Nickel(II) complexes with methyl(2-pyridyl)ketone oxime: Synthesis, crystal structures and DFT calculations

Article abstract of DOI:10.1016/j.saa.2012.12.042

The synthesis and structural characterization of the three novel nickel(II) complexes [Ni(OOCPh)₂(mpkoH)₂] (1), [Ni(NO ₃)₂(mpkoH)₂] (2) and [Ni(mpkoH) ₃](NO₃)₂?1/2H₂O (3?1/2H₂O), with mpkoH = methyl(2-pyridyl)ketone oxime is reported. Geometry optimization and population analyses were performed by means of DFT calculations for the previously mentioned compounds as well as for [NiCl₂(mpkoH)₂] (4). Electronic UV-vis spectra were also simulated in the TD-DFT framework to assign the origin of the absorption bands and in doing so, to have a clear picture of the absorptive features of the coordination compounds under investigation.

Full text of DOI:10.1016/j.saa.2012.12.042

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 105 (2013) 439–445
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Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Nickel(II) complexes with methyl(2-pyridyl)ketone oxime: Synthesis, crystal
structures and DFT calculations
Lorena Martínez a, Jorge S. Gancheff a, F. Ekkehardt Hahn b, Robert A. Burrow c, Ricardo González a,
Carlos Kremer a, Raúl Chiozzone a,
⇑
a Cátedra de Química Inorgánica, Departamento Estrella Campos, Facultad de Química, Universidad de la República, Avda. General Flores 2124, CC 1157 Montevideo, Uruguay
b Institut für Anorganische und Analytische Chemie der Westfälischen Wilhelms-Universität Münster, Correnstrasse 30, 48149 Münster, Germany
c Departamento de Química, Universidade Federal de Santa Maria, Camobi, CEP 97105-900, Santa Maria, RS, Brazil
g r a p h i c a l a b s t r a c t
h i g h l i g h t s
"
"
"
Three mononuclear Ni(II) complexes
with mpkoH have been isolated and
characterized.
Their structural and electronic
properties were also studied by DFT
methods.
Their electronic spectra have been
reproduced by the TD-B3LYP/
LANL2DZ method.
a r t i c l e i n f o
a b s t r a c t
Article history:
The synthesis and structural characterization of the three novel nickel(II) complexes [Ni(OOCPh)2
(mpkoH)2] (1), [Ni(NO3)2(mpkoH)2] (2) and [Ni(mpkoH)3](NO3)2Á½H2O (3Á½H2O), with mpkoH
= methyl(2-pyridyl)ketone oxime is reported. Geometry optimization and population analyses were per-
formed by means of DFT calculations for the previously mentioned compounds as well as for [NiCl2
(mpkoH)2] (4). Electronic UV–vis spectra were also simulated in the TD-DFT framework to assign the
origin of the absorption bands and in doing so, to have a clear picture of the absorptive features of the
coordination compounds under investigation.
Received 29 September 2012
Received in revised form 11 December 2012
Accepted 14 December 2012
Available online 22 December 2012
Keywords:
Nickel(II) complexes
Oxime complexes
Crystal structure
Theoretical calculations
Ó 2012 Elsevier B.V. All rights reserved.
Introduction
belongs to the family of 2-pyridyl oximes, of general formula
(py)(R)C@N@OH with py = pyridine and R @ H, alkyl or aryl group.
Oximes have been known for a long time as spectrophotometric
reagents in analytical chemistry [1], and first reports on methyl(2-
pyridyl)ketone oxime (mpkoH) were dealing with the colorimetric
determination of iron, copper and rhenium [2,3]. This compound
In the last decade, 2-pyridyl oximes became very popular
ligands in molecular magnetism. This is due to their ability to form
polynuclear complexes by acting as versatile and flexible bridging
ligands that efficiently mediate magnetic exchange between para-
magnetic ions. Several nickel(II) complexes with these ligands have
been reported, mostly with 2-pyridinealdoxime (paoH), phenyl
(2-pyridyl)ketone oxime (ppkoH) and mpkoH. Trinuclears [Ni3
(ppko)6]Á2H2OÁ0.5EtOHÁMeOH and [Ni3(mpko)3(HCO2)2(mpkoH)2]
⇑
Corresponding author. Tel.: +598 2924 9739; fax: +598 2924 1906.
E-mail address: rchiozzo@fq.edu.uy (R. Chiozzone).
1386-1425/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.saa.2012.12.042

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L. Martínez et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 105 (2013) 439–445
(ClO4) [4], hexanuclears [Ni6(SO4)2(ppko)8]Á6DMF [5], [Ni6(SO4)4
(OH)(mpko)3(mpkoH)3(MeOH)2(H2O)] and [Ni6(SO4)4(OH)(ppko)3
(ppkoH)3(MeOH)3] [6], and the tetradecanuclear cluster [Ni14
(OH)4(N3)8(pao)14(paoH)2(H2O)2](ClO4)2 [7] are some examples of
nickel compounds that have been synthesized and fully character-
ized, structurally and magnetically. In addition, heteropolynuclear
compounds such as [NiTb(mpko)2(NO3)3(mpkoH)], [Ni2Tb(mpko)6]
(NO3) and [Ni2Ln2(mpko)6(NO3)4] (Ln = Dy, Tb) have been obtained
from the mononuclear precursor [Ni(mpko)2(mpkoH)] in a com-
plex-as-ligand approach [8]. The high-nuclearity spin cluster
[Ni8Dy8O(OH)4(pao)28](ClO4)5(NO3) is a nice example of 3d/4f mol-
ecule that exhibits slow magnetization relaxation [9].
[Ni(NO3)2(mpkoH)2] (2) and [Ni(mpkoH)3](NO3)2Á½H2O (3Á½H2O)
Ni(NO3)2Á6H2O (1 mmol, 291 mg) and mpkoH (3 mmol, 408 mg)
were dissolved in 10 mL of methanol and stirred overnight at
ambient temperature. Afterwards, the orange solution was layered
with Et2O and allowed to stand undisturbed for a few weeks. Crys-
tals suitable for X-ray diffraction of 2 and 3Á½H2O were obtained
directly as violet plates and orange prisms in 25% and 70% yield,
respectively.
Selected IR bands for 2 [m
max/cmÀ1]: 3427 m, 3173 m, 3084 m,
3030 m, 2867 m, 1603 s, 1482 w (sh), 1438 vs, 1385 s, 1309 s,
1288 s, 1139 m, 1103 m, 1047 s, 966 w, 893 w, 821 w, 779 s,
748 w, 682 m, 645 w, 571 w, 468 w, 426 w. UV–vis (CH3NO2) for
Oximes can be easily deprotonated by addition of base and their
ligand properties can be significantly altered in this way. In fact, all
of the polynuclear complexes listed above were obtained when an
external base was added to the reaction media.
2 [k/nm (e
/MÀ1 cmÀ1)]: 563 (12), 780sh (8). Elemental analysis
(%) for NiC14H16N6O8: found, C 37,05, H 3,65, N 18,49; calculated,
C 36,96, H 3,54, N 18,47.
Selected IR bands for 3Á½H2O [
m
max/cmÀ1]: 3401 m (br), 3198 m
On the contrary, only the dinuclear complex [Ni2(SO4)2
(ppkoH)4] and the mononuclear complexes [Ni(ppkoH)3](SO4)
[10], [Ni(SO4)(mpkoH)(H2O)3]ÁH2O, [Ni(SO4)(mpkoH)2(H2O)]ÁH2O
[11], [NiBr2(mpkoH)2], [Ni(mpkoH)(mpko)(H2O)2](NO3) [12],
[NiCl2(paoH)2] and [NiCl2(mpkoH)2] [13] have been obtained in ab-
sence of added base. Interestingly, the latter two compounds were
recently found to be selective ethylene dimerization catalysts [13].
In spite of the several papers dedicated to the synthesis and
characterization of nickel oxime complexes, as far as we know,
no density functional theory (DFT) based calculations on their elec-
tronic spectral properties have been performed. In this study, we
report the synthesis, structural and spectroscopic characterization
of three novel nickel complexes bearing the mpkoH ligand, namely
[Ni(OOCPh)2(mpkoH)2] (1), [Ni(NO3)2(mpkoH)2] (2) and [Ni(mpkoH)3]
(NO3)2Á½H2O (3Á½H2O). Geometry optimization and population
analysis were performed by means of DFT calculations for the
further understanding of geometric and electronic properties of
the complexes. Electronic UV–vis spectra were simulated in the
TD-DFT framework to assign the origin of the absorption bands.
The previously reported [NiCl2(mpkoH)2] (4) was also theoretically
investigated for comparison purposes.
(br), 1600 s, 1481 w, 1384 s, 1329 m, 1258 w, 1162 w, 1139 w,
1100 w, 1063 w, 1037 s, 829 w, 781 s, 749 w, 681 m, 643 w, 570
w, 420 w. UV–vis (CH3OH) for 3Á½H2O [k/nm (
e
/MÀ1cmÀ1)]: 395
(55), 530 (6), 792 (5). Elemental analysis (%) for NiC21H24N8O9:
found, C 42.37, H 4.70, N 18.33; calculated, C 42.67, H 4.09, N
18.96.
[NiCl2(mpkoH)2] (4)
MpkoH (1 mmol, 136 mg) was added to a solution of NiCl2Á6H2O
(1 mmol, 238 mg) in 10 mL of methanol. The resulting green solu-
tion was stirred overnight at ambient temperature. By slow evap-
oration of the solvent, crystals of 4 were obtained as green prisms
in 75% yield. Selected IR bands [m
max/cmÀ1]: 3132 m, 3064 m, 3020
m, 2935 m, 2690 m, 1662 w, 1599 s, 1477 m, 1448 m, 1381 m,
1327 m, 1257 m, 1165 m, 1141 m, 1102 m, 1062 m, 1050 s,
1015 w, 970 m, 892 w, 783 s, 747 m, 704 s, 682 m, 642 m, 568
m, 478 w, 416 m. UV–vis (CH2Cl2) [k/nm (e
/MÀ1 cmÀ1)]: 575
(40). Elemental analysis (%) for NiC14H16N4O2Cl2: found, C 41.52,
H 3.99, N 13.62; calculated, C 41.84, H 4.01, N 13.94.
X-ray data collection and structure refinement
X-ray diffraction data were collected with a Bruker X8 Kappa
APEX II CCD diffractometer equipped with a graphite monochro-
Experimental
mator and a Mo K
were mounted on fine (ca. 100
and data intensities were measured using 0.5°
a
sealed X-ray tube (k = 0.71073 Å). Crystals
m) glass fibers with epoxy glue
and scans to
General procedures
l
x
u
The ligand mpkoH was prepared following a published proce-
dure [14]. All other reagents and solvents were purchased from
commercial sources and were used as received.
Elemental analyses for carbon, hydrogen and nitrogen were per-
formedona CarloErba EA1108 analyzer. IR spectrawere recordedon
a BOMEM MB 102 FT-IR spectrometer as KBr pellets, and UV–vis
spectra were measured on a Shimadzu UV-1603spectrophotometer.
achieve at least four times multiplicity of observation. SAINT [15]
was used to integrate the images using a narrow-frame algorithm
giving the intensity data and the final cell parameters. Scaling and
absorption correction using the multi-scan method was performed
using TWINABS [16] for 1, or SADABS [17] for 2 and 3. The struc-
tures were solved and refined using the Bruker SHELXTL Software
Package [18] on full-matrix least-squares using F2. Hydrogen atoms
on carbon atoms were positioned using geometric restraints.
Hydrogen atoms in hydroxyl groups were refined allowing free tor-
sional rotation and water molecules were refined as rigid groups.
For 1, the crystal was found to be non-merohedrally twinned in
two components with the same cell parameters. Both components
were integrated, the solution made with a crudely detwinned data-
set and the final refinement made on both components (TWIN/
HKLF 5). Crystal data, collection procedures and refinement results
are summarized in Table 1.
Syntheses
[Ni(OOCPh)2(mpkoH)2] (1)
NaOOCPh (1 mmol, 144 mg) and mpkoH (1 mmol, 136 mg)
were added to a solution of Ni(NO3)2Á6H2O (1 mmol, 291 mg) in
methanol (10 mL). The resulting green solution was stirred over-
night at ambient temperature. By slow evaporation of the solvent,
crystals of 1 suitable for X-ray diffraction were obtained as blue
prisms in 50% yield. Selected IR bands [m
max/cmÀ1]: 3108 w, 3061
w, 1845 s(br), 1600 s, 1548 s, 1480 m, 1395 vs, 1328 m, 1298 w,
1257 m, 1143 s, 1099 m, 1071 s, 1047 w, 1026 w, 835 m, 793 m,
783 m, 723 s, 688 m, 676 s, 568 m, 464 s. UV–vis (CH2Cl2) [k/nm
Theoretical calculations
All theoretical investigations have been undertaken at the den-
sity functional level of theory (DFT). To conduct studies on equilib-
rium geometries, optimizations starting from molecular structures
determined by X-ray crystallography were carried out, for which
(e
/MÀ1cmÀ1)]: 396 (81), 562 (21), 782sh (12). Elemental analysis
(%) for NiC28H26N4O6: found, C 58.08, H 4.95, N 9.79; calculated,
C 58.67, H 4.57, N 9.77.

L. Martínez et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 105 (2013) 439–445
441
Table 1
Crystal, X-ray collection and structure refinement data.
Compound
1
2
3Á½H2O
Chemical formula
C
28H26N4NiO6
C14H16N6NiO8
455.04
C42H50N16Ni2O19
1200.40
Molecular weight 573.24
Crystal size (mm3) 0.16 Â 0.23 Â 0.42 0.14 Â 0.15 Â 0.34 0.09 Â 0.33 Â 0.49
Crystal color and
Violet prism
Violet prism
Orange plate
habit
T (K)
Crystal system
Space group
100(1)
Triclinic
296(2)
Monoclinic
Ia
296(2)
Monoclinic
P21/c
ꢀ
P1
Cell dimensions (Å, °)
a
b
c
a
b
c
10.0149(4)
11.2619(5)
11.7052(5)
90.570(2)
92.413(2)
97.528(2)
1307.49(10)
2
8.2935(3)
14.9892(6)
14.9452(7)
11.9191(6)
29.1813(11)
15.7018(6)
90.668(2)
102.546(1)
Volume (Å3)
1857.76(13)
4
1.627
1.92, 30.62
28617
5330.9(4)
4
1.496
1.75, 30.55
65560
Z
qcalc (Mg mÀ3
hmin, hmax (°)
Reflections
collected
)
1.456
1.74, 30.58
76271
Rint, R
Tmin, Tmax
2.99%, 2.45%
0.654, 0.746
3.12%, 3.09%
0.650, 0.746
1.022
4.29%, 5.35%
0.672, 0.746
1.038
r
Goodness-of-fit on 1.034
F2
Fig. 1. Molecular structure and labeling for 1. Ellipsoids are at 50% probability
Parameters, Data
363, 15236
267, 5411
727, 16104
levels.
R1, wR2 [I > 2 (I)] 2.95%, 8.02%
r
2.90%, 6.66%
3.81%, 7.09%
À0.218, 0.357
5.87%, 16.57%
11.80%, 19.67%
À0.813, 1.075
R1, wR2 [all data]
3.28%, 8.20%
qmin, qmax (eÀ ÅÀ3
)
À0.314, 0.645
nickel center via their nitrogen atoms. The remaining positions
are occupied by two benzoato ligands for 1 (Fig. 1) or nitrato
ligands for 2 (Fig. 2) coordinating via one oxygen atom in a cis
arrangement, thereby forming a neutral coordination complex.
The bis-chelate complexes are necessarily enantiomorphic. The
the triplet state (S = 1) was considered. PBE1PBE [19] in combina-
tion with the so-called STMIDI basis set showed to adequately de-
scribe geometries of large complexes [20–22] with a very low
computational cost. The inclusion of PBE1PBE/STMIDI in this work
was decided intending to expand the range of application of this
methodology by testing its reliability in studying geometric and
electronic aspect of complexes bearing different donor and metal
atoms. The valence electrons for non-metal atoms in STMIDI were
treated with MIDI! [23], those for the metal being described by a
basis set (8s7p6d2f1g)/[6s5p3d2f1g] [24]. The core electrons were
replaced by Stuttgart effective core pseudopotentials [24,25]. The
nature of the stationary point was verified through a vibrational
analysis (no imaginary frequencies).
The Time-Dependent DFT (TD-DFT) methodology was em-
ployed to calculate 100 vertical spin-allowed (50 = 50 singlet-trip-
let) transitions in the gas phase and in solution by means of B3LYP
[26] in combination with LANL2DZ [27]. LANL2DZ and STMIDI take
scalar relativistic effects into account, especially important when
systems with transition metal atoms are studied [28]. The effect
of the solvent was described by the conductor-like polarizable con-
tinuum model (C-PCM) [29], which is a valid model to consider the
effects of the solvent as long as specific interactions between the
solute and the solvent are not of significant importance. Electronic
UV–vis spectra were simulated by means of the GaussSum soft-
ware [30] considering all calculated transitions. Natural population
analysis (NPA) calculations were performed with the NBO code
[31] included in the program package Gaussian 03, Rev. D.02
[32], which has been used for all theoretical studies reported in
this work.
crystallographic inversion center in 1 relates the
D form in the fig-
ure to the form, giving a racemic mixture with both enantiomers
K
present in the crystal structure. Compound 2 crystallizes in the
non-centrosymmetric space group Ia with a Flack parameter
x = 0.021(10) [33] – the alternative to Cc was chosen to minimize
the value of the cell angle b – indicating an enantiomorphically
pure crystal in which the
K form was observed for the selected
crystal. Spontaneous resolution of enantiomorphic coordination
compounds is well known [34]. In 3Á½H2O, there are two crystallo-
graphically independent cationic complexes in the asymmetric
unit, namely (I) and (II) (Fig. 3). In both of these, three neutral
mpkoH ligands are coordinated via their nitrogen atoms in a che-
lating fashion to the nickel center in the mer configuration. The
positive charges of the complex cations are balanced by four ni-
trate anions in the asymmetric unit. Additional electron density
roughly corresponding to an isolated oxygen atom was found
and modeled in the structure as a water molecule. Both complexes
shown are in the
centers generate the
racemic.
D
K
configuration. Crystallographic inversion
configurations and the crystal structure is
Verification of the bond distances and angles of the complexes
in the crystal structures with Mogul [35] showed no unusual
values in any complex. The largest values for the z-scores are
1.404 (C41AO42) for 1, 1.445 (Ni1AN12) for 2, 1.334 (Ni1AN12)
for 3-(I), and 1.789 (Ni2AN42) for 3-(II). Two nitrate anions in 3
show high z-score values most likely to unmodeled disorder as also
seen by their large anisotropic thermal parameters. Selected bond
distances and angles for 1, 2 and 3 are given in Table 2.
Results and discussion
The three crystal structures show hydrogen bonding of the
oxime hydroxyl hydrogen atom (Table 3). In 1 and 2, the hydrogen
bonding is intramolecular to the free oxygen atoms of the bound
anions. In 3, the oxime hydroxyl hydrogen atoms form hydrogen
bonds to the free nitrate anions.
Description of the structures
The molecular structures of 1, 2 and 3Á½H2O show six-coordi-
nated nickel(II) centers in slight distorted octahedral environ-
ments. In 1 and 2, two neutral mpkoH oxime ligands chelate the

442
L. Martínez et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 105 (2013) 439–445
for 1 and 2, respectively. The corresponding mean measured values
are 1.60 and 1.88 Å, and 177 and 165°, respectively. For 4, the
OHÁ Á ÁCl length and the OAHÁ Á ÁCl angle were found to be 1.84 Å
and 156°, the mean experimental values being 2.24 Å and 154°,
respectively [13].
Calculated (NPA) charges on selected atoms are displayed in
Table 5. The NPA result for nickel is smaller than the formal value
of +2 as a result of the electron-density donation process. The me-
tal ions feature charges ranging from +1.191 to +1.278, while the
non-metals carry charges in the range from À0.154 to À0.708.
For all complexes, the pyridine N atoms bear a higher charge than
the oxime N atoms. It is worth mentioning that the presence of p-
donor ClÀ ions in 4 results in a transferred density-charge which is
more important than in the other complexes.
Electronic spectra
The electronic spectrum of 3 simulated in the presence of the
solvent is displayed as an example in Fig. 4, which also includes
the experimental one. The spectra for 1, 2 and 4 are depicted in
the Supplementary Material (Figs. S1–S3). Calculated electronic
transitions in the presence of the solvent for all complexes are pre-
sented in Tables 6 (3) and S1–S3 (1, 2 and 4). In the high-energy
part of the spectra, only transitions with oscillator strength (f) lar-
ger than 0.0020 were considered. For all electron excitations, only
contributions larger than 15 % were taken into account. In all cases,
no significant shifts were obtained in going from the gas phase to
the solution.
One well-defined absorption band was simulated in the range
550–900 nm for all theoretically studied complexes. In all cases,
the maximum of the absorption band were simulated red-shifted
with respect to the experimental data, with displacements ranging
from +94 nm for 1 to +115 nm for 2. It can be noted a steady in-
crease in the wavelength of the simulated maxima as the coordina-
tion environment changes from N3O3 in 3 (634 nm) to N2O4 in 1
and 2 (656 and 678 nm respectively) to N2O2Cl2 in 4 (689 nm), in
line with the progressive decrease in the ligand field strength.
The experimental evidence suggests the presence of an absorption
band beyond 900 nm. Also a shoulder at about 800 nm (except for
4) is observed, which originates from the spin-forbidden transition
to the 1Eg singlet term. This finding is in line with the absorptive
features displayed by nickel(II) complexes in octahedral coordina-
tion environment [36]. Neither the lowest-energy band nor the
shoulder has been detected in the simulated spectrum.
Fig. 2. Molecular structure and labeling for 2. Ellipsoids are at 30% probability
levels.
Geometry optimization, electronic structure and NPA results
Geometry optimization gave rise to a minimum as stationary
point in all cases. All optimized structures exhibit the metal center
residing in a slight distorted octahedral environment. Selected
optimized parameters are presented in Table 4. The calculated
geometries are in good agreement with the one observed from
the crystallographic data.
Furthermore, it is worth mentioning that all optimized bis-che-
late complexes showed the presence of the seven-membered-H-
bond ring NOHÁ Á ÁOX (X@C in 1, N in 2) and NOHÁ Á ÁCl (4) in line
with the results from the X-ray diffraction studies. The PBE1PBE/
STMIDI methodology was specially employed to obtain a good
description of all the metric parameters involving the metal ion.
In spite of this, PBE1PBE/STMIDI also leads the calculated bond
lengths and angles in the rings —in the absence of counterions
and crystal-packing-forces effects— to reasonably match the
experimental data. For instance, OHÁ Á ÁO distances of 1.30 and
1.48 Å and OAHÁ Á ÁO angles of 178° and 168° have been calculated
Fig. 3. Molecular structure and labeling for the cationic complexes [Ni(mpkoH)3]2+ (I) and (II) at their relative positions in 3Á½H2O. Ellipsoids are at 30% probability levels.

L. Martínez et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 105 (2013) 439–445
443
Table 2
Table 4
Selected bond lengths (Å) and bond angles (°) for complexes 1, 2 and 3Á½H2O.
Selected geometric parameters as obtained by employing PBE1PBE/STMIDI
(T = 298 K).
Bond lengths for 1
Ni(1)AO(31)
Ni(1)AO(41)
Ni(1)AN(12)
2.0442(8)
2.0632(7)
2.0662(9)
Ni(1)AN(21)
Ni(1)AN(11)
Ni(1)AN(22)
2.0670(8)
2.0793(8)
2.1003(8)
Complex Bond lengths (Å)
Angles (°)
1
NiAN(11) 2.080
NiAN(12) 2.102
NiAN(21) 2.080
NiAN(22) 2.102
NiAO(31) 2.020
NiAO(41) 2.020
N(11)ANiAN(12) 77.5
N(11)ANiAN(21) 161.5
N(11)ANiAN(22) 90.6
N(11)ANiAO(31) 103.5
N(11)ANiAO(41) 89.9
O(31)ANiAO(41) 87.7
Bond angles for 1
O(31)ANi(1)AO(41)
O(31)ANi(1)AN(12)
O(41)ANi(1)AN(12)
O(31)ANi(1)AN(21)
O(41)ANi(1)AN(21)
N(12)ANi(1)AN(21)
O(31)ANi(1)AN(11)
O(41)ANi(1)AN(11)
86.56(3)
174.23(3)
89.45(3)
90.52(3)
102.92(3)
94.43(3)
98.14(3)
89.50(3)
N(12)ANi(1)AN(11)
N(21)ANi(1)AN(11)
O(31)ANi(1)AN(22)
O(41)ANi(1)AN(22)
N(12)ANi(1)AN(22)
N(21)ANi(1)AN(22)
N(11)ANi(1)AN(22)
77.65(3)
165.30(3)
93.09(3)
179.56(3)
90.92(3)
76.82(3)
90.80(3)
2
NiAN(11) 2.065
NiAN(12) 2.079
NiAN(21) 2.065
NiAN(22) 2.079
N(11)ANiAN(12) 77.6
N(11)ANiAN(21) 173.0
N(11)ANiAN(22) 97.8
N(11)ANiAO(1)
N(11)ANiAO(4)
O(1)ANiAO(4)
95.8
89.3
84.0
NiAO(1)
NiAO(4)
2.025
2.025
Bond lengths for 2
Ni(1)AN(12)
Ni(1)AN(21)
2.0521(19)
2.059(2)
2.0610(19)
Ni(1)AN(11)
Ni(1)AO(4)
Ni(1)AO(1)
2.069(2)
2.0701(17)
2.074(2)
3Á½H2O
NiAN(12) 2.076
NiAN(11) 2.066
NiAN(22) 2.102
NiAN(21) 2.066
NiAN(32) 2.107
NiAN(31) 2.068
N(12)ANiAN(11) 77.4
N(12)ANiAN(22) 96.0
N(12)ANiAN(21) 92.4
N(12)ANiAN(32) 96.0
N(12)ANiAN(31) 171.0
N(32)ANiAN(31) 76.7
Ni(1)AN(22)
Bond angles for 2
N(12)ANi(1)AN(21)
N(12)ANi(1)AN(22)
N(21)ANi(1)AN(22)
N(12)ANi(1)AN(11)
N(21)ANi(1)AN(11)
N(22)ANi(1)AN(11)
N(12)ANi(1)AO(4)
N(21)ANi(1)AO(4)
96.60(8)
94.67(8)
77.74(9)
77.19(6)
169.88(8)
94.66(8)
86.84(8)
102.55(8)
N(22)ANi(1)AO(4)
N(11)ANi(1)AO(4)
N(12)ANi(1)AO(1)
N(21)ANi(1)AO(1)
N(22)ANi(1)AO(1)
N(11)ANi(1)AO(1)
O(4)ANi(1)AO(1)
178.43(9)
85.23(8)
172.67(9)
86.53(7)
92.47(8)
100.60(9)
86.01(9)
4a
NiAN(1)
NiAN(2)
NiAN(3)
NiAN(4)
NiACl(1)
NiACl(2)
2.053 (2.048)
N(1)ANiAN(2)
N(1)ANiAN(3)
N(1)ANiAN(4)
N(1)ANiACl(1)
76.3 (76.91)
164.8 (166.64)
93.2 (93.3)
103.4 (101.72)
86.4 (88.69)
100.9 (93.560)
2.111 (2.095)
2.053 (2.039)
2.111 (2.101)
2.312 (2.4236) N(1)ANiACl(2)
2.312 (2.4039) Cl(1)ANiACl(2)
Bond lengths for 3Á½H2O
Ni(1)AN(12)
Ni(1)AN(22)
Ni(1)AN(31)
Ni(1)AN(11)
a
Atom numbering and experimental values in parentheses taken from Ref. [13].
2.0682(18)
2.0693(19)
2.0761(19)
2.0788(19)
2.0822(19)
2.0866(19)
Ni(2)AN(42)
Ni(2)AN(61)
Ni(2)AN(41)
Ni(2)AN(51)
Ni(2)AN(62)
Ni(2)AN(52)
2.0575(18)
2.0631(18)
2.0694(18)
2.0765(18)
2.0943(18)
2.0948(17)
Table 5
Ni(1)AN(32)
Ni(1)AN(21)
Selected atomic charges from the NPA analysis by using PBE1PBE/STMIDI (T = 298 K).
Bond angles for 3Á½H2O
N(12)ANi(1)AN(22)
N(12)ANi(1)AN(31)
N(22)ANi(1)AN(31)
N(12)ANi(1)AN(11)
N(22)ANi(1)AN(11)
N(31)ANi(1)AN(11)
N(12)ANi(1)AN(32)
N(22)ANi(1)AN(32)
N(31)ANi(1)AN(32)
N(11)ANi(1)AN(32)
N(12)ANi(1)AN(21)
N(22)ANi(1)AN(21)
N(31)ANi(1)AN(21)
N(11)ANi(1)AN(21)
N(32)ANi(1)AN(21)
Complex Ni
N(12)
N(22)
N(11)
N(21)
X(1)
X(2)
89.76(7)
172.16(8)
96.73(7)
77.32(7)
96.52(8)
97.51(7)
97.39(7)
171.74(8)
76.48(7)
89.10(7)
96.07(7)
77.18(8)
89.68(7)
171.01(8)
97.87(8)
N(42)ANi(2)AN(61)
N(42)ANi(2)AN(41)
N(61)ANi(2)AN(41)
N(42)ANi(2)AN(51)
N(61)ANi(2)AN(51)
N(41)ANi(2)AN(51)
N(42)ANi(2)AN(62)
N(61)ANi(2)AN(62)
N(41)ANi(2)AN(62)
N(51)ANi(2)AN(62)
N(42)ANi(2)AN(52)
N(61)ANi(2)AN(52)
N(41)ANi(2)AN(52)
N(51)ANi(2)AN(52)
N(62)ANi(2)AN(52)
169.71(7)
77.43(7)
99.69(7)
94.74(7)
89.86(7)
166.57(7)
93.25(7)
76.84(7)
90.91(7)
100.51(7)
96.71(7)
93.28(7)
92.66(7)
77.28(7)
169.94(7)
1a
2b
3c
4d
1.278 À0.502 À0.502 À0.154 À0.154 À0.708 À0.708
1.242 À0.520 À0.520 À0.166 À0.166 À0.578 À0.578
1.245 À0.525 À0.546 À0.224 À0.219 À0.538 À0.231
1.191 À0.481 À0.481 À0.163 À0.163 À0.624 À0.624
a
b
c
X(1) = O(31); X(2) = O(41).
X(1) = O(1); X(2) = O(4).
X(1) = N(32); X(2) = N(31).
N(12), N(22), N(11), N(21), X(1) and X(2) corresponds to N(1), N(2), N(3), N(4),
d
Cl(1) and Cl(2) respectively, in Ref. [13].
Table 3
Hydrogen bonds for 1, 2 and 3Á½H2O (distances in Å and angles in °).
DAHÁ Á ÁA
d(DAH)
d(HÁ Á ÁA)
d(DÁ Á ÁA)
\(DHA)
1
O(11)AH(11)Á Á ÁO(32)
O(21)AH(21)Á Á ÁO(42)
2
0.91(2)
0.904(19)
1.58(2)
1.616(19)
2.4848(11)
2.5190(11)
178.3(19)
176.0(18)
O(11)AH(11)Á Á ÁO(3)
O(21)AH(21)Á Á ÁO(6)
3Á½H2O
0.82
0.82
1.88
1.88
2.686(3)
2.677(3)
166.6
162.5
O(11)AH(11)Á Á ÁO(202)a
O(11)AH(11)Á Á ÁO(203)a
O(21)AH(21)Á Á ÁO(203)
O(31)AH(31)Á Á ÁO(202)a
O(41)AH(41)Á Á ÁO(101)
O(41)AH(41)Á Á ÁO(102)
O(51)AH(51)Á Á ÁO(302)b
O(51)AH(51)Á Á ÁO(303)b
O(61)AH(61)Á Á ÁO(102)
0.82
0.82
0.82
0.82
0.82
0.82
0.82
0.82
0.82
2.45
2.08
2.07
1.96
1.98
2.54
2.10
2.19
1.83
3.210(3)
2.810(3)
2.757(3)
2.689(3)
2.733(3)
3.190(3)
2.854(3)
2.818(4)
2.626(3)
154.3
148.9
141.8
146.9
152.3
136.6
151.9
133.1
162.1
Fig. 4. Visible electronic absorption spectrum of 3 (broken line) calculated in
CH3OH by means of B3LYP/LANL2DZ (the one experimentally observed in solid
line).
a
Symmetry operation: x, Ày + ½, z À ½.
b
Symmetry operation: Àx + 1, y À ½, Àz + 3/2.

444
L. Martínez et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 105 (2013) 439–445
Table 6
Selected orbital excitations calculated for 3 in MeOH employing TD-B3LYP in combination with the LANL2DZ basis set.
Most important orbital excitationsa,b
f
kcalc. (nm)
kexp. (nm)
Originc
HÀ14(b) ? L+4(b), HÀ3(b) ? L+3(b), HÀ3(b) ? L+4(b)
HÀ11(b) ? L+4(b), HÀ10(b) ? L+4(b), HÀ6(b) ? L+4(b)
HÀ11(b) ? L+3(b), HÀ3(b) ? L+3(b)
0.0001
0.0001
0.0003
0.0002
0.1770
0.3168
0.1114
641.2
626.4
425.5
421.0
281.5
275.5
223.7
530
MLMLCT
395
MLMLCT
LLCT
HÀ12(b) ? L+4(b), HÀ4(b) ? L+4(b)
H(
HÀ4(
HÀ11(b) ? L(b)
a) ? L+2(a), H(b) ? L+2(b)
Not observed
Not observed
a) ? L+2(a), HÀ2(b) ? L+2(b)
LLCT
a
b
c
Only those excitation with contribution larger than 15% were considered.
H = HOMO; L = LUMO.
See in text for acronyms employed in assigning origin of absorption bands.
In going to the blue-part of the spectrum, a second low-inten-
for 3 has its origin in excitations from the HOMOÀ14(b), HOMO-
À11(b), HOMOÀ10(b), HOMOÀ6(b) and HOMOÀ3(b), the LU-
MO+3(b) and LUMO+4(b) being the destination MOs. The MOs
implicated (Fig. 5) exhibit an important degree of charge delocal-
ization over the nickel ion and the ligands. The electronic transi-
tions then involve the electron transfer from HOMO orbitals that
are strongly mixed metal-ligand in character, to also strongly
mixed character LUMO orbitals. This kind of so-called MLMLCT
or metal-ligand-to-metal-ligand charge transfer transitions have
been described in other transition metal complexes [20,38] and ex-
plains the origin of the band at 530 nm observed in the spectrum of
3. The situation does not differ significantly for the other com-
plexes. In all of them, despite the different sets of donor atoms,
an important charge delocalization among the metal center and
the ligands can also be observed in those MOs implicated in the
electronic transitions (Figs. S6–S8). Therefore, the origin of the
band at the red region of the visible spectra can be ascribed to a
MLMLCT in all cases.
sity absorption band was experimentally identified for 1 and 3 at
396 and 395 nm, respectively. In both cases, the simulation also
leads to a bathochromic shift of +34 and +28 nm, respectively.
The corresponding bands for 2 and 4 are not seen, probably hided
under the higher-absorptivity bands at this region of the spectrum.
For all complexes, the simulation also accounted for bands at
the UV region (Figs. S4 and S5), which have not been detected
experimentally due to solvent-absorption effects. In such cases,
the theoretical results play an important role for the further under-
standing of the absorptive features of the complexes theoretically
studied in all range of energy experimentally attainable. In all sim-
ulated spectra, two intense absorption bands have been found at
about 280 nm and 220 nm. Their position and intensity show some
degree of dependence on the complex, in some case being simu-
lated as asymmetric bands due to the presence of shoulders [37].
The analysis of MOs is very important to gain insight into the
origin of absorption bands. The absorption simulated at 634 nm
Fig. 5. HOMO- and LUMO-derivatives of 3 as obtained by employing B3LYP/LANL2DZ, involved in the origin of the shoulder experimentally observed at the low-energy part
of the visible spectrum.

L. Martínez et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 105 (2013) 439–445
445
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Appendix A. Supplementary material
Crystallographic data for the structural analysis have been
deposited with the Cambridge Crystallographic Data Centre, CCDC
reference numbers 861664–861666. A copy of this information
may be obtained via http://www.ccdc.cam.ac.uk, or from the
Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge
CB2 1EZ, UK; fax: (+44) 1223-336-033; or e-mail: deposit@ccdc.
cam.ac.uk. Supplementary data associated with this article can be
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a
a