
N12—C13—N14—C15 | −178.25 (16) | C17—C18—C19—C20 | −177.78 (19) |
C18—C13—N14—C15 | 0.8 (3) | C18—C19—C20—C11 | −0.2 (3) |
C13—N14—C15—C16 | −0.3 (3) | N12—C11—C20—C19 | −1.2 (3) |
C13—N14—C15—C15' | 179.29 (18) | N1—C11—C20—C19 | 177.37 (17) |
D—H···A | D—H | H···A | D···A | D—H···A |
N1—H1···O2i | 0.90 (2) | 1.93 (2) | 2.824 (2) | 175.7 (19) |
N3—H3···N12 | 0.91 (2) | 1.91 (2) | 2.676 (2) | 141 (2) |
Symmetry code: (i) −x+2, −y+1, −z+1. |
Experimental details
Crystal data | |
Chemical formula | C15H20N4O |
Mr | 272.35 |
Crystal system, space group | Monoclinic, P21/c |
Temperature (K) | 140 |
a, b, c (Å) | 12.7129 (2), 11.2067 (1), 11.6822 (2) |
β (°) | 109.578 (1) |
V (Å3) | 1568.14 (4) |
Z | 4 |
Radiation type | Mo Kα |
µ (mm−1) | 0.08 |
Crystal size (mm) | 0.40 × 0.20 × 0.08 |
Data collection | |
Diffractometer | Siemens CCD three-circle diffractometer |
Absorption correction | Empirical (SADABS; Sheldrick, 1996) |
Tmin, Tmax | 0.970, 0.994 |
No. of measured, independent and observed [I > 2σ(I)] reflections | 10199, 3174, 2135 |
Rint | 0.051 |
(sin θ/λ)max (Å−1) | 0.626 |
Refinement | |
R[F2 > 2σ(F2)], wR(F2), S | 0.050, 0.136, 1.02 |
No. of reflections | 3174 |
No. of parameters | 192 |
H-atom treatment | H atoms treated by a mixture of independent and constrained refinement |
Δρmax, Δρmin (e Å−3) | 0.29, −0.23 |
Computer programs: SMART (Siemens, 1995), SMART, SAINT (Siemens, 1995), SHELXS97 (Sheldrick, 1990), SHELXL97 (Sheldrick, 1997), XP in SHELXTL-Plus (Sheldrick, 1991).
N1—C11 | 1.391 (2) | C11—N12 | 1.322 (2) |
N1—C2 | 1.400 (2) | N12—C13 | 1.374 (2) |
C2—O2 | 1.249 (2) | C13—N14 | 1.367 (2) |
C2—N3 | 1.337 (2) | N14—C15 | 1.336 (2) |
N3—C4 | 1.483 (2) | ||
C11—N1—C2 | 129.94 (16) | C2—N3—C4 | 125.23 (15) |
O2—C2—N3 | 124.82 (16) | C11—N12—C13 | 118.95 (16) |
O2—C2—N1 | 118.28 (15) | C15—N14—C13 | 117.08 (18) |
N3—C2—N1 | 116.90 (15) | ||
C11—N1—C2—O2 | 179.46 (17) | N1—C2—N3—C4 | 178.18 (16) |
C11—N1—C2—N3 | −0.3 (3) | C2—N1—C11—N12 | −0.2 (3) |
O2—C2—N3—C4 | −1.6 (3) |
D—H···A | D—H | H···A | D···A | D—H···A |
N1—H1···O2i | 0.90 (2) | 1.93 (2) | 2.824 (2) | 175.7 (19) |
N3—H3···N12 | 0.91 (2) | 1.91 (2) | 2.676 (2) | 141 (2) |
Symmetry code: (i) −x+2, −y+1, −z+1. |
Multiple hydrogen bonds attend increasing attention for the formation of host–guest complexes and for supramolecular self-assembly (Zimmerman & Corbin, 2000). Therefore quadruple hydrogen-bonding patterns based on four parallel and anti-parallel hydrogen bonds have been investigated. While a non-self-complementary pattern like DAAD·ADDA (D: hydrogen-bond donor, A: hydrogen-bond acceptor) (Lüning & Kühl, 1998), can be used for molecular recognition, the two conceivable self-complementary patterns of a four hydrogen-bond system AADD or ADAD may form dimers. This has been exploited by Sijbesma et al. (1997) and Beijer et al. (1998) to construct new types of polymers. Here we present a naphthyridyl urea (I) designed for self-complexation. It was synthesized from the literature known 7-amino-2,4-dimethyl-1,8-naphthyridine (Gorecki & Hawes, 1977) by addition to tert-butylisocyanate in 87% yield. \sch
Meijer's AADD systems (Sijbesma et al., 1997; Beijer et al., 1998) possess a linear orientation of the hydrogen bonds leading to dimers held together by four parallel and anti-parallel hydrogen bonds. Such a linear dimer of (I) could only be formed if the urea exists in a Z,Z conformation. However, the naphthyridyl urea (I) first forms an intramolecular hydrogen bond between the hydrogen atom of the tert-butyl NH group and atom N1 of the naphthyridyl ring which leads to a Z,E conformer. This was proven by X-ray analysis (see Figure 1). Bond lengths and angles of (I) are in the usual ranges. The molecule is essentially planar (except for two methyl groups of the tert-butyl group) (r.m.s. deviation 0.05 Å).
The twist from a Z to an E amide bond presents a hydrogen-bond donor D and a hydrogen-bond acceptor A on the surface of (I). Thus, self recognition (AD.DA) forms a dimer which also contains four hydrogen bonds. However, two of these are intramolecular and only two are intermolecular. The dimerization of ureas which are substituted by N-heterocycles in an AD.DA fashion has already been observed for pyridyl ureas (Bolte et al., 2001; Corbin & Zimmerman, 2000). The driving force for a dimer formation by only two hydrogen bonds accompanied by two intramolecular hydrogen bonds is possibly on steric grounds: the 7-methyl group and the tert-butyl group are in closer contact in the strictly intermolecular dimer than in the E,Z form. The new N-substituted naphthyridine (I) is also an interesting ligand for the complexation of two metal atoms in close proximity. Mintert & Sheldrick (1996) have reported complexes of related 2-amino and 2-oxo substituted naphthyridines containing Mo—Mo moieties.