Synthesis and structural characterization of the mononuclear cobalt(II) complex: {5,5′-dihydroxy-2,2′-[o-phenylene-bis(nitrilomethylene)] diphenolato}cobalt(II) dihydrate

Article abstract of DOI:10.1007/s10870-013-0422-1

The Schiff base ligand H₂L·C₂H₅OH derived from the condensation reaction between o-phenylenediamine and 2,4-dihydroxybenzaldehyde as well as its mononuclear complex [CoL]·2H₂O have been synthesized and character

Full text of DOI:10.1007/s10870-013-0422-1

J Chem Crystallogr
DOI 10.1007/s10870-013-0422-1
ORIGINAL PAPER
Synthesis and Structural Characterization of the Mononuclear
0
0
Cobalt(II) Complex: {5,5 -Dihydroxy-2,2 -[o-phenylene-
bis(nitrilomethylene)]diphenolato}cobalt(II) Dihydrate
Alina Soroceanu
Iolanta Balan Natalia Gorinchoy
Constantin Turta
•
Sergiu Shova
•
Maria Cazacu
•
•
•
Received: 20 July 2012 / Accepted: 17 April 2013
Springer Science+Business Media New York 2013
ꢀ
Abstract The Schiff base ligand H LꢀC H OH derived
Introduction
2
2 5
from the condensation reaction between o-phenylenedi-
amine and 2,4-dihydroxybenzaldehyde as well as its
Schiff bases, azomethines or imines, are among the most
used ligands due to their easy preparation as well as ability
to bind a variety of metal ions (Co, Mn, Cu, Ni, Fe, Cr, Zn,
V, etc.) [1]. Different ligand classes were developed based
on the condensation between salicylaldehyde derivatives
with a variety of diamines [2]. Either aliphatic or aromatic
diamines were used resulting in salen and salophen-type
ligands, respectively. These are [N,N,O,O] tetradentate
ligands [3] having four coordinating sites and two axial
sites open to additional ligands [3, 4]. An important pre-
cursor for Schiff base ligands is phenylenediamine. There
are a lot of reports in literature on the complexes of salo-
phen-type ligands based on o-phenylenediamine with dif-
ferent metals [1, 5–7]. One of the most studied is
Co(salophen) complex due to the known biological role of
cobalt, its complexes with tetratendate Schiff base ligands
being widely used to mimic cobalamin (B12) coenzymes,
particularly as dioxygen carriers and oxygen activators [8,
mononuclear complex [CoL]ꢀ2H O have been synthesized
2
1
and characterized by X-ray crystallography, IR, H NMR
and UV–Vis analyses, and density functional theory (DFT
II
B3LYP) calculations. The Co ion has a slightly distorted
square-planar coordination provided by tetradentate dian-
2
ionic N O ligand L . The spin state of the complex was
-
2
2
determined as being S = 1/2. On the basis of DFT calcu-
lations, the UV–Vis absorption bands of the ligand can be
1
1
1
1
assigned to the A ? B (two) and A ? A transi-
1
2
1
1
2
2
tions, while for complex they correspond to the A ? B
two) and A ? A ones.
2
1
2
2
(
2
2
Keywords Schiff base ꢀ Salophen ꢀ Co(II)–complex ꢀ
DFT calculations
9
]. Cobalt complexes that can reversibly coordinate
molecular oxygen have been studied extensively [10]. The
Co(II)–salen complex is extremely sensitive to oxygen and,
in the presence of an additional donor group, forms six
coordinated octahedral cobalt(III) complexes, whereas, in
the same conditions, the Co(II)–salophen complex shows a
low tendency to increase its coordination number [11].
These compounds are also of interest in supramolecular
synthesis [1] or as catalysts for a variety of reactions [12–
Electronic supplementary material The online version of this
article (doi:10.1007/s10870-013-0422-1) contains supplementary
material, which is available to authorized users.
A. Soroceanu ꢀ S. Shova ꢀ M. Cazacu (&) ꢀ C. Turta
‘‘Petru Poni’’ Institute of Macromolecular Chemistry, Aleea Gr.
Ghica Voda 41A, 700487 Iasi, Romania
e-mail: mcazacu@icmpp.ro
1
4]. Thus, cobalt–salen and cobalt–salophen complexes are
S. Shova
Institute of Applied Physics of ASM, Academiei Str. 5,
used as catalysts for oxygen reduction [10]. Co(II) com-
plexes of Schiff bases derived from salicylaldehyde and
o-phenylenediamine have been prepared and used in cata-
lytic oxygenation of 2,6-di-tert-butylphenol leading to the
formation of benzoquinone and diphenoquinone. It has
2
028 Chisinau, Republic of Moldova
I. Balan ꢀ N. Gorinchoy ꢀ C. Turta
Institute of Chemistry of ASM, Academiei Str. 3, 2028 Chisinau,
Republic of Moldova
123

J Chem Crystallogr
been proved that, in this process, the Co(II) complexes
form reversible adducts with molecular oxygen [15].
Different from other articles reporting the Co complexes
of the salophen-type ligands in general based on salycil-
aldehyde and o-phenylenediamine [15–17] or 2,4-dihy-
droxybenzaldehyde and other diamines [18–20], we
prepared the Schiff base, H LꢀC H OH (1), derived from
X-ray Crystallography
Crystallographic measurements for 1 and 2 were carried out
at room temperature with an Oxford-Diffraction XCALI-
BUR E CCD diffractometer equipped with graphite-mono-
chromated Mo Ka radiation. The crystals were placed
40 mm from the CCD detector. The unit cell determination
and data integration were carried out using the CrysAlis
package of Oxford Diffraction [24]. All structures were
solved by direct methods using SHELXS-97 [25] and refined
2
2 5
2
,4-dihydroxybenzaldehyde and o-phenylenediamine and
its Co mononuclear complex, [CoL]ꢀ2H O (2). The
2
1
obtained compounds were investigated by IR, H NMR,
2
UV–Vis spectroscopy, X-ray crystallography, and density
functional theory (DFT B3LYP) calculations methods. The
presence of the additional free OH groups in the resulted
complex would permit its using in the subsequent reactions
or could confer functionality to the supramolecular
assemblies formed through vacant coordination site.
by full-matrix least-squares on Fo with SHELXL-97 [26]
with anisotropic displacement parameters for non-hydrogen
atoms. All H atoms attached to carbon were introduced in
˚
idealized positions (dCH = 0.96 A) using the riding model
with their isotropic displacement parameters fixed at 120 %
of their riding atom. Positional parameters of the water
molecules and OH-groups were obtained from difference
Fourier syntheses and verified by the geometric parameters
of the corresponding hydrogen bonds. The main crystallo-
graphic data together with refinement details are summa-
rized in Table 1.
Experimental
Materials
CCDC-843942 and CCDC-843778 contain the supple-
mentary crystallographic data for this contribution. These
data can be obtained free of charge via www.ccdc.cam.ac.
uk/conts/retrieving.html (or from the Cambridge Crystal-
lographic Data Centre, 12 Union Road, Cambridge CB2
1EZ, UK; fax: (?44) 1223-336-033; or deposit@ccdc.ca.
ac.uk).
Cobalt (II) acetate tetrahydrate, Co(CH COO) ꢀ4H O, [99 %,
3
2
2
was purchased from Sigma-Aldrich. 2,4-Dihydroxybenzalde-
hyde (Aldrich Chemistry), (HO) C H CHO, AR, 98 %, m.p.
2
6 3
1
35–137 ꢁC. o-phenylenediamine, C H N , OPD, [98 %,
6
8 2
m.p. 98–102 ꢁC was purchased from Aldrich Chemistry.
Equipments
Procedure
Fourier transform infrared (FT-IR) spectra were recorded using
a Bruker Vertex 70 FT-IR spectrometer. Registrations were
performed in the transmission mode in the range
0
0
Synthesis of 5,5 -dihydroxy-2,2 -[o-phenylenebis
(nitrilomethylene)]diphenol, H OH, (1)
LꢀC
H
2 5
2
-1
4
00–4,000 cm at room temperature with a resolution of
-1
2
cm and accumulation of 32 scans. The samples were
A solution of o-phenylenediamine (0.39 g, 2.83 mmol) in
5 mL methanol was added with stirring at room tempera-
ture to a solution consisting of 1.0 g (7.24 mmol) 2.4-
dihydroxybenzaldehyde and 5 mL methanol. The mixture
was heated for 2 h at 70ꢁC, then was left to stand overnight
at room temperature and finally the solvent was removed at
rotavap. The remained solid was successively washed with
methanol and diethyl ether and dried at 40ꢁC in vacuum
oven. The compound was dissolved in ethanol to form a
solution of about 2.5 wt%, refluxed for about 30 min after
which was cooled at room temperature and stored in
freezer for 3 days when yellow crystals separated.
incorporated in dry KBr and processed as pellets in order to be
measured.
1
The proton magnetic resonance ( H NMR) spectra were
acquired in DMSO-d at 25 ꢁC with a Bruker Avance DRX
6
4
00 MHz spectrometer operating at 400.13 MHz for 1H. The
spectrometer was equipped with a 5 mm four nuclei, direct
detection z-gradient probehead. Chemical shifts are reported
1
in ppm and are referenced to chloroform d H = 7.26 ppm.
UV–Vis absorption spectra were recorded on spectro-
photometer Shimadzu UV-1700 in DMF solution using
quartz cuvettes of 1 cm.
Magnetic properties of complex at room temperature
were determined by NMR (Bruker Avance DRX 400 MHz
spectrometer) measurement using the Evans method [21–
Yield 73 %. Elemental analysis: Calcd. for C22H N O
22 2 5
-
394.42 g mol ), %C 66.98; H 5.63; N 7.11. Found,
1
(M
% C 67.42; H 4.50; N 7.09.
r
-
1
2
3]. The indicator compound was t-butanol in DMSO. The
‘dopped’’ solution with known quantity of investigated
IR spectrum (KBr pellet), cm : 3,857vw, 3,842vw,
3,825vw, 3,754vw, 3,737vw, 3,679vw, 3,611vw, 3,434m,
2,922m, 2,853w, 1,721m, 1,627vs, 1,610vs, 1,574vs,
1,548m, 1,499s, 1,474m, 1,453m, 1,390w, 1,361m,
‘
substance was prepared in a capillary tube and shift dif-
ference was measured directly.
1
23

J Chem Crystallogr
Table 1 Crystallographic data, details of data collection and struc-
ture refinement parameters for 1 and 2
room temperature. The clear solution was left until dark
yellow prismatic crystals of good quality were formed in a
few weeks. These were separated by filtration, washed with
methanol, dried and analyzed.
Compound
1
2
Empirical formula
Formula weight
Temperature (K)
Crystal system
Space group
C
22
H
22
N
2
O
5
C
20 2 6
H18CoN O
Yield 65 %. Elemental analysis: Calcd. for
-1
394.42
441.29
293
C H N O Co (M 441.30 g mol ), % C 54.43; H 4.11;
2
0
18
2
6
r
200.00(14)
N 6.34. Found, % C 54.21; H 4.02; N 6.15.
-1
IR spectrum (KBr pellet), cm : 3,541w, 3,064vw,
Triclinic
Monoclinic
C2/c
Pꢀ1
2,921w, 1,655m, 1,603vs m(C = N), 1,580vs, 1,554s m(aro-
˚
a (A)
8.7910(7)
10.8502(7)
17.9074(8)
9.3012(5)
90
matic ring), 1,494m, 1,476m, 1,447s m(CH ), 1,382m, 1,368s,
2
˚
b (A)
11.2617(10)
11.5549(10)
116.095(9)
99.706(7)
101.121(7)
965.46(14)
1.357
1
1
,299w, 1,283w, 1,245s, 1,237s, 1,204s, 1,191s, 1,156w,
,120s, 1,044w, 992w, 973w, 903vw, 851m, 842m, 793m,
˚
c (A)
a (ꢁ)
b (ꢁ)
c (ꢁ)
762m, 748w, 732w, 654w, 645w, 532w, 495m, 461vw.
1
H NMR spectrum: capillary filled with solution of
103.327(6)
90
6.7 mg of cobalt complex, 0.030 mL DMSO-d , and
6
3
˚
V (A )
1758.54(17)
1.667
0.970 mL t-butanol was placed in the measuring NMR
spectra tube containing the same mixture without com-
pound under study. Two bands assigned to the protons of
t-butanol were observed in NMR spectrum at 478.956 Hz
(1.197 ppm) and 448.706 Hz (1.121 ppm) corresponding
to the t-butanol from capillary and HMR tube, respectively.
-
3
)
Dcalc (g cm
Z
2
4
-
1
)
l (mm
0.097
1.020
Reflections collected/ 9374/3593
unique
4141/2067
(Rint = 0.0637)
(Rint = 0.0482)
3
-1
-1
Data/restraints/
parameters
3593/0/263
2067/3/139
UV–Vis (DMF), kmax, nm (e, dm mol cm ): 322
e = 19800), 346 (e = 18000), 394 (e = 22800).
(
a
1
R
, [I [ 2r(I)]
0.0791
0.0560
b
wR
2
0.1924
0.1466
c
GOF
1.033
1.033
Results and Discussion
-3
)
˚
Dqmax/Dqmin, (eA
0.45/-0.36
0.381/-0.550
a
Two-step procedure was approached to prepare a Co(salo-
phen) type complex. First, the compound 1 was prepared by
reaction between o-phenylendiamine and 2,4-dydroxybenz-
aldehyde, in 1:2 molar ratio, in refluxing methanol. The for-
mation of azomethine was proved by the presence in FTIR
R
1
= R||F
wR = {R[w (F
GOF = {R[w(F
o c o
| - |F ||/R|F |
b
c
2
2 2
c
2 2 1/2
o
) ]}
1/2
2
o
- F
) ]/R[w(F
2
2 2
o
c
- F ) ]/(n - p)} ; where n is the number of
reflections and p is the total number of parameters refined
-1
1
1
7
4
,324m, 1,308m, 1,250s, 1,190s, 1,175m, 1,160s, 1,123s,
,094m, 1,048m, 1,018w, 977m, 886w, 852m, 842m,
97m, 746m, 602vw, 545w, 531m, 520w, 503w, 488w,
72w, 445w, 428vw, 416vw.
spectrum of the characteristic band at 1,627 cm besides to
-1
other specific bands such as 3,066 cm (aromatic C–H
-1
stretch), 1,610 and 1,574 cm (aromaticringvibrations), and
-1
1
1,250 cm (phenolic C–Ostretch)(Fig. 1S). In H NMR, the
peak of the proton from azomethine (CH=N) group is present
at 8.76 ppm besides to the peaks for OH at 10.26 and
13.40 ppm as well as aromatics in the range 6.29–7.40 in the
ratio corresponding to the presumed structure (Fig. 1).
The obtained ligand was treated with a cobalt salt,
Co(CH COO) ꢀ4H O forming the corresponding complex
1
H NMR (DMSO), d, ppm: 6.29 (2H, d, 2.40 Hz, H-3),
.40 (2H, dd, 8.40, 2.40 Hz. H-2), 7.33-7.40 (4H, m,
6
H-4,5,6,7), 7.44 (2H, d, 8.40 Hz, H-1), 8.76 (2H, s, H-8),
0.27 (2H, s, OH), 13.40 (2H, s, OH); the peaks intensity
ratio 2:2:4:1:1:1:1.
1
3
-1
-1
UV–Vis (DMF), kmax, nm (e, dm mol cm ): 287
e = 30084), 330 (e = 38831), 372 (e = 28042).
3
2
2
(
CoL (compound 2). As a result of the complexation, the
azomethine band in FTIR spectrum shifted from
-1
1,627 cm in free ligand to lower stretching frequency,
0
0
Synthesis of {5,5 -dihydroxy-2,2 -[o-phenylenebis
nitrilomethylene)]diphenolato}-cobalt(II),
CoLꢀ2H O, (2)
-
1,616 cm , in complex. Bathochromic shifts are also
1
(
recorded in the m(phenolic C–O) band from 1250 in ligand
2
-
1
at 1,237 cm in complex that confirms the involving of
oxygen in C–O–Co bond. The new found vibration bands
0
.15 g (0.38 mmol) of the H L was dissolved in a solvent
2
-
1
mixture consisting in 6 mL ethanol, 4 mL methanol and
mL DMF. This solution was added over the other con-
at 495 and 645 cm which are not present in the free
Schiff base are attributed to the m(phenolic O–Co) and
m(N–Co), respectively, due to the involvement of oxygen
and nitrogen atoms in metal complexation [27].
4
sisting in into solution of 0.15 g (0.60 mmol) Co(CH3-
COO) ꢀ4H O in 6 mL ethanol and stirred for 10 min at
2
2
123

J Chem Crystallogr
1
Fig. 1 H NMR spectrum of the compound 1 (ligand H
2
L) in DMSO-d
6
X-ray Crystallography
The X-ray structures of compounds 1 and 2, along with
atom-labelling schemes, are depicted in Figs. 2 and 4,
respectively. Selected bond lengths and angles are sum-
marized in Table 2.
The crystal 1 has a molecular structure built of the
neutral molecules H L and ethanol as solvate molecules in
2
1
:1 ratio associated via intermolecular H-bonds, where
the OH-groups of the solvate molecules act as donor while
the OH-group of the Schiff base as acceptor (Fig. 2). The
conformation of the ligand molecule is stabilized through
two intramolecular O–HꢀꢀꢀN H-bonds (Fig. 2). The H L
2
molecule is essentially non-planar, because the aromatic
ring denoted by C1–C6 atoms being twisted at N1-C8
bond, which arises from the intramolecular steric effect
between two OH groups. The dihedral angle between two
planar moieties is equal to 51.16(4)ꢁ. The main crystal
packing motif of H L (1) is of zigzagging infinite chains
2
Fig. 2 X-ray structure of H
2
LꢀC
2
H
5
OH, 1 thermal ellipsoids are
packed parallel to b crystallographic axis (Fig. 3).
Each chain is built from the H L and solvate ethanol
drawn at 40 % probability level. Intermolecular O5–HꢀꢀꢀO2 [O5–H
2
˚
˚
˚
0
.83 A, HꢀꢀꢀO2 2.05 A, O5ꢀꢀꢀO2 2.814(4) A, \O5–HꢀꢀꢀO2 151.3ꢁ] and
molecules linked via a system of H-bonds and p–p stacking
interactions. One of the H-bond, which involves two of four
hydroxyl groups with distances O3–HꢀꢀꢀO2(1 - x, 1 - y,
˚
two intramolecular hydrogen bonds O1–HꢀꢀꢀN1 [O1–H 0.82 A,
˚
˚
HꢀꢀꢀN1 1.91 A, O1ꢀꢀꢀN1 2.639(4) A, \O1–HꢀꢀꢀN1 147.6ꢁ], O2–HꢀꢀꢀN2
˚
˚
˚
[
1
O1–H 0.85 A, HꢀꢀꢀN1 1.92 A, O1ꢀꢀꢀN1 2.612(3) A, \O1–HꢀꢀꢀN1
37.3ꢁ are also shown
˚
0
˚
0
2
- z) = 1.82 A, O3ꢀꢀꢀO2 = 2.619(4) A and O3–HꢀꢀꢀO2
angle of 165.2ꢁ, is responsible for the formation of
centro-symmetric dimeric entities. Another two H-bonds: O4–
˚
O5ꢀꢀꢀO2 = 2.814(4) A, \O5–HꢀꢀꢀO2 151.3ꢁ sustain the
˚
0
˚
HꢀꢀꢀO5(1 - x, - y,2 - z) = 1.83 A, O4ꢀꢀꢀO5 = 2.649(4) A,
formation of infinite chains. Secondary, there is face stacking
0
˚
\
O4–HꢀꢀꢀO5
173.7ꢁ
and
O5–HꢀꢀꢀO2 = 2.05 A,
of pairs of H L molecules, which is evidenced by the
2
1
23

J Chem Crystallogr
centroid–centroid distance between centro-symmetrically
˚
related C1–C6 aromatic rings equal to 3.82 A.
solvate water molecules with CoL complex occurs through
H-bond, where the phenolic oxygen atoms act as acceptor
(Fig. 4). The key role in crystal structure is played by
O–HꢀꢀꢀO hydrogen bonds, which determine the formation
of the double ribbons extending parallel to the a crystallo-
graphic axis (Fig. 5).
The Co atom in the crystal structure 2 occupies the
special position on twofold axis; therefore the molecular
structure of the CoL complex is characterized by imposed
C symmetry (Fig. 4). The central atom exhibits a slightly
2
distorted N O square-planar environment, provided by
2
2
2
-
L
anion as a tetradentate ligand. The association of
Magnetic Properties
The Eq. (1):
˚
Table 2 Selected bond lengths (A) and bond angles (ꢁ) for 1 and 2
3
m0 ꢁ mi
ðv Þ ¼ 4
þ v0;
ð1Þ
i g
1
2
1
2
pm m0
Co1–O1
Co1–N2
N2–C7
–
1.896(2) C9–C10
1.930(3) C7–C6
1.295(4) C6–C1
1.427(4) C6–C5
1.371(5) 1.376(5)
1.442(5) 1.424(5)
1.400(5) 1.422(5)
1.395(5) 1.431(5)
1.377(5) 1.351(5)
where m is the frequency of the signal in the outer com-
0
–
partment, m the frequency of the signal in the capillary
i
–
(
Fig. 2S), m the mass of paramagnetic substance in 1 mL
of solution, v is the gram susceptibility of solvent, and the
N2–C8
–
o
N2–C13
N2–C14
N1–C7
1.417(4)
1.319(4)
1.287(4)
1.420(4)
–
–
–
C5–C4
experimental data obtained according to Evans method
C8–C9
1.390(5)
1.397(5)
1.382(4)
1.378(5)
1.377(5)
1.405(5)
1.440(5)
1.417(5)
1.378(5)
1.397(5)
1.348(5)
1.406(5)
1.506(8)
–
–
[
21] were used to determine the effective magnetic moment
C14–C15
C13–C12
–
of complex, l . A value of about 1.6 BM was obtained
eff
N1–C8
–
which means that the spin state of the complex S = 1/2 and
C8–C9
1.390(5) 1.373(4) C12–C11
–
its multiplicity is 2.
O2–C3
–
1.356(4) C11–C10
C13–C8
–
O3–C3
1.350(4)
–
–
Electronic Structure
O1–C1
1.355(4) 1.313(3) C15–C20
–
O4–C18
O2–C20
O5–C22
C2–C3
1.341(4)
1.292(4)
1.290(6)
–
–
–
C15–C16
C19–C18
C19–C20
–
–
Both the ligand and the complex spectrum contain three
UV–Vis absorption bands at 287, 330, 372 nm (1) and 322,
346, 394 nm (2), respectively (Fig. 6).
–
1.376(5) 1.380(4) C17–C16
1.368(5) 1.393(5) C17–C18
1.391(5) 1.392(5) C21–C22
–
C2–C1
–
For assignment of these bands, the electronic structures
of the ligand 1 and the complex 2 were calculated at the
DFT B3LYP and Hartree–Fock CI levels. Quantum
chemical calculations were performed using the PC GA-
MESS version [28] of the GAMESS (US) QC package
C3–C4
–
0
O1–Co1–N1
O1–Co1–O1
–
–
94.9(1)
86.4(3)
O1–Co1–N1
172.3(1)
84.9(2)
0
0
N1-Co1–N1
–
0
Symmetry code: ) -x?1, y, -z?3/2
Fig. 3 View of the infinite chain in the crystal structure 1
123

J Chem Crystallogr
[
29]. A full geometry optimization was carried out by
geometries. The CI matrices in both cases included all
configurations produced by single and double excitations
from the five highest occupied to five lower unoccupied
MOs.
means of all-electron spin-restricted DFT calculations
employing the B3LYP hybrid functional [30, 31] in com-
bination with the TZV basis set for all atoms [32, 33].
Electronic terms of excited states and electronic transition
energies were obtained from single-point Hartree–Fock
configuration interaction (CI) calculations at the optimized
As a first step, the geometry optimization was carried
out in the assumption that the spatial nuclear configuration
of considered compounds corresponds to the C2v point
group of symmetry; the z-axis lies in the plane of the ligand
and bisects the latter; the x-axis is perpendicular to the
plane of the ligand. The basis for this choice was the
experimental X-ray data, according to which the central
atom exhibits a slightly distorted N O square-planar
2
2
environment in 2. However, the vibration analysis of
Fig. 4 X-ray structure of CoLꢀ2H
2
O, 2. Thermal ellipsoids are drawn
at 40 % probability level. H-bond parameters: O1w–HꢀꢀꢀO1 [O1w–H
Fig. 6 UV–Vis spectra for: a compound 1 (ligand H
2 (complex CoL) in DMF
2
L); b compound
˚
˚
˚
0
.86 A, HꢀꢀꢀO1 1.95 A, O1wꢀꢀꢀO1 2.796(4) A, \O1w–HꢀꢀꢀO1 167.1ꢁ
˚
˚
Fig. 5 The fragment of the crystal structure of CoLꢀ2H
2
O, 2. H-bond
O1w–HꢀꢀꢀO2 [O1w–H 0.82 A, HꢀꢀꢀO2(1 - x , ? y, 0.5 - z) 2.37 A,
˚
0
˚
parameters: O2–HꢀꢀꢀO1w [O2–H 0.82 A, HꢀꢀꢀO1w(1 - x, 1 - y,
O1wꢀꢀꢀO2 3.181(4) A, \O1w–HꢀꢀꢀO2 159.5ꢁ]
- z) 1.90 A, O2ꢀꢀꢀO1w0 2.720(4) A, \O2–HꢀꢀꢀO1w 175.7ꢁ];
˚
˚
1
1
23

J Chem Crystallogr
considered compounds in the C2v symmetry shows the
presence of one imaginary frequency corresponding to the
The most important bond distances and angles in opti-
mized molecular structures are summarized in Table 3. As
can be seen from Tables 2 and 3, the method used provides
the structural values which are in a close agreement with
the experimental ones. Note also that the calculations
confirm the presence of intramolecular hydrogen bonds
O–HꢀꢀꢀN in compound 1 (the value of the N–H bond order
out-of-plane distortion of the a symmetry leading to the
2
structures of C symmetry. These are the twist of two
2
peripheral phenyl rings around the N1–C8 and N2–C13
bonds (Fig. 2) in the ligand molecule 1, and the ‘‘propel-
ler’’ type distortion of N O moiety around the atom of Co
2
2
in the complex 2. Optimized in C symmetry structures of 1 is approximately 0.2).
2
and 2 correspond to the true minima with all real
frequencies.
The molecular orbital diagrams for the frontier orbitals
in compounds 1 and 2 are depicted in Figs. 7 and 8 toge-
ther with the schemes of the electronic terms obtained from
CI calculations at the optimized geometries. The energies
and electronic configurations of the terms are given in
Tables 4 and 5 together with the experimental data on the
UV–Vis spectra.
˚
Table 3 Most important calculated and experimental distances (A)
o
and bond angles ( ) in ligand 1 and complex 2
1
2
As can be seen from Fig. 7 and Table 4, the low-lying
excited states of the ligand 1 are formed by one-electron
excitations from HOMO (b) and HOMO-1 (a) to the
LUMO (a*) and LUMO ? 1 (b*). These latter, in turn, are
the p and p* molecular orbitals built up from the
pp-functions of the phenyl rings and the corresponding
pp-orbitals of the nitrogens and the oxygens. From the
analysis of composition of these orbitals one can conclude
Geometry
parameters
Calc.
Exp.
Geometry
parameters
Calc.
Exp.
a
a
a
a
O1–H
1.024 (0.63)
1.656 (0.17)
2.57
0.82
Co1–N2
1.909 (0.415)
1.878 (0.457)
93.8
1.930
1.896
94.9
N1ꢀꢀꢀH1
N1ꢀꢀꢀO1
N1–C8
N1–C7
O1–C1
O1–HꢀꢀꢀN1
dihedral
a
1.91
Co1–O1
2.639
1.420
1.287
1.355
147.6
52.93
O1–Co1–N1
O1–Co1–O1
O1–Co1–N1
N1–Co1–N1
0
0
0
1.41
86.8
86.4
1.31
176.9
172.3
84.9
1
1
1.358
85.7
that the 1 A ? 2 A excitation corresponds to a redistri-
bution of the electron density within the central phenyl
146.3
51.16
1
1
ring, whereas the other two 1 A ? 1, 2 B excitations are
accompanied by the electron charge transfer from the
In parentheses is the value of the bond order
Fig. 7 Frontier molecular orbitals and electronic terms of the ligand 1. The arrows on the MO diagram indicate the one-electron excitations that
form corresponding excited states
123

J Chem Crystallogr
Fig. 8 Frontier molecular orbitals and electronic terms of 2. The arrows on the MO diagram indicate the one-electron excitations that form the
corresponding excited states. The nomenclature of 3d-AOs of Co is given in accordance with the coordinate system at the top right
peripheral rings on the central one. Table 4 shows a rather
good agreement between calculated energies of the excited
terms and the UV–Vis spectrum for 1. Thus, the electronic
absorption spectrum of this compound arises from p ? p*
transitions and can be explained by considering the four
frontier orbitals.
Table 4 Relative energies DE (eV) and electronic configurations of
the ground and low-lying excited states for 1
State
DE calc.
DE exp.
Electronic configuration
1
2
2
0
0
1
1
2
2
A
B
A
B
0.00
3.52
3.94
4.49
{…a b | a* b* …}
1
1
1
2
1
1
0
3.33
3.76
4.32
{…a b | a* b* …}
2
1
0
1
{…a b | a* b* …}
In the complex 2, the three highest occupied molecular
orbitals are composed mainly of 3d-orbitals of the metal:
the weight of the 3dxy AO of Co in the single-occupied
HOMO (a) is at &92 %, the HOMO-1 (b) is the linear
1
2
0
1
{…a b | a* b* …}
combination of the 3dxz AO of Co (&70 %) and p AOs of
p
Table 5 Relative energies DE (eV) and electronic configurations of
the ground and low-lying excited states for 2
peripheral rings (&30 %), and the HOMO-2 (a) is at 93 %
the 3dx ꢁz AO of the metal. The two lowest unoccupied
2
2
State
DE calc.
DE exp.
Electronic configuration
MOs (a*) and (b*) are the p*-orbitals of the ligand
2
Fig. 8). The first excited state 1 B of the complex 2 is
2
2
1
0
0
1
A
0.00
3.74
3.79
4.72
{…b a | a* b* …}
(
2
1 B
2
2 B
2
2 A
2
0
0
1
obtained by one-electron excitation a ? b*; its electronic
configuration corresponds to one unpaired electron above
the closed shell. This excitation is characterized by the
electron density transfer from the metal to (mostly) the
central ring of the ligand. The electronic configuration of
3.15
3.58
3.85
{…b a | a* b* …}
1
1
1
0
{…b a | a* b* …}
1
1
0
1
{…b a | a* b* …}
2
2
other two excited states 2 B (b ? a*) and 2 A (b ? b*)
corresponds to three unpaired electrons on three orbitals
transfer both from metal and from the peripheral rings on
the central ring of the ligand. As can be seen from the
Table 5, the calculated energies of the excited states agree
relatively well with the experimental data.
2
2
(
Table 5). These two excitations, 1 A ? 2 B and
2
2
2
1
A ? 2 A, are accompanied by the electron charge
2
1
23

J Chem Crystallogr
Conclusions
7. Kleij AW, Tooke DM, Spek AL, Reek JNH (2005) Eur J Inorg
Chem 4626
8
. Zhang YL, Ruan WJ, Zhao XJ, Wang HG, Zhu ZA (2003)
Polyhedron 22:1535
A Co(II)–complex of salophen type ligand was prepared by
a two-steps procedure, including ligand preparation and its
using in cobalt complexation. Both the ligand and the
complex were isolated as crystals suitable for X-ray dif-
fraction on a single crystal. The results correlate well with
the spectral and analytical data. The calculated value of the
effective magnetic moment of the complex, leff &1.6 BM,
as well as quantum-chemical calculations indicate that the
spin state of the complex S = 1/2, and its multiplicity is 2.
On the basis of quantum chemical calculations, one can
conclude that the electronic absorption spectrum of the
ligand arises from p ? p* transitions and can be explained
within the four-orbital model. The absorption bands of the
complex can be attributed to the electron density transfer
from both the metal and the peripheral rings to the central
ring of the ligand.
9. Leung ACW, MacLachlan MJ (2007) J Inorg Organomet Polym
Mater 17:57
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7. Fasina TM, Ogundele O, Ejiah FN, Dueke-Eze CU (2012) Intern
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Acknowledgments This research was financially supported by
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