Spectral and thermal studies of Mn(II), Co(II), Ni(II), Cu(II), Zn(II) and Cd(II) complexes with 3-methylglutaric ACH

Article abstract of DOI:10.1023/A:1010168825917

Mn(II), Co(II), Ni(II), Cu(II),-Zn(II) and Cd(II) 3-methylglutarates were prepared as solids with general formula KHsCHO, where n=0-8. Their solubilities in water at 293 K were determined (7.0-l(T2-4.2-lr3 mol dm^-3). The IR spectra were recorde

Full text of DOI:10.1023/A:1010168825917

Journal of Thermal Analysis and Calorimetry, Vol. 61 (2000) 135–142
SPECTRAL AND THERMAL STUDIES OF Mn(II),
Co(II), Ni(II), Cu(II), Zn(II) AND Cd(II) COMPLEXES
WITH 3-METHYLGLUTARIC ACID
W. Brzyska and W. O¿ga
Faculty of Chemistry, Marie Curie Sk‡odowska University, PL-20-030 Lublin, Poland
(Received August 3, 1999; in revised form March 7, 2000)
Abstract
Mn(II), Co(II), Ni(II), Cu(II), Zn(II) and Cd(II) 3-methylglutarates were prepared as solids with
general formula MC
6
H
8
–3
O
4
2
⋅nH O, where n=0–8. Their solubilities in water at 293 K were deter-
–
2
–3
mined (7.0⋅10 –4.2⋅10 mol dm ). The IR spectra were recorded and thermal decomposition in
air was investigated. The IR spectra suggest that the carboxylate groups are mono- or bidentate.
During heating the hydrated complexes lose some water molecules in one (Mn, Co, Ni, Cu) or two
steps (Cd) and then mono- (Cu) or dihydrates (Mn, Co, Ni) decompose to oxides directly (Mn, Cu,
Co) or with intermediate formation of free metals (Co, Ni). Anhydrous Zn(II) complex decom-
poses directly to the oxide ZnO.
Keywords: complexes, IR spectra, 3-methylglutaric acid, thermal analysis
Introduction
3-Methylglutaric acid C H (COOH) is a crystalline solid soluble in hot water, ethanol
and ether, and sparingly soluble in benzene and chloroform [1]. The complexes of Ag(I)
4 8 2
and Pb(II) were prepared as solids sparingly soluble in water and those of Na(I), NH (I)
and Ca(II) as soluble in water. The rare earth element 3-methylglutarates were prepared
4
as solids with general formula Ln (C H O ) ⋅nH O, soluble in water [2]. Their solubilities
2
6
8
4 3
2
–2
–3
are of the order 10 mol dm and change periodically in the lanthanide series. During
heating the hydrated complexes are dehydrated in one step and next the anhydrous ones
decompose directly to oxides Ln O , CeO , Pr O and Tb O . (Ce, Pr, Tb–Lu) or with in-
2
3
2
6
11
4
7
termediate formation Ln O CO (Y, La, Nd–Gd). In the studied complexes the
2
2
3
carboxylate groups are bidentate and the complexes are polymers.
The aim of our work was to prepare the complexes of Mn(II), Co(II), Ni(II),
Cu(II), Zn(II) and Cd(II) with 3-methylglutaric acid in solid state and to study their
properties and thermal decomposition in air.
1
418–2874/2000/ $ 5.00
2000 Akadémiai Kiadó, Budapest
Akadémiai Kiadó, Budapest
©
Kluwer Academic Publishers, Dordrecht

Table 1 Analytical data and solubilities in water of 3-methylglutarates of Mn(II), Co(II), Ni(II), Cu(II), Zn(II) and Cd(II)
Metal content/% C/% H/%
�
2
Solubility⋅⋅1 /
Complex
� 3
mol dm
calc.
found
19.03
23.10
23.00
26.10
31.25
28.07
calc.
24.91
28.02
28.03
29.57
34.38
17.98
found
25.02
28.70
28.75
30.05
34.23
18.20
calc.
6.23
5.45
5.45
4.92
3.82
5.99
found
6.02
5.57
5.50
5.02
3.82
5.83
Mn[C
Co[C
4
H
8
(COO)
(COO)
(COO)
(COO)
(COO)
(COO)
2
]•5H
]•3H
]•3H
2
O
19.01
22.93
22.87
26.09
31.22
28.07
4.58
3.50
1.91
0.42
7.00
4.19
4
H
8
2
2
O
Ni[C
4
H
8
2
2
O
Cu[C
4
H
8
2
]•2H
2
O
Zn[C
4
H
8
2
]
Cd[C
4
H
8
2 2
]•8H
O

&
BRZYSKA, OZGA: 3-METHYLGLUTARIC ACID
137
Experimental
The complexes of Mn(II), Co(II), Ni(II), Cu(II), Zn(II) and Cd(II) with 3-methyl-
glutaric acid were prepared by dissolving M(II) ion carboxylates in a hot solution of
0
.1 M solution of 3-methylglutaric acid and after filtration of an excess of carbonate
their crystallization at room temperature. The precipitates formed were filtered off,
washed with water and dried at 303 K to a constant mass. The content of metal ions in
the complexes was determined by AAS method on an atomic absorption spectro-
photometer AAS-3 (Carl-Zeiss, Jena). The carbon and hydrogen content were deter-
mined by elemental analysis on a Perkin Elmer CHN 2400 analyzer. The number of
crystallization water molecules was determined from TG curves and by isothermal
heating of the hydrated complexes. The experimental results confirm the calculated
data (Table 1). The IR spectra of the complexes and spectra of 3-methylglutaric acid
and its sodium salt were recorded as KBr discs on a Specord M-80 spectrophotometer
–
1
(
4000� 400 cm ). The solubilities of Mn(II), Co(II), Ni(II), Cu(II), Zn(II) and Cd(II)
complexes were determined by measuring the concentration of Mn(II) ions in satu-
rated (under isothermal conditions) solution using AAS method. Thermal stabilities
of the prepared complexes were investigated by TG, DTG and DTA curves. Measure-
ments were made with Q-1500 derivatograph with Derill converter at a heating rate
–
1
of 10 K min with full scale. The samples of 100 mg were heated in platinum cruci-
bles in static air to 1273 K with a sensitivity TG=100 mg. The DTG and DTA sensi-
tivities are regulated by computer Derill program. The products of decomposition
were calculated from TG curve and were verified by diffractogram registration.
Results and discussion
3
-Methylglutarates of Mn(II), Co(II), Ni(II), Cu(II), Zn(II) and Cd(II) were prepared
as fine crystalline solids with colour characteristic of M(II) hydrated ions, with a mo-
lar ratio of metal to organic ligand of 1.0:1.0. The complexes of Mn(II), Co(II),
Ni(II), Cu(II) and Cd(II) were prepared as hydrates with different degree of hydration
(
Table 1). Only Zn(II) complex was obtained as anhydrous one. The prepared com-
plexes are characterized by diversity of their structure [3]. Very often the complexes
of Co(II) and Ni(II) are isostructural, but in this case they are characterized by differ-
ent structures.
3
ble in water (Table 1). Their solubilities are of the order 10 mol dm , except for the
-Methylglutarates of Mn(II), Co(II), Ni(II), Cu(II), Zn(II) and Cd(II) are solu-
–3
–
2
–
3
–3
Cu(II) one, the solubility of which is equal to 4.2⋅10 mol dm . The solubilities of
the prepared complexes increase in the order: Cu<<Ni<Co<Cd<Mn<Zn. Usually the
complexes of Cu(II) with carboxylic acids are more sparingly soluble in water than
those of Mn(II), Co(II), Ni(II), Zn(II) and Co(II) [4, 5].
J. Therm. Anal. Cal., 61, 2000

&
1
38
BRZYSKA, OZGA: 3-METHYLGLUTARIC ACID
Infrared spectra
–
1
The 3-methylglutaric acid exhibits a strong absorption band at 1696 cm of C=O in
COOH. When the acid is converted to the salt, the stretching vibration band of C=O
–
1
at 1696 cm disappears, whereas the bands of asymmetric vibrations ν (OCO) at
as
–
1
1
pear. In the IR spectra of the prepared complexes exhibit broad absorption bands with
550–1588 and the bands of symmetric vibrations ν (OCO) at 1404–1440 cm ap-
s
–
1
max. at 3400–3448, and narrow bands of δ(H O) at 1600–1630 cm , confirming the
presence of water molecules linked by hydrogen bonds, and the bands of
2
–
metal-oxygen bond at 520–540 cm .
1
In the IR spectrum of Zn(II) complex the bands of ν(OH) and δ(H O) are absent,
which confirms the anhydrous character of this compound. The IR spectra of Mn(II),
2
Co(II), Ni(II) and Cd(II) 3-methylglutarates are similar to each other, which suggests
similar mode of metal-organic ligand coordination. The bands ν (OCO) and
as
–
1
ν (OCO) for these complexes appear at 1568–1576 and 1404–1416 cm , respectively
and are shifted to lower frequencies compared to those bands of the sodium salt (1580
s
–
1
and 1460 cm ). In the IR spectrum of Zn(II) complex the bands ν (OCO) appear at
as
–
1
1
1
550 and ν (OCO) at 1440 cm and are also shifted to lower frequencies.
s
In the IR spectrum of Cu(II) complex the bands ν (OCO) and ν (OCO) appear at
588 and 1408 cm , and are shifted to higher and to lower frequencies, respectively com-
as
s
–1
pared to those bands in free ion. The values ∆ν=ν –ν for Mn(II), Co(II), Ni(II) and
as
s
–1
Cd(II) are similar to each other (∆ν=160 cm ) and are higher than for the sodium salt
–
1
–1
(
∆ν=120 cm ), whereas for Zn(II) complex ∆ν(110 cm ) is almost close to that for the
–1
sodium salt. The values ∆ν for Cu(II) complex has the highest value (∆ν =180 cm ).
On the basis of the spectroscopic criteria [6� 9], our previous work [10� 12] and
other authors [13], it is possible to suggest that carboxylate group in the complexes of
Mn(II), Ni(II), Co(II), Zn(II) and Cd(II) are bidentate bridging whereas in the Cu(II) one
as monodentate. In the complexes with monodentate carboxylate groups ν (OCO) in-
as
creases and ν (OCO) decreases, whereas in the complexes with bidentate bridging OCO
s
group, the ν (OCO) and ν (OCO) are shifted in the same direction. The oxygen atoms of
as
s
carboxylate group are not only coordinated to metal ion, but they may be linked by hy-
drogen bonds to the water of crystallization [9], which influences, first of all, on the posi-
tion of ν (OCO), which are more diagnostic values than ν (OCO).
as
s
The stretching vibrations of coordinated carboxyl group are determined by com-
bined effect of the mass, radius, negativity of the central atom and some other factors
[
15] and hence the results must be interpreted with certain probability. The water
molecules are probably in inner sphere of the complexes except for Cd(II) complex in
which there are inner and outer sphere water molecules, but the coordinated and un-
coordinated water molecules are not distinguished by the thermogravimetric curve.
The full interpretation of the mode of metal� ligand coordination would be possible
after determination of the crystallographic and molecular structure of monocrystals,
but they were not obtained so far. The frequencies of the M� O stretching vibrations
increases in the order: Ni=Cu=Zn<Mn<Co=Cd. The magnitude of the M� O frequen-
cies and that of the stability constants of the complexes change generally in the same
J. Therm. Anal. Cal., 61, 2000

BRZYSKA, O� GA: 3-METHYLGLUTARIC ACID
139
direction [15]. This is to be expected, since an increase in the M� O bond order means
higher stability of the complex. However, in view of the fact that conjugation of the
M� O, C� O and C� C bonds may occur in the chelate ring of the complex, and hence
there will be no pure M� O stretching vibrations and the results must be interpreted
with great caution.
Table 2 Frequencies of maximum of absorption bands in IR spectra of 3-methylglutarates of
�
1
Mn(II), Co(II), Ni(II), Cu(II), Zn(II), Cd(II) and Na(I) (cm )
Complex
MnL⋅5H
CoL⋅3H
ν(OH)
3400
3416
3448
3400
�
ν
as(OCO)
1568
1568
1576
1588
1550
1570
1580
ν
s
(OCO)
1404
1408
1416
1408
1440
1410
1460
ν
as� ν
s
ν(M� O)
525
2
O
164
160
160
180
110
160
120
2
O
530
NiL⋅3H
CuL⋅2H
ZnL
2
O
520
2
O
O
520
520
CdL⋅8H
2
3425
3450
530
Na
2
L
540
Thermal analysis
The 3-methylglutarates of Mn(II), Co(II), Ni(II), Cu(II), Zn(II) and Cd(II) are stable
at room temperature. During heating they decompose in two or three steps (Figs 1–3,
Table 3). The hydrated complexes of Mn(II), Co(II), Ni(II), Cu(II) and Cd(II) are sta-
ble up to 323–373 K and on farther heating they lose some water molecules in one
(
Mn, Co, Ni, Cu) or two steps (Cd) over the range 323–453 and 323–593 K, respec-
Fig. 1 TG, DTG and DTA curves of Co[C
4
H
8
(COO)
2 2
]⋅3H O
J. Therm. Anal. Cal., 61, 2000

1
40
BRZYSKA, O� GA: 3-METHYLGLUTARIC ACID
4 8 2
Fig. 2 TG, DTG and DTA curves of Zn[C H (COO) ]
Fig. 3 TG, DTG and DTA curves of Cd[C
4
H
8
(COO)
2 2
]⋅8H O
tively. The dehydration process in connected with endothermic effect at 473–533 K
for Cd: at 473 and 553 K). Dihydrated complexes of Mn(II), Co(II), Ni(II) and
Cd(II), monohydrated complex of Cu(II) and anhydrous one of Zn(II) are stable up to
15–613 K and then decompose in different ways. The dihydrated 3-methylglutarates
(
4
of Co(II) and Ni(II) decompose over the range 415–793 K to free metals and next are
oxidized to oxides (NiO, Co O ) over the range 793–823 K. The hydrated complexes
3
4
of Mn(II), Cu(II), Cd(II) and anhydrous complex of Zn(II) decompose directly to ox-
ides over the range 553–853 K. The temperature of oxide formation increases from
J. Therm. Anal. Cal., 61, 2000

Table 3 Data for dehydration and decomposition of 3-methylglutarates of Mn(II), Co(II), Ni(II), Cu(II), Zn(II) and Cd(II)
Mass loss/%
Mass loss/%
calc. found
Mass loss/%
Loss of H
2
O/
Complex
∆T
1
/K
∆T
2
/K
∆T
3
/K
K
T /K
mol
calc.
found
19.0
7.0
calc.
found
73.5
69.0
71.0
67.5
61.2
�
*
MnL ⋅5H
2
O
323� 523
323� 413
323� 413
373� 453
�
18.68
6.95
7.01
7.40
�
3
1
1
1
�
�
�
�
613� 843
793� 823
793� 823
553� 803
593� 783
�
73.58
68.99
70.89
67.35
61.50
�
843
793
793
803
783
�
CoL⋅3H
2
O
415� 793
73.50
73.0
NiL⋅3H
CuL⋅2H
ZnL
2
O
7.0
523� 793
77.13
77.0
2
O
7.5
�
�
�
�
�
�
�
�
�
�
�
�
�
CdL⋅8H
2
O
373� 453
453� 593
8.99
26.90
9.0
2
4
�
27.0
613� 853
67.93
68.0
853
2
�
L* � C
2
4 8 1 2 3
H (COO) , ∆T � temperature range of dehydration, ∆T � temperature range of decomposition to free metals, ∆T � temperature range of
decomposition to oxides

&
1
42
BRZYSKA, OZGA: 3-METHYLGLUTARIC ACID
7
83 for ZnO to 853 K for CdO. The temperatures of oxide formation increase in the
order: Zn<Co=Ni<Cu<Mn<Cd with decreasing electronegativity of the metal (except
for Zn). The results indicate that the thermal decomposition of the prepared com-
plexes can be presented as:
ML⋅nH O→ML⋅mH O→Mn O , CuO, M=Mn, Cu
2
2
3
4
ML⋅3H O→ML⋅2H O→M→Co O , NiO M=Co, Ni
2
2
3
4
ZnL→ZnO
CdL⋅8H O→CdL⋅6H O→CdL⋅2H O→CdO
2
2
2
Conclusions
Complexes of Mn(II), Co(II), Ni(II), Cu(II), Zn(II) and Cd(II) with 3-methylglutaric
acid were prepared as solids with a molar ratio of metal to organic ligand of 1:1, solu-
ble in water. The carboxylate group in the complexes of Mn(II), Ni(II), Co(II), Zn(II)
and Cd(II) are bidentate bridging whereas in the Cu(II) one as monodentate. The oxy-
gen of carboxylate group are not only coordinated to metal ion, but they may be
linked by hydrogen bonds to the water of crystallization. The water molecules are
probably in inner sphere of the complexes except for the Cd(II) complex in which
there are inner and outer sphere water molecules. During heating the hydrated com-
plexes lose some water molecules in one (Mn, Co, Ni, Cu) or two steps (Cd) and then
mono- (Cu) or dihydrates (Mn, Co, Ni) decompose to oxides directly (Mn, Cu, Co) or
with intermediate formation of free metals (Co, Ni). Anhydrous Zn(II) complexes di-
rectly to the oxide ZnO.
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