Solid-phase thermal decomposition of polynuclear nickel(II) and cobalt(II) complexes

Article abstract of DOI:10.1007/s11172-006-0246-7

Solid-phase thermal decomposition of polynuclear Ni^II and Co^II pivalate complexes was studied by differential scanning calorimetry and thermogravimetry. The decomposition of the polynuclear (from bi-to hexanuclear) Co^II carboxylate complexes is accompanied by aggregation to form a volatile octanuclear complex. Thermolysis of the polynuclear NiII carboxylates results in their destructure, and the phase composition of the decomposition products is determined by the nature of coordinated ligands.

Full text of DOI:10.1007/s11172-006-0246-7

Russian Chemical Bulletin, International Edition, Vol. 55, No. 2, pp. 256—266, February, 2006
256
Solidꢀphase thermal decomposition of polynuclear nickel(II)
and cobalt(II) complexes
Zh. V. Dobrokhotova,ꢀ I. G. Fomina, M. A. Kiskin, A. A. Sidorov, V. M. Novotortsev, and I. L. Eremenko
N. S. Kurnakov Institute of General and Inorganic Chemistry, Russian Academy of Sciences,
31 Leninsky prosp., 119991 Moscow, Russian Federation.
Fax: +7 (495) 954 1279. Eꢀmail: ilerem@igic.ras.ru
Solidꢀphase thermal decomposition of polynuclear NiII and CoII pivalate complexes was
studied by differential scanning calorimetry and thermogravimetry. The decomposition of the
polynuclear (from biꢀ to hexanuclear) CoII carboxylate complexes is accompanied by aggregaꢀ
tion to form a volatile octanuclear complex. Thermolysis of the polynuclear NiII carboxylates
results in their destructure, and the phase composition of the decomposition products is
determined by the nature of coordinated ligands.
Key words: polynuclear complexes, cobalt and nickel complexes, carboxylate ligands,
thermal decomposition.
Metal carboxylates represent a vast class of coordinaꢀ
tion compounds. Wide abilities of structural functions of
acid residues provide diverse structures of the carboxylate
complexes. It seems important to study solidꢀphase therꢀ
molysis of transition metal carboxylates for the developꢀ
ment of systems for controlling thermal processes of meꢀ
tallic core modification, preparation of thin films and
coatings with unusual electrophysical properties, and synꢀ
thesis of new polymeric organic or inorganic materials.
In the present work, we studied the solidꢀphase therꢀ
mal decomposition of a series of structurally characterꢀ
ized polynuclear NiII and CoII carboxylates (pivalates) by
differential scanning calorimetry (DSC) and thermoꢀ
gravimetry.
Results and Discussion
According to the Xꢀray diffraction data, biꢀ
nuclear nickel and cobalt complexes Ni2(µꢀ
H2O)(µꢀOOCBut)2(OOCBut)2(Py)4 (1), Ni2(µꢀH2O)(µꢀ
OOCBut)2(OOCBut)2(bipy)2 (2), Ni2(µꢀH2O)(µꢀ
OOCBut)2(OOCBut)2(HOOCBut)4 (3), Co2(µꢀH2O)(µꢀ
OOCBut)2(OOCBut)2(bipy)2 (4), and Co2(µꢀH2O)(µꢀ
OOCBut)2(OOCBut)2(HOOCBut)4 (5)1—4 in the crystalꢀ
line state are characterized by an important feature: the
hydrogen atoms of the bridging water molecule form inꢀ
tramolecular hydrogen bonds with the oxygen atoms of
the terminal carboxylate groups.
Compounds 1—5 decompose in steps (Figs 1 and 2).
For compound 1, this process starts above 70 °C. In the
first step (70—130 °C), 19.0 2.0% weight is lost (content
of two moles of pyridine in compound 1 is 18.45%). Probꢀ
M = Ni (2, 3), Co (4, 5)
ably, this process corresponds to the H bond cleavage, the
removal of two moles of pyridine, and an increase in the
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 250—260, February, 2006.
1066ꢀ5285/06/5502ꢀ0256 © 2006 Springer Science+Business Media, Inc.

Thermal decomposition of NiII and CoII complexes Russ.Chem.Bull., Int.Ed., Vol. 55, No. 2, February, 2006
257
m/mg
m/mg
5.5
a
b
12
11
10
9
5.0
4.5
4.0
3.5
3.0
8
100
200
300 T/°C
100
200
300 T/°C
m/mg
8
6
4
2
m/mg
3.5
3.0
2.5
2.0
1.5
c
d
0
100
200
300
T/°C
60
110
160
210
T/°C
m/mg
e
6
4
2
50
100
150
200
250
T/°C
Fig. 1. Temperature dependences of the weight change for complexes 1 (a), 2 (b), 3 (c), 4 (d), and 5 (e).
dentation of the remaining Oꢀdonor ligands (water and
carboxylate groups). An intermediate that formed is therꢀ
mally stable below 170 °C. In the 170—202 °C interval,
the energy absorption (∆H = 20.2 2.0 kJ mol–1) is acꢀ
companied by the 2.0 0.7% weight loss. This process
(according to the results of studying the thermolysis of
compound 1 in solution5) corresponds to the removal of
the bridging water and formation of the lantern tetraꢀ

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Russ.Chem.Bull., Int.Ed., Vol. 55, No. 2, February, 2006
Dobrokhotova et al.
Q/mW
Q/mW
0
a
b
0.5
–0.5
–1.5
–2.5
–3.5
–1
–2
–3
–4
–5
100
200
300 T/°C
100
200
300 T/°C
Q/mW
Q/mW
c
d
0
–2
–1
–3
–5
–7
–4
–6
–8
–10
–12
–14
100
200
300 T/°C
Q/mW
50
150
250 T/°C
–2
–4
e
–6
–8
–10
–12
50
100
150 T/°C
Fig. 2. Temperature dependences of the change in the heat flow for complexes 1 (a), 2 (b), 3 (c), 4 (d), and 5 (e).
carboxylate complex Ni2(µꢀOOCBut)4(Py)2. In the
206—265 °C temperature interval, an additional weight
loss is 18.0 2.0% with energy absorption (∆H = 126.2 6.8
kJ mol–1). As a result, the formally possible decompoꢀ
sition product formed on heating of 1 to 260 °C is
Ni(OOCBut)2.
Dipyridyl complex 2 begins to decompose at a higher
temperature than 1 because of a different spatial arrangeꢀ
ment of the ligands3 and a much higher boiling point of
the coordinated Nꢀdonor ligand (b.p. of pyridine is
115.5 °C, while b.p. of 2,2´ꢀdipyridyl is 273.7 °C). This
specific feature of compound 2 allowed one the experiꢀ

Thermal decomposition of NiII and CoII complexes Russ.Chem.Bull., Int.Ed., Vol. 55, No. 2, February, 2006
259
Table 1. Temperature dependences of the heat capacity for
pivalic acid and intermediate decomposition products of comꢀ
pounds 1 and 2
mental observation of the cleavage of intramolecular
H bonds in a temperature interval of 56—86 °C with enꢀ
ergy absorption (∆H = 18.0 2.2 kJ mol–1). This process
occurs without changing the sample weight. On heating
in the 100—150 °C interval, the weight loss is 2.2 1.0%
with energy absorption (∆H = 74.5 5.5 kJ mol–1). Probꢀ
ably, as for compound 1, in this temperature range the
bridging water is removed along with the formation of the
mononuclear bipyNi(OOCBut)2 complex containing two
chelated pivalate groups in two independent molecules.5
The resulting product is thermally stable below 260 °C,
whereas an additional weight loss of 34.0 2.0% is obꢀ
served in the 270—300 °C interval along with energy abꢀ
sorption (∆H = 168.6 3.5 kJ mol–1). The amount of the
removed products and the heat effect value (for compariꢀ
son, ∆Hvap(bipy) = 81.9 kJ mol–1) suggest that two moles
of dipyridyl are removed. Probably, the product obtained
below 310 °C has a composition of Ni(OOCBut)2. To
identify the assumed intermediate decomposition prodꢀ
ucts (compound 1 below 260 °C and compound 2 below
310 °C), we measured their heat capacities by differential
scanning calorimetry. The heat capacity of pivalic acid
was measured to confirm reliability of the results (Fig. 3,
Table 1).
T/°C
Cр( 2%)/J mol–1 K–1
Pivalic acid*
Decomposition products
of compounds
I
II
1
2
8
184.37
185.28
189.85
194.40
196.70
204.17
208.53
212.89
217.25
221.61
225.97
230.33
234.67
239.05
185.5
187.0
193.2
223.7
245.8
213.2
209.0
211.3
219.1
222.7
226.4
229.1
235.9
240.0
—
—
10
20
30
35
40
50
60
70
80
90
100
110
120
387.5
396.0
399.3
—
409.2
415.8
422.9
432.6
439.5
448.2
453.0
461.5
470.9
388.5
394.3
401.9
—
407.4
414.6
424.1
430.9
438.2
446.5
453.7
460.4
468.9
* I indicate data in Ref. 6, II are data of the present work.
Our results for pivalic acid agree satisfactorily with
published data,6 and the anomaly found in the temperaꢀ
ture plot of the heat capacity corresponds to the melting
of pivalic acid.6
Compound 3 decomposes similarly to the thermolysis
of compound 1, but decomposition starts at a higher temꢀ
perature. In the 105—176 °C interval, 21.7 1.0% weight
is lost with energy absorption, which corresponds, most
likely, to the removal of two moles of pivalic acid.
The shape of the first endothermic peak suggests that
the decomposition process is preceded by the H bond
cleavage.
The weight loss in temperature interval of
a
176—183 °C is 1.9 0.7%. Probably, this is the removal of
the bridging water molecule to form a relatively stable
intermediate, which additionally loses 23.6 1.5% weight
on further heating. The total weight loss below 237 °C is
47.2 1.5%, which corresponds to the content of the bridgꢀ
ing water and coordinated pivalic acid. We failed to terꢀ
minate the decomposition of compound 3 at the step of
formation of the assumed Ni(OOCBut)2 compound. On
further heating to 360 °C, the product obtained below
237 °C loses additionally 37.8 1.0%. The processes that
occur in an interval of 237—360 °C are accompanied by
complicated energy changes. The total heat effect is posiꢀ
tive, which is probably caused by prevailing of the energy
changes associated with the formation of a new structure.
The total weight loss in the 25—450 °C interval is
85.0 1.5%. The weight fraction of the solid residue is
15.0 1.5%. According to the Xꢀray diffraction data for
compounds 1—3, the final decomposition product is
nickel(II) oxide.
Compounds 4 and 5 decompose via a mechanism that
differs from that for the decomposition of complexes 1—3.
For both compounds, decomposition starts above 65 °C.
Compound 4 loses 3.0 1.0% weight in the 70—130 °C
range with energy absorption (∆H = 94.0 3.0 kJ mol–1).
Probably, in this temperature interval, H bonds are
cleaved, the bridging water is removed, and, according to
the results of studying the thermolysis of this compound
in toluene,4 a binuclear carboxylateꢀbridged complex is
formed. The obtained product is thermally stable below
Cp/J mol–1 K–1
250
220
190
20
40
60
80
100
T/°C
Fig. 3. Temperature dependence of the heat capacity for pivalic
acid (our data are given by points, and the data of Ref. 6 are
shown by solid line).

260
Russ.Chem.Bull., Int.Ed., Vol. 55, No. 2, February, 2006
Dobrokhotova et al.
180 °C. In the 180—210 °C interval, compound 4 loses
22.3 1.0% weight with energy absorption (∆H =
134.6 4.5 kJ mol–1). Above 243 °C, the product that
formed begins to evaporate intensely, and its complete
evaporation is observed below 280 °C.
phase, undergo aggregation to form octanuclear volatile
complexes similar to cluster 6.
A possibility of aggregation during thermal decompoꢀ
sition in the solid phase can be confirmed by the results of
studying the solidꢀphase thermal decomposition of the
tetranuclear complex Co4(µ3ꢀOH)2(µ2ꢀOOCBut)4(η2ꢀ
OOCBut)2(HOEt)6 (7), whose structure has been deꢀ
scribed earlier.8
Compound 5 decomposes in two steps in an interval
of 65—130 °C. In the first step (below 74 °C), 2.3 1.0%
weight is lost, being, probably, the bridging water. The
weight loss in the whole temperature interval is 44.9 1.0%,
which is accompanied by a considerable endothermic efꢀ
fect with a complicated shape (345 8 kJ mol–1). It seems
unreasonable to integrate separately the heat effect in the
70—135 °C temperature interval, because the result obꢀ
tained is ambiguous and has a high error. The presented
value of the heat effect is comparable with the enthalpy of
evaporation of one mole of water and four moles of pivalic
acid. No weight loss was observed in the 140—200 °C
temperature range but the energy was absorbed, which
indicates, possibly, substantial structural changes. The
bright violet product formed on heating to 200 °C is subꢀ
limed with further heating.
After we studied the solidꢀphase thermal decomꢀ
position of the octanuclear complex Co8(µ4ꢀO)2(µ2ꢀ
OOCBut)6(µ3ꢀOOCBut)6 (6), whose structure is deꢀ
scribed in Ref. 7, we could reveal a possible reason for the
sublimation of the decomposition products of comꢀ
plexes 4 and 5.
This compound also decomposes in steps (see Fig. 4).
The first step (50—85 °C) proceeds with the 8.5 0.5%
weight loss and an energy absorption of 92.0 2.5 kJ mol–1
,
which is comparable with the enthalpy of evaporation of
two moles of alcohol. The second step (85—115 °C) is
accompanied by a weight loss of 15.7 1.0% and energy
absorption as well. Finally, 2.0 1.0% weight is additionꢀ
ally lost in an interval of 120—170 °C. The results suggest
that the decomposition product is the octanuclear comꢀ
plex Co8(µ4ꢀO)2(µ2ꢀOOCBut)6(µ3ꢀOOCBut)6 (6). In a
decalin solution at 170 °C, complex 7 is transformed into
octanuclear cluster 6 in high yield.8
One more confirmation of aggregation upon the therꢀ
mal decomposition of the cobalt pivalate complexes
in the solid phase can be the results of studies of the
thermal decomposition of the hexanuclear complexes
(see Fig. 4) Co6(µ4ꢀO)2(OOCBut)10(thf)4 (8) and
Co6(µ4ꢀO)2(OOCBut)10(HOOCBut)4 (9), whose structure
were described in Refs 9 and 10, respectively.
Compound 8 begins to decompose above 70 °C (boilꢀ
ing point of THF is 66 °C). The first step of decomposiꢀ
tion (70—145 °C) is accompanied by energy absorption
(135 3.0 kJ mol–1) (enthalpy of THF evaporation is
32.0 kJ mol–1), the weight loss being 18.0 1.0% (content
of THF is 17.1%). Thus, the coordinated tetrahydrofuran
is removed in the first step. The second step of decompoꢀ
sition (175—210 °C) starts above 175 °C with a weight
loss of 7.5 1.0% and is accompanied by an energy abꢀ
sorption of 59.2 2.5 kJ mol–1. However, it should be menꢀ
tioned that a change in the heat flow in the temperature
interval is nonmonotonic (combination of endothermic
and exothermic peaks in the thermogram). The bright
violet product that formed is sublimed above 210 °C.
Compound 6 is thermally stable below 130 °C (Fig. 4).
Evaporation begins above 130 °C, and 1% weight per
10 °C is lost at a heating rate of 5 deg min–1 in the
130—230 °C interval. The evaporation intensity increases
above 230 °C, and 240.0 3.0 °C can be assumed to be the
equilibrium temperature of evaporation. Thus, cluster 6
has a high vapor pressure and is sublimed without decomꢀ
position.
The results obtained suggest that in the last step of
decomposition of compounds 4 and 5 the fragments,
which appear upon thermal decomposition in the solid

Thermal decomposition of NiII and CoII complexes Russ.Chem.Bull., Int.Ed., Vol. 55, No. 2, February, 2006
261
m/mg
Q/mW
0
2.0
a
e
1.5
1.0
0.5
–1
–2
–3
100
200
300 T/°C
100
200
300 T/°C
m/mg
Q/mW
6.5
5.5
4.5
3.5
2.5
1.5
b
f
–1
–3
–5
–7
–9
100
200
300 T/°C
100
200
300 T/°C
Q/mW
m/mg
2.5
2.0
1.5
1.0
0.5
1.0
0.5
c
g
0
–0.5
–1.0
100
200
300 T/°C
100
200 T/°C
m/mg
Q/mW
4
3
2
1
–1
–2
–3
–4
–5
–6
d
h
100
200
300 T/°C
100
200 T/°C
Fig. 4. Temperature dependences of the weight change (a—d) and heat flow (e—h) for complexes 6 (a, e), 7 (b, f ), 8 (c, g), and 9 (d, h).
Compound 9 begins to decompose above 100 °C. The
weight loss in the first step (100—180 °C) is 23.0 1.0%
(content of pivalic acid is 22.6%). The weight loss in the
second step (185—210 °C) is 6.0 1.0%. Both steps are
accompanied by energy absorption but we cannot sepaꢀ
rate the heat effects. The total heat effect is 352.5 3.5
kJ mol–1. When assuming that pivalic acid, whose evapoꢀ
ration enthalpy is 73.2 kJ mol–1, is removed in the first
step and the heat effect of this step almost corresponds to
the enthalpy of its evaporation (which can be considered
acceptable), then the heat effect of the second step is
59.7 4.0 kJ mol–1. It is seen that the heat effects accomꢀ
panying the transformations of compounds 8 and 9 in the
second step are comparable. The bright violet decompoꢀ
sition product begins to sublime above 210 °C.
To identify aggregation products formed upon the
solidꢀphase thermal decomposition of complexes 7—9,
we measured the specific heat capacity in the 10—120 °C
interval for complex 6 and the intermediate thermolysis
products of complexes 7—9 (Table 2).
Due to quantitative results of the thermogravimetric
study of the thermal decomposition of complexes 7—9
and equal heat capacities of complex 6 and products
formed upon thermolysis of complexes 7—9, we can asꢀ

262
Russ.Chem.Bull., Int.Ed., Vol. 55, No. 2, February, 2006
Dobrokhotova et al.
carboxylate complexes with different number of metal
atoms in the 170—210 °C temperature range.
A possibility of formation of a stable heteronuclear
pivalate cluster Co6Ni2(µ4ꢀO)2(µ2ꢀOOCBut)6(µ3ꢀ
OOCBut)6 (10) with the nickel and cobalt atoms, which is
isostructural to cobalt complex 6, was shown in Ref. 11.
M = Co, Ni
It was of interest to compare the mechanism of the
solidꢀphase thermal decomposition of the octanuclear
homometallic and heterometallic clusters. Compound 10
is thermally stable up to 165 °C (Fig. 5) (homometallic
complex 6, up to 130 °C). In the 170—350 °C temperaꢀ
ture range, the weight decreases stepwise with energy abꢀ
sorption (endothermic peak of a complicated shape). The
total weight loss is 65.2 2.0%. A considerable amount of
energy is released above 340 °C without a weight change,
which is usually caused by energy changes related to the
formation of a new structure. The Xꢀray diffraction analyꢀ
sis of the decomposition product showed the presence of
cobalt and nickel oxides (Table 3).
sert the occurrence of aggregation to form an octanuclear
metallic cage upon the thermal decomposition of the CoII
The behavior of 6 and 10 differs, probably, because an
unstable nickelꢀcontaining octanuclear analog of comꢀ
pound 6 cannot form. Complex 6 contains cobalt atoms
with different environments of oxygen atoms (two metal
atoms in the tetrahedral environment, and the other six
atoms are in a distorted trigonal bipyramidal environꢀ
ment). Unlike the cobalt(II) carboxylate derivatives, the
known nickel pivalates contain metal atoms in the octaꢀ
hedral environment only.
Table 2. Temperature dependences of the specific heat capacity
for complex 6 and decomposition products of complexes 7—9
T/°C
Cp( 3%)/J K–1 g–1
Complex
Decomposition products of complexes
6
7
8
9
10
20
30
40
50
60
70
80
1.550
1.578
1.613
1.629
1.650
1.683
1.711
1.746
1.781
1.809
1.837
1.865
1.523
1.575
1.625
1.631
1.664
1.690
1.705
1.738
1.796
1.800
1.845
1.870
1.534
1.569
1.610
1.628
1.669
1.692
1.726
1.752
1.788
1.819
1.851
1.877
1.559
1.580
1.617
1.638
1.671
1.697
1.718
1.759
1.771
1.793
1.840
1.881
Table 3. Xꢀray diffraction identification of the decomposition
products of complex 10
Decomposition products of 10
CoO
NiO
d/Å
I (%)
d/Å
4.4602
I (%)
d/Å I (%)
90
2.4721
2.4254
2.1403
2.0915
50
15
100
40
65
100
110
120
2.412 60
2.089 100
2.1307 100

Thermal decomposition of NiII and CoII complexes Russ.Chem.Bull., Int.Ed., Vol. 55, No. 2, February, 2006
263
m/mg
Q/mW
2.0
4
a
f
1.6
1.2
0.8
2
0
–2
100
200
300
T/°C
T/°C
T/°C
100
200
300
T/°C
m/mg
m/mg
m/mg
m/mg
Q/mW
9
7
5
3
b
g
15
10
5
0
100
200
300
100
200
300
T/°C
Q/mW
5
4
3
2
c
h
1
0
–1
–2
100
100
100
200
300
400
100
200
300
400 T/°C
400 T/°C
400 T/°C
Q/mW
d
i
4
5
4
3
2
1
0
–4
–8
200
300
400 T/°C
100
200
300
Q/mW
7.8
5.8
3.8
e
j
0.5
0
–0.5
–1.0
200
300
T/°C
100
200
300
Fig. 5. Temperature dependences of the changes in the weight (a—e) and heat flow ( f—l) for complexes 10 (a, f ), 11 (b, g), 12 (c, h),
13 (d, i), and 15 (e, j).

264
Russ.Chem.Bull., Int.Ed., Vol. 55, No. 2, February, 2006
Dobrokhotova et al.
As shown above, the solidꢀphase thermal decomposiꢀ
compensation of the pivalate and hydroxyl anions.8
This process was also studied for the Ni4(µ3ꢀOH)2(µꢀ
OOCBut)6(HOOCBut)4(PhꢀNH2)2•2HOOCBut complex
(13) containing the Ni4(µ3ꢀOH)2(µ2ꢀOOCBut)4 fragment
as complex 11 with ethanol (see Fig. 5).
tion of tetranuclear complex 7 is accompanied by aggreꢀ
gation to form octanuclear complex 6. Therefore, it was
of interest to study the thermolysis of the complex Ni4(µ3ꢀ
OH)2(µꢀOOCBut)4(η2ꢀOOCBut)2(HOEt)6 (11), which is
isostructural to complex 7; its structure has been deterꢀ
mined earlier.8
We studied the thermal decomposition of the
Ni4[η2ꢀ{oꢀC6H4(NH2)(NHPh)}]2(µ3ꢀOH)2(MeCN)2(η2ꢀ
OOCBut)2(µꢀOOCBut)4 complex (12) analogous to
complex 11 and containing the same structural fragꢀ
ment Ni4(µ3ꢀOH)2(µꢀOOCBut)4(η2ꢀOOCBut)2 with
similar geometric characteristics and metal charge with
Complexes 11, 12, and 13 begin to decompose at temꢀ
peratures above 50, 80, and 100 °C, respectively. In the
case of compound 11, 25.0 1.5% weight is lost in the first
step of decomposition (55—155 °C) with energy release
(∆H = 262.7 4.8 kJ mol–1). Comparison of the ethanol
contents in a molecule of 11 (23.95%) and the enthalpies
of ethanol evaporation (∆Hvap = 42.3 kJ mol–1) with the
results obtained shows that the coordinated alcohol molꢀ
ecules are removed in this temperature interval. The first
step of thermal decomposition of complex 12 also conꢀ
sists of two steps: in an interval of 80—190 °C, coordiꢀ
nated acetonitrile is removed and 7.0 1.0% weight is lost
(acetonitrile content is 6.06%) with an energy absorption
of 70.7 2.5 kJ mol–1 (∆Hvap(MeCN) = 33.4 kJ mol–1).
Solvate pivalic acid is removed first during thermolysis
of complex 13. The process occurs in an interval of
100—165 °C (b.p. of HOOCBut is 163 °C), the weight loss
is 12.5 1.0% (solvate acid content is 12.2%), and the
amount of the absorbed energy equals 165.4 3.8 kJ mol–1
(∆Hvap(HOOCBut) = 73.2 kJ mol–1). In the 165—230 °C
temperature range, 25.6 2.0% weight is additionally lost
(content of coordinated acid is 24.35%) with an energy
absorption of 337.0 6.0 kJ mol–1. Intermediate products
obtained in the first step of decomposition of complexes
11—13 contain, probably, the Ni4(µ3ꢀOH)2(OOCBut)6
fragment and are stable to 290 5 °C. Above this temperaꢀ
ture, the weight decreases intensely: 48.2 2.0% (11),
71.7 2.5% (12), and 45.4 1.5% (13). In the case of comꢀ
pound 11, the process is accompanied by energy release,
while for complexes 12 and 13 energy changes are comꢀ
plicated, although their total heat effect is also negative.
The total weight loss in the whole temperature interval
under study (25—470 °C) is 73.2 2.0% (11), 78.7 2.5%
(12), and 83.5 2.0% (13). The Xꢀray diffraction analyꢀ
sis of the decomposition products (Table 4) showed the
presence of NiO (11) and a mixture of NiO and metalꢀ
lic Ni (12, 13).
Probably, the thermolysis of complexes 12 and 13 at
high temperatures after removal of coordinated acetoniꢀ
trile and pivalic acid molecules, under experimental conꢀ
ditions (dry argon atmosphere), results in innerꢀsphere
redox transformations involving the amineꢀcontaining
ligands and NiII and in the formation of products with a
high nickel content.
To reveal the effect of the nature of the metal core
on the phase composition of the solid decomposition
product, we compared the results of thermal decompoꢀ
sition of the tetranuclear isostructural complexes
M4(µ3ꢀOH)2(µꢀOOCBut)4(η2ꢀOOCBut)2(HOEt)6 (M =
Co (7), Ni (11), Fe (14)).12

Thermal decomposition of NiII and CoII complexes Russ.Chem.Bull., Int.Ed., Vol. 55, No. 2, February, 2006
Table 4. Xꢀray diffraction identification of the decomposition products of complexes 11—13 and 15
265
Decomposition products of complexes
12 13
NiO
Ni
11
15
d/Å
I (%)
d/Å
I (%)
d/Å
I (%)
d/Å
I (%)
d/Å
I (%)
d/Å
I (%)
2.4235
2.0921
60
100
2.4153
2.0902
2.0354
1.7598
45
65
100
25
2.4185
2.0907
2.0375
1.7602
40
70
100
20
2.4114
2.0846
50
100
2.412
2.089
60
100
2.034
1.762
100
40
Table 5. Xꢀray diffraction identification of the decomposition
products of complex 14
The decomposition of complexes 7 and 11 is described
above. The thermal decomposition of compound 14 starts
above 60 °C, coordinated ethanol molecules are removed
below 160 °C, and the weight loss is 22.0 1.5% (ethanol
content is 22.38%). The process is accompanied by enꢀ
ergy absorption. The enthalpy change in the 60—160 °C
range is 263.5 6.0 kJ mol–1. This value is comparable
with the enthalpy of evaporation of six moles of ethanol
(42.3×6 kJ mol–1). An energy release is observed above
160 °C without a noticeable weight change, which is usuꢀ
ally related to the formation of a new structure. The
intermediate product contains, probably, the Fe4(µ3ꢀ
OH)2(OOCBut)6 fragment and is stable up to 270 5 °C.
Above this temperature, the weight decreases considerꢀ
ably: 46.6 2.0% in the 270—450 °C temperature interval.
The thermal destruction is accompanied by energy reꢀ
lease. The total weight loss in the temperature interval
under study is 68.6 2.0%. The blackꢀcolored decomposiꢀ
tion product is pyrophoric. According to the Xꢀray difꢀ
fraction data (within an experimental error of 3%), this
is FeOx (Table 5). Thus, the character of decomposition
of the ironꢀcontaining and nickelꢀcontaining complexes
is identical.
Decomposition
FeO (cubic) Fe0.98O (hexagonal)
products of 14
d/Å
I (%)
d/Å
I (%)
d/Å
I (%)
2.5245
2.4864
2.3679
2.1578
2.0675
1.5247
1.5096
20
70
10
100
30
50
2.517
80
2.490
2.153
1.523
80
100
60
2.376
2.078
1.510
80
100
50
10
The decomposition starts above 100 °C. In the first
step, probably, coordinated pivalic acid is lost, and the
process is stepwise. Below 140 °C, the weight loss is
4.4 1.0%, and the absorbed energy is 80.5 2.5 kJ mol–1
.
Further, below 220 °C, 14.0 2.0% weight is lost and an
energy of 245.7 5.3 kJ mol–1 is absorbed. The values of
the weight percentage of volatiles and the heat effect valꢀ
ues are comparable with the calculated acid content and
its evaporation enthalpy. The energy is released below
290 5 °C without a noticeable weight change, which is
probably due to the formation of an intermediate identiꢀ
cal to the product formed upon thermolysis of complex 11
after removal of coordinated ethanol molecules. Above
300 °C, the character of decomposition of complexes 11
and 15 is the same. The decomposition product is nickel
oxide.
We also studied the thermal decomposition of the
nonanuclear
complex
Ni9(µ4ꢀOH)3(µ3ꢀOH)3(µ4ꢀ
OOCBut)(µ3ꢀOOCBut)3(µꢀOOCBut)8(HOOCBut)4 (15),
whose structure has been described earlier8,13 (see Fig. 5).
Thus, we showed that the decomposition of the polyꢀ
nuclear (from biꢀ to hexanuclear) CoII carboxylate comꢀ
plexes is accompanied by aggregation to form a volatile
octanuclear complex. By contrast, the thermolysis of the
polynuclear NiII carboxylates is destructive, and the phase
composition of their decomposition products is deterꢀ
mined by the nature of the coordinated ligands.
Experimental
The thermal decomposition of the complexes was studied by
differential scanning calorimetry and thermogravimetry analysis

266
Russ.Chem.Bull., Int.Ed., Vol. 55, No. 2, February, 2006
Dobrokhotova et al.
on DSCꢀ20 and TGꢀ50 moduli of a Mettler TAꢀ3000 thermal
analyzer. Samples were heated under dry argon with a rate of
5 deg min–1, which was the same in all experiments. For each
compound, four runs were carried out by differential scanning
calorimetry and three thermogravimetric experiments were conꢀ
ducted. The weight loss upon thermal destruction was deterꢀ
mined directly on a TGꢀ50 modulus, and the weighing accuracy
was 2•10–3 mg. The stepꢀbyꢀstep study of thermal decomposiꢀ
tion was carried out by differential scanning calorimetry with
partition of the whole temperature area under study into sepaꢀ
rate intervals. The value and number of these intervals were
determined after the total weight and energy changes upon deꢀ
composition have been found. This experimental procedure made
it possible to measure the weight loss in each temperature interꢀ
val and compare the DSC results with thermogravimetric data.
Satisfactory agreement of the results confirmed confidence and
reliability of the data obtained. The accuracy of determination
of anomalous points and heat effects in thermograms was 1°
and 0.5%, respectively.
2. M. O. Talismanova, A. A. Sidorov, V. M. Novotortsev, G. G.
Aleksandrov, S. E. Nefedov, I. L. Eremenko, and I. I.
Moiseev, Izv. Akad. Nauk, Ser. Khim., 2001, 2149 [Russ.
Chem. Bull., Int. Ed., 2001, 50, 2251].
3. A. A. Sidorov, S. A. Deomidov, S. E. Nefedov, I. G. Fomina,
P. V. Danilov, V. M. Novotortsev, O. G. Volkov, V. N.
Ikorskii, and I. L. Eremenko, Zh. Neorg. Khim., 1999, 44, 3
[Russ. J. Inorg. Chem., 1999, 44 (Engl. Transl.)].
4. T. B. Mikhailova, E. V. Pakhmutova, A. E. Malkov, I. F.
Golovaneva, A. A. Sidorov, I. G. Fomina, G. G.
Aleksandrov, V. N. Ikorskii, V. M. Novotortsev, I. L.
Eremenko, and I. I. Moiseev, Izv. Akad. Nauk, Ser. Khim.,
2003, 1994 [Russ. Chem. Bull., Int. Ed., 2003, 52, 2105].
5. I. L. Eremenko, S. E. Nefedov, A. A. Sidorov, M. A.
Golubnichaya, P. V. Danilov, V. N. Ikorskii, Yu. G.
Shvedenko, V. M. Novotortsev, and I. I. Moiseev, Inorg.
Chem., 1999, 38, 3764.
6. N. B. Singh and M. E. Glicksman, Thermochim. Acta, 1990,
159, 93.
To measure the heat capacity, we used a DSCꢀ30 modulus
of a TAꢀ4000 thermal analyzer. The latter is a differential caloꢀ
rimeter operating in the scan mode of the shell temperature and
designed for quantitative thermal measurements. The relative
error of heat capacity measurement was 2—3%. Heat capacities
of the well studied compounds were periodically determined to
estimate a possible systematic measurement error. For instance,
the deviation of the obtained values of the heat capacity of
corundum from the values presented by the U.S. National
Bureau of Standards (NBS) was 1—2%.
Xꢀray diffraction analysis of decomposition products was
carried out with a STOE Powder Diffraction System and an
FRꢀ552 monochromating chamber (CuꢀKα1 radiation) using
germanium as the internal standard (Xꢀray diffraction patterns
were processed on an IZAꢀ2 instrument with an accuracy
of 0.01 mm).
7. A. A. Sidorov, I. G. Fomina, G. G. Aleksandrov, M. O.
Ponina, S. E. Nefedov, I. L. Eremenko, and I. I. Moiseev,
Izv. Akad. Nauk, Ser. Khim., 2000, 960 [Russ. Chem. Bull.,
Int. Ed., 2000, 49, 958].
8. A. A. Sidorov, I. G. Fomina, S. S. Talismanov, G. G.
Aleksandrov, V. M. Novotortsev, S. E. Nefedov, and I. L.
Eremenko, Koord. Khim., 2001, 27, 584 [Russ. J. Coord.
Chem., 2001, 27 (Engl. Transl.)].
9. A. E. Malkov, T. B. Mikhailova, G. G. Aleksandrov, E. V.
Pakhmutova, I. M. Egorov, A. A. Sidorov, I. G. Fomina,
S. E. Nefedov, I. L. Eremenko, and I. I. Moiseev, Izv. Akad.
Nauk, Ser. Khim., 2001, 2370 [Russ. Chem. Bull., Int. Ed.,
2001, 50, 2485].
10. I. L. Eremenko, V. M. Novotortsev, A. A. Sidorov, and I. G.
Fomina, Ross. Khim. Zh., 2004, 48, 49 [Mendeleev Chem. J.,
2004, 48 (Engl. Transl.)].
11. I. G. Fomina, A. A. Sidorov, G. G. Aleksandrov, V. I. Zhilov,
V. N. Ikorskii, V. M. Novotortsev, and I. L. Eremenko, Izv.
Akad. Nauk, Ser. Khim., 2004, 112 [Russ. Chem. Bull., Int.
Ed., 2004, 53, 114].
12. I. L. Eremenko, M. A. Kiskin, I. G. Fomina, A. A. Sidorov,
G. G. Aleksandrov, V. N. Ikorskii, Yu. G. Shvedenkov, and
V. M. Novotortsev, J. Cluster Science, 2005, 16, 331.
13. M. A. Golubnichaya, A. A. Sidorov, I. G. Fomina, S. E.
Nefedov, and I. L. Eremenko, Izv. Akad. Nauk, Ser. Khim.,
1999, 1773 [Russ. Chem. Bull., 1999, 48, 1751 (Engl.
Transl.)].
This work was financially supported by the Russian
Foundation for Basic Research (Project Nos 05ꢀ03ꢀ32794,
05ꢀ03ꢀ08203, and 04ꢀ03ꢀ32880) and the Russian Acadꢀ
emy of Sciences (Program for Fundamental Research of
the Division of Chemistry and Materials Science of the
Russian Academy of Sciences, OKh7.3).
References
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Sidorov, I. F. Golovaneva, V. I. Burkov, O. G. Ellert, V. M.
Novotortsev, and L. T. Eremenko, Izv. Akad. Nauk, Ser.
Khim., 1998, 725 [Russ. Chem. Bull., 1998, 47, 704 (Engl.
Transl.)].
Received October 13, 2005;
in revised form December 12, 2005