Syntheses and characterization of aryl-substituted pyrogallol[4]arenes and resorcin[4]arenes

Article abstract of DOI:10.1039/c5ce01792k

Seven aryl-substituted pyrogallol[4]arenes and six aryl-substituted resorcin[4]arenes were synthesized through the acid catalyzed reaction of either pyrogallol or resorcinol with a specific alkoxybenzaldehyde. Single crystal X-ray data was obtained for all thirteen compounds. In order to determine the effect of the different pendent -R groups, four properties were investigated: π-π distance, inward tilt, twist angle, and the angle between the planes containing the pendent -R groups. Positioning of the -R groups, the carbon atom chain length of the -R groups, the number of upper-rim hydroxyl groups (resorcin[4]arene vs. pyrogallol[4]arene), and the number of substituted phenyl groups all influenced these four properties. The trends that develop are investigated and discussed.

Full text of DOI:10.1039/c5ce01792k

CrystEngComm
View Article Online
View Journal
PAPER
Syntheses and characterization of aryl-substituted
pyrogallol[4]arenes and resorcin[4]arenes†
Cite this: DOI: 10.1039/c5ce01792k
a
a
b
a
*
Constance R. Pfeiffer, Kyle A. Feaster, Scott J. Dalgarno and Jerry L. Atwood
Seven aryl-substituted pyrogallol[4]arenes and six aryl-substituted resorcin[4]arenes were synthesized
through the acid catalyzed reaction of either pyrogallol or resorcinol with a specific alkoxybenzaldehyde.
Single crystal X-ray data was obtained for all thirteen compounds. In order to determine the effect of the
different pendent –R groups, four properties were investigated: π–π distance, inward tilt, twist angle, and
the angle between the planes containing the pendent –R groups. Positioning of the –R groups, the carbon
atom chain length of the –R groups, the number of upper-rim hydroxyl groups (resorcin[4]arene vs. pyro-
gallol[4]arene), and the number of substituted phenyl groups all influenced these four properties. The
trends that develop are investigated and discussed.
Received 8th September 2015,
Accepted 20th October 2015
DOI: 10.1039/c5ce01792k
www.rsc.org/crystengcomm
reference point, r, is followed by stereochemical positions cis,
c, or trans, t, going counterclockwise around the molecule.
Introduction
Due to their flexibility and bowl-shaped cavity, calix[4]arenes
have garnered attention over the last forty years. They have
found extensive applications in a range of fields due to their
ability to act as host molecules for a variety of guest mole-
cules.1 As a result of the considerable number of applications
of calix[4]arenes, related hosts were synthesized, such as pyro-
gallol[4]arenes and resorcin[4]arenes (see Fig. 1). Pyrogallol[4]
arenes and resorcin[4]arenes imitate the conformation and
shape of calix[4]arenes; however, the possibility of more
hydrogen bonding due to the presence of more hydroxyl
groups on the upper-rim (eight for resorcin[4]arenes and
twelve for pyrogallol[4]arenes) has led to new chemistry and
to supramolecular architectures such as metal-seamed dimers
and hexamers.2,3
Niedel and Vogel led the way in the 1940s with research in
resorcin[4]arenes. Their work concentrated on the reactions
of resorcinol with aliphatic aldehydes. These reactions
resulted in the formation of the all-cis cone stereoisomer (see
Fig. 2).4,5
Later research by Hoegberg exposed three more possible
conformers of resorcin[4]arenes: boat, saddle, and chair.6
The orientations of the pendent –R groups for resorcin[4]
arene are given the nomenclature of rccc (cone), rcct (partial
cone), rcct (saddle), and rctt (chair) and they describe the ori-
entation of the aliphatic or aryl –R group (see Fig. 2). The
Vogel undertook further studies on the conformers of resor-
cin[4]arenes with variable temperature 1H NMR studies. It
was determined that the kinetic product was the chair isomer
while the cone isomer was the thermodynamic product.6
Pyrogallol[4]arenes and resorcin[4]arenes have different
bonding interactions and structure.7 Therefore, manipulation
of the pyrogallol[4]arene and resorcin[4]arene conformers is
most likely different from that with calix[4]arenes. For
instance, for pyrogallol[4]arenes it was determined that in
aprotic solvent the chair conformation was preferred, but in
protic solvent the boat conformation was favored.8 It has
been hypothesized that the pendent –R group also might
have an impact on the resulting conformation.9 A good deal
of information is known about the synthesis pathways for
pyrogallol[4]arenes and resorcin[4]arenes; however, not much
is known about the properties and interactions that govern
these reactions. Thus, characterization and the creation of a
database of modified pyrogallol[4]arenes and resorcin[4]
arenes is needed to provide insight into the interactions
involved with these molecules and their adaptability and flex-
ibility to specific applications. Accordingly, the work herein
was carried out to uncover the properties and trends that
a Department of Chemistry, University of Missouri-Columbia, Columbia, Missouri,
65211, USA. E-mail: Atwoodj@missouri.edu
b Institute of Chemical Sciences, Heriot-Watt University, Edinburgh, EH14 4AS, UK
† Electronic supplementary information (ESI) available: Supplementary informa-
tion regarding experimental procedures is available. CCDC 1405215–1405227.
For ESI and crystallographic data in CIF or other electronic format see DOI:
10.1039/c5ce01792k
Fig.
1 Schematic structures of (a) pyrogallol[4]arene and (b)
resorcin[4]arene.
This journal is © The Royal Society of Chemistry 2015
CrystEngComm

View Article Online
Paper
CrystEngComm
Table 2 Structures with corresponding name and –R group. –R groups
attaches to bridging –CH linker through the top (top left, if more than
one phenyl group) carbon atom
Structure Name
–R group
1
C-4-Methoxyphenylpyrogallolij4]arene
Fig. 2 Possible orientations of the –R groups (a) rccc, (b) rcct, (c) rtct,
and (d) rctt. Reference group is the front, left group.
2
3
C-2-Methoxyphenylpyrogallolij4]arene
C-4-Ethoxyphenylpyrogallolij4]arene
arise from varying the phenyl substituent on pyrogallol[4]
arenes and resorcin[4]arenes.
Several studies have already been carried out with
aryl-substituted
C-phenylpyrogallolij4]arenes10–13
and
C-phenylresorcinij4]arenes.14 These have all produced the
chair conformer unless the hydroxyl group has been alkylated
(see Table 1). Additionally, studies with C-fluorophenyl-
4
5
C-4-Propoxyphenylpyrogallolij4]arene
C-4-Butoxyphenylpyrogallolij4]arene
pyrogallolij4]arene,
C-chlorophenylpyrogallolij4]arene,
and
C-bromophenylpyrogallolij4]arene have been completed (see
Table 1).15 The twist angle (the degree of rotation between
two eclipsed benzene ring substituents) is greatest and
smallest with bromophenyl and fluorophenyl substituents
respectively. Furthermore, it was found that temperature also
played a part in influencing the twist angle. The twist angle
decreased as the temperature decreased from reflux to room
temperature.
Herein seven aryl-substituted pyrogallol[4]arenes and six
aryl-substituted resorcin[4]arenes have been synthesized and
single crystal X-ray data for all thirteen structures has been col-
lected. Both the pendent –R groups and whether the molecule
is a pyrogallol[4]arene or resorcin[4]arene affect several proper-
ties of the resulting structures, including the π–π distance
between pendent –R groups, the inward tilt of the pendent –R
groups, the twist angle of the pendent –R groups, and the angle
between the planes containing the pendent –R groups (ABP).
The trends are investigated and discussed in detail (Table 2).
6
7
C-1-Naphthylpyrogallolij4]arene
C-4-Methoxy-1-naphthylpyrogallolij4]arene
8
C-4-Methoxyphenylresorcinij4]arene
9
C-3-Methoxyphenylresorcinij4]arene
C-2-Methoxyphenylresorcinij4]arene
C-4-Ethoxyphenylresorcinij4]arene
Experimental
Reagents and solvents were obtained commercially and used
without additional purification.
10
11
Synthesis of C-4-methoxyphenylpyrogallolij4]arene (1)
4-Methoxybenzaldehyde. Into 5 grams of 4-hydroxybenz-
aldehyde, 125 mL of DMF was added. The reaction was
Table 1 Previously synthesized aryl-substituted pyrogallol[4]arenes
Pendent –R group
Solvent system
12
13
C-4-Isopropoxyphenylresorcinij4]arene
C-1-Naphthylresorcinij4]arene
Phenyl10a
DMF
DMF
Methanol, pyrazine
DMSO
DMSO
DMSO
DMSO
DMSO
Biphenyl13
Naphthyl11
4-Cyanophenyl15
4-Fluorophenyl15
4-Chlorophenyl15
4-Bromophenyl15
4-Hydroxyphenyl10b
CrystEngComm
This journal is © The Royal Society of Chemistry 2015

View Article Online
CrystEngComm
Paper
stirred until all 4-hydroxybenzaldehyde dissolved. To the reac-
tion, 1.97 grams of sodium hydride was added and the solu-
tion was stirred at room temperature for ten minutes. To the
solution, 3.05 mL of iodoethane was added and the solution
was stirred at room temperature for one hour. The reaction
was quenched with methanol then all solvent was rotovapped
off. The product was washed with a 50/50 water/chloroform
mixture. Since product dissolves in chloroform, the chloro-
form layer was removed and rotovapped off. The remaining
liquid was dried with magnesium sulfate, filtered, and all
remaining solvent was evaporated off yielding 8.3 grams of
orange liquid.
C-4-Methoxyphenylpyrogallolij4]arene. To a round bottom
flask, 3.89 grams of pyrogallol and 50 mL of ethanol were
added. The solution was stirred until the pyrogallol dissolved.
To the solution, 3.75 mL of 4-methoxybenzaldehyde was
added followed by 0.5 mL of concentrated hydrochloric acid.
The solution was heated to 90 °C and refluxed for 8 hours.
The solution was filtered and the powder dried yielding 1.8
grams of white precipitate. Colourless, plate-shaped crystals
were obtained by dissolving the powder in DMSO and
allowing the solution to slowly evaporate.
V = 1840.6(1) Å3, Z = 1, Dc = 1.355 g cm−3, F000 = 796, MoKα
radiation, λ = 0.71073 Å, T = 173 K, 8668 reflections collected.
Final GooF = 1.02, R1 = 0.073, wR2 = 0.102, R indices based
on reflections with I > 2σ(I) (refinement on F2), 465 parame-
ters, 0 restraints. Lp and absorption corrections applied,
μ = 0.26 mm−1.
Cocrystal 4. C176H272O56S24, M = 4053.38, pink prism, a =
13.980(1) Å, b = 16.337(2) Å, c = 24.278(2) Å, α = 77.851IJ1)°, β
3
¯
= 73.707IJ1)°, γ = 73.719IJ1)°, space group P1, V = 5056.3(9) Å ,
Z = 1, Dc = 1.331 g cm−3, F000 = 2160, MoKα radiation, λ =
0.71073 Å, T = 173 K, 20 582 reflections collected. Final GooF
= 1.07, R1 = 0.171, wR2 = 0.265, R indices based on reflections
with I > 2σ(I) (refinement on F2), 1190 parameters, 119
restraints. Lp and absorption corrections applied, μ = 0.33
mm−1.
Cocrystal 5. C92H144O28S12, M = 2082.79, colourless prism,
a = 13.564(1) Å, b = 14.191(1) Å, c = 15.937(1) Å, α =
¯
110.429IJ4)°, β = 109.634IJ4)°, γ = 92.884IJ3)°, space group P1, V
= 2658(3) Å3, Z = 1, Dc = 1.301 g cm−3, F000 = 1112, MoKα radi-
ation, λ = 0.71073 Å, T = 173 K, 10 615 reflections collected.
Final GooF = 1.02, R1 = 0.121, wR2 = 0.193, R indices based
on reflections with I > 2σ(I) (refinement on F2), 662 parame-
ters, 48 restraints. Lp and absorption corrections applied,
μ = 0.32 mm−1.
Synthesis of structures 2–13
Cocrystal 6. C96H132O26S14, M = 2150.86, colourless prism,
a = 12.973(2) Å, b = 14.665(2) Å, c = 15.949(2) Å, α =
Synthesis of structures 2–13 were synthesized with a similar
method as structure 1. Complete synthesis information is
described in ESI.†
¯
97.687IJ2)°, β = 112.271IJ2)°, γ = 98.894IJ2)°, space group P1, V =
2712.0(7) Å3, Z = 1, Dc = 1.317 g cm−3, F000 = 1140, MoKα radi-
ation, λ = 0.71073 Å, T = 173 K, 12 058 reflections collected.
Final GooF = 1.06, R1 = 0.139, wR2 = 0.334, R indices based
on reflections with I > 2σ(I) (refinement on F2), 615 parame-
ters, 36 restraints. Lp and absorption corrections applied,
μ = 0.35 mm−1.
Crystallography
Single crystal X-ray data for structures 2, 8, 10, and 13 were
collected at 173 K on a Bruker Apex II CCD diffractometer
using a CuKα radiation source (1.54178 Å). Data for all other
cocrystals were collected at 100 K or 173 K on a Bruker Apex
Cocrystal 7. C86H99.8O23S7, M = 1725.88, colourless prism,
a = 12.3525(6) Å, b = 13.8124(8) Å, c = 15.0196(8) Å, α =
II CCD diffractometer, using
(0.71073 Å).
a MoKα radiation source
¯
112.326IJ2)°, β = 112.595IJ2)°, γ = 93.556IJ2)°, space group P1, V
Cocrystal 1. C76H104O28S8, M = 1774.15, colourless prism, a
= 16.0033(7) Å, b = 11.5923(5) Å, c = 22.053(1) Å, β =
= 2122.7(2) Å3, Z = 1, Dc = 1.350 g cm−3, F000 = 912, MoKα
radiation, λ = 0.71073 Å, T = 173 K, 7073 reflections collected.
Final GooF = 1.83, R1 = 0.165, wR2 = 0.434, R indices based
on reflections with I > 2σ(I) (refinement on F2), 579 parame-
ters, 66 restraints. Lp and absorption corrections applied,
μ = 0.26 mm−1.
94.549IJ2)°, space group P21/c, V = 4078.3(3) Å3, Z = 2, Dc
=
1.363 g cm−3, F000 = 1776, MoKα radiation, λ = 0.71073 Å,
T = 173 K, 48 413 reflections collected. Final GooF = 1.08,
R1 = 0.070, wR2 = 0.108, R indices based on reflections with
I > 2σ(I) (refinement on F2), 553 parameters, 54 restraints. Lp
and absorption corrections applied, μ = 0.297 mm−1.
Cocrystal 8. C152H216O44S20, M = 1537.97, colourless prism,
a = 10.6715(3) Å, b = 16.8763(5) Å, c = 24.6079(7) Å, α =
¯
Cocrystal 2. C76H123.8O26S10, M = 1774.15, colourless prism,
a = 13.3120(3) Å, b = 17.0039(4) Å, c = 22.7649(5) Å, α =
97.900IJ1)°, β = 102.264IJ1)°, γ = 99.408IJ1)°, space group P1, V =
4203.7(2) Å3, Z = 1, Dc = 1.339 g cm−3, F000 = 1800, CuKα radi-
ation, λ = 1.54178 Å, T = 173 K, 14 941 reflections collected.
Final GooF = 1.09, R1 = 0.138, wR2 = 0.249, R indices based
on reflections with I > 2σ(I) (refinement on F2), 1031 parame-
ters, 30 restraints. Lp and absorption corrections applied,
μ = 3.01 mm−1.
¯
105.340IJ1)°, β = 102.612IJ1)°, γ = 106.369IJ1)°, space group P1,
V = 45.22.76IJ18) Å3, Z = 2, Dc = 1.303 g cm−3, F000 = 1896,
CuKα radiation, λ = 1.54178 Å, T = 173 K, 14 967 reflections
collected. Final GooF = 2.47, R1 = 0.232, wR2 = 0.564, R indi-
ces based on reflections with I > 2σ(I) (refinement on F2),
1021 parameters, 102 restraints. Lp and absorption correc-
tions applied, μ = 2.85 mm−1.
Cocrystal 9. C72H96O20S8, M = 1537.98, colourless plate, a =
12.529(1) Å, b = 13.245(1) Å, c = 13.638(1) Å, α = 112.439IJ1)°, β
3
¯
Cocrystal 3. C72H92O22S6, M = 1501.82, colourless plate, a =
10.3128(4) Å, b = 13.6528(5) Å, c = 15.1819(6) Å, α =
= 109.559IJ1)°, γ = 92.935IJ1)°, space group P1, V = 1929.0(3) Å ,
Z = 1, Dc = 1.324 g cm−3, F000 = 816, MoKα radiation, λ =
0.71073 Å, T = 100 K, 8543 reflections collected. Final GooF =
¯
113.311IJ2)°, β = 105.470IJ2)°, γ = 95.699IJ2)°, space group P1,
This journal is © The Royal Society of Chemistry 2015
CrystEngComm

View Article Online
Paper
CrystEngComm
Table 3 π–π distance and inward tilt of aryl-substituted pyrogallol[4]
arenes and resorcin[4]arenes
1.03, R1 = 0.060, wR2 = 0.104, R indices based on reflections
with I > 2σ(I) (refinement on F2), 482 parameters, 0 restraints.
Lp and absorption corrections applied, μ = 0.30 mm−1.
Cocrystal 10. C80H120O24S12, M = 1850.48, colourless prism,
a = 13.6701(2) Å, b = 16.5031(3) Å, c = 21.1363(3) Å, β =
π–π distance C–C distance C–C distance Tilt inwarda
Structure (Å)
1 (Å)
2 (Å)
(Å)
1
2
4.59
4.29
4.47
4.01
4.45
4.85
4.84
4.77
3.89
4.14
3.93
3.93
4.49
4.08
4.30
4.19
4.46
5.12
4.56
4.88
4.87
4.81
4.91
4.96
4.96
4.96
4.74
4.74
4.77
4.77
4.98
4.84
4.84
4.81
4.82
5.06
4.87
0.59
99.896IJ1)°, space group P21/n, V = 4697.4(1) Å3, Z = 2, Dc
=
4.63
4.42
4.68
4.90
4.90
4.83
4.29
4.40
4.34
4.34
4.74
4.43
4.54
4.46
4.59
5.10
4.68
0.40
0.80
0.46
0.11
0.12
0.19
0.85
0.60
0.84
0.84
0.49
0.76
0.54
0.62
0.36
−0.06
0.31
1.308 g cm−3, F000 = 1968, CuKα radiation, λ = 1.54178 Å,
T = 173 K, 8608 reflections collected. Final GooF = 3.29,
R1 = 0.206, wR2 = 0.602, R indices based on reflections with
I > 2σ(I) (refinement on F2), 552 parameters, 66 restraints. Lp
and absorption corrections applied, μ = 3.16 mm−1.
3
4
5
6
7
8
Cocrystal 11. C156H220O42S18, M = 953.01, colourless plate,
a = 13.887(2) Å, b = 15.638(2) Å, c = 23.205(3) Å, α =
¯
9
10
11
99.446IJ2)°, β = 101.639IJ2)°, γ = 114.753IJ2)°, space group P1, V
= 4304(1) Å3, Z = 1, Dc = 1.290 g cm−3, F000 = 1780, MoKα radi-
ation, λ = 0.71073 Å, T = 100 K, 14 853 reflections collected.
Final GooF = 1.02, R1 = 0.131, wR2 = 0.196, R indices based
on reflections with I > 2σ(I) (refinement on F2), 1019 parame-
ters, 32 restraints. Lp and absorption corrections applied,
μ = 0.30 mm−1.
12
13
a
Tilt inward is calculated as the difference between C–C distance 2
and C–C distance 1.
Cocrystal 12. C160H224O40S16, M = 3300.35, colourless
prism, a = 12.108(1) Å, b = 13.592(1) Å, c = 26.446(3) Å, α =
¯
88.602IJ1)°, β = 85.738IJ1)°, γ = 83.463IJ1)°, space group P1, V =
4311.5(7) Å3, Z = 1, Dc = 1.270 g cm−3, F000 = 1760, MoKα radi-
ation, λ = 0.71073 Å, T = 100 K, 17 182 reflections collected.
Final GooF = 1.02, R1 = 0.100, wR2 = 0.120, R indices based
on reflections with I > 2σ(I) (refinement on F2), 1005 parame-
ters, 0 restraints. Lp and absorption corrections applied,
μ = 0.27 mm−1.
Table 4 Twist angles and angle between the planes of eclipsed –R
groups for aryl-substituted pyrogallol[4]arenes and resorcin[4]arenes
90° −
angle
1 (°)
90° −
angle
2 (°)
Twist
angle
(°)
Angle
1 (°)
Angle
2 (°)
ABP (°)
(esd)
Structure
Cocrystal 13. C128H108O8N12, M = 1942.26, colourless plate,
a = 13.0650(3) Å, b = 14.1576(3) Å, c = 15.2003(3) Å, α =
1
2
85.4
87.1
86.6
85.6
91.6
91.6
84.8
83.0
80.1
83.3
83.0
85.7
84.3
83.8
81.4
83.8
90.1
86.4
85.5
86.3
85.3
88.0
122
4.6
2.9
3.4
4.4
−1.6
−1.6
5.2
7.0
9.9
6.7
7.0
4.3
5.7
6.2
1.2
6.2
−0.1
3.6
4.5
3.7
4.7
2.0
−32
−0.2
0.9
6.4
1.2
4.8
4.8
3.1
5.5
2.0
8.6
0.7
−0.4
3.0
9.1
6.6
8.1
21.57 (0.14)
10.26 (1.14)
16.53 (1.15)
19.12 (0.13)
67.09 (0.55)
67.11 (0.55)
30.52 (0.40)
21.31 (0.18)
16.27 (0.34)
22.75 (0.26)
22.63 (0.26)
49.79 (0.08)
16.42 (0.35)
22.60 (0.29)
21.19 (0.25)
21.63 (0.14)
45.15 (0.10)
14.16 (0.08)
¯
72.404IJ1)°, β = 76.963IJ1)°, γ = 75.955IJ1)°, space group P1, V =
3
4
6.4
2564.45(9) Å3, Z = 1, Dc = 1.258 g cm−3, F000 = 1024, CuKα
radiation, λ = 1.54178 Å, T = 173 K, 8990 reflections collected.
Final GooF = 1.054, R1 = 0.062, wR2 = 0.175, R indices based
on reflections with I > 2σ(I) (refinement on F2), 665 parame-
ters, 0 restraints. Lp and absorption corrections applied,
μ = 0.63 mm−1.
−33.8
−1.8
6.1
13.4
11.1
11.5
11.8
7.4
90.2
89.1
83.6
88.8
85.2
85.2
86.9
84.5
88.0
88.0
89.3
90.4
87.0
5
6
7
8
9
10
11
11.2
8.2
9.8
Results
12
13
6.9
All synthesized structures form the chair conformer pack in a
bilayer arrangement. Four measurements are used to
describe and compare the structures of the aryl-substituted
pyrogallol[4]arenes and resorcin[4]arenes: π–π distance, the
tilt inward, the twist angle, and the angle between the plane
of the pendent –R groups (see Tables 3 and 4). (Note: there
are two sets of pendent –R groups, four pendent –R groups
total. Some of the molecules are symmetric through a C2h
plane so the two groups are equal and thus only one set of
measurements is given.) First, the π–π distance is the dis-
tance measured from the calculated centroids of the phenyl
groups of the pendent –R groups (see Fig. 3). This measure-
ment describes the degree the pendent –R groups are rotated
away from each other and is used with the tilt distance to
express how much the pendent –R groups are tilted inwards
−0.5
6.6
(see Fig. 4). Tilt distance is the difference between the two
C–C distances (see Fig. 5). The first C–C distance is the dis-
tance between the two C4 carbon atoms of the phenyl groups
of the –R groups and the second C–C distance is the distance
between the two C1 carbon atoms of the phenyl groups of
the –R groups (see Fig. 5). The twist angle is found using
equation 1. Angle 1 is the angle that is made up by the points
C1, C2, and C3 (see Fig. 6). Angle 2 is the angle that is made
up by the points C3, C4, and C5 (see Fig. 6). Along with the
angle between the planes of the eclipsed pendent –R groups,
CrystEngComm
This journal is © The Royal Society of Chemistry 2015

View Article Online
CrystEngComm
Paper
Fig. 6 Points C1 and C2 that make up angle 1 (blue atoms) and points
C4 and C5 that make up angle 2 (green atoms). C3 is used to find both
angles and is the orange atom. Hydrogen atoms are removed for
clarity.
Fig.
3 The π–π distance (dashed blue bond) and the calculated
centroids (blue atoms). Hydrogen atoms are removed for clarity.
Twist angle = (90° − angle 1) + (90° − angle 2)
(1)
Discussion
Several trends arose from the change in pendent –R group
and the change from pyrogallol[4]arene to resorcin[4]arene. A
summary of the trends is found at the end of this section in
Table 7 (for compound 13, keep in mind that it is crystallized
in pyridine, not DMSO like all other compounds). First exam-
ined is π–π distance. With the pyrogallol[4]arene-based com-
pounds (excluding naphthalene-based) (2 and 3), the π–π dis-
tance is greater than in resorcin[4]arene-based compounds
(8, 10, and 11) (see Table 5). There are two different trends
for π–π distance in pyrogallol[4]arene and resorcin[4]arene
compounds that have naphthyl as the –R group. In the pyro-
gallol[4]arene compounds, the pyrogallol[4]arene with a para-
methoxyphenyl –R group has a greater π–π distance than the
pyrogallol[4]arene with a naphthyl –R group (5) (4.59 Å and
4.29 Å, respectively). Furthermore, the C-1-naphthylpyrogallol-
ij4]arene has a smaller π–π distance than C-4-methoxy-1-
naphthylpyrogallolij4]arene (6) (4.29 Å and 4.40 Å, respec-
tively). In the resorcin[4]arene compound, the trend is
reversed; the resorcin[4]arene with a para-methoxyphenyl –R
group (7) has a smaller π–π distance than the resorcin[4]
arene with a naphthyl –R group (13) (4.34 Å and 4.68 Å,
respectively). Both the pyrogallol[4]arene and resorcin[4]arene
compounds have the same trend in π–π distance when the
alkoxy group is extended from one carbon atom (methoxy-
phenyl) to three carbon atoms (propoxyphenyl or iso-
propoxyphenyl). As the alkoxy group increases in carbon
atoms, the π–π distance also increases (methoxy to ethoxy to
propoxy: 4.59 Å to 4.68 Å to 4.90 Å for pyrogallol[4]arene com-
pounds and 4.34 Å to 4.46 Å, 4.54 Å to 4.59 Å, 5.10 Å for res-
orcin[4]arene compounds). Finally, both pyrogallol[4]arene
and resorcin[4]arene compounds have the same trend in π–π
Fig. 4 Difference between pendent –R groups tilting inwards and out-
wards. Hydrogen atoms are removed for clarity.
Fig. 5 C4 C–C distance (dashed blue bond) and C1 C–C distance
(dashed green bond). C4 atoms are blue while C1 atoms are green.
Hydrogen atoms are removed for clarity.
the twist angle describes the sterics and torsion between the
two groups. The angle between the planes (ABP) of the
eclipsed pendent –R groups is calculated with the MPLA com-
mand in X-Seed.16 The command creates two planes for the
two phenyl groups and then calculates the angle between.
This journal is © The Royal Society of Chemistry 2015
CrystEngComm

View Article Online
Paper
CrystEngComm
Table 5 Comparison of π–π distances and inward tilt distances for pyro-
gallol[4]arenes vs. resorcin[4]arenes
(methoxy) to three carbon atoms (propoxy or isopropoxy), the
tilt of the pendent –R group inward is smallest for the
methoxyphenyl substituted compounds (methoxy to ethoxy to
propoxy: 0.59 Å to 0.46 Å to 0.11 Å for pyrogallol[4]arene com-
pounds and 0.84 Å to 0.54 Å, 0.62 Å to 0.36 Å, −0.06 Å for res-
orcin[4]arene compounds). Finally, in regard to ortho, meta,
and para positions of the substituents, ortho substituted
compounds have –R groups that tilt more inwards than para
substituted compounds. Meta substituted compounds have
the greatest tilt inwards of the pendent –R groups (para,
ortho, meta: 0.59 Å, 0.52 Å (0.75 Å, second value) for pyrogal-
lol[4]arene compounds and 0.84 Å, 0.76 Å, 0.49 Å for resor-
cin[4]arene compounds).
Structure
1
–R group
π–π distance (Å)
Tilt inward (Å)
0.59
4.59
2
3
4.63
0.40
4.42
4.68
0.80
0.46
Next examined is the twist angle. The greater the twist
angle, the more inward the pendent –R groups are tilted. The
twist angle is greater in resorcin[4]arene compounds than in
pyrogallol[4]arene compounds (see Table 6). Also, naphthyl
substituted pyrogallol[4]arenes (5) have greater twist angles
than 4-methoxylphenyl substituted pryrogallol[4]arenes (13.4°
and 9.1°, respectively). The reverse is true for resorcin[4]arene
compounds (8 and 13). Naphthyl substituted resorcin[4]
arenes have smaller twist angles than 4-methoxylphenyl
substituted resorcin[4]arenes (6.6° and 11.5°, 11.6°, respec-
tively). In regards to naphthyl and 4-methyoxy-1-naphthyl sub-
stituents, the naphthyl-substituted pyrogallol[4]arene (5) has
8
4.34
0.84
4.34
4.43
0.84
0.76
10
11
4.54
0.54
4.46
0.62
a
greater twist angle than the 4-methyoxy-1-naphthyl-
substituted pyrogallol[4]arene (7) (13.4° and 11.1°, respec-
tively). For both the pyrogallol[4]arene and resorcin[4]arene
compounds, when the substituted pendent –R groups expand
distance when the position of the methoxy substituent is
changed. With the meta-methoxyphenyl substituent, the π–π
distance is the greatest, followed by the ortho-methoxyphenyl
substituent, and the para-methyoxyphenyl substituent has the
smallest π–π distance (para, ortho, meta: 4.59 Å, and 4.64 Å
(4.38 Å, second value) for pyrogallol[4]arene compounds and
4.34 Å, 4.43 Å, and 4.74 Å for resorcin[4]arene compounds).
The second measurement inspected is the tilt inward. The
smaller the number, the more the pendent –R groups are
tilted inward. Pyrogallol[4]arene compounds (2 and 3) have
pendent –R groups that tilt inward more than the pendent –R
groups of resorcin[4]arene compounds (8, 10, and 11) (see
Table 5). Once again, with naphthyl as the –R group, the
pyrogallol[4]arene compounds (5) and the resorcin[4]arene
compounds (8 and 13) have opposite trends. The tilt inward
for pendent –R groups on pyrogallol[4]arene compounds is
greater in C-4-methyoxyphenylpyrogallolij4]arene and smaller
in C-1-naphthylpyrogallolij4]arene (0.59 Å and 0.85 Å, res-
pectively). The opposite trend is found for resorcin[4]arene
compounds; the tilt inward for pendent –R groups is greater
in C-1-naphthylresorcinij4]arene and smaller in C-4-
methyoxyphenylresorcinij4]arene (0.31 Å and 0.84 Å, respec-
tively). With naphthyl and 4-methoxy-1-naphthyl substituents,
the naphthyl substituted compound (5) has a smaller tilt
inward than the 4-methoxy-1-naphthyl substituted compound
(6) (0.60 Å and 0.85 Å, respectively). In terms of the number
of carbon atoms in the pendent –R group, pyrogallol[4]arene
and resorcin[4]arene compounds have the same trend. When
the alkoxy group is extended from one carbon atom
Table 6 Comparison of twist angle and ABP for pyrogallol[4]arenes vs.
resorcin[4]arenes
Structure
1
–R group
Twist angle (°)
ABP (°)
9.1
21.57
2
3
6.6
10.26
8.1
6.4
16.53
19.12
8
11.5
22.75
11.8
11.2
22.63
16.42
10
11
8.2
22.60
9.8
21.19
CrystEngComm
This journal is © The Royal Society of Chemistry 2015

View Article Online
CrystEngComm
Paper
from methoxylphenyl to propoxyphenyl or isopropoxy phenyl,
the twist angle decreases (methoxy to ethoxy to propoxy: 9.1°
to 6.4° to −33.8°, −1.8° for pyrogallol[4]arene compounds and
11.5°, 11.8° to 8.2°, 9.8° to −0.5°, 6.9° for resorcin[4]arene
compounds). Ortho-substituted pyrogallol[4]arenes have the
greatest twist angle, followed by para-substituted compounds
(para, ortho: 9.1°, 10.4°, (8.4°, second value). For resorcin[4]
arene compounds, the meta-substituted compounds have the
smallest twist angle and the ortho- and para-substituted com-
pounds have similar twist angles (meta, ortho, para: 7.4°,
11.2°, 11.5°(11.6°)).
Finally, the last measurement looked at is the angle
between the planes of the eclipsed pendent –R groups (ABP).
Resorcin[4]arene compounds (8, 10, and 11) have greater
ABPs than pyrogallol[4]arene compounds (2) (see Table 6).
Pyrogallol[4]arenes and resorcin[4]arenes have the same
trend dealing with the ABP of naphthyl –R groups. In both
the pyrogallol[4]arenes and resorcin[4]arenes, the naphthyl-
substituted compound (6 and 13 respectively) has a smaller
ABP than the methyoxyphenyl-substituted compound (8)
(pyrogallol[4]arene: 21.31° and 21.57° respectively, resorcin[4]
arene: 14.16° and 22.63°, 22.75°, respectively). The naphthyl-
substituted compounds (6) have a greater twist angle than
the 4-methoxy-1-naphthyl-substituted compounds (7) (21.31°
and 16.27°, respectively). When the substituted groups are
expanded from one carbon atom (methyoxyphenyl) to three
carbon atoms (propoxy or isopropoxy), the ABP decreases
from methoxyphenyl to ethoxyphenyl but increases from
ethoxyphenyl to propoxyl/isopropoxyphenyl (methoxy to
ethoxy to propoxy: 21.57° to 19.12° to 67.09°, 67.11° for pyro-
gallol[4]arene compounds and 22.63°, 22.75° to 21.19°,
22.60° to 21.63°, 45.15° for resorcin[4]arene compounds).
Ortho-substituted compounds have the smallest ABP, followed
by para-substituted compounds, and meta-substituted com-
pounds have the largest ABP ((ortho, para, meta: 12.45°
(14.47°, second value), 21.57° for pyrogallol[4]arene com-
pounds and 16.42°, 22.63°(22.75°), 49.79° for resorcin[4]arene
compounds). A summary of all the trends discovered is found
in Table 7.
In order to compare these current results to previously
published crystal structures of aryl-substituted pyrogallol[4]
arenes and resorcin[4]arenes, similar examinations were
performed with the previously reported structures. The
results can be found in Table 8. Comparing the substituted
pyrogallol[4]arenes to the substituted resorcin[4]arenes, with
a phenyl or fluoro –R group, the pyrogallol[4]arenes have a
greater π–π distances and angle between the planes than the
resorcin[4]arenes. However, the substituted resorcin[4]arenes
have a greater inward tilt and twist angle than the substituted
pyrogallol[4]arenes. This is similar to the trends found for
alkoxy substituted pyrogallol[4]arenes and resorcin[4]arenes
except for the angle between the planes. For chloro –R
groups, the pyrogallol[4]arenes have a greater inward tilt and
twist angle than the resorcin[4]arenes and the resorcin[4]
arenes have a greater π–π distances and angle between the
planes. These trends are dissimilar to the trends found in the
alkoxy substituted pyrogallol[4]arenes except for the angle
between the planes (see Table 9 for a summary of the trends).
Table 7 Trends for π–π distance, inward tilt, twist angle, and the angle between the planes (ABP) containing the pendent –R groups for all aryl-
substituted pyrogallol[4]arenes and resorcin[4]arenes
Measurement
Properties
π–π distance
Pyro > res
Inward tilt
Twist angle
ABP
Pyrogallol[4]arene (pyro) vs.
Pyro < res
Pyro < res
Pyro < res
resorcin[4]arene (res)
Naphthyl (naph) vs. methoxyphenyl Pyro met > naph res
Pyro met < naph res
met > naph
1 > 2 > 3
Pyro met < naph res
met > naph
1 > 2 > 3
Pyro met > naph res
met > naph
1 > 2 < 3
(met)
met < naph
1 < 2 < 3
Methoxyl (1), ethoxyl (2), vs.
propoxyphenyl (3)
Ortho (o) vs. meta (m) vs. para (p)
p < o < m
p > o > m
m < o ≈ p
o < p < m
Table 8 π–π distance, inward tilt, twist angle, and angle between the plane of previously reported aryl-substituted pyrogallol[4]arenes and resorcin[4]
arenes
Structure
π–π distance (Å)
Tilt inward (Å)
Twist angle (°)
ABP (°)
C-Phenylpyrogallolij4]arene10a
4.84
0.24
0.8
41.09
C-4-Cyanophenylpyrogallolij4]arene15a
C-4-Cyanophenylpyrogallolij4]arene15a
C-4-Chlorophenylpyrogallolij4]arene15
C-4-Bromophenylpyrogallolij4]arene15a
C-4-Bromophenylpyrogallolij4]arene15a
C-4-Fluorophenylpyrogallolij4]arene15
C-Phenylresorcinij4]arene14a
4.53
4.33
4.33
4.50
4.57
4.25
4.17
4.47, 4.68
4.18
0.62
0.81
0.80
0.64
0.59
0.95
1.12
0.35, 0.68
1.03
8.8
33.60
21.18
18.78
20.05
15.28
25.34
23.30
23.37, 33.57
24.11
15.5
13.3
7.9
8.3
14.9
16.8
4.6, 8.5
16
C-4-Chlorophenylresorcinij4]arene14c b
C-4-Fluorophenylresorcinij4]arene14c
a
b
Two reported structures. Asymmetric structure, two set of phenyl rings.
This journal is © The Royal Society of Chemistry 2015
CrystEngComm

View Article Online
Paper
CrystEngComm
Table 9 Trends for π–π distance, inward tilt, twist angle, and the angle between the planes (ABP) containing the pendent –R groups for previously
reported aryl substituted pyrogallol[4]arenes and resorcin[4]arenes
Measurement
Properties
π–π distance
Inward tilt
Twist angle
ABP
Pyrogallol[4]arene (pyro) vs.
Phenyl, fluoro pyro > res Phenyl, fluoro pyro < res Phenyl, fluoro pyro < res Phenyl, fluoro pyro > res
resorcin[4]arene (res)
Chloro (Cl) vs. bromo (Br) vs. F < Cl < Br
chloro pyro < res
chloro pyro > res
Br < Cl < F
chloro pyro > res
F < Cl < Br
chloro pyro < res
F < Cl < Br
fluoro (F)
When comparing the chloro-, fluoro-, and bromo-
substituted pyrogallol[4]arenes and resorcin[4]arenes, several
trends emerge. For π–π distances, twist angle, and angle
between the planes the bromo-substituted pyrogallol[4]arenes
and resorcin[4]arenes have the greatest values, followed by
the chloro-substituted pyrogallol[4]arenes and resorcin[4]
arenes, and the fluoro-substituted pyrogallol[4]arenes and
resorcin[4]arenes have the smallest values. The opposite is
true for the inward tilt. The bromo-pyrogallol[4]arenes and
resorcin[4]arenes have the smallest inward tilt and the
fluoro-substituted pyrogallol[4]arenes and resorcin[4]arenes
have the greatest inward tilt (see Table 9 for a summary of
the trends).
Daschbach, C. R. Yamnitz, N. Rath and G. W. Gokel, Chem.
Commun., 2009, 7497–7499.
3 (a) S. J. Dalgarno, N. P. Power, J. E. Warren and J. L. Atwood,
Chem. Commun., 2008, 1539–1541; (b) S. J. Dalgarno, N. P.
Power and J. L. Atwood, Coord. Chem. Rev., 2008, 252,
825–841; (c) P. Jin, S. J. Dalgarno and J. L. Atwood, Coord.
Chem. Rev., 2010, 254, 1760–1768; (d) P. Jin, S. J. Dalgarno,
J. E. Warren, S. J. Teat and J. L. Atwood, Chem. Commun.,
2009, 3348–3350; (e) R. M. McKinlay, G. W. V. Cave and J. L.
Atwood, Proc. Natl. Acad. Sci. U. S. A., 2005, 102, 5944–5948.
4 J. B. Niedel and H. J. Vogel, J. Am. Chem. Soc., 1940, 62,
2512–2514.
5 B. O. Nilsson, Acta Chem. Scand., 1968, 22, 732–747.
6 A. G. S. Hoegberg, J. Am. Chem. Soc., 1980, 102, 6046–6050.
7 R. K. Castellano, D. M. Rudkevich and J. Rebek, J. Am. Chem.
Soc., 1996, 118, 10002–10003.
Conclusions
Thirteen new aryl-substituted pyrogallol[4]arenes and resor-
cin[4]arenes were synthesized. It was demonstrated that
small changes in the substituted pendent –R group (position-
ing of alkoxy group and length of alkoxy group) led to struc-
tural changes and several trends arose in π–π distance,
inward tilt, twist angle, and ABP.
8 C. Schiel, G. A. Hembury, V. V. Borovkov, M. Klaes, C.
Agena, T. Wada, S. Grimme, Y. Inoue and J. Mattay, J. Org.
Chem., 2005, 71, 976–982.
9 L. M. Tunstad, J. A. Tucker, E. Dalcanale, J. Weiser, J. A.
Bryant, J. C. Sherman, R. C. Helgeson, C. B. Knobler and
D. J. Cram, J. Org. Chem., 1989, 54, 1305–1312.
Further studies are being undertaken to determine the
effect of substitution on phenylpyrogallol[4]arenes. Longer
alkoxy groups in different positions are being synthesized as
only methoxyphenyl was done in all three (ortho, meta, and
para) positions. Additionally, phenyl rings are being
expanded to determine if anthracene and pyrene groups
could be substituted. Furthermore, studies have been started
to convert the chair conformer of all structures to the boat
conformer. This is being attempted through refluxing, micro-
wave synthesis, or changes in solvent system. With the boat
conformers synthesized, these compounds will be used to
create a library of metal-seamed dimeric and hexameric
nano-capsules.
10 (a) J. P. Kass, C. H. Zambrano, M. Zeller, A. D. Hunter and
E. E. Dueno, Acta Crystallogr., Sect. E: Crystallogr. Commun.,
2006, 62, 3179–3180; (b) E. E. Dueno, T. Ray, R. N. Salvatore,
C. Zambrano, M. Zellar and A. D. Hunter, Acta Crystallogr.,
Sect. E: Crystallogr. Commun., 2007, 63, 3533–3534.
11 C. Zambrano, J. Kass, E. Dueno, Y. Ke and H.-C. Zhou,
J. Chem. Crystallogr., 2006, 36, 67–70.
12 J. Han, X. Song, L. Liu and C. Yan, J. Inclusion Phenom.
Macrocyclic Chem., 2007, 59, 257–263.
13 T. Gerkensmeier, C. Agena, W. Iwanek, R. Frohlich, S. Kotila,
C. Nather and J. Mattay, Z. Naturforsch., B: J. Chem. Sci.,
2001, 56, 1063–1973.
14 (a) M. M. Garcia, C. V. Launizar, F. L. Ochoa, A. Toscano,
G. J. Chen and R. Cruz-Almanza, Supramol. Chem., 2000, 11,
255–261; (b) L. Zhaoa, Y. Wan, S. Huang, G. Liu, L. Chen, S.
Yue, W. Zhang and H. Wu, Lett. Org. Chem., 2013, 10,
298–301; (c) S. F. Alshahateet, S. A. Al-Trawneh, W. A. Al-
Zereini and S. S. Al-Sarhan, Jordan J. Chem., 2014, 9,
170–186.
Acknowledgements
JLA thanks the NSF for funding this work.
Notes and references
1 V. Böhmer, Angew. Chem., Int. Ed. Engl., 1995, 34, 713–745.
2 (a) S. J. Dalgarno, G. W. V. Cave and J. L. Atwood, Angew.
Chem., Int. Ed., 2006, 45, 570–574; (b) O. V. Kulikov, M. M.
15 S. F. Alshahateet, F. Kooli, M. Messali, Z. M. A. Judeh and
A. S. ElDouhaibi, Mol. Cryst. Liq. Cryst., 2007, 474, 89–110.
16 L. J. Barbour, J. Supramol. Chem., 2001, 1, 189–191.
CrystEngComm
This journal is © The Royal Society of Chemistry 2015