Synthesis and structural characterization of a novel seven-coordinate cobalt(II) complex: 2,9-Bis(ethanolamine)-1,10-phenanthrolinechlorocobalt(II) chloride

Article abstract of DOI:10.1016/j.ica.2011.03.050

Condensation reaction of 2,9-dicarboxaldehyde-1,10-phenanthroline with 2-aminoethanol followed by NaBH₄ reduction yielded the polydentate Schiff base ligand 2,9-bis(ethanolamine)-1,10-phenanthroline in its reduced form. This ligand was characterized by elemental analysis, LC-MS, IR, UV-Vis and NMR spectroscopy. Reaction of the reduced Schiff base ligand with aqueous solution of cobalt(II) chloride affords 2,9-bis(ethanolamine)-1,10- phenanthrolinechlorocobalt(II) chloride in high yield. Single crystals of the cobalt(II) complex were obtained from the crystallization in ethanol and its structure was elucidated by X-ray structural analysis. The cobalt(II) complex ion was found to be seven-coordinated in a pentagonal bipyramidal geometry, whereby cobalt(II) ion is surrounded by the six donor atoms in the ligand molecule and a chloride ion.

Full text of DOI:10.1016/j.ica.2011.03.050

Inorganica Chimica Acta 371 (2011) 107–110
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Note
Synthesis and structural characterization of a novel seven-coordinate
cobalt(II) complex: 2,9-Bis(ethanolamine)-1,10-phenanthrolinechlorocobalt(II)
chloride
Akın Baysal a, , Murat Aydemir a, Feyyaz Durap a, Saim Özkar b, Leyla Tatar Yildirim c
⇑
a Dicle University, Department of Chemistry, 21280 Diyarbakır, Turkey
b Middle East Technical University, Department of Chemistry, 06531 Ankara, Turkey
c Hacettepe University, Department of Engineering Physics, Beytepe, 06800 Ankara, Turkey
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 3 August 2010
Received in revised form 3 February 2011
Accepted 16 March 2011
Available online 24 March 2011
Condensation reaction of 2,9-dicarboxaldehyde-1,10-phenanthroline with 2-aminoethanol followed by
NaBH4 reduction yielded the polydentate Schiff base ligand 2,9-bis(ethanolamine)-1,10-phenanthroline
in its reduced form. This ligand was characterized by elemental analysis, LC–MS, IR, UV–Vis and NMR
spectroscopy. Reaction of the reduced Schiff base ligand with aqueous solution of cobalt(II) chloride
affords 2,9-bis(ethanolamine)-1,10-phenanthrolinechlorocobalt(II) chloride in high yield. Single crystals
of the cobalt(II) complex were obtained from the crystallization in ethanol and its structure was eluci-
dated by X-ray structural analysis. The cobalt(II) complex ion was found to be seven-coordinated in a
pentagonal bipyramidal geometry, whereby cobalt(II) ion is surrounded by the six donor atoms in the
ligand molecule and a chloride ion.
Keywords:
1,10-Phenanthroline
Schiff base
Cobalt
Seven-coordinate
X-ray
Ó 2011 Elsevier B.V. All rights reserved.
1. Introduction
for the metal ions. For these reasons, several structural studies
have been carried out on the transition metal complexes of re-
1,10-Phenanthroline and its derivatives are of great interest
since they exhibit interesting catalytic, redox and photoredox
properties and complexation activity [1–3]. Schiff base of aromatic
aldehydes having an effective conjugation system are more stable
than those of aliphatic aldehydes due to their easy polymerization
[4]. Transition metal complexes with Schiff bases containing nitro-
gen and oxygen donor atoms play an important role in biological
systems [5,6]. Some metal complexes incorporating 1,10-phenan-
throline have also been studied for decades as DNA intercalators,
building blocks for multicomponent architectures and molecular
machines [7–11]. Certain metal complexes with phenanthroline
and natural products containing this heterocyclic nucleus possess
interesting anticancer properties [12]. Much effort has been de-
voted on phenanthroline derivatives with amine groups as poten-
tial ligands possessing soft and hard coordination-sites [13,14].
Several multidentate Schiff base ligands in reduced forms are ob-
tained by reducing the azomethine (–CH@N–) moiety of the Schiff
base formed by the condensation of aldehyde and various amines
or natural/synthetic aminoacids. The reduced Schiff base ligands
provide suitable conformational and coordination environments
duced Schiff base derived from 1,10-phenanthroline [15].
Herein, we report the syntheses of a 1,10-phenanthroline
derivative polydentate Schiff base ligand 2,9-bis(ethanolamine)-
1,10-phenanthroline in its reduced form, 3 and its pentagonal
bipyramidal cobalt(II) complex, 4. Structure of cobalt(II) complex
was resolved by single-crystal X-ray diffraction analysis.
2. Experimental
2.1. Materials and methods
2,9-Dimethyl-1,10-phenanthroline (neocuproine) was pur-
chased from (Fluka, Switzerland) and was used as received. 2,9-
Dicarboxaldehyde-1,10-phenanthroline was prepared according
to the literature method [16]. Other reagents and solvents were
of analytical grade and were purchased commercially. Solvent
was purified by standard techniques and were freshly distilled
prior to use. Elemental analyses were performed on a Fisons EA
1108 CHNS-O instrument. Infrared spectra were recorded from
the KBr pellet in the range 4000–400 cmÀ1 on a Mattson 1000
ATI UNICAM FT-IR spectrometer. The NMR spectra were recorded
on Bruker AC 400 spectrometer (400.1 MHz for 1H, 100.6 MHz for
13C) and the UV–Vis spectra were performed on a Shimadzu UV
⇑
Corresponding author.
E-mail address: akinb@dicle.edu.tr (A. Baysal).
0020-1693/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2011.03.050

108
A. Baysal et al. / Inorganica Chimica Acta 371 (2011) 107–110
60 spectrometer. LC–MS spectra were obtained with an Agilent
1100 MSD spectrometer.
matrix least-squares method on F2 assuming anisotropic thermal
parameters for non-hydrogen atoms using SHELXL97 [18]. An empir-
ical absorption correction based on psi-scan data was performed.
All other non-hydrogen atoms were located from a difference-
Fourier synthesis and refined with anisotropic thermal parameters.
Hydrogen atoms on N and O atoms were located from difference
map. All other hydrogen atoms were placed at calculated positions
and riding on their relative atoms and refined isotropically. Atomic
scattering factors were taken from the International Tables for
X-ray Crystallography.
2.2. Synthesis of ligand and its complex
2.2.1. Synthesis of 2,9-bis(ethanolamine)-1,10-phenanthroline, 3
2,9-Dicarboxaldehyde-1,10-phenanthroline, 2 (0.47 g, 2 mmol,
217 g/mol) was suspended in dry MeOH (50 mL) and 2-aminoeth-
anol (0.25 g, d = 1.05 g/mol, 61 g/mol) was added to the solution
which was then stirred for 24 h at room temperature. NaBH4
(1 g, 5 equiv., 38 g/mol) was added in small portions during 1 h.
After 24 h stirring, the result mixture was concentrated to give a
dirty solid, which was dissolved in H2O (50 mL), and extracted
thrice with CHCl3 (50 mL). The organic extract was dried with
anhydrous Na2SO4 and concentrated under reduced pressure to
yield a white solid. Yield (52%); 1H NMR (400.1 MHz, CDCl3)
d = 7.95 (d, 2H, 3J = 8.40 Hz, H-4 and H-7), 7.51 (s, 2H, H-5 and H-
6), 7.35 (d, 2H, 3J = 8.00 Hz, H-3 and H-8), 4.11 (s, 4H, PhenCH2–),
3.60 (t, 4H, 3J = 4.60 Hz, –CH2OH), 4.50 (br, 2H, NH; 2H, OH), 2.83
(t, 4H, 3J = 4.60 Hz, –CH2NH); 13C NMR (100.6 MHz, CDCl3):
d = 52.05 (OCH2–), 60.50 (NCH2–), 54.40 (PhenCH2–), 122.06,
125.68, 136.53 (CH– of Phen.), 127.50, 144.61, 160.38 (quarternary
carbons of Phen.); LC–MS: m/z (%) 327(100) [M+H]+; IR, (KBr):
3. Results and discussion
The reaction between 1,10-phenanthroline-2,9-dicarboxalde-
hyde, copper(I) ion, and certain primary amines was found to give
quantitatively a dicopper double-helicate product by imine self-
assembly around Cu(I) templates by Nitschke and co-workers
[14]. This led us to develop the chemistry of ligand based on
1,10-phenanthroline by reduction to isolate ligand 3 and then its
corresponding seven-coordinated cobalt(II) complex was synthe-
sized. In a preliminary study, SeO2 oxidation of neocuproine 1
afforded dicarboxaldehyde 2 and then treatment of 2 with 2-ami-
noethanol in dry methanol followed by NaBH4 reduction yielded
the corresponding Schiff base derivative bis-aminoalcohol ligand
in its reduced form, 3 (Scheme 1). The 1H NMR spectrum of 3
shows a D2O exchangeable resonance at 4.50 ppm attributed to
OH and NH protons in the molecule. The signals in the range
7.34–7.95 ppm are assigned to 1,10-phenanthroline hydrogens.
The resonances observed at 4.11, 3.60 and 2.83 ppm are attributed
to the –CH2 protons. The 13C NMR spectrum of 3 exhibits reso-
nances in the range 122.06–160.38 ppm for the carbons of the
1,10-phenanthroline ring in the molecule. The three resonances
observed in the range 52.05–60.50 ppm are attributed to methy-
lene carbons in the molecule. The ligand shows two strong absorp-
tion bands in the 220–280 nm region which can be attributed to
m
= 3426, 3314, 2993, 2928, 2798, 2710, 2293, 1606, 1535, 1150,
1085 cmÀ1; UV: kmax ), nm (l molÀ1 cmÀ1) in H2O; 230(52 300),
(e
277(5200); Anal. Calc. C18H22N4O2 (326.40 g/mol): C, 66.23; H,
6.79; N, 17.17. Found: C, 66.18; H, 6.73; N, 17.13%.
2.2.2. [Co(2,9-bis(ethanolamine)-1,10-phenanthroline)Cl]Cl, 4
Preparation of 4: To a sample of, 3 (0.23 mmol, 0.075 g,
326.3974 g/mol) in 10 mL H2O, was added CoCl2Á6H2O (0.21 mmol,
0.05 g, 238 g/mol) and stirred rapidly for 1 h. Yield (84%); 1H NMR
(400.1 MHz, D2O) d = 8.08 (d, 2H, 3J = 7.32 Hz, H-4 and H-7), 7.63
(d, 2H, 3J = 7.32 Hz, H-3 and H-8), 7.26 (s, 2H, H-5 and H-6), 4.69
(4H, PhenCH2), 3.79 (br, 4H, ÀCH2OH–), 3.25 (br, 4H, –CH2NH–);
13C NMR (100.6 MHz, CDCl3): d = 56.61 (OCH2–), 49.27 (NCH2–),
51.38 (PhenCH2–), 123.19, 126.85, 138.83 (CH– of Phen.), 128.94,
144.07, 151.23 (quarternary carbons of Phen.); LC–MS: m/z (%)
p–
p⁄ transitions. The LC–MS spectrum provides strong evidence
for the formation of ligand 3. The main peak in the spectrum
observed at m/z 327.1 (1 0 0) corresponds to [M+H]+.
421(20) [MÀCl]+; IR, (KBr):
m
= 3520, 3198, 3087, 2973, 2916,
), nm
The reduced Schiff base ligand contains both relatively ‘soft’
(two nitrogens of a 1,10-phenanthroline moiety) and ‘hard’ (two
nitrogens and two oxygens of aminoalcohol moieties) donor
atoms; Thus, it is potentially a hexadentate ligand.
2845, 1503, 1440, 1119, 990, 900, 880 cmÀ1; UV: kmax
(e
(l molÀ1 cmÀ1
) in H2O; 230(13 800), 275(8800), 354(488)sh,
522(21), 637(14); Anal. Calc. C18H22N4O2CoCl2 (456.24 g/mol): C,
47.38; H, 4.86; N, 12.28. Found: C, 47.32; H, 4.81; N, 12.24%.
The light brown complex 4 was prepared in high yield from the
reaction of aqueous solution of cobalt(II) chloride with 3. Single
crystals suitable for X-ray analysis were obtained from recrystaliza-
tion of 4 in ethanol solution. The summary of crystal parameters
and refinement results of cobalt(II) complex 4 are given in Table 1.
The complex 4 has an infinite one-dimensional chain structure con-
taining seven-coordinated cobalt(II) ion. The coordination environ-
ment of cobalt(II) ion in complex 4 is shown in Fig. 1a with the atom
numbering scheme. The polymeric cobalt(II) cation has a pentago-
nal-bipyramidal coordination, in which the pentagonal basal plane
is constituted by the system ON4 donor set of the ligand 3. The Co–N
bond lengths are in the range 2.189(3)–2.281(3) Å. The Co–O1 bond
2.3. X-ray crystallography
Single-crystal data collections for 4 were obtained on an Enraf–
Nonius CAD-4 diffractometer. The diffractometer was equipped
with a graphite crystal monochromator. The determination of unit
cell and the data collections were performed with Mo Ka radiation
(k = 0.71073 Å). Three standard reflections were measured every
100 reflections and their intensities showed a good stability. Data
reduction was carried out using XCAD4 [17]. The structure was
solved by direct methods using SHELX97 and refined by the full-
Scheme 1. Synthesis of 2,9-bis(ethanolamine)-1,10-phenanthroline, 3 and [Co(2,9-bis(ethanolamine)-1,10-phenanthroline)Cl]Cl, 4.

A. Baysal et al. / Inorganica Chimica Acta 371 (2011) 107–110
109
Table 1
Crystal data and experimental details of the title compound.
Table 2
Coordination geometry around the Co atom (Å, °).
Compound
[CoCl N4O2C18H22]ÁCl
Co–N1
Co–N2
Co–N3
Co–N4
Co–O1
Co–Cl1
Co–O2
CoÁÁÁCl2
2.273(3)
2.213(3)
2.189(3)
2.281(3)
2.219(3)
2.5070(15)
2.132(3)
4.550(2)
O1–Co–N1
O1–Co–N4
O2–Co–Cl1
N1–Co–N2
N2–Co–N3
N3–Co–N4
O1–Co–Cl1
O1–Co–O2
72.43(12)
78.40(12)
Formula
[CoC18H22N4O2Cl]ÁCl
171.02(10)
69.68(11)
72.07(11)
70.52(12)
88.75(10)
82.87(13)
Formula weight
Crystal shape/color
Crystal size (mm3)
T (K)
Space group
a (Å)
456.23
Prism/colorless
0.3 Â 0.2 Â 0.2
295(2)
ꢀ
P1
6.959(3)
b (Å)
c (Å)
11.339(2)
12.547(2)
91.220(11)
101.614(10)
101.701(10)
947.6(5)
a
(°)
Table 3
b (°)
Structural parameters of hydrogen bonds between donor (D), acceptor (A) and
hydrogen (H).
c
(°)
V (Å3)
D–HÁÁÁA
D–H (Å)
AÁÁÁH (Å)
2.23(5)
2.78
2.13(5)
2.57(5)
DÁÁÁA (Å)
D–HÁÁÁA (°)
158(5)
150
176(5)
159(5)
Z
2
Density (calculated) (Mg m3)
1.599
1.209
470
8.92–18.17
2.4–26.29
4039
O2–H2OÁÁÁCl1i
C13–H13ÁÁÁCl1ii
O1–H1OÁÁÁCl2
N4–H2ÁÁÁCl2
0.85(5)
0.93
0.88(5)
0.86(4)
3.034(4)
3.617(4)
3.009(4)
3.391(4)
l
(mmÀ1
)
F(0 0 0)
h Range for unit cell determination (°)
h Range for data collection (°)
Reflections measured collected
Symmetry codes: [i: À1 + x, y, z; ii: 1 À x, Ày, Àz].
Independent observed reflections
3829
Independent reflections [I > 2
Data/restraints/parameters
Rint
r
]
2768
3829/3/260
0.0666
R1 = 0.0822, wR2 = 0.1358
R1 = 0.0419, wR2 = 0.1150
1.083
À0.449, 0.502
hydrogen bonds. Details of the hydrogen bonding geometry are gi-
ven in Table 3.
R indices (all data)
Although the cobalt(II) complex is paramagnetic, the 13C NMR
Spectrum shows still sharp signals for the organic ligands as the
carbon atoms are not directly bonded to the metal. Comparison
of the 1H NMR chemical shifts of the free ligand and cobalt(II) com-
plex reveals that the signals of the ligand shift to the lower mag-
netic field upon coordination. This coordination shift is in line
R indices [I > 2
Goodness of fit on F2
qmin (e ÅÀ3
r(I)]
D
qmin
,
D
)
length of 2.219(3) Å. The axial positions are occupied by one O
atom of the organic ligand and one chloro ligand. As listed in
Table 2, the Co–Cl1 and Co–O2 bond lengths are 2.5070(15) and
2.132(3) Å, respectively. Selected bond lengths and angles are given
in Table 2.
The large moiety of the molecule which contains phenyl rings
and Co, O1, N2, N3 and Cl2 atoms are nearly planar. In the basal
plane, the N1 and N4 atoms have maximum deviations [N1:
À0.456(4) and N2: 0.779(4) Å] from least square plane defined
by the Co/O1/N2/N3/Cl2 atoms.
Hydrogen bond and molecular packing geometry of the title
molecule was calculated with PLATON [19] and the molecular pack-
ing geometry is shown in Fig. 1b. In the crystal structure, intermo-
lecular OÁÁÁCl contact link the molecules into chains along a axis.
The structure has also two intermolecular and two intramolecular
with notion that metal–ligand bonding is mainly of
r-interaction.
The UV–Vis electronic absorption spectrum of the complex exhib-
its two strong bands at 230 and 275 nm, assigned to the charge
transfer transitions. The shoulder at 354 nm can be attributed to
n–p⁄ transitions. The weak absorption bands at 522 and 637 nm
are attributable to the d–d transitions. The IR spectrum of 4 shows
two strong bands at 1521 and 1593 cmÀ1 for the 1,10-phenanthro-
line ring vibrations of the ligand. The shift by 13 and 14 cmÀ1 to
lower frequencies relative to those of the free ligand upon coordi-
nation indicates the coordination of 1,10-phenanthroline through
its nitrogen atoms. The rigid structure of 1,10-phenanthroline im-
posed by the central ring means that two nitrogen atoms are al-
ways held in juxtaposition. The strong broad band observed at
3520 cmÀ1 is due to
m(N–H) and m(O–H). The large coordination
Fig. 1. (a) Coordination environment around the cobalt(II) atom in 4 with atom numbering scheme. (b) Infinite 1D chain structure of 4 (base vector [1 0 0]). The thermal
ellipsoids are drawn at 40% probability and hydrogen atoms were omitted for clarity [20].

110
A. Baysal et al. / Inorganica Chimica Acta 371 (2011) 107–110
shift in O–H and N–H stretching modes to higher frequencies indi-
cates that the coordination of the ligand to the metal through N
and O atoms is essentially of sigma type. The complex was also
studied by LC–MS, which shows a peak at m/z 421(20) correspond-
ing to the [MÀCl]+ fragment.
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In summary, we have successfully synthesized and structurally
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Acknowledgments
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Appendix A. Supplementary material
CCDC 768856 contains the supplementary crystallographic data
for this paper. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif. Supplementary data associated with this article
can be found, in the online version, at doi:10.1016/j.ica.2011.
03.050.