Spectral, magnetic and thermal investigations of some d-electron element 3-methoxy-4-methylbenzoates

Article abstract of DOI:10.1007/s10973-005-6855-9

Conditions for the preparation of Mn(II), Co(II), Ni(II), Cu(II), Zn(II) and Cd(II) 3-methoxy-4-methylbenzoates were investigated and their quantitative composition and magnetic moments were determined. The IR spectra and powder diffraction patterns of th

Full text of DOI:10.1007/s10973-005-6855-9

Journal of Thermal Analysis and Calorimetry, Vol. 84 (2006) 2, 385–389
SPECTRAL, MAGNETIC AND THERMAL INVESTIGATIONS OF SOME
d-ELECTRON ELEMENT 3-METHOXY-4-METHYLBENZOATES
*
Wanda Brzyska and W. Oüga
Department of General Chemistry, Faculty of Chemistry, Marie Curie SkÓodowska University, 20-031 Lublin, Poland
Conditions for the preparation of Mn(II), Co(II), Ni(II), Cu(II), Zn(II) and Cd(II) 3-methoxy-4-methylbenzoates were investigated
and their quantitative composition and magnetic moments were determined. The IR spectra and powder diffraction patterns of the
9 9 3 2 2
complexes prepared of general formula M(C H O ) ×nH O (n=2 for Mn, Co n=1 for Ni, Cu, n=0 for Zn, Cd) were prepared and their
–2
–4
–3
thermal decomposition in air was studied. Their solubility in water at 293 K is of the order 10 (Mn)–10 (Cu) mol dm . IR spectra
of the prepared 3-methoxy-4-methylbenzoates suggest that carboxylate groups are bidentate bridging. The magnetic moments for
the paramagnetic complexes of Mn(II), Co(II), Ni(II) and Cu(II) attain values 5.50, 4.45, 3.16 and 1.79 B. M., respectively. During
heating the hydrated complexes lose crystallization water molecules in one step and then the anhydrous complexes decompose di-
3 4 3 4
rectly to oxides MO and Mn O . Only Co(II) complex decomposes to Co O with intermediate formation CoO.
Keywords: complexes, d-electron elements, IR spectra, magnetic moments, 3-methoxy-4-methylbenzoic acid, thermal decomposition
Introduction
stoichiometric quantities of 0.2 M solution of ammo-
nium 3-methoxy-4-methylbenzoate (pH 5.5) and 0.2 M
solution of metal(II) chloride. The precipitate was
formed during heating in mother solution. Then it was
3-Methoxy-4-methylbenzoic acid C H (OCH )(CH )
6 3 3 3
COOH, is a crystalline solid, sparingly soluble in water
1]. Its compounds with metal ions are not well-known.
[
heating yet 0.5 h at 343–353 K, was filtered off, washed
+
with hot water to remove NH ions and dried at 303 K
The complexes of rare earth elements [2] have been
prepared as crystalline solid with molar ratio of metal
to organic ligand of 1:3 and general formula
4
to a constant mass. The sodium salt was obtained by
adding 3-methoxy-4-methylbenzoic acid to solution of
NaOH and crystallizing at room temperature.
Ln(C H O ) ×nH O (where n=2 for Y, La–Er and n=0
9 9 3 3 2
for Tm–Lu) sparingly soluble in water. During heating
dihydrated complexes lose crystallization water mole-
cules in one (Y, La, Pr–Er) or two steps (Ce) and then
all the anhydrous complexes decompose directly to ox-
The carbon and hydrogen in the prepared com-
plexes were determined by elemental analysis on a
Perkin-Elmer CHN 2400 analyser. The metal(II) ion
content was determined by AAS method using atomic
absorption spectrophotometer AAS-3 (Carl Zeiss, Jena).
The content of crystallization water molecules was de-
termined from TG curves and by heating the samples
isothermally at defined temperature to a constant mass.
IR spectra of the complexes prepared and spectra of
3-methoxy-4-methylbenzoic acid and its sodium salt
were recorded as KBr discs on FTIR 1725 PerkinElmer
spectrophotometer (range 4000–400 cm ). The solubil-
ities of the prepared complexes in water were deter-
mined at 293 K, preparing saturated solutions in isother-
mal conditions. The concentration of Mn(II), Co(II),
Ni(II), Cu(II), Zn(II) and Cd(II) ions in saturated solu-
tions were determined by AAS method. X-ray diffracto-
grams of the prepared complexes and the products of
their decomposition were recorded using diffractometer
HZG-412. The magnetic susceptibility of the prepared
complexes were measured on a magnetic balance
(Scherwood Scientific MSB MK I) using as a standard
ides Ln O3, CeO , Pr O11 and Tb O . IR spectra of the
2 2 6 4 7
rare earth 3-methoxy-4-methylbenzoates suggest that
carboxylate groups are bidentate chelating.
In the last years there were published some papers
on thermal decomposition of metal carboxylates [3–8].
This work is a continuation of our study on the
physico-chemical properties and thermal decomposition
–1
[9–15] of metal complexes with benzenecarboxylic ac-
ids. Its aim was to prepare solid Mn(II), Co(II), Ni(II),
Cu(II), Zn(II) and Cd(II) 3-methoxy-4-methylbenzoates
and examine some of their physico-chemical properties
and thermal decomposition during heating in static air.
Experimental
3-Methoxy-4-methylbenzoates of Mn(II), Co(II), Ni(II),
Cu(II), Zn(II) and Cd(II) were prepared by reaction of
*
Author for correspondence: BRZYSKA@hermes.umcs.lublin.pl
1
388–6150/$20.00
Akadémiai Kiadó, Budapest, Hungary
Springer, Dordrecht, The Netherlands
©
2006 Akadémiai Kiadó, Budapest

BRZYSKA, O¨GA
–
1
Co[Hg(SCN) ]. The thermal stability of the prepared
4
plexes the absorption band C=O group at 1684 cm
disappears and the bands of asymmetrical (n ) and
complexes was investigated by method TG, DTG and
as
–
symmetrical (n ) vibration of OCO group appear at
DTA. Measurements were made with Q-1500 derivato-
graph by method described earlier [2]. The samples
were heating in air to 1273 K.
s
–1
1560–1540 and 1425–1410 cm , respectively, the
bands of OCH with max. at 1388–1384, 1288–1280,
3
–
1
1
2
250–1248 cm the bands of CH group at 2920 and
3
–1
833–2830, 1408–1404, 1320–1316 cm and bands of
–1
Results and discussion
M–O bond at 580–550 cm . In the IR spectra of the
prepared complexes there are bands of aromatic ring
1610–1607, 1463–1460, 1172–1168, 1112–1106 and
1040 cm , and the CH bands at 878–875, 818–812,
778–775 and 650–640 cm [9–12]. These bands are
shifted insignificantly (10–4 cm ) or do not change
their position compared to the respective bond of
3-methoxy-4-methylbenzoic acid, what indicates that
metal(II) ions have only a weak influence on the ben-
zene ring. In the IR spectra of the prepared complexes
of Mn(II), Co(II), Ni(II) and Cu(II) there are broad ab-
sorption bands of n(OH) with max. at 3400 cm and
–1
narrow bands d(H O) at 1630–1620 cm , that are char-
acteristic for the hydrates. In the IR spectra of Zn(II)
and Cd(II) these bands are absent, what confirms anhy-
drous character of these complexes.
3-Methoxy-4-methylbenzoates of Mn(II), Co(II), Ni(II),
–1
Cu(II), Zn(II) and Cd(II) were prepared as solids with
molar ratio of metal to organic ligand of 1.0:2.0 and
general formula M(C H (OCH )(CH )COO) ×nH O,
–1
–1
6
3
3
3
2
2
where n=2 for Mn(II) and Co(II), n=1 for Ni(II) and
Cu(II) and n=0 for Zn(II) and Cd(II) (Table 1) having
colour characteristic for hydrated metal ions. The pre-
pared complexes are crystalline and have different
structures. They are characterized by different solubility
–2
–3
–1
in water. Their solubilities change from 10 mol dm
–3
–3
for Mn(II) complex, 10 mol dm for Co(II), Ni(II),
2
–4
–3
Zn(II) and Cd(II) to 10 mol dm for Cu(II) one
Table 1). Generally complexes of Cu(II) with different
(
carboxylic acids are more sparingly soluble in water
than the complexes of other 3d metal ions [14, 15].
The prepared 3-methoxy-4-methylbenzoates ex-
hibit similar to each other IR spectra (Table 2) in two
groups: Mn(II)–Cu(II) and Zn(II)–Cd(II) and have
many bands. When the acid is converted to the com-
The separation values n (OCO) and n (OCO) in
as
s
the spectra of the prepared 3-methyl-4-methoxy-
benzoates (125–130 cm ) are similar to that for the so-
dium salt (130 cm ), what shows on the similar degree
of ionic bond in the prepared complexes compared to
–1
–1
Table 1 Analytical data and solubilities in water at 293 K of 3-methoxy-4-methylbenzoates of Mn(II), Co(II), Ni(II), Cu(II),
Zn(II) and Cd(II)
M/%
calcd.
C/%
H/%
–
3
–3
Complex
Solubility/10 mol dm
found
calcd.
found
calcd.
found
MnL
2
×2H
×2H
×H
×H
2
O
13.05
13.86
14.43
15.44
16.53
25.40
13.00
14.00
14.40
15.40
16.50
51.31
50.83
53.11
52.48
54.63
48.82
51.30
51.00
53.00
52.55
54.69
49.00
5.27
5.17
4.92
4.86
4.55
4.06
5.30
5.00
4.90
4.90
4.51
4.00
14.50
10.50
10.50
0.65
CoL
2
2
O
NiL
2
2
O
CuL
2
2
O
ZnL
2
7.54
CdL
2
25.50
7.12
–
6 3 3 3
L*=[C H (CH )(CH )COO
Table 2 Frequencies of characteristic absorption bands in IR spectra and magnetic moment (B. M.) of
4
–
-methoxy-2-methylbenzoates of Mn(II), Co(II), Cu(II), Zn(II), Cd(II) and Na(I) (cm )
1
Complex
MnL *×2H
CoL ×2H
×H
×H
n(OH)
n
as(OCO)
n
s
(OCO)
n
as–n
s
n(M–O)
m
eff/B. M.
n
2
2
O
3400
3400
3400
3400
–
1550
1550
1550
1560
1550
1540
1516
1425
1425
1420
1410
1420
1410
1392
125
125
130
150
130
130
124
575
575
560
580
550
560
–
5.50
4.45
3.16
1.79
–
5
3
2
1
–
–
–
2
2
O
NiL
2
2
O
CuL
2
2
O
ZnL
CdL
NaL×xH
2
2
–
–
2
O
3400
–
–
6 3 3 3
L*=[C H (CH )(OCH )COO] ; n – number of unpaired electrons
386
J. Therm. Anal. Cal., 84, 2006

3
-METHOXY-4-METHYLBENZOATE COMPLEXES
Table 3 Data for dehydration and decomposition of 3-methoxy-4-methylbenzoates of Mn(II), Co(II), Ni(II), Cu(II), Zn(II) and Cd(II)
Mass loss/% Mass loss/%
Loss of
O mol
Complex
DT
1
/K
DT
2
/K
k
T /K
H
2
calcd.
found
calcd.
found
MnL
2
*×2H
×2H
×H
×H
2
O
318–390
320–398
328–423
353–397
9.00
8.47
4.42
4.37
9.5
8.5
4.4
4.4
2
2
1
1
497–999
420–958
428–823
489–895
473–968
452–893
80.17
79.37
80.78
79.78
79.42
70.97
80.2
79.2
80.2
80.1
79.5
71.0
999
958
823
895
968
893
CoL
2
2
O
NiL
2
2
O
CuL
2
2
O
ZnL
2
CdL
2
–
*
L=[C
6 3 3 3 1 2
H (CH )(OCH )COO] ; DT – temperature range of dehydration; DT – temperature range of decomposition;
T
k
– temperature over which the oxides exist
the sodium salt [16–18]. Only for Cu(II) complex
netic moment determined for Cu(II) complex
(1.79 B. M.) is similar to the theoretical (1.73 B. M.) and
experimental values (1.7–2.2 B. M.) with configuration
–1
value of n –n (150 cm ) is a little bigger than for the
as
s
sodium salt. The bands of asymmetric and symmetric
vibrations of OCO groups are shifted to higher fre-
9
d (one unpaired electron) [17, 18] and dimeric struc-
–1
–1
quencies (Dn =24–38 cm , Dn =18–33 cm ). From
ture. The magnetic measurements confirms that in the
hydrated 3-methoxy-4-methylbenzoates the water mole-
cules are in inner sphere. Taking into account the octa-
hedral structure of hydrated complexes it is possible to
suggest that in dihydrated complexes water molecules
act as monodentate ligand.
3-Methoxy-4-methylbenzoates of Mn(II), Co(II),
Ni(II), Cu(II), Zn(II) and Cd(II) are stable at room tem-
perature. During heating they decompose in different
ways (Table 3, Figs 1–3). Hydrated complexes are sta-
ble up to 318–328 K (Mn, Co, Ni) and 353 K (Cu). Di-
hydrated and monohydrated complexes lose crystalliza-
tion water molecules in one step over the range
318–423 K forming anhydrous compounds. The dehy-
as
s
the shifts of n (OCO) and n (OCO) and values of
as
s
(n –n ) in the IR spectra of the prepared complexes
as s
compared to the bands for the sodium salt, it is possible
to suggest that OCO groups are bonded as bidentate
bridging [16–20] and the complexes exist as dimers or
polymers. In the hydrated complexes there are proba-
bly inner sphere water molecules.
The susceptibilities of paramagnetic Mn(II),
Co(II), Ni(II) and Cu(II) complexes calculated from re-
sults of magnetic measurements at 293 K were corrected
by measuring the diamagnetic susceptibility of ligand.
The magnetic moments were calculated by using for-
1/2
mula meff=2.84(X T) . The complexes of Zn(II) and
M
Cd(II) are diamagnetic. The magnetic moments deter-
mined for the complexes of Mn(II), Co(II), Ni(II) and
Cu(II) are equal to 5.50, 4.45, 3.16 and 1.79 B. M., re-
spectively (Table 2).The magnetic moment determined
for Mn(II) 3-methoxy-4-methylbenzoate (5.5 B. M.) has
lower value than theoretical one (5.91 B. M.) calculated
5
for configuration d . The experimental values measured
at room temperature for high spin octahedral structure of
Mn(II) complexes are of the range 5.6–6.1 B. M. [17].
The small value of magnetic moment confirms dimeric
or polymeric structure of this complex and permit to
suggest that reduction of its value is caused by antiferric
action Mn–Mn. For Co(II) and Ni(II) complexes the
measured magnetic moments (4.45 and 3.16 B. M., re-
spectively), differ to some extent from spin-only mo-
7
8
ments for d and d configurations (3 and 2 unpaired
electrons) equal 3.87 and 2.83 B. M. Literature data
[20, 21] show that measured magnetic moments for high
spin Co(II) complex with octahedral structure attains
values 4.3–5.28 B. M. and for octahedral structure of
Ni(II) 2.8–3.5 B. M. This very high value of magnetic
moment for Co(II) complex can be caused by coupling
spin–orbital, which exist for elements of the first row of
9 9 3 2 2
Fig. 1 TG, DTG and DTA curves of Co(C H O ) ×2H O
4
9
transition elements with configuration d –d . The mag-
J. Therm. Anal. Cal., 84, 2006
387

BRZYSKA, O¨GA
The results obtained indicate that the prepared
-methoxy-4-methylbenzoates decompose in the fol-
lowing way:
3
MnL
CoL ×2H O®CoL ®CoO®Co O
4
2 2 2 3 4
×2H O®MnL ®Mn O
2
2
2
3
ML ×H O®ML®MO, M=Ni, Cu
2
2
ML ®MO, M=Zn, Cd.
2
Conclusions
3
-Methoxy-4-methylbenzoates of Mn(II), Co(II),
Ni(II), Cu(II), Zn(II) and Cd(II) were prepared as sol-
ids with molar ratio of metal to organic ligand of
1
.0:2.0. The complexes of Mn(II) and Co(II) were
prepared as dihydrates, these of Ni(II) and Cu(II) as
monohydrates, whereas the complexes of Zn(II) and
Cd(II) as anhydrous ones. These complexes are
characterized by different solubility in water. Their
solubility in water at 293 K changes from
9 9 3
Fig. 2 TG, DTG and DTA curves of Zn(C H O )
–
2
–3
–4
–3
1
0
mol dm for Mn(II) complex to 10 mol dm
for Cu(II) one. During heating hydrated complexes
lose crystallization water molecules in one step and
then the anhydrous complexes decompose directly to
oxides MO and Mn O , whereas Co(II) complex de-
3
4
composes to Co O with intermediate formation CoO.
3
4
The temperature of dehydration changes from 318 K
for Mn(II) to 353 K for Cu(II) one. The temperature
over which exist oxides changes from 823 K for
Ni(II) complex to 999 K for Mn(II) one. The
carboxylate groups in the studied complexes act prob-
ably as bidentate bridging and water molecules are in
inner sphere of the complexes, and the complexes ex-
ist as dimers or polymers. The magnetic moments for
paramagnetic complexes of Mn(II), Co(II), Ni(II) and
Cu(II) attain values 5.50, 4.45, 3.16 and 1.79 B. M.,
respectively.
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9 9 3
Fig. 3 TG, DTG and DTA curves of Cd(C H O )
1
2
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3
4
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-METHOXY-4-METHYLBENZOATE COMPLEXES
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6
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389