Heterovalent trinuclear Co(III)-Co(II)-Co(III) complexes with N-(2-carboxyethyl)salicylaldimines

Article abstract of DOI:10.1134/S1070328412010022

He heterovalent trinuclear cobalt complexes [Co₂ ^IIIL₄ⁱ · Co^II(H ₂O)₄] · nXmY (Lⁱ are deprotonated Schiff bases derived from substituted salicylaldehydes and β-alanine; i = 1-3) were obtained and characterized. An X-ray diffraction study of the trinuclear cobalt complex with N-(2-carboxyethyl)salicylaldimine showed that the central Co(II) ion and the terminal Co(III) ions are linked by bridging carboxylate groups. Either terminal Co(III) atom is coordinated to two ligand molecules. They form an octahedral environment consisting of two azomethine N atoms, two phenolate O atoms, and two O atoms of two carboxylate groups. The central Co(II) atom is coordinated to four water molecules and to two O atoms of two bridging carboxylate ligands involved in the coordination sphere of the terminal Co(III) atoms. Pleiades Publishing, Ltd., 2012.

Full text of DOI:10.1134/S1070328412010022

ISSN 1070ꢀ3284, Russian Journal of Coordination Chemistry, 2012, Vol. 38, No. 2, pp. 140–144. © Pleiades Publishing, Ltd., 2012.
Original Russian Text © S.R. Garaeva, A.A. Medzhidov, O. Beukgunger, A. Aydin, B. Yalcin, M.G. Abbasov, 2012, published in Koordinatsionnaya Khimiya, 2012, Vol. 38, No. 2,
pp. 147–152.
Heterovalent Trinuclear Co(III)–Co(II)–Co(III) Complexes
with Nꢀ(2ꢀCarboxyethyl)salicylaldimines
,
S. R. Garaevaa, A. A. Medzhidova *, O. Beukgungerb, A. Aydinc,
B. Yalcinc, and M. G. Abbasova
a Institute of Chemical Problems, National Academy of Sciences of Azerbaijan, Baku, Azerbaijan
*eꢀmail: ajdarmedjidov@gmail.com
b Istanbul Technical University, Istanbul, Turkey
c Marmara University, Istanbul, Turkey
Received February 9, 2011
III
i
⋅
Abstract—The heterovalent trinuclear cobalt complexes
[
CoII(H2O)4]
i = 1–3) were obtained and characterꢀ
⋅
nXmY
(L
i are deprotonated
Co2 L4
Schiff bases derived from substituted salicylaldehydes and ꢀalanine;
β
ized. An Xꢀray diffraction study of the trinuclear cobalt complex with Nꢀ(2ꢀcarboxyethyl)salicylaldimine
showed that the central Co(II) ion and the terminal Co(III) ions are linked by bridging carboxylate groups.
Either terminal Co(III) atom is coordinated to two ligand molecules. They form an octahedral environment
consisting of two azomethine N atoms, two phenolate O atoms, and two O atoms of two carboxylate groups.
The central Co(II) atom is coordinated to four water molecules and to two O atoms of two bridging carboxꢀ
ylate ligands involved in the coordination sphere of the terminal Co(III) atoms.
DOI: 10.1134/S1070328412010022
Heterovalent trinuclear cobalt complexes are of
R1
interest for better understanding of redox processes in
OH
the formation of polynuclear complexes of the same
metal in different oxidation states.
R2
CH N
COOH
A survey of the literature data showed that variꢀ
ous ligands with different dentate numbers tend to
form heterovalent Co(III)–Co(II)–Co(III) comꢀ
plexes. Such ligands include amino alcohols [1],
dianionic tridentate Schiff bases derived from
amino alcohols [2], amino acids [3, 4], their triꢀ
dentate Schiff bases [5], pyridone oximes [6], tetꢀ
radentate bisalicylidene dianions [7–10], and
bridging pyrazolate ligands [11, 12].
L1H2: R1 = R2 = H;
L2H2: R1 = tertꢀBu, R2 = H;
L3H2: R1 = R2 = tertꢀBu.
EXPERIMENTAL
IR spectra were recorded on a Specord M 80 specꢀ
trophotometer for pellets with KBr. Electronic
absorption spectra were recorded on an EZ 210 specꢀ
trophotometer (Perkin Elmer). Elemental analysis was
performed on a LECO CHNS 932 analyzer at the
Tubitak analytical laboratory (Ankara). Magnetic
moments were measured at room temperature on a
Faraday setup with Hg[Co(SCN)4] as a standard.
An Xꢀray diffraction study was carried out on a
STOE IPDS diffractometer at 296 K (Mo
tion). Crystallographic parameters and the data colꢀ
lection statistics are summarized in Table 1.
The structure was solved by the direct method
(SHELXSꢀ97 [13]) and refined by the fullꢀmatrix
leastꢀsquares method on F 2 with the SHELXSꢀ97 [13]
and WINGX programs [14]. The positions of the nonꢀ
hydrogen atoms were refined anisotropically. The
Earlier, we have examined the structures and propꢀ
erties of a heterovalent trinuclear cobalt complex with
Nꢀ(2ꢀcarboxyethyl)ꢀ2ꢀhydroxynaphthaldimine and
found different types of coordination of the central
Co(II) ion to the terminal Co(III) complexes for
and ꢀamino acid derivatives.
α
ꢀ
β
K radiaꢀ
α
Here we studied the structures and properties of
heterovalent trinuclear Co(III)–Co(II)–Co(III)
complexes with Schiff bases derived from unsubstiꢀ
tuted and substituted salicylaldehydes and ꢀalanine.
β
The trinuclear complexes were obtained by both temꢀ
plate synthesis and by using Schiff bases as the starting
materials.
140

HETEROVALENT TRINUCLEAR Co(III)–Co(II)–Co(III) COMPLEXES
141
Table 1. Crystallographic parameters and the data collecꢀ
hydrogen atoms bound to carbon were located geoꢀ
metrically (C–H, 0.93–0.97 Å) and refined using a
riding model with isotropic thermal parameters UH
that are higher by a factor of 1.2–1.5 than the thermal
parameters UC of the respective carbon atoms (CH,
CH2, and CH3). The H atoms of water molecules were
refined under the constraint that the O–H distance is
0.83 Å. In the refinement of the H atom of the hydroxy
group O(10)H, the O–H distance was taken to be 0.82 Å.
The molecule of the complex was visualized with
the ORTEPIII [15] and MERCURY programs [16].
Geometrical calculations were performed with the
PLATON program [15–17].
tion statistics for structure
I
Parameter
Value
Empirical formula
M
C42H50 N4O19 Co3
1091.67
Temperature, K
Wavelength, Å
Crystal system
Space group
296
0.71073
Monoclinic
C2/c
Unit cell parameters:
a
, Å
, Å
, Å
, deg
, Å3
37.5662(15)
9.5737(4)
13.5911(5)
102.422(3)
4773.6(3)
4
Atomic coordinates and comprehensive structural
data have been deposited with the Cambridge Crystalꢀ
b
lographic
Data
Collection
(no.
778333;
c
deposit@ccdc.cam.ac.uk or http://www.ccdc.cam.ac.uk/
data_request/cif).
β
V
Z
Synthesis of Nꢀ(2ꢀcarboxyethyl)salicylaldimine
(
L1H2). A heterogeneous mixture of
βꢀalanine
ρcalcd, g/cm3
1.628
(0.891 g, 0.01 mol) and salicylaldehyde (1.22 g,
0.01 mol) in ethanol (100 mL) was refluxed until a yelꢀ
low homogeneous solution formed. The solution was
cooled and the yellow needleꢀlike crystals that formed
were isolated, washed with ethanol, and dried. The
µ
, mm–1
1.120
F(000)
2420
Crystal dimensions, mm
scan range, deg
Ranges of , and
0.29
×
0.24 × 0.15
yield of L1H2 was 80%,
T
m = 205 C.
°
θ
2.2 to 26.5
h
,
k
l
indices
–46
–12
–17
≤
≤
≤
h
k
l
≤
≤
≤
46
11
17
For C10H11NO3
anal. calcd, %: C, 62.18;
Found, %: C, 61.18;
H, 3.5;
H, 3.4;
N, 7.2.
N, 7.6.
Number of measured reflecꢀ
tions
17530
Trinuclear cobalt complexes were obtained by temꢀ
plate synthesis, as well as by using the Schiff bases
L1H2, Nꢀ(2ꢀcarboxyethyl)ꢀ3ꢀtertꢀbutylsalicylaldimine
Number of independent reflecꢀ
tions
443
Rint
0.062
(
L2H2), and Nꢀ(2ꢀcarboxyethyl)ꢀ3,5ꢀdiꢀtertꢀbutylsalꢀ
icylaldimine (L3H2) as the starting materials.
Synthesis of [Co(L1)2Co(H2O)4Co(L1)2]
Tmin
,
Tmax
0.7091, 0.8217
1.04
GOOF on F2
⋅
R
R
factor (
factor (for all reflections)
Δρmax),
Å–3
I
> 2
σ
(
I
))
R
1 = 0.040, wR
(
F2)= 0.107
CH3COOH ⋅ H2O (I). A. Cobalt acetate tetrahydrate
(0.249 g, 0.01 mol) in methanol (15 mL) and potasꢀ
sium acetate (0.98 g, 0.01 mol) in water (5 mL) were
added with stirring to L1H2 (0.89 g, 0.01 mol) in methꢀ
anol (10 mL). The reaction mixture was heated at
0.051
Δρmin
/
e
–0.43/0.82
50 С for 0.5 h and cooled. The roseꢀviolet precipitate
°
0.01 mol) in methanol (5 mL) was added. On cooling,
the roseꢀviolet precipitate of a Co(II) complex that
formed was separated. The dark brown mother liquor
was left for three to four days to produce dark brown
orthorhombic crystals suitable for Xꢀray diffraction.
of a Co(II) complex that formed was separated. The
mother liquor was left for 72 h to produce dark brown
crystals of complex I. The yield was 30%.
For C42H50 N4O19 Co3
anal. calcd, %:
The yield of complex
starting ligand).
I was 12% (with respect to the
C, 46.21;
H, 4.61;
H, 4.76;
N, 5.13.
N, 5.39.
Found, %:
C, 46.05;
For C42H50 N4O19 Co3
Template synthesis of [Co(L1)2Co(H2O)4Co(L1)2]
CH3COOH H2O (I). B. A solution of potassium aceꢀ
tate (0.98 g, 0.01 mol) in water (4 mL) was added to
ꢀalanine (0.89 g, 0.01 mol) and salicylaldehyde
(1.22 g, 0.01 mol) in ethanol–water (1 : 1, 20 mL).
The mixing resulted in the formation of a homogeꢀ CH3COOH
neous solution, to which cobalt acetate (2.49 g, and potassium acetate (0.98 g, 0.01 mol) were disꢀ
⋅
anal. calcd, %:
Found, %:
C, 46.21;
C, 46.58;
H, 4.61;
H, 4.28;
N, 5.13.
N, 4.91.
⋅
β
Synthesis of [Co(L3)2Co(H2O)4Co(L3)2]
H2O (III) ꢀAlanine (0.89 g, 0.01 mol)
⋅
⋅
.
β
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 38
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2012

142
GARAEVA et al.
C(22)
O(11)
O(10)
C(4)i
O(3)
C(21)
C(5)i
C(3)i
C(18)
N(2)
O(9)
C(6)i
O(2)
C(10)
C(19)
C(17)
C(16)
C(2)i
O(6)
C(7)i
C(1)i
O(1)i
O(4)i
C(20)
O(5)
O(8)
C(15)
C(14)
N(1)i
O(7)
C(12)i
C(9)
C(13)i
Co(1)i
C(19)i
C(8)i
C(20)i
O(6)i
Co(1)
C(8)
C(11)i
C(11)
O(4)
O(1)
O(8)
O(5)i
Co(2)
C(13)
N(1)
C(12)
C(14)i
O(7)
C(16)i
C(17)i
C(1)
C(9)i
C(15)i
N(2)i
C(7)
C(2)
O(2)i
C(18)i
C(10)
C(6)
C(3)
O(3)i
C(5)
C(4)
Fig. 1. Molecular structure of complex I with atomic thermal displacement ellipsoids (30% probability).
solved in water (3 mL). Then a solution of L3H2
β
ꢀamino acids (LiH2) can be obtained by template
(2.34 g, 0.01 mol) in ethanol (10 mol) was added. The synthesis from cobalt acetate, 2ꢀhydroxyarenecarbalꢀ
resulting solution was mixed with a solution of cobalt dehyde, and an amino acid in the presence of alkali
acetate tetrahydrate (2.45 g, 0.01 mol) in methanol metal acetates.
(10 mL) to produce a dark red homogeneous solution,
which was heated at 60 for 30 min and left for slow
If a Schiff base of an amino acid is stable (as in the
case of the Schiff bases derived from ꢀalanine and salꢀ
icylaldehyde and 2ꢀhydroxynaphthaldehyde [4]), the
above complexes can be obtained directly from cobalt
acetate and an appropriate Schiff base.
°С
β
crystallization. The dark brown fine crystalline precipꢀ
itate that formed was isolated, washed with ethanol,
and dried in vacuo. The yield of complex III was 41%
(with respect to the ligand),
T
m > 250 C. Complex III
°
The electronic absorption spectra of cobalt comꢀ
is well soluble in ethanol, DMF, acetonitrile, and
water.
plexes
I–III in the visible range show two absorption
bands at 15400–14300 and 19200–18700 cm–1,
which can be assigned to the 1A1 Т1 and 1A1
– –Т2
g g g
transitions in octahedral Co(III) complexes. Thegelecꢀ
tronic transitions in the Co(II) centers of heterovalent
complexes are masked by more intense transitions in
the Co(III) centers [2].
For C72H116N4O20Co3
anal. calcd, %:
Found, %:
C, 56.6;
C, 56.9;
H, 7.65;
H, 7.55;
N, 3.66.
N, 3.85.
The complex [Co(L2)2Co(H2O)4Co(L2)2]
⋅
The magnetic moments of complexes I–III (4.4–
4.8 μB) measured at room temperature suggest the
presence of the Co(II) ion.
H3COOH H2O (
⋅
II) was obtained from L2H2 as
described for complex III
.
The IR spectra of complexes I–III show absorpꢀ
For C56H80N4O20Co3
tion bands at 1600 νаs (СОО–) and 1400 cm–1
νs(СОО–)) due to the monodentate carboxylate group
and at 1570 νаs(СОО–) and 1430 cm–1 νs(СОО–) due
to the bridging carboxylate group.
anal. calcd, %: C, 51.76;
H, 6.2;
N, 4.3.
N, 4.2.
Found, %:
C, 52.06;
H, 6.08;
The formation of heterovalent trinuclear cobalt
complexes is usually accompanied by the formation of
RESULTS AND DISCUSSION
Heterovalent trinuclear cobalt complexes Co(II) complexes [4], which precipitate at the beginꢀ
[CoIII(Li)2CoII(H2O)4CoIII(Li)2]
= 1–3) with Schiff bases derived from
⋅
CH3COOH
⋅
H2O ning of the reaction because of their poor solubility in
and common organic solvents.
(
i
α
ꢀ
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 38
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2012

HETEROVALENT TRINUCLEAR Co(III)–Co(II)–Co(III) COMPLEXES
143
mal conditions. In contrast, L2H2 and L3H2 form solꢀ
uble Co(II) complexes and the yields of the correꢀ
sponding trinuclear complexes are high (up to 65%),
regardless of the low Co(II)–>Co(III) oxidation rate.
Table 2. Selected bond lengths and bond angles in strucꢀ
ture
I
*
Bond
d, Å
Bond
d, Å
Co(1)–O(1)
Co(1)–O(2)
Co(1)–O(4)
Co(1)–O(5)
Co(1)–N(1)
1.8842(19) Co(1)–N(2)
1.9211(18) Co(2)–O(6)
1.8767(19) Co(2)–O(7)
1.9622(19) Co(2)–O(8)
1.921(2)
1.911(2)
2.1282(19)
2.083(2)
2.092(2)
According to Xꢀray diffraction data, complex
I
{[Co(Salꢀ
β
ꢀala)2]2Co(H2O)4}, where Salꢀ
ꢀala = L1–
β
L3) consists of three cobalt centers (Fig. 1). In the triꢀ
nuclear complex (on the axis 2), the terminal Co(1)
and Со(1)i ions are each coordinated by two tridentate
ligands Salꢀ ꢀala. The central Co(2) ion is coordiꢀ
β
nated by four O atoms of four water molecules and two
O atoms of two carboxylate groups which bridge the
central Co(2) atom and the terminal Co(1) and Со(1)i
atoms. The diꢀdeprotonated ligands L1 make an octaꢀ
hedral environment around the terminal cobalt ion,
coordinating in a tridentate fashion through two
O atoms of two phenolic groups, two azomethine
N atoms, and two O atoms of the carboxylate groups.
One carboxylate group acts as a monodentate ligand,
while the other acts as a bridging bidentate ligand. The
terminal complex anion can be regarded as a monoanꢀ
ionic monodentate ligand to the central Co atom.
From stoichiometric considerations, the oxidation
state distribution in the trinuclear cobalt complex with
four diꢀdeprotonated ligands L1 must be as follows:
Co(III)–Co(II)–Co(III). This is confirmed by comꢀ
parison of the C–O bond lengths. Because the ionic
radius of Co(II) is larger than that of Co(III), the
Co(2)–O(6) bond (2.1282(19) Å) is substantially
longer than the Co(1)–O(2) and Co(1)–O(5) bonds
(1.9211(18) and 1.9622(19) Å, respectively (Table 2)).
According to the literature data [3, 4, 18], the Co(II)–
Angle
ω
, deg
Angle
ω
, deg
O(1)Co(1)O(2) 173.01(8) O(5)Co(1)N(1) 85.12(8)
O(1) Co(1)O(4) 88.91(8) O(5)Co(1)N(2) 93.43(8)
O(1)Co(1)O(5) 91.05(8) N(1)Co(1)N(2) 178.23(9)
O(1) Co(1) N(1) 92.60(9) O(6)Co(2)O(7)
O(1)Co(1)N(2) 88.44(8) O(6)Co(2)O(8)
O(2)Co(1)O(4) 91.32(8) O(6)Co(2)O(6)#1 178.47(7)
O(2)Co(1)O(5) 89.55(8) O(6)Co(2)O(7)#1 89.38(7)
O(2)Co(1)N(5) 94.39(9) O(6)Co(2)O(8)#1 85.80(8)
91.69(7)
93.11(8)
O(2)Co(1)N(2) 84.58(8) O(7)Co(2)O(8)
90.11(8)
O(4)Co(1)O(5) 173.11(8) O(7)Co(2)O(7)#1 90.80(8)
O(4)Co(1)N(1) 88.00(9) O(7)Co(2)O(8)#1 177.33(8)
O(4)Co(1)N(2) 93.46(8) O(8)Co(2)O(8)#1 89.09(8)
#1
* The symmetry operation code is
x, 1 – y, z – 1/2.
However, if the oxidation rate of Co(II) is high (this
is indicated by an increasing intensity of the absorpꢀ
tion band at 19000 cm–1 with time) or if a primary O bond length is ~2.1 Å, while the Co(III)–O bond
length is ~1.94 Å, which agrees with our data.
Co(II) complex is well soluble in the reaction
medium, heterovalent trinuclear cobalt complexes are
major reaction products. For instance, because Co(II)
complexes with L1H2 are poorly soluble and the Co(II)
to Co(III) oxidation rate is low, no trinuclear cobalt
Structure is stabilized by several types of hydrogen
I
bonds (HBs) (Table 3). The strongest HB
(H(10)⋅⋅⋅O(1)i, 1.87 Å) links the coordinated acetic
acid molecule with the phenolate O atom of the ligand
complex with this ligand can be obtained under norꢀ of an adjacent complex. Through the second O atom,
Table 3. Geometrical parameters of the hydrogen bonds in structure I*
Distance, Å
Hydrogen bond, Å
Angle D–H⋅⋅⋅A, deg
D–H
0.82
H
⋅⋅⋅
A
D⋅⋅⋅A
O(10)–H(10)⋅⋅⋅O(1)#1
O(7)–H(71)⋅⋅⋅O(9)
1.87
2.629(3)
2.751(3)
2.727(3)
2.730(3)
2.874(3)
2.797(3)
3.008(3)
153.2
175(4)
151(4)
175(4)
151(5)
174(4)
161(4)
0.827(18)
0.810(18)
0.830(18)
0.823(18)
0.843(18)
1.927(18)
1.99(2)
O(7)–H(72)⋅⋅⋅O(5)#2
O(8)–H(81)⋅⋅⋅O(11)#3
O(8)–H(82)⋅⋅⋅O(3)#3
O(9)–H(91)⋅⋅⋅O(3)#4
O(9)–H(92)⋅⋅⋅O(6)#3
1.902(18)
2.13(3)
1.957(18)
2.23(2)
0.809(18)
#1
#2
#3
#4
* The symmetry operation codes are
x, 1 –
y,
z
– 1/2 ; 1 –
x,
y, –
z
+ 3/2; 1 –
x, 1 –
y, 1 –
z;
–x, 2 – y, 1 – z.
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 38
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144
GARAEVA et al.
ments of two adjacent trinuclear complex molecules:
0
z
О(9)–Н(91)⋅⋅⋅0(3)i (H⋅⋅⋅O 1.96
v
Å) and О(9)–
Н(92)⋅⋅⋅О(6)iii (2.23
Å).
It is thus safe to say that Schiff bases derived from
ꢀalanine and 2ꢀhydroxyarenecarbaldehydes form
β
heterovalent complexes in which the terminal Co(III)
ions are linked to the central Co(II) ion (the cation
[
α
Co(H2O)4]2+) by carboxylate bridges. In the case of
ꢀamino acids, the central Co(II) ion is hydrogenꢀ
bonded to the terminal Co(III) ions [3].
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the coordinated acetic acid molecule is hydrogenꢀ
bonded to the water molecule coordinated by the cenꢀ
tral Co(II) ion (Н(81)⋅⋅⋅0(11)iii 1.90 Å) of an adjacent
complex molecule (Fig. 2). The intramolecular HB
О(7)–Н(72)–О(5)ii links the coordinated water moleꢀ
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⋅⋅⋅O 1.99 Å). The same coordinated water molecule
is hydrogenꢀbonded (О(8)–Н(82)⋅⋅⋅O(3)iii) to the
uncoordinated carboxylate O atom of the ꢀalaninate
β
ꢀalaninate
13. Sheldrick, G.M., Acta Crystallogr., Sect. A: Found.
Crystallogr., 2008, vol. 64, p. 112.
(
H
14. Farrugia, L.J., J. Appl. Crystallogr., 1999, vol. 32, p. 837.
15. Farrugia, L.J., J. Appl. Crystallogr., 1997, vol. 65, p. 305.
β
fragment of an adjacent trinuclear complex molecule 16. Macrae, C.F., Edgington, P.R., McCabe, P., et al.
,
J. Appl. Crystallogr., 2006, vol. 39, p. 453.
(
H
⋅⋅⋅O 2.13 Å). The coordinated and outerꢀsphere
water molecules are linked by the sufficiently strong
HB O(7)–Н(71)⋅⋅⋅O(9) (H⋅⋅⋅O 1.93
Two HBs link the uncoordinated water molecule
with the carboxylate O atoms of the ꢀalaninate fragꢀ
17. Spek, A.L., PLATON. A Multipurpose Crystallographic
Tool, Utrecht: Utrecht Univ., 2005.
Å).
18. Wang, Y.Qi., Fan, H., Cao, M., et al., J. Mol. Struct.
2004, vol. 73, p. 694.
,
β
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 38
No. 2
2012