´
B. Osmiałowski et al. / Journal of Molecular Structure 1006 (2011) 678–683
682
Table 6
bonyl acceptor was fixed to 1.80 Å and 1.76 Å, respectively (Tables
4–6), in order to gain higher correspondence of chemical shielding
values of amide nitrogen’s. The selected hydrogen bond lengths
were based on linear correlation of shielding values of non-opti-
mized structures and proton optimized structures since the exper-
imental value was between them.
The effect of the hydrogen bond length on the principal shielding tensor d22, which is
the most sensitive to hydrogen bonding [50].
2a
2b
2c
3a
3b
3c
N1H 1ꢀ ꢀ ꢀO10
1.85/1.85
1.70/1.70
1.80/1.80
1.82
1.65
1.76
(Å)
d22
151.8/
152.7
126.1/
124.8
143.7/
142.9
153.4 124.6 143.0
4. Conclusions
Single crystal X-ray structural data of three 2-acylamino-6-
[1H]-pyridones shows that all of them exist as pyridone tautomers
stabilized by intramolecular NHꢀ ꢀ ꢀO@C hydrogen-bonded six-
membered ring structure. Further, the molecules arrange in hydro-
gen-bonded chains, which are packed either with or without base
stacking interactions. The hydrogen bonding geometries in these
chains are quite similar despite of different substituent and the dif-
ference in the side chain seems to affect mostly to the packing of
these chains in respect with each other. No dimer formation via
hydrogen bonding was observed in the single crystals. The intra-
molecular hydrogen bonding is to some extent related to the size
of the substituent. Comparison of liquid and solid-state 13C and
15N NMR data suggests that the preferred tautomer is pyridone
form in both cases. Theoretical GIPAW calculated and experimental
13C CPMAS NMR chemical shifts are in agreement with each other
after optimization of the hydrogen positions derived from the
X-ray structure. In addition, the position of hydrogen in the hydro-
gen bond is needed to manually optimized using linear correlation
of shielding values of 15N in non-optimized and proton optimized
structures in order to gain high correspondence between calcu-
lated and experimental 15N NMR chemical shift values.
molecular structures of the studied compounds are given in the
Supporting information (Fig. S1). In all of the studied conjugates
the amide side chain verges a perfect ziczac illustrated by the
torsion angle C(2)AN(8)AC(9)AR. The two molecules in the asym-
metric unit of 2 differ slightly by the conformation of their side
chains as illustrated by the difference in the absolute value of the
torsion angle C(2)AN(8)AC(9)AR (168.05(11)° for molecule A and
174.49(12)° for molecule B, respectively). Further, in all of the
studied structures the amide carbonyl is cis to ring nitrogen, as
described by the torsion angle N(1)AC(2)AN(8)AC(9) and this
orientation is stabilized by an intramolecular hydrogen bond
(N(1)ꢀ ꢀ ꢀO(10)) with a hydrogen bond motif R11ð6Þ .
In all of these crystals, hydrogen bonding plays important role
in the crystal packing. Besides of the hydrogen bonding interac-
tions, the interactions between the heterocyclic
p-systems may
contribute to the packing in the crystals of 5 and 3. Hydrogen
bonding geometries in the studied crystals are collected in Table
3 and illustrated in Fig. 4. In the crystals of 2-amino-6-[1H]-pyri-
done the hydrogen bonding network (Fig. S2) is constructed by
hydrogen bonded chain C11ð5Þ via N(1)ꢀ ꢀ ꢀO(7) (x ꢂ 1/2, ꢂy ꢂ 1/
2, ꢂz ꢂ 1; 2.74 Å, 163.4°) hydrogen bonds running along a-axis
and further stabilized by N(8)ꢀ ꢀ ꢀO(7) (x ꢂ 1/2, ꢂy ꢂ 1/2, ꢂz ꢂ 1;
3.05 Å, 139.0°) hydrogen bonds and another hydrogen bonded
chain C11ð7Þ via N(8)ꢀ ꢀ ꢀO(7) (ꢂx ꢂ 1/2, ꢂy ꢂ 1,z + 1/2; 2.84 Å, 177°)
hydrogen bonds running along c-axis.
Acknowledgements
Financial support from the Polish Ministry of Science and
Higher Education (Grant No. N N204 174138) is gratefully
acknowledged. The authors acknowledge CSC – IT Center for
Science Ltd. for the allocation of computational resources for
CASTEP calculations. K.A. is grateful to Academy of Finland for
financial support (Project No. 127006). Academy Researcher Elina
Sievänen and Academy of Finland (Project No. 119616 and
255648) are thanked for financial support for M.L. CCDC 839166–
839169 contains the supplementary crystallographic data for this
paper. These data can be obtained free of charge via external link
Cambridge Crystallographic Data Centre, 12, Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033).
In the crystals of 2 hydrogen bonded chains C22ð12Þ where the
molecules A and B alternate are formed via N(8A)ꢀ ꢀ ꢀO(7B) (ꢂx,
ꢂy + 1, ꢂz + 1; 2.74 Å, 167°) and N(8B)ꢀ ꢀ ꢀO(7A) (ꢂx + 1, y ꢂ 1/2,
ꢂz + 3/2; 2.76 Å, 175.9°) interactions. There is also a weak hydro-
gen bonding interaction between the adjacent chains through
N(1B)ꢀ ꢀ ꢀO(7B) (3.11 Å, 122.4°) hydrogen bond. In the crystals of 3
again hydrogen bonded chain C11ð6Þ via N(8)ꢀ ꢀ ꢀO(7) (ꢂx + 3/2,
y ꢂ 1, z ꢂ 1/2; 2.69 Å, 167.0°) hydrogen bond is formed. In these
crystals the parallel chains are piled on top of each other with
the rings stacked offset with 4.97 Å centroid to centroid distance.
Similarly in the crystals of 5 hydrogen bonded chains C11ð6Þ running
along b-axes are formed through N(8)ꢀ ꢀ ꢀO(7) (ꢂx + 1, y + 1/2,
ꢂz ꢂ 1/2; 2.83 Å, 170°) hydrogen bond. Further, the adjacent anti-
parallel chains are assembled in such way that the heterocyclic
rings are stacked offset with centroid to centroid distance of 4.86 Å.
This is worth noting that the intramolecular hydrogen bond
length decreases when the substituent R become larger (the
N(1)ꢀ ꢀ ꢀO(10) distance, Table 3). The opposite is realized for
N–Hꢀ ꢀ ꢀO angle (<(DHA), Table 3).
Appendix A. Supplementary material
Supplementary data associated with this article can be found, in
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