Synthesis, characterization, X-ray structure and DFT calculation of two Mo(VI) and Ni(II) Schiff-base complexes

Article abstract of DOI:10.1016/j.crci.2014.01.009

In this study, the syntheses of two new Mo(VI) and Ni(II) complexes with H₂L tridentate (ONO) Schiff-base ligand have been described and fully characterized by means of elemental analysis, FT-IR, electronic, ¹H-NMR spectroscopy and s

Full text of DOI:10.1016/j.crci.2014.01.009

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CRAS2C-3891; No. of Pages 10
C. R. Chimie xxx (2014) xxx–xxx
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Full paper/M e´ moire
Synthesis, characterization, X-ray structure and DFT
calculation of two Mo(VI) and Ni(II) Schiff-base complexes
a,
b
b,c
Reza Takjoo *, Alireza Akbari , Seyyed Yousef Ebrahimipour
,
d
e
Hadi Amiri Rrudbari , Giuseppe Bruno`
a
Department of Chemistry, School of Sciences, Ferdowsi University of Mashhad, 91775–1436 Mashhad, Iran
Department of Chemistry, Payame Noor University (PNU), 19395–4697 Tehran, Iran
Department of Chemistry, Shahid-Bahonar University of Kerman, Kerman, Iran
Department of Chemistry, University of Isfahan, 81746–73441 Isfahan, Iran
b
c
d
e
Universit a` degli Studi di Messina, dip. Scienze Chimiche, Viale Ferdinando S. d’Alcontres, 98166 Messina, Italy
A R T I C L E I N F O
A B S T R A C T
Article history:
In this study, the syntheses of two new Mo(VI) and Ni(II) complexes with H L tridentate
2
Received 26 September 2013
Accepted after revision 13 January 2014
Available online xxx
(
ONO) Schiff-base ligand have been described and fully characterized by means of
1
elemental analysis, FT–IR, electronic, H-NMR spectroscopy and single-crystal X-ray
diffraction. In both complexes, the Schiff-base completely deprotonates and coordinates to
the metal ion as a dianionic tridentate ligand via the donor oxygens and nitrogen atoms.
The coordination numbers of Mo(VI) and Ni(II) are six and four, respectively. The DFT-
B3LYP/6–31 + G (d,p) and PBEPBE/6–31 + G (d,p) calculations are carried out for the
determination of the optimized structures. Frequency calculations and NBO analysis are
also performed for characterization. According to the theoretical analysis of the
complexes, ligand-to-metal donation is greater than back donation. NBO data revealed
Keywords:
Schiff-base
Molybdenum(VI) complex
Nickel(II) complex
Spectroscopy
Crystal structure
DFT
ꢀ
2
that the main contribution of the frontier orbitals belongs to L
.
ß 2014 Acad e´ mie des sciences. Published by Elsevier Masson SAS. All rights reserved.
1
. Introduction
Schiff-base ligands are an important class of organic
continue to attract great interest because of their aptitude
for possessing uncommon configurations, and their
intrinsic potential in many biochemical processes [9,10].
Nickel complexes play a strong role in bioinorganic
and redox enzyme systems [11,12]. Square planar nickel
in the presence of some other factors can cause plasmid
cleavage [13]. Molybdenum complexes in high oxidation
states are considerable catalysts for some industrial
processes such as epoxidation of olefins and ammoxida-
tion of propene [14]. Many reports show that molybde-
num complexes with O and N donor ligands are potential
catalysts for homogeneous and heterogeneous reactions
[15,16], and in many cases DFT calculations have been
performed for understanding the mechanism of the
reactions as well as the molecular properties of the
compounds, as well as for providing good assignment of
experimental spectra [17].
ligands in coordination chemistry, which increase the
chemical and biological aspects of the compounds because
they act as antibacterial [1], antiviral [2], antifungal agents
[
3], as homogeneous or heterogeneous catalysts [4] and
display magnetic properties [5]. Different types of com-
plexes with various stereochemistries are formed when
Schiff-bases react with metal centers [6]. In recent years, it
has been realized that complexation of anticancer agents
decreases the viability of cells and in many cases reduces
the side effects of their toxicity [7,8]. The Schiff-base
complexes containing oxygen and nitrogen donor atoms
*
Corresponding author.
In this study, we describe the synthesis, characteriza-
tion and DFT calculations of two new square planar
E-mail addresses: rezatakjoo@yahoo.com,
r.takjoo@um.ac.ir (R. Takjoo).
1
631-0748/$ – see front matter ß 2014 Acad e´ mie des sciences. Published by Elsevier Masson SAS. All rights reserved.
http://dx.doi.org/10.1016/j.crci.2014.01.009
Please cite this article in press as: Takjoo R, et al. Synthesis, characterization, X-ray structure and DFT calculation of two
Mo(VI) and Ni(II) Schiff-base complexes. C. R. Chimie (2014), http://dx.doi.org/10.1016/j.crci.2014.01.009

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mixed-ligand Ni(II) and octahedral Mo(VI) complexes with
a tridentate salicylidene derivative ligand.
6
(100 MHz, DMSO-d , ppm): d = 9.3 (s, 1H; C5N), 6.8–8.1 (m,
3
7H; rings), 4.2 (q, 1H; OH), 3.2 (d, H; CH ). UV/Vis (MeOH)
1
ꢀ1
l
max, nm (loge
, Lꢁmolꢀ ꢁcm ): 218 (4.70), 240 (4.56), 302
2
. Experimental
(4.52), 354 (4.12), 426 (3.99).
2.1. Materials and instrumentation
2.4. Imidazole(2-((5-chloro-2-
hydroxyphenylimino)methyl)phenolato) nickel(II)
[Ni(L)(Im)].MeOH (2)
Chemicals were purchased from Merck and Aldrich
Chemicals, and were used without further purification.
Elemental analyses were performed using a Thermo
Finnigan Flash Elemental Analyzer 1112EA. FT–IR spectra
were recorded on a FT–IR 8400-SHIMADZU spectro-
A
methanolic solution (3 mL) of Ni(OAc)
(0.1 mmol, 0.02 g) was added to solution of
(0.1 mmol, 0.03 g) in 2 mL of methanol, and the reaction
mixture was refluxed for 30 min. Then, 3 mL of a
2
ꢁ4H
2
O
a
2
H L
ꢀ1
photometer as KBr discs in the 400–4000-cm
range.
Molar conductance measurements were made by means of
a Metrohm 712 Conductometer in MeOH. H-NMR spectra
methanolic solution of imidazole (0.2 mmol, 0.02 g) was
added to the reaction mixture and the reflux was
continued for an additional 2 h. By slow evaporation of
the resulting solution, red crystals appeared, which were
separated, dried in the air at room temperature and stored
in a desiccator over silica gel.
1
were recorded at 25 8C using a Bruker BRX 100 Avance
spectrometer. Electronic spectra in MeOH solutions of the
complexes were recorded with a Shimadzu model 2550
UV–Vis spectrophotometer. Diffraction data were mea-
sured using a Bruker APEX II CCD area-detector diffract-
ometer.
Irregular red, crystals. Yield: 0.027 g, 67%. m.p.: 208 8C.
ꢀ
3
ꢀ1
ꢀ
2
ꢀ1
.
Molar conductance (10 M, MeOH): 3.9
Anal. calcd. for C17 16ClN NiO
(404.49 gꢁmol ): C, 50.48;
H, 3.99; N, 10.39. Found: C, 50.57; H, 3.85; N, 10.46%. IR
V
cm mol
1
H
3
3
2.2. 2-(((5-chloro-2-hydroxyphenyl)imino)methyl)phenol
ꢀ1
(H
2
L)
(KBr) cm
(C5Cring) 1527s,
(100 MHz, DMSO-d
:
n
(OH) 3139w,
(C–O) 1280 m,
, ppm): = 12.9 (s, 1H, NH), 9.8 (s, 1H;
n
(C5N) 1604s,
n(NH) 3062s,
(C–Cl) 655s. H-NMR
1
n
n
n
H
2
L have been prepared according to our previous
report [18]. A solution of 2-amino-4-chlorophenol (0.3 g,
mmol) in 5 mL of ethanol was added to an ethanolic
solution (5 mL) of 2-hydroxy-benzaldehyde (0.2 g,
6
d
CH5N), 6.4–8.1 (m, 10H; rings), 3.8 (q, H; OH), 3.2 (d, 3H;
3
CH ). UV/Vis (MeOH) lmax, nm (loge
, Lꢁmolꢀ ꢁcm ): 206
1
ꢀ1
2
(4.65), 234 (4.36), 294 (3.95), 428 (4.28), 452 (4.21).
2
1
mmol) under vigorous stirring. After heating for
5 min, the solution was cooled and an orange precipitate
2.5. Crystal structure determination
was separated by filtration, washed with cold ethanol and
dried in a desiccator over silica gel.
The data were collected at room temperature with a
Yield: 0.41 g, 83%. m.p.: 156 8C. Anal. calcd. for
Bruker APEX II CCD area-detector diffractometer using
˚
Mo Ka radiation (l = 0.71073 A). Data collection, cell
ꢀ1
C
13
H
10ClNO
2
(247.68 gꢁmol ): C, 63.04; H, 4.07; N, 5.66.
ꢀ1
Found: C, 63.18; H, 4.01; N, 5.73%. FT–IR (KBr) cm
:
n
(OH)
(C5Cring) 1496s,
(C–Cl) 655 m. H-NMR (100 MHz, DMSO-
= 13.4 (s, 1H; OHaldehyde), 10 (s, 1H;
refinement, data reduction and absorption correction
were performed using multiscan methods with Bruker
software [19]. The structures were solved by direct
methods using SIR2004 [20]. The non-hydrogen atoms
were refined anisotropically by full-matrix least-squares
3
n
047wb,
(C–O) 1307 m,
, 25 8C, ppm): d
n(N–H) 2099sb, n(C5N) 1627s, n
1
n
d
6
OHamin), 9.0 (s, 1H; CH5N), 6.7–7.8 (m, 7H, rings). UV/Vis
2
(
(
methanol) lmax, nm (loge
, Lꢁmolꢀ1ꢁcmꢀ1): 226 (4.49), 268
on F using SHELXL [21]. All hydrogen atoms were placed
4.32), 350 (4.27), 438 (3.53).
at calculated positions and constrained to ride on their
parent atoms. Details concerning collection and analysis
are reported in Table 1.
2
.3. Methanol (2-((5-chloro-2-hydroxyphenylimino)methyl)
phenolato)dioxidomolybdenum(VI)ꢁ [MoO (L)(MeOH)] (1)
2
2.6. Computational
2
The solid Schiff-base ligand H L (0.01 mmol, 0.03 g) was
dissolved in 3 mL of methanol. This solution was added
dropwise to a methanolic solution (3 mL) of MoO (acac)
0.01 mmol, 0.04 g) under constant stirring. The mixture
was refluxed for 1 h. The resulting yellow solution was
then left undisturbed at room temperature. After two days,
yellowish block-shaped XRD-quality single crystals
appeared. These were dried in the air at room temperature
and stored in a desiccator over silica gel.
0
Full geometry optimization of the ground-state (S )
2
2
complexes was carried out using DFT-B3LYP and PBE
methods [22,23] with 6–31 + G(d,p) basis set for C, N, O, Cl,
H and LANL2DZ for Mo and Ni atoms using the G03
program [24]. Crystal structures were used as starting
points for DFT calculations.
To validate the optimization of the structures, fre-
quency calculations were performed, and the results
showed no negative (imaginary) frequency. Furthermore,
the determination of the origin of structural behaviors
has been done with Natural Band Orbital (NBO) analysis at
the same level. UV–Vis spectra, electronic transitions,
absorbance and oscillator strengths are computed with
the time-dependent DFT (TD-DFT) method at the
(
Irregular red, yield: 0.031 g, 77.5%. m.p.: > 300 8C. Molar
ꢀ
3
ꢀ1
2
ꢀ1
conductance (10 M, MeOH): 4.4
calcd. for C14 12ClMoNO
.98; N, 3.45. Found: C, 41.33; H, 2.91; N, 3.52%. IR (KBr)
V
ꢁcm ꢁmol . Anal.
ꢀ1
H
5
(405.64 gꢁmol ): C, 41.45; H,
2
ꢀ1
cm
:
n
(OH) 3371w,
n
(C5N) 1604s, (MoO ) 817, 925s,
n
2
1
n
(C5Cring) 1550 m,
n
(C–O) 1288 m, (C–Cl) 694s. H-NMR
n
Please cite this article in press as: Takjoo R, et al. Synthesis, characterization, X-ray structure and DFT calculation of two
Mo(VI) and Ni(II) Schiff-base complexes. C. R. Chimie (2014), http://dx.doi.org/10.1016/j.crci.2014.01.009

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3
Table 1
Crystal data and structure refinement.
[
MoO
2
(L)(MeOH)]
[Ni(L)(Im)]ꢁMeOH
16ClN NiO
Empirical formula
Formula weight
C1
4
H12ClMoNO
5
C
17
H
3
3
405.64
404.49
296(2)
0.71073
Temperature (K)
Wavelength ( A˚ )
293(2)
0.71073
1
Crystal system, space group
Unit cell dimensions
Triclinic, P
a = 6.881 A˚
Monoclinic, P2(1)/n
a = 5.75500(10) A˚
a
= 112.588
b = 10.429 A˚
c = 11.617 A˚
b
g
= 90.988
= 102.958
b = 11.1307(2) A˚
c = 26.8164(4) A˚
b = 90.9460(10)8
Volume ( A˚ 3
Z, Calculated density (Mg/m )
)
745.2
2, 1.808
1.081
404
1717.55(5)
4, 1.564
1.306
3
ꢀ
1
Absorption coefficient (mm
F(000)
)
832
Crystal size (mm)
0.17 ꢂ 0.12 ꢂ 0.05
0.36 ꢂ 0.22 ꢂ 0.18
Theta range for data collection (8)
Limiting indices
3.06 to 27.00
2.38 to 30.57
–8 ꢃ h ꢃ 8, –13 ꢃ k ꢃ 13, –14 ꢃ l ꢃ 14
18029/3254 [R(int) = 0.0342]
99.9%
–8 ꢃ h ꢃ 8, –15 ꢃ k ꢃ 15, –38 ꢃ l ꢃ 38
74564/5245 [R(int) = 0.0303]
99.6%
Reflections collected/unique
Completeness to
u = 27.00
2
2
Refinement method
Full-matrix least-squares on F
Full-matrix least-squares on F
Data/restraints/parameters
Goodness-of-fit on F^2
3254/1/203
1.045
5245/1/235
1.067
Final R indices [I > 2
R indices (all data)
s
(I)]
R
R
1
= 0.0432, wR
= 0.0584, wR
2
2
= 0.1168
= 0.1279
R
R
1
= 0.0377, wR
= 0.0493, wR
2
2
= 0.1054
= 0.1127
1
1
Largest diff. peak and hole (eꢁ A˚ ꢀ
3
)
1.935 and –0.694
0.366 and –0.433
B3LYP/6–31 + G(d,p) level. Solvent (MeOH) was considered
as a uniform dielectric constant 32.6 and Polarized
Continuum Model (PCM). GAUSSSUM 2.2 with FWHM
respectively, is another reason for the coordination of the
ligand to the metal through the phenolic oxygen atom.
Dioxidomolybdenum(VI) complex with a cis-MoO
2
moiety
exhibits two strong bands at 817 and 925 cm that can be
assigned to symmetrical and asymmetrical (O5Mo5O)
ꢀ
1
0
.3 eV have been used to calculate the DOS diagram and to
analyze the contribution percentage of groups and atoms
to the molecular orbitals [25].
v
vibrations respectively [27]. The OH band vibrations of
coordinated and non-coordinated methanol in 1 and 2
ꢀ1
3
. Results and discussion
appear at about 3100–3400 cm .
1
The H-NMR spectrum of the ligand displayed singlet
signals at 13.4 and 10 ppm, attributed to the OHalhehyde and
OHamine respectively. After complexation, these signals
disappeared, indicating that both phenolic oxygen atoms
are connected to the metal atom.
2
Mo(VI) (1) and Ni(II) (2) complexes of the H L tridentate
Schiff-base ligand can be prepared by reaction of a
methanolic solution of MoO (acac) and Ni(OAc)
2
2
2
2
ꢁ4H O
salts with the ligand, in a 1:1 molar ratio (1 mole imidazole
for 2). The analytical data and other spectral characteriza-
tions support the formulation of the compounds. These
complexes are found to be soluble in most of the common
2
The H L spectrum shows a singlet signal at 9 ppm,
which can be assigned to HCH=N. This signal appeared at 9.3
and 9.8 ppm for 1 and 2, respectively. Therefore, the high-
field shift of these protons proved the coordination of the
azomethine nitrogen to the metal center.
In the Mo(VI) and Ni(II) complexes, the signals at 4.1
and 3.2 ppm correspond to the coordinated methanol
hydroxyl and the lattice methanol, respectively. Also,
protons of the rings revealed at 6.8–8.1 ppm in both
complexes.
3
organic solvents such as methanol, CHCl , DMSO, DMF, and
insoluble in n-hexane and water. Low molar conductivity
values of 1 and 2 indicates that they behave as non-
electrolytes.
3
.1. Characterization
According to our previous work [6], this ligand has two
In compound 2, the NH signal of the imidazole moiety
was at 12.9 ppm and the protons of the azomethine and of
the rings were disclosed to 9.8 and 6.4–8.1 ppm, respec-
tively. Likewise, the OH and methyl groups of methanol
appeared at 3.8 and 3.2 ppm, respectively.
tautomeric forms, enol (benzenoid) or keto (quinoid) forms.
FT–IR spectral studies are performed by comparison of the
free ligand spectrum with those of its Ni(II) and Mo(VI)
ꢀ1
complexes. A
ꢀ1
ligand spectrum shows a red shift to 1604 cm (23 cm )
v(C5N) strong band at 1627 cm in the free
ꢀ1
after coordination, indicating the coordination of the
azomethine nitrogen atom to the metal center. In the IR
3.2. X-ray structures
ꢀ1
spectrum of the ligand, the band observed at 3047 cm is
due to the NH vibration. Its absence in the spectra of 1 and 2
is another evidence that demonstrates the coordination of
the azomethine nitrogen atom to the metal center [26].
ORTEP representations of compounds 1 and 2 are
shown in Figs. 1 and 2; selected bond lengths and angles
are listed in Table 2.
The molybdenum complex has a distorted octahedral
geometry with the ONO deprotonated ligand connected via
two phenolic oxygen and iminic nitrogen atoms in the
ꢀ
1
Moreover, a shift of the C–O bond energyof H L (1307 cm )
2
ꢀ
1
to lower frequencies at 1288 and 1280 cm for 1 and 2,
Please cite this article in press as: Takjoo R, et al. Synthesis, characterization, X-ray structure and DFT calculation of two
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Fig. 1. (Color online.) ORTEP view of 1. Non-H-atoms, represented as displacement ellipsoids, are plotted at the 50% probability level, while H atoms are
shown as small spheres of arbitrary radius.
As it can be seen, the Ni ion has a distorted square planar
coordination sphere in 2and a lattice methanol molecule. The
double deprotonated tridentate ONO ligand is coordinated to
the nickel ion via two phenolic oxygen and iminic nitrogen
atoms. The fourth coordination position is occupied by the
imidazole molecule. In the center of 2, the nickel atom has a
˚
0
.019-A deviation from the best plane formed by O1N1O2N2;
also, the O1–Ni1–O2 (177.70(7)8) and N1–Ni1–N2
175.81(7)8) angles which are close to the ideal value of
808 confirmed the nearly square planar geometry. The Ni1–
(
1
O1 (1.824(2)8) bond length is equal to that in the analogous
compound [33], and the Ni1–N2 (1.905(2)8) bond length is
the smallest one reported in these nickel square planar
complexes [33–36]. Two methanol molecules form N3–
H3ꢁꢁꢁO3 and O3–HꢁꢁꢁO2 intermolecular hydrogen bonds with
Fig. 2. (Color online.) ORTEP view of 2. Non-H-atoms, represented as
displacement ellipsoids, are plotted at the 50% probability level, while H
atoms are shown as small spheres of arbitrary radius. The dotted line
represents hydrogen bond interaction.
adjacent complexes to make supra-molecular dimer with an
4
4
R ð16Þ graph set (Fig. 4). According to the hydrogen bonding
classification [37,38], these intramolecular and intermole-
cularhydrogen bondsare moderate electrostatic interactions.
These dimmers link to each other through C1–Cl
interaction and C5–H5ꢁꢁꢁO1 intermolecular hydrogen
bonds along a and b axis respectively, and form the
three-dimensional lattice.
equatorial plane, two oxido groups and a methanol
˚
molecule. The molybdenum atom has a 0.316 A deviation
from the equatorial mean plane (N1O1O2O3). Comparison
of the Mo–N [28,29] and Mo–O [29–32] band distances
with the other analogues compounds showed some
similarities.
3.3. Computational
˚
3.3.1. Geometry optimization
The Mo1–O2 distance (1.983(4) A) is longer than the
˚
The structures of the complexes are optimized by DFT
using the X-ray structures as input with B3LYP and PBE
exchange functional. The absence of negative normal
modes in frequency calculations emphasize that the
optimized structures are in minimum energy. Comparison
of theoretical results and experimental data shows a good
agreement between them (Table 2). The negligible
difference between experimental and theoretical data
refers to the fact that the experimental data belong to the
solid state and the lattice with interactions in the crystal
structure, while the calculated values refer to a single
molecule in the gas phase. As can be seen, the bond lengths
Mo1–O1 distance (1.922(4) A), which is probably due to
the O5–HꢁꢁꢁO2 hydrogen bond. Two adjacent Mo-com-
plexes bind to each other to form a dimmer via an O5–
HꢁꢁꢁO2 hydrogen bond (Fig. 3). This dimer made a one-
˚
dimensional chain with C9–H9ꢁꢁꢁO4 (3.398(7) A) hydrogen
bonds.
These chains join each other through C3H3ꢁꢁꢁC14H14 C
interactions to form a two-dimensional lattice. Finally, C7–
˚
˚
H7ꢁꢁꢁO4 (3.342(6) A), C5–H5ꢁꢁꢁO4 (3430(7) A), C14–
˚
˚
H14ꢁꢁꢁC9 (3.70(1) A) and C14–H14BꢁꢁꢁO3 (3.388(8) A)
hydrogen bonding interactions complete the third dimen-
sion in the lattice.
Please cite this article in press as: Takjoo R, et al. Synthesis, characterization, X-ray structure and DFT calculation of two
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5
Table 2
Selected bond lengths [ A˚ ] and angles [8] for the title complexes.
[
MoO (L)(MeOH)]
2
[Ni(L)(Im)]ꢁMeOH
exp.
theo.
exp.
theo.
B3LYP
PBE
1.998
B3LYP
PBE
1.857
Mo1–O2
Mo1–N1
Mo1–O4
Mo1–O3
Mo1–O5
Mo1–O1
O2–C13
N1–C7
1.983(4)
2.284(4)
1.686(5)
1.692(3)
2.342(5)
1.922(4)
1.349(5)
1.263(7)
1.444(6)
1.334(7)
1.447(7)
1.399(7)
1.411(6)
74.6(2)
1.981
Ni1–N1
1.859(2)
1.905(2)
1.855(2)
1.824(2)
1.413(3)
1.308(2)
1.295(2)
1.423(2)
1.337(2)
1.421(3)
1.400(3)
175.81(7)
86.73(7)
95.55(7)
90.00(7)
87.74(7)
177.70(7)
124.4(2)
126.3(1)
111.7(1)
121.9(2)
112.2(1)
124.6(2)
122.0(2)
111.7(2)
117.6(2)
127.1(1)
1.881
2.363
1.710
1.717
2.515
1.987
1.340
1.296
1.405
1.336
1.442
1.412
1.423
73.34
103.08
97.8
2.332
1.724
1.737
2.589
1.986
1.342
1.312
1.408
1.331
1.435
1.421
1.432
Ni1–N2
1.937
1.860
1.845
1.434
1.306
1.306
1.416
1.323
1.427
1.415
1.926
1.863
1.849
1.441
1.317
1.322
1.415
1.330
1.415
1.421
Ni1–O2
Ni1–O1
C1–C6
C1–O1
N1–C7
N1–C8
N1–C8
O2–C9
O1–C1
C7–C6
C7–C6
C8–C9
C13–C8
C6–C1
N1–Ni1–N2
N1–Ni1–O2
N1–Ni1–O1
N2–Ni1–O2
N2–Ni1–O1
O2–Ni1–O1
C6–C1–O1
Ni1–N1–C7
Ni1–N1–C8
C7–N1–C8
Ni1–O2–C9
N1–C7–C6
C1–C6–C7
N1–C8–C9
O2–C9–C8
Ni1–O1–C1
175.8
175.5
86.8
95.5
87.3
96.5
O2–Mo1–N1
O2–Mo1–O4
O2–Mo1–O3
O2–Mo1–O5
O2–Mo1–O1
N1–Mo1–O4
N1–Mo1–O3
N1–Mo1–O5
N1–Mo1–O1
O4–Mo1–O3
O4–Mo1–O5
O4–Mo1–O1
O3–Mo1–O5
O3–Mo1–O1
O5–Mo1–O1
Mo1–O2–C13
Mo1–N1–C7
Mo1–N1–C8
Mo1–O1–C1
73.8
98.0(2)
100.4
96.5
88.9
88.2
94.6(2)
88.7
88.1
77.8(2)
78.9
80.1
177.7
123.9
125.4
111.1
123.4
112.0
125.4
121.9
111.8
118.1
127.7
176.2
123.9
125.3
111.7
123.0
111.6
125.4
121.7
111.7
117.8
127.1
150.6(2)
91.2(2)
144.2
92.4
148.5
96.5
161.5(2)
79.0(2)
160.3
77.8
155.1
80.5
82.3(2)
78.9
80.4
105.3(2)
170.0(2)
100.4(2)
84.2(2)
106.8
169.1
100.2
83.4
107.8
176.7
100.2
75.2
102.4(2)
80.2(2)
101.0
73.3
99.4
77.9
121.5(3)
127.2(4)
112.0(3)
136.2(3)
123.3
124.8
110.8
133.0
122.1
125.5
111.4
136.6
exp.: experimental abbreviation; theo.: theoretical abbreviation.
diagrams of absorption spectra for 1 and 2 are shown in
Fig. 5. The spectra of methanolic solution of H L and the
2
related complexes show four and five absorption bands in
the UV–Vis region.
In the electronic spectrum of H
and 268 nm are assigned to * transitions of aromatic
rings. The azomethine * transitions are
* and n!
viewed at 350 nm and 438 nm, respectively [6]. For both
complexes, * transitions showed hypso-
2
L, two bands at 226 nm
p p
!
p
!p
p
p
!p
* and n!
p
chromic shifts. In the Mo(VI) complex, the band that
appeared at 426 nm may be due to a LMCT (O(p) !Mo(d))
transition [39].
0
According to d electronic configuration (+6 formal
oxidation state) of molybdenum, the Mo-complex showed
8
no d–d transition. In the d square planar nickel complex, it
2
2
Fig. 3. (Color online.) Perspective of R ð8Þ graph set in complex 1.
is expected to show three spin-allowed d–d transition
1
1
1
1
bands corresponding to
A
1g! A2g
,
A
1g! B1g and
1
1
A
g
1g! E , while the tailing of CT bands that appeared at
428 nm and 452 nm toward the visible region cause the
and angles around central atoms in the title complexes
determined from PBEPBE method are slightly higher than
that obtained from B3LYP method.
disappearance of these bands [40]. In the calculated
spectra for 2, these bands are located at 527.28 nm,
498.8 nm and 443.04 nm due to transitions of HOMO–2
and HOMO–5 to LUMO+1. Also, two bands at 384.4 and
342.72 can be related to LMCT and ILCT charge transfer
transitions that are centered on 428 nm in the experi-
mental spectra. Other bands that appeared in the
3.3.2. Electronic spectra
UV–Vis spectra of the title compounds were recorded in
MeOH solution. The calculated and experimental
a
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4
4
Fig. 4. (Color online.) Perspective of R ð16Þ graph set in complex 2.
spectra of 1, the transitions between 395.68 and 276.72 nm
are assigned to an admixture of ILCT and LMCT. These
bands mainly arise from HOMO to LUMO ( = 395.68 nm),
HOMO to LUMO+1 ( = 349.92 nm), HOMO–1 to LUMO
= 324.0 nm), HOMO to LUMO+2 ( = 315.76 nm), HOMO
to LUMO+3 = 297.52 nm), HOMO–1 to LUMO+1
= 292.08 nm) and HOMO–2 to LUMO ( = 276.72 nm),
l
l
(
l
l
(l
(
l
l
respectively. The intense band that is located at 240 nm in
the experimental spectra can be assigned to more than one
excitation. In the calculated spectra, the related excitations
are viewed at energies of 3.70 eV (
l = 267.92 nm) and
3
.78 eV ( = 262.16 nm), respectively. The last intense
l
absorption band at 218 nm is attributed to ILCT, whereas
appeared at 253.2 nm in simulated theoretical spectra.
3.3.3. Analysis of frontier molecular orbitals
Frontier molecular orbitals, especially HOMO and
LUMO, have a significant effect on electric properties such
as UV–Vis spectra or NLO behaviors and on the prediction
of the chemical reactivity of the material [41]. The surface
plots of the HOMO and LUMO orbitals of Ni(II) and Mo(VI)
complexes are depicted in Fig. 6.
The HOMO–LUMO energy gap correlates with the
stability of the compounds. According to Fig. 7, the
2
HOMO–LUMO gap in [MoO (L)(MeOH)] is higher than
that in [Ni(L)(Im)]ꢁMeOH complex. Hence, the Ni(II)
complex is chemically more active than 1. Furthermore,
details of the frontier molecular orbitals in complexes 1
and 2 are presented in Table 5.
The HOMO and LUMO orbitals in both complexes are
mainly localized on non-metal atoms. For the Mo(VI)
complex, the value of the contribution for non-metals in
HOMO/HOMO–2 is equal to 99–100% and for LUMO/
LUMO+3, it is equal to 82, 50, 43 and 41%, respectively. In
the higher LUMOs of the Mo center, the contributions of
the d orbitals have been calculated as follows: LUMO+1:
Fig. 5. Experimental and calculated UV–Vis spectra of Mo (a) and Ni (b)
complexes in MeOH solutions.
theoretical spectrum can be described as an ILCT charge
transfer that is mainly due to transitions from lower MOs
to LUMO. Three bands at 294, 234 and 206 nm are
correlated to this.
For more investigations, the observed and computed
electronic transitions based on TD-DFT calculation for
Mo(VI) and Ni(II) complexes are listed in Tables 3 and 4,
respectively. The B3LYP level is selected due to more
accurate results in comparison with those obtained using
ꢀ2
50%, LUMO+2: 57% and LUMO+3: 59%. The L has the
ꢀ
2
major contribution to the frontier orbitals. The L
constructs 96% and 70% of HOMO and LUMO, respectively.
In [MoO (L)(MeOH)], coordinated methanol to the central
2
atom in HOMO–3/–8 played a 26–62% role, whereas it
varies between 18–27% in LUMO+1/+3.
The d orbitals of Ni in the [Ni(L)(Im)]ꢁMeOH have a
significant contribution (18–27%) to lower HOMO
(HOMO–1/–7), also 63 and 14% for LUMO+1 and LUMO+2.
the PBE method. The calculated values of
lmax are in good
agreement with the experimental ones. In the calculated
Please cite this article in press as: Takjoo R, et al. Synthesis, characterization, X-ray structure and DFT calculation of two
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7
Table 3
Main calculated optical transition with composite ion in terms of molecular orbital contribution of the transition, vertical excitation energies and oscillator
strength for [MoO
2
(L)(MeOH)].
Composition
Weight (%)
E (eV)
Oscillatory strength (f)
lmax (calcd.)
l
max (exp.)
Assignment
H ! L
70
70
58
53
33
26
49
29
26
11
64
58
19
61
21
21
63
53
15
18
11
2.51
2.83
3.06
3.14
0.0222
0.0002
0.0196
0.0556
395.68
349.92
324.0
426
354
LMCT, ILCT
LMCT, ILCT
LMCT, ILCT
LMCT, ILCT
H ! L + 1
H-1 ! L
H ! L + 2
H-1 ! L
315.76
302
H ! L + 3
H ! L + 3
H-2 ! L
3.33
0.1125
297.52
LMCT, ILCT
H-1 ! L + 1
H-1 ! L
H-1 ! L + 1
H-2 ! L
3.39
3.58
0.0310
0.2877
292.08
276.72
LMCT, ILCT
LMCT, ILCT
H ! L + 2
H-1 ! L + 4
H-2 ! L
3.70
0.1347
267.92
240
218
ILCT
H-1 ! L + 3
H-1 ! L + 4
H-4 ! L
3.78
3.92
0.0392
0.0035
262.16
253.2
ILCT
ILCT
H-4 ! L + 1
H-4 ! L + 2
H-7 ! L
Table 4
Main calculated optical transition with composition in terms of molecular orbital contribution of the transition, vertical excitation energies and oscillator
strength for [Ni(L)(Im)]ꢁMeOH.
Composition
Weight (%)
E (eV)
Oscillatory strength (f)
lmax (calcd.)
l
max (exp.)
Assignment
H-2 ! L + 1
H-5 !L + 1
H-2 !L + 1
H-5 !L + 1
H-3 !L + 1
H-6 !L + 1
H-7 !L + 1
H-14 !L + 1
H !L + 1
H-1 !L
52
17
71
43
44
13
52
23
67
67
15
61
19
21
18
70
66
13
14
44
43
12
1.88
0.0001
527.28
d–d
1.99
2.24
0.0012
0.0038
498.8
d–d
443.04
452
428
294
LMCT, d–d
2.58
0.0024
384.4
LMCT, ILCT
2.89
3.02
0.2962
0.1400
342.72
328.64
LMCT, ILCT
ILCT
H !L
H !L
3.11
0.0022
319.184
ILCT
H-5 !L + 1
H-3 !L + 1
H-1 !L + 1
H-2 !L
3.34
3.81
0.0003
0.0729
297.12
260.56
ILCT
ILCT
H-3 !L
234
206
H-6 !L
H-5 !L
H-1 !L
3.93
0.0025
222.64
ILCT
H-6 !L
H-3 !L
The ligand’s contributions to the HOMO and LUMO are
equal to 96 and 81%. The minimum contribution in HOMO
and lower MOs belongs to MeOH (0%), but in orbitals
higher than HOMO this value has increased up to 84% for
LUMO+2. The DOS diagrams of complexes 1 and 2 are
presented in Fig. 8.
These diagrams display the orbital composition char-
acteristics of molecular orbitals with respect to particular
fragments or atoms. According to these diagrams, the
ligand plays a significant role in the frontier orbitals,
except for central atoms that have no importance in the
frontier molecular orbitals (especially in HOMO). However,
the central metal ion contributes to a wide range of LUMO
orbitals (Fig. 8).
Based on these data, the first transition state from
HOMO to LUMO in the Ni(II) complex can be assigned to an
intra-ligand charge transfer (ILCT), and for the Mo(VI)
complex it can be predicted as an admixture of ILCT and
LMCT.
3.3.4. Mulliken population analysis
The Mulliken atomic charges inferred from the natural
population analysis (NPA) for the most important atoms in
the complexes are summarized in Table 6. The formal
Please cite this article in press as: Takjoo R, et al. Synthesis, characterization, X-ray structure and DFT calculation of two
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R. Takjoo et al. / C. R. Chimie xxx (2014) xxx–xxx
Fig. 6. (Color online.) Contour plots of the HOMO and LUMO orbitals of Mo(VI) and Ni(II) complexes.
Fig. 7. Diagram of Frontier molecular orbital energies of Mo(VI) and Ni(II) complexes.
Table 5
Orbital energies and atomic orbital contributions for the frontier molecular orbitals for Mo(VI) and Ni(II) complexes.
Ni(II)
Mo(VI)
E (eV)
Ni (%)
Im (%)
L (%)
Met (%)
E (eV)
Mo (%)
Oxo%
L (%)
Meth (%)
LUMO+4
LUMO+3
LUMO+2
LUMO+1
LUMO
–0.08
–0.15
–0.84
–1.3
6
5
50
13
2
28
76
4
16
5
–0.92
–2.11
–2.3
4
59
57
50
18
1
2
27
18
22
12
3
93
13
25
27
70
1
1
0
1
0
0
0
0
1
5
10
63
3
84
1
6
30
97
96
82
0
–2.35
–2.91
–6.26
–6.83
–7.25
–8.09
–8.15
–1.88
–5.17
–5.5
0
0
HOMO
4
0
0
96
96
100
74
32
HOMOꢀ1
HOMOꢀ2
HOMOꢀ3
HOMOꢀ4
18
100
24
28
0
0
1
3
–6.26
–6.35
–6.75
0
0
0
0
3
73
30
0
0
25
63
42
0
0
2
Im: Imidazole; L: deporotonated form of H L; Meth: Methanol.
Please cite this article in press as: Takjoo R, et al. Synthesis, characterization, X-ray structure and DFT calculation of two
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9
Fig. 8. (Color online.) DOS diagrams of complexes 1 and 2.
Table 6
4. Conclusion
Atomic charges from the natural population analysis (NPA) for
[
MoO
2
(L)(MeOH)] and [Ni(L)(Im)]ꢁMeOH.
MoO (L)(MeOH)]
Charge
Mo(VI) and Ni(II) complexes of the general composition
MoO
(L)(MeOH)] and [Ni(L)(Im)]ꢁMeOH have been
[
2
[
2
Atom
Valance arrangement
synthesized and characterized by different spectroscopic
methods. Molecular structures for both complexes have
been identified by single-crystal X-ray analysis. According
to X-ray structural determination, Ni(II) and Mo(VI)
complexes have a square planar and octahedral geometry
respectively and are distorted. DFT calculations were
performed on both kinds of complexes. The theoretical
results and the spectral studies are in agreement with the
proposed structure of all synthesized compounds. Energies
Mo
O1
O2
O3
O4
O5
N1
1.440
[core]4d(3.90)5p(0.45)6S(0.20)
[core]2S(1.62)2p(4.99)
[core]2S(1.63)2p(4.95)
[core]2S(1.80)2p(4.64)
[core]2S(1.80)2p(4.62)
[core]2S(1.67)2p(5.06)
[core]2S(1.29)2p(4.15)
–0.634
–0.604
–0.455
–0.438
–0.748
–0.473
[
Ni(L)(Im)]ꢁMeOH
Atom
Charge
Valance arrangement
of the important MO’s, absorption wavelength (lmax),
Ni
0.813
[core]3d(8.69)4p(0.30)5S(0.18)
[core]2S(1.65)2p(5.00)
[core]2S(1.67)2p(5.02)
[core]2S(1.28)2p(4.17)
[core]2S(1.34)2p(4.15)
oscillator strength and excitation energies of the com-
pounds were also determined from the TD-DFT method
and compared with the experimental values. According to
DFT calculations, the main contribution of HOMO and
LUMO belongs to L , while the central atoms in the two
studied complexes play a little role in frontier orbitals,
especially in HOMO and in lower frontier molecular
orbitals.
O1
O2
N1
N2
–0.672
–0.701
–0.477
–0.510
ꢀ
2
oxidation states expected for the studied complexes are +2
Ni) and +6 (Mo), but the calculated natural charges and
(
electron configuration differ from these values and are
lower than the anticipated values: Ni, 0.813; Mo, 1.44.
Additionally, according to Table 6, electronic configuration
Acknowledgements
2
and charges on the terminal oxido (in [MoO (L)(MeOH)])
and the coordinated oxygen atoms of aromatic rings to the
metal center in both complexes are significantly smaller
than the expected amount.
Natural charges data indicate that the donations from
the ligands to the central ions have the advantage over the
back donations from the metal to the ligands.
This work was supported by Ferdowsi University of
Mashhad and Payame Noor University (PNU). We would
like to thank the Universit a` di Messina (Italy) for technical
assistance in crystallography.
In the Mo(VI) complex, oxygen atoms of the oxido are
less negative from the other oxygen atoms. This is due to
higher electron density delocalization from the terminal
oxido to the Mo and is the reason why their bond length
Appendix A. Supplementary data
Crystallographic data for the structures reported in this
paper have been deposited with the Cambridge Crystallo-
graphic Data Centre, CCDC Nos. 889311 and 889312 for
compound 1 and 2. Copies of this information may be
obtained from the Director, CCDC, 12 Union Road, Cambridge,
CB2 1EZ, UK (fax: +44 1223 336033; e mail: deposit@ccdc.-
cam.ac.uk or http://www.ccdc.cam.ac.uk) and in the online
version at http://dx.doi.org/10.1016/j.crci.2014.01.009.
(Mo5O) is lower in comparison with the case of other Mo–
O bonds. The bond lengths can be arranged as follows:
Mo¼O < MoꢀO ðringsÞ < MoꢀO ðmethanolÞ
In case of 2, electron delocalizations in both Ni–O bonds
are close together and therefore the bond lengths have no
significant differences.
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[
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Please cite this article in press as: Takjoo R, et al. Synthesis, characterization, X-ray structure and DFT calculation of two
Mo(VI) and Ni(II) Schiff-base complexes. C. R. Chimie (2014), http://dx.doi.org/10.1016/j.crci.2014.01.009