Density functional calculations and experimental studies of the sidearm remote controlling effect in eight lariat crown ethers

Article abstract of DOI:10.1016/j.molstruc.2006.07.035

A series of eight lariat 16-crown-5 ethers (LCEs), which have the same parent macrocycle but with a different sidearm, have been synthesized. An experimental study and a quantum mechanical research, which uses the density functional theory (DFT) to calcul

Full text of DOI:10.1016/j.molstruc.2006.07.035

Journal of Molecular Structure 831 (2007) 151–164
www.elsevier.com/locate/molstruc
Density functional calculations and experimental studies of the sidearm
remote controlling eVect in eight lariat crown ethers
Li-Hwa Lu a, Chia-Ching Su b,¤, Tian-Jye Hsieh c
a The Center of Science Education, The Fooyin University, Ta-Liao, Kaohuing 831, Taiwan, ROC
b Department of Applied Science, The ROC Naval Academy, 669, Jiun Shiaw Road, Kaohsiung 813, Taiwan, ROC
c Basic Medical Science Education Center, The Fooyin University, Ta-Liao, Kaohuing 831, Taiwan, ROC
Received 4 May 2006; received in revised form 26 July 2006; accepted 27 July 2006
Available online 14 September 2006
Abstract
A series of eight lariat 16-crown-5 ethers (LCEs), which have the same parent macrocycle but with a diVerent sidearm, have been syn-
thesized. An experimental study and a quantum mechanical research, which uses the density functional theory (DFT) to calculate at the
B3LYP/6-31G¤ level in the Gaussian 98 and Gaussian 03 package program, were conducted on these eight LCEs. The space coordinate
positions of compounds 1–4, obtained from X-ray structural analysis, were used as initial coordinates for these theoretical calculations.
The observed X-ray crystal structures of these LCEs 1–4 were compared with the optimized geometries obtained from DFT calculations.
As a result, an excellent agreement between the X-ray crystallography and the four calculated compounds of conformational analysis has
been found. However, the LCEs 5–8 were based on the LCEs 1–4 molecular model, which is the starting molecular structure that pro-
cesses the geometric optimization calculations. Molecular mechanics and density functions were used in the theoretical study as well to
determine the relative geometric stabilities of the eight compounds. The optimal geometric structures of these compounds were conWrmed
as well. The ionization potentials, highest occupied molecular orbital energy, lowest unoccupied molecular orbital energy, energy gaps,
heat of formation, atomization energies, and vibrational frequencies of these compounds were also calculated. The results of the DFT cal-
culations show that eight diVerent LCEs are stable molecules with various thermodynamic properties. Thus, sidearm eVect appears to
cause strong inXuence on the metal ion binding capability.
© 2006 Elsevier B.V. All rights reserved.
Keywords: Lariat crown ether; DFT; B3LYP; 6-31G¤; HOMO and LUMO energies; Energy gaps
1. Introduction
by designing suitable host molecules based on host–guest
interaction [3]. In addition to its compatibility of shape and
size, eVective molecular recognition requires a precise align-
ment of binding groups on the receptor with complemen-
tary regions on the substrate [4]. Additionally, the
molecular structure switch of crown ether has engendered
great attention historically because of its ability to bind cat-
ions. They have been proposed as separation agents for
removing metal ions from mixed nuclear and chemical
waste [5]. In addition, these compounds are also being stud-
ied for their applications in the analytical, pharmaceutical
Weld, and nanoscience. Therefore, one of the areas of inter-
est is the design of drug delivery vehicles [6].
The Wrst macrocyclic polyether was synthesized by Lüt-
tringhaus in 1937. He obtained dibenzo-20-crown-6 ether in
low yield after the reaction of 3-(2-bromoethoxymeth-
oxymethyl)phenol with potassium carbonate in 1-pentanol
[1]. However, it was not until 1967 that Pedersen’s decisive
work [2] about crown ethers and cryptands became the
focus of research for their remarkable selectivity in the
complexation of metal ions in the past several decades.
High selectivity of molecular recognition can be achieved
*
Corresponding author. Tel.: +886 7 583 4700x1213/+886 7 349 4826;
Studies, using a family of crown ethers containing
oxygen, nitrogen, and sulfur atoms that identify molecular
fax: +886 7 347 2802.
E-mail address: ccsu@cna.edu.tw (C.-C. Su).
0022-2860/$ - see front matter © 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2006.07.035

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L.-H. Lu et al. / Journal of Molecular Structure 831 (2007) 151–164
conformations have been extensively performed with both
experimental and theoretical approaches [7–12]. In addi-
tion, lariat crown ethers (LCEs) are composed of two parts,
the core part and the sidearm attached to it. Because of the
sidearm, crown ethers are called lariat crown ethers. They
are characterized by their parent macrocyclic ring and
ligating arms. Additionally, the relative ability with which
crown ethers can be functionalized with pendant arm (s)
containing additional donor atom (s) allows one to
improve the cation binding ability and selectivity of the
parent crown ether [13]. However, depending on the ring
size, lariat 16-crown-5 ethers can bring about enhanced
complexation, and this is due to the presence of Wve oxygen
atoms which provide additional binding sites. In addition,
the attachment of one sidearm, with potential metal ion
coordination sites, to a crown ether framework produces
complexing agents known as lariat crown ethers. In other
words, the sidearm of the lariat crown ethers can lead to
signiWcant changes in the complexation behavior of the
host molecules.
Awareness of the conformational preference of lariat
crown ether is important for predicting its three-dimen-
sional properties of molecular structures and binding
aYnities with guest molecules. This is especially
important in the Weld of supramolecular chemistry and
molecular recognition [14]. Unfortunately, because of
their large size and complexity, there are few calculations
on LECs in the literature. In recent years, scientiWc stud-
ies using the DFT calculations have become more signiW-
cant. In fact, theoretical and experimental studies are
closely correlated [15]. Without theoretical research,
experimental results alone cannot produce methods to
allow systematic analyses. Likewise, without experimen-
tal studies, the accuracy of theoretical studies cannot be
proven. These two approaches therefore supplement each
other. In addition, theoretical calculations have gradu-
ally become the mainstream of scientiWc research in the
recent decade.
We hereby report the density functional theory geometry
optimization at the B3LYP/6-31G¤ level of theory for the
eight diVerent LCEs. Our main aim is to examine the eVects
of the side arm on molecular conformation. Recent reports
of the theoretical calculations of molecules [16–26] have
shown that the B3LYP method, in the Gaussian 98 or
Gaussian 03 package program together with the 6-31G¤
basis set function (BSF) of the DFT, can be a useful tool in
providing adequately accurate conformational analysis
[27–30]. Furthermore, and importantly, this study show-
cases a comparison of theoretical method that should prove
useful to those interested in modeling eight LCEs. This
research included those using the B3LYP/6-31G¤ method
as well to conduct calculations for the determination of rel-
ative geometric structures, molecular orbital energy, and
other thermodynamic properties of eight LECs. Theoretical
calculations were also used to understand the experimental
Wndings. The eight LCEs were selected to check on the
accuracy of theoretical analysis versus experimental results.
This systematic research about conformational analysis is
also helpful to understand the inXuences of the diVerent
sidearms of LCEs on the metal ions selectivity.
N
R: 1
2
H C
2
OR
H C
2
O
S
3
4
OCH
3
O
O
O
N
N
N
H C
2
O
O
OCH
3
5
6
H C
2
O
OCH
3
CH
2
7
8
O
H C
2
H C
2
CH
3
Fig. 1. Structure of eight lariat crown ethers.

L.-H. Lu et al. / Journal of Molecular Structure 831 (2007) 151–164
153
2. Experimental details
85% (1.86g) yield, mp 122.0–123.0°C. MS (EI, 70eV): m/z
437.2 (M+«, 17%), 328.2 (48%), 148.1 (78%), 135.9 (100%),
121.0 (76%), 91.9 (88%). Elemental analysis: Calcd (found)
for C25H27NO6; C, 68.62 (68.68); H, 6.22 (6.33); N, 3.20
(3.19). 1H NMR (CDCl3): ꢀ 3.92 (m, 4H, OCH2CH2
OCH2CH2O), 4.15 (m, 4H, OCH2CH22OCH2CH2O), 4.29
2.1. Reagents and chemicals
All chemicals used for the synthesis were of available
purity and were used without any further puriWcation. Only
analytical reagent grade chemicals were used in the prepa-
ration of the diVerent eight LCEs. Hydroxy-sym-dibenzo-
16-crown-5-ether was synthesized according to literature
procedures [31] and used after recrystallization from chlo-
roform–hexane (1:5, V:V).
3
(m, 3H, OCHHꢀCHCHHꢀO), 4.40 (dd, JD8.8Hz, J D3.4
Hz, 2H, OCHHꢀCHCHHꢀO), 5.01 (s, 2H, CH2Py), 6.86 (m,
4H, benzo group), 6.97 (m, 4H, benzo group), 7.19 (m, 1H, 5
position H of Py), 7.67 (m, 2H, 3 and 4 position H of Py),
8.55 (d, 3J D4.4 Hz, 1H, 6 position H of Py).
2.2. Synthesis of 2ꢀ-picoyl sym-dibenzo-16-crown-5-ether 1
2.3. Synthesis of methylnaphthalene sym-dibenzo-16-crown-
5-ether 2
Hydroxy-sym-dibenzo-16-crown-5-ether (1.73 g, 5 mmol)
was dissolved in 50 mL anhydrous THF. NaH (0.8g,
20mmol) was added under nitrogen and the reaction
mixture was heated under reXux for 30–40min. After the
addition of 2-picolyl chloride hydrochloride (5 mmol), the
mixture was then heated (under reXux) for another 6h.
Deionized water was then added slowly to destroy the
excess NaH and quench the reaction. The reaction mixture
was then puriWed by column chromatography (silica gel,
70–230 mesh, CHCl3 eluent) to give the desired product 1 in
Hydroxy-sym-dibenzo-16-crown-5-ether (1.73g, 5mmol)
was dissolved in 50 mL anhydrous THF. NaH (0.8 g,
20 mmol) was added under nitrogen and the reaction
mixture was heated under reXux for 30–40 min. After the
addition of the 1-(chloromethyl) naphthalene (5 mmol),
the mixture was heated (under reXux) for 3 h. The excess
NaH was then destroyed with water, and the reaction
mixture was puriWed as describe in 1 to give 2 a 80%
(1.94 g) yield, mp 91.0–92.0 °C. MS (EI, 70 eV): m/z 486.3
Fig. 2. ORTEP diagram of lariat crown ether 1.

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L.-H. Lu et al. / Journal of Molecular Structure 831 (2007) 151–164
(M+«, 55%), 330.2 (4%), 194.3 (6%), 141.1 (100%), 121.1
(23%), 115.1 (13%), 109.1 (5%). Elemental analysis: Calcd
(found) for C30H30O6; C, 74.06 (74.20); H, 6.21 (6.23).
OCHHꢀCHCHHꢀO, 4H, OCH2CH2O CH2CH2O), 4.32
(m, 2H, OCHHꢀCHCHHꢀO), 5.06 (s, 2H, CH2), 6.84–7.00
(m, 8H, benzo group), 7.49 (m, 2H, naphthalene group),
7.61 (dd, 1H, naphthalene group), 7.86 (m, 4H, naphtha-
lene group).
1H NMR (CDCl3):
ꢀ
3.93 (m, 4H, OCH2CH2
OCH2CH2O), 4.16 (m, 2H, OCHHꢀCHCHHꢀO, 1H,
Fig. 3. ORTEP diagram of lariat crown ether 2.
Fig. 4. ORTEP diagram of lariat crown ether 3.

L.-H. Lu et al. / Journal of Molecular Structure 831 (2007) 151–164
155
Fig. 5. ORTEP diagram of lariat crown ether 4.
2.4. Synthesis of 4-methoxybenzenesulfonyl sym-dibenzo-16-
crown-5-ether 3
excess t-BuOK was destroyed with water, and the reaction
mixture was puriWed as describe in 1 to give 4 a 70% (1.67g)
yield, mp 98.0–99.0°C. MS (EI, 70eV): m/z 477.3 (M+«,
100%), 328.1 (9%), 149.1 (11%), 136.1 (29%), 132.0 (55%),
121.1 (48%), 77.1 (29%). Elemental analysis: Calcd (found)
Hydroxy-sym-dibenzo-16-crown-5-ether (1.73g, 5mmol)
was dissolved in 50mL anhydrous THF. NaH (0.8g,
20mmol) was added under nitrogen and the reaction mixture
was heated under reXux for 30–40min. Then, 4-meth-
oxybenzenesulfonyl chloride (5mmol) was added to this
solution. Heating of the mixture was then continued under
the reXux for 1h. Next, the excess NaH was destroyed with
water, and the reaction mixture was puriWed as describe in 1
to give 3 a 80% (2.06g) yield, mp 112.0–113.0°C. MS (EI,
70eV): m/z 516.3 (M+«, 100%), 171.1 (35%), 136.1 (43%), 121.1
(56%), 107.1 (23%), 77.1 (15%). Elemental analysis: Calcd
1
for C26H27N3O6; C, 65.40 (65.34); H, 5.70 (5.69). H NMR
(CDCl3): ꢀ 3.93 (m, 4H, OCH2CH2OCH2CH2O), 4.16 (m,
3H, OCHHꢀ CHCHHꢀO, 4H, OCH2CH2OCH2C H2O), 4.32
(m, 2H, OCHHꢀCHCHHꢀO), 6.38 (s, 2H, CH2), 6.84 –7.00
(m, 8H, benzo group), 7.41 (t, 1H, aromatic group), 7.50
(t, 1H, aromatic group), 7.80 (d, 1H, aromatic group), 8.07
(d, 1H, aromatic group).
2.6. Synthesis of 3,5-dimethoxybenzyl sym-dibenzo-16-
crown-5-ether 5
1
(found) for C26H28SO9; C, 60.45 (60.50); H, 5.46 (5.45). H
NMR (CDCl3): ꢀ 3.85 (S, 3H, OCH3), 3.88 (t, 4H,
3JD6.84Hz, OCH2CH2OCH2 CH2O), 4.10 (t, 4H,
OCH2CH2OCH2CH2O), 4.35 (qq, 4H, OCHHꢀCHCHHꢀO),
5.08 (q, 1H, OCHHꢀCHCHHꢀO), 6.84–7.00 (m, 10H, benzo
group), 7.94 (dd, 2H, benzo group).
Hydroxy-sym-dibenzo-16-crown-5-ether (1.73g, 5 mmol)
was dissolved in 50 mL anhydrous THF. NaH (0.8g,
20mmol) was added under nitrogen and the reaction mix-
ture was heated under reXux for 30–40min. After which,
3,5-dimethoxybenzyl chloride (5mmol) was added and the
reaction mixture was heated under reXux for 1h. The excess
NaH was then destroyed with water, and the reaction mix-
ture was puriWed as describe in 1 to give 5 a 80% (1.98 g)
yield, mp 99.0–100.0°C. MS (EI, 70 eV): m/z 496.1 (M+«,
42%), 206.9 (7%), 151.0 (100%), 121.0 (25%), 77.1 (10%).
Elemental analysis: Calcd (found) for C28H32O8; C, 67.73
2.5. Synthesis of 1-(methyl)-1H-benzotriazole sym-dibenzo-
16-crown-5-ether 4
Hydroxy-sym-dibenzo-16-crown-5-ether (1.73g, 5mmol)
was dissolved in 50mL anhydrous THF. t-BuOK (1.12g,
10mmol) was added under nitrogen and the reaction mixture
was kept at room temperature for 5h. After the addition
of the 1-(chloromethyl)-1H-benzotriazole (5mmol), the
mixture was kept at room temperature for 5h. Then, the
1
(67.67); H, 6.50 (6.46). H NMR (CDCl3): ꢀ 3.79 (S, 6H,
OCH3), 3.93 (m, 4H, OCH2CH2OCH2CH2O), 4.16 (m, 2H,
OCHHꢀCHCHHꢀO, 1H, OCHHꢀCHCHHꢀO, 4H, OCH2

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L.-H. Lu et al. / Journal of Molecular Structure 831 (2007) 151–164
CH2OCH2C H2O), 4.32 (m, 2H, OCHHꢀCHCHHꢀO), 4.84
(S, 2H, CH2), 6.40 (t, 1H, benzo group), 6.63 (d, 2H, benzo
group), 6.84–7.00 (m, 8H, benzo group).
CHCHHꢀ, 4H, OCH2CH2OCH2CH2O), 4.32 (m, 2H,
OCHHꢀCHCHHꢀ), 6.83–7.00 (m, 8H, benzo group), 7.18–
7.32 (m, 5H, benzo group).
2.7. Synthesis of 3-phenylpropyl sym-dibenzo-16-crown-5-
2.8. Synthesis of 3-phenoxypropyl sym-dibenzo-16-crown-5-
ether 6
ether 7
Hydroxy-sym-dibenzo-16-crown-5-ether (1.73g, 5 mmol)
was dissolved in 50mL anhydrous THF. NaH (0.8 g,
20 mmol) was added under nitrogen and the reaction mix-
ture was heated under reXux for 30–40 min. Then, 3-phenyl-
propyl bromide (5mmol) was added to this solution.
Heating was then continued under the reXux for 1h. Then,
the excess NaH was destroyed with water, and the reaction
mixture was puriWed as describe in 1 to give 6 a 79% (1.83g)
yield, mp 84.0–85.0°C. MS (EI, 70 eV): m/z 464.2 (M+«,
13%), 169.1 (10%), 155.0 (100%), 121.0 (8%), 77.0 (3%).
Elemental analysis: Calcd (found) for C28H32O6; C, 72.39
Hydroxy-sym-dibenzo-16-crown-5-ether (1.73 g, 5 mmol)
was dissolved in 50 mL anhydrous THF. t-BuOK (1.12 g,
10 mmol) was added under nitrogen and the reaction mix-
ture was kept at room temperature for 5 h. Afterward, 3-
phenoxypropyl bromide (20 mmol) was added to this
solution, in which the reaction continued to be placed
under room temperature for another 3 h. The excess t-
BuOK was then destroyed with water, and the reaction
mixture was puriWed as describe in 1 to give 7 a 50% (1.2 g)
yield, mp 85.0–86.0 °C. MS (EI, 70 eV): m/z 480.4 (M+«,
100%), 149.2 (4%), 136.1 (5%), 121.1 (33%), 107.1 (21%),
1
(72.28); H, 6.94 (6.81). H NMR (CDCl3): ꢀ 1.55 (q, 2H,
Table 2
OCH2CH2CH2Ph), 2.79 (t, 2H, OCH2CH2CH2Ph), 3.79
(t, 2H, OCH2CH2CH2Ph), 3.93 (m, 4H, OCH2CH2OCH2C
H2O), 4.16 (m, 2H, OCHHꢀCHCHHꢀ, 1H, OCHHꢀ
Crystallographic data and optimized structure of lariat crown ether 2
located using B3LYP/6-31G¤ calculations for atomic bond lengths (Å)
Atomic bond lengths (Å)
Crystallographic data
B3LYP/6-31G¤
O1–C1
O1–C20
O2–C2
O2–C3
O3–C8
1.411(6)
1.408(6)
1.427(6)
1.367(6)
1.372(6)
1.414(6)
1.413(5)
1.412(6)
1.432(6)
1.363(6)
1.382(6)
1.440(6)
1.510(7)
1.504(7)
1.386(7)
1.397(7)
1.388(8)
1.352(9)
1.398(8)
1.362(8)
1.502(7)
1.485(7)
1.382(7)
1.401(8)
1.389(8)
1.367(10)
1.381(9)
1.374(7)
1.497(7)
1.405(8)
1.360(7)
1.364(8)
1.407(8)
1.434(7)
1.416(8)
1.377(10)
1.391(12)
1.355(10)
1.407(8)
1.421(8)
1.424
1.430
1.424
1.369
1.367
1.423
1.415
1.423
1.425
1.364
1.379
1.436
1.532
1.524
1.394
1.419
1.401
1.388
1.401
1.393
1.524
1.522
1.396
1.412
1.399
1.393
1.399
1.391
1.508
1.423
1.378
1.374
1.422
1.420
1.432
1.377
1.416
1.377
1.421
1.421
Table 1
Crystallographic data and optimized structure of lariat crown ether 1
located using B3LYP/6-31G¤ calculations for atomic bond lengths (Å)
Atomic bond lengths (Å)
Crystallographic data
B3LYP/6-31G¤
O1–C1
O1–C3
O2–C8
O2–C9
1.433(4)
1.389(4)
1359(5)
1.440(4)
1.395(5)
1.427(5)
1.439(5)
1.362(4)
1.372(4)
1.459(4)
1.433(4)
1.393(7)
1.333(5)
1.355(5)
1.509(5)
1.486(5)
1.373(5)
1.392(5)
1.386(5)
1.376(7)
1.381(6)
1.400(5)
1.500(6)
1.493(6)
1.381(5)
1.396(5)
1.383(6)
1.366(7)
1.386(6)
1.378(5)
1.505(5)
1.366(5)
1.383(6)
1.349(7)
1.354(7)
1.432
1.374
1.369
1.421
1.411
1.415
1.419
1.368
1.372
1.438
1.424
1.412
1.342
1.337
1.528
1.522
1.392
1.414
1.398
1.391
1.399
1.398
1.516
1.516
1.397
1.413
1.399
1.392
1.398
1.392
1.513
1.398
1.394
1.394
1.396
O3–C9
O4–C10
O4–C11
O5–C12
O5–C13
O6–C18
O6–C19
C1–C2
C1–C19
C3–C4
C3–C8
O3–C10
O3–C11
O4–C12
O4–C13
O5–C18
O5–C19
O6–C1
O6–C20
N1–C21
N–C25
C1–C2
C1–C19
C3–C4
C3–C8
C4–C5
C4–C5
C5–C6
C6–C7
C7–C8
C9–C10
C11–C12
C13–C14
C13–C18
C14–C15
C15–C16
C16–C17
C17–C18
C20–C21
C21–C22
C21–C30
C22–C23
C23–C24
C24–C25
C24–C29
C25–C26
C26–C27
C27–C28
C28–C29
C29-C30
C5–C6
C6–C7
C7–C8
C9–C10
C11–C12
C13–C14
C13–C18
C14–C15
C15–C16
C16–C17
C17–C18
C20–C21
C21–C22
C22–C23
C23–C24
C24–C25

L.-H. Lu et al. / Journal of Molecular Structure 831 (2007) 151–164
157
77.1 (12%). Elemental analysis: Calcd (found) for
C28H32O7; C, 69.98 (69.90); H, 6.71 (6.72). 1H NMR
(CDCl3): ꢀ 2.14 (q, 2H, OCH2CH2CH2O), 3.97 (t, 2H,
OCH2CH2CH2, m, 4H, OCH2CH2OCH2CH2O), 4.16 (m,
3H, OCHHꢀCHCHHꢀ, 4H, OCH2CH2OCH2C H2O, 2H, t,
OCH2CH2CH2O), 4.32 (m, 2H, OCHHꢀCHCHHꢀ), 6.84–
7.00 (m, 11H, benzo group), 7.28 (m, 2H, benzo group).
reaction mixture was puriWed as describe in 1 to give 8 a
80% (2.00 g) yield, mp 144.0–145.0 °C. MS (EI, 70 eV): m/z
500.2 (M+«, 13%), 169.1 (10%), 155.0 (100%), 121.0 (8%), 77
(3%). Elemental analysis: Calcd (found) for C31H32O6; C,
1
74.06 (74.20); H, 6.21 (6.23). H NMR (CDCl3): ꢀ 2.67 (s,
3H, CH3), 3.93 (m, 4H, OCH2CH2OCH2CH2O), 4.16 (m,
2H, OCHHꢀCHCHHꢀO, 1H, OCHHꢀCHCHHꢀO, 4H,
OCH2CH2OCH2CH2O), 4.32 (m, 2H, OCHHꢀ CHCHHꢀO),
5.38 (s, 2H, CH2), 6.84–7.00 (m, 8H, benzo group), 7.36 (m,
3H, naphthalene group), 7.72 (m, 2H, naphthalene group),
8.38 (d, 1H, naphthalene group).
2.9. Synthesis of methyl-2-methylnaphthalene sym-dibenzo-
16-crown-5-ether 8
Hydroxy-sym-dibenzo-16-crown-5-ether (1.73g, 5 mmol)
was dissolved in 50 mL anhydrous THF. NaH (0.8 g,
20 mmol) was added under nitrogen and the reaction mix-
ture was heated under reXux for 30–40 min. After the
addition of the 1-chloromethy-2-methyllnaphthalene
(5 mmol), the mixture was heated (under reXux) for 3 h.
Then, the excess NaH was destroyed with water, and the
2.10. Production of single crystals of four LCEs
Single crystals of LCEs 1–4 were produced by initially
heating the four 16-crown-5 ethers (0.50 g) in n-hexane
(10 mL). Chloroform was then slowly added to the
mixture until the compound fully dissolved. Magnesium
Table 4
Table 3
Crystallographic data and optimized structure of lariat crown ether 4
Crystallographic data and optimized structure of lariat crown ether 3
located using B3LYP/6-31G¤ calculations for atomic bond lengths (Å)
located using B3LYP/6-31G¤ calculations for atomic bond lengths (Å)
B3LYP/6-31G¤
Atomic bond lengths (Å)
Crystallographic data
B3LYP/6-31G¤
Atomic bond lengths (Å)
Crystallographic data
O1–C2
O1–C3
O2–C8
O2–C9
1.420(8)
1.396(8)
1.374(8)
1.443(9)
1.417(10)
1.416(9)
1.423(9)
1.355(9)
1.376(8)
1.420(8)
1.442(9)
1.418(9)
1.347(11)
1.457(10)
1.356(6)
1.310(12)
1.375(11)
1.512(10)
1.515(10)
1.384(10)
1.370(10)
1.406(11)
1.350(12)
1.381(11)
1.390(10)
1.495(11)
1.493(12)
1.372(10)
1.407(10)
1.383(11)
1.359(12)
1.398(11)
1.366(10)
1.380(11)
1.414(12)
1.393(11)
1.383(13)
1.371(14)
1.323(14)
1.434
1.380
1.366
1.428
1.424
1.415
1.422
1.366
1.366
1.422
1.432
1.406
1.372
1.455
1.369
1.291
1.382
1.527
1.526
1.392
1.412
1.398
1.393
1.398
1.397
1.523
1.525
1.393
1.419
1.402
1.388
1.402
1.393
1.409
1.404
1.403
1.387
1.417
1.386
S–O2
S–O3
S–O4
S–C5
O1–C1
O1–C2
O4–C8
O5–C9
O5–C10
O6–C15
O6–C16
O7–C17
O7–C18
O8–C19
O8–C20
O9–C25
O9–C26
C2–C3
1.431(4)
1.412(4)
1.577(3)
1.743(4)
1.414(7)
1.354(6)
1.463(5)
1.418(5)
1.381(5)
1.360(6)
1.437(6)
1.402(6)
1.418(6)
1.442(6)
1.360(6)
1.382(5)
1.423(5)
1.372(7)
1.395(7)
1.364(7)
1.376(7)
1.391(6)
1.356(7)
1.505(6)
1.506(6)
1.372(7)
1.398(7)
1.388(8)
1.349(10)
1.384(8)
1.390(6)
1.489(8)
1.475(8)
1.380(7)
1.400(7)
1.371(7)
1.375(10)
1.395(8)
1.375(7)
1.461
1.466
1.643
1.778
1.422
1.359
1.459
1.431
1.375
1.370
1.421
1.412
1.415
1.420
1.367
1.376
1.438
1.401
1.408
1.396
1.391
1.402
1.385
1.521
1.519
1.391
1.413
1.398
1.391
1.399
1.397
1.516
1.515
1.397
1.413
1.399
1.392
1.398
1.392
O3–C10
O3–C11
O4–C12
O4–C13
O5–C18
O5–C19
O6–C1
O6–C20
N1–N2
N1–C20
N1–C22
N2–N3
N3–C21
C1–C2
C1–C19
C3–C4
C3–C8
C4–C5
C2–C7
C3–C4
C4–C5
C5–C6
C6–C7
C8–C9
C5–C6
C6–C7
C7–C8
C8–C26
C10–C11
C10–C15
C11–C12
C12–C13
C13–C14
C14–C15
C16–C17
C18–C19
C20–C21
C20–C25
C21–C22
C22–C23
C23–C24
C24–C25
C9–C10
C11–C12
C13–C14
C13–C18
C14–C15
C15–C16
C16–C17
C17–C18
C21–C22
C21–C26
C22–C23
C23–C24
C24–C25
C25–C26

158
L.-H. Lu et al. / Journal of Molecular Structure 831 (2007) 151–164
sulfate was then added and the mixture was Wltered while
still hot. The Wltered product was then put into a crystal-
growing bottle and n-hexane vapor was diVused into the
product until a perfect crystal was produced. The struc-
ture of the resulting single crystals was then analyzed by
X-ray crystallography. Data were collected using a
Nonius CAD-4 diVractometer with graphite-monochro-
mated Mo–Kꢀ radiation at 25 °C. Atomic scattering fac-
tors were taken from the International Tables for X-ray
crystallography, and data reduction and structural reWne-
ment were performed using the NRCVAX packages. Cell
parameters for 1–4 were obtained from 25 reXections with
2ꢁ at 21.08–24.94°, 19.58–24.70°, 21.96–28.28°, and 11.98–
22.92°, respectively.
3. Computational method
3.1. Calculation methods and input
All theoretical calculations were performed with the
Gaussian98 and Gaussian03 program packages. The den-
sity function calculations (DFT) used the B3LYP method
Table 6
Crystallographic data and optimized structure of lariat crown ether 2
located using B3LYP/6-31G¤ calculations of atomic torsion angle (°)
Atomic torsion angle (°)
Crystallographic data
B3LYP/6-31G¤
C1–O1–C20
C2–O2–C3
C8–O3–C9
C10–O4–C11
C12–O5–C13
C18–O6–C19
O1–C1–C2
O1–C1–C19
C2–C1–C19
O2–C2–C1
O2–C3–C4
O2–C3–C8
C4–C3–C8
C3–C4–C5
C4–C5–C6
C5–C6–C7
C6–C7–C8
O3–C8–C3
117.1(4)
118.6(4)
117.2(4)
112.5(3)
118.0(4)
112.8(3)
104.0(4)
110.7(4)
109.5(4)
108.3(4)
125.4(5)
115.7(4)
118.8(5)
120.2(5)
120.2(5)
120.4(5)
119.7(5)
114.5(5)
124.9(5)
120.6(5)
107.4(4)
106.7(4)
108.1(4)
107.6(4)
124.6(5)
115.6(4)
119.9(5)
119.1(5)
121.1(5)
119.8(5)
120.4(5)
120.9(4)
119.4(5)
119.7(5)
109.8(4)
105.3(4)
118.8(5)
122.2(5)
118.9(5)
121.5(5)
120.6(5)
122.0(5)
118.5(5)
119.5(5)
118.6(6)
120.8(6)
121.7(6)
120.1(6)
119.2(5)
119.0(5)
121.7(5)
121.3(3)
115.3
117.9
119.0
113.7
119.7
115.0
104.7
112.1
111.1
109.0
124.7
116.0
119.3
120.6
120.1
119.9
120.5
115.7
124.7
119.6
108.9
114.0
108.0
104.7
124.9
115.5
119.6
119.9
120.5
119.6
120.4
120.1
120.0
119.9
109.3
108.7
119.6
121.2
119.1
120.8
121.1
122.5
118.5
118.9
120.8
120.2
120.3
120.9
118.8
118.9
122.3
121.6
Table 5
Crystallographic data and optimized structure of lariat crown ether 1
located using B3LYP/6-31G¤ calculations of atomic torsion angle (°)
Atomic torsion angle (°)
Crystallographic data
B3LYP/6-31G¤
C2–O1–C3
C8–O2–C9
113.4(3)
117.7(3)
112.1(3)
117.8(3)
115.8(3)
115.1(3)
116.6(3)
110.8(3)
108.2(3)
112.5(3)
108.8(3)
119.3(3)
119.7(3)
120.9(3)
119.9(4)
119.8(4)
121.0(3)
119.5(4)
116.9(3)
124.2(3)
119.0(4)
108.0(3)
109.1(3)
108.3(5)
106.2(3)
124.4(3)
115.6(3)
120.0(3)
120.0(4)
120.3(4)
120.1(4)
120.5(4)
122.1(3)
118.6(3)
119.1(3)
106.3(3)
109.9(3)
113.4(3)
123.2(3)
123.3(3)
118.3(4)
119.4(4)
119.3(4)
123.1(4)
117.0
118.5
113.2
119.1
116.3
114.8
117.7
112.2
107.8
111.3
108.2
118.8
121.3
119.7
120.8
119.4
120.4
120.3
116.1
124.7
119.3
108.6
109.6
108.9
107.4
124.7
115.7
119.6
120.1
120.4
119.6
120.8
121.5
118.9
119.5
107.2
110.1
114.7
123.1
122.2
118.4
119.1
118.0
123.7
C10–O3–C11
C12–O4–C13
C18–O5–C19
C1–O6–C20
C21–N–C25
O6–C1–C2
O6–C–C19
C2–C1–C19
O1–C2–C1
O1–C3–C4
O1–C3–C8
C4–C3–C8
C3–C4–C5
C4–C5–C6
C5–C6–C7
C6–C7–C8
O2–C8–C3
O2–C8–C7
C3–C8–C7
O2–C9–C10
O3–C10–C9
O3–C11–C12
O4–C12–C11
O4–C13–C14
O4–C13–C18
C14–C13–C18
C13–C14–C15
C14–C15–C16
C15–C16–C17
C16–C17–C18
O5–C18–C13
O5–C18–C17
C13–C18–C17
O5–C19–C1
O6–C20–C21
N–C21–C20
N–C21–C22
C20–C21–C22
C21–C22–C23
C22–C23–C24
C23–C24–C25
N–C25–C24
O3–C8–C7
C3–C8–C7
O3–C9–C10
O4–C10–C9
O4–C11–C12
O5–C12–C11
O5–C13–C14
O5–C13–C18
C14–C13–C18
C13–C14–C15
C14–C15–C16
C15–C16–C17
C16–C17–C18
O6–C18–C13
O6–C18–C17
C13–C18–C17
O6–C19–C1
O1–C20–C21
C20–C21–C22
C20–C21–C30
C22–C21–C30
C21–C22–C23
C22–C23–C24
C23–C24–C25
C23–C24–C29
C25–C24–C29
C24–C25–C26
C25–C26–C27
C26–C27–C28
C27–C28–C29
C24–C29–C28
C24–C29–C30
C28–C29–C30
C21–C30–C29

L.-H. Lu et al. / Journal of Molecular Structure 831 (2007) 151–164
159
together with a 6-31G¤ basis set function in Gaussian.
3.2. Geometry optimization
The initial three-dimensional coordinates of the com-
pounds 1–4 that were used in the calculation were
obtained from the X-ray structural analysis. However,
for LCEs 5–8, the starting molecular structures were
based on LCEs 1–4.
The results of the DFT calculations were used to con-
Wrm the quality of the input coordinate data. If unreason-
able data were used, either the geometric symmetry of the
molecules would be destroyed or unusual bond length or
bond angle would be produced. Any of these errors would
Table 7
Crystallographic data and optimized structure of lariat crown ether 3
Table 8
located using B3LYP/6-31G¤ calculations of atomic torsion angle (°)
Crystallographic data and optimized structure of lariat crown ether 4
located using B3LYP/6-31G¤ calculations of atomic torsion angle (°)
Atomic torsion angle (°)
Crystallographic data
B3LYP/6-31G¤
Atomic torsion angle (°)
Crystallographic data
B3LYP/6-31G¤
O2–S–C3
O2–S–O4
O2–S–C5
O3–S–O4
O3–S–C5
O4–S–C5
C1–O1–C2
S–O4–C8
C9–O5–C10
C15–O6–C16
C17–O7–C18
C19–O8–C20
C25–O9–C26
O1–C2–C3
O1–C2–C7
C3–C2–C7
C2–C3–C4
C3–C4–C5
S–C5–C4
S–C5–C6
C4–C5–C6
C5–C6–C7
C2–C7–C6
O4–C8–C9
O4–C8–C26
C9–C8–C26
O5–C9–C8
O5–C10–C11
O5–C10–C15
C11–C10–C15
C10–C11–C12
C11–C12–C13
C12–C13–C14
C13–C14–C15
O6–C15–C10
O6–C15–C14
C10–C15–C14
O6–C16–C17
O7–C17–C16
O7–C18–C19
O8–C19–C18
O8–C20–C21
O8–C20–C25
C21–C20–C25
C20–C21–C22
C21–C22–C23
C22–C23–C24
C23–C24–C25
O9–C25–C20
O9–C25–C24
C20–C25–C24
O9–C26–C8
119.7(2)
104.4(2)
109.0(2)
109.6(2)
109.9(2)
103.0(2)
118.3(4)
121.9(3)
114.8(3)
117.1(3)
110.7(4)
118.4(4)
119.3(3)
124.6(5)
115.8(4)
119.6(6)
119.8(4)
120.9(4)
119.7(3)
120.7(4)
119.5(4)
119.6(4)
120.5(4)
109.0(3)
107.4(3)
114.2(4)
108.5(3)
120.4(4)
119.5(4)
120.0(4)
120.1(5)
120.1(5)
121.0(5)
119.6(5)
115.2(4)
125.7(4)
119.0(4)
107.3(4)
110.1(4)
109.8(4)
106.8(4)
124.6(5)
115.9(4)
119.5(5)
119.9(5)
121.3(5)
119.2(5)
120.0(5)
122.6(4)
117.0(5)
120.1(4)
105.4(3)
120.1
118.0
108.9
108.3
109.9
99.8
C2–O1–C3
C8–O2–C9
115.7(5)
117.7(5)
111.2(6)
117.2(6)
117.0(5)
115.6(6)
119.3(7)
111.0(6)
129.3(7)
108.5(6)
107.5(7)
108.3(6)
111.8(5)
110.5(6)
109.5(5)
116.6(6)
122.0(6)
121.4(6)
118.5(7)
119.9(7)
121.3(7)
119.6(7)
117.0(6)
123.7(6)
119.2(6)
108.1(6)
109.6(6)
109.0(6)
107.2(6)
126.1(7)
115.1(6)
118.8(7)
119.9(7)
121.7(7)
118.9(8)
120.0(7)
115.1(6)
124.3(6)
120.5(6)
107.4(5)
112.5(6)
109.5(7)
129.6(8)
121.0(8)
103.5(7)
134.3(7)
122.2(7)
114.5(8)
122.8(9)
123.4(9)
116.1(8)
115.2
119.1
114.0
119.4
118.9
115.4
120.4
109.8
129.6
109.4
108.5
110.8
107.8
111.2
108.7
119.0
121.1
119.8
120.5
119.6
120.4
120.2
116.3
124.3
119.4
105.5
107.4
114.0
108.7
125.1
115.4
119.6
120.4
120.0
120.1
120.4
115.4
125.1
119.5
108.3
112.5
108.6
130.7
120.7
103.7
134.0
122.3
116.2
122.0
121.4
117.3
C10–O3–C11
C12–O4–C13
C18–O5–C19
C1–O6–C20
N2–N1–C20
N2–N1–C22
C20–N1–C22
N1–N2–N3
N2–N3–C21
O6–C1–C2
O6–C1–C19
C2–C1–C19
O1–C2–C1
O1–C3–C4
O1–C3–C8
C4–C3–C8
C3–C4–C5
C4–C5–C6
C5–C6–C7
C6–C7–C8
O2–C8–C3
O2–C8–C7
C3–C8–C7
O2–C9–C10
O3–C10–C9
O3–C11–C12
O4–C12–C11
O4–C13–C14
O4–C13–C18
C14–C13–C18
C13–C14–C15
C14–C15–C16
C15–C16–C17
C16–C17–C18
O5–C18–C13
O5–C18–C17
C13–C18–C17
O5–C19–C1
O6–C20–N1
N3–C21–C22
N3–C21–C26
C22–C21–C26
N1–C22–C21
N1–C22–C23
C21–C22–C23
C22–C23–C24
C23–C24–C25
C24–C25–C26
C21–C26–C25
118.6
119.2
117.0
118.6
113.3
119.0
115.9
124.6
115.4
120.1
119.6
119.8
119.4
119.6
121.0
119.2
120.3
110.8
106.8
112.5
108.5
118.8
121.2
119.8
120.7
119.5
120.5
120.2
116.0
124.7
119.3
108.5
109.6
108.7
107.4
124.7
115.8
119.5
120.1
120.4
119.6
120.7
121.1
119.2
119.7
107.5

160
L.-H. Lu et al. / Journal of Molecular Structure 831 (2007) 151–164
result in the termination of the calculations. It was also
found that the calculations could achieve convergence more
rapidly, if the input data were closer to the experimental
values of the minimal energy points of the molecules. The
converged calculations can then provide the optimal geo-
metric bond length, bond angle, and dihedral angle of the
eight LCEs.
grams of the four lariat crown ethers 1–4 were identiWed
and shown in Figs. 2–5. The structures of the four lariat
crown ethers show diVerent crystal systems and space
groups. The three-dimensional coordinates of the X-ray
structural analysis were also used as input data for theoret-
ical calculations. AM1 semi-empirical method was Wrst
used to conduct calculations until convergence was
achieved. The geometric optimization was then conducted
using the 6-31G¤ BSF and the B3LYP method. Tables 1–4
provide the resulting bond lengths of the LCEs 1–4 from
the X-ray crystallography structural analysis and theoreti-
cal calculations. Similarly, Tables 5–8 provide the torsion
angles obtained using the X-ray crystallography structural
analysis and theoretical calculations. In addition, Table 9
provides the crystallographic data collected during the
study. These tables show that both the bond lengths and
torsion angles obtained from the theoretical calculations
are in good agreement with those from experimental inves-
tigations using X-ray crystallography. Tables 10–13 pro-
vide the resulting bond lengths and torsion angles of the
LCEs 5–8 from the DFT theoretical calculations.
3.3. Orbital Weld energy, vibrational frequency, and
thermodynamic properties
Using the optimized geometry, thermodynamic
properties of orbital energy, vibrational frequency, ioniza-
tion energy, energy gap between HOMO–LUMO, atomic
heat, enthalpy and Gibbs energy, etc., of each LCEs were
calculated. The results were then used to determine the rela-
tive stability of the diVerent sidearm of the eight LCEs.
Therefore, the resulting molecular stability and conductiv-
ity are of special importance and value.
4. Results and discussions
4.1. Geometric structure
4.2. Molecular Wrst ionization potentials, HOMO and
LUMO energies, energy gaps
The structure of molecules plays an especially signiWcant
role in determining their chemical properties. As a result,
the optimization of the compound is particularly impor-
tant. The obtained geometric structure of eight c-pivot lar-
iat crown ethers is shown in Fig. 1. Through structural
analysis, using X-ray crystallography, the ORTEP dia-
Table 14 lists the calculated values of the Wrst ionization
potentials, HOMO, LUMO, and energy gap (ꢁꢂHOMO–
LUMO) of the eight LCEs. From the data, the Wrst ionization
potential of 8 was found to be the lowest. On the other
hand, the energy gap of 4 was found to be the lowest, indi-
Table 9
Crystallographic data
1
2
3
4
Empirical formula
Formula weight
Crystal system
Space group
Unit cell dimensions (Å)
C25H27NO6
437.49
C30H30O6
486.53
C26H28O9S
516.56
C26H27N3O6
477.51
Orthorhombic
P2(1)2(1)2(1)
a D 7.888(2)
b D 11.652(4)
c D 24.416(4)
90.00
2244(1)
4
1.295
Orthorhombic
P2(1)2(1)2(1)
a D 7.3950(8)
b D 15.745(3)
c D 22.214(5)
90.00
2587(1)
4
1.249
Monoclinic
P2(1)/n
a D 12.235(2)
b D 7.674(3)
c D 27.235(7)
94.37
2550(1)
4
1.346
Monoclinic
P2(1)/a
a D 8.245(5)
b D 27.549(5)
c D 10.406(3)
96.23
2350(2)
4
1.350
ꢃ (°)
Volume (Å3)
Z (atoms/unit cell)
Dcalc/mg m¡3
Mu/mm¡1
0.09
0.09
0.18
0.10
F (0 0 0)
928
1032
1088
1008
Range of 2ꢁ/deg
Crystal size
Octants measured
49.8
51.8
51.8
53.8
0.35 £ 0.20 £ 0.15 mm
h(0 to 9)
k(0 to 130)
l(0 to 29)
2277
0.35 £ 0.20 £ 0.10 mm
h(0 to 9)
k(0 to 19)
l(0 to 27)
2897
0.45 £ 0.25 £ 0.15 mm
h(¡15 to 15)
k(0 to 9)
l(0 to 33)
5096
0.50 £ 0.20 £ 0.03 mm
h(¡10 to 10)
k(0 to 35)
l(0 to 13)
5361
Number of reXections measured
Number of unique reXection
2277
2897
4990
5091
Number of reXections with I > 2.5 or 2.0ꢄ (I)
1866
1432
2488
1665
Number of variables
290
326
326
226
Absorption correction
Rf
0.862–0.976
0.037
0.755–0.792
0.037
0.812–0.949
0.049
0.911–0.974
0.067
Rw
0.034
0.028
0.048
0.066
GoF
1.255
1.581
0.807
0.665

L.-H. Lu et al. / Journal of Molecular Structure 831 (2007) 151–164
161
cating higher conductivity. Table 14 also shows that 3 has
the highest Wrst ionization potential whilst 5 has the highest
energy gap.
LCEs to be more rigid, and this is probably the reason that
the entropy change for the reaction is slightly negative.
However, the change in the enthalpy is big and negative
enough to overcome the negative change of entropy. In
addition, the results also show that the eight diVerent LCEs
are stable and easy-to-form molecules with high reactivity.
Calculations also indicate that 8 is formed most readily and
is also the most stable (Table 15).
4.3. Thermodynamic properties
The DFT calculation shows that ꢁHf are between
¡3004.726 and ¡3666.124 kcal mol¡1 for the eight LCEs.
However, the calculated ꢁGf are between ¡2778.627 and
¡3329.091kcalmol¡1 for the eight LCEs. Additionally, the
obtained thermodynamic parameter of eight c-pivot lariat
crown ethers is shown in Fig. 6. In general, the formation of
the eight LCEs is exothermic (ꢁH < 0) and also causes
4.4. Vibrational frequencies
The calculated vibrational frequencies of the eight diVer-
ent geometric structures of the LCEs are all positive, indi-
Table 10
Table 11
Optimized structure of lariat crown ether 5 located using B3LYP/6-31G¤
calculations for atomic bond lengths (Å) and atomic torsion angle (°)
Optimized structure of lariat crown ether 6 located using B3LYP/6-31G¤
calculations for atomic bond lengths (Å) and atomic torsion angle (°)
Atomic bond lengths (Å)
Atomic torsion angle (°)
Atomic bond lengths (Å)
Atomic torsion angle (°)
C1–C2
C1–C6
C2–C3
C2–C3
C3–C4
C4–C5
C5–C6
C5–O1
C6–O4
O1–C7
C7–C8
C8–O2
1.400
C2–C1–C6
C1–C2–C3
C2–C3–C4
C3–C4–C5
C4–C5–C6
C4–C5–O1
C6–C5–O1
C1–C6–C5
C1–C6–O4
C5–C6–O4
C5–O1–C7
O1–C7–C8
C7–C8–O2
C8–O2–C9
O2–C9–C10
C9–C10–O3
C10–O3–C13
C12–C11C16
C11–C12–C13
C11–C12–O5
O3–C13–C14
C12–C13–C14
C13–C14–C15
C14–C15–C16
C11–C16–C15
C6–O4–C24
C18–C17–C22
C17–C18–C19
C17–C18–O7
C18–C19–C20
C19–C20–C26
C21–C20–C26
C20–C21–C22
C17–C22–C21
C17–C22–O8
C21–C22–O8
C12–O5–C23
O5–C23–C25
O4–C24–C25
C23–C25–C24
C23–C25–O6
C24–C25–O6
C25–O6–C26
C20–C26–O6
C18–O7–C27
C22–O8–C28
119.8
120.7
119.4
120.6
119.9
119.7
120.3
119.5
125.3
115.2
115.9
109.3
114.2
115.4
106.2
107.3
115.6
120.1
119.5
124.7
119.8
119.6
120.8
119.5
120.5
119.5
119.3
120.6
124.1
119.6
120.8
118.5
119.2
120.7
114.7
124.5
118.6
106.6
112.9
113.1
111.5
113.0
117.2
109.8
118.3
118.3
C1–C2
C1–C6
C2–C3
C3–C4
C4–C5
C4–O1
C5–C6
C5–C17
O1–C6
1.388
C2–C1–C6
C1–C2–C3
C2–C3–C4
C3–C4–C5
C3–C4–O1
C5–C4–O1
C4–C5–C6
C4–C5–O4
C6–C5–O4
C1–C6–C5
C4–O1–C7
O1–C7–C8
C7–C8–O2
C8–O2–C9
O2–C9–C10
C9–C10–O3
C10–O3–C12
C12–C11C16
C12–C11–O5
C16–C11–O5
O3–C12–C11
O3–C12–C13
C11–C12–C13
C12–C13–C14
C13–C14–C15
C14–C15–C16
C11–C16–C15
C5–O4–C17
O4–C17–C18
C17–C18–C19
C17–C18–O6
C19–C18–O6
C18–C19–O5
C11–O5–C19
C18–O6–C20
O6–C20–C21
C20–C21–C22
C21–C22–C27
C24–C23–C28
C23–C24–C25
C24–C25–C26
C25–C26–C27
C22–C27–C26
C22–C27–C28
C26–C27–C28
C23–C28–C27
121.1
119.9
120.5
119.6
124.7
115.7
119.3
116.0
124.8
120.6
119.0
108.8
114.0
113.7
108.0
104.7
119.7
119.8
120.0
120.1
115.5
124.9
119.6
119.9
120.5
119.6
120.5
117.9
109.0
110.8
104.4
112.9
109.6
115.0
116.2
107.8
112.3
112.8
120.1
119.5
120.1
121.0
120.9
120.8
118.2
121.0
1.398
1.392
1.392
1.398
1.391
1.413
1.378
1.371
1.436
1.523
1.415
1.424
1.520
1.434
1.373
1.397
1.400
1.413
1.371
1.391
1.398
1.391
1.529
1.393
1.405
1.406
1.364
1.387
1.406
1.514
1.395
1.366
1.419
1.535
1.552
1.426
1.423
1.419
1.418
1.401
1.401
1.393
1.419
1.367
1.394
1.369
1.423
1.524
1.415
1.423
1.522
1.425
1.364
1.412
1.391
1.379
1.396
1.399
1.393
1.399
1.424
1.533
1.526
1.420
1.436
1.427
1.524
1.541
1.514
1.396
1.395
1.396
1.396
1.401
1.402
C7–C8
C8–O2
O2–C9
O2–C9
C9–C10
C10–O3
O3–C12
C11–C12
C11–C16
C11–O4
C12–C13
C13–C14
C14–C15
C15–C16
O4–C17
C17–C18
C18–C19
C18–O6
C19–O5
O6–C20
C20–C21
C21–C22
C22–C27
C23–C24
C23–C28
C24–C25
C25–C26
C26–C27
C27–C28
C9–C10
C10–O3
O3–C13
C11–C12
C11–C16
C12–C13
C12–O5
C13–C14
C14–C15
C15–C16
O4–C24
C17–C18
C17–C22
C18–C19
C18–O7
C19–C20
C20–C21
C20–C26
C21–C22
C22–O8
O5–C23
C23–C25
C24–C25
C25–O6
O6–C26
O7–C27
O8–C28

162
L.-H. Lu et al. / Journal of Molecular Structure 831 (2007) 151–164
cating that these molecules are located at the minimal
points of the potential energy surfaces, indicating that all
eight diVerent LCEs are very stable molecules. The calcu-
lated maximum frequencies are between 3227.364 and
3244.571cm¡1 for the eight LCEs, and among the calcu-
lated values, compound 4 is found to have the lowest fre-
quency (10.201 cm¡1).
theoretical calculations. Furthermore, molecular struc-
tural conformation optimized at B3LYP/6-31G¤ level of
theory indicated that there was an existence of consider-
able diVerence in the energy of the eight LCEs. Moreover,
we were computing an optimized structure for the eight
diVerent LCEs, which was also thermodynamically stable
5. Conclusions
Table 13
Optimized structure of lariat crown ether 8 located using B3LYP/6-31G¤
calculations for atomic bond lengths (Å) and atomic torsion angle (°)
Eight LCEs were synthesized and optimal geometric
structures were determined by experimental study and
Atomic bond lengths (Å)
Atomic torsion angle (°)
O1–C1
O1–C20
O2–C6
O2–C3
O3–C8
1.421
C1–O1–C20
C2–O2–C3
C8–O3–C9
C10–O4–C11
C12–O5–C13
C18–O6–C19
O1–C1–C2
O1–C1–C19
C2–C1–C19
O2–C2–C1
O2–C3–C4
O2–C3–C8
C4–C3–C8
C3–C4–C5
C4–C5–C6
C5–C6–C7
C6–C7–C8
O3–C8–C3
115.8
117.9
119.0
113.7
119.6
115.0
104.5
112.8
110.9
108.9
124.8
115.9
119.3
120.6
120.1
119.9
120.5
115.7
124.7
119.6
108.8
114.0
108.0
119.5
125.0
115.4
119.6
119.9
120.5
120.4
120.0
120.1
119.9
109.5
110.1
119.2
120.6
120.2
121.2
120.7
121.7
118.8
119.5
121.1
119.7
120.5
121.4
117.8
119.8
122.5
119.4
121.6
118.9
1.423
1.423
1.370
1.367
1.423
1.415
1.423
1.426
1.364
1.380
1.436
1.533
1.526
1.394
1.418
1.401
1.388
1.401
1.393
1.524
1.522
1.396
1.412
1.399
1.393
1.399
1.520
1.420
1.390
1.373
1.418
1.421
1.434
1.376
1.415
1.378
1.424
1.435
1.514
Table 12
Optimized structure of lariat crown ether 7 located using B3LYP/6-31G¤
calculations for atomic bond lengths (Å) and atomic torsion angle (°)
Atomic bond lengths (Å)
Atomic torsion angle (°)
O3–C9
O4–C10
O4–C11
O5–C12
O5–C13
O6–C18
O6–C19
C1–C2
C1–C19
C3–C4
C3–C8
C1–C2
C1–C6
C1–O1
C2–C3
C2–O4
C3–C4
C4–C5
C5–C6
O1–C7
C7–C8
C8–O2
O2–C9
C9–C10
C10–O3
O3–C12
C11–C12
C11–C16
C11–O4
C12–C13
C13–C14
C14–C15
C15–C16
O4–C17
C17–C18
C18–C19
C18–O6
C19–O5
O6–C20
C20–C21
C21–C22
C22–O7
O7–C23
C23–C24
C23–C28
C24–C25
C25–C26
C26–C27
C27–C28
1.417
C2–C1–C6
C2–C1–O1
C6–C1–O1
C1–C2–C3
C1–C2–O4
C3–C2–O4
C2–C3–C4
C3–C4–C5
C4–C5–C6
C1–C6–C5
C1–O1–C7
O1–C7–C8
C7–C8–O2
C8–O2–C9
O2–C9–C10
C9–C10–O3
C10–O3–C13
C12–C11C16
C12–C11–O5
C16–C11–O5
O3–C12–C11
O3–C12–C13
C11–C12–C13
C12–C13–C14
C13–C14–C15
C14–C15–C16
C11–C16–C15
C2–O4–C17
O4–C17–C18
C17–C18–C19
C17–C18–O6
C19–C18–O6
C18–C19–O5
C11–O5–C19
C18–O6–C20
O6–C20–C21
C20–C21–C22
C21–C22–O7
C22–O7–C23
O7–C23–C24
O7–C23–C28
C24–C23–C28
C23–C24–C25
C24–C25–C26
C25–C26–C27
C26–C27–C28
C23–C28–C27
119.4
115.4
125.2
119.8
115.3
125.0
120.3
120.0
120.1
120.4
118.7
108.7
114.8
116.3
106.6
112.3
115.8
119.5
116.0
124.5
118.7
121.5
119.8
120.6
119.6
120.4
120.2
119.2
106.3
112.7
105.8
112.9
107.1
118.9
114.3
107.7
112.2
107.3
118.7
124.6
115.5
119.8
119.4
121.8
119.2
120.6
120.0
1.393
1.366
1.392
1.366
1.401
1.388
1.402
1.422
1.523
1.412
1.425
1.529
1.432
1.378
1.411
1.398
1.367
1.393
1.398
1.393
1.398
1.421
1.529
1.537
1.419
1.429
1.424
1.524
1.523
1.424
1.367
1.400
1.403
1.399
1.393
1.399
1.390
C4–C5
C5–C6
C6–C7
C7–C8
O3–C8–C7
C3–C8–C5
C9–C10
C11–C12
C13–C14
C13–C18
C14–C15
C15–C16
C16–C17
C20–C21
C21–C22
C21–C30
C22–C23
C23–C24
C24–C25
C24–C29
C25–C26
C26–C27
C27–C28
C28–C29
C29–C30
C30–C31
O3–C9–C10
O4–C10–C9
O4–C11–C12
O5–C12–C11
O5–C13–C14
O5–C13–C19
C14–C13–C18
C13–C14–C15
C14–C15–C16
C16–C17–C18
O6–C18–C13
O6–C18–C17
C13–C18–C17
O6–C19–C1
O1–C20–C21
C20–C21–C22
C20–C21–C30
C22–C21–C30
C21–C22–C23
C22–C23–C24
C23–C24–C25
C23–C24–C29
C25–C24–C29
C24–C25–C26
C25–C26–C27
C26–C27–C28
C27–C28–C29
C24–C29–C28
C24–C29–C30
C28–C27–C30
C21–C30–C29
C21–C30–C31
C29–C30–C31

L.-H. Lu et al. / Journal of Molecular Structure 831 (2007) 151–164
163
Table 14
Comparison of HOMO, LUMO, energy gaps (ꢁꢂHOMO–LUMO), and Wrst ionization potentials of the eight LCEs (eV)
Molecule parameter
1
2
3
4
5
6
7
8
ꢂHOMO
ꢂLUMO
I1st
¡5.6417
¡0.3877
5.6417
¡5.6278
¡0.8789
5.6278
¡5.7933
¡0.5945
5.7933
¡5.6518
¡1.0947
5.6518
¡5.7331
0.0473
5.7331
5.7805
¡5.6110
0.1390
5.6110
5.7500
¡5.6257
0.0207
5.6257
5.6463
¡5.4722
¡0.8247
5.4722
ꢁꢂHOMO–LUMO
5.2540
4.7490
5.1987
4.5771
4.6475
Table 15
Comparison of calculated thermodynamic properties of the eight LCEs (298 K, kcal mol¡1
)
Molecule parameter
1
2
3
4
5
6
7
8
ꢁHf
ꢁGf
ꢁHa
ꢁGa
¡3004.726
¡2718.627
6241.252
¡3551.453
¡3166.117
7127.590
¡3273.530
¡2960.261
6673.034
¡3073.947
¡2770.620
6589.366
¡3445.795
¡3116.350
7092.909
¡3354.591
¡3036.830
6917.714
¡3401.128
¡3078.126
7006.246
¡3666.124
¡3329.091
7405.215
5737.038
6498.545
6123.080
6055.920
6512.582
6356.834
6436.245
6813.601
that the diVerent eight LCEs have low energy gaps
and low Wrst ionization potentials. The electrons on
the outermost molecular orbital are therefore more
easily lost, indicating higher conductivity.
Δ
H
f
f
-4500
-4000
-3500
-3000
-2500
-2000
-1500
ΔG
(3) The calculations of thermodynamic properties and
vibrational frequencies show that the diVerent eight
LCEs are all located at the stable, minimum points of
the potential energy surfaces. They are all therefore
stable structural LCEs with high reactivity.
(4) The eight LCEs have the same parent macrocycle but
contain diVerent sidearms. When the sidearm of the
lariat crown ether is changed, the thermodynamic
properties of the ether would change signiWcantly as
well. Thus, the sidearm eVect appears to be a strong
inXuence on the metal ion binding capability.
-1000
0
2
4
6
8
lariat 16-crown ether
The results of the DFT calculations are in good agree-
ment with the experimental data, indicating that the method
and basis set selected are feasible for calculating such large
molecules. The DFT method appears to provide results that
were in better agreement with the experimental results. In
addition, the calculated geometries are considered to be accu-
rate enough. The sidearm eVect of the lariat 16-crown-5
ethers can also result in higher diVerence in the relative
energy. Therefore, with diVerent sidearms resulting in confor-
mational change, diVerent complex ability between lariat
crown ethers and metals will be shown.
This research was performed to investigate the con-
formational preferences of the eight LCEs that can be
applied as building blocks of the lariat crown ether
macrocycles. The results of this study of high-density,
high-energy lariat crown ethers should provide contribu-
tion to other members of this versatile new class of mac-
rocycles.
Fig. 6. Thermodynamic parameter of eight lariat 16-crown ethers.
and in excellent agreement with the experimental X-ray
diVraction structure. Vibrational frequency analyses per-
formed at the B3LYP/6-31G¤ level of theory yielded zero
imaginary frequency and conWrms that all the optimized
structures are in the ground state. The experimental
results and density functional theory calculations
(B3LYP) also established the electronic structures of these
species and provided insight into the molecular mechan-
ics. From theoretical calculations that use the B3LYP/6-
31G¤ density function method, data of the eight LCEs
conformational analysis were successfully obtained. From
these calculated and analytical results, the main results of
the present study are summarized as follows.
(1) The calculated bond lengths and torsion angles of the
diVerent eight LCEs are very close to the experimen-
tal values and are quite well and rational. These
results prove that the calculations of optimal geomet-
ric three-dimensional structure of the eight com-
pounds were successful.
Acknowledgements
The authors thank the National Science Council of the
Republic of China (Taiwan) for its Wnancial support
(NSC 95-2113-M-012-001). The helpful suggestions from
(2) Through the calculations of the Wrst ionization poten-
tials, HOMO, LUMO, and energy gaps, it was found

164
L.-H. Lu et al. / Journal of Molecular Structure 831 (2007) 151–164
[13] M. González-Lorenzo, C. Platas-lglesias, F. Avecilla, S. Faulkner, S.J.A.
Pope, A. de Bias, T. Rodr´gue-Bias, Inorg. Chem. 44 (2005) 4254.
[14] A. Frontera, M. Orell, C. Garau, D. Quiníñonero, E. Molins, I. Mata,
J. Morey, Org. Lett. 7 (2005) 1437.
[15] M. Montejo, S.L. Hinchley, A.B. Altabef, H.E. Robertson, F.P. Ureka,
D.W.H. Rankin, J.L. González, Phys. Chem. Chem. Phys. 8 (2006) 477.
[16] C. Emmeluth, V. Dyczmons, T. Kinzel, P. Botschwina, M.A. Suhm,
M. Yákez, Phys. Chem. Chem. Phys. 7 (2005) 991.
[17] T.S. Hofer, B.R. Randolf, B.M. Rode, Phys. Chem. Chem. Phys.
7 (2005) 1382.
Operator T.S. Kuo of National Taiwan Normal Univer-
sity, Department of Chemistry, are greatly appreciated.
Dr. Y.C. Su, P.E., of Houston, Texas, USA, is also greatly
appreciated for a critical reading of this manuscript prior
to publication.
Appendix A. Supplementary data
Supplementary data associated with this article can be
found, in the online version, at doi:10.1016/j.molstruc.
2006.07.035.
[18] U. Koert, Phys. Chem. Chem. Phys. 7 (2005) 1501.
[19] A. Lenz, L. Ojamäe, Phys. Chem. Chem. Phys. 7 (2005) 1905.
[20] H. Zhou, Z.H. Peng, Z.Q. Pan, D.C. Li, B. Liu, Z. Zhang, R.A. Chi,
J. Mol. Struct. 743 (2005) 59.
[21] K.K. Laali, V.D. Sarca, T. Okazaki, A. Brock, P. Der, Org. Biomol.
Chem. 3 (2005) 1034.
References
[22] S.L. Richardson, T. Baruah, M.J. Mehl, M.R. Pederson, Chem. Phys.
Lett. 403 (2005) 83.
[1] A. Lüttringhaus, Ann. Chem. 528 (1937) 181.
[2] C.J. Pedersen, J. Am. Chem. Soc. 89 (1967) 7017.
[3] W.S. Tang, X.X. Lu, K.M.C. Wong, V.W.W. Yam, J. Mater. Chem. 15
(2005) 2714.
[4] W.J. Wang, E.V. Ganin, M.S. Fonari, Y.A. Simonov, G. Bocelli, Org.
Biomol. Chem. 3 (2005) 3054.
[23] T. Sordo, P. Campomanes, A. Diéguez, F. Rodriguez, F.J. Fakanás,
J. Am. Chem. Soc. 127 (2005) 944.
[24] Q.S. Li, X.J. Feng, Y. Xie, H.F. Schaefer III, J. Phys. Chem. A 109
(2005) 1454.
[25] H. Shirota, J. Phys. Chem. B 109 (2005) 7053.
[26] S.M. Godfrey, A. HinchliVe, A. Mkadmh, Dalton Trans. (2005)
1675.
[5] S. Krongsuk, T. Kerdcharoen, S. Hannongbua, J. Phys. Chem. B 107
(2003) 4175.
[6] D. Soto-Castro, P. Guadarrama, J. Comput. Chem. 25 (2005) 1215.
[7] K. Janus, J. Sworakowski, J. Phys. Chem. B 109 (2005) 93.
[8] A.A. EI-Azhary, A.A. AI-Kahtani, J. Phys. Chem. A 109 (2005) 4505.
[9] A. Casnati, N.D. Ca’, F. Sansone, F. Ugozzoli, R. Ungaro, Tetrahe-
dron 60 (2004) 7869.
[27] C.C. Su, L.H. Lu, L. Kao-Liu, J. Phys. Chem. A 107 (2003) 4563.
[28] C.C. Su, L.H. Lu, J. Mol. Struct. 702 (2004) 23.
[29] T.J. Hsieh, L.H. Lu, C.C. Su, Biophys. Chem. 114 (2005) 23.
[30] T.J. Hsieh, C.C. Su, C.Y. Chen, C.H. Liou, L.H. Lu, J. Mol. Struct. 741
(2005) 193.
[10] S.T. Liddle, W. Clegg, C.A. Morrison, Dalton Trans. (2004) 2514.
[11] E.S. Stoyanov, C.A. Reed, J. Phys. Chem. A 108 (2004) 907.
[12] R. Chitta, L.M. Rogers, A. Wanklyn, P.A. Karr, P.K. Kahol, M.E.
Zandller, F. D’Souza, Inorg. Chem. 43 (2004) 6969.
[31] (a) E.P. Kyba, R.C. Helegeson, K. Madan, G.W. Gokel, T.L. Tarnow-
ski, S.S. Moore, D.J. Cram, J. Am. Chem. Soc. 99 (1979) 2564;
(b) G.S. Heo, R.A. Bartsch, L.L. Schobohm, J.G. Lee, J. Org. Chem. 46
(1981) 3574.