Thermal decomposition of dinuclear complexes LM(μ-OOCR)4ML (L is α-substituted pyridine):2. Influence of α-amino groups on the nature of the thermolysis products of MnII, FeII, Co II, and CuII pivalat

Article abstract of DOI:10.1007/s11172-007-0267-x

The solid-state thermal decomposition of the dinuclear pivalate complexes LM(μ-OOCR)₄ML, both those synthesized earlier (M = Mn ^II, Fe^II, or Co^II; L = 2,6-(NH ₂)₂C₅H₃N

Full text of DOI:10.1007/s11172-007-0267-x

Russian Chemical Bulletin, International Edition, Vol. 56, No. 9, pp. 1722—1730, September, 2007
1722
Thermal decomposition of dinuclear complexes LM(µꢀOOCR)4ML
(L is αꢀsubstituted pyridine).
2.* Inf luence of αꢀamino groups on the nature of the thermolysis products
of MnII, FeII, CoII, and CuII pivalates**
I. G. Fomina,aꢀ Zh. V. Dobrokhotova,a G. G. Aleksandrov,a M. A. Kiskin,a M. A. Bykov,b 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: mich@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 dinuclear pivalate complexes
LM(µꢀOOCR)4ML, both those synthesized earlier (M = MnII, FeII, or CoII; L =
2,6ꢀ(NH2)2C5H3N)) and new complexes (M = CuII; L = 2,6ꢀ(NH2)2C5H3N or
(2ꢀNH2)(6ꢀCH3)C5H3N), was studied by differential scanning calorimetry and
thermogravimetry. The decomposition of the CoII complexes is accompanied by the aggregaꢀ
tion to form the volatile octanuclear complex Co8(µ ꢀO)2(µ ꢀOOCCMe3)12 (n = 2 or 3),
4
n
whereas the thermolysis of the MnII, FeII, and CuII complexes is destructive, the phase compoꢀ
sition of the decomposition products being substantially dependent on the nature of metal and
the α substituent R in the apical organic ligand.
Key words: tetrabridged dinuclear manganese, iron, cobalt, and copper pivalate complexes,
2,6ꢀdiaminopyridine, 2ꢀaminoꢀ6ꢀmethylpyridine, solidꢀstate thermal decomposition, Xꢀray
diffraction study, magnetic properties.
In the previous paper,1 we have demonstrated that the
early thermolysis steps. The final degradation affords
oxides CuO or NiO, respectively. The related manganese
and iron complexes generate only metal oxides regardless
of their composition. The thermolysis of the correspondꢀ
ing dinuclear cobalt pivalates affords the volatile octaꢀ
nuclear cluster Co8(µ4ꢀO)2(µ2ꢀPiv)6(µ3ꢀPiv)6 already in
the early steps of heating.1,3 Taking into account the obꢀ
served effects, there were reasons to expect that the therꢀ
mal decomposition of these complexes can be controlled
by varying the nature of the apical ligands. In the present
study, we investigated the thermal decomposition of
dinuclear pivalate complexes with NH2ꢀsubstituted pyriꢀ
dine ligands. It is known4,5 that the NH2 group is easily
oxidized and can formally serve as an innerꢀsphere reducꢀ
ing agent or can be involved in condensation reactions.
The choice of the ligand was also based on the known
data on the thermolysis of methylhydrazine complexes of
3d metals yielding6 metals or even alloys (upon the comꢀ
bined thermolysis of the complexes) at rather low temꢀ
peratures (lower than 400 °C).
nature of αꢀsubstituted pyridine L (in particular, the α subꢀ
stituent R) in the dinuclear tetracarboxylate complexes
LM(µꢀOOCBut)4ML (M = Ni or Cu) has a substanꢀ
tial effect on the products of the solidꢀstate thermal
(20—400 °C) decomposition of the complexes. For exꢀ
ample, in the case of αꢀR = Me (in 2,3ꢀdimethylpyridine),
the thermal decomposition of the nickel complex proꢀ
duces nickel metal only, whereas the thermolysis of the
analogous copper complex affords a mixture of products,
viz., CuO, Cu2O, and copper metal. This is a substantial
difference from the situation observed for quinoline deꢀ
rivatives (CH group of the conjugated benzene ring is in
the α position) or complexes with pyridine2 (αꢀR = H, for
the nickel complex), which readily eliminate L in the
* For Part 1, see Ref. 1.
** Dedicated to Academician G. A. Abakumov on the occasion
of his 70th birthday.
† Deceased.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1660—1668, September, 2007.
1066ꢀ5285/07/5609ꢀ1722 © 2007 Springer Science+Business Media, Inc.

Thermolysis of dinuclear pivalate complexes
Russ.Chem.Bull., Int.Ed., Vol. 56, No. 9, September, 2007
1723
Results and Discussion
(Cu—N, 2.243(3) Å), the N—Cu...Cu—N fragment beꢀ
ing virtually linear (N—Cu...Cu angle, 178.8(3)°). The
presence of intramolecular hydrogen bonding is an imꢀ
portant structural feature of complex 5. Since donor solꢀ
vent molecules are absent in the crystal structure of comꢀ
plex 5, the protons of the αꢀamino groups interact
with the oxygen atoms of the bridging pivalate ligands
(N—H...O, 2.109—2.197 Å; N—H...O angles, 145—151°).
This is formally indicative of the possibility of the
chemical interaction between these ligands in the course
of thermal decomposition of the complex. It appeared
that no radical changes are observed upon the replaceꢀ
ment of diaminopyridine L1 by the ligand containing
one amino group, viz., 2ꢀaminoꢀ6ꢀmethylpyridine (L2).
Thus, the reaction of 4 with L2 in benzene (Cu : L2 =
1 : 1, 80 °C) produces the dinuclear complex
[(2ꢀNH2)(6ꢀMe)C5H3N]2Cu2(OOCBut)4 (6) in virtually
quantitative yield.
According to the Xꢀray diffraction study, the distance
between the copper atoms in molecule 6 is 2.730(1) Å
(Fig. 2), which is somewhat shorter than the correspondꢀ
ing distance in complex 5, although the Cu—N (apical
ligand) distance (2.296(3) Å) is slightly longer than
the corresponding distance in diamine complex 5. The
N—Cu...Cu—N fragment is also virtually linear
(N—Cu...Cu angle, 177.14(7)°) like that in 2,6ꢀdiꢀ
aminopyridineꢀcontaining analog 5. In complex 6, there
is intramolecular hydrogen bonding between the hydroꢀ
gen atoms of the transꢀamino groups of two ligands L2
and the oxygen atoms of the bridging transꢀpivalate anions
(N—H...O, 2.200—2.515 Å; N—H...O angles, 127—144°).
Therefore, it can be noted that the dinuclear structures of
complexes 5 and 6 are additionally stabilized by intramoꢀ
lecular hydrogen bonding with the involvement of the
apical ligands.
Earlier, we have synthesized7,8 the dinuclear tetraꢀ
bridged manganese(II) and iron(II) pivalate complexes
[(NH2)2C5H3N]2M2(µꢀOOCCMe3)4•4MeCN (M =
Mn (1) or Fe (2)) with the apical diaminopyridine
ligands by the reaction of the [(EtOH)Mn(OOCBut)2]n or
[Fe(OOCBut)2]n polymers with 2,6ꢀdiaminopyridine (L1)
in acetonitrile. These complexes contain MeCN solvent
molecules, which form hydrogen bonds with the protons
of the amino groups in the α positions of the pyridine
ligand. These compounds proved to be rather stable
under argon as opposed to the nickel and cobalt comꢀ
plexes, which were immediately transformed into amidine
complexes in the presence of acetonitrile.9 The diꢀ
nuclear cobaltꢀcontaining analog of complexes 1 and 2,
[(NH2)2C5H3N]2Co2(µꢀOOCCMe3)4 (3), was syntheꢀ
sized in dichloromethane (as the solvate with two CH2Cl2
molecules),10 whereas attempts to synthesize the related
nickel complex failed.
Synthesis of aminopyridineꢀcontaining copper(II) pivalates
Since the copper(II) complex with L1 was unknown,
we synthesized this compound by the reaction of the
[Cu(OOCBut)2]n polymer (4)11 with this ligand using the
ratio Cu : L1 = 1 : 1. The reaction of 4 with 2,6ꢀdiꢀ
aminopyridine (L1) in inert benzene produced the
[(NH2)2C5H3N]2Cu2(µꢀOOCCMe3)4 complex (5) as the
solvate with one benzene molecule in virtually quantitaꢀ
tive yield. According to the Xꢀray diffraction study, the
distance between the copper atoms in antiferromagnetic
complex 5 (µeff = 1.920 (260 K)—0.171 µB (5 K))
is 2.762(1) Å (Fig. 1), which is longer than the corꢀ
responding distances in the dinuclear fragments
Cu2(µꢀOOCCMe3)4 of the starting polymer 4 (Cu...Cu,
2.580 Å).11 The ligand molecule is coordinated in a
monodentate fashion through the pyridine nitrogen atom
An attempt to prepare an analog of complex 5, viz.,
the dinuclear copper complex, in which the amino
C(5)
C(9)
C(4)
C(3)
C(9)
C(10)
C(8)
C(2)
C(19)
C(7)
C(6)
C(18)
H(2A)
O(2)
C(1)
O(1)
N(2)
C(11)
C(8)
C(17)
C(12)
C(13)
H(5D)
N(5)
C(26)
C(7)
N(3)
O(3)
C(27)
C(28)
H(3E)
C(25)
O(8)
C(24)
O(4)
O(4)
Cu(1)
O(3)
Cu(1)
C(20)
C(10)
N(1)
C(16)
Cu(1)
C(11)
Cu(2)
N(4)
O(7)
N(1)
C(15)
C(23)
O(6)
C(14)
C(16)
C(30)
C(14)
N(1)
O(1)
C(29)
O(5)
C(22)
C(21)
N(2)
N(6)
O(2)
N(2)
H(6A)
C(15)
C(1)
H(2A)
C(5)
H(2A)
C(12)
C(13)
C(2)
C(4)
Fig. 1. Structure of complex 5.
Fig. 2. Structure of complex 6.

1724
Russ.Chem.Bull., Int.Ed., Vol. 56, No. 9, September, 2007
Fomina et al.
groups are involved in hydrogen bonding with an external
solvating agent, for example, with acetonitrile (as was
observed in manganese and iron compounds 1 and 2),
led to an unexpected result. It appeared that the reaction
of copper polymer 4 with L1 in MeCN under an inert
atmosphere produces green cocrystals of the antiferroꢀ
magnetic compound {[(NH2)2C5H3N]2Cu2(OOCBut)4•
•(CH3CN)2Cu2(OOCBut)4]}•2CH3CN (7) (Fig. 3) as a
solvate with two acetonitrile molecules (7•2CH3CN),
angle, 173.03(8)°). The Cu—N distance in 7a
(2.273(3) Å) is slightly longer than that in 5, although the
N—Cu...Cu—N fragment remains linear (N—Cu...Cu
angle, 177.82(8)°). Apparently, this effect is, to some exꢀ
tent, associated with the presence of additional hydrogen
bonding between the protons of the αꢀamino groups and
the nitrogen atoms of the acetonitrile solvent molecules
(N—H...NCMe, 2.26(2) Å) in the crystal structure of 7а,
resulting in the "pushing off" of the L—Cu fragment from
the dimetal tetracarboxylate core. As opposed to comꢀ
plex 7а, this binding is absent in complex 7b, as well as in
complex 5, in which, on the contrary, intramolecular
hydrogen bonding and the tightening effect are observed.
Thermal decomposition of dinuclear aminopyridineꢀconꢀ
taining Mn, Fe, Co, and Cu pivalate complexes. In a search
for ways of using coordination compounds as molecular
precursors of ultrathin films (including nanosized strucꢀ
tures),12,13 it is of particular interest to investigate the
mild thermolysis of dinuclear tetrapivalates with 3d metal
atoms, which are readily soluble in organic solvents and
contain ligands serving as potential reducing agents for
metals. This process holds promise for preparing ultrathin
µ
eff = 2.693 µB (300 K)—0.120 µB (2 K), in nearly quantiꢀ
tative yield in spite of the ratio L1 : Cuat = 1 : 1. Accordꢀ
ing to the Xꢀray diffraction study, the crystal structure
of 7 consists of two different centrosymmetric dinuclear
complexes, viz., the target diaminopyridine complex
[(NH2)2C5H3N]2Cu2(OOCBut)4 (7а) (analog of 5) and
the dinuclear complex (CH3CN)2Cu2(OOCBut)4 (7b),
which is apparently generated in the step of dissolution of
polymer 4 in MeCN. The Cu...Cu distance between the
copper atoms in complex 7a is 2.7059(7) Å, which is
shorter than that observed in compound 5 (Cu...Cu,
2.7621(11) Å) but is somewhat longer than that in 7b
(Cu...Cu, 2.6349(8) Å; Cu—N, 2.209(3) Å; N—Cu...Cu
C(1S)
C(2S)
N(1S)
C(15)
Cu(2)
Cu(2)
O(5)
O(6)
C(13)
C(12)
O(8)
O(7)
C(14)
C(16)
C(17)
C(19)
C(18)
C(20)
O(4)
Cu(1)
C(8A)
O(1)
O(3)
C(6)
C(18)
C(10A)
Cu(1)
C(1)
N(2)
C(25)
O(2)
C(5)
C(4)
N(1)
C(2)
N(3)
C(24)
C(23)
C(21)
C(22)
C(3)
Fig. 3. Structure of the {[(NH2)2C5H3N]2Cu2(OOCBut)4•(CH3CN)2Cu2(OOCBut)4}•2CH3CN cocrystalline complex (7).

Thermolysis of dinuclear pivalate complexes
Russ.Chem.Bull., Int.Ed., Vol. 56, No. 9, September, 2007
1725
metal films at moderate temperatures (<400 °C), due to
which it can compete with the known14,15 energyꢀconꢀ
suming electrochemical methods. For this purpose,
we studied the thermolysis of molecular precursors,
viz., aminopyridineꢀcontaining MnII, FeII, CoII, and
CuII pivalate complexes, which can be synthesized in virꢀ
tually quantitative yields.
The thermolysis of the diaminopyridine manganese
and iron pivalate complexes [(NH2)2C5H3N]2M2(µꢀ
OOCCMe3)4•4MeCN (M = Mn(1) or Fe(2)) was found
to proceed similarly to the thermolysis of their analogs
with lutidine.1 The thermolysis of 1 and 2 starts with the
hydrogen bond cleavage and the removal of the acetoniꢀ
and 154.5 4.0 kJ mol–1 and the weight loss of 24.2 1.0%
and 24.4 1.0%, respectively. It is likely that the neutral
coordinated diaminopyridine ligand is eliminated and
a new structure, presumably, with the composition
[M(µꢀOOCCMe3)2]n, starts to form in this temperature
range;1 however, the step of formation of a stable interꢀ
mediate was not observed for 2. In the case of 1, the
temperature range of the existence of the corresponding
intermediate is rather narrow.
The last thermolysis step (310—485 °C and
315—500 °C for 1 and 2, respectively) is accompanied by
a complexꢀshaped thermal effect. In this step, the weight
loss is 39.6 1.0% and 39.1 1.0% for 1 and 2, respecꢀ
tively. The total weight loss is 81.9 1.5% and 81.7 1.5%
for complexes 1 and 2, respectively. According to the
Xꢀray powder diffraction analysis, the thermolysis affords
mixedꢀvalence oxides Mn3O4 and Fe3O4, respectively, as
the final products (Table 1).
trile solvent molecules (∆evapH = 29.7 kJ mol–1, tevap
=
82 °C)16 in two steps accompanied by energy absorption
(50—108 °C, 128.5 3.5 kJ mol–1 for 1; 50—113 °C,
132 3.5 kJ mol–1 for 2) (Fig. 4). It can be seen that the
thermal effects for both compounds are equal within exꢀ
perimental error. After elimination of the solvent molꢀ
Unlike manganese and iron complexes 1 and 2, the
cobalt compound [(NH2)2C5H3N]2Co2(µꢀOOCCMe3)4•
•2CH2Cl2 (3) contains two dichloromethane solvent molꢀ
ecules. The preliminary thermolysis step of 3 (42—80 °C)
is accompanied by the endotherm ∆H = 58.5 4.5
kJ mol–1, and the weight loss is 19.2 1.0% (Fig. 5). Apꢀ
parently, this effect corresponds to the removal of the
ecules, the product melts without decomposition (tmelt
111.0 1.0 °C, ∆meltH = 38.5 3.0 kJ mol–1 for 1; tmelt
=
=
115.0 1.0 °C, ∆meltH = 47.5 3.0 kJ mol–1 for 2). The
melting point and the enthalpy of melting for the ironꢀ
containing complex are somewhat higher than those for
the manganese complex. The first decomposition step of
dinuclear tetrabridged complexes 1 and 2 proceeds in the
temperature ranges of 148—290 °C and 160—315 °C and
is accompanied by the endotherms of 138.0 4.0 kJ mol–1
solvent molecules (for CH2Cl2, ∆vapH = 28.06 kJ mol–1
,
the boiling point is 40 1 °C).16 At temperatures above
80 °C, the unsolvated dimer is formed. For this dimer,
Q/mW
0
Q/mW
–1
a
b
–2
–3
–4
–5
–6
–2
–4
–6
200
400
T/°C
200
400
T/°C
m/mg
m/mg
6
5
4
3
2
1
5
4
3
2
1
c
d
200
400
T/°C
200
400
T/°C
Fig. 4. Temperature dependences of the heat flux change (Q) (a, b) and the weight loss (m) (c, d) for complexes 1 (a, c) and 2 (b, d).

1726
Russ.Chem.Bull., Int.Ed., Vol. 56, No. 9, September, 2007
Fomina et al.
Table 1. Characteristics of the decomposition of dinuclear tetrabridged cobalt complexes 1—3 and 5—7
Characteristics
1*
2*
3
5*
6*
7*
Boiling point
of the ligand/°C
M—N bond length/Å
285
285
285
285
208
285(L1)
81(MeCN)
2.273(3) (L1)
2.209(3) (MeCN)
2
2.179
2.157—2.169
2.109
2.243(3)
2.296(3)
Number of steps
Temperature of the onset
of decomposition/°C
Temperature range/°C
step I
step II
step III
Temperature of cessation
of decomposition/°C
Final decomposition
product
2
148
2
160
2
165
1
139
1
128
115
148—290
290—310
310—485
485
160—315
**
315—500
510
165—230
**
230—300
230
139—400
***
128—400
***
115—140
150—400
***
***
400
***
400
400
Mn3O4
Fe3O4
Co8(O)2(piv)12
Cu
Cu
Cu, Cu2O
* Decomposition after the removal of the solvate solvent.
** Was not virtually isolated.
*** 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.
Q/mW
step I (165—230 °C) is accompanied by melting with
decomposition (tmelt = 164 1 °C). The total thermal efꢀ
fect of this step is 122.0 6.5 kJ mol–1, and the weight loss
is 22.5 1.5%. Step II of the thermolysis of 3 was not
distinguished. In step III (230—300 °C), the weight loss is
52.3 1.5%. The total weight loss is 94.0 1.5% (residue is
–5
a
6.0% of the initial weight). Hence, the observed situation
is typical of other dinuclear cobalt pivalate complexes.2,17
–10
At temperatures of about 230 °C, the highly volatile
octanuclear cluster Co8(µ4ꢀO)2(µ2ꢀpiv)6(µ3ꢀpiv)6 is
formed, and it is readily removed from the reaction zone.2
–15
This compound is the major final thermolysis product.
The main effects of the αꢀamino substituents in
100
200
T/°C
the thermal decomposition of pivalate dimers are obꢀ
served for complexes 5—7 containing copper(II) atoms.
This electronꢀrich metal has a rather high oxidation poꢀ
tential.
m/mg
6
4
2
In the course of decomposition of diaminopyridine
complex 5, the first thermolysis step involves the intramoꢀ
lecular hydrogen bond cleavage in the temperature range
of 40—70 °C. After the removal of the benzene solvent
molecules (75—120 °C), individual decomposition steps
are virtually indistinguishable. The decomposition starts
at temperatures above 139 °C, the onset of decomposiꢀ
tion being accompanied by melting (first endotherm)
(Fig. 6, a and c). The further deep decomposition proꢀ
ceeds in a wide temperature range from 139 to 400 °C and
is accompanied by a complex endotherm. In this temꢀ
perature range, the weight loss is 81.2 2.0%. The phase
composition of the solid final decomposition product deꢀ
termined by the Xꢀray powder diffraction method (Table 2)
b
150
300
T/°C
Fig. 5. Temperature dependences of the heat flux change (a)
and the weight loss (b) for complex 3.

Thermolysis of dinuclear pivalate complexes
Russ.Chem.Bull., Int.Ed., Vol. 56, No. 9, September, 2007
1727
Q/mW
m/mg
1
0
5
4
a
c
3
2
1
–1
–2
200
400 T/°C
200
400
T/°C
Q/mW
m/mg
7
6
5
4
3
2
1
2
0
b
d
–2
–4
–6
200
400 T/°C
200
400
T/°C
Fig. 6. Temperature dependences of the heat flux change (Q) (a, b) and the weight loss (m) (c, d) for complexes 5 (a, c) and 6 (b, d).
shows that copper metal is the only decomposition
product.
tion proceeds in a wide temperature range from 128
to 400 °C and is accompanied by a complex endotherm.
In this temperature range, the weight loss is 83.2 2.0%.
The phase composition of the solid final decomposition
product determined by Xꢀray powder diffraction (see
Table 2) shows that copper metal is the only decomposiꢀ
tion product.
The decomposition of the cocrystals of
{[(NH2)2C5H3N]2Cu2(OOCBut)4•(CH3CN)2Cu2(OOCBut)4}•
•2CH3CN (7) involves the removal of the acetonitrile
No principal differences in the thermolysis of methylꢀ
aminopyridine complex 6 and diaminopyridine complex 5
were observed. The first decomposition step of complex 6
also involves the intramolecular hydrogen bond cleavage
in the temperature range of 40—80 °C. The decomposiꢀ
tion starts at temperatures above 128 °C, the onset of
decomposition also being accompanied by melting (first
endotherm) (see Fig. 6, b and d). The deep decomposiꢀ
Table 2. Xꢀray powder diffraction analysis of the solid decomposition products of compounds 5—7
Decomposition
Decomposition
Decomposition
Cu
Cu2O
product of 5
product of 6
product of 7
[4ꢀ836]*
[5ꢀ667]*
d/Å
I/I0 (%)
d/Å
I/I0 (%)
d/Å
I/I0 (%)
d/Å
I/I0 (%)
d/Å
I/I0 (%)
2.463
2.130
2.092
1.810
1.510
1.279
40
5
100
50
5
2.465
2.135
100
37
2.090
1.805
100
60
2.085
1.807
100
50
2.088
1.808
100
46
1.510
27
1.278
50
1.278
30
10
1.278
20
*Powder Diffraction File, Swarthmore: Joint Committee on Powder Diffraction Standards.

1728
Russ.Chem.Bull., Int.Ed., Vol. 56, No. 9, September, 2007
Fomina et al.
upon thermolysis of CuII pivalates with quinoline and
lutidine1 or upon decomposition of Cu2(OOCBut)4•
•(HOOCBut)2 and polymer 4.18 In our opinion, these
results open possibilities for the directed formation of
films (including multilayer films) starting from dinuclear
3d metal pivalates as molecular precursors. In this case, it
is necessary to vary only the nature of the apical ligand,
which presents no serious difficulties.
Q/mW
10
5
0
–5
a
–10
–15
–20
Experimental
All synthetic operations were carried out under pure argon
with the use, if necessary, of deaerated or anhydrous solvents
using the standard Schlenk technique. The starting pivalates 1,7
2,8 and 4 (see Ref. 19) were synthesized according to procedures
described earlier. The synthesis of new compounds was carried
out with the use of trimethylacetic acid (Acros Organics), 2,6ꢀdiꢀ
aminopyridine (Acros Organics), and 2ꢀaminoꢀ6ꢀmethylpyridine
(MerckꢀSchuchardt).
The IR spectra were recorded on a Specord Mꢀ80 spectroꢀ
photometer in KBr pellets. The elemental analysis of comꢀ
pounds 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 magnetic susceptibility of compound
5•C6H6 was measured on a SQUID MPMSꢀ59 Quantum Deꢀ
sign magnetometer in the temperature range of 2—300 K. The
effective magnetic moments were calculated by the equation
200
400 T/°C
m/mg
3
2
1
b
200
400 T/°C
Fig. 7. Temperature dependences of the heat flux change (a)
and the weight loss (b) for complex 8.
µ
eff = (8χ T )1/2
.
M
The thermal decomposition of compounds 1—3 and 5—7
was studied by differential scanning calorimetry (DSC) and
thermogravimetry (TG) on DSCꢀ20 and TGꢀ50 units of a
Mettler TAꢀ3000 thermoanalyzer. Samples of compounds 1—3
and 5—7 were heated under dry argon at a constant rate of
5 deg min–1. For each compound, two DSC experiments and
three TG experiments were performed. The weight loss upon
thermal degradation was determined directly on tthe TGꢀ50
unit; the accuracy of weighing was 2•10–3 mg. The thermal
decomposition was studied in steps by DSC, 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 TG data.
The results of these methods were in satisfactory agreement,
which confirms the reliability of the experimental data. The
accuracy of the determination of anomalous points and thermal
effects in the DSC curves was 1° and 0.5%, respectively.
The Xꢀray powder diffraction analysis of the decomposition
products was carried out on a FRꢀ552 monochromator chamber
(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.
solvent molecules at the first step (68—101 °C); the
weight loss is 6.3 2.0%. At temperatures above 101 °C,
unsolvated cocrystals exist. For this compound, the weight
loss in step I (115—140 °C) is 5.9 1.0%. In this case, the
onset of decomposition is not accompanied by melting as
opposed to complexes 1—3, 5, and 6 (Fig. 7). In this
temperature range, the coordinated acetonitrile molecules
are apparently removed from the dinuclear complex
(CH3CN)2Cu2(OOCBut)4 (7b). This suggestion is conꢀ
firmed by the weight loss (percentage of two acetonitrile
molecules is 5.68%). Step II of decomposition (>150 °C)
occures in a wide temperature range (150—400 °C) and is
accompanied by energy changes. In step II, the weight
loss is 70.1 1.5%. The total weight loss is 82.3 1.5%.
The phase composition of the solid final decomposition
product determined by the Xꢀray powder diffraction
method (see Table 2) shows that the decomposition afꢀ
fords only a mixture of copper metal and copper(I) oxide
in a ratio of ~2 : 1.
The appearance of Cu2O among the thermolysis prodꢀ
ucts of complex 7 is, apparently, attributed to the presꢀ
ence of acetonitrile compound 7b involved in cocrystals 7.
At the same time, the presence of complex 7a containing
the diaminopyridine ligand in cocrystals 7 promotes the
formation of copper metal and is, presumably, responꢀ
sible for the absence of copper(II) oxide, which is formed
Synthesis of complexes
Complex
Co2[2,6ꢀ(NH2)2C5H3N]2(µ ꢀOOCCMe3)4•
2
•2CH2Cl2 (3•2CH2Cl2) (see Ref. 10). Dichloromethane (35 mL)
was added to the [Co(OOCCMe3)2]n polymer (0.5 g, 1.92 mmol;

Thermolysis of dinuclear pivalate complexes
Russ.Chem.Bull., Int.Ed., Vol. 56, No. 9, September, 2007
1729
per formula unit Co(OOCCMe3)2) and 2,6ꢀdiaminopyridine
(0.209 g, 1.92 mmol), and the reaction mixture was stirred at
35 °C for 10 min until the reagents were completely dissolved.
The solution was concentrated at 0.1 Torr and 20 °C to 10 mL
and kept at 5 °C for 12 h. Green crystals that precipitated were
separated by decantation, washed with cold dichloromethane,
and dried under a stream of argon. The solvate of compound 3
with two CH2Cl2 molecules was obtained in a yield of 0.83 g
(95% based on the starting amount of cobalt) Found (%):
C, 41.81; H, 6.03; 9.34. Co2C32H54Cl4N6O8 . Calculated (%):
C, 42.18; H, 5.93; N, 9.23. IR (KBr), ν/cm–1: 3490 m, 3360 m,
3420 s, 3236 w, 2960 s, 2868 s, 2814 m, 2336 m, 1636 s, 1612 v.s,
1592 v.s, 1536 m, 1484 s, 1460 s, 1456 v.s, 1420 v.s, 1376 m,
1360 v.s, 1308 s, 1268 s, 1228 s, 1176 s, 1104 w, 1028 w, 936 w,
896 m, 788 v.s, 776 s, 728 m, 696 m, 668 w, 608 v.s, 476 m,
424 w, 404 s, 308 m.
The crystals were used for the Xꢀray diffraction study.
Bis(2ꢀaminoꢀ6ꢀmethylpyridino)tetra(µ ꢀO,O´ꢀtrimethylacetꢀ
2
ato)dicopper(II), [(2ꢀNH2)(6ꢀCH3)C5H3N]2Cu2(OOCBut)4 (6).
Benzene (30 mL) was added to polymer 4 [Cu(OOCCMe3)2]n
(0.3 g, 1.129 mmol; per formula unit Cu(OOCCMe3)2) and
2ꢀaminoꢀ6ꢀmethylpyridine (0.122 g, 1.129 mmol), and the reꢀ
action mixture was stirred at 80 °C for 20 min until the reagents
were completely dissolved. The solution was concentrated at
0.1 Torr and 20 °C to 15 mL and kept at ~20 °C. Green crystals
that precipitated were separated by decantation, washed with
cold benzene, and dried in air. Compound 6 was obtained in a
yield of 0.41 g (96% based on the starting amount of copper).
Found (%): C, 51.86; H, 7.34; N, 7.26. C32H52Cu2N4O8. Calꢀ
culated (%): C, 51.39; H, 7.01; N, 7.49. IR (KBr), ν/cm–1
:
3444 m, 3368 m, 3320 m, 2964 s, 2908 m, 2864 m, 1696 m,
1668 m, 1636 s, 1616 s, 1600 s, 1540 m, 1516 m, 1480 s, 1456 s,
1416 s, 1375 m, 1356 m, 1276 w, 1260 m, 1224 s, 1192 w,
1172 w, 1096 m, 1028 m, 936 w, 896 m, 884 w, 868 w, 800 m,
788 m, 732 w, 716 w, 668 w, 624 m, 600 w, 552 w, 532 w, 444 w,
436 w, 400 w, 388 w, 356 w, 312 w.
The crystals were used for the Xꢀray diffraction study.
Bis(2,6ꢀdiaminopyridino)tetra(µ ꢀO,O´ꢀtrimethylacetato)diꢀ
2
copper(II), Cu2[2,6ꢀ(NH2)2C5H3N]2(µ ꢀOOCCMe3)4•C6H6
2
(5•C6H6). Benzene (30 mL) was added to polymer 4
[Cu(OOCCMe3)2]n (0.331 g, 1.169 mmol; per formula
unit Cu(OOCCMe3)2) and 2,6ꢀdiaminopyridine (0.136 g,
1.169 mmol), and the reaction mixture was stirred at 80 °C for
20 min until the reagents were completely dissolved. The soluꢀ
tion was concentrated at 0.1 Torr and 20 °C to 15 mL and kept at
~20 °C for 24 h. The green crystals that precipitated were sepaꢀ
rated by decantation, washed with cold benzene, and dried
in air. The solvate of compound 5 with one benzene molecule
was obtained in a yield of 0.5 g (96% based on the starting
amount of copper). Found (%): C, 52.29; H, 6.34; N, 10.09.
C36H56Cu2N6O8. Calculated (%): C, 52.22; H, 6.82; N, 10.15.
IR (KBr), ν/cm–1: 3492 s, 3472 s, 3376 s, 3256 m, 3232 m,
3176 w, 3148 w, 2980 m, 2960 m, 1636 s, 1616 s, 1596 v.s,
1484 s, 1468 s, 1420 s, 1376 m, 1364 m, 1308 m, 1228 m, 1180 w,
1116 w, 1064 w, 1032 w, 992 w, 900 w, 788 m, 728 w, 692 m,
624 w, 520 w, 448 w, 420 w, 388 w, 356 w, 316 w.
The crystals were used for the Xꢀray diffraction study.
Cocrystals of bis(2,6ꢀdiaminopyridino)tetra(µ ꢀO,O´ꢀ
2
trimethylacetato)dicopper(II) and bis(acetonitrilo)tetra(µ ꢀ
O,O´ꢀtrimethylacetato)dicopper(II), {2,6ꢀ(NH2)2C5H3N]2(µ ꢀ
2
2
OOCCMe3)4•(CH3CN)2Cu2(µ ꢀOOCCMe3)4}•2CH3CN
2
(7·2CH3CN). Acetonitrile (40 mL) was added to polymer 4
[Cu(OOCCMe3)2]n (0.331 g, 1.169 mmol; per formula
unit Cu(OOCCMe3)2) and 2,6ꢀdiaminopyridine (0.136 g,
1.169 mmol), and the reaction mixture was stirred at 80 °C for
10 min until the reagents were completely dissolved. The soluꢀ
tion was concentrated at 0.1 Torr and 20 °C to 25 mL and kept
at ~5 °C for 24 h. Green crystals that precipitated were sepaꢀ
rated by decantation, washed with cold acetonitrile, and dried in
air. Crystals of compound 7 with two acetonitrile molecules
were obtained in a yield of 0.798 g (89% based on the starting
amount of copper). Found (%): C, 48.44; H, 6.35; N, 9.36.
Table 3. Crystallographic parameters of complexes 5—7
Parameter
5
6
7
Molecular formula
Molecular weight
C36H56Cu2N6O8
827.95
C32H52Cu2N4O8
747.86
C58H92Cu4N10O16
1439.58
Space group
a/Å
b/Å
P6(5)
Triclinic, P–1
9.5206(10)
10.8447(10)
11.0699(10)
62.067(10)
72.395(10)
83.133(10)
962.16(16)
1
Triclinic, P–1
11.2647(6)
11.8627(6)
15.6881(8)
99.5010(10)
72.395(10)
110.8230(10)
1878.73(17)
1
12.4581(14)
12.4581(14)
48.519(6)
90
90
120
6521.5(13)
6
1.265
c/Å
α/deg
β/deg
γ/deg
V/Å3
Ζ
ρ
calc/g cm–3
1.291
1.764
1.272
1.180
µ/mm–1
1.0291
Radiation
MoꢀKα (λ = 0.71073 Å) CuꢀKα (λ = 1.5418 Å)
θꢀ2θꢀScan range/deg
Number of measured reflections
1.89—28.00
4.71—74.91
2.13—29.56
19440
12787
5807
Number of reflections with I > 2σ(I )
5401
3875
9290
R1
wR2
0.0574
0.1165
0.0452
0.1260
0.0543
0.0937

1730
Russ.Chem.Bull., Int.Ed., Vol. 56, No. 9, September, 2007
Fomina et al.
C58H92Cu4N10O16. Calculated (%): C, 48.39; H, 6.44; N, 9.73.
IR (KBr), ν/cm–1: 3472 s, 3380 s, 3264 m, 3168 w, 3180 w,
2960 s, 2932 s, 2904 m, 2868 m, 2828 w, 1644 s, 1612 s, 1596 s,
1484 s, 1468 s, 1420 s, 1376 s, 1364 m, 1308 m, 1260 w, 1224 s,
1180 m, 1120 w, 1072 w, 1032 w, 988 w, 940 w, 896 m, 788 s,
756 w, 728 m, 668 w, 620 s, 540 w, 500 w, 444 m, 412 m, 400 w,
388 m, 316 m.
The crystals were used for the Xꢀray diffraction study.
Xꢀray diffraction study. Xꢀray reflections for complexes 5
and 6 were measured on an automated Bruker Pꢀ4 (graphiteꢀ
monochromated λMoꢀKα) and EnrafꢀNonius CADꢀ4 (graphiteꢀ
monochromated λCuꢀKα) diffractometers, respectively; for
complex 7; on an automated Bruker AXS SMART 1000 diffractoꢀ
meter (graphiteꢀmonochromated λMoꢀKα, 250 K) equipped
with a CCD detector according to a standard procedure.20
Semiempirical absorption corrections were applied.21 The crysꢀ
tallographic parameters and the refinement statistics for the
structures of 5—7 are given in Table 3.
The structures of all complexes were solved by direct methods
and refined by the fullꢀmatrix leastꢀsquares method with anisoꢀ
tropic displacement parameters for all nonhydrogen atoms. The
hydrogen atoms of the tertꢀbutyl substituents of the pivalate
ligands and the pyridine rings in the coordinated amine molꢀ
ecules were positioned geometrically and refined using a riding
model. All calculations were performed with the use of the
SHELX97 program package.22
Nauk, Ser. Khim., 2006, 1841 [Russ. Chem. Bull., Int. Ed.,
2006, 55, 1909].
4. Advanced Organic Chemistry: Reactions, Mechanisms and
Structure, Ed. J. March, Wiley, New York, 1992, p. 1195.
5. J. D. Roberts and M. C. Caserio, Basic Principles of Organic
Chemistry, 2nd ed., W. A. Benjamin, Inc., 1977, p. 1122.
6. B. Takayuki, O. Yutaka, and T. Yasutaka, Mater. Chem.
Phys., 2003, 78, 645.
7. M. A. Kiskin, I. G. Fomina, G. G. Aleksandrov, А. А.
Sidorov, V. M. Novotortsev, Y. V. Rakitin, Z. V. Dobrohotova,
V. N. Ikorskii, Y. G. Shvedenkov, I. L. Eremenko, and I. I.
Moiseev, Inorg. Chem. Commun., 2005, 8, 89.
8. I. L. Eremenko, M. A. Kiskin, I. G. Fomina, A. A. Sidorov,
G. G. Aleksandrov, V. N. Ikorskii, Yu. G. Shvedenkov, Yu. V.
Rakitin, and V. M. Novotortsev, J. Cluster Sci., 2005, 331.
9. 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].
10. E. V. Pakhmutova, A. E. Malkov, T. B. Mikhailova, A. A.
Sidorov, I. G. Fomina, G. G. Aleksandrov, V. M.
Novotortsev, V. N. Ikorskii, and I. L. Eremenko, Izv. Akad.
Nauk, Ser. Khim., 2003, 2006 [Russ. Chem. Bull., Int. Ed.,
2003, 52, 2117].
11. E. G. Il´ina, S. I. Troyanov, and K. M. Dunaeva, Koord.
Khim., 1992, 18, 882 [Russ. J. Coord. Chem., 1992, 18, 882
(Engl. Transl.)].
This study was financially supported by the Russian
Foundation for Basic Research (Project Nos 07ꢀ03ꢀ00408,
07ꢀ03ꢀ00707, 05ꢀ03ꢀ32767, 05ꢀ03ꢀ794, and 06ꢀ03ꢀ08086),
the Russian Academy of Sciences (Target Program for
Basic Research of the Division of Chemistry and Materiꢀ
als Science of the Russian Academy of Sciences "Chemisꢀ
try and Physical Chemistry of Supramolecular Systems
and Atomic Clusters" and the Programs of the Presidium
of the Russian Academy of Sciences "Molecular Design
of Magnetoactive Compounds and Materials (Molecular
Magnets)" and "Polyfunctional Materials for Molecular
Electronics"), the Council on Grants of the President of
the Russian Federation (Program for State Support of
Leading Scientific Schools of the Russian Federation,
Grant NSh 4959.2006.03), and the Federal Agency for
Science and Innovations of the Russian Federation (Proꢀ
gram "Nanotechnologies and Nanomaterials").
12. V. N. Vertoprakhov, L. D. Nikulina, and I. K. Igumenov,
Usp. Khim., 2005, 797 [Russ. Chem. Rev., 2005, 725 (Engl.
Transl.)].
13. K. A. Vorotilov, M. I. Yanovskaya, and E. P. Turevskaya,
J. SolꢀGel Sci. Technol., 1999, 16, 109.
14. J. Musil and J. Vlcek, Surface and Coatings Technology, 2001,
142, 557.
15. H. S. Myung, H. M. Lee, L. R. Shaginyan, and J. G. Han,
Surface and Coatings Technology, 2001, 163, 591.
16. V. Majer and V. Svoboda, Enthalpies of Vaporization of Orꢀ
ganic Compounds: A Critical Review and Data Compilation,
Blackwell Scientific Publications, Oxford, 1985, 300.
17. S. E. Nefedov, T. O. Denisova, Zh. V. Dobrokhotova, F. M.
Dolgushin, G. V. Romanenko, V. N. Ikorskii, and V. I.
Ovcharenko, Zh. Neorg. Khim., 2006, 51, 1687 [Russ. J. Inorg.
Chem., 2006, 51, 1587 (Engl. Transl.)].
18. E. G. Il´ina, N. A. Santalova, and K. M. Dunaeva, Zh. Neorg.
Khim., 1991, 9, 2301 [J. Inorg. Chem. USSR, 1991, 9 (Engl.
Transl.)].
19. T. O. Denisova, E. V. Amel´chenkova, I. V. Pruss, Zh. V.
Dobrokhotova, O. P. Fialkovskii, and S. E. Nefedov,
Zh. Neorg. Khim., 2006, 51, 1098 [Russ. J. Inorg. Chem.,
2006, 51, 1020 (Engl. Transl.)].
20. SMART (Control) and SAINT (Integration) Software, Verꢀ
sion 5.0, Bruker AXS Inc., Madison, WI, 1997.
21. G. M. Sheldrick, SADABS, Program for Scanning and Corꢀ
rection of Area Detector Data, Göttingen University,
Göttinngen, Germany, 1997.
22. G. M. Sheldrick, SHELX97, Program for the Solution of Crysꢀ
tal Structures, Göttingen University, Götinngen, Gerꢀ
many, 1997.
References
1. I. G. Fomina, Zh. V. Dobrokhotova, M. A. Kiskin, G. G.
Aleksandrov, O. Yu. Proshenkina, A. L. Emelina, V. N.
Ikorskii, V. M. Novotortsev, and I. L. Eremenko, Izv. Akad.
Nauk, Ser. Khim., 2007, 1650 [Russ. Chem. Bull., Int. Ed.,
2007, 56, 1712].
2. Zh. V. Dobrokhotova, I. G. Fomina, M. A. Kiskin, A. A.
Sidorov, and I. L. Eremenko, Izv. Akad. Nauk, Ser. Khim.,
2006, 250 [Russ. Chem. Bull., Int. Ed., 2006, 55, 256].
3. I. G. Fomina, G. G. Aleksandrov, Zh. V. Dobrokhotova,
O. Yu. Proshenkina, M. A. Kiskin, Yu. A. Velikodnyi, V. N.
Ikorskii, V. M. Novotortsev, and I. L. Eremenko, Izv. Akad.
Received May 5, 2007