Synthesis and structure of new polynuclear cobalt(II) complexes with 3,5-di-tert-butylbenzoic acid anions

Article abstract of DOI:10.1007/s11172-013-0277-9

Trinuclear complex Co₃(O₂CR)₆(EtOH) ₂ (1) crystals were obtained in good yield (75%) by the exchange reaction between cobalt(II) chloride and potassium 3,5-di-tert-butyl- benzoate (KO₂CR) in EtOH. Com

Full text of DOI:10.1007/s11172-013-0277-9

Russian Chemical Bulletin, International Edition, Vol. 62, No. 8, pp. 1924—1929, August, 2013
1924
Brief Communications
Synthesis and structure of new polynuclear cobalt(II) complexes
with 3,5ꢀdiꢀtertꢀbutylbenzoic acid anions*
E. N. Egorov, M. A. Kiskin, A. A. Sidorov, and I. L. Eremenko
N. S. Kurnakov Institute of General and Inorganic Chemistry, Russian Academy of Sciences,
31 Leninsky prosp., 119991 Moscow, Russian Federation.
Fax: +7 (495) 955 4835. Eꢀmail: mkiskin@igic.ras.ru
Trinuclear complex Co3(O2CR)6(EtOH)2 (1) crystals were obtained in good yield (75%)
by the exchange reaction between cobalt(II) chloride and potassium 3,5ꢀdiꢀtertꢀbutylꢀ
benzoate (KO2CR) in EtOH. Complex 1 undergoes hydrolysis during recrystallization from
nonꢀanhydrous benzene to form the hexanuclear hydroxocarboxylate complex
Co6(OH)2(O2CR)10(HO2CR)4 (2).
Key words: cobalt(II), 3,5ꢀdiꢀtertꢀbutylbenzoic acid, polynuclear complexes, Xꢀray diffracꢀ
tion analysis.
Polymeric cobalt(II) pivalate [Co(Piv)2]n, having the
products. The results obtained are important for underꢀ
standing of possible reaction pathways in the reaction of
polymeric carboxylates of general formula {M(O2CR)2}n
with molecules of different solvents and Oꢀdonor ligands.
As to their chemical properties, such compounds are
a convenient source of cobaltꢀcarboxylate fragments, that,
depending on the nature of different organic ligands, makes
it possible to construct polynuclear cobaltꢀcontaining molꢀ
ecules of various structure.3—11 The bulky tertꢀbutyl fragꢀ
ments in substituents at the carboxy group, undoubtedly,
play a key role, protecting the metal core from undesirable
hydrolysis of the reaction products. At the same time, they
considerably increase solubility of new compounds, that
allows one to easily handle organic solutions, including
processes of growing single crystals of target compounds
necessary for the highꢀquality physicochemical studies. In
particular, 3,5ꢀdiꢀtertꢀbutylbenzoic acid contains two
structure of coordination 1Dꢀpolymer,1 was shown to be
able to quantitatively transform to homoꢀ and heteroꢀ
metal complexes of various structure in the reactions with
Nꢀdonor ligands.2—10 Such reactions can proceed in
very different solvents, including EtOH. However, upon
dissolution of [Co(Piv)2]n in ethanol (96%), though
the crystallization of the tetranuclear complex
Co4(OH)2(Piv)6(EtOH)6 occurs2, the greater part of the
polymer is transformed to the poorly soluble amorphous
hydrolysis products.
The cobalt(II) compounds with 3,5ꢀdiꢀtertꢀbutylbenꢀ
zoic acid anions considered below are formed in >50%
yields without the loss of the metal as insoluble hydrolysis
* To the memory of Corresponding Member of the Russian
Academy of Sciences M. Yu. Antipin (1951—2013).
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1941—1944, August, 2013.
1066ꢀ5285/13/6208ꢀ1924 © 2013 Springer Science+Business Media, Inc.

Cobalt(II) complexes
Russ.Chem.Bull., Int.Ed., Vol. 62, No. 8, August, 2013
1925
Scheme 1
tertꢀbutyl groups, which are quite remote from the carbꢀ
oxylate fragment. The metal complexes based on such
anion should possess good solubility in organic solvents.
In the present work, we consider approaches to the
synthesis of polynuclear cobaltꢀcontaining molecules
through the chemical selfꢀassembling in ethanol and the
buildingꢀup the complex metal core in nonpolar benzene.
The exchange reaction of CoCl2•6H2O and potassium
3,5ꢀdiꢀtertꢀbutylbenzoate (KO2CR, obtained by the reacꢀ
tion of 3,5ꢀdiꢀtertꢀbutylbenzoic acid with KOH) in EtOH
at room temperature was found to form a bluish violet
solution, from which the trinuclear complex
Co3(O2CR)6(EtOH)2 (1, R = 3,5ꢀ(Me3C)2C6H3) was isoꢀ
lated as violet crystals in 75% yield (Scheme 1).
other by four bridged (Co(1)—O 2.0251(17), 2.0890(18) Å,
Co(2)—O 1.9309(17), 1.979(2) Å) and two chelateꢀ
bridged (Co(1)—O 2.1115(17) Å, Co(2)—O 2.004(2),
2.2713(19) Å) 3,5ꢀdiꢀtertꢀbutylbenzoate anions (Fig. 1).
The central atom Co(1) is in the distorted octahedral
surrounding of six O atoms from six carboxylate anꢀ
ions. The surrounding of the terminal Co(2) atoms
(four O atoms from one chelateꢀbridged, two from
bridged carboxylate anions, and one O atom from the
EtOH molecule (Co(2)—O 2.0395(18) Å)) corresponds
to the distorted trigonal bipyramid,  = 0.23.12 The hydroꢀ
gen atom of the EtOH molecule forms the intermolecuꢀ
lar Hꢀbond with the O atom of the bridged carboxyꢀ
late group of the neighboring complex molecule
...
...
Compound 1 has the linear structure, the central Co(1)
atom is placed in the inversion center. The cobalt(II) atꢀ
oms (Co(1)...Co(2) 3.499(1) Å) are bound between each
(O(7) O(5B) 2.710(3) Å, H O(5B) 1.84(1) Å, the angle
O(7)—H—O(5B) 154.4(1)), forming a chain parallel to
the axis a.
c
a
b
O(3)
O(4)
O(7)
Co(2)
O(2A)
O(6)
O(5)
O(1)
O(5B)
Co(2B)
Co(2A)
Co(1)
O(2)
O(6A)
O(4A)
O(7B)
Fig. 1. Fragment of complex 1 crystal packing (tertꢀbutyl substituents of 3,5ꢀdiꢀtertꢀbutylbenzoic acid anions and hydrogen atoms at
carbon atoms are not shown, thermal ellipsoids are given with 30% probability).

1926
Russ.Chem.Bull., Int.Ed., Vol. 62, No. 8, August, 2013
Egorov et al.
Compound 1 is formally a structural analog of the
known complexes Co3(O2CR)6(L)2 (R = Ph, L is the quinꢀ
oline,13 pyridine14), in which the metal chain structure is
close to the linear. Nonetheless, the structure 1 considerꢀ
ably differs from the geometry of the heteronuclear comꢀ
plexes with cobalt(II) atoms and 4fꢀelements of general
formulas Co2Ln(O2CR)7L2 and Co2Ln(O2CR)6(NO3)L2
with a monodentate L, in which the angle Co—Ln—Co of
the metal framework is considerably smaller 180 and lie
within 133.7—152.4 (see Refs 6 and 15—21). The reason
for this is the presence of an additional chelateꢀcoordinatꢀ
ed carboxylate or nitrate group bonded with the fꢀmetal to
attain coordination number equal to 8.
Linear complex 1 contains an apical labile ligand EtOH
capable of easy elimination upon mild heating. This type
complexes with the transition element atoms containing
a monodentate Oꢀdonor neutral ligand are few.22—24 Supꢀ
posedly, the formation of compound 1 in ethanol demonꢀ
strates one of the possible pathways of fragmentation of the
1Dꢀpolymeric cobalt(II) carboxylates in alcoholic solutions.
It was found that mild heating of a solution of 1 in
benzene (60 C) leads to the elimination of the coordinatꢀ
ed EtOH molecules. This reaction carried out in air
leads to the buildingꢀup the metal core and the formaꢀ
tion of the hexanuclear hydroxocarboxylate complex
Co6(OH)2(O2CR)10(HO2CR)4 (2), which crystallizes as a
solvate with nine benzene molecules (2•9C6H6). The same
compound can be also obtained by the solidꢀphase reacꢀ
tion of cobalt(II) chloride and KO2CR (mechanochemical
synthesis) with subsequent crystallization from benzene.
The structure of complex 2 can be pictured as two
{Co3(OH)} triangles bound by four carboxylate groups
(Fig. 2, Scheme 1). The triangle fragments {Co3(OH)} are
combined with each other by two 2ꢀbridged and two 3ꢀbridꢀ
ged carboxylate groups (Co—O 1.967(2)—2.174(2) Å).
...
In each triangle, the cobalt(II) atoms (Co Co
3.226(1)—3.458(1) Å) are bound by the OH group
(Co—O 1.992(2)—2.132(2), the O atom deviates from the
plane of Co3 atoms by 0.573(2) Å for O(1M) and 0.638(2) Å
for O(2M)). The sides of the triangle fragments are fastened
by four bridged carboxylate anions (Co—O 1.951(2)—
2.137(3) Å). The terminal cobalt atoms (Co(4), Co(6))
additionally coordinate two oxygen atoms of two acid molꢀ
ecules (Co—O 2.129(2)—2.182(2) Å), completing their
surrounding to distorted octahedron. Two atoms Co(1)
and Co(2) are also in the octahedral surrounding of six O
atoms, whereas atoms Co(3) and Co(5) are in the tetraheꢀ
dral surrounding of four O atoms. The H atoms of the
coordinated acid molecules form an intramolecular
Hꢀbond with the O atoms of the bridged carboxylate group
...
...
(HO O 2.550(4)—2.595(4) Å, H O 1.72(1)—1.77(1) Å,
the angle HO—H—O 165.5(1)—172.3(1)) (Fig. 2).
Complex 2, which can be considered as the dimerꢀ
ization and hydrolysis product of compound 1 in the
nonpolar solvent, is a structural analog of the known
trimethylacetate compounds Co6(OH)2(Piv)10(L)4
(L = HPiv,11 Py (see Ref. 25)) and hexanuclear triꢀ
methylacetate complexes, in which two carboxylate anꢀ
ion are substituted by two 2ꢀhydroxyꢀ6ꢀmethylpyridine
anions.4
O(2)
O(28)
O(20)
O(13)
O(11)
Co(3)
O(1)
O(19)
O(27)
O(1)
O(12)
O(5)
O(8)
O(25)
O(1M)
O(2M) Co(1)
O(7)
Co(6)
Co(4)
Co(2)
O(15)
O(21)
O(9)
O(26)
O(24)
O(22)
O(17)
O(4)
Co(5)
O(3)
O(10)
O(23)
O(18)
Fig. 2. Molecular structure of 2 (tertꢀbutyl substituents of 3,5ꢀdiꢀtertꢀbutylbenzoic acid anions and hydrogen atoms at carbon atoms are
not shown, thermal ellipsoids are given with 30% probability).

Cobalt(II) complexes
Russ.Chem.Bull., Int.Ed., Vol. 62, No. 8, August, 2013
1927
CoCl2•6H2O (99%), KOH (98%), 3,5ꢀdiꢀtertꢀbutylbenzoic acid
(99%). IR spectra of complexes 1 and 2 were recorded on a Perkin
Elmer Spectrum 65LS Fourierꢀtransform IR spectrophotometer
in KBr pellets. Microanalysis of compounds was performed on
a Carlo Erba CHNSꢀanalyzer.
In conclusion, the synthesis of complexes of 3,5ꢀdiꢀ
tertꢀbutylbenzoic acid with cobalt(II) atoms can be carried
out under conditions similar to those for the synthesis of
pivalate, though, in this case trinuclear molecules with
labile apical ligands EtOH are isolated. It can be expected
that the synthesized trinuclear complex 1 will be a conveꢀ
nient metalꢀcontaining precursor for further buildingꢀup
the metal framework in the syntheses of both homoꢀ
and heteronuclear molecules with cobalt(II) atoms. The
cobalt(II) complex with 3,5ꢀdiꢀtertꢀbutylbenzoic acid anꢀ
ions demonstrates the higher stability to hydrolysis in ethꢀ
anol as compared to the trimethylacetate analogs.
It is possible that the stability of 1 to hydrolysis, like in
the case of similar complexes with Nꢀdonor ligands,4,5,26—28
is determined by both the stabilization of compound by
the coordinated ethanol molecules and its insolubility in
it. Hydrolysis of 1 in nonꢀanhydrous benzene, in which
the complex solubility is relatively high, is probably caused
by the presence of water impurities (1 wt. %, that is
higher by the order of magnitude calculated per 1 mole of
cobalt), which reacts with the dissociated forms of the
complex.
2
Bis(ꢀO,O,O´ꢀ3,5ꢀdiꢀtertꢀbutylbenzoatoꢀ O,O´)tetrakisꢀ
(ꢀO,O´ꢀ3,5ꢀdiꢀtertꢀbutylbenzoato)di(ethanolꢀO)tricobalt(II),
2
Co3(ꢀO2CRꢀ O,O´)2(ꢀO,O´ꢀO2CR)4(EtOHꢀO)2 (1). A soꢀ
lution of potassium 3,5ꢀdiꢀtertꢀbutylbenzoate (obtained by the
reaction of KOH (0.112 g, 2.0 mmol) and 3,5ꢀdiꢀtertꢀbutylbenꢀ
zoic acid (0.468 g, 2.0 mmol) in EtOH (15 mL)) was added to
a solution of CoCl2•6H2O (0.238 g, 1.0 mmol) in EtOH (10 mL).
The reaction mixture was stirred at room temperature for 15 min,
then a white precipitate of KCl was filtered off. The bluish violet
mother liquor obtained was kept at room temperature. The vioꢀ
let crystals formed within 24 h, suitable for Xꢀray diffraction
analysis, were separated from the solution by decantation, washed
with cold ethanol (5 C), and dried in air. The yield of comꢀ
pound 1 was 0.417 g (75 % calculated on the starting amount of
CoCl2•6H2O). Found (%): C, 67.81; H, 8.33. C94H138Co3O14.
Calculated (%): C, 67.67; H, 8.28. IR, /cm–1: 3411 m.br, 2964 v.s,
2905 m, 2869 m, 1612 m, 1571 v.s, 1526 s, 1478 m, 1462 s, 1443 s,
1394 v.s, 1364 s, 1289 m, 1249 m, 1202 w, 1164 w, 1046 w, 924 w,
897 m, 821 w, 790 m, 753 w, 732 m, 704 m, 627 v.w, 550 v.w,
532 v.w, 493 v.w, 437 v.w.
Bis( ꢀhydroxo)bis( ꢀO,O,O´ꢀ3,5ꢀdiꢀtertꢀbutylbenzoato)ꢀ
3
3
Experimental
octakis(ꢀO,O´ꢀ3,5ꢀdiꢀtertꢀbutylbenzoato)tetrakis(3,5ꢀdiꢀtertꢀ
butylbenzoic acidꢀO)hexacobalt(II), solvate with nine benzene
molecules, Co6( ꢀOH)2( ꢀO,O,O´ꢀO2CR)2(-O,O´ꢀO2CR)8ꢀ
Solvents and reagents were used in syntheses without
additional purification: EtOH (96%), C6H6 (reagent grade),
3
3
(HO2CR-O)4•9C6H6 (2•9C6H6). Procedure A. Compound 1
Table 1. Crystallographic parameters and refinement details for the structure of 1 and 2•9C6H6
Parameter
1
2•9C6H6
Molecular formula
M/g mol–1
T/K
C94H138Co3O14
1668.83
296(2)
C264H354Co6O30
4361.05
160(2)
Crystal system
Space group
a/Å
b/Å
c/Å
/deg
/deg
Tricl–inic
P1
Triclinic
P–1
11.051(3)
14.042(4)
17.074(4)
73.376(4)
83.476(4)
73.842(4)
2436.8(10)
1
16.9931(7)
22.8217(10)
35.2266(15)
94.8930(10)
90.4370(10)
108.3680(10)
12909.4(10)
2
/deg
3
V/Å
Z

calc/g cm–3
1.137
0.560
27.88
1.122
0.438
27.48
/mm–1
max/deg

Tmin/Tmax
0.8867/0.9461
25093/11609
0.9175/0.9372
129358/59056
Number of measured/
independent reflections
Number of reflections with I>2(I)
Rint
7389
0.0371
33256
0.0611
GOOF
1.071
1.101
R1 (I > 2(I))
0.0488
0.0682
wR2 (I > 2(I))
0.1265
–0.588/0.583
0.1710
–0.707/1.319
–3

min/max/e Å

1928
Russ.Chem.Bull., Int.Ed., Vol. 62, No. 8, August, 2013
Egorov et al.
(0.175 g, 0.105 mmol) was dissolved in C6H6 (10 mL) with heatꢀ
ing (60 C) during 20 min. A blue solution obtained was concenꢀ
trated to 5 mL and kept at room temperature. The violet crystals
formed within 24 h, suitable for Xꢀray diffraction analysis, were
separated from the solution by decantation, washed with cold
benzene (5 C), and dried in air. The yield of compound 2 was
0.098 g (51 %). Found (%): C, 68.76; H, 8.32. C210H300Co6O30
(without solvent molecule). Calculated (%): C, 68.97; H, 8.21.
IR, /cm–1: 3453 m, 3427 m.br, 2964 v.s, 2905 m, 2869 m, 1689 m,
1668 m, 1617 m, 1578 v.s, 1478 m, 1461 s, 1442 s, 1396 v.s, 1364 s,
1334 m, 1288 m, 1271 m, 1249 m, 1202 w, 1163 w, 1130 v.w,
1025 w, 923 w, 898 m, 821 w, 791 m, 735 m, 703 m, 591 v.w,
550 v.w, 531 v.w, 487 v.w, 428 v.w.
Procedure B. The weighed amounts of CoCl2•6H2O (0.486 g,
2.042 mmol) and sodium 3,5ꢀdiꢀtertꢀbutylbenzoate (obtained by
mechanical trituration of 3,5ꢀdiꢀtertꢀbutylbenzoic acid (0.956 g,
4.084 mmol) and KOH (0.228 g, 4.084 mmol)) were placed into
a 25ꢀmL grinding vessel made of stainless steel and steel balls
(10 g, 2—8 mm diameter) were added. The mechanochemꢀ
ical synthesis was carried out on a Retsch MM 400 vibrating ball
mill for 2 h at the amplitude of 25 Hz, preliminary cooling down
the grinding vessels to –60 C every 30 min. A weighed amount
of the mixture obtained (0.152 g) was dissolved in C6H6 (10 mL)
with heating (60 C) during 15—20 min. A blue solution was
filtered from a white precipitate and kept at room temperature.
The violet crystals formed within 24 h, suitable for Xꢀray diffracꢀ
tion analysis, were separated from the solution by decantation,
washed with cold benzene (5 C), and dried in air. The crystalloꢀ
graphic parameters of the crystals (T = 181(2) K, triclinic P1,
a = 17.064(8), b = 22.889(10), c = 35.320(2) Å,  = 95.090(10),
 = 90.523(7),  = 108.370(2), V = 13030(20) Å3) were the
same as those obtained for a single crystal of the compound
synthesized by procedure A (see Table 1).
Xꢀray diffraction studies of compounds 1 and 2•9C6H6 were
performed on a Bruker Apex II diffractometer equipped with
a CCDꢀdetector (MoꢀK,  = 0.71073 Å, graphite monoꢀ
chromator).29 A semiempirical correction for the absorption was
made for both compounds.30 The structures of all the complexes
were solved by direct method. For compound 1, the refinement
was performed in the fullꢀmatrix anisotropic approximation for
all the nonhydrogen atoms. In the structure of compound 2, all
the atoms, except the carbon atoms of the benzene solvent molꢀ
ecule, were refined in the fullꢀmatrix anisotropic approximation
for all the nonhydrogen atoms. Positions of the methyl carbon
atoms of the disordered CMe3 fragments in 1 and 2•9C6H6 were
localized in differential Fourier synthesis. The occupation of the
disordered tertꢀbutyl group for 1: 0.339(15) and 0.661(15) at atom
C(12); for 2•9C6H6: 0.312(9) and 0.688(9) at atom C(53). The
H atoms at carbon and oxygen atoms of organic ligands were
generated geometrically and refined using the riding model.
The calculations were performed using the SHELXSꢀ97 and
SHELXLꢀ97 software.31 The crystallographic parameters and
refinement details of the structures are given in Table 1.
This work was financially supported by the Russian
Foundation for Basic Research (Project Nos 11ꢀ03ꢀ00735
and 13ꢀ03ꢀ12430), the Council on Grants at the President
of the Russian Federation (Program of State Support for
Leading Scientific Schools of the Russian Federation,
Grants NShꢀ2357.2012.3 and NShꢀ1670.2012.3), the Preꢀ
sidium of the Russian Academy of Sciences.
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Cobalt(II) complexes
Russ.Chem.Bull., Int.Ed., Vol. 62, No. 8, August, 2013
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Received April 21, 2013,
in revised form June 14, 2013