Characterization and TG-MS studies of lactato and bipyridine-lactato complexes of Co(II) and Ni(II)

Article abstract of DOI:10.1023/B:JTAN.0000046111.38978.4f

Two lactates and four new mixed ligand complexes with formulae Co(lact)₂·2H₂O, Ni(lact)₂·3H ₂O, Co(4-bpy)(lact)₂, Co(2,4'-bpy)₂(lact) ₂, Ni(4-bpy)(lact)₂·2H₂O and Ni(2,4'-bpy)₂(lact)₂ (where 4-bpy=4,4'-bipyridine, 2,4'-bpy=2,4'-bipyridine, lact=CH₃CH(OH)COO^-) were isolated and investigated. The thermal behaviour of compounds was studied by thermal analysis (TG, DTG, DTA). In the case of hydrated complexes thermal decomposition starts with the release of water molecules. The compounds decompose at high temperature to metal(II) oxides in air. A coupled TG-MS system was used to analyse the principal volatile products of thermolysis and fragmentation processes of obtained complexes.

Full text of DOI:10.1023/B:JTAN.0000046111.38978.4f

Journal of Thermal Analysis and Calorimetry, Vol. 78 (2004) 461–471
CHARACTERIZATION AND TG-MS STUDIES OF
LACTATO AND BIPYRIDINE-LACTATO COMPLEXES
OF Co(II) AND Ni(II)
*
D. Czakis-Sulikowska , A. Malinowska and A. ˜uczak
Institute of General and Ecological Chemistry, Technical University of ˜ódü, ˜ódü, Poland
Abstract
Two lactates and four new mixed ligand complexes with formulae Co(lact)
Co(4-bpy)(lact) , Co(2,4’-bpy) (lact) , Ni(4-bpy)(lact) ·2H O and Ni(2,4’-bpy)
-bpy=4,4’-bipyridine, 2,4’-bpy=2,4’-bipyridine, lact=CH
2
·2H
2
O, Ni(lact)
(lact)
3
CH(OH)COO ) were isolated and
2
·3H
2
O,
2
2
2
2
2
2
2
(where
–
4
investigated. The thermal behaviour of compounds was studied by thermal analysis (TG, DTG,
DTA). In the case of hydrated complexes thermal decomposition starts with the release of water
molecules. The compounds decompose at high temperature to metal(II) oxides in air. A coupled
TG-MS system was used to analyse the principal volatile products of thermolysis and fragmentation
processes of obtained complexes.
Keywords: 2,4’-bipyridine, 4,4’-bipyridine, Co(II) and Ni(II) lactates, TG-MS data,
thermal decomposition
Introduction
The present work is a continuation of our previous studies on the synthesis, properties
and thermal decomposition of metal complexes with bipyridine isomers and
carboxylates [1–8]. Mixed ligand complexes of metal containing anion of biologically
active 2-hydroxypropanoic acid (lactic acid) and their thermal behaviour are not well
known [9–11]. Only complexes of Cu(II) with lactates and 2,2’-bipyridine (2-bpy) or
4,4’-bipyridine (4-bpy) were prepared and described by Caraballo et al. [10, 11]. Lactic
acid and its compounds are a subject of considerable interest as a consequence of their
application e.g. in the pharmaceutical, agrochemical and food-stufts industries [9–17].
The complexes of Co(II) and Ni(II) with lactates (lact) and 4,4’-bipyridine or
2
,4’-bipyridine (2,4’-bpy) described in present paper were obtained in our laboratory.
The compounds were characterized by chemical, elemental analysis and molar con-
ductivity. The thermal decomposition of the complexes was studied by TG, DTG and
DTA techniques. A coupled TG-MS system was used to investigation of the principal
*
Author for correspondence: E-mail: dczakis@p.lodz.pl
1
388–6150/2004/ $ 20.00
Akadémiai Kiadó, Budapest
©
2004 Akadémiai Kiadó, Budapest
Kluwer Academic Publishers, Dordrecht

4
62
CZAKIS-SULIKOWSKA et al.: BIPYRIDINE-LACTATO COMPLEXES
gaseous products involved during the pyrolysis or fragmentation of the compounds.
All the thermal measurements were carried out in air.
Experimental
Materials
4
,4’-Bipyridine, 2,4’-bipyridine, dimethylformamide (DMF), dimethylsulfoxide
DMSO) and methanol (MeOH) (anhydrous) p.a. were obtained from Aldrich and
(
Lab-Scan., respectively. Lactic acid p.a. (85% aqueous solution d=1.2 g cm ) and
other chemical were p.a. products from POCh-Gliwice.
–
3
Measurements
The thermal stabilities of the complexes were studied by means of TG, DTA and DTG
techniques. The measurements were made with a Q-1500 Derivatograph, using Al O as
2
3
a standard. Samples of 100 mg were heated in ceramic crucibles in air static atmosphere.
All the thermal investigations were carried out in range of temperature 20–1000°C, at
–1
heating rate of 10°C min . A coupled TG-MS system was used to analysis of principal
volatile products of thermal decomposition and fragmentation processes of the
complexes. Data were performed with using on line connected computer system with
commercial software (Derivatograph TG/DTA-SETSYS-16/18, coupled to a Mass
Spectrometer QMS-422 model ThermoStart from Balzers); platinum crucible, samples
of mass 6–10 mg; dynamic measurements were carried out in air atmosphere (at flow rate
3
–1
of 1 dm h ); an ion source temperature of ca. 150°C by using 70 eV electron impact
ionization. The synthesized Co(II) and Ni(II) complexes and solid products of thermal
decomposition were characterized by X-ray powder diffraction patterns as previ-
–3
–3
ously [2]. Molar conductivity (Λ ) of complexes was measured using 1·10 mol dm
M
solutions in MeOH, DMSO and DMF. Experimental conditions and apparatus were the
same as those described earlier [4].
Synthesis of the compounds
Preparation of Co(II) and Ni(II) lactates
3
To 20 cm water solution of lactic acid (60 mmol) freshly precipitated carbonates of
the metal(II) in ca. stoichiometric quantities were slowly added with stirring. The
obtained suspension was heated to ca. 40°C for 1 h. Then the warm mixture was
filtered off. The after day the crystalline product was separated, washed with water
and dried at room temperature.
Preparation of Co(II) and Ni(II) bipyridine-lactato complexes
4
4
6
,4’-Bipyridine complexes of Co(II) and Ni(II) were obtained by mixing 6 mmol of
3
-bpy (in 23.4 cm of 96% v/v ethanol) with solutions of metal(II) lactates (3 mmol in
3
.6 cm of water). 2,4’-Bipyridine complexes of Co(II) and Ni(II) were prepared by
J. Therm. Anal. Cal., 78, 2004

CZAKIS-SULIKOWSKA et al.: BIPYRIDINE-LACTATO COMPLEXES
463
3
adding 6 mmol of 2,4’-bpy (in 10 cm of water with 0.2 cm 96% v/v ethanol) to solu-
3
3
tion of metal(II) lactates (3 mmol in 10 cm of water). During the synthesis of all
complexes the reaction mixtures were stirred and heated to ca. 40°C for 15 min. After
several days solid products were formed and filtered off. They were washed
with 40% v/v ethanol (or water for 2,4’-bpy complexes) and then with ethanol and di-
ethyl ether mixture (1:1) and dried at room temperature.
The Co(II) and Ni(II) analyses in obtained compounds were carried out by
complexometric titration with EDTA. The contents of C, H and N were determined
by elemental analysis with V O as oxidizing agent.
2 5
Results and discussion
The empirical formulae of the isolated compounds, analytical results and molar
conductivities are collected in Table 1. All the complexes are small crystalline solids
and air stable. They are fairly soluble in water but insoluble in common organic
solvents (e.g. CCl , CHCl ). The molar conductivity values in MeOH, DMSO and
4
3
DMF (Table 1) show that all complexes behave as non-electrolytes [18], indicating
probably coordination of the lactato ligands to metal(II).
M
Table 1 Analytical data and molar conductivity (Λ ) in MeOH, DMSO and DMF
–
c=1·10 mol dm at 25°C)
3
–3
(
–
1
2
/Ω cm mol
–1
Analysis found (calculated)/%
Λ
M
Complex
(colour)
M
C
N
H
MeOH DMSO DMF
(
(
1) Co(lact)
pink)
2
·2H
2
O
21.39
29.93
5.82
(5.95)
24.2
18.8
22.7
23.2
15.2
18.2
7.2
5.7
*
(21.57) (30.40)
21.52 25.37
(20.18) (24.77)
14.17 48.06
(14.99) (48.87)
10.90 56.51
(10.73) (56.86) (10.19) (4.77)
14.16 45.41 6.25 5.09
(13.68) (44.79) (6.53) (5.17)
11.19 57.32 9.99 4.82
(
(
2) Ni(lact)
light green)
2
·3H
2
O
5.40
(5.54)
*
(
(
3) Co(4-bpy)(lact)
light pink)
2
7.52
4.48
(7.12) (4.61)
*
28.1
22.7
22.2
21.7
(
(
2 2
4) Co(2,4’-bpy) (lact)
light pink)
10.29 4.80
11.6
11.9
13.1
(
(
2 2
5) Ni(4-bpy)(lact) ·2H O
light green-blue)
(
(
6) Ni(2,4’-bpy)
light green-blue)
2 2
(lact)
(10.69) (56.86) (10.20) (4.77)
–
solubility less than 1·10 mol dm
3
–3
*
Thermal properties of compounds
The thermoanalytical data are given in Table 2. The results of thermal, chemical and
X-ray analyses were used to postulate decomposition of the complexes. The thermal
profiles (TG, DTA and DTG) of some complexes are presented in Figs 1 and 2. Thermal
J. Therm. Anal. Cal., 78, 2004

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64
CZAKIS-SULIKOWSKA et al.: BIPYRIDINE-LACTATO COMPLEXES
J. Therm. Anal. Cal., 78, 2004

CZAKIS-SULIKOWSKA et al.: BIPYRIDINE-LACTATO COMPLEXES
465
2 2 2
Fig. 1 Thermoanalytical curves for: a – Co(lact) ·2H O, b – Co(4-bpy)(lact) (mass sample 100 mg)
Fig. 2 Thermoanalytical curves for: a – Ni(lact)
mass sample 100 mg)
2 2 2 2
·3H O, b – Ni(4-bpy)(lact) ·2H O
(
J. Therm. Anal. Cal., 78, 2004

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66
CZAKIS-SULIKOWSKA et al.: BIPYRIDINE-LACTATO COMPLEXES
decomposition of Co(lact) ·2H O and Ni(lact) ·3H O proceeds in three stages. The
2
2
2
2
Co(lact) ·2H O is stable up to 120°C and then lost water in one step. In contrast to Co(II)
2
2
lactate, Ni(II) lactate is thermally less stable. For Ni(lact) ·3H O the elimination of water
2
2
begins at 50°C. According to the DTG curve, molecules of water are lost stepwise in two
stages. Dehydration process of these lactates is connected with endothermic effects
at 160 and 100°C, 180°C for Co(II) and Ni(II), respectively. Anhydrous compounds
undergo decomposition to appropriate metal oxides. The DTA curves exhibit several
exothermic peaks, which are associated with oxidation of organic fragments. The mass
loss observed on the TG curves corresponds to the formation of Co O and NiO at 520
3 4
o
and 530°C, respectively. The small endothermic peak at 930 C is accompanied with the
transformation of Co O to CoO.
3
4
The thermal decompositions of the complexes Co(4-bpy)(lact)2,
Co(2,4’-bpy) (lact) are similar. In the first step (ca. 120–450°C) the TG curves show a
2
2
very rapid mass loss, which is connected with decomposition of organic ligands and the
formation of Co O . X-ray diffractogram of Co(4-bpy)(lact) sintered at 450°C indicates
presence of Co O (Fig. 3a). Very strong and broad exothermic peaks originating from
3
4
2
3
4
decomposition and oxidation of organic fragments are observed (Table 2). Apparently in
the case of Co(2,4’-bpy) (lact) nature of DTG change shows the stepwise decomposi-
tion. However, these processes are not detected on the TG curve. Above 900°C, Co O is
2
2
3
4
very slowly converted into CoO (Fig. 3b). This transformation is demonstrated by small
endothermic peak at 930°C for both bipyridine-lactato complexes of Co(II).
The pyrolysis of Ni(4-bpy)(lact) ·2H O runs in two steps. The complex is stable
2
2
up to 70°C, then whole water is eliminated. Dehydration process is characterized by
small endothermic effect at 180°C. Next, the decomposition of Ni(4-bpy)(lact)2
begins at 240°C and is represented in the DTA curve by two broad exothermic peaks
with maximum at 310, 440°C. Pure NiO is the final product of decomposition.
The complex Ni(2,4’-bpy) (lact) is more stable than Ni(4-bpy)(lact) ·2H O. It
2
2
2
2
starts to decompose at 140°C. In the temperature range 140–330°C, sudden loss of
mass occurs on the TG curve. This decrease in mass is connected with sharp DTG
peak and exoeffect observed in the DTA curve. The X-ray diffractometric analysis
indicates a mixture of organic fragments and NiO in the sinter of Ni(2,4’-bpy) (lact)
2 2
heated up to 330°C (Fig. 4). A strong exothermic peak at 440°C in the DTA curve is
associated with combustion of the remaining organic products. A constant mass level
for pure NiO begins at 480°C.
TG-MS measurements
Thermal behaviours of complexes also were carried out with a coupled TG-MS
system.This method was used to analyse of major gaseous products evolved during
the dynamic thermal decomposition and fragmentation processes of investigated
1
12
14
16
complexes in air atmosphere. The m/z values are given based on: H, C, N and O
(
1
additionally C and O in the case of CO ).
3
18
2
MS data for all the complexes detected several profiles of ion current. As an ex-
ample, Fig. 5 shows these lines for some m/z detected in mass spectrometer as a func-
J. Therm. Anal. Cal., 78, 2004

CZAKIS-SULIKOWSKA et al.: BIPYRIDINE-LACTATO COMPLEXES
467
2
Fig. 3 X-ray diffractograms of Co(4-bpy)(lact) sintered at: a – 450°C; b – 900°C
2 2
Fig. 4 X-ray diffractogram of Ni(2,4’-bpy) (lact) sintered at 330°C
J. Therm. Anal. Cal., 78, 2004

4
68
CZAKIS-SULIKOWSKA et al.: BIPYRIDINE-LACTATO COMPLEXES
Fig. 5 Ion current detected in the mass spectrometer vs. time for Ni(lact)
Curves for m/z: 1 – 12; 2 – 15; 3 – 17; 4 – 18; 5 – 32; 6 – 44; 7 – 45; 8 – 46;
– 60 (mass sample 6.41 mg)
2 2
·3H O.
9
tion of time for Ni(lact) ·3H O. The ion signals of Co(lact) ·2H O and Ni(lact) ·3H O
2
2
2
2
2
2
are very similar. In the case of Co(II) lactate the profils of ion signals are broad. The
+
first peaks of ion current for H O and OH (m/z=18 and 17) appear at 184 and 177°C
+
2
for Co(II) and Ni(II) lactates, respectively. They correspond to elimination of crystal-
line water. Major maxima of ion current are observed in range ca. 280–380°C for
compounds (1) and 330–370°C for (2). In gaseous pyrolysis products dominate the
+
molecular ion CO formed probably by total decomposition of lactate groups. MS
+
2
+
peaks with m/z=44 (CO ) and low intensity signals for m/z=45, 46 (CO containing
2
2
1
isotope C or O) appear at 321°C (1) and 354°C (2). The second peaks of H O and
3
18
+
2
+
OH (which are also produced during decomposition of lactates) exist at 322°C (1)
and 357°C (2). Additionally low intensities for ion currents with m/z=1, 12, 15, 26,
2
+
9 and 60 (H , C , CH ,C H ,C H and C H O traces) were monitored. The max-
+
+
+
+
+
3 2 2 2 5 2 4 2
ima of ion signals are coincided with mass loss occurred on TG curves. Correlation of
selected ion currents and TG curve is presented in Fig. 6 for Co(lact) ·2H O.
2
2
Figures 7a and 7b show the some profiles of ion current detected in mass spec-
trometer as a function of time for bipyridine-lactato complexes of Co(II). For com-
plexes Co(4-bpy)(lact) , Ni(4-bpy)(lact) ·2H O and Ni(2,4’-bpy) (lact) main MS
2
2
2
2
2
peaks occur in following range of temperature ca.: 270–320, 260–310 and 290–340°C,
respectively. However, all maxima of ion current for Co(2,4’-bpy) (lact) are observed
at ca. 210°C and in range 340–370°C. In the case of complexes Ni(4-bpy)(lact) ·2H O
2
2
2
2
+
+
the first signals for m/z=18 and 17 (H O and OH ) appear at ca. 170°C. They are coin-
2
cided with elimination of coordination (or crystalline) water. MS data for all
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CZAKIS-SULIKOWSKA et al.: BIPYRIDINE-LACTATO COMPLEXES
469
Fig. 6 TG curve and ion current detected in the mass spectrometer for Co(lact)
Curves for m/z: 1 – 15; 2 – 18; 3 – 44 with sensitivity of ion current: E-11,
2
·2H
2
O.
E-10, E-10 A, respectively (mass sample 10.46 mg)
Fig. 7 Ion current detected in the mass spectrometer vs. time for a – Co(4-bpy)(lact)
and b – Co(2,4’-bpy) (lact) . Curves for m/z: 1 – 12; 2 – 15; 3 – 17; 4 – 18;
– 30; 6 – 32; 7 – 44; 8 – 45 (mass sample 9.25 and 8.03 mg for
2
2
2
5
2 2 2
Co(4-bpy)(lact) and Co(2,4’-bpy) (lact) , respectively)
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4
70
CZAKIS-SULIKOWSKA et al.: BIPYRIDINE-LACTATO COMPLEXES
bipyridine-lactato complexes of Co(II) and Ni(II) indicate that in gaseous pyrolysis
+
+
products dominate the molecular ions CO , H O and OH as consequence of decom-
+
2
2
+
position of organic ligands. Very strong CO peaks (m/z=44) occur at ca. 294°C (3),
2
210 and 359°C (4), 275°C (5) and 327°C (6). At the same time low intensity ion cur-
rents are observed forCO (m/z=45, 46). The peaks for m/z=18 and 17 (H O and OH )
appear at ca.: 300°C (3), 215 and 363°C (4), 272 and 290°C (5) and 300°C (6). The ion
+
+
+
2
2
+
+
+
+
+
+
+
for m/z=1, 12, 15, 26, 29 (H , C , CH , C H or CN , C H or CHO ) at ca.
3
2
2
2
5
270–290°C (3), 211 and 340–360°C (4), 270–290°C (5) and 320–325°C (6) were de-
tected. The fragments with m/z=30 (correspond probably to CH O or NO ) occur at
+
+
2
297°C (3), 211 and 360°C (4), 267 and 306°C (5) and 329°C (6). The identification of
volatile species in appropriate temperature range corresponds exactly to the sudden
mass loss presented by TG curve. Figure 8 shows correlation of some profiles of ion
current with TG curve for Ni(4-bpy)(lact) ·2H O.
2 2
Fig. 8 TG curve and ion current detected in the mass spectrometer for
Ni(4-bpy)(lact) ·2H O. Curves for m/z: 1 – 15; 2 – 18; 3 – 44 with sensitivity of
ion current: E-11, E-10, E-10 A, respectively (mass sample 8.56 mg)
2
2
Conclusions
Thermal decomposition of investigated hydrated compounds begins with the release of
water. Generally anhydrous Co(II) and Ni(II) lactates are thermally more stable than
corresponding bipyridine-lactato complexes. All the compounds decompose to oxides
NiO and CoO, respectively (for Co(II) complexes via Co O ). As it is seen from data
3
4
obtained by coupled TG-MS system, major volatile species evolved during pyrolysis
of Co(II) and Ni(II) lactates and as well as bipyridine-lactato complexes of these met-
als(II) are produced almost simultaneously. It suggests that steps of decomposition
of these compounds are very weakly separated one from another (except dehydration).
In bipyridine-lactato complexes elimination and pyrolysis of N-donor ligands (4-bpy or
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CZAKIS-SULIKOWSKA et al.: BIPYRIDINE-LACTATO COMPLEXES
471
2,4’-bpy) and lactates probably take place at the same time (maxima of ion current for
CN , NO andCO appear at very similar temperature). These results are in agreement
+
+
+
2
with thermal behaviour of complex Cu(2-bpy)(lact) ·2H O [11].
2
2
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