Coordination polymer [Li2Co2(Piv)6(μ-L)2] n (L = 2-amino-5-methylpyridine) as a new molecular precursor for LiCoO2 cathode material

Article abstract of DOI:10.1016/j.poly.2009.07.065

The solid-state thermolysis (420-450 °S{cyrillic}) of the new heterometallic coordination polymer [Li₂Co₂(Piv)₆(μ-L)₂] _n (1, Piv is the anion of pivalic acid, L is 2-amino-5-methylpyridine) followed b

Full text of DOI:10.1016/j.poly.2009.07.065

Polyhedron 28 (2009) 3628–3634
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Coordination polymer [Li Co (Piv) (l-L) ] (L = 2-amino-5-methylpyridine)
2
2
6
2 n
as a new molecular precursor for LiCoO cathode material
2
b
b
a,*
a
a
Mikhail Bykov , Anna Emelina , Mikhail Kiskin , Aleksei Sidorov , Grigory Aleksandrov ,
c
a
a
a
Artem Bogomyakov , Zhanna Dobrokhotova , Vladimir Novotortsev , Igor Eremenko
a
N.S. Kurnakov Institute of General and Inorganic Chemistry, Russian Academy of Sciences, Leninsky Prosp. 31, 119991 Moscow, GSP-1, Russian Federation
Department of Chemistry, M.V. Lomonosov Moscow State University, 1 Leninskie Gory, 119992 Moscow, Russian Federation
International Tomography Centre, Siberian Branch of the Russian Academy of Sciences, Institutskaya Str. 3a, 630090 Novosibirsk, Russian Federation
b
c
a r t i c l e i n f o
a b s t r a c t
Article history:
The solid-state thermolysis (420–450 °C) of the new heterometallic coordination polymer
Received 30 April 2009
Accepted 22 July 2009
Available online 15 August 2009
[
Li
annealing of the decomposition products at 500 °C was shown to afford LiCoO
Compound 1 was characterized by X-ray diffraction and magnetic measurements.
Ó 2009 Elsevier Ltd. All rights reserved.
2
Co
2
(Piv)
6
(
l
-L)
2
]
n
(1, Piv is the anion of pivalic acid, L is 2-amino-5-methylpyridine) followed by
2
in quantitative yield.
Keywords:
Cobalt
Lithium
Heterometallic complex
Coordination polymer
Carboxylate ligands
X-ray analysis
Magnetic properties
Thermal decomposition
Heat capacity
Phase transition
1
. Introduction
mixtures of LiOH with Co(OH)
at 400–800 °C is complicated by the instability of the resulting
LiCO to the mechanochemical action due to redox processes with
2
and CoOOH followed by heating
Mixed-oxide ceramics belong to an important class of solid-
2
state materials used in modern electronics. Materials for positive
electrodes in lithium-ion batteries occupy an important place
among oxide ceramics. Lithium cobaltate used in batteries is pre-
pared primarily by the direct solid-state synthesis from lithium
oxide or hydroxide and cobalt carbonate or oxide at rather high
temperatures [1–4]. The main drawbacks of this method are that
this process is time and energy consuming and, what is most
important, that the lithium content decreases because prolonged
annealing leads to lithium evaporation. The sol–gel synthesis of
this material with the use of metal salts (nitrates or acetates) in
the presence of polybasic carboxylic acids [5–8] affords more
homogeneous samples, reduces the time of thermal processing,
and allows a decrease in the temperature for the synthesis of com-
plex oxides with desired structures. Among other methods for the
synthesis of lithiated cobalt oxide, the mechanochemical synthesis
is worthy of note [9]. However, the mechanochemical synthesis of
crystalline lithium cobaltate by the mechanical treatment of
the involvement of the gas phase [10]. The compositional homoge-
neity and particle size uniformity are most important for the prep-
aration of high-quality cathode materials, because these
parameters have a great influence on the electrochemical charac-
teristics of positive electrodes [5–7]. Actually, the two last-men-
tioned methods provide sufficient homogeneity upon mixing of
the starting compounds, as well as compositional homogeneity
and particle size uniformity. It was shown that highly dispersed
2
LiCoO powders exhibit good cyclic performance [11].
An alternative approach to the solution of the problem of
preparing compositionally homogeneous lithium cobaltate (in
particular as thin films or highly dispersed powders) can be based
on the use of heterometallic coordination compounds containing
cobalt and lithium atoms in a ratio of 1:1 as molecular precursors
capable of generating lithium cobaltate through mild thermolysis
(400–500 °C). This method can be efficiently used to prepare vari-
ous materials. However, this strategy has not yet found extensive
application. It should be noted that the possibility of preparing thin
mixed-metal Cu–Co and Ni–Cu oxide films starting from cubane-
like molecular heterometallic precursors has been examined in
*
Corresponding author. Tel.: +7 495 955 4835; fax: +7 495 952 1279.
E-mail address: mkiskin@igic.ras.ru (M. Kiskin).
0
277-5387/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2009.07.065

M. Bykov et al. / Polyhedron 28 (2009) 3628–3634
3629
recent years [12]. Analogous approaches were employed to decom-
pose complex heterometallic compounds with the composition
displacement parameters for all non-hydrogen atoms. The hydro-
gen atoms of the carbon-containing ligands were positioned geo-
metrically and refined using a riding model. All calculations were
carried out with the use of the SHELX97 program package [16]. The
tert-butyl substituents at the carboxylate groups are partially dis-
ordered. The positions of all methyl carbon atoms in the disordered
[
Li(H
2
O)M(N
2
H
3
CO
2
)
3
]ꢀ0.5H
2
O (M = Co or Ni), which were consid-
ered as the only precursors for the preparation of layered LiMO
2
materials [13]. In this case, a very low yield of the starting molec-
ular precursors presents a serious problem. Apparently, this pre-
cludes the extensive use of these precursors in thermal synthesis.
The aim of the present study was to search for new molecular
systems capable of generating lithium cobaltate through mild ther-
molysis. The requirement for the organic components involved in
the heterometallic complexes is that they can be easily eliminated
with the retention of the ratio of metals in the final product.
3
CMe fragments were located in difference Fourier maps and
refined with occupancies of 0.506(12) and 0.494(12) for the tert-
butyl group at the atom C(1), 0.674(10) and 0.326(10) at the atom
C(6), and 0.531(17) and 0.469(17) at the atom C(11). The crystallo-
graphic parameters for complex 1 at T = 293 K are as follows:
C
0
1
21
H
35CoLiN
.23 ꢃ 0.25 mm, monoclinic system, space group P2
2.4255(10) Å, b = 22.1287(10) Å, c = 9.4545(10) Å, b = 103.253(10)°,
2
O
6
, fw = 477.38, blue, prismatic, crystal size 0.45 ꢃ
1
/c, a =
2
. Experimental
3
ꢁ3
V = 2530.4(4) Å , k = 0.71073, Z = 4,
q
calc = 1.253 g cm
.13 cm , 5775 measured reflections, 3113 reflections with
I > 4.0 (I), Rint = 0.0843, hmax = 26.97, GOF = 1.047, R (I > 2 (I)) =
.0502, wR (I > 2 (I)) = 0.1365, R (all data) = 0.1173, wR (all
,
l =
ꢁ1
7
2.1. Synthesis
r
1
r
0
2
r
1
2
The new coordination polymer 1 was synthesised with the use
data) = 0.1663, Tmin/max = 0.9006/0.7397 [17], full-matrix least-
of freshly distilled THF and MeCN. The starting cobalt pivalate
Co(Piv) was prepared according to a known procedure [14]. In
the synthesis of complex 1, commercial 2-amino-5-methylpyridine
Fluka) was used.
2
squares on F .
[
2 n
]
The X-ray powder diffraction analysis of the solid decomposi-
tion products in air was carried out on a G670 (HUBER) Guinier
(
camera using CuK
ysis of the solid decomposition products in an inert atmosphere
was performed on a FR-552 monochromator chamber (CuK 1 radi-
a1 radiation. The X-ray powder diffraction anal-
2
.1.1. [Li
Tetrahydrofuran (40 ml) was added to a mixture of [Co(Piv)
0.5 g, 1.9 mmol), LiPiv (0.207 g, 1.9 mmol) and 2-amino-5-methyl-
pyridine (0.205 g, 0.9 mmol). The reaction mixture was stirred at
0 °C for 20 min. The resulting brown solution was concentrated
2 2 6 2 n
Co (Piv) (2-amino-5-methylpyridine) ] (1)
a
2 n
]
ation) using germanium as the internal standard (X-ray diffraction
patterns were processed on an IZA-2 comparator with an accuracy
of ±0.01 mm).
(
6
to 10 ml, MeCN (40 ml) was added, and the mixture was concen-
trated to 10 ml at 80 °C. The solution was kept at +5 °C for 24 h.
Brown crystals suitable for X-ray diffraction were separated from
the solution by decantation, washed with cold MeCN, and dried
2.4. Thermal decomposition
The thermal decomposition of compound 1 was studied by dif-
ferential scanning calorimetry (DSC) and thermogravimetry (TGA).
The thermogravimetric measurements were performed in an arti-
ficial air flow (20 ml/min) and in an argon flow (20 ml/min) on a
NETZSCH TG 209 F1 instrument in alundum crucibles at a heating
rate of 10 °C/min. The composition of the gas phase below 250 °C
was studied on a QMS 403C Aëolos mass-spectrometric unit under
TGA conditions. The ionizing electron energy was 70 eV; the larg-
est determined mass number (the mass-to-charge ratio) was
in air. The yield of crystals of 1 is 81% based on [Co(Piv)
2
]
n
. Found
: C, 52.84; H, 7.39; N,
.87. IR, m/cm : 3384 m, 3130 m, 2960 s, 2928 m, 2868 m, 1612
(
2 6
%): C, 52.95; H, 7.35; N, 5.66. C21H35CoLiN O
ꢁ
1
5
v.s, 1572 v.s, 1564 v.s, 1520 m, 1504 s, 1484 v.s, 1424 v.s, 1400
v.s, 1376 m, 1364 v.s, 1300 w, 1260 w, 1228 c, 1144 w, 1120 w,
1
8
4
044 w, 1032 m, 972 m, 952 m, 936 m, 904 s, 848 m, 824 m,
00 s, 792 s, 764 s, 744 w, 664 m, 608 v.s, 568 s, 528 m, 452 v.s,
36 v.s, 416 v.s, 400 v.s.
3
00 amu. The weight of the samples for thermogravimetric exper-
iments was 0.5–3 mg. The differential scanning calorimetry study,
in a dry artificial air flow (O , 20.8%; CH , <0.0001%) and in an ar-
gon flow (Ar, >99.998%; O , 0.0002%; N , <0.001%; aqueous vapor,
0.0003%; CH , <0.0001%), was carried out on a NETZSCH DSC 204
F1 calorimeter in aluminum cells at a heating rate of 10 °C/min.
The weight of the samples was 4–10 mg. Each experiment was re-
peated at least three times. The temperature scales and the calo-
rimeter were calibrated based on the phase transition
2
.2. Methods
2
4
2
2
The elemental analysis of complex 1 was carried out on a Carlo
<
4
Erba analyzer in the Center of Collaborative Research of the N.S.
Kurnakov Institute of General and Inorganic Chemistry of the Rus-
sian Academy of Sciences. The spectra were measured on a Specord
M-80 IR spectrometer in KBr pellets. The magnetochemical mea-
surements were performed on a MPMS-5S SQUID magnetometer
6 3
temperatures of standard compounds (C H12, Hg, KNO , In, Sn, Bi
and CsCl; 99.99% purity; ISO/CD 11357-1). For the TGA and DSC
(
Quantum Design) in the 2–300 K temperature range at a magnetic
field strength H = 5 kOe. The molar magnetic susceptibility was
v
experiments, the samples were weighed on a SARTORIUS RESEARCH
calculated taking into account the atomic diamagnetism according
to the Pascal additive scheme. In the paramagnetic region, the
effective magnetic moment was calculated by the equation
ꢁ2
R 160P analytical balance with an accuracy of 1 ꢃ 10 mg.
1
/2
1/2
l
eff = [(3k/N
A
b2)v
T] ꢂ (8
vT) , where k is the Boltzmann con-
2.5. Heat capacity
stant, N
A
is Avogadro’s number and b is the Bohr magneton.
The heat capacities were measured by DSC on a NETZSCH 204 F1
2.3. X-ray data collection
instrument in a dry argon flow (10 ml/min) in the 123–373 K tem-
perature range at a heating rate of 10 °C/min in aluminum speci-
3
The X-ray diffraction study of complex 1 was carried out on an
Enraf Nonius CAD-4 diffractometer (kMo, graphite monochroma-
tor, -scanning technique, the scan step was 0.3°, the exposure
men containers (V = 56 mm , d = 6 mm) equipped with lids with
a hole (the ratio of the surface area of the bottom of the container
to the surface area of the hole was about 36).
x
time per frame was 10 s) according to a standard technique [15].
The structure of complex 1 was solved by direct methods and
refined by the full-matrix least-squares method with anisotropic
The average weight of the samples for heat capacity measure-
ments was about 10 mg. The heat capacity was calculated in accor-
dance with the ASTM E 1269 standard by the equation:

3
630
M. Bykov et al. / Polyhedron 28 (2009) 3628–3634
m
m
St DSC
S
ꢁ DSCBL
Table 1
C
p;S
¼
C
p;St
ð1Þ
Selected bond lengths [Å] and bond angles [°] for compound 1.
S
DSCSt ꢁ DSCBL
Parameter
Value
where the indices S, St and BL refer to the cell containing the sam-
ple, the cell containing the standard compound, and the empty cell,
respectively. Sapphire (m = 12.69 mg) was used as the standard.
Four series of measurements were carried out. The results were pro-
cessed statistically. The controlled cooling of the measuring cells
was performed manually using a liquid-nitrogen cooling system.
The differential scanning calorimeter was calibrated against the
heat flux with the use of sapphire as the standard (ISO/CD 11357-
Li(1A)–Li(1)–Co(1)
Li(1)–Co(1)–N(1)
Li(1)–Co(1)–N(2)
Li(1)–O(6)–Li(1A)
O–C–O (range)
Co(1)ꢀ ꢀ ꢀLi(1)
Li(1)ꢀ ꢀ ꢀLi(1A)
Co(1)–N(1)
125.7(3)
156.76(15)
113.79(13)
88.7(3)
119.3(3)–123.7(3)
3.074(5)
2.709(11)
2.131(3)
2.372(3)
Co(1)–N(2A)
Co(1)–O(1)
Co(1)–O(2)
1
) according to the equation:
2.141(3)
2.225(3)
EðTÞ ¼ DSCSt
ðTÞ ꢁ DSCBLðTÞ
Co(1)–O(3)
Co(1)–O(5)
Li(1)–O(2)
2.004(2)
2.026(2)
1.947(6)
ð2Þ
m
St
C
p;StðTÞb
Li(1)–O(4)
Li(1)–O(6)
Li(1)–O(6A)
C–O (range)
1.876(6)
1.901(6)
1.973(6)
1.234(4)–1.265(4)
2.828(4)
where the indices St and BL refer to the cell containing the standard
and the empty cell, respectively, E(T) is the temperature-dependent
calibration coefficient, DSC is the experimental DSC signal, m is the
*
mass, C
p
is the isobaric heat capacity, and b is the heating rate of the
N(2)ꢀ ꢀ ꢀO(3)
furnace. The calibration against the heat flux was carried out before
each measurement throughout the temperature range of interest.
The experimental data were processed using the NETZSCH Proteus
Thermal Analysis program package.
*
N(2)–H(2B)–O(3) 155.3°, H(2B)ꢀ ꢀ ꢀO(3) 1.98 Å.
polymer chain is formed by linking adjacent cobalt atoms from dif-
ferent repeating heteronuclear fragments {Li Co (Piv) -L) } by
two bridging 2-amino-5-methylpyridine molecules (Fig. 1, Table
). In the elementary unit, each cobalt atom is coordinated by
2
2
6
(l
2
3
. Results and discussion
1
3
.1. Synthesis, structure and magnetic properties of the coordination
the pyridine nitrogen atom of one bridging N-donor ligand and
the amino nitrogen atom of the bridging ligand from the adjacent
fragment. The proton of the coordinated amino group is involved in
hydrogen bonding with the oxygen atom of the bridging carboxyl-
ate group (Fig. 1, Table 1).
It should be noted that the distance between the cobalt atom
and the nitrogen atom of the amino group (Co(1)–N(2)) is substan-
tially elongated (2.372(3) Å), which is indicative of weak interac-
tions between these atoms. This situation is typical of amino
derivatives of pyridine serving as a bridging ligand in polynuclear
cobalt-containing pivalates, and has been observed earlier [18,19].
The magnetic behavior of compound 1 is unusual. At room tem-
polymer [Li Co (Piv) -L)
2
2
6
(l
2 n
]
We chose the product prepared by the reaction of polymeric co-
balt(II) pivalate [Co(Piv) , lithium pivalate LiPiv and 2-amino-5-
methylpyridine (L) in the Co:Li:L ratio of 2:2:1 in THF as the possi-
ble molecular precursor for the synthesis of LiCoO . This reaction
afforded coordination polymer with the composition
Li Co (Piv) -L) (1) in high yield (81%).
According to X-ray diffraction data, compound 1 is a 1D poly-
mer containing the heteronuclear fragment {Li Co (Piv) -L)
as the elementary unit (Fig. 1). This fragment consists of two sym-
metrically arranged dinuclear units {LiCo(Piv) }, in which the co-
2 n
]
2
a
[
2
2
6
(l
2 n
]
2
2
6
(l
2
}
perature, the effective magnetic moment of compound 1 is 4.77 l
B
3
balt and lithium atoms are linked by three non-equivalent
bridging pivalate anions. The centrosymmetric repeating unit {Li2-
(per cobalt atom) (Fig. 2), which is close to the known experimen-
tal values for high-spin Co atoms (S = 3/2) taking into account
II
2
Co (Piv)
(l-L)
6 2
} contains the square O
Li
2 2
fragment (Table 1). The
B
spin-orbital interactions (4.4–5.2 l ) [20]. The magnetic moment
Fig. 1. Fragment of the polymer chain of compound 1 (only one component of each of the distorted tert-butyl groups is drawn, hydrogen atoms of the carboxylate and 2-
amino-5-methylpyridine ligands (except for amino groups) are omitted for clarity, 50% thermal probability ellipsoids).

M. Bykov et al. / Polyhedron 28 (2009) 3628–3634
3631
7
3.5 ± 5.3 kJ/mol per elementary unit of Li
2
Co
2
(Piv)
6
(L)
2
. The end
4
4
4
4
4
.8
.6
.4
.2
.0
of the second endothermic peak (260 ± 3 °C) corresponds to a
22.4 ± 1.5% weight loss. The number of 5-methyl-2-pyridineamine
molecules calculated from the empirical formula is 22.67% per
1
7
5
2
0
00
2 2 6 2
Li Co (Piv) (L) formula unit. Presumably, heating in air in the
5
above-mentioned temperature range leads to elimination of the
N-donor ligand. Under an inert atmosphere, the endothermic effect
in this temperature range has a complex character, and it is impos-
sible to separate the thermal effect associated with elimination of
the N-donor ligand. The inflection point in the weight loss curve at
χ
μ
0
5
2
80 ± 3 °C corresponds to a 21.7 ± 1.5% weight loss. At higher tem-
peratures, further destructive decomposition of complex 1 is ob-
served. It should be noted that the processes under an inert
atmosphere differ from those in air. In an air flow, a highly exother-
mic oxidative destruction occurs in the 260–410 °C temperature
range. The temperature of the end of the exothermic peak in air
is virtually equal to the temperature of the end of the weight loss
0
50
100
150
T, K
200
250
300
Fig. 2. Magnetic properties of complex 1: the temperature dependence of the
magnetic moment (.), the curve 1/v (h); the calculated data are represented by the
(
Fig. 3b).
Under an inert atmosphere, the further weight loss occurs in the
80–470 °C temperature range. This process is accompanied by
line.
2
complex energy changes. According to the X-ray powder diffrac-
tion data, a heterogeneous mixture of cobalt oxide CoO and lithium
l
B
eff decreases with decreasing temperature (to 4.10 l at 14 K).
This fact can be attributed to both antiferromagnetic spin-spin ex-
change interactions between the cobalt atoms and the spin-orbital
effect. However,
reaches 4.25 at 2 K. Apparently, this effect is indicative of a fer-
romagnetic contribution to the exchange interactions between the
Co atoms in the polymer chain.
In the 50–300 K temperature range, the temperature depen-
dence of the inverse susceptibility follows the Curie–Weiss law
oxide Li
plex 1 under an inert atmosphere at temperatures below 500 °C
Table 2). The weight of the solid residue was 19.5 ± 1.5% of the
2
O is formed as the solid decomposition product of com-
leff increases at temperatures below 14 K and
(
l
B
weight of the starting sample, which agrees within experimental
error to the value of 18.91% calculated from the empirical formula
on the assumption that the decomposition affords a mixture of the
II
Li
2
O and CoO phases.
Unlike the inert conditions, the decomposition of polymer 1 in
ꢁ3
with the parameters C = 2.96 mol cm and h = ꢁ11.96 K (Fig. 2).
air (below 500 °C) affords a solid heterogeneous mixture of
mixed-valence cobalt oxide Co , lithium oxide Li O and lithium
cobaltate LiCoO (X-ray powder diffraction data; Table 2). How-
The value C = 2.96 is larger than the theoretical pure spin value
3
O
4
2
(C = 1.875 for S = 3/2 and g = 2), which is consistent with the orbital
2
II
contribution to the magnetic susceptibility, typical of Co ions and
g factors larger than 2.
ever, the further storage of the thermolysis product under temper-
ature-controlled conditions at 500 °C for 30–90 min led to the
complete disappearance of the simple oxides, which is confirmed
by the disappearance of reflections of the simple oxides in the X-
ray diffraction patterns (Table 3). The weight of the solid residue
upon thermolysis in air is 22.3 ± 1.5% of the weight of the starting
sample, which agrees within experimental error to the value of
20.69% calculated from the empirical formula on the assumption
3.2. Thermal decomposition
According to the TGA data, the decomposition of complex 1 in
an artificial air flow and in a dry argon flow does not afford stable
intermediates (Fig. 3).
The decomposition onset temperature for complex 1 is virtually
2
that the decomposition affords LiCoO .
the same (180 ± 3 °C) both in air and under an inert atmosphere
(
argon). The mass spectra of the gas phase in the 150–250 °C tem-
perature range correspond to the spectrum of 2-amino-5-methyl-
3.3. Heat capacity measurements
pyridine [21]. The initial step of decomposition of complex 1
(
180–280 °C) is endothermic (the second endothermic peak in
Differential scanning calorimetry studies showed that the endo-
the DSC curves; see Fig. 3); the absorbed energy in air is
thermic effect in the 77–130 °C (350–405 K) temperature range
a
100
50
b
100
2
0
2
4
4
0
8
6
4
2
0
0
0
0
8
0
30
60
40
20
Q
2
0
0
0
Q
-
-
1
1
00
200
300
o
400
500
100
200
300
400
500
o
t, C
t, C
Fig. 3. Dependence of the weight loss (s) and the heat flux (5) for the sample upon heating (a) under an inert atmosphere and (b) in an air flow.

3
632
M. Bykov et al. / Polyhedron 28 (2009) 3628–3634
Table 2
Phase analysis of the solid decomposition products of compound 1.
*
*
*
*
Decomposition product
under an inert atmosphere
Decomposition product in air without storage
under temperature-controlled conditions
2
Li O [12–0254]
CoO [48–1719]
Co
3
O
4
[43–1003]
2
LiCoO [50–653]
d (Å)
I (%)
d (Å)
I (%)
d (Å)
I (%)
d (Å)
I (%)
d (Å)
I (%)
d (Å)
I (%)
4
2
.695
.850
100
20
4.667
2.858
16
33
4.6771
87
2
2
.670
.455
50
50
2.664
100
2.4602
2.1307
65
2
2
.435
.410
80
40
2.4374
100
20
2.4001
2.0019
48
2
.130
100
100
2.0210
2.005
1.550
1.395
60
20
20
100
1
.650
.500
20
40
1.6307
40
1.5558
32
1
1.5066
54
1.4074
30
*
Powder Diffraction File, Swarthmore: Joint Committee on Powder Diffraction Standards.
The results of heat capacity measurements for complex 1 ob-
tained by the statistical processing of experimental data are pre-
sented in Fig. 5. The experimental points deviate from the
average smoothed curve by no more than 1.4%. The temperature
dependence of C for complex 1 shows some anomalies. These
p
anomalies are well reproduced, the characteristics of the anomalies
being independent of the thermal history of the sample (anomaly
Table 3
Phase analysis of the solid decomposition product of compound 1 in air after storage
under temperature-controlled conditions at 500 °C.
*
Decomposition product
2
LiCoO [50-653]
d (Å)
I (%)
d (Å)
I (%)
4
2
2
1
.695
.409
.000
.162
100
65
65
4.6771
2.400
2.002
1.152
87
48
100
14
1: Tonset = 232.5 ± 0.5 K, Q = 79.1 ± 8.8 J/mol; anomaly 2: Tonset
78.32 ± 0.26 R, Q = 6531 ± 715 J/mol).
According to the X-ray diffraction data, the crystal system and
the space group of complex 1 remain unchanged in the 300–
90 K temperature range (Table 4), but the unit cell parameters
=
3
20
*
Powder Diffraction File, Swarthmore: Joint Committee on Powder Diffraction
Standards.
1
and the unit cell volume change non-monotonically. Hence, the
low-temperature anomaly is presumably attributed to the phase
transition associated with freezing of vibrations of the tert-butyl
substituents at the carboxylate groups. Earlier, we have observed
an analogous situation for the heteronuclear pivalate complex
Co Sm(Piv) (2,4-Lut) [22].
The endothermic effect in the 350–405 K temperature range is
apparently attributed to the cleavage of a large number of hydro-
gen bonds formed between the protons of the coordinated amino
group and the oxygen atoms of the bridging and chelate bridging
carboxylate groups, accompanied by energy release. The thermal
effect of this transformation is comparable with the hydrogen bond
energy [23].
observed both under an inert atmosphere and in air is not associ-
ated with decomposition of the samples (Fig. 3) and is reproduced
upon successive cooling and heating of the samples (Fig. 4).
To elucidate the nature of this thermal transformation, we
measured the temperature dependence of the heat capacity. In
addition, we intended to obtain thermodynamic characteristics
for complex 1, which are necessary for the construction of the
thermodynamic model of the thermolysis. This model and the
temperature program maintaining the constant level of gas evolu-
tion throughout the temperature range of thermolysis, which was
calculated from the results of the thermal analysis, allow the opti-
mization of the conditions for the preparation of lithium cobaltate
films from the molecular precursor under consideration.
2
7
2
1
1
200
100
2400
a
0
0
.20
.15
2000
C
1000
b
1
1
600
200
9
00
2
00
225
T, K
250
275
mean Cp
range Cp
C
8
2
00
00
Q,
-
-
-
0.15
0.20
0.25
0
200
250
300
T, K
350
400
4
0
60
80
100
120
Fig. 5. Average smoothed curve C
between the maximum and minimum experimental values of C
smoothed curve C (T) in the 190–280 K temperature range (b) (DSC, HR = 10 °C/min,
Ar (10 ml/min), m ꢄ 10 mg).
(T), the confidence interval, and the difference
p
o
t
, C
(a), the average
p
p
Fig. 4. Changes in the heat flux during heating (4) and cooling (s) of complex 1.

M. Bykov et al. / Polyhedron 28 (2009) 3628–3634
3633
Table 4
Unit cell parameters for compound 1 depending on the temperature.
T (K)
t (°C)
a (Å)
b (Å)
c (Å)
b (°)
V (Å3)
403
300
280
260
210
190
130
27
7
ꢁ13
ꢁ63
ꢁ83
12.596(14)
12.568(18)
12.476(12)
12.484(11)
12.430(7)
12.414(5)
22.305(16)
22.32(3)
22.17(2)
22.20(2)
22.130(11)
22.122(8)
9.537(6)
9.534(13)
9.461(9)
9.458(8)
9.366(5)
9.332(4)
102.83(5)
103.37(5)
103.53(3)
103.67(5)
103.939(17)
103.931(17)
2614(51)
2602(5)
2545(2)
2547(5)
2501(4)
2487.4(1.5)
Table 5
Thermodynamic functions of compound 1.
1
1
1
500
350
200
o
o
170
o
T
T (K)
C
p
(±11.1) (J/mol K)
H ꢁH
(kJ/mol)
S
(J/mol K)
T
170
828.5
0
403
1
1
80
90
867.8
914.2
8.4
451
500
17.3
26.7
36.3
46.3
78.3
89.5
101.0
112.8
124.9
137.4
150.2
163.4
177.0
190.9
205.3
200
952.0
547
595
642
778
822
866
909
952
994
1036
1078
1120
1162
1204
2
2
2
2
2
2
2
2
3
3
3
3
3
10
20
50
60
70
80
90
98
10
20
30
40
50
987.2
1018.7
1105.2
1138.5
1168.8
1199.8
1234.0
1267.7
1300.4
1342.3
1380.1
1420.0
1467.2
C
1050
900
2
00
250
300
350
T, K
Fig. 6. Dependence of the heat capacity of complex 1: experimental data (s); the
calculated data are represented by the line (a = 1396, = 437, = 7779,
= 2617).
1
h
1
a
2
h
2
The absolute entropies of complex 1 were calculated from the
standard entropies (the latter parameters were determined with
limited region of the heat capacity curve (120–350 K) by extrapo-
lating the results of DSC heat capacity measurements from the
boiling point of liquid-nitrogen to the absolute zero temperature
o
the use of the calculated value of S 98).
2
Hence, the study of the heat capacity of coordination polymer 1
in the 123–373 K temperature range revealed two anomalies asso-
ciated with phase transitions. The parameters of these transitions
(
0 K). This method gives the physically correct behavior of the tem-
perature dependence of the heat capacity and the mathematically
correct standard entropies [22]. To calculate the thermodynamic
functions of the complexes, we separated the regular heat capacity
contribution and approximated it to 0 by the function:
o
p
0
were determined. The thermodynamic functions (C (T), S (T) and
0
0
H (T)–H (170)) in the 170ꢁ350 K temperature range were calcu-
lated based on the results of the calorimetric measurements.
ꢀ
ꢁ
X
h
i
c
p
ðTÞ ¼
a
i
C
En
ð3Þ
4
. Conclusions
T
i
The above-considered data show that the new heterometallic
expðxÞ
expðxÞ ꢁ 1ꢅ
h
2
where
C
EnðxÞ ¼ 3Rx
;
x ¼ T
coordination polymer 1 can apparently be used as an efficient
molecular precursor for the synthesis of lithium cobaltate. Under
the conditions of the experiments (heating at a rate of 10 °C/
2
½
2
min), LiCoO can be prepared as the only solid thermolysis product,
The best results were obtained by approximating with function
only after additional storage under temperature-controlled condi-
tions at 500 °C. Preliminary investigations into the preparation of
films from saturated solutions of complex 1 on different supports
(
3), consisting of two summands (Fig. 6).
o
The standard entropies S2 of the complexes were estimated by
98
the equation:
(
an alundum support, a stabilized zirconium dioxide support and
ꢀ
ꢁ
X
h
i
a sapphire support) showed that homogeneous uniform LiCoO
2
SðTÞ ¼
a
i
S
En
ð4Þ
T
films can be formed with the use of a temperature program, which
was calculated from the kinetic model of the thermolysis of com-
plex 1, designed based on the results of thermal analysis and which
maintains a constant (3%/min) gas evolution rate during decompo-
sition of coordination polymer 1.
i
ꢂ
ꢃ
x
h
where
S
EnðxÞ ¼ 3R
ꢁ lnð1 ꢁ expðꢁxÞÞ ; x ¼ T
:
ðexpðxÞ ꢁ 1Þ
We took into account the change in the entropy as a result of
the transition associated with the anomaly in the curve for C
p
Supplementary data
ꢆ
AREA
according to the equation
sured surface area of the peak in the experimental temperature
dependence of the heat capacity. Table 5 gives the experimental
D
S
¼
onset, where AREA is the mea-
T
onset
T
CCDC 730046 contains the supplementary crystallographic data
for compound 1. These data can be obtained free of charge via
http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the
Cambridge Crystallographic Data Centre, 12 Union Road, Cam-
(
average and smoothed) heat capacities, the temperature contribu-
tions to the enthalpy calculated from the heat capacities, and the

3
634
M. Bykov et al. / Polyhedron 28 (2009) 3628–3634
bridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or e-mail:
deposit@ccdc.cam.ac.uk.
[10] N.V. Kosova, T.V. Larina, E.T. Devyatkina, J. Chem. Sustain. Develop. (2001) 235.
[
[
[
[
11] K. Kanamura, A. Goto, R. Young Ho, T. Umegaki, K. Toyoshima, K. Okada, Y.
Hakuta, T. Adschiri, K. Aria, Electrochem. Solid-State. Lett. 3 (2000) 256.
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Chem. 45 (2006) 10457.
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Acknowledgments
This study was supported by the Russian Foundation for Basic
Research (project nos. 07-03-00707, 08-03-00091, 09-03-90441,
14] M.A. Golubnichaya, A.A. Sidorov, I.G. Fomina, M.O. Ponina, S.M. Deomidov, S.E.
Nefedov, I.L. Eremenko, I.I. Moiseev, Russ. Chem. Bull. (Engl. Transl.) 48 (1999)
1751.
0
9-03-12228, 09-03-12122, and 08-03-00343), the Council on
Grants of the President of the Russian Federation (grants NSh-
324.2008.3, NSh-1518.2008.3, MK-156.2009.3), the Federal
[
15] SMART (Control) and SAINT (Integration) Software, Version 5.0, Bruker AXS Inc.,
Madison, WI, 1997.
1
[16] G.M. Sheldrick, SHELX97, Program for the Solution of Crystal Structures,
Göttingen University, Götinngen, Germany, 1997.
Agency for Science and Innovations, the Russian Science Support
Foundation, the Russian Academy of Science, the Siberian Branch
of the Russian Academy of Sciences and the Department of Chem-
istry and Materials Science.
[
17] G.M. Sheldrick, SADABS, Program for Scanning and Correction of Area Detector
Data, Göttingen University, Göttinngen, Germany, 1997.
[18] E.V. Pakhmutova, A.E. Malkov, T.B. Mikhailova, A.A. Sidorov, I.G. Fomina, G.G.
Aleksandrov, V.M. Novotortsev, V.N. Ikorskii, I.L. Eremenko, Russ. Chem. Bull.
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