Synthesis, spectral investigation and thermal aspects of coordination polymeric chain assemblies of some transition metal ions with bis-pyrazolones

Article abstract of DOI:10.1016/j.saa.2008.06.024

A few coordination chain polymeric assemblies of the type [M(SB)(H₂O)₂]_n·xH₂O or [VO(SB)(H₂O)]_n·H₂O [where M = Mn(II), Cu(II) and Zn(II), x = 1; Co(II) and Ni(II) x = 2, H_2<

Full text of DOI:10.1016/j.saa.2008.06.024

Spectrochimica Acta Part A 71 (2009) 1741–1748
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Synthesis, spectral investigation and thermal aspects of coordination
polymeric chain assemblies of some transition metal ions with
bis-pyrazolones
C.K. Modi∗
Department of Chemistry, Sardar Patel University, Vallabh Vidyanagar, Gujarat 388120, India
a r t i c l e i n f o
a b s t r a c t
Article history:
A
few coordination chain polymeric assemblies of the type [M(SB)(H2O)2]n·xH2O or [VO(SB)-
Received 19 April 2008
Received in revised form 23 May 2008
Accepted 24 June 2008
(H2O)]n·H2O [where M = Mn(II), Cu(II) and Zn(II), x = 1; Co(II) and Ni(II) x = 2, H2SB = (4Z,
4ꢀZ)-4,4ꢀ-(2,2ꢀ-(4,4ꢀ-methylenebis(4,1-phenylene)bis(azanediyl))bis(1-hydroxy ethan-2-yl-1-ylidene))-
bis(3-methyl-1-phenyl-1H-pyrazol-5(4H)-one)] have been investigated. Structural and spectroscopic
properties have been studied on the basis of elemental analyses, infrared spectra, 1H and 13 C NMR
Keywords:
spectra, electronic spectra, magnetic measurements and thermo gravimetric analyses. FT-IR, 1H and 13
C
Coordination polymers
Tautomeric studies of H2SB
Freeman–Carroll method
TG/DTG
NMR studies reveal that the ligand (H2SB) exists in the tautomeric enol form in both the states with
intramolecular hydrogen bonding. Magnetic moment and reflectance spectral studies reveal that an
octahedral geometry has been assigned to all the prepared coordination polymers. The kinetic parameters
such as order of reaction (n) and the energy of activation (Ea) have been reported using Freeman–Carroll
method. The pre-exponential factor (A), the activation entropy (ꢀS#), the activation enthalpy (ꢀH#) and
the free energy of activation (ꢀG#) have been calculated.
DTA and DSC studies
© 2008 Elsevier B.V. All rights reserved.
1. Introduction
study of polymeric ligands and their metal complexes is very use-
ful as a catalyst in metal separation and in bio-inorganic chemistry
The design of new coordination supramolecules and polymers
based on transition metal compounds and multidentate organic lig-
ands has attracted much interest in recent years [1,2]. Dependent
on the nature of the metal and the coordination behavior of the lig-
and one can develop synthetic strategies to influence the one-, two-
or three-dimensional arrangement in the crystal in a more directed
way [3]. Furthermore, it is now realized that weak hydrogen bond(s)
that involve O H· · ·O hydrogen bond stacking interactions also play
a significant and predictable structure determining role. Their rep-
resenting reliable and ubiquitous supramolecules show that they
already have been applied in a broad range of systems and have ana-
logues in the context of coordination supramolecules and polymers
[1a,1b]. Coordination polymers are usually known for their thermal
stability [4,5]. However, some additional equally good applications
have been reported, such as use solar energy converters [6] and
removal of SOx and NOx from the environment [7]. One major goal
in this area is the preparation of new compounds with interesting
properties such as functional materials in molecular magnetism
[8], catalysis [9], optoelectronic devices and gas sorption [10]. The
[11–13].
Pyrazolone and its derivatives form an important class of
such compounds and have attracted considerable scientific and
applied interest. Furthermore, 4-acyl-pyrazolone derivatives have
the potential to form different types of coordination com-
pounds due to the several electron-rich donor centers [14–16]
and tautomeric effect of the enol form and keto form [17–20].
Therefore, the 4-acyl-pyrazolone derivatives are broadly used
in many fields, especially in biological, clinical and analytical
applications [21–23]. The flexibility and conformational free-
dom of 4-acetyl-pyrazolone ligands give rise to a variety of
interesting structural motifs. In the previous work, the present
author have synthesized a series of 4-acyl-pyrazolone deriva-
tives and reported several transition metal complexes [24–26],
but no detailed studies on coordination polymeric chain assem-
blies of transition metal ions with bis-pyrazolones as a ligand
have been carried out so far. Hence, information about the struc-
tural properties of coordination polymers with bis-pyrazolones
is important to examine further the coordination abilities and
complexation behavior of pyrazolone-based ligand and to inves-
tigate the building blocks for the supramolecular networks.
The suggested structure of the ligand (H2SB) is shown in
Scheme 1.
∗
Tel.: +91 2692 226856; fax: +91 2692 236475.
E-mail addresses: chetank.modi1@gmail.com, modi ck@yahoo.co.in.
1386-1425/$ – see front matter © 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2008.06.024

1742
C.K. Modi / Spectrochimica Acta Part A 71 (2009) 1741–1748
Scheme 1. Synthesis and structure of the ligand (H2SB).
2. Experimental
2.3. Synthesis of (Z)-4-(2-chloro-1-hydroxyethylidene)-3-
methyl-1-phenyl-1H-pyrazol-(4H)-one
2.1. Materials
The literature procedure [29] with some modifications in the
reaction time and work-up was followed. In a two-necked round
bottomed flask with magnetic stirrer, a reflux condenser and a
dropping funnel, compound 1-phenyl-3-methyl-2-pyrazoline-5-ol
(17.07 g, 0.098 mol) was dissolved in dry dioxane (100 mL), and
then Ca(OH)2 (10.37 g, 0.14 mol) was added. Chloroacetyl chlo-
ride (7.97 mL, 0.1 mol) was added drop wise with precaution, as
this reaction was exothermic. During this addition the whole
mass was converted into a thick paste. After the complete addi-
tion, the reaction mixture was heated to reflux for about 4 h
and then it was cooled to room temperature. The mixture was
poured slowly into 2 M chilled HCl (200 mL) with constant stir-
ring until the light yellow precipitate was formed. The colored
crystals thus obtained were separated by filtration and recrystal-
lized from methanol–chloroform mixture (MeOH:CHCl3 = 80:20).
Yield 64%, mp: 80 ◦C. Elemental analysis found (%) C, 57.52; H,
4.41; N, 11.23; calculated for C12H11 ClN2O2: C, 57.49%; H, 4.42%;
N, 11.17%.
All the chemicals used were of analytical grade and used
without further purification. The compound 1-phenyl-3-methyl-
2-pyrazoline-5-ol was purchased from E. Merck Ltd. (India).
4,4ꢀ-Methylenedianiline and chloroacetyl chloride were purchased
from Qualigens Fine Chemicals, India and used without further
purification.
2.2. Instruments
Carbon, hydrogen and nitrogen were analyzed with the
PerkinElmer, USA 2400-II CHN analyzer. The metal content of the
coordination polymers were analyzed by the EDTA titration tech-
nique [27]. A 100 mg sample of the vanadyl coordination polymer
was placed in a silica crucible, decomposed by gentle heating
and then treated with 1–2 ml of concentrated HNO3, 2–3 times.
Orange colored residues (V2O5) were obtained after decomposi-
tion and complete drying [28]. Infrared spectra (4000–400 cm−1
)
were recorded on Nicolet-400D spectrophotometer using KBr pel-
lets. 1H and 13C NMR spectra were recorded on a model Advance
400 Bruker FT-NMR instrument and DMSO-d6 used as a sol-
vent. The reflectance spectra of the coordination polymers were
recorded in the range of 1700–350 nm (as MgO discs) on a Beck-
man DK-2A spectrophotometer. The magnetic moments were
obtained by the Gouy’s method using mercury tetrathiocyanato
cobaltate(II) as a calibrant (ꢁg = 16.44 × 10−6 c.g.s. units at 20 ◦C).
Diamagnetic corrections were made using Pascal’s constant. A
simultaneous TG/DTG and DTA had been obtained by a model
5000/2960 SDT, TA Instruments, U.S.A. The experiments were per-
formed in N2 atmosphere at a heating rate of 10 ◦C min−1 in
the temperature range 50–800 ◦C, using Al2O3 crucible. The sam-
ple sizes are ranged in mass from 4.5 to 10 mg. The DSC was
recorded using DSC 2920, TA Instrument, U.S.A. The DSC curves
were obtained at a heating rate of 10 ◦C min−1 in N2 atmosphere
over the temperature range of 50–400 ◦C, using aluminum cru-
cible.
2.4. Synthesis of (4Z,4ꢀZ)-4,4ꢀ-(2,2ꢀ-(4,4ꢀ-methylenebis(4,1-
phenylene)bis(azanediyl))bis(1-hydroxy ethan-2-yl-1-ylidene))-
bis(3-methyl-1-phenyl-1H-pyrazol-5(4H)-one) (H2SB)
The performed ligand 4-(2-chloro-1-hydroxyethylidene)-3-
methyl-1-phenyl-1H-pyrazol-(4H)-one (10 mmol, 2.50 g) was dis-
solved in 50 mL of rectified spirit. To this solution, a solution of
4,4ꢀ-methylenedianiline (5 mmol, 0.99 g) in rectified spirit (25 mL)
was added dropwise with constant stirring. Then a solution of
anhydrous K2CO3 (10 mmol, 1.38 g) in rectified spirit (25 mL) was
added in it. The resulting mixture was then refluxed for 5–7 h. The
reaction mixture was then poured into crushed ice with constant
stirring when a light brown precipitate was obtained. It was filtered,
washed several times with water and dried in vacuo. Yield 67%. Ele-
mental analysis found (%) C, 70.96; H, 5.48; N, 13.52; calculated for
C
37H34N6O4: C, 70.91%; H, 5.47%; N, 13.41%. FT-IR (KBr, cm−1): 3390

C.K. Modi / Spectrochimica Acta Part A 71 (2009) 1741–1748
1743
Table 1
Analytical and physical data of the ligand H2SB and its coordination polymersa
Empirical formula of monomer unit
Formula weight Color (yield %)
mp (◦C) Found (calculated) (%)
ꢂeff (B.M.)
C
H
N
M
H2SB, C37H34N6O4
626.70
Yellowish brown (74)
171b
>300
>300
>300
>300
>300
>300
70.96 (70.91)
60.67 (60.57)
58.83 (58.81)
58.85 (58.83)
59.92 (59.87)
59.81 (59.72)
61.12 (61.07)
5.48 (5.47)
5.24 (5.22)
5.35 (5.34)
5.32 (5.34)
5.18 (5.16)
5.17 (5.15)
5.02 (4.99)
13.45 (13.41)
11.53 (11.45)
11.29 (11.12)
11.18 (11.12)
11.30 (11.32)
11.33 (11.29)
11.59 (11.55)
–
–
6.01
4.06
2.91
1.79
Diamagnetic
1.81
[Mn(SB)(H2O)2]n·H2O, C37H38MnN6O7 734.68
Dark brown (68)
Dark brown (64)
Dark green (72)
Dark brown (70)
Brown (65)
7.54 (7.49)
7.91 (7.80)
7.81 (7.77)
8.63 (8.56)
8.84 (8.79)
7.07 (7.00)
[Co(SB)(H2O)2]n·2H2O, C37H40CoN6O8
[Ni(SB)(H2O)2]n·2H2O, C37H40N6NiO8
[Cu(SB)(H2O)2]n·H2O, C37H38CuN6O7
756.69
756.45
743.29
745.15
728.67
[Zn(SB)(H2O)2]n·H2O, C37
H38N6O7Zn
[VO(SB)(H2O)]n·H2O, C37H36N6O7V
Brown (66)
a
H2SB = (4Z,4ꢀZ)-4,4ꢀ-(2,2ꢀ-(4,4ꢀ-methylenebis(4,1-phenylene)bis(azanediyl))bis(1-hydroxy ethan-2-yl-1-ylidene))bis(3-methyl-1-phenyl-1H-pyrazol-5(4H)-one).
Decomposed.
b
␯(O H) of hydroxy ethylidene group, 3145 ␯(N H), 2820 ␯( CH3),
where M = Mn(II), Cu(II) and Zn(II), x = 1; Co(II) and Ni(II), x = 2.
VOSO4·5H2O + H2SB → [VO(SB)(H2O)]n·H2O + H2SO4 + 3H2O
1630 ␯(C O) of pyrazol-5-one, 1590 ␯(C N) of pyrazolone-ring
[30]. 1H NMR (400 MHz, DMSO-d6): ı (ppm) = 2.46 (6H, s, 2CH3);
3.39 (2H, m, CH2); 4.10 (4H, s, 2CH2); 6.54 (2H, s, 2NH); 7.15–7.99
(18H, m, 4Ph-ring); 12.83 (2H, s, 2O H· · ·O hydrogen bonds). 13C
NMR (400 MHz, DMSO-d6): ı (ppm) = 16.40 (C8), 39.8 (C24), 61.40
(C2), 99.42 (C4), 112.8 (C21 and 23), 118.68 (C19), 124.77 (C13 and
15), 125.97 (C17), 129.31 (C12 and 16), 130.58 (C18 and 20), 139
(C14), 143.20 (C22), 146.87 (C5), 159.99 (C3), 167.12 (C1).
All the coordination polymers are insoluble in all common
organic solvents. It was not possible to characterize them by con-
ventional methods, like osmometry, viscometry, conductometry,
etc., as they are insoluble. The nature of the ligand, high thermal
stability, metal–ligand ratio (1:1) and insolubility in all common
organic solvents suggest their polymeric nature.
2.5. Synthesis of coordination polymers
3.1. IR spectra
The performed ligand H2SB (5 mmol, 3.13 g) was dissolved
in 10 mL of DMF. To this solution, the methanolic solution of
25 mL metal nitrate (5 mmol) or an aqueous solution (25 mL) of
VOSO4·5H2O (5 mmol, 1.45 g) was added slowly with constant stir-
ring over the period of 30 min in 1:1 molar ratio. The pH of the
solution was adjusted 5–6 with the drop wise addition of methano-
lic solution of sodium acetate in it. The resulting mixture was
heated with stirring at reflux temperature for 4–5 h. The obtained
coordination polymers were filtered off, washed with hot water,
hot methanol and diethyl ether and finally dried in a vacuum
desiccator over anhydrous CaCl2. The coordination polymers are
insoluble in all common organic solvents like methanol, ethanol,
chloroform, acetone, benzene, dimethyl formamide and dimethyl
sulfoxide.
The important infrared spectral bands and their tentative
assignments for the synthesized ligand H2SB and its coordination
polymers were recorded as KBr disks and are discussed.
The molecular structure of the ligand H2SB is such that they can
exist in six tautomeric forms as shown in Fig. 1. Detailed solution
and solid-state studies of this ligand were carried out to estab-
lish their geometry. The IR spectrum of this ligand exhibits two
characteristic bands at 3390 and 1630 cm−1, which can either be
assigned to ␯(O H) of the pyrazolone group and ␯(C O) of the
lateral chain, respectively for the tautomeric form (Fig. 1A) or
␯(O H) and ␯(C O), respectively for the tautomeric form (Fig. 1D)
of the ligand. We assigned these two peaks to ␯(O H) and ␯(C O),
respectively for the later form based on the information obtained
from 1H and 13C NMR studies in solution state (discussed later).
The observed low frequency of ␯(O H) with respect to the free
hydroxyl group is believed to be due to intramolecular H-bonding
between H of OH of hydroxyethylidene group of the lateral chain
and oxygen of pyrazolone-ring as illustrated in Fig. 1Dꢀ. All of
these data suggest that hydrogen bond exists in the free ligand
H2SB.
3. Results and discussion
The analytical and physical properties of the ligand H2SB and its
coordination polymers are listed in Table 1. The following reaction
describes the formation of the coordination polymers:
In the investigated coordination polymers, the bands observed
in the region 3400–3450, 1295–1300, 860–870 and 715–717 cm−1
are attributed to OH stretching, bending, rocking and wagging
M(NO3)2·nH2O + H2SB → [M(SB)(H2O)2]n·xH2O
+ 2HNO3 + (n − x)H2O
Fig. 1. Possible tautomers of the ligand H2SB (3).

1744
C.K. Modi / Spectrochimica Acta Part A 71 (2009) 1741–1748
vibrations, respectively due to the presence of water molecules [31].
The presence of rocking band indicates the coordination nature of
the water molecule [32]. The ␯(N H) band at 3145 cm−1 of the free
ligand (H2SB) is unaffected in the spectra of polymers that indicate
non-involvement of this group. The infrared spectra of all the coor-
dination polymers show a considerable negative shift 10–15 cm−1
in ␯(C O) absorption of the pyrazolone group, indicating a decrease
in the stretching force constant of C O as a consequence of coor-
dination through the oxygen atom of the ligand. Meanwhile, the
new absorption bands attributed to ␯(C O−) [33] are observed
at 1323–1326 cm−1. From these observations, it is concluded that
the ligand reacts in enol form with prototropy, which incorpo-
rates into proton transfer through oxygen atom of the lateral
chain forming covalent bond with the metal ion. The oxovana-
dium(IV) coordination polymer exhibits a strong absorption band
near ∼958 cm−1, which has been assigned to ␯(V O) band [24]. In
the far-IR region, two new bands at 480–495 and 420–435 cm−1
in the coordination polymers are assigned to ␯(M O)pyrazolone and
␯(M O)lateral chain, respectively. It is thus believed that the oxygens
of the pyrazolone-ring and hydroxyethylidene group of the lateral
chain are coordinated to metal ions.
is known that proton transfer between pyrazole C4 and OH is usu-
ally slow [35,43]. Consequently, in DMSO-d6 solution, the ligand
(H2SB) (3) exist mainly as hydroxyethylidene form (Fig. 1Dꢀ) with
intramolecular hydrogen bond, in agreement with other reports
[35,36,44,45].
3.3. Magnetic moments and electronic spectra
The information regarding geometry of the coordination poly-
mers were obtained from their electronic spectral data and
magnetic moment values. The reflectance spectrum of the Mn(II)
coordination polymer shows absorption bands at ∼15,050, ∼19,970
and ∼24,800 cm−1 assignable to A1g → T1g (ꢃ1), A1g → T2g
6
4
6
4
6
4
(ꢃ2) and A1g → A1g
,
4Eg (ꢃ3) transitions, respectively, in an
octahedral environment around the Mn(II) ion [46]. The mag-
netic moment value of the Mn(II) coordination polymer was 6.01
B.M. due to a high-spin d5-system with an octahedral geometry
[47]. The observed magnetic moments 4.06 and 2.91 B.M., for the
Co(II) and Ni(II) coordination polymers, respectively, are within
the range for an octahedral geometry [48,49]. The reflectance
spectrum of Co(II) coordination polymer shows medium inten-
sity bands at ∼9,300, ∼18,300 and ∼19,050 cm−1, which may
3.2. Tautomerism studies of H2SB (3)
4
4
4
4
be assigned to T1g(F) → T2g(F) (ꢃ1), T1g(F) → A2g(F) (ꢃ2) and
4T1g(F) → T1g(P) (ꢃ3) transitions, respectively, of an octahedral
4
Specifically the tautomerism of 1-aryl-4-acyl-pyrazolones has
been the subject of various studies [34–40]. Based upon 1H and
13C NMR studies, Kurkovskaya et al. [35] concluded that in CDCl3
solution, and at low temperature, 4-acetyl- and 4-benzoyl deriva-
tives are mainly present in the associated OH form (Aꢀ) (Fig. 1)
with a minor portion of NH form (B). In the case of the ligand
H2SB (3), the possible tautomers are shown in Fig. 1. Relevant
1H and 13C NMR data of the compound 3 are given in Section
2. Data agree with the existence of enol form. 1H NMR chemical
shift for the OH group was observed at ı 12.83 ppm. This signal
disappeared when a D2O exchange experiment was carried out. It
can be assigned either to OH of pyrazolone-ring or OH of hydrox-
yethylidene group of the lateral chain, in either case it is strongly
deshielded because of hydrogen bonding with the other oxygen
atom. It may be noted that the integration of this signal perfectly
matches with one proton and there is no other fragment(s) of
this signal, which suggests that only one tautomeric form of the
ligand exists in solution under the experimental conditions. Any
temperature-dependent experiments have not been carried out.
Comparing with the solid-state study, we prefer to assign this sig-
nal to OH of the lateral chain; however, assignment of this peak to
OH of the pyrazolone-ring cannot be ruled out provided solid-state
structural evidence is not considered [41]. On the basis of 13C sig-
nal for the carbonyl carbon of the pyrazolone-ring is observed at
166 ppm [42] clearly correspond to a ketone form (Fig. 1Dꢀ). These
values are very close to those already reported by other authors
[35]; showing that the pyrazole-5-ol form (Fig. 1A and Aꢀ) can
be excluded. The presence of ethanone form of the lateral chain
(Fig. 1C) is not likely because this form requires an additional signal
set (approximately at 195.0–204.5 ppm) [37] in 13C NMR spectra,
clearly correspond to a ketone form of the lateral chain, which was
not observed. The presence of a CH form (C) is not likely because it
geometry. The reflectance spectrum of the Ni(II) coordination poly-
mer exhibit three bands at ∼10,300, ∼17,650 and ∼24,000 cm−1
3
3
3
3
assignable to A2g(F) → T2g(F) (ꢃ1), A2g(F) → T1g(F) (ꢃ2) and
3A2g(F) → T1g(P) (ꢃ3) transitions, respectively, in an octahedral
3
geometry. The reflectance spectrum of Cu(II) coordination poly-
mer displays a broad band at ∼15,450 cm−1 due to the 2Eg → T2g
2
transition and the observed magnetic moment is 1.79 B.M., which
is close to spin-only value (1.73 B.M.) expected for an unpaired
electron offering the possibility of an octahedral geometry [50].
The reflectance spectrum of oxovanadium(IV) coordination poly-
mer exhibits three spin-allowed transitions at ∼13,350, ∼15,980
and ∼23,850 cm−1, which have been assigned to 2B2 → E (ꢃ1),
2
2B2 → B1 (ꢃ2) and 2B2 → A1 (ꢃ3) transitions, respectively [24].
The oxovanadium(IV) coordination polymer exhibits magnetic
moment corresponding to the spin-only value of 1.80 B.M. The
Zn(II) coordination polymer is diamagnetic as expected for d10
system. The values of the electronic parameters, such as the
ligand field splitting energy (10 Dq), Racah interelectronic repul-
sion parameter (B), nephelauxetic ratio (ˇ) and ratio ꢃ2/ꢃ1 for
the Co(II) and Ni(II) coordination polymers have been calcu-
lated using the secular equations given by König [51] and are
summarized in Table 2. The ˇ values indicate that the coordi-
nation polymers have appreciable covalent character [52]. The
suggested structure of the coordination polymers are shown in
Fig. 2.
2
2
3.4. Thermal studies
The thermodynamic activation parameters of the decompo-
sition process of the coordination polymers such as energy of
activation (Ea) and order of reaction (n) were evaluated graphically
Table 2
Electronic parameters of the Co(II) and Ni(II) coordination polymers
Coordination polymers
Observed bands (cm−1
)
ꢃ2/ꢃ1
B
ˇ
ˇ0
10 Dq
ꢃ1
ꢃ2
ꢃ3
[Co(SB)(H2O)2]n·2H2O
[Ni(SB)(H2O)2]n·2H2O
9, 300
10, 500
18,180
17,500
18,940
24,600
1.95
1.67
717
707
0.73
0.69
26.0
31.4
10,419
10,500

C.K. Modi / Spectrochimica Acta Part A 71 (2009) 1741–1748
1745
Fig. 2. Suggested structure of the coordination polymers.
by employing the Freeman–Carroll method [53] using the following
relation:
where T is the temperature in K, R is gas constant, wr = wc − w; wc
is the weight loss at the completion of the reaction and w is the total
mass loss up to time t. Ea and n are the energy of activation and order
of reaction, respectively. A typical curve of [ꢀlog(dw/dt)/ꢀ log wr]
vs. [ꢀ(1/T)/ꢀlog wr] for the Co(II) coordination polymer is shown
in Fig. 3. The slope of the plot gave the value of Ea/2.303R and the
order of reaction (n) was determined from the intercept.
[(−Ea/2.303R)ꢀ(1/T)]
ꢀ log wr
ꢀ log(dw/dt)
ꢀ log wr
= −n +
(1)
3.4.1. The thermal behavior of the prepared coordination
polymers
Thermal data and kinetic parameters of the coordination
polymers are given in Tables 3 and 4, respectively. The typi-
cal TG/DTG, DTA and DSC curves of the coordination polymer
[M(SB)(H2O)y]n·xH2O (where M = Co(II), y = 2, x = 2) are represented
in Fig. 4. The thermal fragmentation scheme for Mn(II), Ni(II) and
VO(IV) coordination polymers is shown below:
◦
50−130 C
[M(SB)(H2O)y]n · xH2O −→ [M(SB)(H2O)y]n + xH2O
dehydration
where M = Mn(II), VO(IV), x = 1 and Ni(II), x = 2.
◦
[M(SB)(H2O)y]nremoval of coordinated water molecules
130−−→280 C
[M(SB)]n + yH2O
Fig. 3. Freeman–Carroll plot for thermal dehydration of [Co(SB)(H2O)2]n·2H2O.

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C.K. Modi / Spectrochimica Acta Part A 71 (2009) 1741–1748
Table 3
Thermo analytical data of the coordination polymers
Heterochelates
TG range (◦C)
DTGmax (◦C)
DTAmax (◦C)
DSCmax (◦C)
Mass loss (%) obs. (calc.)
Assignment
50–130
130–260
63.50
–
62.17 (+)
–
122.91 (+)
187.68 (+)
215 (+)
2.28 (2.45)
4.85 (4.90)
Loss of one lattice water molecule
Loss of two coordinated water molecules
[Mn(SB)(H2O)2]n·H2O
260–780
427.89
378.30 (−)
253.25 (+)
360.15 (+)
81.94 (81.80)
89.07a (89.15)
Removal of (SB) ligand molecule
Leaving Mn2O3 residue
50–260
67.94
75.11 (+)
156.47 (+)
–
9.36 (9.51)
Loss of two lattice + two coordinated
water molecules
Removal of (SB) ligand molecule
Leaving CoO residue
[Co(SB)(H2O)2]n·2H2O
[Ni(SB)(H2O)2]n·2H2O
[Cu(SB)(H2O)2]n·H2O
[Zn(SB)(H2O)2]n·H2O
[VO(SB)(H2O)]n·H2O
260–760
431.78
459.77 (−)
80.62 (80.57)
89.98a (90.08)
50–130
130–280
280–760
68.72
–
471.52
73.66 (+)
–
439.39 (−)
–
4.88 (4.76)
4.61 (4.76)
Loss of two lattice water molecules
Loss of two coordinated water molecules
Removal of (SB) ligand molecule
Leaving free Ni residue
160.14 (+)
–
82.69 (82.58)
92.18a (92.10)
50–240
60.66
66.15 (+)
161.33 (+)
7.17 (7.26)
Loss of one lattice + two coordinated
water molecules
Removal of (SB) ligand molecule
Leaving CuO residue
240–720
495.73
407.68 (−)
274.15 (+)
358.97 (+)
82.09 (82.03)
89.26a (89.29)
50–230
62.94
64.61 (+)
149.06 (+)
–
7.15 (7.24)
Loss of one lattice + two coordinated
water molecules
Removal of (SB) ligand molecule
Leaving free Zn residue
230–740
521.91
503.75 (−)
83.86 (83.83)
91.01a (91.10)
50–130
130–250
250–700
60.51
–
448.61
65.28 (+)
–
433.18 (−)
132.58 (+)
207.88 (+)
342.91 (+)
2.51 (2.47)
2.50 (2.47)
Loss of one lattice water molecule
Loss of one coordinated water molecule
Removal of (SB) ligand molecule
Leaving V2O5 residue
82.31 (82.44)
87.32a (87.38)
(+) Endothermic and (−) exothermic.
a
Total mass loss.
The anhydrous coordination polymers show great thermal sta-
bility up to 260 ◦C; and in the second subsequent stage for Co, Cu
and Zn coordination polymers whereas in the third subsequent
stage for Mn, Ni and VO coordination polymers, the decomposi-
tion and combustion of ligand (H2SB) occurs. The removal of ligand
(H2SB) undergoes decomposition forming free metal ion for Ni and
Zn [24,54] or metal oxides for Mn, Co, Cu and V as the final residue.
where M = Mn(II), Ni(II), y = 2 and VO(IV), y = 1.
◦
280−780 C
[M(SB)]nremoval of H SB ligand molecule
−→
metal residue∗
2
where metal residue* = Mn2O3, V2O5 or free Ni residue.
Whereas for Co(II), Cu(II) and Zn(II) coordination polymers, the
thermal fragmentation scheme is shown below:
◦
50−260 C
[M(SB)(H2O)y]n · xH2O
−→
[M(SB)]n + yH2O + xH2O
removal of lattice water molecules+coordinated water molecules
where M = Cu(II), Zn(II), y = 2, x = 1 and Co(II), y = 2, x = 2.
The thermodynamic activation parameters of the decom-
position process of dehydrated complexes such as activation
entropy (ꢀS#), pre-exponential factor (A), activation enthalpy
(ꢀH#) and free energy of activation (ꢀG#), were calculated using
the reported equations [55,56]. According to the kinetic data
◦
260−760 C
[M(SB)]nremoval of H SB ligand molecule
−→
metal residue∗
2
where metal residue* = CoO, CuO or f ree Zn residue.
Table 4
Kinetic parameters of the coordination polymers
Compounds
TG range (◦C)
Ea (kJ mol−1
)
n
A (s−1
)
ꢀS# (J K−1 mol−1
)
ꢀH# (kJ mol−1
)
ꢀG# (kJ mol−1
)
50–130
130–260
260–780
3.52
5.19
45.35
0.00
1.50
1.00
0.13
0.11
−102.25
−101.98
−95.67
0.73
1.36
39.52
35.13
48.34
106.58
[Mn(SB)(H2O)2]n·H2O
0.26 × 103
50–260
260–760
3.80
81.40
0.00
1.00
0.15
−102.00
−93.60
0.96
75.50
35.80
141.00
[Co(SB)(H2O)2]n·2H2O
[Ni(SB)(H2O)2]n·2H2O
0.21 × 106
50–130
130–280
280–760
3.81
4.90
101.02
0.00
1.49
1.00
0.15
0.12
−102.02
−101.98
−93.00
0.97
1.28
94.83
35.83
45.46
164.07
0.26 × 106
50–240
240–720
3.36
69.88
0.00
1.00
0.12
−102.38
−94.45
0.59
63.49
34.75
136.09
[Cu(SB)(H2O)2]n·H2O
[Zn(SB)(H2O)2]n·H2O
[VO(SB)(H2O)]n·H2O
0.79 × 104
50–230
230–740
3.51
44.10
0.00
1.00
0.13
−102.00
−96.10
0.72
37.60
35.10
114.00
0.81 × 102
50–130
130–250
250–700
3.39
4.66
61.20
0.00
1.50
1.00
0.12
−102.00
−103.00
−94.60
0.61
0.65
55.30
34.80
50.00
122.00
0.07
0.49 × 104

C.K. Modi / Spectrochimica Acta Part A 71 (2009) 1741–1748
1747
Fig. 4. TGA/DTG, DTA and DSC curves of [Co(SB)(H2O)2]n·2H2O.
obtained from DTG curves, all the coordination polymers have
negative entropy, which indicates that the studied coordination
polymers have more ordered systems than reactants [57]. The
kinetic parameters, especially energy of activation (Ea) is help-
ful in assigning the strength of the coordination polymers. The
calculated Ea values of the investigated coordination polymers
for the first dehydration step are in the range 3.36–3.81 kJ mol−1
(Table 4). Based on the activation energy values the thermal
stabilities of the coordination polymers in the decreasing order is:
Ni(II) > Co(II) > Mn(II) > Zn(II) > Cu(II) > VO(IV).
It is evident that the thermal stabilities of the coordination
polymers increase as the ionic radii decrease. The thermal sta-
bilities of the Ni(II), Mn(II) and VO(IV) coordination polymers
in the solid-state follow the general trend found by Irving and
Williams [58] for the stabilities of complexes in solution. The Co(II),
Cu(II) and Zn(II) coordination polymers deviate from this general
behavior. Since the Irving–Williams series reflects electrostatic
effects, this observation indicates that the water–metal interaction
in these coordination polymers is almost of ion-dipole type.
Head, Department of Chemistry, Sardar Patel University, Vallabh
Vidyanagar, India, for providing the necessary laboratory facilities.
Analytical facilities provided by the SAIF, Central Drug Research
Institute, Lucknow, India and the Sophisticated Instrumentation
Centre for Applied Research & Testing (SICART), Vallabh Vidyanagar,
Gujarat, India is gratefully acknowledged.
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