Synthesis and crystal structure of copper complex of 7,16-bis(2-hydroxy-5-methyl-3-nitrobenzyl)-1,4,10, 13-tetraoxa-7,16-diazacyclooctadecane

Article abstract of DOI:10.1016/S0022-2860(02)00441-6

A lariat crown ether compound 7,16-bis(2-hydroxy-5-methylbenzyl)-1,4,10,13-tetraoxa-7, 16-diazacyclooctadecane has been prepared via one-pot Mannich reaction. A copper(II) complex with the ligand 7,16-bis(2-hydroxy-5-methyl-3-nitrobenzyl)-1,4,10,13-tetrao

Full text of DOI:10.1016/S0022-2860(02)00441-6

Journal of Molecular Structure 643 (2002) 141–146
www.elsevier.com/locate/molstruc
Synthesis and crystal structure of copper complex
of 7,16-bis(2-hydroxy-5-methyl-3-nitrobenzyl)-1,4,10,
1
3-tetraoxa-7,16-diazacyclooctadecane
*
Shu-lan Ma, Wen-xiang Zhu
Department of Chemistry, Beijing Normal University, Beijing 100875, People’s Republic of China
Received 16 May 2002; revised 12 August 2002; accepted 12 August 2002
Abstract
A lariat crown ether compound 7,16-bis(2-hydroxy-5-methylbenzyl)-1,4,10,13-tetraoxa-7,16-diazacyclooctadecane has
been prepared via one-pot Mannich reaction. A copper(II) complex with the ligand 7,16-bis(2-hydroxy-5-methyl-3-
nitrobenzyl)-1,4,10,13-tetraoxa-7,16-diazacyclooctadecane was unexpectedly synthesized and characterized by elemental
analysis, IR and UV spectra. The crystal structure of the complex has been determined by X-ray diffraction. Both crystal
structure analysis and spectroscopy study indicated that the side-arm phenols of lariat crown ether are nitrated while
3 2
complexing with Cu(NO ) . Structure shows that the copper(II) ion is coordinated to two nitrogen and four oxygen atoms, two
from the crown ether and other two from the deprotonated phenolate groups. The coordination polyhedron is a distorted
octahedron.
q 2002 Elsevier Science B.V. All rights reserved.
0
Keywords: N,N -Disubstituted diaza-18-crown-6; Copper complex; Crystal structure
1
. Introduction
the quantitative determination of those cations [4].
Side-armed crown ethers have proved to be efficient
carriers for liquid membranes [5,6], and pH switching
complexing agents [7]. Some of the azacrown ethers
with two ionizable arms exhibit favourable complex-
ing abilities toward many divalent metal ions [8].
Moore and coworkers [9] have reported the first
ligand which contains phenolic pendent arms and
Macrocycles functionalized with coordinating
pendent arms have received much attention recently
as a result of their enhanced coordinating ability and
their favourable kinetics for the overall formation
process of complexes [1]. Many azacrown macro-
cycles functionalized with chromophoric groups were
found to be efficient photometric agents [2,3]. Their
complexes with particular cations exhibit specific UV
or fluorescence response and can be used for
3
þ
prepared its Gd complex. Some lariat crown ethers
containing hydroxyl functional groups, such as 2-
hydroxybenzyl, 3-tert-butyl-2-hydroxy benzyl [10],
attached to the secondary amine nitrogen on triaza
macrocycles, were also reported. The crystal struc-
*
Corresponding author. Tel.: þ86-10-6220-7838; fax: þ86-10-
2
þ
tures of their copper complexes showed that the Cu
center is in a square-based-pyramidal environment of
6220-0567.
E-mail address: wx-zhu@263.net (W. Zhu).
0022-2860/02/$ - see front matter q 2002 Elsevier Science B.V. All rights reserved.
PII: S0022-2860(02)00441-6

142
S.-l. Ma, W.-x. Zhu / Journal of Molecular Structure 643 (2002) 141–146
three nitrogen donors and of two phenolate oxygen
atoms. In 1999, Dewall and co-workers [11] prepared
arms have been prepared and their properties have
been studied [19,20]. The 7,16-bis(2-hydroxy-5-
methylbenzyl)-1,4,10,13-tetraoxa-7,16-diazacyclooc-
tadecane was synthesized in 1995 for the first time
[16], but its complex has not been synthesized and
studied yet. In this paper, we report the synthesis
and structure of a new copper complex in which
the ligand was not the original lariat crown ether
but its nitro derivative.
1
a ligand, H L and found this receptor complexes K
þ
2
by using the phenolic sidearms as p-donor groups but
not when the macrocycle-bound
2. Experimental
þ
2.1. Materials and methods
cation is Na . Recently, four 8-hydroxyquinoline-
containing tetraaza crown ethers were studied for their
2
potential application as highly selective Cu recep-
þ
Diaza-18-crown-6 was prepared according to the
literature method [21]. All commercially available
chemicals were of reagent grade and were used
without further purification except toluene which was
dried with sodium.
2
tors [12]. Among Co , Ni , Cu , Zn , Cd , and
þ
2þ
2þ
2þ
2þ
2
Pb , the most stable complexes were formed with
þ
þ
2
Cu . In the other example [13], the X-ray crystal
2
structure of [Cu (L )] (ClO ) had confirmed the
2
4 2
C, H and N were determined using an Elementar
Vario EL elemental analyzer. UV spectra were
measured using a WFZ-900-D4 spectrophotometer
in methanol solution. The IR spectra were recorded on
a NEXUS670 FTIR spectrometer using KBr pellets in
binuclear nature of the compound with both metal
ions identical coordination environment and each one
placed out of the crown hole but efficiently encapsu-
lated by the corresponding pendent arm. Our very
recent paper reported the synthesis of a new sidearm
3
diaza-18-crown-6 ligand, H L , and its copper nitrate
2
1
the 400–4000 cm region.
2
complex. The crystal structure of the complex showed
that the two unionized phenolic groups are coordi-
2.2. Preparation of the lariat crown ether
2
þ
nated to the central Cu from above and below the
ring plane [14].
The crown ether was prepared as follows.
Many of the double-armed crown ethers were
0
An anhydrous toluene solution (45 ml) containing
4,13-diaza-18-crown-6 (0.262 g, 1.00 mmol), paraf-
ormaldehyde (0.074 g, 2.45 mmol), and 4-methylphe-
nol (0.259 g, 2.40 mmol) was refluxed at 110 8C for
24 h. The solvent was evaporated by rotatory
evaporation, and a small amount of MeOH was
added. The mixture was ultrasonicated for 20 min.
obtainable by treatment N,N -bis(methoxymethyl)-
4
,13-diaza-18-crown-6 with appropriate substituted
phenols [15–17] until Ki-Whan Chi and co-workers
18] reported a new convenient one-pot Mannich
[
reaction method. Since then, a wide variety of
lariat crown ethers containing different pendent

S.-l. Ma, W.-x. Zhu / Journal of Molecular Structure 643 (2002) 141–146
143
The resulting solid was collected by filtration and
dried. Mp 104–106 8C. Elemental analysis and
spectroscopy study showed a good agreement with
that reported [18].
detector diffractometer at 293 K with graphite mono-
˚
chromatized Mo Ka radiation (l ¼ 0.71073 A). The
structure was solved by direct methods and refined by
2
full-matrix least-squares on F using the SHELXS-97
and SHELXL-97 programs [22]. All nonhydrogen atoms
were refined anisotropically. A summary of
2
.3. Preparation of the complex
Cu(NO ) ·3H O (0.180 g, 0.60 mmol) in 6 ml
3
the crystallographic data and details of the structure
refinements are listed in Table 1.
2
2
acetone and 2 ml acetonitrile mixture solution was
added dropwise to the solution of 7,16-bis(2-hydroxy-
5
-methylbenzyl)-1,4,10,13-tetraoxa-7,16-diazacy-
clooctadecane (0.100 g, 0.20 mmol) in 6 ml acetone.
The colour of the reaction solution changed to dark
brown and some brown powder precipitated from the
solution. It was refluxed with stirring 4 h. The
precipitate was collected by filtration. The mother
liquor was stored at room temperature for several days
and some dark yellow crystals were obtained from the
mother liquor. Anal. calcd for C H CuN O
3. Results and discussion
3.1. IR and UV spectra
For the original free ligand 7,16-bis(2-hydroxy-5-
methylbenzyl)-1,4,10,13-tetraoxa-7,16-diazacyclooc-
21
tadecane, the multiple bands at 1143–1112 cm
assigned to n (C–O–C) and n (C–N–C) are shifted
2
8
38
4
10
2
to 1137–1083 cm , indicating the complexation of
1
(
M ¼ 654.16) (%): C, 51.36; H, 5.81; N, 8.56;
r
found (%): C, 51.43; H, 4.90; N, 8.63. To our
surprise, the analytical result does not fit the formula
C H N O ·Cu(NO ) which corresponds to the
Table 1
Summary of data collection and crystal parameters
2
8
42
2
6
3 2
complex copper nitrate with original lariat crown
ether but fits the formula C H CuN O , which
Empirical formula
Formula weight
C28H38CuN O
4
10
654.16
2
8
38
4 10
Temperature
293(2) K
˚
0.71073 A
¯
Triclinic, P1
indicated a copper complex with the lariat crown ether
nitro derivative. Single crystal analysis showed the
original pendent side-arm crown ether has been
converted to its nitro derivative (see below). The
spectroscopy measurements also support this sugges-
tion. According to the experimental results, we
suppose that the lariat azacrown ether was nitrated
Wavelength
Crystal system, space group
Unit cell dimensions
˚
a ¼ 8.571(4) A, a ¼ 102.073(9)8
b ¼ 8.784(4) A˚ , b ¼ 100.994(8)8
˚
c ¼ 11.582(6) A, g ¼ 115.197(8)8
3
˚
Volume
732.1(6) A
3
Z, calculated density
Absorption coefficient
F(000)
2, 1.484 Mg/m
21
0.810 mm
2
þ
þ
by HNO3 (NO3 from Cu(NO ) , and H from
3 2
343
2
phenolic hydroxyl) while coordinated to Cu ion.
3
Crystal size
0.30 £ 0.25 £ 0.20 mm
Q range for data collection
Limiting indices
1.90–25.028
210 # h # 8, 24 # k # 10,
2
.4. X-ray crystallography
2
13 # l # 12
Reflections collected/unique
Refinement method
3064/2578 [R(int) ¼ 0.0248]
Full-matrix least-squares on F
0.984
3
2
A crystal with dimensions 0.30 £ 0.25 £ 0.20 mm
2
Goodness-of-fit on F
was selected for X-ray diffraction experiment. The
measurements were performed on a CCD area
Final R indices [I . 2s(I )]
R1 ¼ 0.0419, wR2 ¼ 0.0848

144
S.-l. Ma, W.-x. Zhu / Journal of Molecular Structure 643 (2002) 141–146
Fig. 1. An ORTEP-3 [23] drawing of the complex with the atom numbering scheme. The displacement ellipsoids are drawn at the 50%
probability level.
the ether oxygen and the secondary amine nitrogen
3.2. Crystal structure
2
atoms to Cu ion. In the complex we found two new
þ
2
1
intense bands at 1471 and 1350 cm which can be
assigned to the asymmetric and symmetric –NO2
stretching vibrations, indicating the side-arm phenols
of the original lariat crown ether being nitrated while
Fig. 1 shows the molecular structure of the
complex. Fig. 2 shows the molecular packing
arrangement in the unit cell viewed along the b-axis.
The selected bond lengths and angles are given in
Table 2.
2
þ
complexing with Cu . No bands for the free nitrate or
coordinated nitrate have been observed in the complex.
This also verified the nitration of the side-arm phenols.
The molecular structure of the complex comprises
2
þ
2þ
a centrosymmetric Cu ion, and the central Cu ion
is six-coordinated to four oxygen atoms (two, O(3)
and O(3A), from two side-arm phenolate groups, and
the other two, O(2) and O(2A), from the crown ether
ring) and two tertiary amine nitrogen atoms N(1) and
2
1
The band at 3428 cm
assigned to the side-arm
phenolic hydroxyl in free lariat crown ether disap-
peared in complex indicating the deprotonation of the
2
phenols on coordinating to Cu . The aromatic ring
þ
2
vibration at 1498 cm in the original free ligand was
1
˚
N(1A).The long distance (3.832(2) A) of Cu–O(1)
2
shifted to a higher frequency 1513 cm also showing
1
and Cu–O(1A) shows that these two ether oxygen
atoms O(1) and O(1A) were not coordinated to the
2
þ
the coordination of side-arm phenols to Cu
.
The UV spectra of the original ligand in methanol
solution exhibit two intense absorption bands at 226
p
and 284 nm, corresponding to p–p transitions of
the aromatic ring. In the spectra of the complex, these
two bands were expectedly shifted to higher wave-
lengths at 231 and 303 nm. The deprotonated
phenolate ions cause an increase in electron density
of the aromatic rings, which results in the large
bathochromic shifts of the UV bands and an
enhancement in absorption intensity [17]. The two
less intense shoulders at 210 and 270 nm, which are
p
assigned to the n–p transitions of the NO groups,
2
p
were obscured by the very intense p–p transition of
the aromatic ring at 231 nm.
Fig. 2. Molecular packing arrangement in the unit cell viewed along
the b-axis.

S.-l. Ma, W.-x. Zhu / Journal of Molecular Structure 643 (2002) 141–146
145
Table 2
˚
The selected bond lengths (A) and angles (8) for the complex
Bond lengths
Cu(1)–O(3)
Cu(1)–N(1)
Cu(1)–O(2)
O(4)–N(2)
C(12)–N(2)
1.932(2)
2.092(2)
2.647(3)
1.224(4)
1.461(4)
Cu(1)–O(3A)
Cu(1)–N(1A)
Cu(1)–O(2A)
O(5)–N(2)
1.932(2)
2.092(2)
2.647(3)
1.227(4)
1.306(3)
O(3)–C(13)
Bond angles
O(3A)–Cu(1)–O(3)
O(3A)–Cu(1)–N(1A)
O(3)–Cu(1)–N(1A)
C(1)–N(1)–Cu(1)
C(7)–N(1)–Cu(1)
C(11)–C(12)–N(2)
O(4)–N(2)–O(5)
O(5)–N(2)–C(12)
180.000(1)
91.70(9)
N(1A)–Cu(1)–N(1)
O(3)–Cu(1)–N(1)
O(3A)–Cu(1)–N(1)
C(6)–N(1)–Cu(1)
C(13)–O(3)–Cu(1)
C(13)–C(12)–N(2)
O(4)–N(2)–C(12)
180.000(1)
91.70(9)
88.30(9)
88.30(9)
111.69(18)
110.76(17)
116.3(3)
111.27(18)
127.93(18)
119.9(3)
122.9(3)
119.4(3)
117.7(3)
Symmetry transformations used to generate equivalent atoms: 2x, 2y, 2z þ 2.
2
þ
Cu ion. The crown ether ring is twisted to meet the
requirement of the coordination geometry.
O(3)–Cu(1)–N(1) and O(3A)–Cu(1)–N(1) indicate
that the line connecting the two oxygen atoms, O(3)
and O(3A), is nearly vertical to the above plane.
In bibrachial lariat ether complexes, generally,
when two side arms are attached to a macroring,
complexation may be augmented by ligation from the
same or opposite sides of the macroring. When
complexation occurs from the same side (syn fashion),
the complexes are expected to resemble cryptate
complexes [24,25]. The two sidearms were found to
arrange in a syn fashion in the sodium complexes of
some lariat ethers based on the 4,13-diaza-18-crown-6
system [24–26]. However, the sidearms being in anti
fashion may keep less conformational strain in the
ligand, thus binding metal ion such as potassium
cation more strongly than syn fashion. In our present
copper complex of the bibrachial lariat ether, the side
arms are arranged in a anti fashion as in the potassium
2
The crystal structure shows no NO3 existing in
the complex, and the two pendent arms of ligand
existing in deprotonated phenolate forms. The bond
˚
lengths of N(2)–O(4) (1.224(4) A) and N(2)–O(5)
˚
(1.227(4) A) showed the existence of NO group
2
and verified that the two side-arm phenols of the
lariat crown ether were nitrated while complexing
2
þ
with Cu . It is also worthy of note that the
nuclear distances of Cu(1)–O(3) (1.932(2) A˚ ) and
0
iodide complex of N,N -bis(3-oxabutyl)-1,10-diaza-
1
8-crown-6 [24]. This may be attributed to the
octahedral geometry request of the copper complex
and the steric hindrance between the two phenolate
groups in the ligand. Fig. 3 shows the skeletal drawing
of its donor atoms and the metal ion. The donor atoms
N(1), N(1A), O(2) and O(2A) of the crown ether ring
2
þ
are coplanar, and the centrosymmetric Cu
resides in the N O plane of the four donor atoms, and
ion
2
2
the oxygen atoms of the two sidearms, O(3) and
O(3A), are located above and below the plane of the
ring. The bond angles of 91.90(7) and 88.30(9)8 for
Fig. 3. Skeletal drawing of the copper complex.

146
S.-l. Ma, W.-x. Zhu / Journal of Molecular Structure 643 (2002) 141–146
˚
Cu(1)–O(3A) (1.932(2) A) are significantly shorter
˚
than that of Cu(1)–O(2) (2.647(3) A), Cu(1)–
[8] M. Hiraoka, Crown Ethers and Analogous Compounds,
Elsevier, Amsterdam, 1992, p. 126.
[
9] D.A. Moore, P.E. Franwick, M.J. Welch, Inorg. Chem. 28
1989) 1504.
˚
O(2A) (2.647(3) A), Cu(1)–N(1) (2.092(2) A) and
˚
(
˚
Cu(1)–N(1A) (2.092(2) A). This is probably due to
[
10] U. Auerbach, U. Eckert, K. Wieghardt, B. Nuber, J. Weiss,
Inorg. Chem. 29 (1990) 938.
the fact that O(3) and O(3A) have a favourable
geometry for coordination compared to the donors
on the ring. The latter donors have to overcome a
larger strain coming from the ring twisting distor-
tion. The coordination polyhedron could be
described as a distorted octahedron. This special
coordination geometry of the complex may be due
to the flexibility of the ligand and the John–Teller
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2
þ
9
[
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