Molecular, supramolecular structure and catalytic activity of transition metal complexes of phenoxy acetic acid derivatives

Article abstract of DOI:10.1016/j.poly.2007.07.033

Six mononuclear complexes [M(L₁)₂(H₂O)₄] (M = Co(II), 1a and M = Mn(II), 1b), [Cu(L₁)₂(H₂O)₂] (1c), [Cu(L₁)₂(H₂O)(Py)₂] (1d

Full text of DOI:10.1016/j.poly.2007.07.033

Available online at www.sciencedirect.com
Polyhedron 26 (2007) 5225–5234
www.elsevier.com/locate/poly
Molecular, supramolecular structure and catalytic
activity of transition metal complexes of phenoxy
acetic acid derivatives
*
Avijit Pramanik, Srinivas Abbina, Gopal Das
Department of Chemistry, Indian Institute of Technology Guwahati, Guwahati 781 039, Assam, India
Received 7 February 2007; accepted 17 July 2007
Available online 28 August 2007
Abstract
Six mononuclear complexes [M(L1)2(H2O)4] (M = Co(II), 1a and M = Mn(II), 1b), [Cu(L1)2(H2O)2] (1c), [Cu(L1)2(H2O)(Py)2] (1d),
[Cu(L3)(H2O)Cl] Æ H2O (3a) and [Co(Sal)(H2O)(Py)3] Æ 2ClO4 Æ H2O (3b) of phenoxyacetic acid derivatives and Schiff base were deter-
mined by single crystal X-ray diffraction. The Co(II) (1a) and Mn(II) (1b) complexes are isomorphous. X-ray crystal structural analyses
reveal that these coordination complexes form polymeric structure via formation of different types of hydrogen bonding and p-stacking
interactions in solid. Thermal analysis along with the powder X-ray diffraction data of these complexes shows the importance of the
coordinated and/or crystal water molecules in stabilizing the MOF structure. Complexes 1a, 1c, 3a show marginal catalytic activity
in the oxidation of olefins to epoxides in the presence of i-butyraldehyde and molecular oxygen.
Ó 2007 Elsevier Ltd. All rights reserved.
Keywords: Metallacycles; Hydrogen bonds; Crystal engineering; Metal–organic framework; Thermal analysis; Catalytic activity
1. Introduction
able structures and properties can be created. Thus, the
prospect of tuning the properties of metal–organic frame-
works through a systematic change of the coordination
environment provides an impetus to further research of
metal–organic architectures. Similarly hydrogen bonded
networks of organic molecules [14] or coordination com-
plexes [15] can also lead to highly ordered 2-D and 3-D
structures. A well-known example of an organic functional
group that forms hydrogen bonded network structures is
carboxylic acid [16–19]. Carboxylate ligands can bridge
two or more different metal centers and produce neutral
architectures. These structures can be rapidly and conve-
niently built [20,21] using the modular or tinkertoy
approach where topology of multidentate ligands as well
as the coordination characteristics of the metal ions direct
the self-assembly process.
In recent years, the main focus of supramolecular and
materials chemistry has been the area of coordination
frameworks, which are also known as coordination poly-
mers or metal–organic frameworks (MOF) [1–3]. The
increasing interest in this field is justified not only by their
potential application as functional materials [4–6] but also
by intriguing structural diversities of the architectures [7–
9]. Synthesis of MOF structures is an active area of
research, as these compounds can be potentially useful in
several contemporary problems [10–12]. Coordination
frameworks are also significant from a structural chemistry
perspective with new structural types being discovered as
well as providing numerous examples of phenomena such
as the interpenetration of networks [13]. By closely control-
ling the coordination environment, frameworks with desir-
We have previously demonstrated that tripodal ligand
bearing carboxylic acid group can act as a mononuclear
building block for the formation of an extended MOF
[22,23]. The present investigation is an extension of the
*
Corresponding author. Tel.: +91 3612582313; fax: +91 3612582349.
E-mail address: gdas@iitg.ernet.in (G. Das).
0277-5387/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2007.07.033

5226
A. Pramanik et al. / Polyhedron 26 (2007) 5225–5234
above studies in which the phenoxy acetic acid derivatives
(HL1, HL2 and HL3) with carboxylate groups to form
extended solid state structures has been explored. We
reported herein the six mixed-ligand mononuclear com-
plexes of Cu(II), Co(II), Co(III) and Mn(II).
NMR (100 MHz, CDCl3, 25 °C, TMS) d (ppm): 42.8,
58.3, 79.8, 116.8, 121.5, 123.7, 131.2, 132.6, 161.4, 165.2,
174.1. FT-IR (KBr): 3442 m(OH); 3351 m(NH2); 1765
m(C@O); 1602 m(C@N); 1490 m(C@C); 1164 m(COC) cmꢀ1
.
2.3. Synthesis of complexes
2. Experimental
2.3.1. Synthesis of [Co(L1)2(H2O)4] (1a)
2.1. Materials and methods
To a stirred solution of HL1 (18 mg, 0.1 mmol) in
MeOH (5 ml) was added CoCl2 Æ 6H2O (23.8 mg, 0.1
mmol) in water (5 ml) at RT. The resulting solution was
continued to stir for another 30 min. Slow evaporation of
the reaction mixture afforded the complex 1a as red crys-
tals. These were employed directly for the X-ray crystallo-
graphic study. Yield: 85%, Anal. Calc. for CoC18H22O12: C,
44.18; H, 4.53; Co, 12.04. Found: C, 44.24; H, 4.51; Co,
The aldehydes and the liquid olefins were distilled prior
to use. Metal salts and solid olefins are used as supplied
from commercial sources. All the solvents were purified
prior to use by standard procedure. The IR spectra were
recorded on a Perkin–Elmer-Spectrum One FT-IR Spec-
trometer with KBr disks in the range 4000–400 cmꢀ1
.
The thermo gravimetric analyses (TGA) of the compounds
were performed by using an SDTA 851e TGA thermal ana-
lyzer (Mettler Toledo) with a heating rate of 2 °C per min
in a N2 atmosphere. Optical spectra were recorded in
CH3CN on a Perkin–Elmer-Lambda 25-UV–Visible Spec-
trometer at 298 K. Solid-state magnetic susceptibility of
the complexes at room temperature was recorded using
Sherwood Scientific balance MSB-1. Solution electrical con-
ductivity measurements measured with a Systronics Con-
ductivity meter 306. Elemental analyses were done using
Carlo Erba 1108 and Perkin–Elmer series II 2400 instru-
ment. GCMS analyses were performed using a Perkin–
Elmer Clarus 500 gas chromatograph coupled with the
Perkin–Elmer Clarus 500 mass spectrometer.
12.11%. Molar conductance (in CH3CN): 4.1 S cm2 molꢀ1
;
solid-state RT leff = 5.22 BM; UV–Vis: 456 nm (sh)
4
4
[4A1g ! A2g(F)], 511 nm [4T1g(F) ! T1g(P)].
2.3.2. Synthesis of [Mn(L1)2(H2O)4] (1b)
Complex 1b was synthesized following the same proce-
dure as 1a, only MnCl2 Æ 4H2O (20 mg, 0.1 mmol) was
used instead of Co-salt. A light pink colored crystal of
1b was studied by X-ray crystallography. Yield: 78%.
Anal. Calc. for MnC18H22O12: C, 44.54; H, 4.56; Mn,
11.32. Found: C, 44.51; H, 4.52; Mn, 11.39%. Solid-state
RT leff = 5.91.
2.3.3. Synthesis of [Cu(L1)2(H2O)2] (1c)
Complex 1c was synthesized following the same proce-
dure as 1a, only CuCl2 Æ 2H2O (27 mg, 0.2 mmol) was used
instead of Co-salt. A blue colored crystal of 1c was studied
by X-ray crystallography. Yield: 55%. Anal. Calc. for
CuC18H18O10: C, 47.21; H, 3.96; Cu, 13.87. Found: C,
2.2. Synthesis of ligands HL1–3
Both the ligands (Scheme 1) (4-formyl-phenoxy)-acetic
acid (HL1) [24] and (2-formyl-phenoxy)-acetic acid (HL2)
[25] were synthesized following the reported procedure.
2
47.17; H, 3.99; Cu, 13.92%; UV–Vis: 720 nm [2E ! T2],
900 nm (sh).
2.2.1. Synthesis of ligands HL3
To a stirred solution of HL2 (111 mg, 0.5 mmol) in
MeOH (10 ml) was added ethylene diamine (30 mg,
0.5 mmol) in MeOH (2 ml) at ice-cold condition. Mixture
was then refluxed for 15 min and then allowed to cool to
RT. Slow evaporation results the formation of yellow crys-
tals, which was washed several times with cold MeOH.
Yield 65%, m.p.: 186 °C; ESI–MS, m/z (%): 222 (86)
[HL3]+; Anal. Calc. for C11H14N2O3: C, 59.45; H, 6.35;
2.3.4. Synthesis of [Cu(L1)2(H2O)(Py)2] (1d)
Complex 1d was synthesized following the same proce-
dure as 1c, only pyridine (24 mg, 0.3 mmol) was added
after addition of metal salt solution and stirring was con-
tinued for additional 45 min in a closed container at RT.
Dark blue crystal of 1d was studied by X-ray crystallogra-
phy. Yield: 42%. Anal. Calc. for CuC30H26N2O9: C, 57.92;
H, 4.21; N, 4.50; Cu, 10.21. Found: C, 57.96; H, 4.25; N
4.46; Cu, 10.27%.
1
N, 12.60. Found: C, 59.63; H, 6.31; N 12.55%. H NMR
(400 MHz, CDCl3, 25 °C, TMS) d (ppm): 3.2 (t, 2H), 3.8
(t, 2H), 4.7 (s, 2H), 6.8–7.6 (m, 4H), 8.2 (s, 1H), 13C
2.3.5. Synthesis of [Cu(L3)(H2O)Cl] Æ H2O (3a)
To a stirred solution of HL3 (11 mg, 0.05 mmol) in
MeOH (3 ml) was added CuCl2 Æ 2H2O (7 mg, 0.05 mmol)
in water (5 ml) at RT. The resulting solution was refluxed
with continues stirring for another 15 min. The mixture
was cooled to RT and slow evaporation of the reaction
mixture afforded the complex 3a as blue crystals. These
crystals were used directly for the X-ray crystallographic
study. Yield: 52%. Anal. Calc. for CuC11H18N2O5Cl: C,
COOH
COOH
COOH
NH2
OHC
O
O
O
N
CHO
HL1
HL2
HL3
Scheme 1. The phenoxy acetic acid derivatives HL1, HL2 and HL3.

A. Pramanik et al. / Polyhedron 26 (2007) 5225–5234
5227
36.97; H, 5.07; N, 7.84; Cu, 17.78. Found: C, 36.91; H,
5.02; N, 7.91; Cu, 17.72%.
All non-hydrogen atoms were refined anisotropically. Most
of the hydrogen atoms were located from the difference
Fourier maps and refined isotropically. While other hydro-
gen atoms are added in a fixed geometry. Selected crystal-
lographic data summarized in Table 1.
2.3.6. Synthesis of [Co(Sal)(H2O)(Py)3] Æ 2ClO4 Æ H2O
(3b)
To a stirred solution of HL3 (11 mg, 0.05 mmol) in
MeOH (3 ml) was added Co(ClO4)2 Æ 6H2O (18.3 mg,
0.05 mmol) in water (5 ml) at RT. After 45 min of stirring
at RT, excesses pyridine was added to this mixture. The
resulting mixture was continued to stir for additional
45 min in a closed container at ꢁ60 °C. Green crystal of
3b was studied by X-ray crystallography. The perchlorate
salts must be handled with care as this form potentially
explosive mixtures with organic compounds. Yield: 48%.
Anal. Calc. for CoC25H24N3O12Cl2: C, 43.62; H, 3.51; N,
6.10; Co, 8.56. Found: C, 43.66; H, 3.54; N 6.17; Co,
8.51%; UV–Vis: 648 nm (e 101 Mꢀ1 cmꢀ1) and 364 nm (e
1420 Mꢀ1 cmꢀ1).
3. Results and discussion
3.1. Crystal structure of [Co(L1)2(H2O)4] (1a) and
[Mn(L1)2(H2O)4] (1b)
The complexes 1a and 1b were crystallized from metha-
nol/water (1:1) mixture as red and pink colored crystals
respectively. The molecular structures with atom number-
ing scheme of the Co(II) complex (1a) and Mn(II) complex
2.4. X-ray crystallography
The intensity data were collected using a Bruker
SMART APEX-II CCD diffractometer, equipped with a
fine focus 1.75 kW sealed tube Mo Ka radiation (k =
˚
0.71073 A) at 273(3) K, with increasing x (width of 0.3°
per frame) at a scan speed of 3 s/frame. The SMART software
was used for data acquisition. Data integration and reduc-
tion were undertaken with SAINT and XPREP [26] software.
Multi-scan empirical absorption corrections were applied
to the data using the program SADABS [27]. Structures were
solved by direct methods using SHELXS-97 [28] and refined
with full-matrix least squares on F2 using SHELXL-97 [28].
Fig. 1. ORTEP plot of complexes 1a and 1b with atom numbering
scheme. Selected bond lengths for 1a: Co(1)–O(4) = 2.1424(10), Co(1)–
O(5) = 2.1029(14), Co(1)–O(6) = 2.0841(13); 1b: Mn(1)–O(4) = 2.2301(9),
Mn(1)–O(5) = 2.2018(12), Mn(1)–O(6) = 2.1596(12).
Table 1
Crystallographic refinement parameters of complexes 1a–3b
Parameters
1a
1b
1c
1d
3a
3b
Empirical formula
CCDC number
Fw
C
18H22CoO12
C18H22MnO12
616709
485.30
C18H18CuO10
616707
457.87
C28H26CuN2O9
616706
598.06
C11H17ClCuN2O5
616708
356.27
C22H14ClCoN3O8
616705
552.82
616704
489.29
Temperature (K)
298(2)
298(2)
298(2)
298(2)
298(2)
298(2)
Radiation
Wavelength (A)
Crystal system
Space group
Mo Ka
0.71073
monoclinic
P21/c
13.1134(4)
9.8258(3)
8.0525(2)
90.00
106.2470(10)
90.00
996.13(5)
2
Mo Ka
0.71073
Mo Ka
0.71073
triclinic
Mo Ka
0.71073
Mo Ka
0.71073
orthorhombic
Pbca
Mo Ka
0.71073
˚
monoclinic
P21/c
13.2560(2)
9.86910(10)
8.10040(10)
90.00
106.4830(10)
90.00
1016.18(2)
2
monoclinic
C2/c
15.0747(9)
5.9673(3)
30.8247(17)
90.00
98.996(4)
90.00
2738.7(3)
4
monoclinic
C2/c
11.6418(3)
24.3575(7)
17.9014(5)
90.00
94.838(2)
90.00
5058.1(2)
8
ꢀ
P1
˚
a (A)
5.1099(6)
7.0884(9)
13.0500(17)
80.172(3)
87.763(3)
77.215(3)
454.20(10)
1
7.4235(17)
18.289(4)
21.406(5)
90.00
90.00
90.00
˚
b (A)
˚
c (A)
a (°)
b (°)
c (°)
3
˚
V (A )
2902.4(11)
8
Z
l
0.932
0.709
1.260
0.849
1.698
0.827
F(000)
392
446
235
1188
1337
3248
Goodness-of-fit (S)
Final R indices
[I > 2r(I)]
1.040
0.948
0.982
0.974
0.959
1.164
R1 = 0.0307
wR2 = 0.0481
R1 = 0.0415
wR2 = 0.493
R1 = 0.0301
wR2 = 0.1071
R1 = 0.0356
wR2 = 0.1157
R1 = 0.0311
wR2 = 0.1046
R1 = 0.0318
wR2 = 0.1057
R1 = 0.0436
wR2 = 0.1117
R1 = 0.0788
wR2 = 0.1300
R1 = 0.0569
wR2 = 0.1365
R1 = 0.0874
wR2 = 0.1607
R1 = 0.0551
wR2 = 0.1660
R1 = 0.0979
wR2 = 0.1913
R indices (all data)

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A. Pramanik et al. / Polyhedron 26 (2007) 5225–5234
(1b) are shown in Fig. 1. Single-crystal X-ray analyses
revealed both 1a and 1b are neutral and mononuclear in
nature. In both the complex, metal ion is in similar coordi-
nation environment and each of them exhibits an octahe-
dral geometry with MO6 coordination. Bond angles and
distances of mononuclear complex indicate a slightly dis-
torted octahedral coordination with trans-geometry. Among
the six O atoms around the metal ion, two carboxylato
oxygen atoms are of ligand L1 and four oxygen atoms
are from water molecules. Metal bound four water mole-
cules form the equatorial planes and L1 is bonded in the
axial positions. The little elongation of the M–O4 bond
lengths agree with the bulkier nature of the ligand com-
pared to the water molecules. The Co(II)/Mn(II) atom lies
on a centre-of-inversion in the crystal structure. All the O
atoms of the water and the Co or Mn atom lie exactly on
the O4 plane.
As shown in Fig. 1, carboxylate act as a uni-dentate
ligand. In the crystal lattice, the coordinated water mole-
cules are in two different environments within the 3D net-
work. One set of water molecules has chelate type
intramolecular hydrogen bonding with carbonyl group of
carboxylate. The other set is hydrogen bonded to aldehyde
group in the para position. This results in the formation of
hydrogen bonded 2D tape type network along crystallo-
graphic a axis (see Supporting information). In the 2D tape
network, the two neighboring M(II) ions show a distance
[29]. This result is in good agreement with the crystal struc-
ture analysis. The OH stretching for water appearing at
3571 cmꢀ1 and 3483 cmꢀ1 shows that there are two differ-
ent types of environment for water molecules.
Solid-state arrangement of complex 1b is similar to that
of 1a, they are isostructural. The Mn–O bond distances
for equatorially coordinated hetero atoms are typical for
Mn(II) octahedral complexes [30,31]. It also shows the for-
mation of similar 2D hydrogen bonded tape as well as the
3D stair case network viewed along a axis. The separation
(D) between masym(CO2) and msym(CO2) is 405 cmꢀ1 in the
IR spectrum of 1b, which also confirms the uni-dentate
binding nature of the carboxylic acid group. In both the
complex, the overall structure is stabilized by several weaker
C–Hꢂ ꢂ ꢂO and C–Hꢂ ꢂ ꢂp interactions in addition to the stron-
ger O–Hꢂ ꢂ ꢂO hydrogen bonding (see Supporting informa-
tion). Complex 1b is very faint pink in color and have no
absorption bands in the visible region, in accordance with
the high-spin d5 electronic configuration of the Mn(II)
ion. This complex is very stable in spite of being based on
Mn(II). They may be stored in normal laboratory atmo-
sphere without taking any precautions for more than two
months.
3.2. Crystal structure of [Cu(L1)2(H2O)2] (1c) and
[Cu(L1)2(H2O)(Py)2] (1d)
˚
˚
of 13.113 A (in 1a) and 13.256 A (in 1b). However, the dis-
The molecular structures with atom numbering scheme
of both the Cu(II) complexes 1c and 1d are shown in Fig. 3.
˚
˚
tance between benzene ring is 5.908 A (in 1a) and 5.945 A
(in 1b) and they form an oval-shaped metallocycle unit.
Uncoordinated O3 atom of carboxylic acid is intramolecu-
larly hydrogen bonded to the nearest coordinated water
molecule. Due to this each axial M–O4 bond is slightly
tilted towards the M–O6 bond (\O(6a)–Co(1)–O(4) =
88.26 and \O(6a)–Mn(1)–O(4) = 87.92). In addition to
this, both the carboxylate oxygen atoms are intermolecu-
larly hydrogen bonded to the neighboring coordinated
water molecules. Overall hydrogen bonding results the for-
mation of staircase network viewed along crystallographic
a axis (Fig. 2), Individual molecule is arranged in zig-zag
fashion and helps to make the alternate steps of the stair-
case network.
The IR spectrum of complex 1a shows typical antisym-
metric and symmetric stretching bands of carboxylate
groups at 1710 and 1280 cmꢀ1, respectively. The separation
(D) between masym(CO2) and msym(CO2) is 430 cmꢀ1, indicat-
ing the presence of uni-dentate coordination modes in 1a
Fig. 3. ORTEP plot of complexes 1c and 1d. Selected bond lengths for
1c: Cu(1)–O(2) = 2.4141(14), Cu(1)–O(4) = 1.9487(15), Cu(1)–O(5) =
1.9457(15); 1d: Cu(1)–N(1) = 2.015(3), Cu(1)–O(3) = 1.962(2), Cu(1)–
O(5) = 2.184(3).
Fig. 2. Stair case network of 1a along a axis.

A. Pramanik et al. / Polyhedron 26 (2007) 5225–5234
5229
In complex 1c the Cu(II) atom is in the MO6 coordina-
tion environment. It is ligated by six oxygen atoms: two
carboxylato oxygen and two ether oxygen from ligand L1
and two oxygen from water molecules. The carboxylato
oxygen atoms bonds more strongly with the Cu(II) than
ether oxygen atoms. Complex 1c has two five-membered
O,O-chelate rings. Bond angles and distances of neutral,
mononuclear complex indicate a slightly distorted octahe-
dral coordination with trans-geometry. The bond distances
and bond angles involving the metal ions are similar with
the similar type of coordination environment [32,33]. The
shortening of the Cu–O4 bond lengths agree with the
stronger chelating ability of the carboxylate oxygen com-
pared to ether oxygen atoms. Due to the formation of
five-membered chelate rings both the axial bonds are
inclined towards the carboxylate donor in the equatorial
plane (\O(3)–Cu(1)–O(10) = 88.6 and \O(7)–Cu(1)–O(6) =
74.70). Carboxylate oxygen atoms and water molecules
form the equatorial plane while weakly bonded ether oxy-
gen atoms occupy the axial positions. Cu(II) atom exactly
lie within the equatorial plane without any deviation from
the plane. The strong O–Hꢂ ꢂ ꢂO and weaker C–Hꢂ ꢂ ꢂO and
C–Hꢂ ꢂ ꢂp type intermolecular hydrogen bonding play a
major role in stabilizing the solid-state structure. Each car-
boxylate oxygen atom form hydrogen bond with coordi-
nated water molecules, which result in the formation of
2D sheet of metallacycle along b axis (see supporting infor-
mation). All the Cu atoms form linear arrays in all three
directions. Shortest Cu–Cu distance in each layer of 2D
Weaker coordination of the ether oxygen to the Cu(II)
centre is lost, when stronger coordinating ligand pyridine
is added during complex preparation. Complex 1d crystal-
lizes as a neutral monomer. The overall coordination envi-
ronment changes from distorted octahedral to square
pyramidal with trans geometry (Fig. 3), where the O atom
of the water occupies the axial position. Square plane is
formed by N2O2 coordination from L1 and pyridine mole-
cules. In this complex also, L1 ligand coordinates to the
copper in a uni-dentate fashion. Selected bond length and
bond angels confirm the slightly distorted square pyrami-
dal mononuclear Cu(II) complex. The equatorial Cu–O
and Cu–N bond lengths are comparable with square-pyra-
midal CuN2O3 coordination spheres [36,37]. The axial Cu–
˚
O(5) bond length (2.184(3) A) is consistent with the trend
observed in other square-pyramidal Cu(II) complexes
[38]. Cu(II) lies in the N2O2 mean plane with out any devi-
ation. Both the ligands are bent in the opposite direction
with respect to the coordinated water molecule that results
in the formation of V-shape architecture. Fig. 5 shows the
formation of 2D tape structure along b axis via formation
of strong O–Hꢂ ꢂ ꢂO hydrogen bond between carboxylate
oxygen and water molecule. Shortest Cu–Cu distance in
˚
the same plane is 8.106 A whereas shortest Cu–Cu distance
˚
between adjacent planes is 15.412 A. It is also interesting to
note that the pyridine molecules in the basal plane are
twisted such that they are inclined at an angle of 38.93°
from a common plane. This puckering brings the carbonyl
group of the carboxylic acid group to the proximity of a
hydrogen atom present at the 3-position of a coordinated
pyridine molecule, resulting in a weak C–Hꢂ ꢂ ꢂO interaction
in the lattice. Due to steric crowding, two basal pyridines
do not remain in the same plane. Water molecules are
arranged in opposite direction on adjacent layer i.e. adja-
cent layer propagate along b axis in the opposite direction.
Adjacent 2D tape is connected through C–Hꢂ ꢂ ꢂO type
˚
sheet is 7.088 A, while shortest Cu–Cu distance between
˚
layers is 13.050 A. Adjacent layers run in the same direc-
tion along the b axis. Each aldehyde oxygen forms two
C–Hꢂ ꢂ ꢂO type bond which leads to the formation of 3D
double-staircase network in solid-state (Fig. 4). The
m(COC) band near 1105 cmꢀ1 is shifted by 35 cmꢀ1 in the
FT-IR spectrum of complex 1c to a lower frequency than
the free ligand, which is also confirmed form X-ray struc-
ture analysis. Carboxylic acid is uni-dentate ligand here
also, which shows the separation (D) between masym(CO2)
and
m .
sym(CO2) stretching frequency of 395 cmꢀ1
Solid-state magnetic moment of 1c is 1.85 BM. This value
is consistent with a Cu(II) complex having an octahedral
coordination geometry [34,35].
Fig. 5. Packing of 1d along b axis showing O–Hꢂ ꢂ ꢂO and C–Hꢂ ꢂ ꢂO
Fig. 4. Double-staircase network along b axis in 1c.
interactions.

5230
A. Pramanik et al. / Polyhedron 26 (2007) 5225–5234
hydrogen bond involving the aldehyde groups (Fig. 5), In
contrast to the complex 1c, benzene ring of the ligand in
1d form p–p stacking interactions with another benzene
ring in the adjacent layer. Upon complex formation in-
pane ring deformation frequency of pyridine at 604 cmꢀ1
is shifted to 643 cmꢀ1 [39]. Although the electronic spectra
of the copper complexes with multidentate Schiff base
ligands are not in general good indicators of geometry
[40], but act as supporter of it. The solid-state Nujol mull
absorption spectrum for 1d appeared at 650, 340 and
244 nm. The broad absorption band at 650 nm is attribut-
able to a copper ion in square pyramidal chromophore
CuN2O3 [41]. This broad visible absorption band at
650 nm is shifted slightly to a lower energy (678 nm) in ace-
tonitrile solution, consistent with square pyramidal geome-
try in solution phase. The complex displays two strong
absorption bands at 340 and 244 nm in solid which are
clearly r(N) ! Cu(II) LMCT in origin and these two
bands are shifted to 348 and 248 nm, respectively, in solu-
tion. The solid-state magnetic moment number for 1d is
1.91, which is typical [42] of a discrete mononuclear Cu(II)
complex.
bonds more strongly with the Cu(II) than ether and water
oxygen atoms. The geometry of the ligand forced the ether
oxygen to form a bond with the Cu(II) in more strongly
nature than water molecule, which is not common to our
knowledge. Complex 3a has two five-member O,O and
N,N-chelate rings along with one six-member N,O-chelate
ring. Bond angles and distances of this mixed-ligand mono-
nuclear complex indicate a slightly distorted octahedral
coordination [18]. Water oxygen atom and chloride ion
occupy the axial positions. Cu(II) atom exactly lie within
the N2O2 equatorial plane without any deviation from
the plane. Due to the formation two five-member and
one six-member chelate rings in the same side of the com-
plex, both the axial bonds are inclined towards the benzene
ring of the donor in the equatorial plane. Uncoordinated
carboxylate oxygen form hydrogen bond with neighboring
coordinated water molecule. Hydrogen of NH2 group
simultaneously forms hydrogen bond with coordinated
carboxylate oxygen atom and crystal water molecule.
Chloride ion form relative weaker hydrogen bond with
both coordinated and uncoordinated water molecules (see
Supporting information). The conventional strong O–
Hꢂ ꢂ ꢂO, N–Hꢂ ꢂ ꢂO hydrogen bonding along with unconven-
tional weaker C–Hꢂ ꢂ ꢂO, C–Hꢂ ꢂ ꢂCl type intermolecular
hydrogen bonding and pꢂ ꢂ ꢂp interactions form 3D zig-zag
network (Fig. 7). All the benzene rings of the ligand form
continuous p-stacking along a axis. Overall network is
formed by 2D sheet arrangement of metallacycle along a
axis. All the Cu atoms form rectangular boxes when viewed
3.3. Crystal structure of [Cu(L3)(H2O)Cl] Æ H2O (3a)
Complex 3a crystallizes as a neutral monomer. The
molecular structures with atom numbering scheme of the
Cu(II) complex is shown in Fig. 6. In the complex Cu(II)
atom is in the N2O3Cl coordination environment. Here
all six coordination site is occupied by six different coordi-
nation group. Three oxygen atoms ligate it: one carboxyla-
to oxygen, one ether oxygen from ligand L3 and one from
water molecule. Two nitrogen atoms are from imine and
primary amine groups. The carboxylato oxygen atoms
˚
˚
along b axis with a Cu–Cu distance of 9.347 A and 7.848 A,
respectively. Each of the crystal water is acting as single
acceptor and double donor, which stabilize the overall
network.
In aqueous solution, complex has a kmax value of 619 nm
(e = 46 Mꢀ1 cmꢀ1) in the visible region due to a d–d tran-
sition and a kmax value of 244 nm (e = 5055 Mꢀ1 cmꢀ1) in
the UV region due to a LMCT transition. As these values
are far from that of aqueous CuCl2 at 819 nm, it is reason-
able to assume that at least most of complex species of 3a
are not dissociated in solution.
Fig. 6. ORTEP plot of Complex 3a. Selected bond lengths are Cu(1)–
O(1) = 2.051(2), Cu(1)–O(2) = 1.933(3), Cu(1)–O(4) = 2.529(3), Cu(1)–
Cl(1) = 2.7102(12), Cu(1)–N(1) = 1.940(3) and Cu(1)–N(2) = 2.004(3).
Fig. 7. Packing of 3a along a axis.

A. Pramanik et al. / Polyhedron 26 (2007) 5225–5234
5231
3.4. Crystal structure
[Co(Sal)(H2O)(Py)3] Æ 2ClO4 Æ H2O (3b)
ing information). All the Co(III) atoms form rectangular
˚
boxes along b axis with a Co–Co distance of 11.642 A
˚
and 6.819 A, respectively.
When L3 was treated with Co(ClO4)2 salt in open atmo-
sphere with subsequent treatment of excesses pyridine, we
got salicylaldehyde Co(III) complex 3b. Both the Schiff
base and ether linkage has been cleaved and Co(II) is oxi-
dized to Co(III) species during complex formation in open
atmospheric condition. Unit cell contains one mononuclear
Co(III) complex, one water and two perchlorate ions.
Fig. 8 shows the ORTEP plot of complex 3b without the
counter anions. The geometry of the complex is distorted
octahedral. Three pyridine nitrogen atoms and phenolate
oxygen form the equatorial plane while axial positions
are occupied by aldehyde and water oxygen. Pyridine mol-
ecules in the trans position are almost orthogonal to each
other with an torsion angle \C23–N4–N2–C10 = 86.10°.
There is no deviation of Co(III) from N3O basal plane.
p-stacking interaction between pyridine rings forms the
dimmer.
A strong peak in FT-IR spectrum of 3b in 1625 cmꢀ1 is
attributable to the g1-bonded aldehyde (C@O) stretching
vibrations. Another strong peak at 1118 cmꢀ1 is attributed
to the ClOꢀ4 ion.
3.5. Thermal and powder XRD analysis
Both 1a and 1b decomposed thermally in a number of
steps. These complexes show successive thermal release of
coordinated water molecules and the CO2 followed by
complete decomposition of the complex. The robustness
of the framework is reflected in the thermo gravimetric
analysis (TGA). TG analysis of complex 1a in N2 atmo-
sphere shows the release of four coordinated water mole-
cules (50–150 °C; Dm = 14.66% Calc.; 15.68% found) and
two CO2 molecules from the two coordinated carboxylate
groups (230–420 °C; Dm = 21.00% Calc.; 20.93% found)
(Fig. 10), which is in good agreement with the X-ray crystal
structure. Complete decomposition is achieved at ꢁ600 °C.
The DSC-plot shows two endothermic peaks at 60 °C and
100 °C due to the loss of water molecules. It also shows two
exothermic peaks at 260 °C and 330 °C due to the decom-
position of the carboxylic acid groups. For complex 1b,
dehydration occurs at same temperature range that of 1a,
but decarboxylation occurs at 230–420 °C.
Crystal water forms hydrogen bonds with two perchlo-
rate anions and coordinated water molecule in single
acceptor–double donor way. Overall metallacycle formed
2D MOF along ab plane by water and perchlorate anion
(Fig. 9). Overall, 3D mosaic structure is obtained via for-
mation of different types of hydrogen bonds (see Support-
Thermal analysis of complex 1c shows 8.69% (calculated
7.82%) weight loss in the 120–180 °C due to the removal of
two coordinated water molecules. It also shows the releases
of two CO2 molecules in the temperature range of 260–
320 °C associated with 21.42% weight loss (calculated
20.75%). Complete decomposition takes place at 580 °C.
DSC profile shows two endothermic and one exothermic
Fig. 8. ORTEP plot of complex 3b, perchlorate anions are omitted for
clarity. Selected bond lengths are Co(2)–O(1) = 2.036(2), Co(2)–
O(2) = 2.055(2), Co(2)–O(4) = 2.067(3), Co(2)–N(1) = 2.124(3), Co(2)–
N(2) = 2.104(3), Co(2)–N(4) = 2.105(3).
Fig. 9. Water and perchlorate assisted MOF along ab plane of 3b.
Fig. 10. TG–DSC curve of complex 1a.

5232
A. Pramanik et al. / Polyhedron 26 (2007) 5225–5234
peak at 140 °C, 480 °C and 280 °C, respectively. TG anal-
ysis of 1d exhibits a curve that corresponds to a weight loss
of 28.88% (Calculated 21.17%) in the 110–190 °C range
corresponds to the removal of one water, two pyridine
and a further 21.42% (Calculated 20.75%) loss in the
300–490 °C temperature range, which corresponds to the
release of two CO2 molecules. DSC analysis shows one
endothermic peak at 180 °C and one exothermic peak at
400 °C. Generally, a lattice water molecule is expected to
be lost at a lower temperature. Thus, one would anticipate
a loss of two water molecules of crystallization at a lower
temperature than the coordinated water molecules in com-
plex 3a. TG analysis of complex 3a in N2 atmosphere
shows the sequential release of crystal water (90–180 °C;
Dm = 5.05% Calc.; 6.37% found) and coordinated water
molecule (180–230 °C; Dm = 5.32% Calc.; 6.72% found).
In the temperature range 300–410 °C it shows the release
of chloride and one CO2 (Dm = 24.82% Calc.; 36.47%
found). The DSC-plot shows two endothermic peaks at
125 °C and 205 °C due to the loss of water molecules. It
also shows two exothermic peaks at 470 °C and 500 °C.
Thermal analysis was not performed with 3b due to the
presence of perchlorate salt.
PXRD patterns also confirm the crystalline nature of
the complexes. PXRD patterns of 1a show significant
changes in the peak positions as well as intensities before
and after water removal (Fig. 11). After heating the crystal
of 1a at 200 °C for 5 h in a muffle furnace, powder XRD
was recorded. Loss of overall crystallinity after water
removal confirms that the stability of MOF in the solid
state is a result of the strong hydrogen bonding interactions
involving coordinated water molecules. Similar observa-
tion was made with 1b also. Complex 1b was heated at
180 °C for 5 h in a muffle furnace to get rid of the coordi-
nated water molecules. All the other complexes shows the
similar type of changes in the PXRD pattern before and
after the removal of water molecules (see Supporting
information).
3.6. Catalytic activities of the complexes
All six water soluble complexes are tested as a catalyst in
the epoxidation of linear and cyclic olefins under Mukaiy-
ama’s conditions [43]. It is found that only Co(II) complex
1a, Cu(II) complexes 1c and 3a are found to be able to act
as a catalyst in the epoxidation of alkenes by molecular
oxygen in the presence of a sacrificial aldehyde, i-butyral-
dehyde [43–47] (Table 2). In all cases, blank tests per-
formed in identical conditions but without metal catalyst
gave negligible conversions of the substrates. It is interest-
ing to note that the pyridine complexes (1d, 3b) show very
poor catalytic activity in the same reaction condition.
Compared to the complexes 1a, 1c and 3a, pyridine com-
plexes required more reaction time and yielded less amount
of product. In a typical experiment, a substrate (10 mmol)
and i-butyraldehyde (20 mmol) were added to acetonitrile
(15 ml) containing 5 mol% catalyst under an atmosphere
of molecular oxygen at ambient pressure and temperature.
TLC followed progress of the reaction. After completion or
interruption of the reaction, the solid catalyst was filtered
through a short plug of silica gel. The i-butyric acid formed
is removed by washing with an aqueous NaHCO3 solution.
The excess of unreacted i-butyraldehyde is evaporated
under vacuum together with the solvent. Aqueous workup
followed by column chromatography afforded the corre-
sponding epoxides. The epoxides were identified by com-
parison of their MS spectra and retention times in GC
analysis with those of authentic samples. In absence of i-
butyraldehyde, none of the complexes was able to cause
epoxidation even if used stoichiometrically. This simple,
environment friendly methodology has some drawbacks.
It is not applicable to unreactive olefins. Yields are not
quantitative. One has to invest stoichiometric amounts of
i-butyraldehyde as a sacrificial reducer, whose role is that
of an oxygen transfer agent. The likely mechanism is co-
oxidation of the sacrificial aldehyde and the olefin. The
mechanism can be compared with that of the reported in
literature [47]. Detailed mechanisms of the catalytic pro-
cesses are currently being investigated in our laboratory
with some other acid–metal complexes, which are already
published from our laboratory. A direct oxidation without
using these catalysts i.e. the control reaction did not lead to
any substantial oxidation product.
4. Conclusion
In conclusion, we reports the synthesis and crystal struc-
ture of six mononuclear mixed-ligand complexes of phe-
noxyacetic acid derivatives and Schiff base of Cu(II),
Co(II)/(III), Mn(II). The carbonyl groups in the acetic acid
Fig. 11. Powder XRD pattern of complex 1a. (a) Before water removal
and (b) after water removal.

A. Pramanik et al. / Polyhedron 26 (2007) 5225–5234
5233
Table 2
Summary of catalyzed aerobic epoxidation of olefin
Entry
1
Olefin
Catalyst
Time (min)
Conversion (%)
Yield (%)
1a
1c
1d
3a
3b
45
20
480
20
95
98
71
98
67
58
64
33
68
28
300
2
1a
1c
1d
3a
3b
30
15
600
10
89
92
69
90
61
55
60
21
62
16
380
3
1a
1c
1d
3a
3b
50
30
420
15
94
97
66
98
70
52
68
31
65
23
O
240
4
5
1a
1c
1d
3a
3b
25
15
540
10
82
87
59
92
51
45
57
18
52
10
480
1a
1c
1d
3a
3b
20
10
360
10
92
96
62
98
56
48
58
26
63
17
240
6
7
1a
1c
1d
3a
3b
20
10
360
10
76
84
43
81
36
37
48
18
51
10
240
1a
1c
1d
3a
3b
30
25
420
20
94
98
58
98
47
52
63
21
71
14
300
8
1a
1c
1d
3a
3b
45
40
480
30
88
93
57
98
48
66
74
31
81
22
360
moiety provide the anchor to form two distinguishable sets
of hydrogen-bonded motifs in all the complexes. It is inter-
esting to note that carboxylic acid acts as a uni-dentate
ligand in all the complexes. The Schiff base ligand has
unique structure, which contains four different ligating
atoms in one molecule. We have shown in the manuscript
that ether oxygen can also bind to the metal center, which
has very poor ligating capability. We demonstrated in the
manuscript that the precise control of the coordination
environment of the metal center has an effect on the forma-
tion of 3D metallo-organic framework (MOF) in the solid
state. 3D MOF structure has been critically analyzed and
explained based on the monomer structure. We have tested
the catalytic properties of all the metal complexes. We
observed that subtle change in the coordination environ-
ment changes the catalytic properties drastically. Out of
six complexes, 1c and 3a complexes shows marginal cata-
lytic activities in the epoxidation of olefins by molecular

5234
A. Pramanik et al. / Polyhedron 26 (2007) 5225–5234
[13] S.R. Batten, CrystEngComm 3 (2001) 67.
oxygen in the presence of i-butyraldehyde under Mukaiy-
ama’s conditions. We have not been able to observe addi-
tion or insertion of oxygen into the aromatic ring with
any of these complexes.
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[19] J.-R. Galan-Mascaros, J.-M. Clemente-Juan, K.R. Dunbar, J. Chem.
The financial support from the Council of Scientific and
Industrial Research (CSIR) of India to GD (Grant No.
01(1948)/04/EMR-II) is gratefully acknowledged. A.P.
thanks CSIR for JRF. We thank Central Instrument Facil-
ity, Centre for Nanotechnology and Department of Chem-
istry IIT Guwahati for SEM, Powder XRD and Single
crystal XRD measurements.
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Appendix A. Supplementary material
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Madison, Wisconsin, USA, 1995.
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CCDC 616704, 616709, 616707, 616706, 616708 and
616705 contain the supplementary crystallographic data
for 1a, 1b, 1c, 1d, 3a and 3b. These data can be obtained
free of charge via http://www.ccdc.cam.ac.uk/conts/
retrieving.html, or from the Cambridge Crystallographic
Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK;
fax: (+44) 1223-336-033; or e-mail: deposit@ccdc.cam.
ac.uk. Supplementary data associated with this article can
be found, in the online version, at doi:10.1016/
j.poly.2007.07.033.
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