New complexes of some d-electron elements with 3-methyladipic acid

Article abstract of DOI:10.1023/B:JTAN.0000032267.08534.f7

Conditions for the preparation of Mn(II), Co(II), Ni(II), Cu(II) and Zn(II) 3-methyladipates were investigated and their qualitative composition and magnetic moments were determined. The IR spectra and powder diffraction patterns of the complexes prepared

Full text of DOI:10.1023/B:JTAN.0000032267.08534.f7

Journal of Thermal Analysis and Calorimetry, Vol. 76 (2004) 823–828
NEW COMPLEXES OF SOME d-ELECTRON
ELEMENTS WITH 3-METHYLADIPIC ACID
W. Brzyska* and I. A. Juíko
Department of General Chemistry, Marie Curie SkÓodowska University, 20 030 Lublin, Poland
(Received October 13, 2003)
Abstract
Conditions for the preparation of Mn(II), Co(II), Ni(II), Cu(II) and Zn(II) 3-methyladipates were
investigated and their qualitative composition and magnetic moments were determined. The IR spectra
and powder diffraction patterns of the complexes prepared of the general formula M(C7H10O4)×nH2O
(n=0–11) were recorded and their thermal decomposition in air were studied. During heating the
hydrated complexes are dehydrated in one (Co, Ni) or two steps (Mn, Zn) losing all crystallization water
molecules (Co, Ni) or some water molecules (Mn, Zn) and then anhydrous (Co, Ni, Cu) or hydrated
complexes (Mn, Zn) decompose directly to oxides (Mn, Co, Zn) or with intermediate formation the
mixture of M+MO (Ni, Cu). The carboxylate groups are bidentate (Mn, Co, Ni, Cu) or monodentate
(Zn). The complexes exist as polymers. The magnetic moments for the paramagnetic complexes of
Mn(II), Co(II), Ni(II) and Cu(II) attain values 5.48, 4.49, 2.84 and 1.45 B.M., respectively.
Keywords: DTA, IR spectra, magnetic moments, 3-methyladipate, synthesis, TG
Introduction
3-Methyladipic acid C5H10(COOH)2 is a crystalline solid soluble in water, ether, acetone,
chloroform and acetic acid, sparingly soluble in benzene, toluene and xylene, and
practically insoluble in petroleum benzine [1]. The salts of Na(I) and K(I) [1, 2] are
soluble in water, whereas the complexes of Cu(II), Ag(I) and Ba(II) [1] are sparingly
soluble in water. Ikeda et al. [3] determined the stability constants of rare earth element
3-methyladipates by potentiometric method. The stability constants of 3-methyladipates
are smaller than those of adipates. The 3-methyladipates of rare earth elements (Y,
La–Lu) [4] have been prepared as hydrates with general formula Ln2L3×nH2O, sparingly
soluble in water. The IR spectra of the prepared complexes suggest that the carboxylate
groups are bidentate chelating. During heating the complexes lose all crystallization
water molecules in one (Ce–Lu) or two steps (Y) (exception of La complex which
undergoes to monohydrate) and then decompose directly to oxides (Y, Ce) or with
intermediate formation of oxocarbonates Ln2O2CO3 (Pr–Tb) or Ln2O(CO3)2 (Gd–Lu).
*
Author for correspondence: E-mail: BRZYSKA@hermes.umcs.lublin.pl
1388–6150/2004/ $ 20.00
Akadémiai Kiadó, Budapest
© 2004 Akadémiai Kiadó, Budapest
Kluwer Academic Publishers, Dordrecht

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BRZYSKA, JUŸKO: 3-METHYLADIPIC ACID
Only La(III) complex decomposes in four steps forming additionally unstable
La2(C7H10O4)CO3.
The aim of our work was to prepare the complexes of Mn(II), Co(II), Ni(II),
Cu(II) and Zn(II) with 3-methyladipic acid in solid state under the same conditions
and to study their properties and thermal decomposition in air.
Experimental
The complexes of Mn(II), Co(II), Ni(II) and Zn(II) with 3-methyladipic acid were
prepared by dissolving the fresh precipitated metal(II) carbonates in hot 0.2 M solution
of 3-methyladipic acid, filtering excess of carbonate and crystallizing at room
temperature. The precipitation formed were filtered off and washed with hot water. The
complex of Cu(II) with 3-methyladipic acid was prepared by adding 0.2 M solution of
ammonium 3-methyladipate (pH 5.0) to a hot 0.3 M solution of copper(II) nitrate. The
precipitate formed was heated in mother solution for 0.5 h, filtered off and washed with
hot water to remove ammonium ions. All precipitates were dried at 303 K to a constant
mass. The carbon and hydrogen contents in the prepared complexes were determined
by elemental analysis on a Perkin Elmer CHN 2400 analyser. The content of metal was
determined by AAS method using atomic absorption spectrophotometer AAS–3 (Carl
Zeiss, Jena). The number of crystallization water molecules was determined from TG
curve and by heating of the hydrated complexes at define temperature. The
experimental results of the analysis confirm the calculated data (Table 1). The IR
spectra of the prepared 3-methyladipates and spectra of 3-methyladipic acid and its
sodium salt were recorded as KBr discs on a Specord M–80 spectrophotometer
(4000–400 cm–1). The powder diffraction patterns of the prepared complexes and the
products of their decomposition were recorded by using X-ray 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
Co[Hg(SCN)4]. The thermal stability of the prepared complexes was investigated by
method TG, DTG and DTA. Measurements were made with Q 1500 derivatograph by
method described earlier [5]. The samples were heating in air to 1273 K.
Table 1 Analytical data and colour of Mn(II), Co(II), Ni(II), Cu(II) and Zn(II) 3-methyladipates
M%
C%
H%
Complex
Colour
M
calc.
19.29
23.32
23.32
28.67
15.52
found
19.3
23.4
23.5
28.7
15.3
calc.
29.47
33.20
33.24
37.92
19.93
found
30.0
33.2
33.3
34.0
20.0
calc.
6.31
5.53
5.54
4.51
7.59
found
6.3
MnL×4H2O
CoL×2H2O
NiL×2H2O
CuL
beige
violet
green
blue
284.0
253.0
252.7
221.5
421.4
5.5
5.5
4.4
ZnL×11H2O
7.7
white
L – C7H10O24–
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BRZYSKA, JUŸKO: 3-METHYLADIPIC ACID
825
Results and discussion
3-Methyladipates of Mn(II), Co(II), Ni(II), Cu(II) and Zn(II) were prepared as solids
of general formula M(C7H10O4)×nH2O, where n=4 for Mn, n=2 for Co and Ni, n=0 for
Cu and n=11 for Zn having colour characteristic for hydrated metal(II) ions. The
complexes of Ni(II), Cu(II) and Zn(II) are crystalline, whereas those of Mn(II) and
Zn(II) are radiographically amorphous and form glass. All complexes with exception
of Cu(II) complex are well soluble in water.
The susceptibilities of paramagnetic Mn(II), Co(II), Ni(II) and Cu(II) complexes
calculated from results of magnetic measurements at 295 K were corrected by measuring
the diamagnetic susceptibility of ligand. The magnetic moments were calculated by
using formula meff=2.84(cMT)1/2. The complex of Zn(II) was diamagnetic. The magnetic
moments determined for the complexes of Mn(II), Co(II), Ni(II) and Cu(II) are equal to:
5.48, 4.49, 2.84 and 1.46 B.M., respectively (Table 1). The magnetic moments
determined for Mn(II) and Ni(II) complexes are similar to theoretical values for
octahedral complexes with configuration d5 and d8, respectively. The value of meff for
Mn(II) complex shows on high spin – only configuration (meff=5.6–6.10 B.M.) [6] and
octahedral structure. For Co(II) complex the measured magnetic moment (4.49 B.M.)
differs to some extent from spin – only moment. Its magnetic moment, instead of spin –
only moment 3.88 B.M. characteristic for d7 configuration (three unpaired electrons) is
equal to 4.49 B.M. Literature data [6, 7] show that measured magnetic moments for
Co(II) complexes with different ligand attain values 4.3–5.28 B.M. The magnetic
moment value (1.45 B.M.) for Cu(II) complex is smaller than theoretical value 1.72 B.M.
for the tetrahedral complex with configuration d9 and polymeric structure. The small
value of magnetic moment confirms the polymeric structure of the complex, because in
polymeric compounds Cu–Cu action reduces its value.
All prepared 3-methyladipates exhibit similar solid-state IR spectra (Table 2).
When the acid is converted to the complex, the stretching vibrations of C=O group,
n(C=O) in COOH at 1700 cm–1 disappear, whereas the band of asymmetric vibrations
nas(OCO) at 1564–1588 cm–1 and the bands of symmetric vibrations ns(OCO)
at 1384–1420 cm–1 appear. In the IR spectra of Mn(II), Co(II), Ni(II), and
Zn(II) 3-methyladipates broad absorption bands of n(OH) with max. at 3424–3432 cm–1
and narrow bands of d(H2O) at 1620–1630 cm–1 are observed confirming the presence of
crystallization water molecules linked by hydrogen bonds. Those bands do not appear in
the IR spectrum of Cu(II) complex confirming its anhydrous character. In the spectra of
all prepared complexes similarly as in the IR spectrum of free acid there are the bands of
CH3 vibrations at 2960, 2930 and 1164–1172 cm–1, and the bands of C–H vibrations
at 1330–1350, 1100, 900–700 cm–1. The splitting of the absorption bands of valency
vibrations nas(OCO) and ns(OCO) (Dn=nas–ns) in the IR spectra of Mn(II) and Cu(II)
have values 152 and 168 cm–1 and those of Co(II), Ni(II) and Zn(II) are bigger and
amount to 180–188 cm–1. The values of Dn for all complexes (except of Mn(II) one) are
bigger than for the sodium salt (Dn=160 cm–1) suggesting the great degree of ionic bond
character in these complexes. The bands of nas(OCO) in the IR spectra of Mn(II), Co(II),
Ni(II) and Zn(II) do not change practically their position and the bands ns(OCO) are
J. Therm. Anal. Cal., 76, 2004

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BRZYSKA, JUŸKO: 3-METHYLADIPIC ACID
shifted to lower frequencies or do not change their position compared to those for the
sodium salt. In the IR spectrum of Cu(II) 3-methyladipate the band nas(OCO) is shifted to
higher and the band of ns(OCO) to lower frequencies compared to those bands for the
sodium salt. On the basis of spectroscopic criteria [7–9], Dn values and shifts of the
nas(OCO) and ns(OCO) compared to the bands for the sodium salt and our previous
works [4, 5] it is possible to suggest that in the complexes of Mn(II), Co(II), Ni(II) and
Cu(II) the carboxylate groups act as bidentate and in the Zn(II) complex as monodentate.
In the Zn(II) and Mn(II) complexes there are probably both inner and outer sphere water
molecules, whereas in the complexes of Co(II) and Ni(II) water is only in inner sphere.
Taking into account spacial structure of the 3-methyladipate ligand and the complexes it
is possible to suggest, that the prepared 3-methyladipates exist as polymers.
Table 2 Frequencies of characteristic absorption bands in IR spectra of Na(I), Mn(II), Co(II),
Ni(II), Cu(II) and Zn(II) 3-methyladipates [cm–1] and the magnetic moments
Complex
n(OH)
d(H2O)
nas(OCO)
ns(OCO)
nas–ns
meff/B.M.
MnL×4H2O
CoL×2H2O
NiL×2H2O
CuL
3432
3432
3432
–
1630
1620
1620
–
1564
1568
1568
1588
1572
1568
1408
1384
1384
1420
1384
1408
156
184
184
168
188
160
5.48
4.49
2.84
1.45
–
ZnL×11H2O
Na2L×nH2O
3432
3432
1630
–
–
L – C7H10O24–
The complexes prepared are stable at room temperature. During heating in air they
decompose in different ways (Table 3). Hydrated complexes of Mn(II), Co(II), Ni(II) and
Zn(II) are stable up to 323 K. Dihydrated complexes of Co(II) and Ni(II) lose in one step
all crystallization water molecules over the range 323–583 K forming anhydrous
compounds. The hydrated complexes of Mn(II) and Zn(II) heated lose some
crystallization water molecules in two steps over the range 323–613 K forming partially
hydrated complexes, which are dehydrated and decompose simultaneously. The
dehydration process is connected with strong endothermic effect. The anhydrous
complexes of Co(II), Ni(II) and Cu(II) during heating decompose in two or three steps
over the range 373–673 to 613–883 K. 3-Methyladipate of Co(II) decomposes directly to
Co3O4, whereas the complexes of Ni(II) and Cu(II) decompose to MO with intermediate
formation of mixture of M+MO. Dihydrated Mn(II) complex and pentahydrated Zn(II)
complex heated decompose directly to Mn3O4 and ZnO, respectively. The dehydration
processes are connected with endothermic effect, whereas the combustion of organic
ligand, products of decomposition and oxidation of free metal to oxide proceed with
strong exothermic effects. The temperature of oxide formation change in the order:
Cu<Co<Mn<Zn<Ni from 613 for Cu(II) to 883 for Ni(II).
The results indicate, that the prepared 3-methyladipates decompose in the fol-
lowing way:
J. Therm. Anal. Cal., 76, 2004

BRZYSKA, JUŸKO: 3-METHYLADIPIC ACID
827
J. Therm. Anal. Cal., 76, 2004

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BRZYSKA, JUŸKO: 3-METHYLADIPIC ACID
MnL×4H2O ® MnL×3H2O ® MnL×2H2O ® Mn3O4,
CoL×2H2O ® CoL ® Co3O4,
NiL×2H2O ® NiL ® Ni+NiO ® NiO,
CuL ® Cu+CuO ® CuO,
ZnL×11H2O ® ZnL×9H2O ® ZnL×5H2O ® ZnO.
Conclusions
3-Methyladipates of Mn(II), Co(II), Ni(II), Cu(II) and Zn(II) were prepared as solids
with molar ratio of metal to organic ligand of 1.0:1.0. The complexes of Mn(II),
Co(II), Ni(II) and Zn(II) were prepared as hydrates, whereas the complex of Cu(II) as
anhydrous one. When heated the hydrated complexes were dehydrated in
one (Co, Ni) or two steps (Mn, Zn) losing all crystallization water molecules (Co, Ni)
or some water molecules (Mn, Zn) and then the anhydrous (Co, Ni, Cu) or partially
hydrated complexes (Mn, Zn) decompose directly to oxides (Mn, Co, Zn) or with in-
termediate formation the mixture of M+MO (Ni, Cu). The complexes exist probably
as polymers. The magnetic moments for paramagnetic complexes of Mn(II), Co(II),
Ni(II) and Cu(II) attain values 5.48, 4.49, 2.84 and 1.45 B.M., respectively.
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J. Therm. Anal. Cal., 76, 2004