Synthesis, characterization, thermal and theoretical studies of cobalt(II) addition compounds with 2-hydroxy-phenones and α-diimines. Crystal and molecular structures of [Co(2-hydroxy-benzophenone)2(bipy)]·2- hydroxy-benzophenoneH (3) and [Co(2

Article abstract of DOI:10.1016/j.poly.2010.11.010

Ten Co(II) addition compounds [Co(ketone)₂Y], where ketone is the anion of 2-hydroxy-phenones and Y = the neutral α-diimines(bipy or phen), were synthesized and characterized by physicochemical and spectral (IR, UV-Vis) data. The molecular stru

Full text of DOI:10.1016/j.poly.2010.11.010

Polyhedron 30 (2011) 486–496
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Synthesis, characterization, thermal and theoretical studies of cobalt(II)
addition compounds with 2-hydroxy-phenones and a-diimines. Crystal
and molecular structures of [Co(2-hydroxy-benzophenone)2(bipy)]ꢀ2-hydroxy-
benzophenoneH (3) and [Co(2-hydroxy-benzophenone)2(phen)] (8)
Christos D. Papadopoulos a, Antonios G. Hatzidimitriou a, Miguel Quirós b, Michael P. Sigalas c,
Maria Lalia-Kantouri a,
⇑
a Aristotle University of Thessaloniki, Department of Chemistry, Laboratory of Inorganic Chemistry, P.O. Box 135, Thessaloniki 54 124, Greece
b University of Granada, Department of Inorganic Chemistry, Faculty of Science, Granada 18071, Spain
c Aristotle University of Thessaloniki, Department of Chemistry, Laboratory of Applied Quantum Chemistry, Thessaloniki 54 124, Greece
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 6 July 2010
Accepted 9 November 2010
Available online 16 November 2010
Ten Co(II) addition compounds [Co(ketone)2Y], where ketone is the anion of 2-hydroxy-phenones and
Y = the neutral
a-diimines(bipy or phen), were synthesized and characterized by physicochemical and
spectral (IR, UV–Vis) data. The molecular structures, vibrational and electronic spectra, and the energetics
of the metal–ligand interactions for compounds [Co(2-hydroxy-benzophenone)2(bipy)]ꢀ2-hydroxy-ben-
zophenoneH (3) and [Co(2-hydroxy-benzophenone)2(phen)] (8) were studied by means of density func-
tional calculations (DFT). Good correlation was found between the theoretical calculations and the
experimental values. The cyclic voltammetry study in CH3CN gave all the expected waves for the redox
processes of the metal Co(II) and the studied ligands. The X-ray diffraction study of the two compounds
(3) and (8) verified their analogous proposed octahedral arrangement of the ligands around the cobalt(II)
atom. The thermal behaviour was investigated by means of simultaneous TG/DTG-DTA technique in
nitrogen atmosphere up to 1000 °C, where metallic cobalt was found as the solid residue.
Ó 2010 Elsevier Ltd. All rights reserved.
Keywords:
Cobalt
2-Hydroxy-phenones
a-Diimines
Crystal structure
Thermal study
Theoretical (DFT) study
1. Introduction
metal ions cobalt(II, III) or iron(III) and ligands with N and/or O do-
nor atoms [12]. It has been found that the Lewis acidity of [CoII(sa-
Cobalt chelates with
a
-diimines such as 2,20 bipyridine (bipy) or
lo)2] chelates, renders them susceptible to nucleoplilic attack and
addition compounds can be obtained, such as [Co(salo)2( -dii-
1,100-phenanthroline (phen) form cationic octahedral complexes,
e.g. [Co(bipy)3]2+ [1], which are known to have important biologi-
cal properties [2]. Besides, the strong coordinating properties of 2-
hydroxy-phenones or 2-hydroxy-benzaldehydes (salicylaldehyde,
saloH) and their derivatives with 3d transition metals have stimu-
lated research in these compounds, which find applications in both
pure [3] and applied chemistry fields, especially in extractive met-
allurgy as analytical reagents [4,5] and specifically for cobalt com-
pounds in tire industry as adhesion promoters [6]. These ligands
are known to coordinate in a bidentate manner with transition
metals in the mono-anionic form, adopting square-planar geome-
try, [Zn(salo)2], [Zn-5-Br-salo] [7], [Cu(5-Br-salo)2] [8], [FeII(salo)2]
[9] or octahedral arrangement [VO(3-OCH3-salo)2(H2O)] [10],
[FeIII(2-hydroxy-propiophenone)3] [11].
a
mines)] [13,14]. In this paper, our approach to the field concerns
the synthesis of a series of 10 new cobalt(II) addition compounds
under the formula [Co(2-OH-phenone)2(a-diimine)]. The resultant
octahedral compounds were characterized by physico-chemical
methods and spectroscopic (IR, UV–Vis) studies. A cyclic voltam-
metry (CV) study was employed to investigate their electrochemi-
cal behavior. The structures of two representative compounds
were verified by X-ray diffraction analysis. The thermal stability
and decomposition mode for four of the new compounds were
studied in nitrogen atmosphere by using the simultaneous thermo-
gravimetric and differential thermal analysis technique (TG/DTG-
DTA).
Results of density functional calculations (DFT) for compounds
[Co(2-hydroxy-benzophenone)2(bipy)]ꢀ2-hydroxy-benzophenoneH
(3) and [Co(2-hydroxy-benzophenone)2(phen)] (8) were used to
interpret the vibrational and electronic spectra, as well as to ex-
plore the energetics of the metal–ligand interactions and the possi-
bility for the compound to adopt different conformations.
For a better understanding of the bonds and properties in these
compounds we have recently initiated a research project with the
⇑
Corresponding author. Tel./fax: +30 2310 997844.
E-mail address: lalia@chem.auth.gr (M. Lalia-Kantouri).
0277-5387/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2010.11.010

C.D. Papadopoulos et al. / Polyhedron 30 (2011) 486–496
487
The 2-OH-phenones presented in this work have the molecular
formula 2-OH-C6H4C(R)O, where R = CH3, C2H5 or C6H5, commonly
known and abbreviated as 2-OH-acetophenone(Hapo) (10), 2-OH-
propiophenone(Hppo) (20), 2-OH-benzophenone(Hbpo) (30),
respectively, as well as their derivatives 2-OH, 5-CH3–acetophe-
none(Hmpo) (40) and 2-OH, 4-OCH3-benzophenone(Hopo) (50),
(Scheme 1).
out in the potential region ꢁ1900 to +2200 mV at ambient temper-
ature. Recrystallized TEA perchlorate 0.1 M was used as the elec-
trolyte at a scan rate 100 mV/s. All scans were recorded in
degassed solvent and under current of moisture free argon over
the solution surface. The thermal behavior of the title compounds
was studied in nitrogen using the simultaneous TG/DTG-DTA tech-
nique, over the temperature range ambient-to-1000 °C, using a
Setaram Model Setsys-1200 thermogravimetric analyzer. The sam-
ples, with a mass of about 12 mg were heated in platinum cruci-
bles, at a heating rate 10 °C/min.
2. Experimental
Computationaldetails: the electronic structure and geometries of
the complexes studied were computed within the density func-
tional theory (DFT) using gradient corrected functionals, at the
Becke3LYP computational level [16,17]. The effective core potential
(ECP) approximation of Hay and Wadt was used [18–20]. For Co
atom, the electrons described by the ECP were those of 1s, 2s
and 2p shells. The basis set used was of valence double-f quality
[21]. Full geometry optimizations were carried out without sym-
metry constraints. A frequency calculation after each geometry
optimization ensured that the calculated structures are real min-
ima or transition states in the potential energy surface of the mol-
ecules and allowed the calculation of the zero point energy. In
calculating the interaction energies between molecular fragments
in the complexes, we accounted for the basis set superposition er-
ror (BSSE) by recalculating the monomer energies using the full di-
mer basis at the optimized geometry of the dimer using the
counterpoise method [22,23]. Time-dependent density functional
theory (TD-DFT) calculations were performed employing the same
functional and basis set for the analysis of the excitation energies
for both compounds. Solvent (methanol) effects were computed
by using the integral equation formulation-polarized continuum
model IEF-PCM [24,25]. All the calculations were performed using
the GAUSSIAN-03W ver. 6.0 package [26].
2.1. Materials
The ligands, 2-hydroxy-phenones (10–50), the
a
-diimines (2,20-
bipyridine, bipy and 1,100-phenanthroline, phen), and the metal
salt CoBr2ꢀ6H2O were obtained as reagent grade from Aldrich and
used as received. The precursor compounds [Co(a-diimine)2Br2]
were prepared according to the literature[15]. Solvents for prepa-
ration and physical measurements of ‘‘extra pure’’ grade were ob-
tained from Fluka without further purification.
2.2. Instrumentation/analytical procedures
Microanalyses were carried out using a Perkin–Elmer 240 B
CHN microanalyzer and Perkin–Elmer 5100 PC Atomic Absorption
Spectrophotometer for the metal content. Infrared spectra were re-
corded on a Perkin–Elmer 1600 FT-IR spectrometer in KBr discs at
room temperature and are reported in cmꢁ1. Electronic absorption
spectra in CH3CN solutions were obtained on a Shimatzu 160 A
spectrometer. Molar conductivities were measured in CH3CN solu-
tions, employing a WTW conductivity bridge and a calibrated dip
type cell. Magnetic susceptibility measurements on powdered
samples were performed at 25 °C employing the Faraday method
on a home-build balance calibrated against Hg[Co(SCN)4].
Cyclic voltammetry technique (CV) was used for the electro-
2.3. Preparation of the addition compounds [Co(2-OH-phenone)2(a-
chemical measurements on a
l
-AUTOLAB Potentio-Galvanostat
diimine)] (1–10)
(ECO CHEMIE, Netherlands). A saturated calomel electrode was
used as a reference electrode and a platinum plate one as an aux-
iliary electrode for all measurements. As a working electrode a
platinum wire was used. The tests in CH3CN solution were carried
All complexes have been prepared by the following general pro-
cedure: a solution of 1 mmol 2-hydroxy-phenone and CH3ONa
(1 mmol) in MeOH (25 mL), was added drop-wise to a solution of
Scheme 1. Structural formulae of the 2-hydroxy-phenone ligands.

488
C.D. Papadopoulos et al. / Polyhedron 30 (2011) 486–496
[Co(bipy)2Br2] or [Co(phen)2Br2] (0.5 mmol) in H2O (15 mL) at
room temperature. The solution was stirred for 2 h and then turned
darker and an orange-brownish solid was formed. The solid was fil-
tered, washed with water and dried in vacuo (mean yield 60%). All
compounds were prepared in inert, under argon, conditions and
well degassed solutions have been used.
1665 s, 1618 vs 1580 vs 1369 s, 856 m, 729 s, 570 m, 514, 437,
249 m.
2.3.5. Preparation of [Co(opo)2(bipy)]ꢀHopo (5)
A solution of 2-OH, 4-OCH3-benzophenone(Hopo) (228 mg,
1 mmol) and CH3ONa (54 mg, 1 mmol) in MeOH (25 mL), was
added drop-wise to a solution of [Co(bipy)2Br2] (0.266 g, 0.5 mmol)
in H2O (15 mL) at room temperature, under argon atmosphere. The
solution was stirred for 2 h and then turned darker and an orange-
brownish solid was formed. The solid was filtered, washed with
water and dried under vacuo (0.20 g, 44% yield). The crystalline
compound analyzed as Anal. Calc. for C52H42N2O9Co1 (MW 897):
C, 69.56; H, 4.68; N, 3.12; Co, 6.57. Found: C, 69.46; H, 4.62; N,
2.3.1. Preparation of [Co(apo)2(bipy)]ꢀHapo (1)
A solution of 2-OH–acetophenone(Hapo) (136 mg, 1 mmol) and
CH3ONa (54 mg, 1 mmol) in MeOH (25 mL), was added drop-wise
to a solution of [Co(bipy)2Br2] (0.266 g, 0.5 mmol) in H2O (15 mL)
at room temperature, under argon atmosphere. The solution was
stirred for 2 h and then turned darker and an orange-brownish so-
lid was formed. The solid was filtered, washed with water and
dried under vacuo (0.20 g, 64% yield). The crystalline compound
analyzed as Anal. Calc. for C34H30N2O6Co1 (MW 621): C, 65.70; H,
4.83; N, 4.51; Co, 9.49. Found: C, 65.57; H, 4.80; N, 4.49; Co,
3.12; Co, 6.55%. Magnetic value (
leff = 4.26 lB), conductivity in
CH3CN 2.2
l
S/cm. IR spectrum (KBr): selected peaks in cmꢁ1
:
1665 s, 1605 vs 1575 vs 1381 s, 832 m, 733 s, 572 m, 514, 413,
249 m.
9.45%. The magnetic value (
acter of the cobalt ion in octahedral environment. The conductivity
in freshly prepared CH3CN solutions was found equal to 2.0 S/cm,
denoting the neutral character of the compound. IR spectrum
(KBr): selected peaks in cmꢁ1: 1666 s, 1604 vs 1574 vs 1360 s,
828 m, 729 s, 585 m, 514, 420, 260 m.
leff = 4.24 lB) gives the bivalent char-
2.3.6. Preparation of [Co(apo)2(phen)] (6)
A solution of 2-OH–acetophenone(Hapo) (136 mg, 1 mmol) and
CH3ONa (54 mg, 1 mmol) in MeOH (25 mL), was added drop-wise
l
to
a solution of [Co(phen)2Br2] (0.290 g, 0.5 mmol) in H2O
(15 mL) at room temperature, under argon atmosphere. The solu-
tion was stirred for 2 h and then turned darker and an orange-
brown solid was formed. The solid was filtered, washed with water
and dried under vacuo (0.17 g, 66% yield). The crystalline com-
pound analyzed as Anal. Calc. for C28H22N2O4Co1 (MW 509): C,
66.01; H, 4.32; N, 5.50; Co, 11.58. Found: C, 65.88; H, 4.30; N,
2.3.2. Preparation of [Co(ppo)2(bipy)]ꢀHppo (2)
A solution of 2-OH–propiophenone(Hppo) (150 mg, 1 mmol)
and CH3ONa (54 mg, 1 mmol) in MeOH (25 mL), was added drop-
wise to a solution of [Co(bipy)2Br2] (0.266 g, 0.5 mmol) in H2O
(15 mL) at room temperature, under argon atmosphere. The solu-
tion was stirred for 2 h and then turned darker and an orange-
brownish solid was formed. The solid was filtered, washed with
water and dried under vacuo (0.19 g, 57% yield). The crystalline
compound analyzed as Anal. Calc. for C37H36N2O6Co1 (MW 663):
C, 66.97; H, 5.43; N, 4.22; Co, 8.88. Found: C, 66.57; H, 5.41; N,
5.42; Co, 11.55%. Magnetic value (
leff = 4.24 lB), conductivity in
CH3CN 2.0
l
S/cm. IR spectrum (KBr): selected peaks in cmꢁ1
:
1601 vs 1588 s, 1362 s, 848 m, 725 s, 575 m, 515, 430, 250 m.
2.3.7. Preparation of [Co(ppo)2(phen)] (7)
A solution of 2-OH–propiophenone(Hppo) (150 mg, 1 mmol)
and CH3ONa (54 mg, 1 mmol) in MeOH (25 mL), was added drop-
wise to a solution of [Co(phen)2Br2] (0.290 g, 0.5 mmol) in H2O
(15 mL) at room temperature, under argon atmosphere. The solu-
tion was stirred for 2 h and then turned darker and an orange-
brown solid was formed. The solid was filtered, washed with water
and dried under vacuo (0.13 g, 48% yield). The crystalline com-
pound analyzed as Anal. Calc. for C30H26N2O4Co1 (MW 537): C,
67.04; H, 4.84; N, 5.21; Co, 10.97. Found: C, 66.87; H, 4.80; N,
4.20; Co, 8.84%. Magnetic value (
leff = 4.23 lB), conductivity in
CH3CN 5.2
l
S/cm. IR spectrum (KBr): selected peaks in cmꢁ1
:
1662 s, 1603 vs 1584 vs 1363 s, 855 m, 728 s, 562 m, 512, 418,
248 m.
2.3.3. Preparation of [Co(bpo)2(bipy)].Hbpo (3)
A solution of 2-OH-benzophenone(Hbpo) (198 mg, 1 mmol) and
CH3ONa (54 mg, 1 mmol) in MeOH (25 mL), was added drop-wise
to a solution of [Co(bipy)2Br2] (0.266 g, 0.5 mmol) in H2O (15 mL)
at room temperature, under argon atmosphere. The solution was
stirred for 2 h and then turned darker and an orange-brownish so-
lid was formed. The solid was filtered, washed with water and
dried under vacuo (0.17 g, 42% yield). The crystalline compound
analyzed as Anal. Calc. for C49H36N2O6Co1 (MW 807): C, 72.80; H,
4.40; N, 3.40; Co, 7.30. Found: C, 72.50; H, 4.35; N, 3.38; Co,
5.17; Co, 10.77%. Magnetic value (
leff = 4.16 lB), conductivity in
CH3CN 3.2
l
S/cm. IR spectrum (KBr): selected peaks in cmꢁ1
:
1608 vs 1590 s, 1372 s, 852 m, 729 s, 567 m, 512, 420, 248 m.
2.3.8. Preparation of [Co(bpo)2(phen)] (8)
A solution of 2-OH-benzophenone(Hbpo) (198 mg, 1 mmol) and
CH3ONa (54 mg, 1 mmol) in MeOH (25 mL), was added drop-wise
to
a solution of [Co(phen)2Br2] (0.290 g, 0.5 mmol) in H2O
7.28%. Magnetic value
(leff = 4.16 lB), conductivity in CH3CN
(15 mL) at room temperature, under argon atmosphere. The solu-
tion was stirred for 2 h and then turned darker and an orange-
brown solid was formed. The solid was filtered, washed with water
and dried under vacuo (0.15 g, 47% yield). The crystalline com-
pound analyzed as Anal. Calc. for C38H26N2O4 Co1 (633): C, 71.49;
H, 4.00; N, 4.59; Co, 9.31. Found: C, 71.39; H, 4.00; N, 4.52; Co,
2.7
l
S/cm. IR spectrum (KBr): selected peaks in cmꢁ1: 1662 s,
1602 vs 1585 vs 1360 s, 862 m, 737 s, 591 m, 516, 419, 250 m.
2.3.4. Preparation of [Co(mpo)2(bipy)]ꢀHmpo (4)
A
solution of 2-OH, 5-CH3–acetophenone(Hmpo) (150 mg,
1 mmol) and CH3ONa (54 mg, 1 mmol) in MeOH (25 mL), was
added drop-wise to a solution of [Co(bipy)2Br2] (0.266 g, 0.5 mmol)
in H2O (15 mL) at room temperature, under argon atmosphere. The
solution was stirred for 2 h and then turned darker and an orange-
brownish solid was formed. The solid was filtered, washed with
water and dried under vacuo (0.22 g, 66% yield). The crystalline
compound analyzed as Anal. Calc. for C37H36N2O6Co1 (MW 663):
C, 66.97; H, 5.43; N, 4.22; Co, 8.88. Found: C, 66.87; H, 5.42; N,
9.29%. Magnetic value
(leff = 4.29 lB), conductivity in CH3CN
3.0
l
S/cm. IR spectrum (KBr): selected peaks in cmꢁ1: 1608 s,
1585 vs 1351 s, 843 m, 727 s, 591 m, 513, 421, 275 m.
2.3.9. Preparation of [Co(mpo)2(phen)] (9)
A
solution of 2-OH, 5-CH3–acetophenone(Hmpo) (150 mg,
1 mmol) and CH3ONa (54 mg, 1 mmol) in MeOH (25 mL), was
added drop-wise to solution of [Co(phen)2Br2] (0.290 g,
a
4.20; Co, 8.85%. Magnetic value (
l
eff = 4.20
l
B), conductivity in
0.5 mmol) in H2O (15 mL) at room temperature, under argon atmo-
sphere. The solution was stirred for 2 h and then turned darker and
CH3CN 3.7
l
S/cm. IR spectrum (KBr): selected peaks in cmꢁ1
:

C.D. Papadopoulos et al. / Polyhedron 30 (2011) 486–496
489
an orange-brown solid was formed. The solid was filtered, washed
3.2. Description of the structures
with water and dried under vacuo (0.11 g, 41% yield). The crystal-
line compound analyzed as Anal. Calc. for C30H26N2O4Co1 (MW
537): C, 67.04; H, 4.84; N, 5.21; Co, 10.97. Found: C, 66.97; H,
In the unit cell of [Co(bpo)2(bipy)]ꢀHbpo (3) four independent
mononuclear neutral Co(II) complexes together with four proton-
ated 2-OH-benzophenones (bpo) free ligands can be found. Nhe
unit cell of [Co(bpo)2(phen)] (8) contains just four independent
mononuclear neutral Co(II) complexes. In both cases the com-
plexes are formatted as the metal ion is coordinated to two depro-
tonated 2-OH-benzophenones ligands and one nitrogenous base
molecule. Figs. 1 and 2 present the clinographic projections of
the complexes 3 and 8, while selected distances and bond angles
are given as supplementary material in Tables 1s and 2s,
respectively.
All ligands act as chelates donors. 2-OH-benzophenones are
coordinated through the phenolic deprotonated oxygen atoms, as
well as through the carbonyl oxygen atoms, while the nitrogenous
bases are coordinated through both pyridyl nitrogen atoms. These
six coordinated atoms form a distorted octahedron around the me-
tal ion. Nitrogen atoms from the nitrogenous base coordinated al-
ways have on their diagonal carbonyl oxygen atoms from the 2-
OH-benzophenones ligands while the deprotonated phenolic oxy-
gens lie on the remaining axis of the octahedron.
4.78; N, 5.20; Co, 10.78%. Magnetic value (leff = 4.28 lB), conduc-
tivity in CH3CN 3.6 lS/cm. IR spectrum (KBr): selected peaks in
cmꢁ1: 1603 s, 1595 vs 1365 s, 848 m, 725 s, 570 m, 514, 420,
260 m.
2.3.10. Preparation of [Co(opo)2(phen)] (10)
A solution of 2-OH, 4-OCH3-benzophenone(Hopo) (228 mg,
1 mmol) and CH3ONa (54 mg, 1 mmol) in MeOH (25 mL), was
added drop-wise to
a solution of [Co(phen)2Br2] (0.290 g,
0.5 mmol) in H2O (15 mL) at room temperature, under argon atmo-
sphere. The solution was stirred for 2 h and then turned darker and
an orange-brown solid was formed. The solid was filtered, washed
with water and dried under vacuo (0.18 g, 52% yield). The crystal-
line compound analyzed as Anal. Calc. for C40H30N2O6Co1 (MW
693): C, 69.26; H, 4.33; N, 4.04; Co, 8.50 Found: C, 69.20; H, 4.00;
N, 4.03; Co, 8.40%. Magnetic value (
leff = 4.25 lB), conductivity in
CH3CN 2.0
l
S/cm. IR spectrum (KBr): selected peaks in cmꢁ1
:
1606vs, 1584 vs 1365 s, 847 m, 727 s, 570 m, 514, 417, 260 m.
In both complex structures the most axial vector is the one
passing through one nitrogen and its diagonal carbonyl oxygen
atom but the vector passing through the deprotonated phenolic
oxygen atoms is only about 1° up to 1.5° less axial than the previ-
ous described. We prefer to consider the deprotonated phenolic
oxygens as lying on the axial positions of the coordination octahe-
dron and the nitrogen atoms as well as the carbonyl oxygens on
their diagonals forming the equatorial plane. These atoms forming
the equatorial plane are in both cases placed at considerably longer
distances from the metal ion than those lying on the axial positions
and thus the coordination octahedron can be better described as
tetragonally distorted. In the case of complex 8, the cobalt ion lies
0.146 Å lower the mean equatorial plane passing through N(1),
N(2), O(2) and O(4) directed towards O(1), which is the closest
from the two axially placed oxygen atoms. The mean amine plane
is not coplanar with the mean equatorial plane forming with it an
angle of 8.33°. On the contrary in the case of complex 8, the cobalt
atom lies practically on the equatorial coordination plane formed
from N(1P), N(10P), O(7A) and O(7B) with a deviation smaller than
the error. The equatorial plane forms an angle of 7.22° with the
mean bipy plane.
2.4. X-ray crystallography
All crystals were obtained from the reaction mixture after slow
evaporation. They were air and beam stable during the data collec-
tion. Data for single crystals of both compounds [Co(bpo)2(bi-
py)].Hbpo (3) and [Co(bpo)2(phen)] (8) (Table 1) were collected
with a Bruker SMART APEX CCD system with Mo K
(K = 0.71073 Å) and corrected for absorption by semi-empirical
a radiation
methods (multiscan).
All data for both crystals were collected at ambient tempera-
ture. Both structures were solved using direct methods. Data
refinement of (3) was finalized using SHELXS [27] while for (8) CRYS-
TALS version 12.86 was used [28]. All nonhydrogen atoms were re-
fined anisotropically. Hydrogen atoms were revealed to be at their
expected positions and refined using riding constraints to their
parent atoms. Final unit cells parameters were determined by
least-squares method using all unique reflections. Further details
concerning data collection, crystals analysis and structures refine-
ment are summarized in Table 1.
3.3. Theoretical calculations
3. Results and discussion
The molecular structure of complexes [Co(bpo)2(bipy)] (3) and
[Co(bpo)2(phen)] (8) in their quadruple ground state was opti-
mized under no symmetry constrains at the density functional le-
vel of theory using the B3LYP. Fig. 3 shows the optimized
structures, whereas selected calculated bond lengths and angles
concerning the coordination sphere are given in Table 2. Mean
experimental bond lengths, determined by X-ray structure analy-
sis, are also given for comparison. In both cases the final optimized
structure has essentially C2 symmetry with the two fold rotational
axis passing through the Co atom and bisecting the NꢀꢀꢀN line. An
overall agreement has been found between the calculated and
experimental structure in each case with the largest deviation of
bond distances being about 0.04 Å, while this of bond angles being
about 6°. The two rings of benzophenone deviate from planarity by
40° in both 3 and 8, with the experimental values being 5° and 45°,
respectively. This discrepancy is possibly due to crystal packing
effects.
3.1. Synthesis and characterization
The reaction of the precursor compounds [Co(
a-diimine)2Br2]
(a-diimine = bipy or phen) with the anion of a 2-OH–phenone li-
gand (keto), under proper inert conditions, led to the formation
of ten microcrystalline orange-brown products. They are stable in
air, soluble in almost all the organic solvents, but insoluble in
diethylether and water. Their elemental analyses and the absence
of electrical conductivity in CH3CN solutions indicated neutral
compounds, with the general formulae [CoII(keto)2(bipy)]ꢀHketo
or [CoII(keto)2(phen)], while their magnetic moments at room tem-
perature (mean
l
eff = ꢂ4.2
lB) corroborate with high-spin octahe-
dral coordination of the cobalt(II) ion, in accordance with other
analogous complexes [29,30].
The coordination mode of the ligands in the new cobalt com-
pounds was examined using spectroscopic methods (IR and elec-
tronic excitation spectra). The X-ray diffraction study of two of
them provided evidence regarding the geometry around cobalt(II)
ion and the configuration of the ligands.
The adiabatic interaction energy between molecular fragments
within each complex was also calculated including the BSSE error.
Thus, the interaction energy of the a-diimine chelate ligands bipy

490
C.D. Papadopoulos et al. / Polyhedron 30 (2011) 486–496
Table 1
Crystal data for compounds [Co(bpo)2(bipy)]ꢀHbpo (3) and [Co(bpo)2(phen)] (8).
3
8
Empirical formula
Formula weight
Wavelength (Å)
Crystal system
Space group
Unit cell dimensions
a (Å)
C49H36Co1N2O6
807.73
0.71073
monoclinic
P 21/c
C38H26Co1N2O4
633.57
0.71073
monoclinic
P 21/c
9.5296(15)
22.753(4)
20.084(3)
111.229(4)
4059.3(11)
4
11.6020(10)
17.185(2)
16.951(2)
92.180(10)°
3377.3(6)
4
b (Å)
c (Å)
b (°)
Volume (Å3)
Z
Calculated density
1.322
1.25
(Mg mꢁ3
)
Absorption
0.476
0.549
coefficient
(mmꢁ1
F(0 0 0)
)
1676
1308
Crystal size (mm)
h Range for data
collection (°)
0.64 ꢃ 0.21 ꢃ 0.14
0.21 ꢃ 0.23 ꢃ 0.23
1.41–28.16
1.77–25.27
Limiting indices
ꢁ12 6 h 6 12, ꢁ25 6 k 6 29,
ꢁ22 6 l 6 26
ꢁ13 6 h 6 13, 0 6 k 6 20, 0 6 l 6 20
Reflections
(observed/
24627/9080
14178/6124
unique)
Completeness to h
max (%)
Refinement
method
99.1
99.9
full-matrix least-squares on F2 full-matrix least-squares on F2
Weighting scheme
w = 1/
w = [w]*[1 ꢁ (
DF/6*D
F)2]2
where w* = [P0T00 (x) + P1T01(x) + . . ....Pn–1Tn—1(x)]ꢁ1, and Pi are the
0
[R
2(F2o )+(0.055P)2 + 1.5P]
coefficients of a Chebychev series in ti(x), and x = Fcalc2/Fcalc
2
where P = (F2o + 2Fc2)/3
max
Data/restraints/
parameters
Goodness-of-fit on
F2
9080/1/526
4309/0/406
1.061
1.041
Final R indices
R1 = 0.0632, wR2 = 0.1297
R1 = 0.0549, wR2 = 0.0602
[I > 2r
(I)]
[I > 1r(I)]
Largest diff. peak
0.46 and ꢁ0.26
ꢁ0.35 and ꢁ0.38
and hole (e Åꢁ3
)
Fig. 1. Clinographic projection of [Co(bpo)2(bipy)]ꢀHbpo (3) with 30% present
probability of the ellipsoids. The free protonated ligand (Hbpo) present in the unit
cell and the hydrogen atoms are omitted for clarity.
Fig. 2. Clinographic projection of [Co(bpo)2(phen)] (8) with 30% present probability
of the ellipsoids. Hydrogen atoms are omitted for clarity.

C.D. Papadopoulos et al. / Polyhedron 30 (2011) 486–496
491
for the Co–O bond distances. The BSSE error in all cases is about
2–3%.
In both complexes 3 and 8, as well as in all the closely related
substituted bis salicylaldehydo Co(II) complexes we have recently
studied [13,14], the two salicylaldehydo ligands adopt a mutual
orientation where the two carbonyl oxygen atoms adopt a cis ori-
entation and are coplanar with the two nitrogen atoms of the
a-
diimine chelate ligand, consisting thus the [NNOO] basal plane of
the octahedron, while the two phenolic oxygen atoms occupy the
axial trans positions. To explore any other possible mutual orienta-
tion of the two salicylaldehydo ligands a series of calculations were
carried out on a model representative complex namely [Co(salo)2(-
bipy)], 11 (salo = salicylaldehyde anion). Starting from appropriate
initial structures full optimizations at the same level of theory gave
three isomeric conformations as shown in Fig. 4. All isomers are
minima in the potential energy hyper-surface of the molecule
according to the hessian calculations. The conformation of the first
isomer, 11a, is identical to that found in the experimental com-
plexes with the calculated bond distances and angles being very
close to the experimental ones. In the second, 11b, the [NNOO] ba-
sal plane of the octahedron includes one carbonyl and one phenolic
oxygen atom, while in the third, 11c, the basal plane includes the
two phenolic oxygen atoms and the two carbonyl oxygen atoms
occupy the axial trans positions. The calculated relative total ener-
gies of the isomers are 1.7, 0.0 and 0.8 kcal/mol, whereas those
including the zero point energy are 1.8, 0.0 and 0.9 kcal/mol for
11a, 11b and 11c, respectively. These energy differences are quite
low, but the apparent conclusion is that isomer 11a, although cor-
responds to the experimentally found conformation, has the higher
energy.
Taking into account that the preceding density functional calcu-
lations were done in gas phase, we performed a single point calcu-
lation for the optimized structures 11a, 11b and 11c in the
presence of the methanol solvent, used in the preparation of all
the experimental complexes. Indeed, according to these calcula-
tions the isomer 11a is greatly stabilized in the presence of solvent
and seems to be the more stable structure, as the calculated rela-
tive total energies of the isomers are now 0.0, 0.9 and 1.2 kcal/
mol for 11a, 11b and 11c, respectively.
Fig. 3. Optimized geometries of complexes [Co(bpo)2(bipy)] (3) and [Co(bpo)2
(phen)] (8). Hydrogens not shown for clarity.
3.4. Electronic excitation (UV–Vis) study
Table 2
Selected bond distances (Å) and angles (deg) calculated for complexes [Co(bpo)2(-
The experimental UV–Vis spectra of the title compounds in ace-
tonitrile solutions presented five dominant bands in the region
250–1100 nm, a representative one given for compound 8 in Fig. 5.
The assignment of the bands observed in the experimental UV–
Vis spectra of the studied compounds and the evaluation of the
properties of their excited states were done by means of TD-DFT
calculations on the optimized structures of complexes 3 and 8.
The calculated excitation energies are shown in Fig. 6, where rep-
resentative density diagrams of the MOs participating in each elec-
tron transition with the higher CI coefficient are also depicted, in
order to intuitively understand the absorption process. The com-
puted electronic transitions are in good agreement with the exper-
imental ones. The three calculated low energy excitations at 980–
995 nm, 650–670 nm and 500–515 nm are of d–d character. The
first two bands are clearly located in the experimental spectra of
bipy)] (3) and [Co(bpo)2(phen)] (8)a.
3
8
Co–N
Co–O(1)
Co–O(2)
O(1)–Co–O(1)’
O(2)–Co–O(2)’
O(1)–Co–O(2)
N–Co–N’
2.129 (2.112)b
2.031 (2.025)
2.108 (2.100)
174.4 (173.4)
92.0 (85.9)
2.149 (2.143)
2.027 (2.058)
2.106 (2.071)
175.3 (171.9)
91.9 (86.8)
92.6 (84.7)
77.0 (77.1)
93.2 (84.6)
78.0 (79.7)
N–Co–O(1)
N–Co–O(2)
96.0 (93.2)
168.9 (173.6)
94.8 (94.1)
169.6 (171.3)
a
Numbering scheme as in Fig. 3.
Mean experimental values in parentheses.
b
and phen with the metal fragment [Co(bpo)2] is equal to 52.2 kcal/
mol and 49.7 kcal/mol, respectively. These values are in accordance
with the shorter calculated and experimental Co-N bond distances
found in complex 3 than in 8. Moreover, the almost equal interac-
tion energy of the metal fragments [Co(bipy)]2+ and [Co(phen)]2+
with the two 2-hydroxy-benzophenone, [(bpo)2]2ꢁ, calculated
equal to 494.1 kcal/mol and 491.7 kcal/mol, respectively, account
well for the almost identical calculated and experimental values
the complexes [3: 1010 (
e = 20), 640 ( e = 80); 8: 1020 (e = 25),
660 ( = 100)], while the third one is not shown, possibly masked
e
due to the neighbouring position and the higher
gand bands.
The two calculated excitations at 410–440 nm are of MLCT
character as they arise from electronic transitions between low en-
ergy MOs, located at the d-orbitals of the metal and the highly
e of the intra-li-
delocalized unoccupied
p-MOs of the bipy or phen ligand. These

492
C.D. Papadopoulos et al. / Polyhedron 30 (2011) 486–496
Fig. 5. Electronic excitation (UV–Vis) spectrum of the complex [Co(bpo)2(phen)] (8)
in 10ꢁ4 M CH3CN.
Finally, the calculated excitations at 310–320 nm and 280–
290 nm arise from intra-ligand
and bipy or phen ligands, respectively and are clearly seen in the
spectra of the complexes [3: 283 ( = 13000), 317 ( = 11000); 8:
284 ( = 13000), 318 ( = 10500)].
p–p transitions within the bpo
e
e
e
e
3.5. Infrared spectra (IR)
In the spectra of the free 2-hydroxy-phenone ligands the in-
tense bands stemming from the stretching and bending vibra-
tional modes of the phenolic OH around 3200 cmꢁ1 and
1410 cmꢁ1, respectively, disappear from the spectra of all com-
plexes indicating the ligand deprotonation [31]. Also, the bands
originating from the C–O stretching vibrations at 1245–
1285 cmꢁ1 in the complexes exhibit positive shifts at 1342–
1385 cmꢁ1 while their intensity is enhanced appreciably denoting
coordination through the carbonyl oxygen of the phenone ligand.
The band at ꢂ1660 cmꢁ1 attributable to the carbonyl bond
v
(C@O) of the free ligand, upon coordination, in the complexes
is shifted to lower frequencies at ꢂ1605 cmꢁ1 thus denoting the
bidentate mono- anionic character of the studied hydroxyl–phe-
none ligands (Table 3). In the case of the studied cobalt com-
pounds with bipy, however, the presence of an extra intense
band at ꢂ1660 cmꢁ1 suggests the existence of a neutral non-coor-
dinated ketone ligand.
The intense bands at 1596 cmꢁ1, attributable to the stretching
vibration of C@N (aromatic bond) are present in all complexes.
The band at 750 20 cmꢁ1, ascribed to the rocking vibrations of
the pyridyl C–H bonds and the band at 870 15 cmꢁ1, attributable
to the deformation vibrations of the pyridyl C–H bonds, disclosed
the occurrence of the nitrogenous bases in the studied compounds.
The medium to low intensity bands at about 590 and 512, 421,
270 cmꢁ1 are attributed to the coordination bonds (Co–O and
Co–N, respectively) according to the literature [32].
For better certainty the assignment of the Co–N and Co–O
stretching frequencies was done with the aid of frequencies calcu-
lation on the optimized structures of complexes 3 and 8, which
gave the frequencies of the fundamental vibrations of the com-
plexes. The calculated frequencies for the Co–N (281 cmꢁ1 for
comp.3; 290 cmꢁ1 for comp.8), and Co–O (579,603,
aver.591.0 cmꢁ1, for comp.3; 579,604, aver.591.5 cmꢁ1 for comp.8)
stretching vibrations, as well as the corresponding normal modes
for both complexes are those shown in Fig. 7. Thus the medium
to low intensity experimental bands located at ꢂ260 cmꢁ1 and
ꢂ590 cmꢁ1 for all complexes should be assigned to these Co–N
and Co–O vibrations, respectively.
Fig. 4. Optimized geometries of the three isomers, 11a, 11b and 11c, of the complex
[Co(salo)2(bipy)]. Hydrogens not shown for clarity.
bands are seen in the experimental spectra as a shoulder at about
420 nm.

C.D. Papadopoulos et al. / Polyhedron 30 (2011) 486–496
493
Fig. 6. Excitation energies, oscillator strengths and single-electron transition with the higher CI coefficient in the TD-DFT calculations for the MLCT band of [Co(bpo)2(bipy)]
(3) and [Co(bpo)2(phen)] (8) complexes.

494
C.D. Papadopoulos et al. / Polyhedron 30 (2011) 486–496
Table 3
Characteristic frequencies in the IR spectra of the cobalt compounds [Co(keto)2(bipy)]ꢀHketo and [Co(keto)2(phen)].
a
/
a
Complex
m(C@O)
m(C@N)
m
(C-J)
m
(@C–Y) (py)
m(Co–J)
m(Co–N)
1
2
3
4
5
6
7
8
9
[Co(apo)2(bipy)]ꢀHapo
[Co(ppo)2(bipy)]ꢀHppo
[Co(bpo)2(bipy)]ꢀHbpo
[Co(mpo)2(bipy)]ꢀHmpo
[Co(opo)2(bipy)]ꢀHopo
[Co(apo)2(phen)]
[Co(ppo)2(phen)]
[Co(bpo)2(phen)]
[Co(mpo)2(phen)]
[Co(opo)2(phen)]
1666s,1604vs
1662s,1603vs
1662s,1602vs
1665s,1618vs
1665s,1605vs
1601vs
1608vs
1608vs
1603vs
1606vs
1574vs
1584vs
1585vs
1580vs
1574vs
1588vs
1590s
1585vs
1595vs
1584vs
1360s
1363s
1360s
1369s
1381s
1362s
1372s
1351s
1365s
1365s
828m,729s
855m,728s
862m,737s
856m,729s
832s,733s
848s,725s
852s,729s
843s,727s
848s,725s
847s,727s
585m
562m
591m
570m
572m
575m
567m
591m
570m
570m
514,420m,260
512,418m,248
516m,419m,250
514,437m,249
514,413m,249
515,430m,250
512,420m,248
513,421m, 275
514,420m,260
514,417m,260
10
vs = Very strong, s = strong, m = medium, br = broad.
Fig. 7. Characteristic normal modes and calculated IR frequencies (cmꢁ1) of the Co–N and Co–O stretching vibrations for [Co(bpo)2(bipy)] (3) and [Co(bpo)2(phen)] (8)
complexes (experimental frequencies in italics).
3.6. Cyclic voltametry (CV)
All the studied compounds exhibit similar behavior during the
cyclic voltammetry experiments. The typical CV diagrams of com-
pounds 3 and 8 are representatively depicted in Figs. 8 and 9, while
the experimental data for the studied compounds are presented in
Table 4. The CVs in the region ꢁ1950 mV to 2100 mV revealed five
or six waves depending on the crystal ingredients of the studied
compounds. The well separated reversible waves of the couples
Co(I)–Co(II) around ꢁ830 mV (Wave I) and Co(II)–Co(III) around
550 mV (Wave II) were the first assigned. Both waves represent a
one electron redox transformation as figured out by comparison
Fig. 9. Cyclic voltammetry diagram of [CoII(2-hydroxy-benzophenone)2(phen)] in
CH3CN (0.1 M TEAP, C = 10ꢁ3 V, scan rate 100 mV/s).
with the wave observed from an equimolar amount of ferrocene
under the same experimental conditions. These values were situ-
ated very close to them found from the CVs of similar compounds
[[13,14] and references therein].
The wave in the anodic region around 1510 mV (Wave III) and
the cathodic wave around ꢁ1820 mV (Wave IV) are due to the oxi-
dation and the reduction, respectively of the phenolic oxygen of
the ligand in the addition compounds. Both are two electron waves
and this suggests that the ligands in the complex are equivalent as
expected. These values are lower compared with the redox values
of the same group in the free ligand. This fact could be expected
upon coordination of the studied groups.
The peaks in the anodic region at around 1860 mV and at higher
voltage values (Wave V) can be attributed to the oxidation of the
nitrogen atoms of the nitrogenous base. The oxidation of the nitro-
gen atoms belonging to the bipyridine ligand seems to occur at
higher voltage values compared with them of the phenanthroline
ligand and appears around 1940 mV.
One more wave around 1730 mV (wave VI), present in the vol-
tammograms of compounds (1) until (4), can be assigned to the
oxidation of the phenolic oxygen of the free ligand, present in
the unit cell of these compounds. It represents one electron oxida-
tion, as expected and is found in the same region compared with
the voltage values of the waves present in the cyclic voltamograms
of the free ligands, when scanned alone under the same experi-
mental conditions.
Fig. 8. Cyclic voltammetry diagram of [CoII(2-hydroxy-benzophenone)2(bipy)]
10ꢁ3 V in CH3CN (0.1 M TEAP, C = 10ꢁ3 M, scan rate 100 mV/s).

C.D. Papadopoulos et al. / Polyhedron 30 (2011) 486–496
495
Table 4
Redox waves of the studied compounds in CH3CN. (0.1 M TEAP, C = 10ꢁ3 V, scan speed 100 mV/s).
Compounds
Wave I
Wave II
Wave III
Wave IV
Wave V
Wave VI
Epa
Epc
E1/2
Epa
Epc
E1/2
Epa
Epc
Epa
Epa
1
2
3
4
5
6
7
8
ꢁ0.86
ꢁ0.85
ꢁ0.87
ꢁ0.85
ꢁ0.86
ꢁ0.86
ꢁ0.85
ꢁ0.86
ꢁ0.84
ꢁ0.83
ꢁ0.85
ꢁ0.83
ꢁ0.84
ꢁ0.85
ꢁ0.83
ꢁ0.84
ꢁ0.83
ꢁ0.81
ꢁ0.83
ꢁ0.81
ꢁ0.82
ꢁ0.84
ꢁ0.82
ꢁ0.82
0.57
0.56
0.55
0.56
0.56
0.58
0.57
0.55
0.55
0.54
0.53
0.55
0.54
0.56
0.56
0.53
0.53
0.52
0.51
0.54
0.52
0.54
0.54
0.52
1.52
1.54
1.50
1.51
1.52
1.50
1.52
1.53
ꢁ1.84
ꢁ1.83
ꢁ1.80
ꢁ1.82
ꢁ1.83
ꢁ1.81
ꢁ1.82
ꢁ1.83
1.93
1.94
1.95
1.94
1.86
1.87
1.86
1.85
1.74
1.72
1.74
1.73
3.7. Thermal studies
The thermal decomposition of the second group is even more
complicated. For the compounds 8, 9 and 10 (Fig. 2s for compound
10) the TG and DTG plots until 430 °C represent two multi-step
decomposition stages with mass loss corresponding to the mass
loss of one ketone ligand. This means that the cleavage of the coor-
dination bonds Co–O happens together with the rupture of the
bonds inside the ketone ligand. (mass loss for comp.8: 30.5% f.
and 31.1% c.; for comp. 9: 27% f. and 27.7% c.; for comp. 10:
32.0% f. and 32.7% c.).
Taking into account the amount of the residue, as it was calcu-
lated by TG measurements, we can conclude that the decomposi-
tion was not completed until the temperature 980 °C leading to a
solid mixture of CoO, Co and a large amount of carbon (ꢂ30%).
The thermal behavior for five of the title compounds (1, 3, 8, 9
and 10) was studied in nitrogen atmosphere, over the temperature
range ambient to 980 °C by using the simultaneous TG/DTG-DTA
technique. The studied compounds can be separated in two groups,
according to their thermal behavior. In the first group belong the
compounds 1 [Co(apo)2(bipy)]ꢀHapo and 3 [Co(bpo)2(bipy)]ꢀHbpo
and in the second one the compounds 8 [Co(bpo)2(phen)], 9 [Co(m-
po)2(phen)], and 10 [Co(opo)2(phen)]. The thermoanalytical curves
(mass loss-TG, derivative mass loss-DTG, and heat flow-DTA) are
given as supplementary material in Figs. 1s and 2s for the com-
pounds 1 and 10 (one from each group), respectively. The studied
compounds are unstable upon heating, decomposing in many suc-
cessive endothermic stages. The decomposition for all the com-
pounds is very complicated. It presents at least three different
areas of mass loss and each area starts before the ending of the pre-
vious one. For this reason it is very difficult to correspond to differ-
ent areas of mass loss in as specific way of decomposition of the
compounds.
For both groups the main residue at 980 °C is metallic cobalt,
proved by powder XRD measurements. In the first group the exper-
imental mass loss at 980 °C is about 85–90%, while for the second
one is only 60–63%. This means that the bulkier base phenanthro-
line, which is the component of the second group of the studied
compounds, can not be pyrolized completely leaving an amount
of un-combusted carbon in the solid residue, in comparison with
the base bipyridine, which is the component of the first group of
the studied compounds and is completely decomposed.
Using mass loss and derivative mass loss plots (TG/DTG) we can
conclude that the first mass loss of the first group (Fig. 1s for com-
pound 1) coincides with the mass loss of a phenol molecule (PhOH)
derived from a ketone ligand (comp.1: DTG peak is ending at
200 °C, experimental mass loss 14.5% f. and theoretical 14.9% c.;
comp.3: DTG peak is ending at 160 °C, experimental mass loss
11.0% f. and theoretical 11.5% c.). The second and sudden mass loss
until 310 °C for compound 1 coincides with the mass loss of one
acetaldehyde molecule (CH3CHO) plus two moieties (L–O), where
L = the coordinated acetophenone ligand, apo (45% f. and 45.3%
c.). For compound 3, the second mass loss at 310 °C coincides with
the mass loss of a benzaldehyde molecule (PhCHO) plus one moi-
ety (L–O), where L = the coordinated benzophenone ligand, bpo
(35.0% f. and 35.5% c.).
4. Conclusions
Ten novel octahedral compounds [Co(ketone)2Y] where ketone
is the anion of 2-hydroxy-phenones and Y = the neutral
(bipy or phen), were synthesized and characterized.
a-diimines
The theoretical DFT investigation with GAUSSIAN-03 for the pre-
diction of the electronic and vibrational spectra, gave good correla-
tion with the experimental values.
X-ray study of the compounds 3 and 8 verified the existence of
mononuclear octahedral Co(II) compounds with similar geometries
around the metal ion. The cyclic voltammetry study in CH3CN gave
all the expected waves for the redox processes of the metal Co(II)
and the studied ligands.
The compounds are stable at ambient temperature, but unsta-
ble upon heating decomposing in several stages, giving at 980 °C
in nitrogen atmosphere a solid product consisting of carbonaceous
metallic cobalt.
Appendix A. Supplementary material
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.poly.2010.11.010.
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