Thermal and other properties of new 4,4'-bipyridine-trichloroacetato complexes of Mn(II), Ni(II) and Zn(II)

Article abstract of DOI:10.1023/A:1014365007321

New mixed-ligand complexes of general formulae Mn(4-bpy)(CCl₃COO)₂·H₂O, Ni(4-bpy)₂(CCl₃COO)₂·2H₂O and Zn(4-bpy)₂(CCl₃COO)₂·2H₂O (where 4-bpy=4,4'-bipyridine) were obtained and characterized. The IR spectra, conductivity measurements and other physical properties of these compounds were discussed. The central atoms M(II) form coordinate bonds with title ligands. The thermal behaviour of the synthesized complexes was studied in air. During heating the complexes decompose via different intermediate products to Mn₃O₄, NiO and ZnO; partial volatilization of ZnCl₂ was observed. A coupled TG-MS system was used to the analysis of the principal volatile thermal decomposition products of Mn(II) and Ni(II) complexes. The principal volatile mass fragments correspond to: H₂O⁺, OH⁺, CO₂¹, HCl⁺, Cl₂¹, CCl⁺ and other.

Full text of DOI:10.1023/A:1014365007321

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Journal of Thermal Analysis and Calorimetry, Vol. 67 (2002) 667–678
THERMAL AND OTHER PROPERTIES OF NEW
4,4’-BIPYRIDINE-TRICHLOROACETATO
COMPLEXES OF Mn(II), Ni(II) AND Zn(II)
D. Czakis-Sulikowska, A. Czylkowska and A. Malinowska
Institute of General and Ecological Chemistry, Technical University of £ódŸ, 90-924 £ódŸ, Poland
(Received May 3, 2001)
Abstract
New mixed-ligand complexes of general formulae Mn(4-bpy)(CCl3COO)2·H2O,
Ni(4-bpy)2(CCl3COO)2·2H2O and Zn(4-bpy)2(CCl3COO)2·2H2O (where 4-bpy=4,4’-bipyridine)
were obtained and characterized. The IR spectra, conductivity measurements and other physical
properties of these compounds were discussed. The central atoms M(II) form coordinate bonds
with title ligands. The thermal behaviour of the synthesized complexes was studied in air. During
heating the complexes decompose via different intermediate products to Mn3O4, NiO and ZnO;
partial volatilization of ZnCl2 was observed. A coupled TG-MS system was used to the analysis of
the principal volatile thermal decomposition products of Mn(II) and Ni(II) complexes. The princi-
pal volatile mass fragments correspond to: H2O+, OH+, CO+2, HCl+, Cl+2, CCl+ and other.
Keywords: 4,4’-bipyridine, IR spectra, mass spectrometry, thermal decomposition, transi-
tion-metal complexes, trichloroacetate
Introduction
The work presented here is a continuation of our studies on transition–metal com-
plexes with bipyridine isomers and carboxylates [1–7]. The properties of mixed
acetato-bipyridine complexes of metal(II) have been the subject of extensive investi-
gations during the last years. The nature of bonds between M(II) ions and acetate ions
and bipyridine isomers (2,2’-, 4,4’-, 2,4’-bpy) is discussed in [1, 2, 7–10]. Thermal be-
haviour of the mixed complexes of the formula M(CH3COO)2(2,4’-bpy)2·2H2O
(where M(II)=Mn, Co, Ni, Cu, Zn, Cd) also was studied [1, 2, 7]. However, there is
scanty information on the mixed-ligand complexes of metal(II) with bipyridine and
chloroacetates. The presence of halogen atoms in the carboxylate ligands does not
take place in the coordination of metal ion but their influence on the structure and
properties of the complexes is considerable. The complexes of the formulae
[Zn(µ-4-bpy)(4-bpy)2(CCl3COO)2(H2O)4]n and [Zn(2-bpy)(CCl3COO)2·(H2O)] were
described by Sen et al. [11]. Shova et al. [12] have prepared trichloroacetate of man-
ganese(II) and its molecular structure has been determined. Thermal decomposition of
some copper(II) halogenoacetates was carried out by Obier et al. [13] and described in
1418–2874/2002/ $ 5.00
Akadémiai Kiadó, Budapest
© 2002 Akadémiai Kiadó, Budapest
Kluwer Academic Publishers, Dordrecht

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CZAKIS-SULIKOWSKA et al.: TRICHLOROACETATO COMPLEXES
other papers [14, 15]. Thermal properties of zinc(II) monochloroacetates and its com-
plexes with nicotinamide and caffeine were reported by Zeleòák et al. [16].
In our earlier papers [17, 18] we described the preparation, IR and VIS spectra and
thermal decomposition of complexes: M(4-bpy)2(ClCH2COO)2·nH2O (where M(II)= Mn,
Co, Ni, Cu), M(4-bpy)2(CCl3COO)2·nH2O (M(II)=Co, Cu) and Cd(4-bpy)(CCl3COO)2·
H2O. IR studies of mixed 4,4’-bipyridine–trichloroacetato complexes of Co(II), Cu(II)
and Cd(II) indicate that 4-bpy is coordinated with metal ions and the trichloroacetate
groups are bonded as bidentate chelating ligands. The principal volatile thermal decom-
position products in air of those complexes were identified. It was thus of interest to ex-
amine the behaviour of 4-bpy and trichloroacetate groups in other mixed-ligand com-
plexes.
In this paper we present the results of the synthesis and properties of new mixed-
ligand complexes of Mn(II), Ni(II) and Zn(II) with 4-bpy and trichloroacetates. The
thermal decomposition of obtained compounds was investigated in air. The TG-MS
system was used to analyse the principal volatile thermal decomposition products of
these complexes.
Experimental
Materials
4,4’-bipyridine (m.p. 69.9°C) and trichloroacetic acid p.a. were obtained from
Aldrich; methanol (anhydroscan) was from Lab. Scan. Hydroxyloamine (50% v/v
water solution) was purchased from Fluka. The remaining starting materials were p.a.
from POCh-Gliwice. Water solutions of metal(II) trichloroacetates were prepared by
adding 20 mL 2 M trichloroacetic acid to freshly precipitated metal(II) carbonate in
ca. stoichiometric quantities. In the case of the preparation of Mn(CCl3COO)2 the re-
action mixture contains 2 mL of 10% v/v hydroxyloamine (to stop the oxidation pro-
cess of Mn(II)). The metal(II) contents in solutions of trichloroacetates were analysed
by complexometry.
Table 1 Analytical data, effective magnetic moments µeff (B.M.) at room temperature, solubility
S (mol L–1) in water at 21°C and molar conductivity ΛM (Ω−1 cm2 mol–1) in methanol
(concentration 1·10–3 mol L–1) at 25°C of the complexes (where L=CCl3COO–)
Analysis found (calculated)/%
Complex
(colour)
S·103
µeff
ΛM
M
C
N
H
Mn(4-bpy)L2·H2O
(white)
10.15
30.66
5.26
(5.06)
1.78
(1.82)
5.72
3.61
–
1.48
0.30
0.13
96.9
62.1
75.3
(9.92) (30.36)
7.60 39.50
(7.66) (39.39)
9.33 39.22
(8.85) (39.03)
Ni(4-bpy)2L2·2H2O
(light-green)
8.05
(8.02)
2.62
(2.75)
Zn(4-bpy)2L2·2H2O
(white)
8.00
(7.59)
2.80
(2.73)
J. Therm. Anal. Cal., 67, 2002

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CZAKIS-SULIKOWSKA et al.: TRICHLOROACETATO COMPLEXES
669
Synthesis of complexes
A solution of 4-bpy (12.8 mmol) in 96% v/v ethanol (31.3 mL) was added to freshly
obtained solution of metal(II) trichloroacetate (4.3 mmol) in water (8.7 mL) at room
temperature. The precipitate was filtered off, washed with 40% v/v ethanol and then
with ethanol-diethyl ether mixture (1:1) and dried in open air. The contents of C, H
and N were determined by elemental analysis with V2O5 as oxidizing agent; metal(II)
in mineralized samples of the obtained compounds was determined complexo-
metrically. These analytical results are presented in Table 1.
Measurements
The thermal stability of the complexes was studied by TG, DTG and DTA. Measure-
ments were made by using a derivatograph Q-1500 at heating rate 10°C min–1.
α-Al2O3 served as reference material. The samples (100 mg) were heated in the range
25–1000°C in air atmosphere. Mass spectrometer was used for the characterization of
volatile thermal decomposition products of the Mn(II) and Ni(II) complexes (with
samples of mass 5.18 and 8.73 mg, respectively). The TG-MS system: derivatograph
TG/DTA-SETSYS-16/18, mass spectrometer ThermoStar from Balzers, platinum
crucible 100 µL. The other apparatus and experimental conditions were described in
previous papers [1, 2, 19].
Results and discussion
The analytical results for the obtained compounds are collected in Table 1, together
with other characteristic data. All of the complexes are air stable. The solubilities of
compounds in water at 21°C are in the order of 10–3 mol L–1. All the complexes dis-
solved fairly in methanol, decomposed in aqueous acid and alkali and were insoluble
in most organic solvents (CCl4, CHCl3, (CH3)2CO). The molar conductivities in meth-
anol indicate that the complex Mn(4-bpy)(CCl3COO)2·H2O behaves as 1:1 electro-
lyte, while the remaining complexes show intermediate behaviour between those of
non- and 1:1 electrolytes [20]. Higher than the expected values of molar conductivi-
ties are possible due to the substitute of trichloroacetate ligands by solvent molecules.
Similar situation was observed in metal complexes with bipyridine and other ligands
[4, 17, 18]. The experimental magnetic moments of Mn(4-bpy)(CCl3COO)2·H2O
(5.72 M.B.) and Ni(4-bpy)2(CCl3COO)2·2H2O (3.61 M.B.) are close to the values cal-
culated for the metal ion in octahedral environment [21].
Spectroscopic characteristics
For consistency, only fundamental vibration modes of 4-bpy and OCO groups for
synthesized complexes are reported in Table 2. Infrared spectra of Mn(II), Ni(II) and
Zn(II) complexes with 4-bpy have several absorption bands characteristic of CC, CN
and CH of the bipyridine and are in good accord with the previous observations on
their complexes with metal salts [3, 8, 17, 18]. IR spectra of these compounds suggest
that 4-bpy is coordinated to a metal ion.
J. Therm. Anal. Cal., 67, 2002

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CZAKIS-SULIKOWSKA et al.: TRICHLOROACETATO COMPLEXES
Table 2 Principal IR bands (cm–1) for 4-bpy and OCO groups in free ligands and their complexes
Complexes
CCl3COONa [22]
4-bpy modes
Assignment
4-bpy
Mn(II)
Ni(II)
Zn(II)
ν(C=N)
ν(C=C)
γ(CH)
γra
1596.9 vs
1531.4 s
810.0 vs
993.3 vs
1604.7 vs
1533.3 s
825.5 vs
1006.8 m
1610.5 vs
1537.2 s
812.0 s
1608.5 vs
1535.2 s
810.0 vs
1010.6 w
1010.6 w
carboxylate group modes
1677.0
1676.4 vs
1666.4 vs
1693.4 vs 1691.5 vs, pd
1683.7 vs, pd
νas(OCO)
νs(OCO)
1353.0
1384.8 vs
1352.0 vs
1375.0 vw
*
432.0 w
466.7 w
455.2 s pd
474.5 s pd
472.5s
ν
(MO)+δ(OCO)
324.0
291.2
314.4
316.5
308.7
∆ν
–
;
aγr – ring ‘breathing’ mode; ∆ν=νas(OCO)–νs(OCO) * – overlaid by 4-bpy absorption;
v, s, m, w, pd – very, strong, medium, weak, poorly resolved doublet
The principal absorption bands νas(OCO) and νs(OCO) of CCl3COONa and its complexes
are also given in Table 2. The compounds present carboxylate stretching frequencies,
as(OCO) at the range 1693.4–1666.4 cm–1 and νs(OCO) at 1384.8–1352.0 cm–1. The analysis of
OCO group bands frequencies allowed the determination of parameter ∆ν=νas(OCO)–νs(OCO)
ν
,
whose magnitude is used as a criterion of the carboxylate bonding with metal ions. Cal-
culations from the examined spectra of Mn(II) and Zn(II) complexes give ∆ν values in
the range 316.5–291.2 cm–1, less than for the sodium salt (∆ν=324 cm–1). According to
this fact it is possible to assume that the carboxylate ion is bonded as a bidentate chelating
ligand [23–26]. However, the νas(OCO) and νs(OCO) bands of Mn(II) complex and νas(OCO) band
of Zn(II) complex are splitted into doublet. From here is probable that non-completely
equivalent degree of ionity of bonds formed between M(II) and carboxylate groups of the
trichloroacetate ligand exist [27, 28]. The frequency νs(OCO) for Ni(II) complex is superim-
posed by the absorption of the 4-bpy. Thus, it is difficult to discuss the nature of the
nickel-trichloroacetate bonds. The ν(M–O)+δ(OCO) vibrations are observed in the interval ca.
474.5–432.0 cm–1.
IR spectra of complexes exhibit broad absorption bands in the water stretching
region (3440–3500 cm–1). The H2O wagging vibration of coordinated water is ob-
served at 536.2 cm–1 only for Mn(II) complexes.
VIS spectra was obtained in Nujol mulls for the nickel(II) complex within the
26 000–12 000 cm–1 region. The observed bands at 12 200, 16 800 and 25 000 cm–1
1
3
3
we ascribe to the following transitions: Eg, T1g(F) and T1g(P), respectively. The
electronic spectrum of this complex is consistent with a distorted octahedral environ-
ment around the nickel atom [21, 29].
J. Therm. Anal. Cal., 67, 2002