Cobalt(II) complex with new terpyridine ligand: An ab initio geometry optimization investigation

Article abstract of DOI:10.1016/j.molstruc.2010.03.057

Structural parameters of a complex formed between Co(II), and a terpyridine ligand were investigated using the unrestricted Becke three-parameter hybrid exchange functional combined with the Lee-Yang-Parr correlation functional (B3LYP) with the LANL2DZ, 6-31G(d,p), and 6-31G++(d,p) basis sets applied for geometry optimizations. The computations reveal that frequently used methods, which take into consideration primary and secondary interactions, can often be efficient in optimizing structural geometries of systems based on organic molecules and transition-metal ions.

Full text of DOI:10.1016/j.molstruc.2010.03.057

Journal of Molecular Structure 973 (2010) 130–135
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Cobalt(II) complex with new terpyridine ligand: An ab initio geometry
optimization investigation
*
´
Artur Ciesielski , Adam Gorczynski, Piotr Jankowski, Maciej Kubicki, Violetta Patroniak
Faculty of Chemistry, Adam Mickiewicz University, Grunwaldzka 6, 60780 Poznan´, Poland
a r t i c l e i n f o
a b s t r a c t
Article history:
Structural parameters of a complex formed between Co(II), and a terpyridine ligand were investigated
using the unrestricted Becke three-parameter hybrid exchange functional combined with the Lee–
Yang–Parr correlation functional (B3LYP) with the LANL2DZ, 6-31G(d,p), and 6-31G++(d,p) basis sets
applied for geometry optimizations. The computations reveal that frequently used methods, which take
into consideration primary and secondary interactions, can often be efficient in optimizing structural
geometries of systems based on organic molecules and transition-metal ions.
Received 12 January 2010
Received in revised form 22 March 2010
Accepted 22 March 2010
Available online 25 March 2010
Keywords:
Coordination chemistry
Cobalt(II)
Ó 2010 Elsevier B.V. All rights reserved.
DFT
Geometry optimization
1. Introduction
pected accuracy of 0.02 Å or better for bond lengths in the sys-
tems consisting of main group elements [17]. However,
Coordination complexes of transition-metals are the subject of
detailed investigation in coordination chemistry since a few dec-
ades. The use of homotopic N donor ligands and metal ions in
self-assembly processes has attracted much attention for the de-
sign and synthesis of novel functional materials [1,2]. Recent appli-
cations range from the controlled deposition of grid-type [2 ꢀ 2]
cobalt(II) complexes onto graphite into ordered supramolecular
assemblies [3,4], to new electrochemical approach to detect target
DNA molecules from solution based on catalytic oxidation of cobal-
t(II) complex containing 4,40-di-t-butyl-2,20-bipyridine [5]. Terpyr-
idine ligand, i.e. polypyridyls derivative has been employed to
generate many metallosupramolecular architectures such as heli-
cates, grids, metal-chain oligo-pyridylamido systems, metallacy-
cles [6]. Their applications include molecular machines [7–9],
liquid crystals [10], catalysts for both organic and inorganic reac-
tions [11–14], and as both therapeutic and imaging agents in med-
icine [15,16]. Of particular relevance to the above expectations is
the accurate prediction of molecular geometries in the complex.
The geometrical optimizations of the systems consisting of up to
50 atoms, is now a routine. A lot of experience has been collected
using the performance of Hartree–Fock (HF) approaches and meth-
ods based on Møller–Plesset (MP) perturbation theory or density
functional theory (DFT) These methods perform well within an ex-
transition-metal (TM) compounds are more difficult to handle
due to partially filled d shells, which render classical HF and MP
approaches incapable of taking up the challenge, apart from special
situations e.g. d0 or d10 systems, or closed shell species with large
gaps. Thus, bearing in mind the cost of more computationally
demanding methods such as CCSD(T), we have chosen DFT as a
suitable technique allowing us to perform geometry optimization
at an affordable cost and acceptable accuracy. Bühl et al. carried
out a thorough research where a number of density-functional/ba-
sis-set combinations was tested, including B3LYP, for their ability
to reproduce the geometries of first [18], second [19] and third
row [20] transition-metal complexes. It concluded that although
a slight advantage of hybrid functionals like B3P86 or B3PW91 is
noticeable, restricting ourselves to the selected few may be mis-
leading as for the performance of each functional is not uniform
and depends on the evaluated property and the nature of the sys-
tem investigated. Among the plethora of existing functionals,
B3LYP has been given particular attention especially over the past
few years. In spite of its decreasing popularity in favour of more
sophisticated density approximations, i.e. Hybrid Meta GGA (gen-
eralized gradient approximation) and Fully Non Local description,
B3LYPs appliance is still being discussed in terms of general perfor-
mance [21] and determination of complexes geometry and multi-
plicity to name a few [22]. Ramos et al. published an interesting
review [21] concerning not only the general performance of
density functionals, but also attempted to emphasize and compare
the results obtained by the B3LYP functional with other well-
established ones. The results varied from excellent to poor
* Corresponding author. Present address: ISIS/UMR CNRS 7006, Université de
Strasbourg, 8 allée Gaspard Monge, 67000 Strasbourg, France.
E-mail address: ciesielski@unistra.fr (A. Ciesielski).
0022-2860/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2010.03.057

A. Ciesielski et al. / Journal of Molecular Structure 973 (2010) 130–135
131
depending on the property and the system under study, confirming
at the same time that despite being outperformed in certain in-
stances, for the other ones B3LYP may still compete with more
elaborated basis sets. In this paper we investigate the molecular
geometries of metal–ligand complex {[CoLCl2](CH3CN)}, computed
with the unrestricted B3LYP functional with the LANL2DZ, 6-
31G(d), and 6-31G++(d,p) basis sets.
are usually quite consistent with experimental results [22,30,31].
Gaussian 03 program [32], running on an SGI Altix 350 Linux server
in 1 Itanium 2 processor at 1.5 GHz was used for calculations [33].
2.5. Crystal structure determination of complex {[CoLCl2](CH3CN)}
Diffraction data were collected at 200(1)K by the
nique on a KUMA-KM4CCD diffractometer with graphite–mono-
chromatized Mo radiation (k = 0.71073 Å). Data were
x-scan tech-
Ka
2. Experimental section
corrected for Lorentz-polarization and absorption effects [34].
Accurate unit-cell parameters were determined by the least-
squares fit of 3836 reflections of highest intensity, chosen from
the whole experiment. The structure was solved with SIR-92 [35]
and refined with the full-matrix least-squares procedure on F2 by
2.1. General
The metal salts were used without further purification as sup-
plied from Aldrich. NMR spectrum was obtained with a Varian
Gemini 300 MHz spectrometer and was calibrated against the
residual protonated solvent signals (CDCl3: d = 7.24 ppm) which
are given in ppm. Mass spectra were determined by using a Waters
Micromass ZQ spectrometer. Sample solutions were introduced
into the mass spectrometer source with a syringe pump at a flow
SHELXL97 [36] Scattering factors incorporated in SHELXL97 were
P
used. Function
w(|Fo|2 ꢁ |Fc|2)2 was minimized, with wꢁ1
=
[r
2(Fo)2 + 0.013 P2], where P is ½MaxðFo2; 0Þ þ 2F2c ꢃ=3. All non-hydro-
gen atoms were refined anisotropically, the hydrogen atoms were
placed geometrically, in idealized positions, and refined as rigid
groups; Uiso’s of these hydrogen atoms were set as 1.2 (1.3 for
methyl groups) times Ueq’s of the appropriate carrier atoms. Rele-
vant crystal data are listed in Table 1, together with refinement
details.
rate of 40 l
L minꢁ1 with a capillary voltage of +3 kV and a desolv-
ation temperature of 300 °C. Source temperature was 120 °C. The
cone voltage (Vc) was set to 30 V to allow transmission of ions
without fragmentation processes. Scanning was performed from
m/z = 200 to 1000 for 6 s, and 10 scans were summed to obtain
the final spectrum. Microanalyses were obtained by using a Per-
kin–Elmer 2400 CHN microanalyser. Mass FAB+ spectrum was
determined by using ZAB-HF VG spectrometer in m-nitrobenzylal-
cohol matrix.
3. Results and discussion
Metal-catalysed coupling reactions of halopyridines and their
derivatives are a long-established means of synthesis of polypyri-
dines, including quaterpyridines, though milder and more selective
procedures have been more recently developed [37–39]. In the
present case, multidentate ligand L was obtained as a side product
of a Stille coupling reaction [40], as outlined in Scheme 1. Further-
more, we also found another side product 4; unfortunately the
main reaction product 3 was not found, which is not surprising
for such a kind of reaction [26].
2.2. Preparation of L
To
a mixture of 2-(6-methylpyridin-2-yl)-6-(trimethylstan-
nyl)pyridine [23,24] (0.955 g, 2.9 mmol), 4,6-dichloro-2-phenyl-
pyrimidine [25] (0.258 g, 1.15 mmol) and LiCl (0.31 g, 7.3 mmol)
was gradually added degassed toluene (40 mL) and [Pd(PPh3)4]
(0.065 g, 0.056 mmol) under an argon atmosphere. The reaction
mixture was stirred and heated at reflux for 24 h, and then the tol-
uene was evaporated under reduced pressure. The residue was
purified by column chromatography on alumina (dichlorometh-
ane/hexane, 4:6) and 5% methanol in dichloromethane to afford
(0.167 g, 34%) of compound 4 [26] and (90 mg, 22%) of ligand L.
5(L): 1H NMR (300 MHz, CDCl3, 25 °C): d = 8.68 (t, 1H, J = 7.5 Hz),
8.60 (m, 3H), 8.47 (s, 1H), 8.42 (d, 2H, J = 7.8 Hz), 8.04 (t, 1H,
J = 7.8), 7.96 (t, 1H, J = 7.8), 7.56 (m, 3H), 2.67 (s, 3H). FAB–MS:
m/z = 359.1 (M+, 10). C21H15ClN4 (358.82) calcd. C = 70.29,
H = 4.21, N = 15.61, found C = 70.21, H = 4.24, N = 15.99.
Table 1
Experimental crystal data, data collection and structure refinement details.
Formula
C21H15Cl3CoN4ꢂ(CH3CN)
529.70
Triclinic
Formula weight
Crystal system
Space group
a (Å)
b (Å)
c (Å)
P-1
7.6694(4)
12.9089(6)
12.9769(7)
65.591(5)
76.513(4)
82.018(4)
1136.34(10)
2
a
(°)
b (°)
c
(°)
V (Å3)
Z
2.3. Preparation of Co(II) complex {[CoLCl2](CH3CN)}
Dx (g cmꢁ3
F (0 0 0)
l
)
1.55
538
1.13
A mixture of CoCl2ꢂ6H2O (7 mg, 0.028 mmol) and L (47 mg,
0.028 mmol) in CH3CN/CH2Cl2 (1:1, 4 mL) was stirred at room tem-
perature for 48 h. Pink complex {[CoLCl2](CH3CN)} was isolated in
quantitative yield by evaporation of the solvent. ESI–MS: m/z = 467
(100%) [CoLCl(H2O)]+, 359 (35%) [HL]+. {[CoLCl2](CH3CN)} (529.71)
calcd. C = 52.15, H = 3.43, N = 13.22, found C = 52.21, H = 3.39,
N = 13.26.
(mmꢁ1
)
Crystal size (mm)
0.3 ꢀ 0.15 ꢀ 0.03
2.73–28.01
ꢁ9 6 h 6 9
ꢁ16 6 k 6 16
ꢁ16 6 l 6 17
H
range (°)
h k l range
Reflections
Collected
9824
Unique (Rint
)
4965(0.037)
2559
291
0.035
0.051
0.072
0.055
0.93
0.33/ꢁ0.41
2.4. Calculation methods
With I > 2
No. of parameters
R(F) [I > 2 (I)]
wR(F2) [I > 2
(I)]
r(I)
The molecular geometries of complex {[CoLCl2](CH3CN)} (Fig. 1)
have been fully optimized using the unrestricted Becke three-
parameter hybrid exchange functional combined with the Lee–
Yang–Parr correlation functional (B3LYP) [27,28] which was used
with the LANL2DZ [29], 6-31G(d,p), and 6-31G++(d,p) basis sets
for geometry optimization. Calculations with these basis sets were
r
r
R(F) [all data]
wR(F2) [all data]
Goodness of fit
max/min
D
q
(e Åꢁ3
)

132
A. Ciesielski et al. / Journal of Molecular Structure 973 (2010) 130–135
Scheme 1. Reaction scheme for the synthesis of ligand L.
An equimolar reaction of cobalt(II) chloride with ligand L pro-
atom in ortho-position, with respect to the ring junction, remains
approximately coplanar with the plane of bipyridine and Co atom
(Fig. 2). The Co–N14 distance, of 2.551(2) Å is outside the range of
typical Co–N bonds. Interestingly, the contacts of this length are
quite rare: in the Cambridge Crystallographic Database there are
only 12 examples of intramolecular Co–N distances within the
range 2.5–2.6 Å (excluding the Coꢂ ꢂ ꢂNO3 contacts). This contact
might be therefore regarded as the weak bond, and the Co atom
will be 5-coordinated. The coordination can be described as de-
formed trigonal bipyramid (Fig. 3), with the nitrogen and Co atoms
making the basal plane (maximum deviation of 0.050 Å) and Cl1
and Cl2 at its apexes (deviations from the basal plane of 1.683 Å
and ꢁ2.157 Å, respectively). The terminal phenyl ring is inclined
by 11.90(12)° with respect to the pyrimidine ring, and by
38.98(7)° to the opposite terminal pyridine ring. This last value
can be the measure of the overall conformation of the ligand mol-
ecule. The crystal structure is determined mainly by van der Waals
vided a new complex. The complex was characterized with electro-
spray ionization mass spectrometry. The ESI–MS spectrum of
complex showed the signals at m/z = 467 [CoLCl(H2O)]+, 359
[HL]+ which means that in solution mononuclear species and li-
gand molecules occur.
3.1. Crystal data for complex {[CoLCl2](CH3CN)}
The bipyridine fragment is almost planar, with the dihedral an-
gle between the two rings of 2.38(9)°. The disposition of nitrogen
atoms is cis, thus allowing to coordinate to the same Co atom, with
typical Co–N distances of 2.154 Å and 2.040 Å. The pyrimidine ring
is significantly twisted, by 27.3(1)°, with respect to the bipyridine
plane. Nevertheless, the sense of the twist is such that the nitrogen
interactions and some weak intermolecular C–Hꢂ ꢂ ꢂCl and C–Hꢂ ꢂ ꢂ
p
interactions (Fig. 4, Table 2). The packing of complex molecules
creates voids in the structure which are filled by acetonitrile mol-
ecules, which are also connected with the ligand by relatively short
C–Hꢂ ꢂ ꢂN contact.
Fig. 1. Perspective view of one of the complex {[CoLCl2](CH3CN)} together with the
numbering scheme. The anisotropic displacement ellipsoids are drawn at 50%
probability level, hydrogen atoms are depicted as spheres with arbitrary radii.
Fig. 2. Perspective of the N14 atom to the plane of bipyridine fragment in the
crystal structure of the {[CoLCl2](CH3CN)} complex.

A. Ciesielski et al. / Journal of Molecular Structure 973 (2010) 130–135
133
Table 2
Experimental hydrogen bond data (Å, °; Cg1 describes the centroid of the phenyl
ring).
D
H
A
D–H
Hꢂ ꢂ ꢂA
Dꢂ ꢂ ꢂA
D–Hꢂ ꢂ ꢂA
C4
H4
Cl17a
Cl2b
0.95
0.95
0.95
0.98
2.86
2.72
2.42
2.76
3.561(2)
3.584(2)
3.338(3)
3.630(4)
132
151
164
148
C12
C18
C33
H12
H18
H331
N31c
Cg4d
Symmetry codes:
a
x, y, ꢁ1 + z.
b
ꢁx, 1 ꢁ y, ꢁz.
c
x, 1 + y, z.
1 ꢁ x, ꢁy, 1 ꢁ z.
d
d orbitals. Taking into consideration these two factors the quadru-
plet state is more feasible to occur and this indeed is consonant
with the experimental data. Theoretical calculations of the ground
state of Co(II) complex revealed that, regardless of the basis set ap-
plied, quadruplet state is always more thermodynamically stable
than the doublet state. The energetic difference deriving from the
complexes’ multiplicity expressed in kcal/mol is as follows: 9.92,
10.95 and 8.85 for 6-31G(d,p), 6-31G++(d,p) and LANL2DZ basis
set, respectively. These results conform well with the hypothesis
stated above.
For the quadruplet state, the values of Co1–N1 and Co1–N8
bond distances are well reproduced, with the smallest deviation
for LANL2DZ basis set (+0.0156 Å) and underestimation of less than
0.01 Å (6-31G(d,p) and 6-31G++(d,p)) for Co1–N1 and Co1–N8,
respectively. Calculations performed for the doublet state appeared
to be largely underestimated; deviations within a range of 0.118–
0.2 Å. Uniqueness of the Co1–N14 bond is obvious, as for values ob-
tained with the use of B3LYP function are completely not in line
with those obtained from the X-ray structural analysis. Neverthe-
less, deviations computed for quadruplet state are about half the
value of doublet state, with the 6-31G(d,p) basis set being the least
inaccurate of them all (0.2265 Å). As far as the Co1–Cl1 bond is
concerned, the best estimates of these values are given by 6-
31G(d,p)-quadruplet state and LANL2DZ doublet state (deviation
of +0.045 Å and +0.047 Å, respectively). It is noteworthy that 6-
31G(d,p) basis set-quadruplet state also compares well with the
experimental values of Co1–Cl2 bond distance, the deviation being
slightly greater than the former one (0.0557 Å) yet still about twice
less than the remaining ones (errors in the range from 0.071 Å to
0.111 Å for Co1–Cl1 and from 0.0947 Å to 0.1367 Å for Co1–Cl2).
Computational data concerning the remaining bond distances
Fig. 3. The coordination of Co in the crystal structure of the {[CoLCl2](CH3CN)}
complex.
3.2. Calculations data
The effect of state must be taken under consideration with re-
gard to geometry optimization of {[CoLCl2](CH3CN)} complex. Solid
state structures, which can be obtained from X-ray diffraction
technique by measurement of the distances between regions of
electron density, might simultaneously be distorted by the packing
effects. In contrast, quantum calculations, which interpret the
compound within the framework of fixed nuclei, presented in this
paper correspond to the gas phase, hence we must realize that the
results will vary to a certain extent as it is principally impossible to
directly compare the results acquired from DFT and XRD-analysis.
No polarizable continuum model (PCM) was used in order to ac-
count the effect of solvent as, contrary to the packing effects in so-
lid, even in more complex and charged biological molecules such
an effect may in general be neglected without making serious er-
rors [41]. Table 3 summarizes key computed parameters of the
{[CoLCl2](CH3CN)} complex, which consist of the selected bond dis-
tances, angles between them as well as torsions. What is substan-
tial, the calculations have been performed assuming that the Co(II)
ion might exist in its doublet or in quadruplet state, what reflects
the differences in the data acquired, especially the one concerning
ions coordination sphere. It is generally considered that chlorine
ions are classified as the low-field ligands. Furthermore, nitrogen
donor atoms also relatively weakly split energetic levels of cobalts
Fig. 4. Crystal packing of the {[CoLCl2](CH3CN)} as seen approximately along [0 0 1] direction.

134
A. Ciesielski et al. / Journal of Molecular Structure 973 (2010) 130–135
Table 3
Experimental and theoretical characterization of [CoLCl2] (distances in Å, dihedral angles in degrees).
Exp.
UB3LYP
UB3LYP
UB3LYP
UB3LYP
UB3LYP
UB3LYP
6-31G(d,p)
doublet state
6-31G++(d,p)
doublet state
LANL2DZ
doublet state
6-31G(d,p)
quadruplet state
6-31G++(d,p)
quadruplet state
LANL2DZ
quadruplet state
Co1–N1
Co1–Cl1
Co1–N14
N1–C2
N8–C7
N14–C13
Co1–N8
Co1–Cl2
2.1536(19)
2.2329(7)
2.5515(18)
1.346(3)
1.348(2)
1.355(2)
2.0402(17)
2.2583(7)
1.353(2)
1.347(3)
1.339(3)
2.654(3)
78.28(7)
92.57(5)
126.19(5)
73.05(6)
88.31(4)
118.8(2)
1.975
2.304
1.999
1.346
1.338
1.369
1.922
2.353
1.366
1.335
1.354
2.505
81.45
89.30
108.04
81.71
91.82
119.76
1.956
2.345
1.990
1.360
1.350
1.385
1.920
2.395
1.378
1.347
1.372
2.441
82.01
88.78
109.50
82.48
91.42
120.50
118.28
2.05
ꢁ4.09
ꢁ33.39
92.50
164.43
96.66
153.74
94.33
124.01
119.31
1.953
2.278
1.989
1.350
1.345
1.370
1.882
2.357
1.366
1.342
1.360
2.422
82.09
88.76
116.24
82.30
92.44
119.50
117.05
2.94
ꢁ4.42
ꢁ38.04
93.38
164.34
98.38
145.28
94.70
122.50
118.78
2.181
2.280
2.325
1.344
1.347
1.351
2.032
2.316
1.350
1.341
1.355
2.447
78.19
92.09
117.07
75.84
91.19
120.29
117.14
8.99
ꢁ16.37
ꢁ26.69
97.56
153.80
103.74
139.15
97.33
121.27
118.10
2.179
2.344
2.275
1.360
1.355
1.371
2.043
2.376
1.365
1.353
1.370
2.464
77.29
87.62
114.35
77.85
2.138
2.320
2.184
1.342
1.338
1.356
2.004
2.366
1.354
1.338
1.344
2.368
78.14
89.22
109.10
79.43
93.14
119.50
117.71
2.40
ꢁ5.88
ꢁ32.93
92.62
157.51
97.91
152.73
95.48
122.90
117.59
N1–C6
N8–C9
N14–C15
Cl2–H(C20)
N1–Co1–N8
N1–Co1–Cl2
N8–Co1–Cl1
N8–Co1–N14
Cl1–Co1–N14
C2–N1–C6
C13–N14–C15
N1–C6–C7–N8
N8–C9–C13–N14
N14–C15–C19–C20
N1–Co1–Cl1
N1–Co1–N14
N8–Co1–Cl2
Cl1–Co1–Cl2
Cl2–Co1–N14
C7–N8–C9
C15–N16–C17
93.13
120.48
118.50
2.82
ꢁ12.37
ꢁ25.44
94.27
154.95
104.02
141.05
101.38
122.44
118.63
116.44(18) 117.35
0.6(3)
1.99
ꢁ2.73
ꢁ46.28
92.25
163.12
97.93
ꢁ25.1(3)
ꢁ11.7(4)
105.95(6)
151.08(6)
111.56(6)
121.56(3)
101.28(5)
153.93
94.19
119.73(18) 123.06
116.40(19) 118.21
listed in Table 3 are in good agreement with each other, regardless
of the basis set applied. In general, their average deviation does not
exceed 0.02 Å, with Cl2–H(C20) distance as an exception since DFT
calculations, as seen above, not necessarily need to apply perfectly
to the systems containing halogen complexes [37]. From these data
it is apparent that performed quadruplet state calculations are in
far greater consonance with corresponding X-ray crystallographic
data than the doublet ones, with the 6-31G(d,p) being the most
accurate among them. The same tendency might be observed for
the bond angles, i.e. the best results are found for 6-31G(d,p) where
the maximum estimation error does not exceed 2.88° excluding
the following angles: N8–Co1–Cl1, N8–Co1–Cl2, Cl2–Co–N14,
Cl1–Co–Cl2. First three are underestimated for 9.13°, 7.93° and
3.96°, respectively, while the positive deviation of the latter one
exceeds 17°. Nevertheless we must remember that lack of an
appropriate description of the dispersion effect in DFT approaches
might result in such deviations, which are even greater for other
basis sets presented and B3LYP functional in general while consid-
ering halides. Furthermore, such inaccuracies are a consequence of
the marked above effect of state of the complex under study and
the fact that DFT approaches parameterize molecules geometry
in the framework of fixed nuclei, not electron density. Such incom-
plete electron–nuclear distribution description is even more visible
while considering dihedral angles, which did not appear to be well
comparative. Torsion coordinates take up large place in molecular
space at the same time having volumes relative to those of electron
densities within those vibrational elements, hence the errors. The
so far most exact basis set largely deviated from the N1–C6–C7–
N8 value, the deviation being about four times larger than others.
The remaining data also include relatively high errors, albeit the
data most approximate to experimental N8–C9–C13–N14 and
N14–C15–C19–C20 values are performed by both 6-31G(d,p) and
6-31G++(d,p) basis sets. Therefore, considering and summarizing
whole acquired data,
6-31G(d,p) basis set is recommended for computational study of
presented complex when using DFT functionals.
4. Conclusions
We report the synthesis of a new terpyridine ligand L and its
Co(II) complex, which may be of interest in several fields of cobalt
coordination chemistry such as catalysis, crystal engineering and
(molecular) electronics [42,43].
The present study shows that DFT calculations can be used as an
additional tool to investigate the molecular geometries of transi-
tion-metal complexes with good accuracy. Results of our research
show that by performing calculations with the unrestricted B3LYP
functional and applying the 6-31G(d,p) basis set with the polariz-
able continuum model of theory we are very close to predict the
real structure of metal–ligand complex molecule. One must note
that the largest deviations, regardless of the basis set applied, ap-
peared to concern not only the unusual Co–N14 bond which is
however outside the range of typical Co–N bonds, but also angles
and torsions. The inaccuracies arise from limitations of fixed-nu-
clear theory in quantum chemistry, as for we have performed com-
parison between gas phase optimized geometry and the solid state
structure obtained from X-ray diffraction analysis. Theoretical cal-
culations of the ground state of the complex evaluated proved that
what we face is Co(II) in its quadruplet state. It is also noteworthy
that such calculations let us easily determine the multiplicity of
the complexated metal ion and thus foresee its magnetic proper-
ties what is, as mentioned above, crucial in establishment of the
compounds potential applications.
5. Supplementary material
Crystallographic data (excluding structure factors) have been
deposited with the Cambridge Crystallographic Data Centre, No.

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