Supramolecular architectures of conformationally controlled 1,3-phenyl-dioxalamic molecular clefts through hydrogen bonding and steric restraints

Article abstract of DOI:10.1039/c1ce05302g

In this contribution the supramolecular architecture of a series of six 1,3-phenyl-dioxalamic molecular clefts is described. The conformation was controlled by the use of Me and OMe group substitution in the phenyl spacer. The structural and conformational study was carried out by X-ray diffraction analysis, DFT calculations at PBEPBE 6-31+G (3df, 3pd) theory level and variable temperature ¹H NMR in solution. The C2-Me group exerts a dual influence on the conformation adopting the endo(sc) or exo(ac) conformations in the oxalamic arms, meanwhile the C2-OMe group leads to the adoption of the exo(ap) conformation. DFT study results showed that the exo(ap)-exo(ap) conformation is more stable than the other conformations due to the conjugation that stabilizes the molecule and minimizes the conformational energy. Supramolecular arrays in oxalamate/oxalamide derivatives of 1,3-diaminobenzene, 2-methyl-benzene-1,3-diamine and 2,4,6-trimethyl-benzene-1,3-diamine are directed by self-complementary N-H...O hydrogen bonding interactions, whose organization in the crystal depends on the twist of the oxalamic arms, meanwhile in oxalamate/oxalamide derivatives of 5-tert-butyl-2,6-diamineanisol with an exo(ap)-exo(ap) conformation, the supramolecular arrays are directed by π-stacking, dipolar carbonyl-carbonyl interactions and C-H...O soft contacts. N¹,N¹′-(1,3-(2,4,6-Trimethyl)-phenyl)-bis- (N²-(2-(2-hydroxyethoxy)ethyl)oxalamide) adopts the form of a supramolecular meso-helix, which is the first example of helical 1,3-phenyl-dioxalamide. The Royal Society of Chemistry 2011.

Full text of DOI:10.1039/c1ce05302g

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PAPER
Supramolecular architectures of conformationally controlled 1,3-phenyl-
dioxalamic molecular clefts through hydrogen bonding and steric restraints†
a
Juan Saulo Gonzalez-Gonzalez, Francisco Javier Martınez-Martınez, Ana Lilia Peraza Campos,
a
a
ꢀ
ꢀ
Maria de Jesus Rosales-Hoz, Efren V. Garcıa-Baez and Itzia I. Padilla-Martınez
ꢀ
ꢀ
b
c
c
*
ꢀ
ꢀ
ꢀ
ꢀ
Received 10th March 2011, Accepted 19th April 2011
DOI: 10.1039/c1ce05302g
In this contribution the supramolecular architecture of a series of six 1,3-phenyl-dioxalamic molecular
clefts is described. The conformation was controlled by the use of Me and OMe group substitution in
the phenyl spacer. The structural and conformational study was carried out by X-ray diffraction
1
analysis, DFT calculations at PBEPBE 6-31+G (3df, 3pd) theory level and variable temperature H
NMR in solution. The C2-Me group exerts a dual influence on the conformation adopting the endo(sc)
or exo(ac) conformations in the oxalamic arms, meanwhile the C2-OMe group leads to the adoption of
the exo(ap) conformation. DFT study results showed that the exo(ap)–exo(ap) conformation is more
stable than the other conformations due to the conjugation that stabilizes the molecule and minimizes
the conformational energy. Supramolecular arrays in oxalamate/oxalamide derivatives of 1,3-
diaminobenzene, 2-methyl-benzene-1,3-diamine and 2,4,6-trimethyl-benzene-1,3-diamine are directed
by self-complementary N–H/O hydrogen bonding interactions, whose organization in the crystal
depends on the twist of the oxalamic arms, meanwhile in oxalamate/oxalamide derivatives of 5-tert-
butyl-2,6-diamineanisol with an exo(ap)–exo(ap) conformation, the supramolecular arrays are directed
by p-stacking, dipolar carbonyl–carbonyl interactions and C–H/O soft contacts. N1,N1 -(1,3-(2,4,6-
0
Trimethyl)-phenyl)-bis-(N2-(2-(2-hydroxyethoxy)ethyl)oxalamide) adopts the form of
a supramolecular meso-helix, which is the first example of helical 1,3-phenyl-dioxalamide.
intra-molecular hydrogen bonding has been extensively used in
the production of complex organized systems due to the reversi-
bility, specificity, directionality and cooperativity of such
interactions.
1. Introduction
Non-covalent interactions are recognized to be involved in
crystal engineering and molecular recognition.1 They have been
increasingly used as a powerful tool for construction of many
supramolecular architectures, devices and nanostructured
materials.2 Among them, hydrogen bonding is particularly
important from the biological point of view, because of its
participation in several biological processes such as: the stabili-
zation of the double helix of DNA,3 enzyme–substrate interac-
tions,4 recognition among proteins5 and drug–acceptor
interactions.6 Hydrogen bonding is the most important element
in the design of self-assembled organic molecules, sometimes
with the participation of other intermolecular forces.7 Inter- and
Oxalamates are composed of an amide and an ester group
directly connected to each other. Thus the functionalities N–H,
C]O and O–R allow them to form one dimensional (1-D)
networks through intermolecular hydrogen bonding,8 but they
also can form two (2-D) and three dimensional (3-D) networks
whose architecture in the solid state will depend on the side-arm
substituent.
Oxalamides, which are mono-substituted diamides of oxalic
acid, represent construction units with high in-plane hydrogen
bonding potential; they are self-complementary and capable of
unidirectional hydrogen bonding. In many cases, their self-
assembly produces robust one-dimensional hydrogen-bonded
chains, although, depending on the substitution and presence of
additional hydrogen bonding units, a variety of more complex
structures might be observed. The NH and amide carbonyl are
usually in a trans disposition as also are amide and ester
carbonyls or both carbonyl amides, in oxalamate and oxala-
mide, respectively, thus the most common conformation is
trans–anti (t,a) in oxalamates and trans–anti–trans (t,a,t) in
oxalamides.9
aFacultad de Ciencias Quꢀımicas, Universidad de Colima, Km. 9 Carretera
ꢀ
ꢀ
Colima-Coquimatlan, C.P. 28400 Coquimatlan, Colima, Mexico
bDepartamento de Quꢀımica, CINVESTAV-IPN, Av. Instituto Politeꢀcnico
Nacional 2508, Col. San Pedro Zacatenco, Apartado postal: 14-740,
ꢀ
07000, C.P. 07360 Mexico, D.F., Mexico
cDepartamento de Ciencias Baꢀsicas, Unidad Profesional Interdisciplinaria
ꢀ
de Biotecnologıa del Instituto Politecnico Nacional, Av. Acueducto s/n
Barrio la Laguna Ticomaꢀn, 07340 Meꢀxico, D. F., Mexico
ꢀ
† CCDC reference numbers 2 795133, 3 801211/795129, 4 795131, 5
801212, 6 801213, and 7 801214. For crystallographic data in CIF or
other electronic format see DOI: 10.1039/c1ce05302g
4748 | CrystEngComm, 2011, 13, 4748–4761
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1,3-Phenyl-dioxalamates and 1,3-phenyl-dioxalamides are
good candidates to be used in molecular recognition processes,
because of the cavity formed in between the two side arms with
a bent conformation and the open possibility of p-stacking
between the phenyl spacer. The relative disposition of both arms
in relation to the 2-substituted phenyl spacer and among them
gives rise to several conformations.
Fig. 1 Newman projections of conformers derived from the C2–C1–N7–
C8 torsion angle, viewed along the C1–N7 bond.
the cavity, whereas the anti-conformers are exo positioned.
Taking into account the two arms, ten combinations are possible:
three exo–exo (ap–ap, ac–ac, ap–ac), four exo–endo (ap–sc,
ap–sp, ac–sc, ac–sp) and three endo–endo (sc–sc, sc–sp, sp–sp).
There are two reported polymorphs of diethyl 1,3-phenyl-
dioxalamate 110b and 10.10c In the conformation exhibited by
polymorph 1, both amide carbonyls are located pointing endo to
the cavity and syn (sc–sp) positioned regarding to the phenyl ring
with C2–C1–N7–C8 and C1–N7–C8–O8 torsion angles of
37.0(3)ꢁ and ꢂ4.1(3)ꢁ, respectively. This conformation allows
a full intramolecular hydrogen bonding scheme combining one
O/H2/O three centred and two NH/O hydrogen bonding
interactions, respectively. Thus a set of four adjacent intra-
molecular rings are formed, which are described by the graph set
notation12 as [S(5)S(6)S(5)S(6)] motif. Meanwhile in 10, the
torsion angles C6–C1–N7–C8 and C1–N7–C8–O8 take values of
32.6(5)ꢁ and 179.3(3)ꢁ, respectively, in agreement with an exo
(ac)–exo(ac) conformation of both oxalamate arms. This
conformation favors the formation of two sets of intramolecular
six and five membered hydrogen bond motifs [S(6)S(5)]. A
common feature of conformers 1 and 10 is the twist of both
oxalamate side arms, one of them tilted up and the other tilted
down with regard to the mean plane of the phenyl ring. The out-
of-plane conformation is characteristic of disubstituted ethyl
o- and p-phenyl-bis-oxalamates,13 in contrast with the reported
planar conformation of monosubstituted ethyl N-phenyl
oxalamate.14
In this contribution the molecular and supramolecular struc-
ture of 1,3-phenyl-dioxalamate 1 is revisited, and those corre-
sponding to three 2-substituted 1,3-phenyl-dioxalamates 2–4 are
reported. This series of compounds was synthesized starting from
1,3-diaminobenzene C-2 substituted with Me or OMe groups.
The presence of these groups bisecting the central phenyl ring
was used to tilt the oxalyl side arms out of the plane and thus
favor intermolecular hydrogen bonding. In order to test the
utility of the hydroxyl group to increase the self-assembling
capabilities of the oxalamide moiety into predictable structural
patterns, oxalamides with side-arm substituents derived from
ethanolamine 5–7 were prepared. Furthermore, the molecular
and supramolecular 1,3-phenyl-dioxalamides 5–7 are also
analyzed and compared with their parent dioxalamates 2–4. To
the best of our knowledge there are recent reports on the topo-
logical control10a of their dimensionality in the solid state, but
there are no reports about the use of steric effects to control the
conformation and so the hydrogen bond directed self-assembly
in the solid state of these molecules. Results were supported by
1
DFT calculations and H NMR measurements.
2. Results
The relative disposition of the carbonyl group of the phenyl-
amide moiety (PhNHCO) regarding the 2-substituent in the
phenyl ring, as a plane of reference, gives rise to several
conformers: antiperiplanar (ap), anticlinal (ac), synclinal (sc) and
synperiplanar (sp), in agreement with the torsion angle C2–C1–
N7–C8 values of ꢀ180–150ꢁ, ꢀ150–90ꢁ, ꢀ90–30ꢁ and ꢀ30–0ꢁ,
respectively. In Fig. 1 are shown the Newman projections along
the C1–N7 bond.11
2.1 Intramolecular hydrogen bonding and molecular structure
Oxalamates 2–4 in the solid state. The molecular structures
and intramolecular hydrogen bonding schemes of compounds
2–4 are shown in Fig. 2 and a summary of bond lengths and
angles is listed in Table 1. The OC–CO distances are similar to
the reported structure of diethyl 1,3-phenyl-dioxalamate 1 in
agreement with OC–CO single bond and anti disposition
between amide and ester carbonyls in both oxalamate arms. In
compounds 2–4, the amide proton is located trans to the amide
In both syn-conformers, the PhNHCO carbonyl is pointing
towards the 2-substituent, thus endo positioned with regard to
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a
ꢁ
Table 1 Selected bond lengths (A) and angles (deg) of compounds 2–7
Compounds
2
3
4
5
6
7
ꢁ
Bond lengths/A
Atoms
C1–N7
C3–N17
N7–C8
1.431(3)
1.433(3)
1.335(3)
1.417(5)
1.429(5)
1.344(5)
1.402(4)
1.413(4)
1.345(4)
1.440(6)
1.415(6)
1.324(6)
1.317(6)
1.338(6)
1.337(6)
1.505(7)
1.517(6)
1.441(3)
1.409(3)
1.397(3)
1.344(3)
1.319(3)
1.353(3)
1.330(4)
1.538(4)
1.527(4)
1.317(4)
1.313(5)
N10–C9
N17–C18
N20–C19
C8–C9
C18–C19
Atoms
1.335(3)
1.331(5)
1.342(4)
1.535(3)
1.543(3)
1.532(6)
1.524(6)
1.529(4)
1.543(5)
1.525(5)
Torsion angles/ꢁ
C2–C1–N7–C8
C2–C3–N17–C18
C6–C1–N7–C8
C1–N7–C8–O8
C4–C3–N17–C18
C3–N17–C18–O18
O8–C8–C9–O9
O18–C18–C19–O19
N7–C8–C9–X10
N17–C18–C19–X20
N10–C11–C12–O13
N20–C21–C22–O23
O13–C14–C15–O16
64.4(3)
67.4(3)
ꢂ60.4(5)
179.5(3)
ꢂ178.4(3)
ꢂ126.5(5)
ꢂ144.5(4)
55.4(7)
ꢂ72.4(4)
ꢂ176.1(3)
ꢂ177.6(3)
ꢂ4.9(5)
ꢂ2.3(5)
ꢂ1.6(5)
2.5(5)
179.7(3)
178.0(3)
ꢂ179.7(2)
177.7(2)
ꢂ59.5(3)
66.2(3)
ꢂ103.5(4)
123.4(4)
ꢂ9.5(6)
76.5(4)
ꢂ117.0(2)
0.3(5)
ꢂ3.6(5)
108.0(3)
10.3(6)
ꢂ0.2(4)
ꢂ1.2(9)
ꢂ113.7(2)
ꢂ0.8(3)
0.8(5)
38.5(7)
1.8(8)
ꢂ2.1(6)
165.0(4)
168.6(4)
170.0(3)
169.9(3)
ꢂ4.5(5)
ꢂ167.9(2)
ꢂ177.3(2)
ꢂ176.1(3)
ꢂ177.4(4)
ꢂ178.6(3)
ꢂ178.1(3)
ꢂ169.1(5)
ꢂ179.6(4)
ꢂ165.1(5)
ꢂ177.2(4)
179.1(3)
176.3(3)
ꢂ169.14(18)
179.97(18)
ꢂ177.3(3)
69.1(4)
a
X ¼ O in 2–4 and X ¼ N in 5–7.
carbonyl as in most secondary amides. The amide and ester
carbonyls are anti to each other with similar O8]C8–C9]O9
and O18]C18–C19]O19 torsion angle values between ꢀ165
and ꢀ178ꢁ. The N7–C8–C9–O10 and N17–C18–C19–O20
torsion angle values are near to 180ꢁ, in close agreement with
those values reported for diethyl phenyl-dioxalamates.10
become twisted by ꢂ60.4(5)ꢁ and ꢂ103.5(4)ꢁ for C2–C1–N7–C8
and C2–C3–N17–C18 torsion angles, respectively. This result is
in agreement with the mean value of ca. 70ꢁ reported for 2,4,6-
trimethyl-benzene-1,3-diamine.18 The oxalamate arms are also
up and down, adopting a synclinal (sc) and anticlinal (ac)
The introduction of a CH3 group in the C-2 position,
compound 2, increases the twisting out of the ethyl oxalamate
arms from 37.0(3)ꢁ in polymorph 1 to 64.4(3) and 67.4(3)ꢁ (C2–
C1–N7–C8 and C2–C3–N17–C18 torsion angles, respectively),
as reported for diamides derived from 2-methyl-benzene-1,3-
diamine.15 Thus both oxalamate arms are toward one another,
one above the plane of the phenyl ring and the other below this
plane with both amide carbonyls in synclinal (sc) disposition in
relation to the phenyl ring, but even endo to the cavity. This
conformation allows the formation of a set of four adjacent
intramolecular rings [S(5)S(7)S(7)S(5)] with the participation of
NH and C2–CH3 hydrogen atoms as donors and both carbonyls
as acceptors: N7–H7/O9, N17–H17/O19, C23–H23A/O18
and C23–H23B/O18, Fig. 2(a). It is worthy to note that, in this
compound and in related diamides, the methyl group is pointing
towards the amide carbonyl thus favoring the S(7) ring, whereas
in monoamides derived from o-tolylamine16 it is always in the
opposite direction. In spite of the steric requirements of the C2–
CH3 group, this conformer strongly resembles that of polymorph
1, where the central S(6) intramolecular hydrogen bonded rings
are substituted by larger S(7) ring motifs. In Table 2 the
geometric parameters associated with intramolecular hydrogen
bonding of compounds 2–4 are summarized. The interaction
lengths are shorter than the sum of the van der Waals radii of the
17
ꢁ
atoms involved (H ¼ 1.20, C ¼ 1.70, N ¼ 1.55, O ¼ 1.50 A).
Further increasing the steric restraints with CH3 substituent
groups in C2, C4 and C6, compound 3, the oxalamate arms
Fig. 2 Molecular structure at 30% probability level and intramolecular
interactions of dioxalamates 2–4.
4750 | CrystEngComm, 2011, 13, 4748–4761
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Table 2 Geometric parameters of intramolecular interactions in compounds 2–7a
D–H/A/ꢁ
HB motif
ꢁ
D–H/A
ꢁ
ꢁ
Comp.
D–H/A
H/A/A
D/A/A
2
N7–H7/O9
0.86
0.86
0.96
0.96
0.86
0.86
0.86
0.86
0.86
0.86
0.93
0.93
0.86
0.86
0.86
0.86
0.93
0.86
0.86
0.86
0.86
0.86
0.86
0.86
0.86
0.93
0.93
2.31
2.31
2.44
2.58
2.39
2.37
2.20
2.27
2.25
2.25
2.34
2.37
2.26
2.39
2.25
2.36
2.51
2.29
2.32
2.20
2.27
2.33
2.24
2.30
2.32
2.30
2.38
2.696(3)
2.693(2)
3.156(3)
3.115(3)
2.727(4)
2.728(4)
2.640(4)
2.694(3)
2.678(4)
2.703(4)
2.940(4)
2.967(4)
2.659(5)
2.749(5)
2.670(5)
2.727(5)
2.977(6)
2.675(3)
2.701(4)
2.647(3)
2.692(3)
2.714(3)
2.665(3)
2.704(3)
2.693(3)
2.912(3)
2.974(3)
107
107
131
115
104
105
111
110
111
110
122
121
109
106
110
106
111
107
107
112
110
107
110
109
106
123
121
S(5)
S(5)
S(7)
S(7)
S(5)
S(5)
S(5)
S(5)
S(5)
S(5)
S(6)
S(6)
S(5)
S(5)
S(5)
S(5)
S(6)
S(5)
S(5)
S(5)
S(5)
S(5)
S(5)
S(5)
S(5)
S(6)
S(6)
N17–H17/O19
C23–H23A/O18
C23–H23B/O8
N7–H7/O9
3
4
N17–H17/O19
N7–H7a/O9
N7–H7a/O23
N17–H17b/O19
N17–H17b/O23
C4–H4/O18
C6–H6/O8
5
N7–H7/O9
N10–H10/O8
N17–H17/O19
N20–H20/O18
C4–H4/O18
N7–H7/O9
6
7
N10–H10/O8
N7–H7/O9c
N7–H7/O24c
N10–H10/O8
N17–H17/O19d
N17–H17/O24d
N20–H20/O18
C4–H4/O18
C6–H6/O8
a
S:N7H7/ꢁ ¼ 359 (a), 360 (c); S:N17H17/ꢁ ¼ 360 (b), 359 (d).
disposition, in relation to the mean plane of the phenyl ring, and
endo–exo positioned to the cavity. Intramolecular hydrogen
bonding is reduced to only two S(5) ring motifs, formed by N7–
H7/O9 and N17–H17/O19 interactions, Fig. 2(b).
and the other to an ethylamine residue (RNHCO). The mole-
cular structures and intramolecular hydrogen bonding schemes
of compounds 5–7 are shown in Fig. 3 and a summary of bond
In compound 4, the bulkiest OCH3 substituent in C2 leads to
the full rotation of both oxalamate side arms to locate them
almost in the same plane of the phenyl ring, C2–C1–N7–C8 and
C2–C3–N17–C18 torsion angles of 179.5(3)ꢁ and ꢂ178.4(3)ꢁ, as
found in diamides derived from 2-methoxy-5-methyl-benzene-
1,3-diamine,19 both adopting an antiperiplanar (ap) disposition,
in relation to the mean plane of the phenyl ring and exo–exo
positioned to the cavity. In this molecule the t-Bu substituent is
far away from the cavity, thus the steric effect is mainly exerted
by the methoxy group. The OMe group is almost perpendicular
to the phenyl ring (C1–C2–O23–C24 ¼ 91.3(3)ꢁ) leading the
oxygen atom in the same plane. This conformation is probably
assisted by cooperative intramolecular hydrogen bonding.20 The
amide hydrogen atoms are involved in a three-centred hydrogen
bonding with both O-atoms from the ester carbonyl and
methoxy groups (O9/H7/O23 and O19/H17/O23), an
important feature of this interaction is that the sum of angles
around the amide H-atom (S:NH) is close to 360ꢁ.21 In the
opposite side, the amide carbonyls are also interacting with the
aromatic hydrogen atoms H4 and H6 (C4–H4/O18 and C6–
H6/O8). The full system is composed of six adjacent rings
described by the graph set notation as an [S(5)S(6)S(5)S(5)S(6)S
(5)] ring system, Fig. 2(c).
Oxalamides 5–7 in the solid state. Dioxalamides 5–7 are
symmetrical but each arm is composed of two different amide
groups, one of them directly linked to the phenyl ring (PhNHCO)
Fig. 3 Molecular structure at 30% probability level and intramolecular
interactions of dioxalamides 5–7.
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lengths and angles is listed in Table 1. The OC–CO distances are
similar to the reported structures of phenyl oxalamides22 in
agreement with OC–CO single bond. As in most of secondary
oxalamides, both amide groups are anti to each other with
N7–C8–C9–N10 and N17–C18–C19–N20 torsion angles
between ꢀ165 and ꢀ180ꢁ.
Gas phase structure of 2–7. Ab initio theoretical calculations
performed in diethyl N,N’-[1,3-phenyl]dioxalamate have pointed
out that the conformer exo(ap)–exo(ap), polymorph 10, is more
stable than the endo(sp)–endo(sp) conformer, polymorph 1, just
by 1.0–2.0 kcal molꢂ1, this energy becomes smaller when acetone
is included as a solvent.10a,23 This small difference in energy has
been used to explain the occurrence of both polymorphs. In order
to gain more information about the preferred conformation and
the intramolecular hydrogen bonding interactions, density
functional theoretical (DFT) calculations were performed in
compounds 2–7. The exo(ap)–exo(ap) conformer is predicted as
the most stable for compounds 2, 4, 5, and 7. In the case of
compound 2 and its derived oxalamide 5, DFT calculations do
not agree with XRD. Compound 2 showed two energy minima,
one of which correspond to the conformer exo(ap)–exo(ap) with
C2–C1–N7–C8 and C2–C3–N17–C18 torsion angles very close
to 180ꢁ and the other corresponding to the conformer endo(sc)–
endo(sc) with C2–C1–N7–C8 and C2–C3–N17–C18 torsion
angles of 59.9ꢁ and 66.7ꢁ, respectively. The energy difference
between both conformers is 5.7 kcal molꢂ1 in favor of the exo
(ap)–exo(ap) conformer, larger than the conformational barrier
of 4.4 kcal molꢂ1 reported for compound 1.10a This gap in energy
is expected because of the steric restraints to rotation imposed by
C2-Me group. It is worthy to mention that this last conformer
has the largest dipole moment of 4.07 Debyes, against 0.29
Debyes shown by the conformer endo(sc)–endo(sc). The amide N
atom bears a positive formal charge (0.201) in the exo(ap)–exo
(ap) conformer and a negative formal charge (ꢂ0.152 and
ꢂ0.149) in the endo(sc)–endo(sc) conformer, in agreement with
the absence of the N lone pair conjugation into the phenyl ring in
the last conformer.
In compound 5, both oxalamide side arms are almost planar
with C1–N7–C8–O8 and C3–N17–C18–O18 torsion angles close
to 0ꢁ. Phenylamide carbonyls (C8]O8 and C18]O18) are both
exo positioned to the cavity and anticlinal (ac) to the mean
plane of the phenyl ring, one of them above and the other below
the phenyl ring plane with C2–C1–N7–C8 and C2–C3–N17–
C18 torsion angles of ꢂ126.5(5)ꢁ and ꢂ144.5(4)ꢁ, respectively.
This last conformation brings about the formation of intra-
molecular C4–H4/O18 HB, S(6) ring, at the expense of two
S(7) rings in the parent oxalamate 2. In addition N7–H7/O9,
N10–H10/O8, N17–H17/O19 and N20–H20/O18 hydrogen
bonding, typical of oxalamides, are observed. Therefore, the
intramolecular hydrogen bonding pattern is depicted by two
sets of adjacent HB ring systems [S(5)S(5)S(6)] and [S(5)S(5)],
Fig. 3(a).
Compound 6 has a crystallographic plane of symmetry and
thus only one half of the molecule is observed. The fragment N–
CO–CO–N of the oxalamide arms is almost planar with C1–N7–
C8–O8 and N10–C11–C12–O13 torsion angles of 10.3(6)ꢁ and
ꢂ177.3(3)ꢁ, respectively. The OH group at the end of the arm is
in a gauche conformation with O13–C14–C15–O16 torsion angle
of 69.1(4)ꢁ. Both arms are synclinarly (sc) positioned with respect
to the mean plane of the phenyl ring, with C2–C1–N7–C8 torsion
angle of ꢂ72.4(4)ꢁ and the phenylamide carbonyl pointing
towards the cavity. The intramolecular HB scheme is described
as two sets of [S(5)S(5)] ring systems, Fig. 3(b).
When the steric effect is increased by substitution in C4 and C6
positions, compounds 3 and 6, both oxalamate groups are tilted
out of the phenyl mean plane to give conformers very similar to
those found by X-ray. In compound 3, the conformers endo(sc)–
endo(sc), exo(ac)–exo(ac) and exo(ac)–endo(sc) (from XRD) were
tested, this last one is more stable than the other two by 1.8 and
1.1 kcal molꢂ1, respectively. In the case of oxalamide 6, the endo
(sc)–endo(sc) conformer was the predicted one, in close agree-
ment with the XRD structure. The calculated planar exo(ap)–exo
(ap) conformers of 4 and 7 are in close agreement with XRD
structures. In both cases, the N atoms bear a positive formal
charge as a consequence of the conjugation of the lone pair of
electrons into the phenyl ring. The optimized structures and
formal charges are shown in Fig. 4. The exo(ap)–exo(ap)
conformation is more stable than the other conformations due to
the conjugation that stabilizes the molecule and minimizes the
conformational energy.
The conformation of oxalamide 7 strongly resembles the
conformation observed for the parent oxalamate 4: the oxala-
mide arms are ap to the phenyl ring (C2–C1–N7–C8 ¼ ꢂ176.1
(3)ꢁ and C2–C3–N17–C18 ¼ ꢂ177.6(3)ꢁ), both are exo disposed
to the cavity and the OMe group is almost perpendicular to the
phenyl ring (C1–C2–O24–C25 ¼ 88.6(3)ꢁ). The OH group at the
end of the arm is in a gauche conformation with N10–C11–C12–
O13 and N20–C21–C22–O23 torsion angles of ꢂ59.5(3)ꢁ and
66.2(3)ꢁ, respectively, Fig. 3(c).
The substitution of EtO in oxalamates 2–4 for RNH in oxa-
lamides 5–7 increases the intramolecular HB, allowing the
formation of an additional S(5) ring in each arm due to the (t,a,t)
conformation of the dioxalamide RHN–CO–CO–NHPh frag-
ment. Therefore, the following patterns are observed: [S(5)S(5)S
(6)] and [S(5)S(5)] for 5, two sets of [S(5)S(5)] rings for 6 and
eight adjacent rings [S(5)S(5)S(6)S(5)S(5)S(6)S(5)S(5)] for 7. At
this point it is worthy to note that the C1–N7/C3–N17 distances
enlarge when the oxalyl arm is out of the mean plane of the
phenyl ring. This result is consistent with the C1–N7 distance
1
Hydrogen bonding in solution by H NMR. At this point the
question remains whether, in the case of compounds 4 and 7, the
observed conformers are the result of the minimization of elec-
tronic repulsive interactions between amide and OMe oxygen
atoms or hydrogen bonding interactions. To address this issue,
the dependences of the chemical shift with temperature (Dd/DT)
of the amide protons were measured in DMSO-d6 solutions. This
coefficient has been routinely used to estimate the proton
mobility and the thermodynamic parameters associated with
intra or intermolecular hydrogen bonding formation.22–24 In
ꢁ
value of 1.414 A measured in planar N,N’-bis(3,5-dimethyl-
phenyl)oxalamide,13 similar to the C1–N7/C3–N17 distance
values observed in the corresponding in plane arm of compounds
ꢁ
3–5 and 7. In contrast, a C1–N7 distance value of 1.435 A has
been measured in the almost perpendicular N,N’-bis-(2,4,6-tri-
methyl-phenyl)oxalamide,13 in agreement with C1–N7/C3–N17
distance values observed in the corresponding out of plane arm
of compounds 2, 3, 5 and 6.
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Fig. 4 Molecular structures and charges of the most stable optimized conformers of compounds 2 (a), 3 (b), 4 (c) and 6 (d) at DFT/PBEPBE 6-31+G
(3df, 3pd) level of theory.
amides, DdNH/DT values smaller than 3.0 ppb Kꢂ1, in DMSO,
are associated with low mobility protons and thus indicate
a strong intramolecular hydrogen bond. Another indicator of
low mobility is a small difference between chemical shifts
measured in DMSO-d6 and CDCl3 solutions (DdNH). In Table 3
hydrogen bonds O9/H7/O23/H17/O19. The correspon-
ding value in compound 4 is in accordance with moderate
intramolecular hydrogen bonding but the smallest DdNHPh
value indicates the lowest mobility among the oxalamates 1–4.
Besides, the IR vibrational frequency of NHPh is shifted from
3378 cmꢂ1 in 4 to 3357 cmꢂ1 in 7 as reported for three-centred
hydrogen bonded oxalamates25 and bisoxalamides.22 These
results confirm that the same scheme of intramolecular hydrogen
bonding found by XRD in compounds 4 and 7 is persistent in
solution and thus the hydrogen bonding nature of the observed
conformation.
1
are summarized the relevant H NMR data of compounds 1–7.
The chemical shifts of the NHPh signals of compounds 1–7 in
DMSO-d6 appear in the range of 10.8 to 9.9 ppm, in agreement
with their more acidic character than the NHR signals, in
compounds 5–7, which are at lower frequencies, 9.0–8.8 ppm.
Nevertheless DdNH/DT values of both amide protons indicate
moderate intramolecular hydrogen bonding in compounds 1–4
and 6. It is worthy to note that the mobility of the NHPh proton
is increased in oxalamide 5 (DdNHPh ¼ ꢂ9.3 ppb Kꢂ1) in
comparison with its parent oxalamate 2 (DdNHPh ¼ ꢂ4.7 ppb
Kꢂ1), in agreement with more intermolecular hydrogen bonding
character in 5. In contrast, intramolecular hydrogen bonding is
strengthened in oxalamide 7 if compared to its parent oxalamate
4. Actually, the DdNHPh/DT value of ꢂ2.0 ppm Kꢂ1, in the
former, is in agreement with strong intramolecular three-centred
2.3 Crystal packing and supramolecular arrangement
Compounds 2 and 3 crystallize as monoclinic systems, space
group P21/c with four molecules in the unit cell, compounds 4
ꢂ
and 5 as triclinic, space group P1 with two molecules in the unit
cell, whereas compounds 6 and 7 crystallize as monoclinic, space
group C2/c with four molecules in the unit cell. Compound 7 is
a special case in which the monoclinic structure has a b angle
indistinguishable from 90.0ꢁ. The geometric parameters asso-
ciated with intermolecular non-covalent interactions D–H/A
are summarized in Table 4. In order to avoid data duplication,
the reader is referred to the corresponding entry. Classic
hydrogen bonding26 and C–H/O27 or C–H/p28 interactions
are in agreement with accepted criteria. Classification and
geometry of CO/CO interactions29 and p-stacking30 are in
accordance with accepted values.
Table 3 dX1H and DdX1H/DT NMR data (X ¼ N, O) of compounds 1–7
a
in DMSO-d6
Compound
Parameter
1
2
3
4
5
6
7
dNHPh
DdNHPha
10.82 10.48 10.37 10.04 10.29
1.89 1.62 1.90 0.79
10.25 9.90
DdNHPh/DT ꢂ5.50 ꢂ4.70 ꢂ5.21 ꢂ4.20 ꢂ9.30 ꢂ5.39 ꢂ2.00
Oxalamates 2–4. The zero dimensional array (0-D) of
compound 2 is given by pairing of two centrosymmetric mole-
cules through self-complementary strong N17–H17/O8ii
hydrogen bonding, with the participation of the amide group as
both hydrogen donor and acceptor. Intercentroid and inter-
dNHR
8.81
ꢂ4.96 ꢂ5.50 ꢂ4.9
n.o. 4.65 n.o.
ꢂ5.43
8.80 8.97
DdNHR/DT
dOH
DdOH/DT
a
d1HDMSO-d ꢂ d1HCDCl available only for 1–4 for solubility restrictions.
6
3
ꢁ
planar distances of 4.5642(14) and 3.6254(9) A, respectively,
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suggest a parallel displaced pd–p/pii stacking interaction
between phenyl rings (symmetry code ii: 1 ꢂ x, ꢂy, 1 ꢂ z). The
2
resulting ring motif R2 (16) is developed into 1-D columns by
self-complementary amide N7–H7/O18i hydrogen bonding
2
interactions, which describe a second R2 (16) ring motif. In
addition, two p-interactions strengthen the column assembly:
N7–H7/pi and pd–p-stackingi, this last with 4.5383(14) and
ꢁ
3.5815(9) A of intercentroid and interplanar distances (i: 2 ꢂ x,
ꢂy, 1 ꢂ z). The whole 1-D array is depicted as a column devel-
2
2
2
oped by antiparallel C2 (8)[R2 (16) R2 (16)] chains (second level
graph set descriptor) developing along the direction of the a axis,
Fig. 5. The second dimension (2-D) is arranged by C11–H11A/
2
O18iii soft interactions that link the columns forming R2 (24) ring
motifs along the direction of the c axis (iii: 2 ꢂ x, ꢂy, 2 ꢂ z).
Fig. 5 1-D columns along the a axis formed by N–H/O, N–H/p and
pd–p-stacking interactions in compound 2.
Compound
3 also forms amide-linked centrosymmetric
dimers, as in 2, through the ac-oxalamate side arm N17–H17/
O8v (v: 1 ꢂ x, ꢂy, ꢂz) to define a R2 (16) ring motif. In this case
2
ꢁ
ꢁ
[O18/C9 ¼ 3.144(4) A, C18]O18/C9 ¼ 101.9(3) ]. Inter-
each dimer is connected with four other dimers through N7–
H7/O18iv hydrogen bonding and C24–H24C/O18iv interac-
ꢁ
centroid and interplanar distances of 3.7950(18) A and 3.4580
1
1
ꢁ
(13) A, respectively, are in agreement with face to face p-stack-
tion, to form R2 (7)[C(8)C(9)] second level ring motif (iv: x, /2 ꢂ
1
ingviii (viii: ꢂx, ꢂy, 1 ꢂ z), Fig. 7(a). These pairs are linked
through weak C24–H24C/O9vii interactions with the partici-
pation of the methyl group from OMe as the donor and ester
y,ꢂ /2 + z). This arrangement, viewed in the bc plane, looks like
2
a brick wall-sheet of alternating squared R2 (16) and hexagon
R6 (32) ring motifs, Fig. 6. The R2 (16) dimers are pd–p-stackedvi
as the intercentroid and interplanar distances of 4.540(2) and
6
2
2
carbonyl as the acceptor (vii: ꢂx, 1ꢂy, 1 ꢂ z). Thus R2 (18) ring
ꢁ
motifs are outlined developing 1-D zig-zagging tapes along the
direction of the a axis. If intramolecular HB is included, [S(5)S
(5)] motifs, chair like H4O4, octagons are also observed, Fig. 7(b).
3.6204(13) A (vi: 2 ꢂ x, ꢂy, ꢂz), respectively, indicate.
The extended embracement disposition of 4 and the steric
hindrance of the C2-OMe group do not allow intermolecular
hydrogen bonding. However, dipolar carbonyl–carbonyl and p-
stacking interactions direct the formation of centrosymmetric
pairs. Two self-complementary sheared parallel carbonyl–
carbonyl interactions are formed: C8]O8/C19viii [O8/C19 ¼
T-Shaped C21–H21B/pii interactions, R2 (14) motif, are
responsible to generate 2-D walls in the direction of the c axis.
2
2
2
2
Oxalamides 5–7. The typical R2 (10)[R2 (16) R2 (24)] ring
motif, in which the anti network is used, gives rise to hydrogen
ꢁ
viii
ꢁ
3.270(4) A, C8]O8/C19 ¼ 104.7(3) ] and C18]O18/C9
Table 4 Geometric parameters of intermolecular interactions in compounds 2–7a
D–H/A/ꢁ
HB motif
ꢁ
D–H/A
ꢁ
ꢁ
Comp.
D–H/A
H/A/A
D/A/A
2
R2 (16)
R2 (6)
2
R2 (16)
2
R2 (24)
2
N7–H7a/O18i
0.86
0.86
0.86
0.97
0.86
0.96
0.86
0.96
0.96
0.86
0.86
0.86
0.86
0.86
0.86
0.84
0.86
0.84
0.96
0.97
0.84
0.86
0.96
2.39
3.18
2.32
2.59
2.24
2.52
2.15
2.41
2.85
2.18
2.19
2.20
2.49
2.12
2.07
1.97
2.40
2.08
2.53
2.46
2.03
2.14
2.55
3.074(2)
3.710(2)
2.995(2)
3.433(3)
3.060(4)
3.281(4)
2.903(4)
3.348(5)
3.668(4)
2.937(5)
2.969(6)
2.932(5)
3.306(5)
2.928(4)
2.888(4)
2.798(3)
3.139(3)
2.893(3)
3.274(4)
3.279(3)
2.817(3)
2.922(3)
3.377(4)
137
123
136
145
160
136
149
167
142
146
151
142
159
157
158
167
144
164
134
142
156
150
144
2
N7–H7/pi
N17–H17b/O8ii
C11–H11A/O18iii
N7–H7c/O18iv
C24–H24C/O18iv
N17–H17d/O8v
C24–H24C/O9vii
C21–H21B/pii
N7–H7e/O18viii
N10–H10f/O8ix
N17–H17g/O19x
N20–H20/O9viii
N7–H7h/O16xi
N10–H10i/O8xii
O16–H16/O9xiii
N10–H10j/O13xiv
O13–H13/O19xiii
C25–H25A/O9xiii
C22–H22A/O8xv
O23–H23/O9xvi
N20–H20k/O23xvii
C27–H27B/O24xvii
3
C(8)
C(9)
2
R2 (16)
2
R2 (18)
4
5
2
R2 (14)
2
R2 (16)
2
R2 (10)
2
R2 (10)
2
R2 (24)
2
R2 (30)
6
7
2
R2 (10)
2
R2 (34)
2
R2 (10)
2
R2 (30)
2
R2 (18)
C(13)
C(15)
2
R2 (10)
2
R2 (16)
a
S:N7H7/ꢁ ¼ 332 (a), 351 (c), 355 (e), 349 (h); S:N17H17/ꢁ ¼ 332 (b), 348 (d), 354 (g); S:N10H10/ꢁ ¼ 356 (f), 360 (i), 342 (j); S:N20H20/ꢁ ¼ 357
(k). Symmetry codes: (i) ¼ 2 ꢂ x, ꢂy, 1 ꢂ z; (ii) ¼ 1 ꢂ x, ꢂy, 1 ꢂ z; (iii) ¼ 2 ꢂ x, ꢂy, 2 ꢂ z; (iv) ¼ x, 1/2 ꢂ y,ꢂ /2 + z; (v) ¼ 1 ꢂ x, ꢂy, ꢂz; (vi) ¼ 2 ꢂ x, ꢂy,
1
ꢂz; (vii) ¼ ꢂx, 1 ꢂ y, 1 ꢂ z; (viii) ¼ ꢂx, ꢂy, 1 ꢂ z; (ix) ¼ ꢂx, 1 ꢂ y, ꢂz; (x) ¼ ꢂ1 ꢂ x, ꢂy, 1 ꢂ z; (xi) ¼ 1/2 + x, 1/2 ꢂ y, 1/2 + z; (xii) ¼ 1/2 ꢂ x, 1/2 ꢂ y, ꢂz;
(xiii) ¼ ꢂ /2 ꢂ x, 1/2 ꢂ y, ꢂz; (xiv) ¼ ꢂx, ꢂy, ꢂz; (xv) ¼ ꢂ /2 + x, /2 + y, z; (xvi) ¼ ꢂ /2 ꢂ x, /2 + y, 1/2 ꢂ z; (xvii) ¼ ꢂx, y, 1/2 ꢂ z.
1
1
1
1
1
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develop a rough sheet in the [2 8 11] mean plane. The whole
crystal packing, Fig. 8(a), is strengthened by the cooperative
participation of intramolecular hydrogen bonding S(5) motifs.
Thus three centred hydrogen bonding O9/H7/O18 (S:H7 ¼
355ꢁ) and O9/H20/O18 (S:H20 ¼ 354ꢁ) depict intra-dimers,
and O8/H10/O8 (S:H10 ¼ 356ꢁ) and O19/H17/O19 (S:
2
H17 ¼ 346ꢁ) inter-dimer H2O2 squares. The resulting R2 (4)
pattern is a common structural motif in oxalamide supramole-
cular architecture. In this molecule both ethanolamine residues
are disordered. In one arm the residual ethanolamine fragment
C11–C12–O13–H13 is moving in three positions with 24, 30 and
46 percent of occupancy and on the other arm, the residual
hydroxyl group O23–H23 is moving in two positions with 51%
(O23A) and49% (O23B) percent of occupancy. For this last, the
Fig. 6 View in the bc plane of a brick wall-sheet of alternating squared
2
6
R2 (16) and hexagon R6 (32) like ring motifs, formed by N–H/O
hydrogen bonding interactions in compound 3.
bonded centrosymmetric dimers linked through two self
2
ꢁ
O23A/O23B distance of 2.810(3) A was measured, in agreement
complementary N–H/O interactions, N7–H7/O18viii (R2 (16))
with other similar structures9d forming a R2 (8) ring to reinforce
2
2
and N20–H20/O9viii (R2 (24)), in compound 5. In these motifs
2-D, Fig. 8(b).
the hydrogen bonding donor NH and the acceptor CO belong to
the same amide type, or amide-like interactions, that is phenyl-
Molecule 6 is linked to other molecule, forming centrosym-
metric pairs, by N10–H10/O8xii (xii: 1/2 ꢂ x, 1/2 ꢂ y, ꢂz), N7–
1
1
1
H7/O16xi (xi: /2 + x, /2 ꢂ y, /2 + z) and O16–H16/O9xiii
amide or hydroxyethylamide. The intercentroid distance of 4.986
(3) Aviii between the phenyl spacers in the R2 (16) motif is beyond
2
ꢁ
2
hydrogen bonding to form R2 (16)[R2 (10)R2 (36)] ring motif.
2
2
2
The intermolecular spacing along the oxalamide R2 (10) motif is
ꢁ
5.060(3) A. The propagation of these hydrogen bonding inter-
the limit for a pd–p-stacking interaction. Each dimer is linked to
other two also using the N–H/O anti network between the NH
of phenylamide and the CO of hydroxyethylamide residue and
actions along the (2 0 ꢂ2) direction gives rise to a meso-helix. The
2
conversely or amide-dislike interactions, forming two R2 (10)
ring motifs: N10–H10/O8ix (ix: ꢂx, 1 ꢂ y, ꢂz) and N17–H17/
ꢁ
turn of the helix measures 18.0 A between two0 phenyl rings,
10c
ꢁ
longer than 15.0 A measured in the polymorph 1 . The meso-
helix can be regarded as the alternate propagation of helical
conformers of opposite chirality (M and P) around the inversion
O19x (x: ꢂ1 ꢂ z, ꢂy, 1 ꢂ z). The intermolecular spacing along
ꢁ
these oxalamide motifs is 5.137(3) and 5.035(3) A, respectively.
The four N–H/O hydrogen bonds can be described, at the
4
second level graph set descriptor, as two C4 (16)[R2 (16) R2 (10)
2
2
2
R2 (10) R2 (24)] chains running in the opposite direction, to
2
Fig. 8 (a) Partial view of the rough complex sheet of compound 5,
developed by N–H/O and O–H/O hydrogen bonding interactions in
the [2 8 11] mean plane (hydrogen atoms not involved in HB have been
Fig. 7 Supramolecular structure of compound 4. (a) Centrosymmetric
pair linked by C]O/C]O dipolar and pd–p-stacking interactions
(hydrogen atoms and t-Bu group are omitted for clarity). (b) 1-D zig-
zagging tape linked through weak C24–H24C/O interactions along the
a axis, chair like H4O4 octagons are also included.
2
2
omitted for clarity). Oxalamide R2 (10) and R2 (16) ring motifs are clearly
appreciated as well as disordered ethanolamine fragment C11–C12–O13–
H13. (b) A detail of the disordered hydroxyl group O23–H23 showing the
2
R2 (8) ring motif through O–H/O interactions.
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centre thus the twist sense changes every half-turn of the helix,
Fig. 9(a). To the best of our knowledge compound 6 is the first
example of helical 1,3-phenyl-dioxalamide. An infinite number of
second dimension is strengthened by the soft contact C27–
H27B/O24xvii between t-Bu and OMe groups, dipolar carbonyl–
carbonyl and p-stacking interactions to form p-stacked pairs.
Both p-stacked molecules are related by C2 symmetry axis, in
close similarity with the parent oxalamate 4: two self-comple-
mentary sheared parallel carbonyl–carbonyl interactions C8]
1
helixes are interlinked by O16–H16/O9xiii (xiii: ꢂ /2 ꢂ x, 1/2 ꢂ y,
ꢂz) interactions through the ending ethanolamine OH and the
2
ethanolamide CO, forming R2 (34) ring motifs, which combined
O8/C19xvii [O8/C19 ¼ 3.235(4) A, C8]O8/C19 ¼ 105.2(2) ],
ꢁ
ꢁ
with the above mentioned N7–H7/O16 interactions depict
2
2
2
C18]O18/C9xvii [O18/C9 ¼ 3.284(4) A, C18]O18/C9 ¼
ꢁ
a R2 (7)[R2 (30) R2 (34)] second level ring motif. A view of the
full set of hydrogen bonding motifs in the ac plane is shown in
Fig. 9(b). H2O2 squares and H4O4 boat like octagons appear as
intrahelix and interhelix motifs, when three-centred HB is
considered: O8/H10/O8 (S:H10 ¼ 360ꢁ) and O9/H7/O16
(S:H7 ¼ 349ꢁ), respectively. Better appreciated is the 20-
membered ring in the top view of the helix shown in Fig. 9(c). The
whole 2-D architecture is composed of independent-weaving
sheets propagating in the (2 0 ꢂ2) direction.
100.4(2)ꢁ] and a face-to-face p-stackingxvii with intercentroid and
ꢁ
interplanar distances of 3.6756(17) and 3.3608(11) A, respec-
tively, Fig. 10(b). Thus the full architecture is seen, in the bc
plane, as a wall formed by lines of molecules alternately linked
only by HB and then by a combination of HB and p-stacking
interactions, running along the (ꢂ1 0 14) direction, Fig. 10(c).
Hydrophobic contacts among these blocks along the direction of
the a axis are given between tert-butyl groups with C29/C29
ꢁ
In molecule 7, where the adopted conformation maximizes the
intramolecular hydrogen bonding, also centrosymmetric dimers
are formed by hydrogen bonding between one ending hydroxyl
group and RNHCO amide carbonyl O13–H13/O19xiii, and also
distance of 4.184(4) A.
3. Discussion
2
2
by C25–H25A/O9xiii soft interactions to form R2 (16)[R2 (30)
The lengthening of the C1–N7/C3–N17 bonds suggests that the
twisted conformation breaks the conjugation between the phenyl
ring and the amide bond and directs the two oxalyl arms one
above and the other below the plane of the phenyl ring. The
XRD conformations exhibited by compounds 2–7 are the result
of maximization of intramolecular hydrogen bonding and C–
H/OC interactions, both assisted by dipole–dipole interactions
coming from favorable antiparallel arrangements of the local N–
H/OC dipoles. The conformation of oxalamates 3 and 4 is
reliable; it is almost the same in oxalamides 6 and 7, whereas the
2
R2 (18)] second level ring motif. One dimension is generated by
the propagation of this motif along the direction of the b axis
through N10–H10/O13xiv (xiv: ꢂx, ꢂy, ꢂz) hydrogen bonding
1
2
to form R2 (10) ring motifs and C22–H22A/O8xv (xv: ꢂ /2 + x,
1
/
+ y, z) forming C(13) chains, Fig. 10(a). The curvature of the
2
assembly is inherently imprinted by the exo–exo symmetric
disposition of the oxalamide arms. The remaining OH, NH and
CO groups link the curved chains through O23–H23/O9xvi
1
(xvi: ꢂ /2 ꢂ x, 1/2 + y, 1/2 ꢂ z) and N20–H20/O23xvii (xvii: ꢂx, y,
1
2
/
ꢂ z) interactions, to form C(15) and R2 (10) ring motifs. The
2
conformation of oxalamate 2 does not remain in the
Fig. 9 (a) View of supramolecular meso-helix of compound 6, hydrogen bonding interactions lie in the plane. (b) View of the full set of hydrogen
2
bonding motifs in the ac plane: N10–H10/O8 (R2 (10)), N7–H7/O16 and O16–H16/O9, intrahelix H2O2 squares and interhelix H4O4 boat like
2
octagons are highlighted. (c) Top view of R2 (20) interhelical ring motif.
4756 | CrystEngComm, 2011, 13, 4748–4761
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Fig. 10 (a) Supramolecular 1-D chains formed by O–H/O, N–H/O and C–H/O interactions along the b axis in compound 7. (b) Molecular pair
formed by C]O/C]O dipolar and face-to-face p-stacking interactions. (c) Full supramolecular architecture shown as a wall formed by lines of
molecules alternately linked only by HB and then by a combination of HB and p-stacking interactions, running along the (ꢂ1 0 14) direction.
corresponding oxalamide 5. The transformation of oxalamate
into the corresponding oxalamide is accompanied with an
increase in the hydrogen bonding capabilities. Intramolecular
hydrogen bonding is increased by one S(5) ring motif per arm.
The hydrogen bonding nature of the intramolecular O9/H7/
O23/H17/O19 interactions in compound 7 was confirmed by
bonding in dioxalamates 2 and 3 whereas the 2-D is structured
through weak C–H/O interactions. Hydroxyl combined with
amide moieties are not enough to develop a strong 3-D in oxala-
mides 5 and 6, although they show more complex networks in
comparison with their parent oxalamates.
2
Instead of the characteristic R2 (10) ring motif frequently
DdNHPh/DT measurements, with a value of ꢂ2.0 ppm Kꢂ1
.
observed in oxalamide and oxalamate supramolecular architec-
2
tures, the R2 (16) ring motif is recurrent in oxalamates 2 and 3,
Theoretical calculations predict the exo(ap)–exo(ap)
conformer as the most stable in compounds 2, 4, 5 and 7 and
conformer endo(sc)–endo(sc) in compounds 3 and 6 in agreement
with the steric effects exerted by the substituents in the phenyl
ring. Differences between theoretical predictions and XRD
structures in compounds 2 and 5 can be attributed to intra-
molecular C–H/OC interactions which are strong enough to
overcome the small energy difference between both conformers.
There is a clear trend, in the solid state, to adopt an exo(ap)–
exo(ap) conformation by increasing the steric requirements of the
C2-substituent. Further substitution in C4 and C6 leads to both
oxalyl arms almost perpendicularly positioned to the phenyl ring
resulting in a very reliable conformation also observed in
diamides derived from 2,4,6-trimethyl-benzene-1,3-diamine.18
Intermolecular NH/O]C(amide) hydrogen bonds are
preferred over NH/O]C(ester) as supramolecular synthons in
the formation of crystal networks by dioxalamates 2 and 3. This
last interaction is exclusively used for intramolecular hydrogen
bonding. Carbonyl amide groups are also differentially used for
hydrogen bonding in oxalamides, NH/O]C amide dislike
interactions are mainly used for intramolecular HB in oxala-
mides 5–7 and for supramolecular synthons only when also
involved in intramolecular three-centred hydrogen bonding.
NH/O]C amide-like interactions are exclusively used for
intermolecular hydrogen bonding in compound 5.
and in oxalamide 5. This motif appears associated with pd–p-
stacking interactions between the phenyl spacers in oxalamates 2
and 3, but not in 5. This motif is also observed in diamides
derived from 2,4,6-trimethyl-benzene-1,3-diamine18 and strongly
resembles the supramolecular staircase 1-D motif shown by
polymorph 1.
In spite of the presence of sterically demanding groups in 5 and
2
6, the R2 (10) (NH/OC) oxalamide supramolecular motif
persists, in contrast with CCDB searches which suggest that in
most of the cases when this motif was not present this was due to
severe derivatization or the presence of sterically demanding
groups.31 The intermolecular spacing along the oxalamide
2
R2 (10) tape, in 5 and 6, is in the reported range for other
oxalamides.7e Among the set of compounds analyzed, compound
2
2
5 shows both R2 (10) and R2 (16) ring motifs, however this last is
not associated with p-stacking interactions, mainly because of
2
the length of the oxalamide arm whose involvement in R2 (10)
hydrogen bonding motif slips the phenyl planes beyond the limits
for such interaction. Whereas the 1-D meso-helix arrangement of
oxalamide 6 is similar to that reported for polymorph 10.
On the other hand, the PhNHCO groups are exclusively
engaged in intramolecular three-centred hydrogen bonding, in
compounds 4 and 7, and thus are not available for intermolecular
interactions. Extensive intramolecular hydrogen bonding, espe-
cially when at least four adjacent rings of six or five members are
formed, avoids the participation of the amide group in inter-
molecular hydrogen bonding as has also been observed for
oxalamides derived from amino acids.7e Such is the case of
compounds 4 and 7. However, in contrast with similar
This set of compounds appears as centrosymmetric pairs in the
0-D which further develop 1-D as p-stacked columns, tapes, helix
or chains. Walls or zig-zagging, rough or weaving sheets give
shape to the 2-D. It is worthy to note that 0-D and 1-D arrays are
directed by strong amide N–H/O self-complementary hydrogen
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bis-aryloxalamides/oxalamates o-substituted with groups
capable of HB, which are characterized for their lack of
a supramolecular structure,22 compounds 4 and 7 form well
defined 2-D crystal networks built by the concurrence of more
varied interactions: CO/CO, C–H/A (A]O, p) and p-
stacking interactions, additionally strengthened by NH/OH,
OH/O]C HB in oxalamide 7. Among them, CO/CO inter-
actions play an important role since they are comparable with
hydrogen bonding.28
(0-D), p-stacked columns, tapes, chains, or helixes (1-D) and
sheets or walls (2-D). The lengthening of the oxalyl arm in
oxalamides in comparison with oxalamates, slips the phenyl rings
beyond p-stacking interactions, in compound 5, and enlarges the
turn of the helix in compound 6. Dimensionality is not increased
on going from oxalamates 2–4 to oxalamides 5–7, just the 2-D is
strengthened showing more complex networks.
The conformations of amide/oxalamate/oxalamide derivatives
of the parent 2,4,6-trimethyl-benzene-1,3-diamine and 5-tert-
butyl-2,6-diamineanisol are reliable, the former is twisted up and
down from the phenyl spacer and the latter is planar and exo to
the cavity. In contrast, amide/oxalamate/oxalamide derivatives
of both 1,3-diaminobenzene and 2-methyl-benzene-1,3-diamine
are more versatile, their final conformation will depend on the
forces that bind the crystal lattice.
Blocking 4 and 6 positions is required to maintain a reliable
out of-the-plane conformation on the transformation from
oxalamates to oxalamides. Nevertheless, the twisted conforma-
tion is not enough for intermolecular HB as reported in bis-
oxalamides. Neither twisted nor planar conformation forms
homomeric intermolecular hydrogen bonding, since bis-oxala-
mides are discrete units in the solid state.13 The increase in the
number of moieties per molecule capable of forming non-cova-
lent interactions plays a decisive role. Thus in 1,3-phenyl-diox-
alamates/dioxalamides both twisted and planar conformations
are capable to develop 2-D networks.
Among the set of studied compounds, oxalamide derivatives
of 2,4,6-trimethyl-benzene-1,3-diamine are prone to form 1-D
meso-helix supramolecular architectures. The turn of the helix
could be modulated by the pendant RNHCO residue.
5. Experimental
4. Conclusions
5.1 General methods
Conformational control of the oxalamate/oxalamide cavities was
demonstrated through the use of substituents in the C-2 position.
The bulky methyl group favours the out-of-plane conformation
in compounds 2 and 5. Whereas the participation of the methyl
group in C–H/OC interactions favors the endo conformation of
the phenylamide carbonyl. Further increasing steric strain with
methyl groups in C–4 and C–6 permanently fixes the twisted
conformation in compounds 3 and 6. Meanwhile the cooperative
participation of the bulky OMe group and its hydrogen-bonding
accepting nature leads to the exo conformation in compounds 4
and 7. Particularly the role of intramolecular three-centred
hydrogen bonding interactions in the stabilization of the exo
(ap)–exo(ap) conformation was demonstrated by variable
All chemicals and solvents were of reagent grade and used as
received. Melting points were measured on an Electrothermal IA
9100 apparatus and were uncorrected. IR spectra were recorded
neat using a Varian 3100 FT-IR with ATR system Excalibur
Series spectrophotometer. Mass spectra were obtained in
a Bruker Esquire 6000 spectrometer with an electron ionization
mode. 1H and 13C NMR spectra were recorded on a Varian
Mercury 300 (1H, 300.08; 13C, 75.46 MHz) instrument in CDCl3
solutions (2–4) or DMSO-d6 (5–7), measured with SiMe4 as the
n
internal reference, chemical shifts are in ppm and J(H–H) in
hertz. Variable temperature experiments were performed in the
same apparatus equipped with a temperature controller to keep
the temperature constant within 0.3 ꢁC, from 20–120 ꢁC in 10 ꢁC
increments with a delay of 5 min for temperature stabilization.
Each spectrum was recorded with 16 scans.
1
temperature H NMR experiments and IR spectra.
Intramolecular hydrogen-bonding interactions are determi-
nant in the adopted conformation and exert a strong influence on
the nature of non-covalent interactions that rule the organization
at the supramolecular level. More than four adjacent S(n) rings
(n ¼ 5, 6), in the same molecule, avoid intermolecular hydrogen
bonding leading to CO/CO, C–H/A (A]O, p) and p-stack-
ing interactions to direct the crystal organization in compound 4
and 7, strengthened by NH/OH, OH/O]C hydrogen
bonding in this last.
XRD experiments. Single-crystal X-ray diffraction data for
molecules 2–7 were collected on a Bruker Apex II or Nonius
Kappa area detector diffractometers at 293(2) K (2–4) or 173(2)
ꢁ
K (5–7) with Mo Ka radiation, l ¼ 0.71073 A. A summary of
crystal data and collection parameters is listed in Table 5. A
semiempirical absorption correction was applied using
SADABS31 and the program SAINT32 was used for integration
of the diffraction profiles. The structures were solved by direct
methods using SHELXS9733 program of WinGX package.34 The
final refinement was performed by full-matrix least-squares
methods on F2 with SHELXL9732 program. H atoms on C, N
and O were positioned geometrically and treated as riding atoms,
The twisted conformation of the oxalamate moiety, in
2
compounds 2 and 3, allowed the formation of R2 (16) NH/OC
motif which appears associated with pd–p-stacking interactions
between the phenyl spacers. This motif strongly resembles the
reported one for polymorph 1. In contrast, the twisted confor-
mation of the oxalamide moiety, in compound 6, forms the
robust oxalamide tapes characterized by the occurrence of the
ꢁ
with C–H ¼ 0.93–0.98 A, and with Uiso(H) ¼ 1.2Ueq(C). The
2
R2 (10) NH/OC motif, developing meso-helixes in 1-D, in close
program Mercury was used for visualization, molecular graphics
and analysis of crystal structures,35 the software used to prepare
material for publication was PLATON.36 Molecule 4 is disor-
dered in both ethyl and t-Bu groups. The ethyl group is disor-
dered over two positions (C11A and C11B, C12A and C12B)
with refined occupancy factors 0.538(17) and 0.462(17) while
similarity with the reported structure of polymorph 10. Oxala-
2
2
mide 5 shows both R2 (16) and R2 (10) motifs forming rough 2-D
sheets.
Supramolecular versatility of phenyl-oxalamate/oxalamide
moieties was demonstrated by means of the formation of dimers
4758 | CrystEngComm, 2011, 13, 4748–4761
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appropriate similarity restraints were applied to the displacement
parameters of both components. The tert-butyl group exhibits
orientational disorder, which was modelled with two positions.
The disordered C atoms were presumed to have the same
anisotropic displacement parameters. Furthermore, C–C
(methyl) distances in the tert-butyl group were restrained to be
the same for both orientations. The occupancies of the two sites
converged at 0.646 (14) and 0.354 (14). Crystals suitable for
X-ray analysis were obtained from THF (compounds 3 and 4),
DMSO (compounds 5, 6 and 7) or N,N-dimethylformamide
(compound 2). Three batches of crystals from compound 5 were
independently obtained and analyzed by XRD to give the same
space group and thus the same crystalline structure.
(C1, C3), 132.7 (C4, C6), 130.8 (C5), 130.4 (C2), 63.9 (C11), 18.5
(2Me), 14.3 (Me), 14.1 (C12). ESI MS [M + Na]+ ¼ 372.8 m/z.
Anal. Calcd for C17H22N2O6 (%): C 58.28, H 6.33, N 8.00. Found
C 58.03, H 6.25, N 10.56.
Diethyl N,N’-[1,3-(5-tert-butyl-2-methoxy)phenyl]-dioxalamate
4. 5-tert-Butyl-2,6-diamineanisol (2 g, 10.2 mmol) in THF
(50 ml) and triethylamine (3.15 ml, 22.61 mmol) was treated
dropwise under vigorous stirring with ethyl chlorooxalacetate
(2.52 ml, 22.61 mmol) at 5–10 ꢁC. After stirring for an additional
ꢁ
24 h at 25 C, the solid was removed and washed with THF to
give 4 (12.43 g, 87.2% yield) as a yellow solid, mp: 173–175 ꢁC. IR
n (neat) (cmꢂ1): 3372 (N–H), 1708 (C]O). 1H NMR: 9.25 (s, 2H,
NH), 8.21 (s, 2H, Ph), 4.40 (q, 4H, O–CH2, 3J ¼ 7.1), 3.81 (s, 3H,
O–CH3), 1.38 (t, 6H, –CH2–CH3, 3J ¼ 7.1), 1.28 (s, 9H, 3CH3).
13C NMR: 160.8 (C9), 154.1 (C8), 149.2 (C2), 137.0 (C5), 129.4
(C1, C3), 114.7 (C4, C6), 63.9 (C11), 61.7 (MeO), 35.3 (C(Me)3),
31.3 (3Me), 14.3 (C12). ESI MS [M + Na]+ ¼ 416.9 m/z. Anal.
Calcd for C19H26N2O7 (%): C 57.86, H 6.64, N 7.10. Found (%):
C 57.80, H 6.60, N 7.44.
Theoretical calculations. Geometry optimization was carried
out using the DFT/PBEPBE method with the 6-31+G (3df, 3pd)
basis set. All calculations were done using the Gaussian98
program.37
5.2 Synthesis of compounds
N1,N1 -(1,3-(2-Methyl)-phenyl)-bis-(N2-(2-hydroxyethyl)-oxa-
0
Compounds 2 and 3 were prepared as reported.38
lamide) 5. A solution of 2 (0.3 g, 0.930 mmol) in methanol (30 ml)
and ethanolamine (0.111 ml, 1.861 mmol) was refluxed for 24 h.
The suspension was filtered off and the resulting solid was
washed with acetone (3 ml) and dried to yield 0.327 g (50.6%) of
Diethyl N,N0-[1,3-(2-methyl)phenyl]dioxalamate 2. White solid,
mp: 134–136 C, IR n (neat) (cmꢂ1): 3241 (N–H), 1681 (C]O).
ꢁ
3
1H NMR: 8.86 (s, 2H, NH), 7.70 (d, 2H, J ¼ 8.2), 7.28 (t, 1H,
a white solid, mp: 232–234 C. IR n (neat) (cmꢂ1): 3282 (N–H),
ꢁ
3J ¼ 8.2), 4.42 (q, 4H, O–CH2, 3J ¼ 7.0), 2.20 (s, 3H, CH3), 1.42
1
1657 (C]O) cmꢂ1. H NMR: 10.28 (s, 2H, N7–H), 8.78 (t, 2H,
3
(t, 6H, CH2–CH3, J ¼ 7.0). 13C NMR: 161.1 (C9), 154.5 (C8),
N10–H), 7.18–7.29 (m, 3H, Ph), 4.70 (b, 2H, OH), 3.48 (t, 4H,
OCH2), 3.26 (q, 4H, NCH2), 2.01 (s, 3H, Ar–CH3). 13C NMR:
160.2 (C9), 159.4 (C8), 136.4 (C1), 129.2 (C5), 126.3 (C2), 124.3
(C4), 59.8 (C12), 42.5 (C11), 13.4 (Me). ESI MS [M + Na]+ ¼
374.8 m/z. Anal. Calcd for C15H20N4O6 (%): C 51.13, H 5.72, N
15.90. Found (%): C 51.03, H 6.00, N 15.90.
134.9 (C1, C3), 127.4 (C5), 123.0 (C2), 121.4 (C4, C6), 64.1 (C11),
14.2 (C12), 12.3 (Me). ESI MS [M + Na]+ ¼ 344.8 m/z. Anal.
Calcd for C15H18N2O6 (%): C 55.90, H 5.63, N 8.69. Found: C
55.58, H 5.75, N 9.09.
Diethyl N,N’-[1,3-(2,4,6-trimethyl)phenyl]dioxalamate 3. White
solid, mp: 194–196 ꢁC, IR n (neat) (cmꢂ1): 3225 (N–H), 1685 (C]
O). 1H NMR: 8.47 (s, 2H, NH), 7.00 (s, 1H, Ph), 4.39 (q, 4H, O–
CH2, 3J ¼ 7.1), 2.17 (s, 6H, 2CH3), 2.06 (s, 3H, CH3), 1.41 (t, 6H,
N1,N1 -(1,3-(2,4,6-Trimethyl)-phenyl)-bis-(N2-(2-(2-hydroxy-
0
ethoxy)ethyl)oxalamide) 6. A solution of 3 (0.5 g, 1.427 mmol) in
3
CH2–CH3, J ¼ 7.1). 13C NMR: 160.9 (C9), 155.1 (C8), 135.3
methanol (30 ml) and 2-(2-aminoethoxy)-ethanol (0.284 ml,
Table 5 Crystal data and collection parameters
Compound
Parameter
2
3
4
5
6
7
CCDC no.
Formulae
795133
C15H18N2O6
322.31
Monoclinic
P21/c
8.2302(12)
23.218(3)
8.1795(12)
90
94.665(2)
90
1557.8(4)
4
14 126
2745
1.160
0.030
0.054
0.125
801211/795129
C17H22N2O6
350.37
Monoclinic
P21/c
8.0352(7)
16.0173(14)
14.3980(14)
90
102.681(2)
90
1807.9(3)
4
10 973
3184
1.050
0.060
0.052
0.103
795131
801212
801213
C21H32N4O8
468.5
Monoclinic
C2/c
11.4567(6)
12.9050(7)
16.4558(10)
90.000(0)
101.828(2)
90.000(0)
2381.31(10)
4
7143
2096
0.820
0.050
0.068
0.170
801214
C19H28N4O7
424.5
Monoclinic
C2/c
13.0660(30)
24.3840(50)
13.3030(30)
90.000(0)
90.000(30)
90.000(0)
4238.35(16)
8
11 757
3613
1.121
0.071
0.055
0.186
C19H26N2O7
394.42
Triclinic
C15H20N4O6
352.35
Triclinic
Form. Wt.
Crystal system
Space group
ꢂ
ꢂ
P1
P1
ꢁ
a/A
9.9640(3)
10.2180(3)
10.5790(4)
80.969(2)
87.691(2)
87.649(2)
1062.20
2
11 563
3246
1.157
0.125
0.082
0.215
9.0080(18)
9.5510(19)
10.5930(19)
94.800(20)
99.010(30)
109.340(30)
840.3(3)
2
5214
2956
0.960
0.033
ꢁ
b/A
ꢁ
c/A
a/ꢁ
b/ꢁ
g/ꢁ
V/A
Z
3
ꢁ
Measured reflections
Independent reflections
GOOF
Rint
R[F2 >2s(F2)]
wR(F2)
0.080
0.243
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B. Dinkelmeyer, F. W. Fowler and J. W. Lauher, New J. Chem.,
1998, 129.
2.854 mmol) was refluxed for 24 h. The suspension was filtered
off and the resulting solid was washed with acetone (3 ml) and
dried to yield 0.462 g (70.29%) of a white solid, mp: 192–194 ꢁC.
IR n (neat) (cmꢂ1): 3299 (N–H), 1663 (C]O). 1H NMR: 10.20 (s,
broad 2H, N7–H), 8.73 (t, 2H, N10–H), 7.00 (s, 1H, Ph), 4.20
(broad, 2H, OH), 3.53 (m, 4H, CH2OH), 3.48 (m, 4H, CH2O–
CH2), 3.46 (m, 4H, CH2–OCH2), 3.36 (m, 4H, NCH2), 2.09 (s,
6H, 2CH3), 1.91 (s, 3H, CH3). 13C NMR (d ppm DMSO-d6):
160.6 (C9), 159.5 (C8), 134.5 (C4), 133.4 (C1), 132.9 (C5), 129.4
(C2), 72.7 (C12), 68.9 (C15), 60.8 (C14), 39.7 (C11), 18.5 (2Me),
14.1 (Me). Anal. Calcd for C22H34N4O7 (%): C 53.84, H 6.88, N
11.96. Found (%): C 53.60, H 7.20, N 11.19.
~
10 (a) M. C. Munoz, G. Blay, I. Fernandez, J. R. Pedro, R. Carrasco,
M. Castellano, R. Ruiz-Garcıa and J. Cano, CrystEngComm, 2010,
ꢀ
ꢀ
ꢀ
12, 2473; (b) I. I. Padilla-Martınez, M. Chaparro-Huerta,
F. J. Martınez-Martınez, H. Hopfl and V. Garcıa-Baez, Acta
ꢀ
ꢀ
€
ꢀ
ꢀ
Crystallogr., Sect. E: Struct. Rep. Online, 2003, 59, o825; (c)
ꢀ
~
G. Blay, I. Fernandez, J. R. Pedro, R. Ruiz-Garcıa, M. C. Munoz,
J. Cano and R. Carrasco, Eur. J. Org. Chem., 2003, 1627; (d)
G. Francese, A. Neels, H. Stoeckli-Evans and S. Decurtins, Acta
Crystallogr., Sect. C: Cryst. Struct. Commun., 1998, 54, o1858.
11 A. D. McNaught and A. Wilkinson, IUPAC. Compendium of
Chemical Terminology (the ‘‘Gold Book’’), Blackwell Scientific
Publications, Oxford, UK, 2nd edn, 1997.
12 J. Bernstein, R. E. Davis, L. Shimoni and N.-L. Chang, Angew.
Chem.,Int. Ed. Engl., 1995, 34, 1555.
13 B. Piotrkowska, M. Gdaniec, M. J. Milewska and T. Po1onski,
CrystEngComm, 2007, 9, 868.
14 E. V. Garcia-Baez, C. Z. Gomez-Castro, H. Hopfl, F. J. Martinez-
Martinez and I. I. Padilla-Martinez, Acta Crystallogr., Sect. C:
Cryst. Struct. Commun., 2003, 59, o541.
15 G. Pickaert, M. Cesario and R. Ziessel, J. Org. Chem., 2004, 69, 5335.
16 (a) P. Gilli, V. Bertolasi, V. Ferretti and G. Gilli, J. Am. Chem. Soc.,
2000, 122, 10405; (b) A. Saeed, S. Hussain and M. Bolte, Acta
Crystallogr., Sect. E: Struct. Rep. Online, 2008, 64, o521; (c)
C. P. Price, A. L. Grzesiak, J. W. Kampf and A. J. Matzger, Cryst.
Growth Des., 2003, 3, 1021.
N1,N10-(1,3-(5-tert-Butyl-2-methoxy)-phenyl)-bis-(N2-(2-hydroxy-
ethyl)oxalamide) 7. A solution of 4 (0.4 g 1.01 mmol) in ethanol
(30 ml) and ethanolamine (0.122 ml, 2.02 mmol) was refluxed for
24 h. The solution was evaporated and the resulting solid was
washed with cold ethanol (3 ml) and dried to yield 0.205 g
(47.7%) of a white solid, mp: 234–237ꢁC. IR n (neat) (cmꢂ1): 3351
(N–H), 1667 (C]O). 1H NMR: 9.86 (s, 2H, N7–H), 8.91 (t, 2H,
N10–H), 7.88 (s, 2H, Ph), 4.83 (t, 2H, OH), 3.76 (s, 3H O–CH3),
3.50 (t, 4H, OCH2), 3.25 (q, 4H, NCH2), 1.24 (s, 9H, 3CH3). 13
C
17 A. Bondi, J. Phys. Chem., 1964, 68, 441.
ꢃ
18 H. Allouchi, M. Cotrait and J. Malthete, Mol. Cryst. Liq. Cryst.,
2001, 362, 101.
NMR: 160.3 (C9), 158.6 (C8), 147.5 (C2), 140.3 (C5), 130.0 (C1,
C3), 116.1 (C4, C6), 59.7 (3CH3), 61.7 (O–Me), 42.7 (C–(CH3)3).
Anal. Calcd for C19H28N4O7 (%): C 53.76, H 6.65, N 13.20.
Found (%): C 53.73, H 6.71, N 12.78.
19 Y.-Y. Zhu, J. Wu, C. Li, J. Zhu, J.-L. Hou, C.-Z. Li, X.-K. Jiang and
Z.-T. Li, Cryst. Growth Des., 2007, 7, 1490.
20 (a) R. Wieczorek and J. J. Dannenberg, J. Am. Chem. Soc., 2003, 125,
14065; (b) R. Viswanathan, A. Asensio and J. J. Dannenberg, J. Phys.
Chem. A, 2004, 108, 9205.
21 R. Taylor, O. Kennard and W. Versichel, J. Am. Chem. Soc., 1984,
106, 244.
Acknowledgements
ꢀ
22 F. J. Martınez-Martınez, I. I. Padilla-Martınez, M. A. Brito,
E. D. Geniz, R. C. Rojas, J. B. R. Saavedra, H. Hopfl,
ꢀ
ꢀ
This work was supported by CONACYT grant 83378, SIP-IPN
€
ꢀ
(Secretarıa de Investigacion y Postgrado del Instituto Politecnico
ꢀ
ꢀ
M. Tlahuextl and R. Contreras, J. Chem. Soc., Perkin Trans. 2,
1998, 401.
ꢀ
Nacional), CGIC-UC (Coordinacion General de Investigacion
ꢀ
ꢀ
ꢀ
ꢀ
23 I. I. Padilla-Martınez, F. J. Martınez-Martınez, C. I. Guillen-
Hernandez, M. Chaparro-Huerta, L. C. Cabrera-Perez,
ꢀ
ꢀ
Cientıfica de la Universidad de Colima) and PROMEP-SEP.
ꢀ
ꢀ
ꢀ
C. Z. Gomez-Castro, B. A. Lopez-Romero and E. V. Garcıa-Baez,
ARKIVOC, 2005, 401.
ꢀ
ꢀ
ꢀ
References
24 H. O. Desseyn, S. P. Perlepes, K. Clou, N. Blaton, B. J. V. d. Veken,
R. Dommisse and P. E. Hansen, J. Phys. Chem. A, 2004, 108, 5175.
1 J. W. Steed and J. L. Atwood, Supramolecular Chemistry, John Wiley
& Sons, Ltd., UK, 2nd edn, 2009.
2 (a) T. Shimizu, M. Masuda and H. Minamikawa, Chem. Rev., 2005,
105, 1401; (b) E. R. Kay, D. A. Leigh and F. Zerbetto, Angew.
Chem., Int. Ed., 2007, 46, 72; (c) J. D. Fox and S. J. Rowan,
Macromolecules, 2009, 42, 6823–6835.
3 E. T. Kool, Chem. Rev., 1997, 97, 1473.
4 T. Bugg, Introduction to Enzyme and Coenzyme Chemistry, Blackwell
Publishing Ltd, Oxford, UK, 2004.
5 O. Keskin, A. Gursoy, B. Ma and R. Nussinov, Chem. Rev., 2008,
108, 1225.
ꢀ
25 I. I. Padilla-Martınez, F. J. Martınez-Martınez, E. V. Garcıa-Baez,
J. M. Torres-Valencia, S. Rojas-Lima and H. Hopfl, J. Chem. Soc.,
ꢀ
ꢀ
ꢀ
ꢀ
€
Perkin Trans. 2, 2001, 1817.
26 T. Steiner, Angew. Chem., Int. Ed., 2002, 41, 48.
27 G. R. Desiraju, Acc. Chem. Res., 1996, 29, 441.
28 M. Nishio, CrystEngComm, 2004, 6, 130.
29 F. H. Allen, C. A. Baalham, J. P. M. Lommerse and P. R. Raithby,
Acta Crystallogr., Sect. B: Struct. Sci., 1998, 54, 320.
30 (a) J. H. Williams, Acc. Chem. Res., 1993, 26, 593; (b) I. Dance and
M. Scudder, Chem.–Eur. J., 1996, 2, 481.
_
31 M. Hoffman, U. Rychlewska and B. Warzajtis, CrystEngComm,
6 S. D. Sarker and L. Nahar, Chemistry for Pharmacy Students:
General, Organic and Natural Product Chemistry, John Wiley &
Sons Ltd, London, England, 2007.
7 (a) P. W. Baures, J. R. Rush, A. V. Wiznycia, J. Desper, B. A. Helfrich
and A. M. Beatty, Cryst. Growth Des., 2002, 6, 653; (b) O. Ugono,
N. P. Rath and A. M. Beatty, Cryst. Growth Des., 2009, 9, 4595; (c)
C. B. Aakeroy, J. Desper and J. F. Urbina, Chem. Commun., 2005,
2820; (d) C. B. Aakeroy, J. Desper and I. Hussain, Cryst. Growth
Des., 2006, 6, 474; (e) T. L. Nguyen, F. W. Fowler and
J. W. Lauher, J. Am. Chem. Soc., 2001, 123, 11057.
2005, 7, 260.
32 Bruker, APEX II, SAINT, SADABS and SHELXTL, Bruker AXS
Inc., Madison, Winsconsin, USA, 2004.
33 G. M. Sheldrick, Acta Crystallogr., Sect. A: Found. Crystallogr., 2008,
64, 112.
34 L. J. Farrugia, J. Appl. Crystallogr., 1999, 32, 837.
35 C. F. Macrae, P. R. Edgington, P. McCabe, E. Pidcock, G. P. Shields,
R. Taylor, M. Towler and J. van de Streek, J. Appl. Crystallogr., 2006,
39, 453.
36 A. L. Spek, J. Appl. Crystallogr., 2003, 36, 7.
8 J. W. Lauher, ACA Trans., 2004, 39, 31.
9 (a) R. Marx, S. J. Glasera and M. Bolte, Acta Crystallogr., Sect. E:
37 M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria,
M. A. Robb, J. R. Cheeseman, V. G. Zakrzewski,
J. A. Montgomery, R. E. Stratmann, Jr, J. C. Burant, S. Dapprich,
J. M. Millam, A. D. Daniels, K. N. Kudin, M. C. Strain,
O. Farkas, J. Tomasi, V. Barone, M. Cossi, R. Cammi,
B. Mennucci, C. Pomelli, C. Adamo, S. Clifford, J. Ochterski,
G. A. Peterson, P. Y. Ayala, Q. Cui, K. Morokuma, D. K. Malick,
ꢀ
Struct. Rep. Online, 2003, 59, o1425; (b) F. J. Martınez-Martınez,
P. Maya-Lugardo, E. V. Garcıa-Baez, H. Hopfl, J. Hernandez-Dıaz
ꢀ
ꢀ
ꢀ
€
ꢀ
ꢀ
ꢀ
and I. I. Padilla-Martınez, Acta Crystallogr., Sect. E: Struct. Rep.
Online, 2005, 61, o2994; (c) S. Coe, J. J. Kane, T. L. Nguyen,
L. M. Toledo, E. Wininger, F. W. Fowler and J. W. Lauher, J. Am.
Chem. Soc., 1997, 119, 86; (d) T. L. Nguyen, A. Scott,
4760 | CrystEngComm, 2011, 13, 4748–4761
This journal is ª The Royal Society of Chemistry 2011

View Article Online
A. D. Rabuck, K. Raghavachari, J. B. Foresman, J. Cioslowski,
J. V. Ortiz, A. G. Baboul, B. B. Stefanov, G. Liu, A. Liashenko,
P. Piskorz, I. Komaromi, R. Gomperts, R. L. Martin, D. J. Fox,
T. Keith, M. A. Al-Laham, C. Y. Peng, A. Nanayakkara,
M. Challacombe, P. M. W. Gill, B. Johnson, W. Chen,
M. W. Wong, J. L. Andres, C. Gonzalez, M. Head-Gordon,
E. S. Replogle and J. A. Pople, Gaussian 98, Revision A.9,
Gaussian, Inc., Pittsburgh, PA 1998.
38 (a) J. B. Wright, C. M. Hall and H. G. Johnson, J. Med. Chem., 1978,
ꢀ
21, 930; (b) E. Pardo, R. Ruiz-Garcıa, F. Lloret, M. Julve, J. Cano,
J. Pasan, C. Ruiz-Perez, Y. Filali, L.-M. Chamoreau and
Y. Journaux, Inorg. Chem., 2007, 46, 4504.
This journal is ª The Royal Society of Chemistry 2011
CrystEngComm, 2011, 13, 4748–4761 | 4761