Thermal decomposition of dinuclear complexes LM(μ-OOCR)4ML (L is α-substituted pyridine): 1. Synthesis, structures, and solid-state thermolysis of MnII, FeII, CoII, Ni II, and CuII pivalate

Article abstract of DOI:10.1007/s11172-007-0266-y

The solid-state thermal decomposition of the tetrabridged dinuclear Mn ^II, Fe^II, Co^II, Ni^II, and Cu ^II pivalate complexes with apical α-substituted pyridine ligands containing different substituents (

Full text of DOI:10.1007/s11172-007-0266-y

Russian Chemical Bulletin, International Edition, Vol. 56, No. 9, pp. 1712—1721, September, 2007
1712
Thermal decomposition of dinuclear complexes LM(µꢀOOCR)4ML
(L is αꢀsubstituted pyridine).
1. Synthesis, structures, and solidꢀstate thermolysis of MnII, FeII, CoII, NiII, and CuII
pivalates with apical 2,3ꢀdimethylpyridine and quinoline ligands
a
a
a
a
b
I. G. Fomina,a Zh. V. Dobrokhotova, M. A. Kiskin, G. G. Aleksandrov, O. Yu. Proshenkina, A. L. Emelina,
ꢀ
V. N. Ikorskii,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,
1 Leninskie Gory, 119992 Moscow, Russian Federation.
Eꢀmail: emelina@td.chem.msu.ru
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: ikorsk@tomo.nsc.ru
The solidꢀstate thermal decomposition of the tetrabridged dinuclear MnII, FeII, CoII, NiII,
and CuII pivalate complexes with apical αꢀsubstituted pyridine ligands containing different
substituents (2,3ꢀdimethylpyridine or quinoline) was studied by differential scanning caloꢀ
rimetry and thermogravimetry. The decomposition of the CoII complexes is accompanied by
the aggregation to form the volatile octanuclear complex Co8(µ ꢀO)2(µ ꢀOOCCMe3)12, where
4
n
n = 2 or 3, whereas the thermolysis of the MnII, FeII, NiII, and CuII complexes is accompanied
by the degradation of the starting compounds, the phase composition of the decomposition
products being substantially dependent on the nature of metal and the apical organic ligand.
Key words: dinuclear tetrabridged manganese, iron, cobalt, nickel, and copper pivalate
complexes, 2,3ꢀdimethylpyridine, quinoline, solidꢀstate thermal decomposition, Xꢀray diffracꢀ
tion study, magnetic properties.
Dinuclear complexes of Group VII and VIII 3d
transition metals with four bridging pivalate ligands
LM(µꢀOOCR)4ML are readily soluble in organic solvents.
Among these compounds, the CoII,1—3 NiII,4,5 FeII,
and MnII (see Ref. 6) complexes have received the most
study. These compounds have attracted attention as conꢀ
venient models for studying the magnetic behavior of sysꢀ
tems containing two highꢀspin centers.7—9 The relative
ease of their synthesis gives hope that these compounds
can find wider application. In particular, these complexes,
including copper derivatives, are of interest for the prepaꢀ
ration of various coatings. To predict the prospects of the
application of such dinuclear systems in the formation of
films or nanosized coatings, it is important to study the
thermal decomposition steps and determine the character
of thermolysis products. Their composition often depends
on the nature of precursors, in particular, on the nature of
the organic moiety in the starting complex molecules,
because the latter has a considerable effect on intraꢀ
molecular redox reactions involved in the thermolysis of
the complexes.
In the present study, we synthesized dinuclear tetraꢀ
bridged Mn, Fe, Co, Ni, and Cu pivalate complexes with
αꢀsubstituted pyridines containing different substituꢀ
ents, viz., 2,3ꢀdimethylpyridine (2,3ꢀ(CH3)2C5H3N) and
quinoline (C9H7N), as the apical ligands L and studied
the thermolysis of these complexes.
Results and Discussion
The main synthetic goal of the present study was to
prepare dinuclear pivalate complexes with apically coorꢀ
dinated substituents of different nature.
† Deceased.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1650—1659, September, 2007.
1066ꢀ5285/07/5609ꢀ1712 © 2007 Springer Science+Business Media, Inc.

Solidꢀstate thermolysis of pivalate complexes
Russ.Chem.Bull., Int.Ed., Vol. 56, No. 9, September, 2007 1713
Scheme 1
We expected that in the ligands used in the present
study (L1 is 2,3ꢀdimethylpyridine and L2 is quinoline),
the protons of the Me groups in the α position of the
ligand L1 would be most active with respect to the metal
carboxylate core due to their geometric arrangement in
the dinuclear complexes and could formally interact with
the oxygen atoms of the carboxylate bridges. Unlike these
protons, the proton in the α position of the ligand L2 is
substantially more distant (~2 Å) from the oxygen atoms
of the pivalate bridges and is unlikely to interact with this
fragment.
1. Synthesis of dinuclear Mn, Co, Ni, and Cu pivalates
Although some LM(µꢀOOCBut)4ML complexes of the
series under consideration (L = L1; M = Co 3 or Ni 3,4
;
L = L2, M = Co 1; L is 2ꢀmethylquinoline, M = Ni 5)
have been characterized, and the procedures for their
synthesis have been documented, we supplemented the
scope of these compounds. The directed degradation of
the [M(OOCBut)2]n (M = Co (1), Ni (2), or Cu(3)) or
[(EtOH)Mn(µꢀOOCCMe3)2]n (4) polymers in benzene
with 2,3ꢀdimethylpyridine (L1) or quinoline (L2) was used
as the main procedure for the synthesis of new complexes
(Scheme 1). In spite of the different structures of polyꢀ
mers 1—3 (cobalt polymer has a chain structure with two
carboxylate bridges between the metal atoms,3 the nickel
compound exists as a sixꢀmembered ring,3 and the strucꢀ
ture of the copper polymer can be described as a complex
network, in which the dinuclear tetrabridged dimeric fragꢀ
ments are linked to each other via a Cu—O interaction
with the carboxylate group of the adjacent dinuclear fragꢀ
ment10), the reactions with Nꢀdonors procduce the target
dinuclear structures in virtually quantitative yields. The
reaction of polymer 1 or hexamer 2 (n = 6) with quinoꢀ
line (L2) in benzene at 80 °C under an inert atmoꢀ
sphere affords the green dinuclear lanternꢀtype comꢀ
plexes (C9H7N)2M2(µꢀOOCCMe3)4, where M = Co (5)
or Ni (6), respectively, in yields close to 100% (see
Scheme 1). The spectroscopic characteristics of these
complexes are very similar to those of the structurally
characterized quinolineꢀcontaining pivalates.1,5
The reaction of polymer 3 with L2 in benzene at
80 °C in air produces the green dinuclear complex
(C9H7N)2Cu2(µꢀOOCCMe3)4 (7) in 89% yield (see
Scheme 1).
According to the Xꢀray diffraction study, the distance
between the copper atoms in molecule 7 is 2.6543(9) Å
(Fig. 1), this distance being somewhat shorter than the
corresponding distances found earlier in the related strucꢀ
turally similar dinuclear cobalt and nickel complexes,
(C9H7N)2Co2(µꢀOOCCMe3)4 (Co...Co, 2.785 Å)1 and
(MeC9H7N)2Ni2(µꢀOOCCMe3)4 (Ni...Ni, 2.754(3) Å),5
but longer than those in the dinuclear fragments of the
starting polymer 3 (Cu...Cu, 2.580 Å).10 It should also be
L = L1, L2; M = Co (1, 5), Ni (2, 6), Cu (3, 7), Mn (4, 8), n = 6
L = L2 (5, 6, 7), L1 (8)
i. L : Mat = 1 : 1
noted that the Cu—N distance between the copper atom
and the nitrogen atom of the quinoline ligand (2.223(3) Å)
is substantially longer than the corresponding distances
in the aboveꢀmentioned dinuclear cobalt and nickel
complexes (Co—N, 2.090 Å; Ni—N, 2.047(9) Å). The
N—Cu...Cu—N fragment is virtually linear (N—Cu...Cu
angle, 176.32(8)°), unlike the N—Ni...Ni—N fragment
characterized by substantial bending (N—Ni...Ni angle,
167.2(4)°).
The investigation of the magnetic properties showed
that complexes 5, 6, and 7 exhibit antiferromagnetic spinꢀ
spin exchange interactions. The effective magnetic moꢀ
ment µeff monotonically decreases with decreasing temꢀ
perature from 5.494 µB at 300 K to 0.308 µB at 2 K for 5,
C(5)
C(2)
C(4)
C(3)
C(8)
C(9)
C(17)
C(1)
C(16)
C(7)
O(2)
C(6)
O(1)
Cu(1)
O(4)
O(3)
C(18)
C(15)
C(19)
C(10)
O(4)
N(1)
C(11)
Cu(1)
O(3)
C(14)
C(13)
O(2)
O(1)
C(12)
Fig. 1. Structure of the dinuclear complex (C9H7N)2Cu2(µꢀ
OOCCMe3)4 (7).

1714
Russ.Chem.Bull., Int.Ed., Vol. 56, No. 9, September, 2007
Fomina et al.
µ
eff/µ
B
µ
eff/µ
B
µ
eff/µ
B
3.0
2.6
2.2
1.8
1.4
5
4
3
2
1
1.6
1.2
0.8
0.4
a
b
c
0
0
100
200
T/K
100
200
T/K
100
200
T/K
Fig. 2. Magnetic properties of complexes 5 (a), 6 (b), and 7 (c).
from 3.058 µB at 300 K to 1.287 µB at 5 K for 6, and from
1.889 µB at 300 K to 0.105µB at 5 K for 7 (Fig. 2).
aboveꢀdescribed approach. It appeared that the reaction
of L1 (L : Mat = 1 : 1; 80 °C, C6H6) with polymeric copꢀ
per(II) trimethylacetate 3 in air also produced the crystalꢀ
line complex (2,3ꢀMe2C5H3N)2Cu2(µꢀOOCCMe3)4 (11)
(see Scheme 1). The spectroscopic characteristics of this
complex are virtually identical to those of the related
derivatives of 5 with manganese (8), cobalt (9), and nickel
(10) atoms.
Although we failed to isolate the related complex with
MnII atoms (apparently, due to its very high sensitivity to
atmospheric oxygen), we found that the reaction of polyꢀ
mer 4 with L1 in benzene at 80 °C under argon produces
the dinuclear complex (Me2C5H3N)2Mn2(µꢀOOCCMe3)4
(8) in 73% yield (see Scheme 1).
According to the Xꢀray diffraction study, the distances
between the metal atoms in molecule 8 are 3.0542(19)
and 3.0637(13) Å (in two independent molecules) (Fig.
3), the observed interatomic distances in 8 being substanꢀ
tially shorter than the corresponding distances found earꢀ
lier in the structurally similar dinuclear manganese comꢀ
plexes (C10H9N)2Mn2(OOCCHPh2)4,11 (C10H9N)2Mn2ꢀ
(OOCCMePh2)4,11 and (OC(CMe3)OHNEt3)2Mn2(µꢀ
OOCCMe3)4 (see Ref. 12) (Mn...Mn, 3.131(2), 3.168(4),
and 3.108(8) Å, respectively). The N—Mn...Mn—N
fragment (Mn—N, 2.181(5)—2.184(5) Å) in molꢀ
ecule 8 is virtually linear (N—Mn...Mn angle is
173.66(13)—177.93(15)°). There are short contacts beꢀ
tween the hydrogen atoms of the αꢀMe substituent in the
pyridine ring and the oxygen atoms of the carboxylate
groups (2.52—2.61 Å) (see Fig. 3).
The investigation of the magnetic properties
showed that complexes 8 and 11, like analogous tetraꢀ
bridged pivalate complexes 9 and 10,3,4 as well as
(MeC5H3N)2Cu2(µꢀOOCCMe3)4,13 exhibit antiferromagꢀ
netic spinꢀspin exchange interactions. The effective magꢀ
netic moment µeff monotonically decreases from 6.615 µB
µ
eff/µ
B
7
6
5
4
3
a
Analogous compounds with cobalt (9) and nickel (10)
atoms have been synthesized in our earlier study.3 In the
case of the complex with copper atoms, we also used the
100
200
T/K
µ
eff/µ
B
C(37)
C(44)
2.0
1.6
1.2
0.8
0.4
C(43)
C(38)
C(41)
C(42)
C(36)
b
C(35)
C(39)
C(40)
O(11)
N(3)
C(50)
C(49)
O(10)
C(51)
O(12)
O(9)
C(48)
Mn(3)
Mn(3)
C(47)
C(46)
C(45)
0
100
200
T/K
Fig. 3. Structure of complex 8.
Fig. 4. Magnetic properties of complexes 8 (a) and 11 (b).

Solidꢀstate thermolysis of pivalate complexes
Russ.Chem.Bull., Int.Ed., Vol. 56, No. 9, September, 2007 1715
at 300 K to 2.781 µB at 2 K for 8 and from 1.883 µB at
300 K to 0.088 µB at 5 K for 11 (Fig. 4).
loss is 80.7 2.0%. According to the Xꢀray powder diffracꢀ
tion analysis, nickel oxide is the final solid decomposition
product.
Therefore, we synthesized series of the dinuclear
pivalate complexes with the apical quinoline and
2,3ꢀdimethylpyridine ligands of the composition
(C9H7N)2M2(µꢀOOCCMe3)4 (M = Co (5), Ni (6), or
Cu (7)) and (Me2C5H3N)2M2(µꢀOOCCMe3)4 (M =
Mn (8), Co (9), Ni (10), or Cu (11)), respectively, as well
as the known dinuclear iron complexes. These compounds
were used to study the thermolysis.
Isostructural copper complex 7 is also thermally
stable. The decomposition starts at a temperature above
207 2.0 °C (see Fig. 5, c, f ). The process proceeds in a
rather narrow temperature range from 210 to 310 °C.
In this case, two decomposition steps can be distinguished.
In step I (210—245 °C), melting with decomposition ocꢀ
curs. The melting point is 234.5 1.0 °C. When melting
begins, the weight loss is 8.5 1.0%, which is, apparently,
indicative of the partial removal of the apical ligand. The
end of the melting process (245 2.0 °C; the beginning of
the second endotherm) corresponds to the weight loss of
33.1 1.0%. In step II (245—310 °C), the processes is
endothermic (total thermal effect of melting with decomꢀ
position is 390.0 9.0 kJ mol–1). The weight loss in the
second step is 44.4 1.5%. The total weight loss in the
temperature range under investiagtion is 77.5 1.5%. The
composition of the solid decomposition product correꢀ
sponds to copper(II) oxide (Table 1).
2. Solidꢀstate thermolysis of dinuclear
tetrabridged Mn, Fe, Co, Ni, and Cu pivalates
The solidꢀstate decomposition of the tetrabridged
dinuclear pivalate complexes with Mn, Fe, Co, Ni,
and Cu atoms proceeds in steps. The following three main
steps can be distinguished: the elimination of solvate solꢀ
vent molecules (if they are present in the crystals), the
elimination of neutral Nꢀdonor ligands, and the degradaꢀ
tion of the metal carboxylate core as the major processes.
As a rule, the latter step proceeds through the formation
of [M(OOCR)2]n polymers. However, the compositions
of the final thermolysis products substantially depend on
the nature of metal atoms and the Nꢀdonor apical organic
ligand.
In summary, the decomposition of the dinuclear coꢀ
balt, nickel, and copper complexes under study generates
either oxides (in the case of nickel and copper) or volatile
clusters (in the case of cobalt) (Table 2).
2.2. Dinuclear pivalates with 2,3ꢀdimethylpyridine
2.1. Quinoline derivatives
The presence of the αꢀmethyl substituent in the pyriꢀ
dine ring leads to substantial changes in the character of
thermolysis, although the composition of the final solid
product substantially depends on the nature of metal.
However, the processes with the involvement of dinuclear
structures containing electronꢀdeficient metal atoms,
which tend to undergo easy oxidation and are near the
middle of the row of the Periodic table (for example,
the dimers of manganese and iron (Me2C5H6N)2M2(µꢀ
OOCCMe3)4, where M = Mn (8) or Fe (12)),7 afford
oxides as the final products.
Manganeseꢀcontaining compound 8 retains thermal
stability only below 100 °C (Fig. 6, a, 7, a). In the temꢀ
perature range of 100—230 °C, the weight loss in two
endothermic steps (∆H = 87.4 3.0 kJ mol–1, which is
comparable with ∆vapH for 2,3ꢀdimethylpyridine,14 two
first endotherms) is 30.0 2.0%. In the temperature range
of 230—470 °C, the weight loss persists, and the processes
are accompanied by rather complex energy changes. The
total weight loss is 79.3 2.0%. According to the Xꢀray
powder diffraction analysis, Mn3O4 is the final solid deꢀ
composition product. Unlike the manganeseꢀcontaining
analog, iron compound 12 retains stability in a broader
temperature range, up to 160 °C (Figs 6, e and 7, e). The
decomposition starts at 161—165 °C. The first step in the
temperature range of 165—225 °C is endothermic (∆H =
80.5 2.5 kJ mol–1, the value is comparable with ∆vapH
The thermal decomposition of the quinoline comꢀ
plexes (C9H7N)2M2(µꢀOOCCMe3)4) (M = Co (5), Ni (6),
or Cu (7)) proceeds similarly. For example, the deꢀ
composition of cobalt complex 5 starts at 157 2.0 °C
(Fig. 5, a, d). In the first step (157—222 °C), the proꢀ
cesses is endothermic ∆H = 116.5 8.5 kJ mol–1, and the
weigh loss is 33.5 1.0%. Under the experimental condiꢀ
tions, step II is almost not manifested in the thermoꢀ
grams, whereas the weight loss in step III (222—300 °C) is
61.7 1.0%.
The total weight loss is 95.2 1.0%. This is not surprisꢀ
ing because, as we have demonstrated in the recent study,3
the highly volatile octanuclear complex Co8(µ4ꢀO)2(µ2ꢀ
piv)6(µ3ꢀpiv)6 is the final decomposition product under
these conditions, and it is readily removed from the reacꢀ
tion zone.
Nickel complex 6 proved to be thermally more stable
(decomposition starts at 231 2 °C; see Fig. 5, b, e). In the
first step (230—280 °C), the process is endothermic, and
the weight loss is 33.9 1.5%. The second step (weight
loss is 46.8 1.5%) proceeds in the temperature range of
285—370 °C and is accompanied by energy release (beꢀ
ginning of the exotherm). In the temperature range of
370—450 °C, no weight loss is observed, but the energy is
released (exotherm of a complex shape). The total weight

1716
Russ.Chem.Bull., Int.Ed., Vol. 56, No. 9, September, 2007
Fomina et al.
Q/mW
Q/mW
Q/mW
5
–5
–2
–4
–6
–8
35
25
a
b
c
15
–15
–25
–35
5
–5
–15
–10
100
200 T/°C
150
300
T/°C
200
400 T/°C
m/mg
m/mg
m/mg
8
6
4
2
8
6
4
2
10
8
d
e
f
6
4
0
200
400 T/°C
150
300
T/°C
200
400 T/°C
Fig. 5. Temperature dependences of the heat flux (a—c) and the weight loss (d—f ) for complexes 5 (a, d), 6 (b, e), and 7 (c, f ).
Table 1. Xꢀray powder diffraction analysis of solid decomposition products of compounds 7 and 11
Decomposition
Decomposition
CuO
Cu2O
Cu
product of 7
product of 11
[48—1548]*
[5—667]*
[4—836]*
d/Å
I/I0 (%)
d/Å
I/I0 (%)
d/Å
I/I0 (%)
d/Å I/I0 (%)
d/Å I/I0 (%)
2.535
2.530
30
100
2.530
2.520
2.465
2.330
2.135
2.090
1.855
1.505
1.375
1.278
20
100
20
80
5
40
10
10
10
20
2.532
2.524
37
100
2.465
2.135
100
37
2.330
80
2.324
99
2.088
1.278
100
80
1.860
1.505
1.375
10
10
10
1.868
1.506
1.375
30
20
14
1.510
27
* Powder Diffraction File, Swarthmore: Joint Committee on Powder Diffraction Standards.

Solidꢀstate thermolysis of pivalate complexes
Russ.Chem.Bull., Int.Ed., Vol. 56, No. 9, September, 2007 1717
Table 2. Characteristics of the decomposition of the dinuclear tetrabridged cobalt complexes
Characteristics
5
6
7
Boiling point of the ligand/°C
Number of steps
238
2
157
238
2
231
238
2
207
Temperature of the onset of decomposition/°C
Temperature range of step I/°C
Temperature range of step II/°C
Temperature range of step III/°C
Temperature of cessation of decomposition/°C
Final decomposition product
157—222
*
222—300
300
231—280
**
285—370
450
207—245
245—310
—
320
CuO
Co8(O)2(piv)12
NiO
* Was not isolated.
** Was not virtually isolated.
for 2,3ꢀdimethylpyridine14), and the weight loss in this
step is 30.3 1.5% (theoretical percentage of 2,3ꢀdimethylꢀ
pyridine in the complex is 29.3%). Presumably, the proꢀ
cess proceeding in this temperature range corresponds to
the removal of the coordinated ligand. In the temperature
range of 225—275 °C, no weight loss is observed, but the
energy is released, which is generally characteristic of the
formation of a new structure. The further heating in the
temperature range of 275—440 °C leads to the further
weight loss (48.5 1.5%) accompanied by complex energy
transformations in the sample. The energy changes qualiꢀ
tatively correspond to those observed earlier in the course
of thermal decomposition of the [Fe(µꢀOOCCMe3)2]n
polymer at temperatures above 280 °C.15 This suggests
that the polymeric iron pivalate complex is formed in the
temperature range of 225—275 °C, and then this complex
is decomposed. The total weight loss is 78.8 2.0%, and
αꢀFe2O3 is the final decomposition product (Xꢀray powꢀ
der diffraction data).
The decomposition of the cobalt complex
(2,3ꢀMe2C5H3N)2Co2(OOCꢀBut)4 (9) starts already at
97 2 °C (see Figs 6, b and 7, b). In the first step
(97—170 °C), the processes are endothermic (∆H =
89.5 5.0 kJ mol–1), and the weight loss is 29.8 1.0%,
which corresponds to elimination of both 2,3ꢀdimethylꢀ
pyridine molecules. Neither the weight loss nor changes
in the heat flux are observed in step II (170—210 °C).
In step III (220—280 °C), the weight loss is 65.0 1.0%.
The total weight loss is 94.8 1.0%, which correꢀ
sponds primarily to the formation of the volatile cluster
Co8(µ4ꢀO)2(µ2ꢀpiv)6(µ3ꢀpiv)6.
The nickel complex (2,3ꢀMe2C5H3N)2Ni2(OOCꢀ
But)4 (10) is thermally stable, and its decomposition starts
at temperatures above 225 °C (see Figs 6, c and 7, c). Two
Q/mW
Q/mW
Q/mW
2
–2
–0.1
–0.2
–0.3
1.0
a
b
c
0.5
0
–6
–10
–0.5
200
400
T/°C
100
200 T/°C
200
400 T/°C
Q/mW
Q/mW
d
e
5
–5
0
–0.4
–0.8
–1.2
–1.6
–15
–25
100
200
300
T/°C
200
400
T/°C
Fig. 6. Temperature dependences of the heat flux change for complexes 8 (a), 9 (b), 10 (c), 11 (d), and 12 (e).

1718
Russ.Chem.Bull., Int.Ed., Vol. 56, No. 9, September, 2007
Fomina et al.
m/mg
m/mg
m/mg
10
6
3
2
1
2.0
1.5
1.0
0.5
a
b
c
2
0
250
500 T/°C
100
m/mg
200 T/°C
150
300
T/°C
m/mg
8
6
4
2
1.6
d
e
1.2
0.8
150
300
T/°C
150
300
T/°C
Fig. 7. Temperature dependences of the weight loss for complexes 8 (a), 9 (b), 10 (c), 11 (d), and 12 (e).
steps are clearly distinguished. The weight loss in the first
step is 38.0 2.0%, which is substantially larger than the
theoretical percentage of 2,3ꢀdimethylpyridine in the
complex (28.9%) and is, apparently, indicative of intramoꢀ
lecular reactions proceeding with the involvement of carꢀ
boxylate groups. The process is endothermic. At temperaꢀ
tures above 280 °C, the process is exothermic. The total
weight loss in the overall temperature range is 84.0 2.0%.
According to the Xꢀray powder diffraction analysis, nickel
metal is the final decomposition product. This result is
quite unexpected because the earlier study16 has demonꢀ
strated that the thermolysis of dinuclear nickel complexes
containing the structurally similar tetrabridged metal carbꢀ
oxylate core with the apical pyridine16 and quinoline
ligands affords NiO. Apparently, this is due to the influꢀ
ence of the methyl group in the α position acting as an
intramolecular reducing agent and promoting intramoꢀ
lecular ligandꢀligand redox reactions already in the first
step of decomposition.
Several steps are clearly distinguished in the thermal
decomposition process of the copper complex
(2,3ꢀMe2C5H3N)2Cu2(µꢀOOCCMe3)4 (11) (see Figs 6, d
and 7, d). In the first step, in the temperature range of
153—230 °C ( 2 °C), the total weight loss is 30.0 1.0%,
which is also slightly larger than the theoretical percentꢀ
age of 2,3ꢀdimethylpyridine in the molecule. This step
includes, in turn, the following two steps: the step in the
temperature range of 153—188 °C with the weight loss of
14.3 1.0% and the step in the temperature range of
188—230 °C with the weight loss of 15.7 1.0%. Both
steps are accompanied by energy absorption (endotherms),
which does not excludes intramolecular interactions.
Step II (230—260°C ( 2 °C)) is accompanied by
a small weight loss but by a rather large endotherm
(266.7 9.5 kJ mol–1), which apparently corresponds to
the structural rearrangement of the compound. Finally,
in step III (260—320 °C), the weight loss is 50.2 1.5%,
the processes are exothermic, and the energy changes are
rather complex. The total weight loss in the temperature
range under study is 80.0 1.5%. The phase composition
of the final solid decomposition product determined by
Xꢀray powder diffraction (see Table 1) is rather complex
and corresponds to a mixture of the CuO, Cu2O, and Cu
phases. A comparison of the intensities of the main reꢀ
flections for the phases and the results of the thermoꢀ
gravimetric analysis suggest that the phases are present in
a ratio of 4 : 1 : 2.
The decomposition of dinuclear pivalate complexes of
3d metals, from manganese to copper, with 2,3ꢀdimethylꢀ
pyridine ligands showed that active hydrocarbon substituꢀ
ents in the α position can substantially influence the charꢀ
acter of the thermolysis products, particularly, in the case
of the thermal degradation of complexes with metals at
the end of the row of the Periodic table having a rather
high oxidation potential (Table 3).
To summarize, we found possible ways of varying mild
thermolysis products of the whole class of coordination
precursors, in particular, of dinuclear tetrabridged pivalate
dimers with Group VII and VIII 3d metals and copper.
In our opinion, this result opens possibilities for the prepaꢀ
ration of various films and coatings based on this class of
carboxylates, whose synthesis presents no difficulties.

Solidꢀstate thermolysis of pivalate complexes
Russ.Chem.Bull., Int.Ed., Vol. 56, No. 9, September, 2007 1719
Table 3. Characteristics of the decomposition of the dinuclear tetrabridged complexes with 2,3ꢀdimethylpyridine
Characteristics
8
12
9
10
11
Boiling point of the ligand/°C
Number of steps
163.7
3
100
100—230
265—290
290—380
420
163.7
3
163.7
3
97
97—170
170—210
220—280
280
163.7
2
229
230—280
280—380
*
163.7
3
153
153—230
230—260
260—320
400
Temperature of the onset of decomposition/°C
Temperature range of step I/°C
Temperature range of step II/°C
Temperature range of step III/°C
Temperature of cessation of decomposition/°C
Final decomposition product
161—165
165—225
275—300
300—380
420
420
Ni
Mn3O4
Fe2O3
Co8(O)2(piv)12
CuO, Cu2O, Cu
* The steps of melting of the complex, the removal of the coordinated ligand, and the complete degradation of the metal core were not
distinguished in the temperature dependence of the weight loss.
(CuKα1 radiation) using germanium as the internal standard
(Xꢀray diffraction patterns were processed on an IZAꢀ2 comꢀ
parator with an accuracy of 0.01 mm) and with the use of the
STOE Powder Diffraction System.
Experimental
All synthetic operations were carried out under pure argon
with the use of oxygenꢀfree or anhydrous solvents using the
standard Schlenk technique. The starting polynuclear pivalates
[M(OOCBut)2]n (M = Co,3 Ni,3 or Cu17), [(η ꢀEtOH)Mn(µꢀ
1
Synthesis of complexes
OOCCMe3)2]n,18 and (Me2C5H3N)2M2(µꢀOOCCMe3)4 (M =
Co,3 Ni,3 or Fe7) were prepared according to procedures deꢀ
scribed earlier. The synthesis of new compounds was carried out
with the use of trimethylacetic acid (Acros Organics), 2,3ꢀdiꢀ
methylpyridine (Acros Organics), and quinoline (Aldrich).
The IR spectra of compounds 5—11 were recorded on a
Specord Mꢀ80 spectrophotometer in KBr pellets. The elemental
analysis of compounds 5—11 was carried out on a Carlo Erba
C,H,N analyzer in the Center of Collaborative Research of the
N. S. Kurnakov Institute of General and Inorganic Chemistry of
the Russian Academy of Sciences. The static magnetic susceptiꢀ
bility was measured on a SQUID MPMSꢀ59 Quantum Design
magnetometer in the temperature range of 2—300 K. The efꢀ
fective magnetic moments were calculated by the equation
Bis(quinolino)tetra(µ ꢀO,O´ꢀtrimethylacetato)dicobalt(II),
2
(C9H7N)2Co2(µ ꢀOOCCMe3)4 (5). A solution of quinoline
2
(0.198 g, 1.53 mmol) in benzene (30 mL) was added to
[Co(OOCCMe3)2]n (0.4 g, 1.53 mmol; per formula unit
Co(OOCCMe3)2). The solution was stirred at 80 °C for 20 min.
The resulting redꢀcrimsonꢀcolored solution was concentrated at
0.1 Torr and 20 °C to 15 mL and allowed to crystallize at 5 °C.
Green crystals that precipitated after storage for 24 h were sepaꢀ
rated by decantation, washed with benzene, and dried under a
stream of argon. The yield of compound 5 was 0.57 g (95.0%
based on the starting amount of the ligand). Found (%): C, 58.02;
H, 6.58; N, 3.38. Co2C38H50N2O8. Calculated (%): C, 58.48;
H, 6.41; N, 3.6. IR (KBr), ν/cm–1: 3272 w, 2960 w, 2364 w,
2344 m, 2324 w, 1700 w, 1684 w, 1668 w, 1610 v.s, 1512 m,
1480 s, 1456 m, 1420 v.s, 1372 m, 1356 m, 1224 m, 1052 s,
956 w, 892 m, 804 s, 784 s, 736 w, 608 s, 488 w, 420 w, 324 w.
The synthesis afforded crystals suitable for Xꢀray diffraction.
µ
eff = (8χMT )1/2
The thermal decomposition of compounds 5—12 was studꢀ
.
ied by differential scanning calorimetry and thermogravimetry
on DSCꢀ20 and TGꢀ50 units of a Mettler TAꢀ3000 thermoꢀ
analyzer. Samples of compounds 5—12 were heated under dry
argon at a constant rate of 5 deg min–1 (in all experiments). For
each compound, two differential scanning calorimetry experiꢀ
ments and three thermogravimetric experiments were perꢀ
formed. The weight loss upon thermal degradation was deterꢀ
mined directly on the TGꢀ50 unit; the accuracy of weighing
was 2•10–3 mg. The thermal decomposition was studied in
steps by differential scanning calorimetry, which involved the
division of the total temperature range into intervals. The size
and number of these intervals were determined based on the
overall pattern of the weight loss upon decomposition. This
approach allowed us to determine the weight loss in each temꢀ
perature range and compare the results of DSC with the
thermogravimetric data. The results of these methods were in
satisfactory agreement, which confirms the reliability of the exꢀ
perimental data. The accuracy of the determination of anomaꢀ
lous points and thermal effects in the DSC curves was 1° and
0.5%, respectively.
Bis(quinolino)tetra(µ ꢀO,O´ꢀtrimethylacetato)dinickel(II),
2
(C9H7N)2Ni2(µ ꢀOOCCMe3)4 (6). A solution of quinoline
2
(0.148 g, 1.15 mmol) in benzene (25 mL) was added to
Ni6(OOCCMe3)12 (0.3 g, 0.15 mmol). The paleꢀgreen reaction
solution was stirred at 80 °C for 20 min, concentrated at 0.1 Torr
and 20 °C to 10 mL, and allowed to crystallize at 20 °C. Darkꢀ
green crystals that precipitated after storage for 24 h were sepaꢀ
rated by decantation, washed with cold benzene, and dried unꢀ
der a stream of argon. The yield of compound 6 was 0.39 g
(87% based on the starting amount of the ligand). Found (%):
C, 58.12; H, 6.90; N, 3.83. Ni2C38H50O8N2. Calculated (%):
C, 58.5; H, 6.4; N, 3,6. IR (KBr), ν/cm–1: 3226 w, 2956 w,
2924 w, 1772 w, 1684 w, 1614 w, 1595 v.s, 1484 s, 1456 m,
1420 v.s, 1376 m, 1360 m, 1224 m, 1052 s, 960 w, 896 m, 800 s,
780 s, 736 w, 616 s, 492 w, 432 m.
The synthesis afforded crystals suitable for Xꢀray diffraction.
Bis(quinolino)tetra(µ ꢀO,O´ꢀtrimethylacetato)dicopper(II),
2
(C9H7N)Cu2(µ ꢀOOCCMe3)4 (7). Quinoline (0.146 g,
2
The Xꢀray powder diffraction analysis of the decomposition
products was carried out on a FRꢀ552 monochromator chamber
1.13 mmol) was added to a solution of [Cu2(OOCCMe3)4]n
(0.3 g, 1.13 mmol; per formula unit Cu(OOCCMe3)2) in benꢀ

1720
Russ.Chem.Bull., Int.Ed., Vol. 56, No. 9, September, 2007
Fomina et al.
Table 4. Crystallographic parameters of complexes 7 and 8
Parameter
7
8
Molecular formula
Molecular weight
C
38H50Cu2N2O8
789.88
C34H54Mn2N2O8
728.67
Space group
a/Å
b/Å
P2(1)/c
11.7401(10)
18.7762(10)
9.3483(10)
90
96.669(10)
90
2046.7(3)
2
P2(1)/c
11.096(3)
18.743(5)
32.408(8)
90
91.373(10)
90
6738(3)
6
c/Å
α/deg
β/deg
γ/deg
V/Å3
Z
ρ
calc/g cm–3
1.282
1.677
1.077
0.602
µ/cm–1
Radiation
CuꢀKα (λ = 1.5418 Å)
MoꢀKα (λ = 0.71073 Å)
θꢀ2θꢀScan range/deg
3.79—74.90
1.66—25.03
Number of measured reflections
4280
26592
Number of reflections with I > 2σ(I )
4034
10075
R1
wR2
0.0614
0.1884
0.0908
0.2168
zene (30 mL). The reaction solution was stirred at 80 °C for
15 min, concentrated at 0.1 Torr and 20 °C to 15 mL, and
allowed to crystallize at 20 °C. Green crystals that precipitated
after storage for 24 h were separated by decantation, washed
with cold benzene, and dried in air. The yield of compound 7
was 0.4 g (89.7% based on the starting amount of copper).
Found (%): C, 57.82; H, 6.48; N, 3.31. C38H50Cu2N2O8. Calꢀ
20 °C to 15 mL, and allowed to crystallize at ~20 °C. Darkꢀ
green crystals that precipitated after storage for 24 h were sepaꢀ
rated by decantation, washed with cold benzene, and dried in air.
The yield of compound 11 was 0.404 g (80.8% based on the
starting amount of copper). Found (%): C, 54.83; H, 7.95;
N, 3.37. C34H54Cu2N2O8. Calculated (%): C, 54.69; H, 7.24;
N, 3.75. IR (KBr), ν/cm–1: 3852 w, 3428 w, 2960 m, 2456 w,
2328 m, 2064 w, 1732 w, 1612 v. s, 1480 s, 1372 s, 1224 m, 896 s,
788 w, 724 w, 624 w, 436 w, 356 w, 320 s.
The synthesis afforded crystals suitable for Xꢀray diffraction.
Xꢀray diffraction study. Xꢀray reflections for complex 7 were
measured on an automated EnrafꢀNonius CADꢀ4 diffractometer;
for complex 8, on an automated Bruker AXS SMART 1000
diffractometer equipped with a CCD detector (graphite monoꢀ
chromator, 120 K, ωꢀscanning technique, the scan step was 0.3°,
the exposure time per frame was 30 s) using a standard proceꢀ
dure.19 Semiempirical absorption corrections were applied.20
The crystallographic parameters and the refinement statistics
for the structures of 7 and 8 are given in Table 4.
The structures of both complexes were 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 groups, which were refined isotropically). The hydroꢀ
gen atoms of the tertꢀbutyl substituents of the pivalate ligands
and the pyridine rings in the coordinated amine molecules were
positioned geometrically and refined using a riding model. All
calculations were performed with the use of the SHELX97 proꢀ
gram package.21
culated (%): C, 57.72; H, 6.33; N, 3.54. IR (KBr), ν/cm–1
:
3232 m, 2960 w, 1664 w, 1508 m, 1480 m, 1416 m, 1360 w,
1316 w, 1260 w, 1044 s, 952 w, 896 w, 816 w, 804 s, 780 s, 736 w,
616 s, 488 w, 440 m.
The synthesis afforded crystals suitable for Xꢀray diffraction.
Bis(2,3ꢀdimethylpyridino)tetra(µ ꢀO,O´ꢀtrimethylacetato)diꢀ
2
manganese(II), (2,3ꢀ(CH3)2C5H3N)2Mn2(µ ꢀOOCCMe3)4 (8).
2
A solution of 2,3ꢀdimethylpyridine (0.16 g, 1.5 mmol) in benꢀ
1
zene (20 mL) was added to [(η ꢀEtOH)Mn(µꢀOOCCMe3)2]n
(0.3 g, 1.0 mmol). The reaction mixture was stirred at 80 °C
under argon for 1 h. The resulting solution was filtered, concenꢀ
trated to 8 mL, and kept at 20 °C for 3 days. Colorless crystals
that precipitated were separated from the solution by decantaꢀ
tion, washed with cold benzene (10 °C), and dried under a
stream of argon. The yield of compound 8 was 0.27 g (73% based
on the starting amount of manganese). Found (%): C, 56.3;
H, 7.6; N, 4.0. C34H54Mn2N2O8. Calculated (%): C, 56.04;
H, 7.47; N, 3.84. IR (KBr), ν/cm–1: 2956 m, 2928 m, 2872 w,
1664 m, 1612 s, 1480 m, 1456 w, 1420 s, 1372 m, 1360 m,
1284 w, 1260 w, 1228 m, 1192 w, 1140 w, 1140 w, 1100 w,
1016 m, 936 w, 892 m, 856 w, 812 m, 788 m, 748 w, 724 w,
672 w, 604 s, 572 w, 416 s.
The synthesis afforded crystals suitable for Xꢀray diffraction.
Bis(2,3ꢀdimethylpyridino)tetra(µ ꢀO,O´ꢀtrimethylacetato)diꢀ
2
This study was financially supported by the Russian
Foundation for Basic Research (Project Nos 07ꢀ03ꢀ00408,
07ꢀ03ꢀ00707, 05ꢀ03ꢀ32767, 05ꢀ03ꢀ794, 05ꢀ03ꢀ08203, and
06ꢀ03ꢀ08086), the Russian Academy of Sciences (Target
Program for Basic Research of the Division of Chemistry
copper(II), (CH3)2C5H3N)2Cu2(µ ꢀOOCCMe3)4 (11). 2,3ꢀDiꢀ
2
methylpyridine (0.202 g, 1.88 mmol) was added to a solution of
[Cu2(OOCCMe3)4]n (0.5 g, 1.88 mmol; per formula unit
Cu(OOCCMe3)2) in benzene (30 mL). The reaction mixture
was stirred at 80 °C for 5 min, concentrated at 0.1 Torr and

Solidꢀstate thermolysis of pivalate complexes
Russ.Chem.Bull., Int.Ed., Vol. 56, No. 9, September, 2007 1721
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Received February 1, 2007;
in revised form April 25, 2007