Carboxylate clusters with the M4O4 cubane-like core: Pivalate cocrystal containing CoII and NiII

Article abstract of DOI:10.1007/s11172-010-0149-5

Joint thermolysis of the dinuclear pivalate complexes M₂(μ- H₂O)(μ-Piv)₂(Piv)₂(HPiv)₄ (M = Co (1) and Ni (2), Piv^- is the pivalate anion), in decane at 174 °C at the reactant ratio 1: 1 followed by treatment of the dry thermolysis product with methanol afforded crystals of a new cocrystallization product of the molecules containing the heterometallic cubane-like core M₄(Co,Ni) O₄. According to the X-ray diffraction data and the results of magnetic measurements, inductively coupled plasma atomic emission spectrometry (ICP-AES), and investigations of the solid-state thermal decomposition products, the isolated cocrystallization product has the general formula [Co _1.6Ni_2.4(μ₃-OMe)₄(μ ₂-Piv)₂(pg² -Piv)₂(MeOH) ₄] ?4MeOH (3?4MeOH). Thermolysis of the crystals of the solvate 3?4MeOH is a destructive process accompanied by the intramolecular redox reaction. A mixture of metallic Ni and cobalt oxide (CoO) are the final solid decomposition products of 3 ? 4MeOH in an argon atmosphere, whereas a mixture of the phases NiO, Co₃O₄, and NiCo ₂O₄ is formed in air.

Full text of DOI:10.1007/s11172-010-0149-5

Russian Chemical Bulletin, International Edition, Vol. 59, No. 4, pp. 699—705, April, 2010
699
Carboxylate clusters with the M4O4 cubaneꢀlike core:
pivalate cocrystal containing CoII and NiII
I. G. Fomina,a Zh. V. Dobrokhotova,a G. G. Aleksandrov,a M. L. Kovba,b
V. I. Zhilov,a A. S. Bogomyakov,c V. M. Novotortsev,a and I. L. Eremenkoa
aN. 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: fomina@igic.ras.ru
bDepartment of Chemistry, M. V. Lomonosov Moscow State University,
Build. 3, 1 Leninskie Gory, 119992 Moscow, Russian Federation
cInternational Tomography Center, Siberian Branch of the Russian Academy of Sciences,
3a ul. Institutskaya, 630090 Novosibirsk, Russian Federation.
Fax: +7 (383 2) 33 1399. Eꢀmail: bus@tomo.nsc.ru
Joint thermolysis of the dinuclear pivalate complexes M2(μꢀH2O)(μꢀPiv)2(Piv)2(HPiv)4
(M = Co (1) and Ni (2), Piv– is the pivalate anion), in decane at 174 °C at the reactant ratio 1 : 1
followed by treatment of the dry thermolysis product with methanol afforded crystals of a new
cocrystallization product of the molecules containing the heterometallic cubaneꢀlike core
M4(Co,Ni)O4. According to the Xꢀray diffraction data and the results of magnetic measureꢀ
ments, inductively coupled plasma atomic emission spectrometry (ICPꢀAES), and investiꢀ
gations of the solidꢀstate thermal decomposition products, the isolated cocrystallization prodꢀ
2
uct has the general formula [Co1.6Ni2.4(μ ꢀOMe)4(μ ꢀPiv)2(η ꢀPiv)2(MeOH)4]•4MeOH
3
2
(3•4MeOH). Thermolysis of the crystals of the solvate 3•4MeOH is a destructive process
accompanied by the intramolecular redox reaction. A mixture of metallic Ni and cobalt oxide
(CoO) are the final solid decomposition products of 3•4MeOH in an argon atmosphere, whereas
a mixture of the phases NiO, Co3O4, and NiCo2O4 is formed in air.
Key words: cubaneꢀlike cobalt and nickel pivalate clusters, cocrystallization, solidꢀstate
thermal decomposition, Xꢀray diffraction study, magnetic properties.
Homonuclear 3dꢀmetal carboxylates containing the
cubaneꢀlike core M4O4 with highꢀspin cobalt(II) and
nickel(II) atoms are well known and have attracted attenꢀ
tion because of unusual magnetic properties.1—16 These
compounds with alkanoate anions can serve as molecular
precursors for a wide range of oxide materials2,3,9,17—20
where the composition of the final material can be speciꢀ
fied in the step of the chemical assembly of the starting
precursor molecule. Taking into account the high volatility
of many alkanoate clusters and the fact that the metal core
M4O4 (M is a divalent metal) in cubaneꢀlike systems is
ready for the formation of an oxide lattice through the
elimination of organic components of the complexes, the
formation of oxide ultrathin films would be expected upon
mild thermolysis (at temperatures below 450—500 °C) of
molecular alkanoate cubaneꢀlike compounds deposited on
a substrate, for example, by the CVD (chemical vapor depꢀ
osition) method. However, there is no progress in the deꢀ
velopment of this strategy for the synthesis of oxide mateꢀ
rials because of the lack of efficient methods for the synꢀ
thesis of the corresponding heterometallic molecular preꢀ
cursors. There are only a few publications on the methods
for the assembly and physicochemical properties of the
latter compounds.9,18—20
In the present study, we report on the method for the
synthesis of the heterometallic pivalate derivative conꢀ
taining the cubaneꢀlike core M4(Co,Ni)O4 and the results
of investigation of the structure, magnetic properties, and
mild thermolysis under argon and in air. A new compound
was isolated as crystals with the composition [Co1.6Ni2.4
ꢀ
(μ3ꢀOMe)4(μ2ꢀPiv)2(η2ꢀPiv)2(MeOH)4]•4MeOH (Piv– is
the pivalate anion).
Results and Discussion
Previously,21 we have shown that the mild thermolysis
of the isostructural dinuclear complexes MII2(μꢀH2O)ꢀ
(μꢀPiv)2(Piv)2(Piv)4 (M = Co (1) or Ni (2)) in decane
at 174 °C afforded polynuclear pivalates having differꢀ
ent structures. The thermolysis of cobalt complex 1
resulted in the elimination of the water molecule and the
coordinated pivalic acid molecules to form the coordinaꢀ
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 685—691, April, 2010.
1066ꢀ5285/10/5904ꢀ0699 © 2010 Springer Science+Business Media, Inc.

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Fomina et al.
tion polymer [Co(Piv)2]n having a chain structure in the
crystals. As opposed to cobalt pivalate 1, the thermolysis
of dinuclear complex 2 under the same conditions afforded
crystalline cyclic hexanuclear complex Ni6(μ2ꢀPiv)6ꢀ
(μ3ꢀPiv)6.21
the known homonuclear complexes with cobalt and nickel
atoms isolated as solvates with 4.5 methanol molecules.6,12
In the structure of 3, the methanol molecules coordinated
in a monodentate fashion are linked to methanol solvaꢀ
tion molecules by short hydrogen bonds (OMeOH...Osolv
,
We found that the joint thermolysis of dinuclear comꢀ
plexes 1 and 2 in a ratio of 1 : 1 in decane at 174 °C gives
an extremely airꢀsensitive fineꢀcrystalline blue product.
Recrystallization of this product from methanol resulted
in pink crystals of [MII4(μ3ꢀOMe)4(μ2ꢀPiv)2(η2ꢀPiv)2ꢀ
(MeOH)4] (3, M = Co, Ni), which are very sensitive to
atmospheric moisture. The crystals were isolated as the
solvate with four molecules of methanol (3•4MeOH) in
76% yield. According to the inductively coupled plasma
atomic emission spectrometry (ICPꢀAES) data, the Co to
Ni ratio in the crystals of the solvate 3•4MeOH is 2 : 3.
According to the Xꢀray diffraction data, the general
geometric characteristics of product 3 are virtually identiꢀ
cal to those of the known homonuclear complexes conꢀ
taining the cubaneꢀlike core {MII4O4} (M = Co or Ni);6,12
the M—μ3ꢀO (M—O, 2.023(7)— 2.062(8) Å), M(1)...M(2)
(2.830(3) Å), and M(3)...M(4) (2.896(3) Å) bond lengths
(Fig. 1) are equal, within the experimental error, to those
found in the homonuclear analogs. Since it is virtually
impossible to distinguish between the positions of nickel
and cobalt atoms in the metal core and taking into acꢀ
count that the occupancies of the metal positions are difꢀ
ferent, the structure was refined using the model with four
nickel atoms (the refinement using the {Co4} model led to
similar results).
2.61—2.65 Å). The methanol solvation molecules also inꢀ
teract with the oxygen atoms of the carboxylate groups of
the cluster (OOOCR...Osolv, 2.60—2.64 Å) (Fig. 2).
Since we failed to unambiguously establish the heteroꢀ
metallic nature of the molecule based on the Xꢀray difꢀ
fraction data (product 3 can be a cocrystallization product
of two homonuclear cobalt and nickel complexes in the
ratio 2 : 3), we studied the magnetic properties of the crysꢀ
tals of the solvate 3•4MeOH. According to the results of
magnetic measurements, the effective magnetic moment
μeff of the product 3•4MeOH per molecule monotonicalꢀ
ly decreases with decreasing temperature (μeff
=
= 8.158—3.729 μB (300—2 K)) (Fig. 3). This behavior is
typical of antiferromagnetically coupled systems and
strongly differs from the properties of the analogous homoꢀ
nuclear nickelꢀcontaining complex characterized by ferꢀ
romagnetic spinꢀspin exchange interactions.6 This is
evidence for the absence of pure nickel complexes in
the crystals, which, according to the aboveꢀconsidered
ICPꢀAES data, suggests the presence of cocrystals conꢀ
taining heterometallic structures. Taking into account the
analytical data, the general formula of 3 can be representꢀ
ed as [Co1.6Ni2.4(μ3ꢀOMe)4(μ2ꢀPiv)2(η2ꢀPiv)2(MeOH)4].
At the same time, the deficiency in cobalt atoms in the
structure of 3 suggests that pure cobalt complexes are abꢀ
sent in the crystals. Hence, the formula of 3 can be reꢀ
presented, for example, as the solvate of two cocrystalꢀ
lized heterometallic pivalate complexes containing the
It should be noted that there are four methanol solvaꢀ
tion molecules in the crystal structure of 3 as opposed to
O
O
M(3)
Ni(2)
Ni(1)
O
M(4)
M(1)
O
O
Co(1)
Co(2)
M(2)
Fig. 2. Fragment of the packing of the complex [MII4(μ ꢀOMe)4ꢀ
3
2
(μ ꢀPiv)2(η ꢀPiv)2(MeOH)4] (3, M = Co, Ni) with four methꢀ
2
Fig. 1. Structure of product 3 (the molecule with two cobalt
anol solvation molecules (3•4MeOH). The hydrogen atoms are
atoms and two nickel atoms is shown).
not shown.

{MII4(Co,Ni)O4} Pivalate with the cubaneꢀlike core Russ.Chem.Bull., Int.Ed., Vol. 59, No. 4, April, 2010
701
μ
eff/μB
structural studies according to which the methanol moleꢀ
cules coordinated in a monodentate fashion are linked to
the methanol solvation molecules by short hydrogen bonds
and the analysis of the observed thermal effects (the first
endothermic effect Q = 18 3 kJ mol–1 of the complex is
comparable to the hydrogen bond energy22 and the second
endothermic effect Q = 220 10 kJ mol–1 (this is the sum
of the energies of detachment of the coordinated methaꢀ
nol molecules, the evaporation of the solvation and coorꢀ
dinated molecules, and the formation of new bonds) proꢀ
vide evidence that the hydrogen bond cleavage is the first
thermal transformation.
9
8
7
6
5
4
In an argon atmosphere, the weight loss during heatꢀ
ing started at 49 2 °C and was accompanied by the energy
absorption (the endothermic effect of a complex shape).
The mass spectrum of the gas phase in the temperature
range of 50—170 °C corresponds to the spectrum of methꢀ
anol (The NIST Chemistry WebBook). Hence, the deꢀ
composition step under consideration is apparently acꢀ
companied by the removal of volatile methanol solvation
molecules and coordinated methanol molecules. Howevꢀ
er, we failed to separate the steps of the removal of differꢀ
ent types of methanol molecules. In the temperature range
of 49—170 °C, the weight loss was 25.8 1.0%. The theoꢀ
retical content of four methanol solvent molecules and
four coordinated methanol molecules is 25.17%, which is
in good agreement, within the experimental error, with
the results of thermogravimetry.
It was noted that the the initial decomposition step of
the sample affords intermediates stable in the temperature
range of 170—210 °C. At temperatures above 210 °C, final
destruction of the sample occurs, the process being accomꢀ
panied by complex energy changes. In the temperature
range of 220—310 °C, the weight loss occurs with an endoꢀ
thermic effect. In the temperature range of 310—470 °C,
the process is exothermic and occurs without weight loss,
which is characteristic of the formation of a solid decomꢀ
position product. According to the Xꢀray powder diffracꢀ
tion data, the decomposition affords a mixture of metallic
nickel and CoO. The total weight loss in the temperature
range under study is 73.1 1.5%. According to the TGA
data, the weight of the solid product is 26.9 1.5% of the
weight of the initial sample.
50
100
150
200
250
300 T/K
Fig. 3. Temperature dependence of the effective magnetic moꢀ
ment (μeff) for the product 3•4MeOH.
cubaneꢀlike cores: 3[Co2Ni2(μ3ꢀOMe)4(μ2ꢀPiv)2(η2ꢀPiv)2ꢀ
(MeOH)4]•2[CoNi3(μ3ꢀOMe)4(μ2ꢀPiv)2(η2ꢀPiv)2ꢀ
(MeOH)4]•20MeOH.
The investigation of the solidꢀstate thermolysis of the
crystals of the solvate 3•4MeOH in an inert atmosphere
and in air showed that the character of decomposition at
temperatures below 174 °C in air is virtually identical to
that under argon (Fig. 4). During heating of the sample,
the endothermic processes are observed at 35 2 °C (see
Fig. 4, a), whereas the weight loss occurs only on heating
to temperatures higher than 49 2 °C (see Fig. 4, b). The
results of the stepwise DSC experiment with the visual
control after each step suggest that no melting of the samꢀ
ple occurs at temperatures below 200 °C. The results of
Q/mW mg–1
a
1
10
0
2
–10
100
200
300
400
T/°C
According to the ICPꢀAES analysis, the Ni : Co ratio
in the product 3•4MeOH is 3 : 2. These data suggest that
the solid decomposition product contains 2.4 moles of Ni
and 1.6 moles of CoO, whereas the weight of the solid
residue calculated taking into account the molecular forꢀ
mula should be 26.67%, which is equal, within the experiꢀ
mental error, to the value 26.9 1.5% determined by TGA.
This result additionally confirms the quantitative metal
content in the sample under study.
m/mg
12
b
1
8
4
2
100
200
300
400
500
T/°C
Apparently, the phase composition of the decomposiꢀ
tion products of 3•4MeOH is determined by the different
nature of the metal centers, as well as by the nature of the
Fig. 4. Temperature dependences of the heat flux (a) and the
weight loss (b) during heating of the product 3•4MeOH in an
inert atmosphere (1) and in air (2).

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Russ.Chem.Bull., Int.Ed., Vol. 59, No. 4, April, 2010
Fomina et al.
coordinated ligands and the structural features of the metꢀ
al core, as has previously been shown for other pivalate
complexes of nickel(II)16,21,23,24 and cobalt(II).16,21,23—25
The first decomposition step of the crystals of
3•4MeOH in air is also accompanied by the elimination
of the methanol molecules and their transition to the gas
phase. In the temperature range of 49—65 °C, four methaꢀ
nol solvation molecules (12.5 1.5%) are apparently reꢀ
moved; the coordinated methanol molecules (14.6 2.0%)
are eliminated in the temperature range of 65—130 °C.
According to the TGA data, the total content of methanol
is 27.1 2.0%, which is, within experimental error, equal
to eight methanol molecules in the solvate 3•4MeOH
(25.17%) calculated from the molecular formula. Acꢀ
cording to the TGA data, the decomposition of the
sample in air affords virtually no stable intermediates.
The first decomposition step is followed by the comꢀ
plete oxidative destruction. It should be noted that
the weight loss is not accompanied by energy changes
in the temperature range of 140—270 °C. In the tempeꢀ
rature range of 250—390 °C, exothermic processes ocꢀ
cur, but they are not accompanied by the weight
loss, which can be associated with the formation of new
solid decomposition products. According to the Xꢀray
powder diffraction data, the decomposition affords a mixꢀ
ture of the phases NiO, Co3O4, and NiCo2O4 as solid
products (Table 1). The formation of oxides upon therꢀ
molysis is associated with the presence, first, of the oxiꢀ
dizing atmosphere and, second, of the bridging pivalate
groups, when the CO2 fragments that are formed as
a result of the cleavage of the pivalate ligands serve as the
oxidizing agent.
It was demonstrated above that, based on the analysis
of the magnetic behavior and the analytical ICPꢀAES data,
the crystals of the solvate 3•4MeOH is the solvate of the
cocrystallized heterometallic complexes containing the
cubaneꢀlike core M4O4. This suggestion is confirmed also
by the results of the comparative analysis of the solidꢀstate
thermolysis under argon of two homometallic complexꢀ
es [M4(μ3ꢀOMe)4(μ2ꢀPiv)2(η2ꢀPiv)2(MeOH)4]•4MeOH
(M = CoII (4•4MeOH) and NiII (5•4MeOH)) with
μ3ꢀmethoxide bridges, which we have synthesized and
characterized previously,16 and the newly synthesized
product 3•4MeOH (Fig. 5).
It can be seen that the onset of the endothermic proꢀ
cesses for the crystals of 3•4MeOH, 4•4MeOH, and
5•4MeOH corresponds to 35 2 °C. The first endothermic
effect for all samples is observed in the temperature range
of 35—65 °C. Apparently, the processes associated with
the hydrogen bond scission and the removal of the methaꢀ
nol solvation molecules occur in this temperature range.
For the complexes 4•4MeOH and 5•4MeOH, the
weight loss in this temperature range is 12.5 1.0 and
13.1 1.0%, respectively (the theoretical percentage of the
methanol solvation molecules is 12.55%), and further heatꢀ
ing of the complexes in the temperature ranges of 65—145
and 65—180 °C accompanied by the energy absorption
(the double endothermic effect) leads to the weight loss of
13.08 1.0 and 12.6 1.0%, respectively The latter process
corresponds to the removal of coordinated methanol,
whose theoretical percentage is 12.55%. For the product
3•4MeOH, it is impossible to separate the elimination
step of the methanol solvation molecules based on the
TGA data because the continuous weigh loss occurs in the
Table 1. Data from the analysis of the phase composition of the solid thermolysis product of
the cocrystal 3•4MeOH in air
Product
NiO[44ꢀ1159]*
Co3O4[43ꢀ1003]*
NiCo2O4[20ꢀ0781]*
d/Å
I (%)
d/Å
I (%)
d/Å
I (%)
d/Å
I (%)
—
4.67 br
—
2.87 br
—
2.44 br
—
10
—
30
—
0.—
0.—
0.—
0.—
0.—
0.—
—
—
—
—
—
—
00—
4.6670
00—
2.8580
00—
00—
—
16
—
33
—
—
4.69
0—
2.869
0—
2.447
2.4374
14
—
25
—
100
100
100
2.42
2.35
2.085
—
2.03 br
—
1.56 br
1.48
1.44
1.43
20
5
100
—
30
—
40
40
10
10
2.412
0.—
2.089
0.—
0.—
0.—
0.—
1.4768
0.—
61
—
100
—
—
—
—
35
—
00—
00—
00—
00—
2.0210
00—
1.5558
00—
00—
1.4291
—
—
—
—
20
—
32
—
—
38
0—
2.342
0—
2.029
0—
1.562
0—
0—
1.434
0—
—
10
—
25
—
30
—
—
45
—
0.—
—

{MII4(Co,Ni)O4} Pivalate with the cubaneꢀlike core Russ.Chem.Bull., Int.Ed., Vol. 59, No. 4, April, 2010
Q/mW mg–1
703
lic complexes 4•4MeOH and 5•4MeOH and the product
3•4MeOH suggest that the product 3•4MeOH is neither
a mechanical mixture nor the cocrystallization product of
the homometallic complexes 4•4MeOH and 5•4MeOH.
The physicochemical studies (Xꢀray diffraction, ICPꢀ
AES, magnetic measurements, DSC, and TGA) showed
that the product 3•4MeOH is the solvate of the cocrystalꢀ
lized heterometallic pivalate clusters containing the cuꢀ
baneꢀlike core M4(Co,Ni)O4. The thermolysis of the cocꢀ
rystal 3•4MeOH, like the thermolysis of the analogous
homometallic cubaneꢀlike structures 4•4MeOH and
5•4MeOH, is a destructive process and is accompanied
by the intramolecular redox process. The phase composiꢀ
tion of their decomposition products is determined by the
nature of the metal centers and the coordinated ligands, as
well as by the structural features of the metal core. A mixꢀ
ture of metallic Ni and cobalt oxide (CoO) are the final
solid decomposition products of 3•4MeOH in an argon
atmosphere, whereas the decomposition of compounds
4•4MeOН and 5•4MeOH affords oxide Co3O4 and an
equimolar mixture of Ni and NiO, respectively. The deꢀ
composition of 3•4MeOH in air gives a mixture of the
phases NiO, Co3O4, and NiCo2O4. In our opinion, these
results provide evidence that the desired oxide materials of
different nature can be synthesized with the use of cubaneꢀ
like divalent cobalt and nickel complexes as molecular
precursors.
a
1
2
3
15
5
–5
–15
100
200
300
400
500
T/°C
b
m/mg
1
2
10
6
3
2
100
200
300
400
500
T/°C
Fig. 5. Temperature dependences of the heat flux (a) and the
weight loss (b) during heating of the product 3•4MeOH (1) and
the complexes 4•4MeOH (2) and 5•4MeOH (3) in an inert
atmosphere.
range of 49—170 °C, which corresponds to the removal of
both types of methanol molecules. This process is accomꢀ
panied by energy changes, whose character differs from
that observed for 4•4MeOH and 5•4MeOH. The absence
of individual homometallic complexes in the crystals of
3•4MeOH is confirmed by the character of the further
destructive decomposition of the intermediate. For all the
samples under consideration, the onset of energy changes
in this decomposition step corresponds to 200 5 °C. For
the cobaltꢀcontaining complex 4•4MeOH, the exotherꢀ
mic effect is observed in the range of 205—350 °C, and the
weight loss (43.6 1.0%) occurs in the range of 210—310 °C.
For the nickelꢀcontaining compound 5•4MeOH, the enꢀ
ergy changes in the temperature range of 205—430 °C
have a complex character (successive alternation of the
exoꢀ and endothermic effects), and the weight loss in the
range of 230—350 °C is 47.9 1.0%. This character of the
energy changes in the last decomposition step for comꢀ
pounds 4•4MeOH and 5•4MeOH is apparently attributꢀ
ed to the difference in the redox processes16 that occur in
the thermolysis in an inert atmosphere. Thus the mixedꢀ
valence oxide Co3O4 is the only solid thermolysis product
of 4•4MeOH, whereas the thermal decomposition of comꢀ
pound 5•4MeOH affords a virtually equimolar mixture of
Ni and NiO. For the product 3•4MeOH, the weigh loss is
also observed in the range of 215—325 °C, and complex
energy changes occur in the range of 210—440 °C, but
their character differs from that observed for compound
5•4MeOH.
Experimental
All synthetic operations were carried out under pure argon
with the use of the standard Schlenk technique. The starting
compounds 1 and 2 were synthesized according to known proceꢀ
dures.6,26 The synthesis of 3•4MeOH was carried out with the
use of decane (Merck, 95% for synthesis) and methanol (Merck,
99.8% for liquid chromatography). The elemental analysis for C
and H was carried out on an Euro Vector CHN Elemental Analꢀ
yser (Model EA 3000) at the Center of Collective Use of the N.
S. Kurnakov Institute of General and Inorganic Chemistry of
the Russian Academy of Sciences. The IR spectra were recorded
on a Specord Mꢀ80 spectrophotometer in KBr pellets. The static
magnetic susceptibility measurements were carried out on
a SQUID MPMSꢀ5S Quantum Design magnetometer in the
2—300 K temperature range. The effective magnetic moments
were calculated by the equation μeff = (8χT)0.5. The metal conꢀ
tents were determined by inductively coupled plasma atomic
emission spectrometry on an IRIS Advantage instrument. The
thermal decomposition was studied by differential scanning calꢀ
orimetry and thermogravimetric analysis on DSCꢀ20 and TGꢀ50
units of a Mettler TAꢀ3000 thermoanalyzer. For each sample,
three DSC experiments and three TGA experiments were perꢀ
formed (the heating rate in all experiments was 10 deg min–1).
The weight loss upon thermal degradation was determined directꢀ
ly on the TGꢀ50 unit; the accuracy of weighing was 2•10–3 mg.
The accuracy of the determination of anomalous points in the
thermograms and of the thermal effects was 1° and 0.5%,
respectively. The Xꢀray powder diffraction analysis of the
Therefore, the data from the analysis of the solidꢀstate
thermolysis under argon of the crystals of the homometalꢀ

704
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Fomina et al.
decomposition products was carried out with a FRꢀ552 monoꢀ
1360 s, 1260 w, 1224 s, 1104 w, 1032 m, 936 w, 896 m, 796 s,
604 m, 416 m, 324 w.
chromator chamber (CuꢀKα radiation) using germanium as the
1
internal standard (Xꢀray diffraction patterns were processed on
an IZAꢀ2 comparator with an accuracy of 0.01 mm) and on
a STOE Powder Diffraction System. In addition, the thermoꢀ
gravimetric measurements were carried out in a flow of artificial
air (20 ml min–1) and argon (20 mL min–1) on a NETZSCH TG
209 F1 instrument in alundum crucibles at a heating rate of
10 deg min–1. The composition of the gas phase at temperatures
below 200 °C was studied on a QMS 403C Aеolos mass specꢀ
trometer under TGA conditions. The ionizing electron enerꢀ
gy was 70 eV; the maximum determined mass number (the
m/z ratio) was 300 amu.
The synthesized crystals were suitable for Xꢀray diffraction
analysis.
Xꢀray diffraction study. The Xꢀray diffraction data for the
crystals of 3•4MeOH were measured on a Bruker AXS SMART
1000 diffractometer equipped with a CCD area detector (graphꢀ
ite monochromator, 120(2) K, ωꢀscanning technique with a step
of 0.3° and exposure time of 30 s per frame) according to
a standard procedure.27 A semiempirical absorption correction
was applied.28 The crystallographic parameters and the refineꢀ
ment statistics for the structure of 3•4MeOH are given in Table 2.
The structure of the complex was solved by direct methods and
refined by the fullꢀmatrix leastꢀsquares method with anisotropic
displacement parameters for all nonhydrogen atoms (except for
the methyl carbon atoms of the disordered tertꢀbutyl group at the
C(7) atom (C(8)—C(10) and C(8a)—C(10a), which were reꢀ
fined isotropically with the occupancies of 0.6 and 0.4, respecꢀ
tively). The metal centers were refined as the Ni atoms. The
refinement of the metal core using the Co4 model led to similar
results. The hydrogen atoms of the tertꢀbutyl substituents of the
pivalate ligands were positioned geometrically and refined using
a riding model. The calculations were carried out with the use of
the SHELX97 program package.29
2
Tetra(μ ꢀmethoxo)di(μ ꢀO,O´ꢀtrimethylacetato)di(η ꢀO,O´ꢀ
3
2
1
trimethylacetato)tetra(η ꢀmethanol)1.6cobalt(II)2.4nickel(II) meꢀ
thanol tetrasolvate [Co1.6Ni2.4(μ ꢀOMe)4(μ ꢀPiv)2(η ꢀPiv)2ꢀ
2
3
2
1
(η ꢀMeOH)4]•4MeOH (3•4MeOH). The complex Ni2(μꢀH2O)ꢀ
(μꢀPiv)2(Piv)2(HPiv)4 (0.25 g, 0.264 mmol) and oxygenꢀfree deꢀ
cane (50 mL) were added to Co2(μꢀH2O)(μꢀPiv)2(Piv)2(HPiv)4
(0.25 g, 0.264 mmol). The resulting blueꢀgreen solution was heatꢀ
ed under argon to 174 °C and kept until a dry blue fineꢀcrystalꢀ
line product formed. The latter was cooled to 20 °C, and then
methanol (60 mL) was added. The reaction mixture was stirred
under argon at 60 °C until the starting compound completely
dissolved. The resulting crimsonꢀgray solution was filtered, conꢀ
centrated to 40 mL at 0.1 Torr and 20 °C, and kept at 5 °C for 8 h.
Pink crystals that formed were separated from the solution by
decantation, washed with cold methanol, and dried under
a stream of argon. The yield of the solvate of product 3 with four
MeOH molecules was 0.41 g (76%). Found (%): C, 37.75;
H, 8.18. C32H80Co1.6Ni2.4O20. Calculated (%): C, 37.68; H, 7.91.
The quantitative ratio Co : Ni = 2 : 3. IR, ν/cm–1: 3384 m,
3268 m, 2956 s, 2928 s, 2908 m, 2872 m, 2836 m, 1684 m, 1668 m,
1584 s, 1572 s, 1552 s, 1536 s, 1484 s, 1456 m, 1416 s, 1372 m,
This study was financially supported by the Russian
Foundation for Basic Research (Project Nos 07ꢀ03ꢀ00408,
08ꢀ03ꢀ00343, and 08ꢀ03ꢀ00365), the Council on Grants
at the President of the Russian Federation (Program for
the State Support of Leading Scientific Schools of the
Russian Federation, Grant NShꢀ3672.2010.3), the Diviꢀ
sion of Chemistry and Materials Science of the Russian
Academy of Sciences (Program of Basic Research "Chemꢀ
istry and Physical Chemistry of Supramolecular Systems
and Atomic Clusters"), and the Presidium of the Russian
Academy of Sciences (Program "Development of Methꢀ
ods for the Synthesis of Chemical Compounds and the
Design of New Materials").
Table 2. Crystallographic parameters for the product 3•4MeOH
Parameter
Characteristics
Molecular formula
Molecular weight
Space group
a/Å
b/Å
C
32H80Ni4O20
1019.80
Pbca
15.327(1)
41.83(3)
15.887(9)
90
90
90
10186(1)
8
1.330
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Received May 25, 2009;
in revised form February 2, 2010