Extended chains via hydrogen bond linkages of dinuclear copper(II) and cadmium(II) complexes with a new flexible disulfoxide ligand

Article abstract of DOI:10.1016/S0022-4596(03)00055-0

A new flexible disulfoxide ligand 1,6-bis(benzylsulfinyl)hexane (L), which is a mixture of the meso and rac isomers, was treated with Cu^II or Cd^II nitrate and obtained dimeric complex [Cu₂(L)₃(H₂O) ₂(NO₃)₄] 2 or [Cd₂(L)₃(H₂O) ₂(NO₃)₄] 3. In the reacting system the crystals of meso isomer 1 of L together with 2 or 3 were obtained. 2 and 3 have similar molecular structures. In the neutral dimer, three ligands present two kinds of coordination models: monodentate and bis-monodentate. The neutral dimeric units in 2 and 3 are linked by hydrogen bonds to yield a chain structure. Crystal structures of all three compounds were determined by single-crystal X-ray diffraction methods. Crystal data for 1: monoclinic, space group Cc, a=41.95(2), b=5.132(2), c=8.660(4)A, β=94.898(9)°, V=1857.7(15)A³, Z=4, final refinement (I>2σ(I)): R1=0.0659, wR2=0.1415. Crystal data for 2: triclinic, space group P-1, a=9.242(4), b=9.539(4), c=21.042(9)A, α=83.888(9), β=87.971(8), γ=74.177(9)°, V=1774.6(13)A³, Z=2, final refinement (I>2σ(I)): R1=0.0577, wR2=0.0954. Crystal data for 3: triclinic, space group P-1, a=9.203(4), b=9.831(3), c=20.860(7)A, α=84.313(6), β=86.432(7), γ=74.188(6)°, V=1805.9(11)A³, Z=2, final refinement (I>2σ(I)): R1=0.0548, wR2=0.1192.

Full text of DOI:10.1016/S0022-4596(03)00055-0

Journal of Solid State Chemistry 173 (2003) 20–26
Extended chains via hydrogen bond linkages of dinuclear copper(II)
and cadmium(II) complexes with a new flexible disulfoxide ligand
ꢀ
Jian-RongLi, Miao Du, Xian-He Bu, and Ruo-Hua Zhang
Department of Chemistry, Nankai University, 94 Weijin Road, Tianjin 300071, China
Received 30 September 2002; received in revised form 6 December 2002; accepted 19 December 2002
Abstract
A new flexible disulfoxide ligand 1,6-bis(benzylsulfinyl)hexane (L), which is a mixture of the meso and rac isomers, was treated
with CuII or CdII nitrate and obtained dimeric complex [Cu2(L)3(H2O)2(NO3)4] 2 or [Cd2(L)3(H2O)2(NO3)4] 3. In the reactingsystem
the crystals of meso isomer 1 of L together with 2 or 3 were obtained. 2 and 3 have similar molecular structures. In the neutral dimer,
three ligands present two kinds of coordination models: monodentate and bis-monodentate. The neutral dimeric units in 2 and
3 are linked by hydrogen bonds to yield a chain structure. Crystal structures of all three compounds were determined by
single-crystal X-ray diffraction methods. Crystal data for 1: monoclinic, space group Cc; a ¼ 41:95ð2Þ; b ¼ 5:132ð2Þ; c ¼ 8:660ð4Þ A,
b ¼ 94:898ð9Þ1; V ¼ 1857:7ð15Þ A3, Z ¼ 4; final refinement (I42sðIÞ): R1 ¼ 0:0659; wR2 ¼ 0:1415: Crystal data for 2: triclinic,
space group P21; a ¼ 9:242ð4Þ; b ¼ 9:539ð4Þ; c ¼ 21:042ð9Þ A, a ¼ 83:888ð9Þ; b ¼ 87:971ð8Þ; g ¼ 74:177ð9Þ1; V ¼ 1774:6ð13Þ A3,
Z ¼ 2; final refinement (I42sðIÞ): R1 ¼ 0:0577; wR2 ¼ 0:0954: Crystal data for 3: triclinic, space group P21; a ¼ 9:203ð4Þ;
b ¼ 9:831ð3Þ; c ¼ 20:860ð7Þ A, a ¼ 84:313ð6Þ; b ¼ 86:432ð7Þ; g ¼ 74:188ð6Þ1; V ¼ 1805:9ð11Þ A3, Z ¼ 2; final refinement (I42sðIÞ):
R1 ¼ 0:0548; wR2 ¼ 0:1192:
r 2003 Elsevier Science (USA). All rights reserved.
Keywords: Disulfoxide; Flexible ligand; Copper(II); Cadmium(II); Coordination compound; Metal organic dimer; Hydrogen bond; Chain structure;
Crystal structure
1. Introduction
these materials are formed with rigid ligands, such as
4,40-bipyridine and pyrazine [6], which can assist the
design of predictable networks, simultaneously it
frequently limits their ability to accommodate ionic or
non-ionic species. Studies on flexible ligands are still
relatively rare [7], and we are interested in coordination
polymers containingflexible ligands such as disulfoxide,
dithioether, and trithioether. We have used these flexible
ligands to generate polymeric metal complexes, which
possess unique lamellar square array [3–5] topological or
pseudo-octahedral metal-organic frameworks, etc., and
we have substantiated that the cavities of the coordina-
tion networks can be controlled by varyingthe chain
length of the ligands [8]. As a continuation of our work
to investigate the coordination chemistry of disulfoxide
ligands and the architecture of their polymeric metal
complexes, we synthesized a new flexible disulfoxide
ligand 1,6-bis(benzylsulfinyl)hexane (L) which has a
longer spacer than those previous reported. We expect
that this ligand is more flexible and its metal complexes
may display unprecedented structure.
A particularly active field of chemical research in
recent years has been the design of extended molecular
system [1]. Advances in this general area have employed
a range of synthetic strategies and the products have
taken a variety of forms [2]. An important goal in this
developingfield has been the rationalization of the
structures of supramolecular crystals based on the
structures of their component molecules [3]. Strong,
selective, and directional hydrogen bonding has been
noted as a most powerful organizing force in molecular
assembly, and the vast majority of publications and
reviews have been devoted to the self-organization of
organic molecules into multi-dimensional hydrogen-
bonded architectures [4]. By contrast, relatively less is
known about hydrogen-bonding control of self-assem-
bly of coordination compounds [5]. In addition, most of
ꢀCorrespondingauthor. Fax: +86-22-2350-2458.
E-mail address: buxh@nankai.edu.cn (X.-H. Bu).
0022-4596/03/$ - see front matter r 2003 Elsevier Science (USA). All rights reserved.
doi:10.1016/S0022-4596(03)00055-0

J.-R. Li et al. / Journal of Solid State Chemistry 173 (2003) 20–26
21
2.2.2. 1,6-Bis(benzylsulfiny)hexane
Ph CH2
S
CH
S
CH2 Ph
(
)
6
2
To a vigorously stirred solution of 1,6-bis(ben-
zylthio)-hexane (13.2 g, 0.04 mol) in benzene (50 mL)
concentrated nitric acid (63%, 6 mL) was added drop-
wise. After stirringfor 24 h on ice bath, 15% sodium
hydrogen carbonate solution was added to the resulting
mixture to adjust the pH value to ca. 7 and the solid
product was filtered, and washed with distilled water,
ethanol and ether. Yield: 60%. FT-IR (cm–1): 696 m,
761w, 1023 s, 1454 m. Anal. calcd for C20H26O2S2: C,
O
O
H2O M (NO3)2
O
S
Ph CH2
CH2
(
S
CH2 Ph
)
6
O
H2O M (NO3)2
O
O
Ph CH2
S
CH2
S CH2 Ph
(
)
6
1
66.20; H, 2.78. Found: C, 66.28; H, 2.69%. H NMR
M = Cu (2), Cd (3)
(300 MHz): d1.394 (q, 4 H), 1.736 (t, 4 H), 2.529 (t, 4H),
3.975 (q, 4H), 7.258–7.375 (m, 10H). Colorless cubic
crystals of 1 (mp: 181–1831C) were obtained together
with those of 2 or 3 as described below, and also can be
separated by fractional crystallization from methanol
and chloroform from rac isomer (mp: 158–1601C).
Chart 1. The chemical structures of complexes 2 and 3.
The ligand L was treated with Cu(NO3)2 and
Cd(NO3)2 to produce neutral dimeric [Cu2(L)3(H2O)2
(NO3)4] 2 and [Cd2(L)3(H2O)2(NO3)4] 3 (Chart 1), self-
assembled by hydrogen-bonding to form one-dimen-
sional chain structure. Herein, we report the syntheses
and crystal structures of the ligand and its two
complexes.
2.3. Preparation of complexes
[Cu2L3(H2O)2(NO3)4] 2. Diethoxyethane (2.5 mL)
was added to the CHCl3 solution (5 mL) of L (219 mg,
0.75 mmol), and the mixture was stirred for ca. 20 min.
Then Cu(NO3)2 ꢁ 3H2O (60 mg, 0.25 mmol) in anhydrous
methanol (5 mL) was added to the above mixture and
further stirred at 70–801C for about 4 h. After the
mixture was cooled to room temperature and filtered,
the clear green filtrate was allowed to stand at room
temperature for ca. 1 week, and blue flaky crystals
suitable for X-ray investigation were obtained. Yield:
25%. Anal. calcd for C30H41CuN2O10S3: C, 48.04; H,
5.51; N, 3.74. Found: C, 48.15; H, 5.44; N, 3.70%. FT-
IR (cm–1): 506m, 620m, 688s, 765m, 990w, 1025s,
1437m, 1383s, 1461m, 1496w, 2860m, 2920m and
3062w.
2. Experimental
2.1. Materials and general methods
All the reagents and solvents employed were commer-
cially available and used without further purification.
The C, H and N analyses were performed on a Perkin-
Elmer 240C analyzer. FT-IR spectra (KBr pellets) were
taken on a FT-IR 170SX (Nicolet) spectrometer and 1H
NMR spectra were measured on a Bruker AC-P 200
spectrometer usingTMS as the internal standard and
CDCl3 as the solvent.
[Cd2L3(H2O)2(NO3)4] 3. This complex was pre-
pared usinga similar procedure to that described for 2
but usingCd(NO ) ꢁ 4H2O instead of Cu(NO3)2 ꢁ 3H2O
3 2
2.2. Syntheses of ligand
in 20% yield. Anal. calcd for C30H41CdN2O10S3: C,
45.10; H, 5.18; N, 3.51. Found: C, 45.21; H, 5.04; N,
3.48%. FT-IR (cm–1): 505m, 617m, 697s, 754m, 992w,
1026s, 1119s, 1245m, 1297m, 1324w, 1384s, 1460m,
1495w, 2855m, 2917m and 3061w.
The ligand was synthesized by a similar method
accordingto the Ref. [9].
2.2.1. 1,6-Bis(benzylthio)hexane
Potassium hydroxide (80%, 7.2 g, 0.1 mol) and benzyl
mercaptan (12.4 g, 0.1 mol) were dissolved in anhydrous
ethanol (75 mL) at 701C, then 1,6-dibromohexane
(12.2 g, 0.05 mol) was added to the above solution with
stirringover 1 h. The mixture was cooled to room
temperature and filtrated to remove KBr precipitate.
Then the solvent was removed under reduced pressure
from above filtrate. The crude product was dissolved in
chloroform (100 mL) and washed with 5% potassium
hydroxide solution and distilled water, then dried over
MgSO4. The product was obtained after the solvent was
evaporated. Yield: 92%.
2.4. Crystal structure determinations
Single crystals of 1, 2 and 3 suitable for X-ray
diffraction analysis with dimensions of 0.30 ꢂ 0.25
ꢂ 0.20, 0.30 ꢂ 0.25 ꢂ 0.30 and 0.25 ꢂ 0.40 ꢂ 0.30 mm3,
respectively, were selected and mounted on top of a
glass fiber. Single-crystal X-ray diffraction measure-
ments of 1–3 were carried out at 293(2) K on a Bruker
Smart 1000 CCD area detector equipped with a
graphite-monochromator situated in the incident beam
for data collection. The determinations of unit cell
parameters and data collections were performed with

22
J.-R. Li et al. / Journal of Solid State Chemistry 173 (2003) 20–26
Table 1
Crystal data and details of measurements for compounds 1, 2 and 3
1
2
3
Formula
Mr
C
362.53
20H26O2S2
[Cu(L)1.5(H2O)(NO3)2]2
749.37
293(2)
[Cd(L)1.5(H2O)(NO3)2]2
798.23
293(2)
T(K)
System
293(2)
Monoclinic
Cc
Triclinic
P21
Triclinic
P21
Space group
a/A
b/A
41.95(2)
5.132(2)
8.660(4)
9.242(4)
9.539(4)
21.042(9)
83.888(9)
87.971(8)
74.177(9)
1774.6(13)
1.402
9.203(4)
9.831(3)
20.860(7)
84.313(6)
86.432(7)
74.188(6)
1805.9(11)
1.468
c/A
a/degree
b/degree
94.898(9)
g/degree
V/A3
1857.7(15)
1.296
Dc (g/cm3)
Z
4
2
2
Min., max. transmission
m (MoKa) mmꢃ1
Measured reflections
Unique reflections
Refined parameters
Final R1 ,wR2 ðI42sðIÞÞ
wR2 (F2, all data)
0.9164, 0.9431
0.296
3588
0.7853, 0.8490
0.846
7319
0.8190, 0.8513
0.832
7543
2351
217
6223
415
6347
415
0.0659, 0.1415
0.1868
P
0.0577, 0.0954
0.1508
0.0548, 0.1415
0.1443
P
P
P
Note. R1= ||Fo|–|Fc||/ |Fo|. wR2={ [w(F2oꢃFc2)2]/ [w(Fo2)2]}1/2
.
CH OH/CHCl
diethoxyethane
MoKa radiation (l ¼ 0:71073 A). Unit cell dimensions
were obtained with least-squares refinements and all the
structures were solved by the direct methods using
SHELXS-97 program [10]. The final refinements for the
three structures were done by full matrix least-squares
methods with anisotropic thermal parameters for non-
hydrogen atoms on F2 [11]. The hydrogen atoms were
added theoretically, and ridingon the concerned atoms
and refined with fixed thermal factors. Semi-empirical
absorption correction was applied usingthe SADABS
program [12]. Crystallographic data and the experi-
mental details for structural analyses are summarized in
Table 1. Molecular drawings were produced by the
SHELXTL-XP program [13].
3
3
.
M(NO3)2
n
H2O + L
M2(L)3(H2O)2(NO3)4
room temperature
[M=Cu for 2, Cd for 3; L=1,6-bis(benzylsulfinyl)hexane]
Scheme 1.
soluble in CH3OH and CH3CN, and almost insoluble in
H2O and acetone. The IR spectrum of 1 shows a strong
band at 1023 cm–1 assigned to nS¼O: The spectra of
complexes 2 or 3 have a nS¼O band at 1025 or 1026 cm–1
approximately identical to that of the free ligand, and a
nS¼O band at 990 or 992 cm–1 shifted to the frequency
lower than that for the free ligand. It indicates that the
ligand does not behave as a complete bidentate ligand
but does coordinate, at least partially, as a monodentate
ligand [14]. The existence of nitrate anions in the
complexes was confirmed by IR spectra.
3. Results and discussion
3.1. Syntheses and general characterizations
3.2. Description of the crystal structures
The ligand was prepared by a similar method to our
previous work [9]. When M(NO3)2 ꢁ nH2O (M=Cu or
Cd) was treated with the mixture ligand of meso and rac
isomers, crystals of meso isomer of the ligand together
with the crystals of 2 or 3 were isolated. The meso isomer
of the ligand can also be separated from rac isomer by
fractional crystallization in CH3OH/CHCl3. The com-
plexes were prepared by the reaction of M(NO3)2 ꢁ nH2O
with the ligand in CH3OH/CHCl3 in the presence of
diethoxyethane to dehydrate (Scheme 1). Both com-
plexes are soluble in DMF and DMSO, and slightly
C20H26O2S2 1. The X-ray analysis of 1, as shown in
Fig. 1, has revealed that it corresponds to the meso
diastereomer havingan R,S conformation. All atoms
between two S atoms, benzyl methene carbon atom
C(14) and phenyl carbon atom C(15) lie almost on one
plane, which form distinct dihedral angles of 68.0(2) and
143.6(3)1 with two phenyl rings, respectively, and the
dihedral angle between them is 76.3(4)1. Two S ¼ O
groups lie on the opposite sides of that plane with the
distance of 9.157(5) A for two O donors and their
pseudo-torsion angle (S ¼ O?S ¼ O) is –160.5(4)1. The

J.-R. Li et al. / Journal of Solid State Chemistry 173 (2003) 20–26
23
Fig. 1. An ORTEP view of 1.
torsion angles of O(2)–S(1)–C(7)–C(6) and O(1)–S(2)–
C(14)–C(15) are –76.8(2) and –83.5(3)1, respectively.
Bond lengths and angles of the sulfinyl groups in 1, with
the average values of 1.475(5) A for the S ¼ O bond
distance and 107.1(8)1 for the O–S–C bond angle, are in
agreement with the values reported for uncoordinated
mono-sulfoxide (DMSO) (S ¼ O, 1.48(1) A O–S–C,
106.7(1)1), but the average value of 104.4(6)1 for the
C–S–C angle is larger than the reported value (96.4(2)1)
[15].
[Cu2(L)3(H2O)2(NO3)4] 2. An ORTEP view of
2 includingthe atomic numberingscheme is shown in
Fig. 2a. The structure of 2 consists of a neutral
[Cu2(L)3(H2O)2(NO3)4] dimer havingan inversion cen-
ter. Each CuII ion is coordinated to two oxygen atoms
from monodentate and bis-monodentate L molecules,
two oxygen atoms of two nitrate ions and one water
molecule, showinga distorted square pyramidal co-
ordination geometry. The equatorial plane is built up by
two oxygen atoms of two nitrates, one oxygen atom of
water molecule and one oxygen atom of the ligand, and
the apical site is occupied by another ligand oxygen
atom. The two nitrate groups are almost coplanar. The
Cu–O(disulfoxide) distances are 1.975(5) in equatorial
plane and 2.254(5) A in axial position, respectively being
similar to those of other CuII complexes of disulfoxide
[16]. The Cu–O(water) distance is 2.000(5) A in normal
bond length range [17], and the average bond length of
Cu–O(nitrate) is 1.979(6) A.
[Cd2(L)3(H2O)2(NO3)4] 3. The ORTEP structure
of 3 with atom labelingis shown in Fig. 2b. The
structure of 3 consists of a neutral [Cd2(L)3(H2O)2
(NO3)4] molecule with inversion center. Each CdII ion
has hepta-coordinate geometry. Two oxygen atoms of
the monodentate and bis-monodentate L molecules,
four oxygen atoms of two bidentate nitrate ions and one
water molecule surround each metal center to form a
distorted pentagonal bipyramidal polyhedron. Two
nitrate ions and a sulfoxide group are at the equatorial
position, and an oxygen atom of water molecule and an
oxygen atom of L at the apical position. The coordi-
nated oxygen atoms at the equatorial position are
almost coplanar, but the alignment of the apical oxygen
atoms is somewhat deviated from 1801 [O(1)–Cd(1)–
O(10), 178.3(2)1]. Two oxygen atoms of each nitrate ion
coordinated to CdII unequally with the average Cd–
O(nitrate) bond lengths of 2.365(3) and 2.503(5) A in
equatorial plane, and these are different from those
of {[Cd2(m-bet)3](NO3)4} which are almost equal for
Cd–O(nitrate) bond lengths but similar to {[Cd2(m-3,30-
pytz)3(NO3)4](EtOH)} [18]. The Cd–O(L) distance is
2.285(4) A in the equatorial plane and 2.238(4) A
in the apical position, and the bond length of Cd–
O(water) is 2.269(4) A which is shorter than other
analogous apical position Cd–O(water) bond length
[19].
In the dimeric complexes 2 and 3, the ligands take two
kinds of coordination modes on the coordination
donors. One reserved as a bridge to link two adjacent
metal ions by its two distinct O donors to form a dimer
with two metal ions separated by 11.085(5) and
10.260(7) A for 2 and 3, and the other two ligands
coordinate to two metal ions, respectively by one oxygen
donor. As shown in Fig. 3a and b, the neutral dimeric
units in 2 and 3 are bridged alternately by the hydrogen
bonds formed by metal-coordinated water molecules
of one complex unit, and nitrate oxygen atoms and
uncoordinated O donors of L in the other complex
molecule. The O?O(L) and O?O(nitrate) separations
are 2.658(4) and 2.728(5) A in 2 and 2.681(3) and
2.751(4) A in 3, fallinginto the normal raneg of the
O?O separation for hydrogen bonding [20]. In com-
plexes 2 and 3, the bis-monodentate ligand has a
symmetric center, and the quasi-torsion angle of O–
S?S–O is 1801, and the S–O vectors are parallel to each
other but pointingto opposite directions; however, the
S–O vectors of the monodentate ligand form 91.3 and
98.81 angles, respectively. This may be due to the reason
that one oxygen donor of the ligand coordinates to the
metal center. The distances between two oxygen atoms
in the bis-monodentate ligand are 10.048(3) and
9.457(3) A, respectively, and the distances in the mono-
dentate ligand are 11.206(3) and 8.400(6) A for 2 and 3,
respectively. To our knowledge 3 is the first structurally
determined cadmium(II) complex with flexible sulfoxide
ligand.

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J.-R. Li et al. / Journal of Solid State Chemistry 173 (2003) 20–26
Fig. 2. The Z-shaped dimetric unit of (a) 2 and (b) 3.
In summary, (a) only the meso isomer complexes were
the chain structure is formed by hydrogen bonds. For
free sulfoxide, the formation of hydrogen bonding is
common phenomenon, but the chain structure of the
metal complexes constructed by hydrogen bonds is less;
(d) in both complexes, nitrate ions adopt different
coordination modes, probably due to the result of a
delicate balance between electronic and steric factors.
obtained when the startingligand is a mixture of the rac
and meso forms; (b) the bindingof the ligands to Cu II or
CdII ions is in two kinds of coordination modes, i.e.,
monodentate and bis-monodentate. It is rare that two
kinds of coordination modes present simultaneously in a
complex molecule with disulfoxide; (c) in the complexes,

J.-R. Li et al. / Journal of Solid State Chemistry 173 (2003) 20–26
25
Fig. 3. Extended chain of (a) 2 and (b) 3 via hydrogen bond linkage.
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