Versatile Reactivity and Theoretical Evaluation of Mono- and Dinuclear Oxidovanadium(V) Compounds of Aroylazines: Electrogeneration of Mixed-Valence Divanadium(IV,V) Complexes

Article abstract of DOI:10.1021/acs.inorgchem.6b01001

The substituted hydrazones H₂L^1-4 (L^1-4 = dibasic tridentate ONO^2- donor ligands) obtained by the condensation of 2-hydroxy-1-naphthaldehyde and 2-aminobenzoylhydrazine (H₂hnal-abhz) (H₂L

Full text of DOI:10.1021/acs.inorgchem.6b01001

Article
pubs.acs.org/IC
Versatile Reactivity and Theoretical Evaluation of Mono- and
Dinuclear Oxidovanadium(V) Compounds of Aroylazines:
Electrogeneration of Mixed-Valence Divanadium(IV,V) Complexes
Subhashree P. Dash,† Satabdi Roy, Monalisa Mohanty, M. Fernanda N. N. Carvalho,
,‡
†
†
§
§
̃
Maxim L. Kuznetsov, Joao Costa Pessoa,* Amit Kumar, Yogesh P. Patil, Aurel
́
ien Crochet,¶
,§
§,∥
⊥
,†
and Rupam Dinda*
†
Department of Chemistry, National Institute of Technology, Rourkela 769008, Odisha, India
‡
§
∥
Department of Chemistry, Indira Gandhi Institute of Technology, Sarang, Parjang, Dhenkanal 759146, India
Centro de Química Estrutural, Instituto Superior Tecnico, Universidade de Lisboa, Avenida Rovisco Pais, 1049-001 Lisboa, Portugal
Centre for Nano and Material Sciences, Jain University, Jain Global Campus, Jakkasandra Post, Bangalore 562112, India
́
⊥
Department of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore 560012, India
¶
Department of Chemistry, Fribourg Center for Nanomaterials, University of Fribourg, CH-1700 Fribourg, Switzerland
S Supporting Information
*
ABSTRACT: The substituted hydrazones H L (L1−4 = dibasic
1
−4
2
2−
tridentate ONO donor ligands) obtained by the condensation of
-hydroxy-1-naphthaldehyde and 2-aminobenzoylhydrazine
H hnal-abhz) (H L ) , 2-hydroxy-1-naphthaldehyde and 2-
2
(
1
2 2
2
hydroxybenzoylhydrazine (H hnal-hbhz) (H L ), 2-hydroxy-1-
2
2
3
acetonaphthone and benzoylhydrazine (H han-bhz) (H L ), or 2-
2
2
hydroxy-1-acetonaphthone and 2-aminobenzoylhydrazine (H han-
2
4
abhz) (H L ) are prepared and characterized. Reaction of
2
1−4
ammonium vanadate with the appropriate H L
results in the
2
V
1−4
formation of oxidoethoxidovanadium(V) [V O(OEt)(L )] (1−
) complexes. All compounds are characterized in the solid state
4
1
13
and in solution by spectroscopic techniques (IR, UV−vis, H, C,
and 51V NMR, and electrospray ionization mass spectrometry).
Single-crystal X-ray diffraction analysis of 1, 3, and 4 confirms the coordination of the corresponding ligands in the dianionic
2
−
V
(
ONO ) enolate tautomeric form. In solution, the structurally characterized [V O(OEt)(L)] compounds transform into the
V
1
13
51
monooxido-bridged divanadium(V,V) [(V OL) -μ-O] complexes, with the processes being studied by IR and H, C, and
NMR. The density functional theory (DFT) calculated Gibbs free energy of reaction 2[V O(OEt)(L )] + H O ⇆ [(V OL ) -μ-
V
2
V
4
V
4
2
2
−1
O] + 2EtOH is only 2−3 kcal mol , indicating that the dinuclear complexes may form in a significant amount. The
V
IV
red
electrochemical behavior of the complexes is investigated by cyclic voltammetry, with the V −V E
values being in the range
1/2
IV
V
0
.27−0.44 V (vs SCE). Upon controlled potential electrolysis, the corresponding (L)(O)V −O−V (O)(L) mixed-valence
V
species are obtained upon partial reduction of the [(V OL) -μ-O] complexes formed in solution, and some spectroscopic
2
characteristics of these dinuclear mixed-valence complexes are investigated using DFT calculations and by electron paramagnetic
IV
V
resonance (EPR), with the formation of V −O−V species being confirmed by the observation of a 15-line pattern in the EPR
spectra at room temperature.
INTRODUCTION
Vanadium complexes possess versatile oxidation states (from
III to +V). Among these, +IV and +V are the most common
■
−
Interest in the coordination chemistry of vanadium, with
1
1a,b,d,2
and can be accessed easily under aerobic conditions. A good
number of structural, spectroscopic, and solution studies of
such vanadium compounds, in which the element is present in
these high oxidation states under assorted N/O-donor
particular emphasis on its biological, structural,
and
3
−6
catalytic properties,
has increased over the past 2 decades.
Prospective therapeutic applications of vanadium compounds,
namely, for the treatment of Diabetes mellitus and cancer and
more recently promising antiamoebic activity against Entamoe-
ba histolytica as well as antitrypanosomal activity against
8a−c,g,11
environments, have been reported.
1c,e
Trypanosoma cruzi, stimulated research to better understand
Received: April 21, 2016
7
−10
the behavior of vanadium complexes in solution.
©
XXXX American Chemical Society
A
DOI: 10.1021/acs.inorgchem.6b01001
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Scheme 1. Schematic Diagram of the Synthesis of Monooxidoalkoxidovanadium(V) [V O(OEt)(L1−4)] (1−4) and the Various
V
Pathways through Which the Compounds May Be Transformed in Solution
While the solid-state structural aspects and reactivity of the
ligands may be considered as azine analogues. We also show
that the transformation of the structurally characterized
monooxidoalkoxidovanadium(V) compounds [V O(OEt)(L)]
V
+
well-known vanadium(V) complexes containing V O2 units
have been satisfactorily exposed, not so much is known of their
V
1b,12
solution behavior.
Subjects of interest include the stability
in solution lead to the corresponding monooxido-bridged
V
12b
of mononuclear species in solution, possibility of formation of
divanadium(V,V) compounds [(V OL) -μ-O]. The mono-
2
1
2a,e
10,12b,c
oxido-bridged divanadium(IV,V) mixed-valence species are also
obtained by controlled potential electrolysis of the correspond-
ing divanadium(V,V) precursors in solution. These mixed-
valence species are characterized by IR, electron paramagnetic
resonance (EPR), and 51V NMR, and their formulation was
corroborated by density functional theory (DFT) calculations.
Theoretical calculations were also carried out for most
complexes reported to support and substantiate the measured
structural and spectroscopic properties. We should highlight
coordination isomers,
formation of di-
or polynuclear
1
2d
complexes, and electron-transfer capabilities of mono- and
1
0,12b
dinuclear species.
Mixed-valence metal complexes have received much
1
3
attention, and one of the relevant aspects in this area
includes an understanding of the role of the ligand environment
in the extent of electron localization/delocalization among the
metal centers and the potential use of mixed-valence systems in
molecular electronics and molecular computing. The
chemistry of mixed-valence vanadium incorporating O/N-
coordinating ligands is of enduring interest. In contrast to the
well-known oxidovanadium(IV or V) complexes containing
V O or V O units,
1
4
15a
that, in agreement with Young, we are designating here, as
3
+
15
mixed-valence V O3 compounds, both those that correspond
2
IV
V
to complexes with localized V and V centers, exhibiting 8-
line EPR spectra, and those where the unpaired electron is
delocalized throughout the two V nuclei, exhibiting a 15-line
EPR spectra due to the effective hyperfine coupling of the two
IV 2+
V
3+
15b,16
relatively few mixed-oxidation
(
IV,V) complexes have been isolated and structurally
characterized. In the context of the present study, it is relevant
to mention that, although the chemistry of mixed-valence
divanadium(IV,V) complexes generated through chemical
51
V centers. It is demonstrated that spin localization/
delocalization takes place between two V atoms, and, hence,
a different pattern of EPR spectra for various compounds (15-
line vs 8-line) is determined by the geometry of the V−O−V
fragment (linear vs bent).
15,17
synthesis is reasonably developed,
there are only a few
reported examples of compounds isolated through electro-
1
2b,15d,18
synthesis.
We describe herein the synthesis and characterization of
mononuclear monoalkoxido-bound monooxidovanadium(V)
complexes (1−4) of the ligands derived from the substituted
EXPERIMENTAL SECTION
Materials and Methods. Elemental analyses were carried out on a
PerkinElmer C, H, and N analyzer. IR spectra of solid compounds
[V O(OEt)(L)] (1−4) as KBr pellets and in a CHCl solution in a
NaCl cell were recorded on a PerkinElmer 783 spectrometer. H
■
1
−4
1−4
1−4
V
hydrazones H L (H L = aroylhydrazones, where L act
2
2
3
1
as dibasic tridentate ONO-donor ligands; Scheme 1); these
B
DOI: 10.1021/acs.inorgchem.6b01001
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
NMR spectra were recorded with a Bruker ADVANCE DPX 300 MHz
Table 1. Crystal Data and Refinement Details for 1, 3, and 4
51
spectrometer using SiMe as an internal standard. V NMR spectra
4
were obtained on a Bruker Avance III 400 MHz spectrometer in
1
3
4
deuterated acetonitrile:dimethylsulfoxide (MeCN-d :DMSO-d ), and
1
6
empirical formula
Mw
C
20
H
18
N
3
O
V
4
C
21
H
19
N
2
O
V
4
C H N O V
21 20 3 4
chemical shift 51V values (δ ) were referenced relative to neat V OCl
V
V
3
415.31
293(2)
414.32
200(2)
429.34
200(2)
0.71073
as the external standard. Mass spectrometry (MS) spectra were
obtained on a SQ-300 MS instrument operating in the electrospray
ionization (ESI) negative mode. Electronic spectra were recorded on a
Shimadzu UV−vis recording spectrophotometer. Electrochemical
studies were made by cyclic voltammetry (CV) and controlled
potential electrolysis (CPE) at room temperature under a nitrogen
atmosphere using a PC-controlled VoltaLab PST 050 potentiostat.
Measurements were made in a three-compartment cell provided with
platinum wire (working and auxiliary) and silver wire (reference)
electrodes using tetrabutylammonium tetrafluoroborate (0.10 M)/
temperature (K)
wavelength (Å)
cryst syst
space group
unit cell dimens
a (Å)
0.71073
0.71073
monoclinic
monoclinic
monoclinic
P2 /n
P2 /n
P2 /n
1
1
1
7.5992(7)
10.0073(19)
15.0465(18)
13.023(2)
90
10.305(2)
10.502(2)
18.603(3)
90
b (Å)
12.7639(11)
19.5684(17)
90
c (Å)
α (deg)
CH CN as the supporting electrolyte. Potentials were referred to a
3
β (deg)
90.373(2)
90
91.581(15)
90
92.716(16)
90
saturated calomel electrode (SCE) using the ferrocene/ferrocenium
γ (deg)
5
0/+
couple ([Fe(η -C H ) ] ; E1/2 = 0.382 V) as the internal standard.
3
5
5 2
volume (Å )
1898.0(3)
4
1960.2(6)
4
2011.0(6)
4
Electron paramagnetic resonance (EPR) spectra were recorded with a
Bruker ESP 300E X-band spectrometer either at 77 K or at room
temperature, and the spin Hamiltonian parameters were obtained by
simulation of the spectra with the computer program of Rockenbauer
Z
density (calcd)
1.453
1.404
1.418
−3
(
Mg m
)
abs coeff (mm−1) 0.554
0.535
0.526
888
19
et al. The calibrant was 2,2-diphenyl-1-picrylhydrazyl (g: 2.0037).
Crystal Structure Determinations. Single crystals of compounds
were mounted on a Bruker Smart Apex CCD diffractometer (1)
equipped with a graphite monochromator and a Stoe IPDS 2
diffractometer (3 and 4) equipped with an Oxford Cryosystem open-
flow cryostat and a Mo Kα radiation (λ = 0.71073 Å). The
crystallographic data and details of refinement are given in Table 1.
The unit cell dimensions and intensity data were measured at 293(2)
K (1) and 200 (2) K (3 and 4). Absorption correction was partially
F(000)
856
856
θ range for data
collection (deg)
1.90−26.00
2.07−25.00
2.192−24.995
reflns collected
indep reflns
19292
24699
25250
3732 [R(int) = 3452 [R(int) = 3549 [R(int) =
.0788] 0.0843] 0.1342]
0
completeness to θ 100.0 100.0 100.0
25.00° (%)
=
2
0
refinement
method
full-matrix least2
full-matrix least2
full-matrix least
squares on F
integrated in the data reduction procedure for crystals of 3 and 4.
2
squares on F
squares on F
The intensity data were corrected for Lorentz, polarization, and
absorption effects. Absorption corrections were applied using
SADABS, and the structures were solved by direct methods using
data/restraints/
param
GOF on F2
3732/1/262
3452/48/255
3549/0/265
1.045
1.043
0.920
21
the program SHELXS-97 and refined using least squares with the
21
final R indices [I > R1 = 0.0939,
σ(I)] wR2 = 0.2142
R1 = 0.0382,
wR2 = 0.1034
R1 = 0.0497, wR2
= 0.1164
SHELXL-97 software program. H atoms were either found or placed
in calculated positions and isotropically refined using a riding model.
The non-H atoms were refined anisotropically.
2
R indices (all data) R1 = 0.1668,
R1 = 0.0512,
wR2 = 0.1091
R1 = 0.1224, wR2
= 0.1521
wR2 = 0.2584
CV and CPE. The redox properties of complexes 1−4 were studied
by CV, and the potentials were measured versus SCE using ferrocene
as the internal standard. CPE was carried out at the potential of the
reduction process (selected according to CV data) using a typical
procedure: the addition of a weighed amount of complex [1 (5.0 mg),
largest diff peak
0.589 and
0.230 and
0.257 and −0.365
and hole (e Å−3)
−0.319
−0.287
structures to prove the location of correct minima (no imaginary
frequencies) and to estimate the thermodynamic parameters, with the
latter being calculated at 25 °C.
Magnetic shielding was calculated for the equilibrium geometries
using the GIAO method at the IEFPCM-B3P86/6-311+G(2d,p)//6-
2
(5.0 mg), 3 (7.0 mg), and 4 (8.0 mg)] to the electrolyte solution (10
mL; NBu BF /CH CN, 0.10 M, under a nitrogen atmosphere),
4
4
3
waiting ca. 1 h, and then proceeding with the chronocoulometric
process until it reached the number of coulombs (Q) corresponding to
transfer of half an electron per mole of complex. Then, a cyclic
voltammogram was obtained, a sample of the electrolyzed solution was
collected and immediately transferred to an EPR tube (previously
purged with nitrogen gas), and the solution was frozen by emersion of
the tube in liquid nitrogen.
2
7
51
31G(d) level. The V chemical shifts were estimated relative to
V
V OCl calculated at the same level of theory.
3
5
1
The V hyperfine coupling constants were estimated at the single-
point calculations using the BHandHLYP functional and 6-311G*
basis set for all atoms on the basis of the equilibrium geometry
obtained at the B3P86/6-31G*(V-ECP) level of theory. The
anisotropic 51V hyperfine coupling constants A , A , and A were
Computational Details. Full geometry optimization of the
molecular structures was carried out at the DFT level of theory
x
y
z
22a
using the B3P86 functional with the help of the Gaussian09 program
estimated as the sum of the isotropic Fermi contact term and
corresponding dipolar hyperfine interaction term. It must be
23
28
package. This functional was found to be sufficiently accurate for
51
theoretical studies of structural parameters and V NMR chemical
emphasized that for a vanadium(IV) species the hyperfine coupling
constant (A) values may be negative, but in the literature, normally it is
their absolute value that is reported. This simplification was also
adopted in this work. Previously, it was found that half-and-half
functionals such as BHandHLYP demonstrate better performance in
calculations of the EPR parameters than many other hybrid functionals
because of more accurate estimates of the Fermi contact term.
For the dinuclear vanadium(V,V) compounds [(V OL) -μ-O], two
isomers were calculated, i.e., the trans isomer with the opposite
positions of the VO bonds relative to the V−O−V bridge and the
gauche isomer with the OV···VO torsion angle of 78−103°. The
latter isomer is thermodynamically more stable, and mainly structures
of this type are discussed below.
24
shifts of various vanadium complexes. For some calculations,
22a,c
22d
22e
B3LYP,
M06,
and TPSSH
functionals were also used.
Optimization was carried out in both gas and solution phases. In
25
the latter case, the IEFPCM solvation model with the UAKS
molecular cavity and dispersion, repulsion, and cavitation contribu-
tions were applied, and DMSO, ethanol (EtOH), or MeCN were used
as the solvent. No symmetry operations were applied for any of the
structures calculated. Geometry optimization was carried out using a
relativistic Stuttgart pseudopotential, which describes 10 core
electrons, and the appropriate contracted basis set (8s7p6d1f)/
28a−c
V
2
26
[
6s5p3d1f] for the V atom and the 6-31G(d) basis set for other
atoms. The Hessian matrix was calculated analytically for all optimized
C
DOI: 10.1021/acs.inorgchem.6b01001
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
1
−4
Preparation of Compounds H L . The substituted hydrazones
170.93, 164.64, 164.46, 164.18, 149.78, 149.65, 148.26, 148.11, 135.71,
135.52, 135.15, 132.91, 132.78, 132.65, 132.41, 130.97, 130.57, 129.44,
129.34, 128.82, 128.54, 128.48, 124.71, 124.35, 122.45, 122.11, 119.90,
2
1
2
3
H hnal-abhz (H L ), H hnal-hbhz (H L ), and H han-bhz (H L ),
and H han-abhz (H L ) were prepared by similar procedures; we
describe here the preparation of H L : a solution of 2-amino-
benzoylhydrazine (1.51 g, 10.0 mmol) in EtOH (20 mL) was added to
a filtered solution of 2-hydroxy-1-naphthaldehyde (1.72 g, 10.0 mmol)
in EtOH (15 mL) with stirring. The obtained mixture was refluxed and
stirred for 2 h. The resulting pale-yellow compounds were filtered,
washed with EtOH, and dried over fused CaCl . Elemental analysis
results and NMR ( H and C) and IR data for all compounds
corroborate with their formulation.
2
2
2
2
2
2
4
2
2
1
119.03, 116.39, 115.17, 111.82, 111.67, 111.05, 110.36, 81.80, 56.52,
2
1
19.03, 18.84. H NMR (400 MHz, DMSO-d + EtOH): δ 9.80 (s, 1H,
6
HCN), 8.49−6.57 (m, 10H, aromatic), 5.73−5.54 (m, 2H,
CH (OEt)), 4.33 (s, 20H, NH ), 3.49−3.44 (q, 46H, CH (EtOH)),
2
2
2
1
3
1.60−1.57 (t, 3H, CH (OEt)), 1.09−1.05 (t, 67H, CH (EtOH)).
NMR (100 MHz, DMSO-d + EtOH): δ 171.06, 164.22, 149.65,
C
3
3
2
6
1
13
148.15, 135.04, 132.88, 132.27, 130.54, 129.23, 128.54, 128.39, 124.24,
121.94, 119.79, 116.31, 115.08, 111.65, 111.07, 81.70, 56.54, 18.75,
1
51
H hnal-abhz (H L ). Yield: 65%. Anal. Calcd for C H N O : C,
0.81; H, 4.95; N, 13.76. Found: C, 70.77; H, 4.98; N, 13.75. Selected
IR peaks with proposed assignments (KBr pellet, νmax/cm ): 3472
18.64. V NMR (DMSO-d /MeCN-d1 (1:10)): δ −548 (85.0%),
2
2
18 15
3
2
6
7
−576 (15.0%).
−1
V
[V O(OEt)(hnal-hbhz)] (2). Yield: 65%. Anal. Calcd for
ν(O−H); 3367 ν(NH ) ; 3201 ν(NH ) ; 3037 ν(N−H); 1637 ν(C
C H N O V: C, 57.70; H, 4.12; N, 6.73. Found: C, 57.72; H,
2
as
2
s
20 17
2
5
1
O); 1555 ν(CN). H NMR (400 MHz, DMSO-d ): δ 12.97 (s, 1H,
4.08; N, 6.77. Selected IR peaks with proposed assignments (KBr
6
−1
naphthyl−OH), 11.95 (s, 1H, NH), 9.47 (s, 1H, HCN), 8.18−6.63
pellet, νmax/cm ): 3442 ν(O−H); 1597 ν(CN); 1254 ν(C−
13
−1
(
m, 10H, aromatic), 6.61 (s, 2H, NH ). C NMR (100 MHz, DMSO-
O)enolic; 996 ν(VO). IR (CHCl , cm ): 1006, 980 (VO); 823
2
3
−1
−1
d6): δ 165.12, 158.33, 150.93, 146.33, 133.18, 132.91, 132.07, 129.45,
(V−O−V). UV−vis [CHCl ; λ , nm (ε, M cm )]: 425 (12649);
339 (20637); 273 (27392); 245 (27822). ESI-MS (DMSO): m/z
387.08 (100%, [V O (L )] , MW = 387.02), 758.05 (30%,
3
max
1
1
28.57, 128.25, 128.16, 123.96, 120.88, 119.42, 117.12, 115.14, 112.62,
09.06.
V
2
−
2
2
V
IV
2
−
1
H hnal-hbhz (H L ). Yield: 75%. Anal. Calcd for C H N O : C,
[V V O (L ) ] , MW = 758.48). H NMR (400 MHz, DMSO-d ):
2
2
18 14
2
3
3
2
6
7
0.58; H, 4.61; N, 9.15. Found: C, 70.59; H, 4.58; N, 9.12. Selected IR
δ 11.60 (s, 1H, OH), 11.42 (s, 1H, OH), 10.09 (s, 1H, HCN), 9.95
(s, 1H, HCN), 8.65−6.83 (m, 20H, aromatic), 5.86−5.66 (m, 2H,
CH (OEt)), 3.47−3.41 (q, 4H, CH (EtOH)), 1.63−1.59 (t, 3H,
−1
peaks with proposed assignments (KBr pellet, νmax/cm ): 3466 ν(O−
1
H); 3022 ν(N−H); 1640 ν(CO); 1578 ν(CN). H NMR (400
2
2
13
MHz, DMSO-d ): δ 12.74 (s, 1H, naphthyl−OH), 12.07 (s, 1H, NH),
CH (OEt)), 1.07−1.04 (t, 6H, CH (EtOH)). C NMR (100 MHz,
6
3
3
1
1.87 (s, 1H, aryl−OH), 9.54 (s, 1H, HCN), 8.33−6.62 (m, 10H,
DMSO-d ): δ 169.95, 164.66, 164.29, 158.96, 158.90, 149.52, 136.06,
6
13
aromatic). C NMR (100 MHz, DMSO-d ): δ 163.72, 158.51, 157.89,
135.73, 133.98, 133.80, 133.01, 129.72, 129.51, 129.45, 129.34, 128.90,
6
1
1
47.44, 133.78, 132.68, 131.44, 128.69, 128.55, 127.57, 127.50, 123.33,
20.73, 118.92, 118.65, 117.05, 115.48, 108.36.
128.62, 124.85, 124.53, 122.64, 122.29, 119.76, 119.57, 118.90, 117.31,
114.69, 114.30, 111.62, 111.46, 83.32, 56.50, 19.02, 18.81. H NMR
1
3
H han-bhz (H L ). Yield: 58%. Anal. Calcd for C H N O : C,
(400 MHz, DMSO-d + EtOH): δ 11.61 (s, 1H, OH), 9.94 (s, 1H,
2
2
19 16
2
2
6
7
4.98; H, 5.30; N, 9.20. Found: C, 74.96; H, 5.32; N, 9.21. Selected IR
HCN), 8.56−6.97 (m, 10H, aromatic), 5.86−5.66 (m, 2H,
−1
peaks with proposed assignments (KBr pellet, νmax/cm ): 3337 ν(O−
CH (OEt)), 3.47−3.41 (q, 46H, CH (EtOH)), 1.63−1.59 (t, 3H,
2
2
1
13
H); 3071 ν(N−H); 1659 ν(CO); 1573 ν(CN). H NMR (400
CH (OEt)), 1.07−1.04 (t, 68H, CH (EtOH)). C NMR (100 MHz,
3
3
MHz, DMSO-d ): δ 10.31 (s, 1H, naphthyl−OH), 9.55 (s, 1H, NH),
DMSO-d + EtOH): δ 170.25, 164.36, 159.04, 149.04, 135.35, 133.31,
6
6
13
7
.91−7.27 (m, 11H, aromatic), 2.34 (s, 3H, CH ). C NMR (100
132.92, 129.35, 129.05, 128.61, 128.34, 124.18, 121.80, 119.49, 119.05,
3
MHz, DMSO-d ): δ 153.71, 152.63, 134.24, 131.82, 131.51, 130.21,
116.95, 114.67, 111.41, 83.14, 56.57, 18.25. 51V NMR (DMSO-d6/
6
1
1
29.06, 128.76, 128.36, 128.23, 127.86, 127.43, 126.99, 123.67, 123.19,
18.99, 118.71, 113.74, 24.30.
MeCN-d (1:10)): δ −554 (80.0%), −594 (20.0%).
1
V
[V O(OEt)(han-bhz)] (3). Yield: 66%. Anal. Calcd for
4
H han-abhz (H L ). Yield: 64%. Anal. Calcd for C H N O : C,
C H N O V: C, 60.88; H, 4.62; N, 6.76. Found: C, 60.86; H,
2
2
19 17
3
2
21 19
2
4
7
1.46; H, 5.37; N, 13.16. Found: C, 71.48; H, 5.37; N, 13.14. Selected
4.58; N, 6.77. Selected IR peaks with proposed assignments (KBr
−1
−1
IR peaks with proposed assignments (KBr pellet, νmax/cm ): 3473
ν(O−H); 3410 ν(NH ) ; 3329 ν(NH ) ; 3221 ν(N−H); 1663 ν(C
pellet, νmax/cm ): 1595 ν(CN); 1239 ν(C−O)
; 999 ν(VO).
enolic
−1
IR (CHCl , cm ): 1004, 966 (VO); 820 (V−O−V). UV−vis
2
as
2
s
3
1
−1
−1
O); 1553 ν(CN). H NMR (400 MHz, DMSO-d ): δ 10.35 (s, 1H,
[CHCl ; λ , nm (ε, M cm )]: 430 (7003); 343 (14511); 286
6
3
max
naphthyl−OH), 9.17 (s, 1H, NH), 7.91−6.23 (m, 10H, aromatic),
(21713); 234 (25207). ESI-MS (DMSO): m/z 385.10 (64%,
13
V
3
−
V
IV
3
−
6
.05 (s, 2H, NH ), 2.35 (s, 3H, CH ). C NMR (100 MHz, DMSO-
[V O (L )] , MW = 385.27), 754.19 (100%, [V V O (L ) ] , MW
2
3
2
3
2
1
d6): δ 153.98, 152.47, 152.36, 149.84, 132.47, 131.56, 130.22, 129.09,
1
1
= 754.53). H NMR (400 MHz, DMSO-d ): δ 7.98−7.22 (m, 22H,
6
28.34, 127.98, 127.67, 123.78, 123.14, 118.94, 117.04, 115.46, 114.69,
aromatic), 5.54−5.41 (m, 2H, CH (OEt)), 3.47−3.42 (q, 4H,
2
13.59, 24.22.
CH (EtOH)), 2.92 (s, 3H, CH ), 2.84 (s, 3H, CH ), 1.52−1.48 (t,
2
3
3
V
13
Preparation of [V O(OEt)(L)] (1−4). We describe here a general
3H, CH (OEt)), 1.08−1.04 (t, 6H, CH (EtOH)). C NMR (100
3
3
V
synthetic procedure taking NH V O as the metal precursor.
NH V O (1.0 mmol) was added to a hot solution of the appropriate
H2L (1.0 mmol) in EtOH (20 mL); the color changed instantly to
brown, and after 3 h of refluxing, the reaction mixture was filtered off
and kept for precipitation of the compounds. After 3−4 days, crystals
of diffraction quality were obtained and used for X-ray diffraction
MHz, DMSO-d ): δ 170.91, 170.36, 166.64, 166.47, 166.16, 160.17,
4
3
6
V
134.85, 134.75, 133.89, 132.13, 131.82, 131.77, 130.94, 130.66, 130.01,
129.95, 129.56, 129.35, 128.97, 128.70, 128.61, 128.53, 128.00, 127.58,
126.54, 126.17, 124.99, 124.88, 124.34, 119.50, 118.75, 118.17, 118.03,
4
3
1
−4
1
117.86, 80.23, 56.51, 24.09, 23.84, 19.01, 18.67. H NMR (400 MHz,
DMSO-d + EtOH): δ 8.09−7.20 (m, 11H, aromatic), 5.54−5.41 (m,
6
(
XRD) structure determination.
2H, CH (OEt)), 3.48−3.43 (q, 56H, CH (EtOH), 2.92 (s, 3H, CH ),
2
2
3
V
13
[
V O(OEt)(hnal-abhz)] (1). Yield: 61%. Anal. Calcd for
1.53−1.49 (t, 3H, CH (OEt)), 1.08−1.04 (t, 83H, CH (EtOH)). C
NMR (100 MHz, DMSO-d + EtOH): δ 170.87, 166.13, 159.73,
3
3
C H N O V: C, 57.84; H, 4.37; N, 10.12. Found: C, 57.83; H,
20
18
3
4
6
4
.39; N, 10.08. Selected IR peaks with proposed assignments (KBr
133.80, 131.99, 131.75, 131.69, 129.58, 129.26, 128.86, 128.49, 127.47,
−1
51
pellet, νmax/cm ): 3461 ν(NH ) ; 3322 ν(NH ) ; 1595 ν(CN);
126.10, 124.25, 119.41, 118.16, 80.20, 56.53, 23.68, 18.77, 18.50.
V
2
as
2 s
−
1
1
255 ν(C−O)
; 991 ν(VO). IR (CHCl , cm ): 1002, 977 (V
NMR (DMSO-d /MeCN-d (1:10)): δ −500 (100.0%).
enolic
3
6
1
−1
−1
V
O); 821 (V−O−V). UV−vis [CHCl ; λ , nm (ε, M cm )]: 434
[V O(OEt)(han-abhz)] (4). Yield: 64%. Anal. Calcd for
3
max
(
15257); 336 (19651); 286 (26852); 248 (30614). ESI-MS (DMSO):
C H N O V: C, 58.75; H, 4.70; N, 9.79. Found: C, 58.74; H,
21
20
3
4
V
1
−
m/z 386.16 (100%, [V O (L )] , MW = 386.26), 756.13 (14%,
4.73; N, 9.78. Selected IR peaks with proposed assignments (KBr
2
V
IV
1
−
1
−1
[
V V O (L ) ] , MW = 756.51). H NMR (400 MHz, DMSO-d ): δ
pellet, νmax/cm ): 1567 ν(CN); 1238 ν(C−O)
; 996 ν(VO).
3
2
6
enolic
−
1
9
.99 (s, 1H, HCN), 9.94 (s, 1H, HCN), 8.59−6.43 (m, 20H,
IR (CHCl , cm ): 1004, 969 (VO); 821 (V−O−V). UV−vis
3
−1
−1
aromatic), 5.76−5.54 (m, 2H, CH (OEt)), 4.32 (s, 2H, NH ), 3.48−
[CHCl ; λ , nm (ε, M cm )]: 419 (14445); 307 (18634); 277
2
2
3
max
3
.43 (q, 4H, CH (EtOH)), 1.60−1.57 (t, 3H, CH (OEt)), 1.08−1.05
(24006); 253 (30231). ESI-MS (DMSO): m/z 400.02 (100%,
2
3
13
V
4
−
V
IV
4
−
(
t, 6H, CH (EtOH)). C NMR (100 MHz, DMSO-d ): δ 171.22,
[V O (L )] , MW = 400.28), 784.30 (50%, [V V O (L ) ] , MW
3
6
2
3
2
D
DOI: 10.1021/acs.inorgchem.6b01001
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Inorganic Chemistry
Article
Figure 1. ORTEP (30%) diagrams of (a) 1, (b) 3, and (c) 4.
1
V
=
784.56). H NMR (400 MHz, DMSO-d ): δ 8.21−6.31 (m, 20H,
Transformation of the structurally characterized [V O(OEt)-
(L)] complexes in solution, leading to the formation of the
6
aromatic), 5.56−5.42 (m, 2H, CH (OEt)), 4.52 (s, 2H, NH ), 3.50−
.45 (q, 4H, CH (EtOH)), 2.95 (s, 3H, CH ), 2.87 (s, 3H, CH ),
.54−1.51 (t, 3H, CH (OEt)), 1.10−1.07 (t, 6H, CH (EtOH)).
NMR (100 MHz, DMSO-d ): δ 171.89, 171.39, 166.55, 166.22,
66.03, 159.23, 158.05, 150.01 149.87, 134.68, 133.78, 132.85, 132.59,
31.98, 131.72, 130.73, 130.61, 129.93, 129.56, 129.33, 127.99, 127.56,
26.52, 126.16, 124.95, 124.33, 119.51, 118.45, 118.16, 117.99, 117.89,
16.40, 115.38, 115.13, 111.26, 110.04, 80.15, 56.57, 24.19, 23.96,
2
2
3
1
2
3
3
corresponding monooxido-bridged divanadium(V,V) com-
pounds [{V O(L)} -μ-O] (eq 2), is demonstrated. The
mixed-valence vanadium(IV,V) species V O3 were generated
in solution by constant potential electroreduction, at −0.10 V,
of the corresponding [{V O(L)} -μ-O] species (eq 3).
13
C
V
3
3
2
6
3+
2
1
1
1
1
1
V
2
V
V
1
2[V O(OEt)(L)] + H O ⇆ [{V O(L)} ‐μ‐O] + 2EtOH
9.03, 18.74. H NMR (DMSO-d + EtOH, 400 MHz): δ 8.09−6.60
2
2
6
(2)
(
m, 10H, aromatic), 5.56−5.41 (m, 2H, CH (OEt)), 4.51 (s, 2H,
2
NH ), 3.52−3.47 (q, 48H, CH (EtOH)), 2.86 (s, 3H, CH ), 1.55−
2
2
3
V
−
V
IV
−
1
3
[{V O(L)} ‐μ‐O] + e → [{V O(L)}{V O(L)}‐μ‐O]
1
(
.52 (t, 3H, CH (OEt)), 1.11−1.07 (t, 72H, CH (EtOH)). C NMR
2
3
3
100 MHz, DMSO-d + EtOH): δ 171.97, 165.94, 158.21, 149.79,
(3)
6
1
1
33.63, 132.36, 131.91, 130.51, 129.14, 127.34, 126.02, 124.18, 119.28,
Scheme 1 provides an overview of the compounds described
in this work and of how they are obtained. The structural
formulas of complexes are based on elemental analyses,
spectroscopic (IR, UV−vis, EPR, H, C, and V NMR, and
ESI-MS) data, and single-crystal XRD analyses of compounds
1, 3, and 4.
51
18.09, 116.28, 115.27, 111.23, 80.00, 56.61, 23.64, 18.50, 18.35.
V
NMR (DMSO-d /MeCN-d (1:10)): δ −511 (100%).
6
1
1
13
51
RESULTS AND DISCUSSION
■
V
Synthesis. The reaction of NH V O with an equimolar
4
3
1
2
amount of H hnal-abhz (L ), H hnal-hbhz (L ), H han-bhz
Structure Description. The IR spectra of complexes 1−4
2
2
2
3
4
(
L ), and H han-abhz (L ) (cf. Scheme 1 and eq 1) in EtOH
showed the characteristic VO stretching band at ca. 991−999
2
V
−1
yielded the oxidovanadium(V) complexes [V O(OEt)(hnal-
cm , and the observed elemental (C, H, and N) analytical data
V
V
abhz)] (1), [V O(OEt)(hnal-hbhz)] (2), [V O(OEt)(han-
bhz)] (3), and [V O(OEt)(han-abhz)] (4), respectively, in
of all of them are consistent with their formulations as
V
V
[V O(OEt)(L)] compounds. The preliminary characterization
good yield. These compounds are soluble in CH Cl , N,N-
dimethylformamide, and DMSO, sparingly soluble in methanol,
data (microanalysis and IR) indicated the presence of the
ligand, oxido, and ethoxido moieties in the complexes. To
confirm the binding mode of the azine-type ligands in these
compounds, the molecular structure of some of the monomeric
complexes was determined by a single-crystal XRD technique.
The atom numbering for complexes 1, 3, and 4 is given in
Figure 1 with the relevant bond distances and angles collected
in Table 2. The ORTEP image of complex 4 identifies the C19
2
2
EtOH, and CH CN, and diamagnetic and nonconducting in
3
solution.
NH VO + H L + EtOH
4
3
2
V
→
[V O(OEt)(L)] + NH OH + H O
(1)
4
2
E
DOI: 10.1021/acs.inorgchem.6b01001
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Table 2. Selected Bond Distances (Å) and Angles (deg) for
but do not allow clear conclusions regarding the possibility of
1
, 3, and 4
the existence of mononuclear− dinuclear equilibria.
1
NMR Spectral Studies. The H NMR spectra of 1−4 in
parameter
1
3
4
DMSO-d (which contained trace water) yielded two close but
6
V1−O1
V1−O2
V1−O3
V1−O4
V1−N1
N1−N2
1.834(4)
1.914(4)
1.606(5)
1.730(7)
2.075(5)
1.384(6)
1.835(2)
1.908(2)
1.587(2)
1.753(2)
2.093(2)
1.395(3)
1.810(3)
1.897(3)
1.573(4)
1.712(5)
2.088(3)
1.396(5)
separate sets of bands in an approximate 1:1 ratio (part a,
1
Figure 2A,B; H NMR spectra of 1 are taken as representative).
1
The set of sharp H NMR signals marked with pink rectangles
V
correspond to the monomeric form M of species 1, which was
isolated in the solid state and structurally characterized. The
relatively less sharp signals marked with blue rectangles were
V
V
assigned to a distinct species designated by M -M (the
corresponding second species, probably a dinuclear μ-oxido
complex) generated in situ in solution. So, as is also discussed
O1−V1−O3
O1−V1−O4
O1−V1−N1
O2−V1−O3
O2−V1−O4
O2−V1−N1
O3−V1−O4
O3−V1−N1
106.70(2)
99.40(3)
82.50(2)
107.10(2)
90.20(3)
74.40(2)
105.10(3)
97.00(2)
108.11(8)
99.03(8)
81.91(7)
110.68(9)
89.39(8)
74.36(7)
105.20(9)
97.15(8)
107.40(2)
96.90(2)
82.10(1)
106.90(2)
89.20(2)
75.10(1)
109.50(2)
97.40(2)
1
below, the H NMR results for 1−4 indicate that, in each case,
at least two species exist in DMSO solution.
The spectra of 1 and 2 exhibit two sets of −CH singlets in
the ranges of 9.99−9.94 and 10.09−9.95 ppm, respectively. The
spectrum of 2 exhibits two sets of −OH (phenolic) resonances
at 11.60 and 11.42 ppm. The spectra of 3 and 4 exhibit two sets
of −CH (methyl) resonances in the ranges of 2.92−2.84 and
3
2
.95−2.87 ppm, respectively. The spectra of 1 and 4 exhibit a
atom as slightly disordered, which is reflected as B-level
CheckCIF alerts. In all compounds, the V center is surrounded
V
broad signal for two −NH protons in the range of 4.52−4.32
2
ppm. Finally, the aromatic protons of 1, 2, and 4 (a total of 20)
and of 3 (a total of 22) appear in the range of 8.65−6.31 ppm.
In addition, all of the complexes exhibit separate bands
corresponding to bound ethoxido in the ranges of 5.86−5.41
by a O N binding set, constituting a distorted square pyramidal
4
structure, as indicated by the geometric parameter τ: 0.25 (1),
29
0
.33 (3), and 0.19 (4). The basal plane is made up of the
phenolato O, enolato O, and imine N atoms from the ligand
and the O atom from deprotonated alkoxide. The Schiff base
ligands form six- and five-membered chelate rings, with the
O1−V1−N1 and O2−V1−N1 angles in the range of
12b,d,17q
ppm (−CH ) and 1.63−1.48 ppm (−CH ),
and the
2
3
sharp peaks observed in the ranges of 3.50−3.41 ppm (−CH )
2
and 1.10−1.04 ppm (−CH ) were assigned to free, nonligated
3
EtOH that is most likely to be formed in situ in solution.
Although the chemical shifts of the methylene and methyl
protons of EtOH are very close to those of free EtOH, the
alcoholic proton is not detected, probably because of the low
concentration or overlap of signals.
8
2.50(2)−81.91(7)° and 75.10(1)−74.36(7)°, respectively.
The apical positions of the square pyramids are occupied by
the terminal oxido O3 atoms. The short V1−O3 distance, in
the range of 1.606(5)−1.573(4) Å, indicates the presence of a
V−O(oxido) bond, which is commonly found in five- and six-
coordinated octahedral complexes of vanadium(IV) and
Upon the addition of a few drops of EtOH to the DMSO
solution of 1−4, the second set of bands (blue) disappeared
and cleaner spectra were obtained (part b, Figure 2A,B); these
exhibit only one −OH (phenolic) resonance at 11.61 ppm for
2, one −CH proton signal in the range of 9.94−9.80 ppm for 1
and 2, and signals for a total of 10 aromatic protons for 1, 2,
and 4 and 11 aromatic protons for 3 in the range of 8.56−6.57
ppm. In addition, the coordinated ethoxido bands in the ranges
1
5b,16
vanadium(V).
Considering compounds 1, 3, and 4, overall
the V−O bond lengths follow the order V−O(oxido) < V−
O(alkoxido) < V−O(naphthalato) < V−O(enolato). These
data indicate stronger binding of the alkoxido moiety compared
to those of naphthalato and enolato O atoms.
IR Spectra in Solution. The IR spectra of complexes 1−4
in chloroform/DMSO depict two VO stretching bands at
−
1
∼
1004 and ∼970 cm , which may be indicative of the
of 5.86−5.41 ppm (−CH
2
) and 1.63−1.49 ppm
broadened, and the intensity of the free
EtOH bands in the ranges of 3.52−3.41 ppm (−CH ) and
) increased.
12b
12b,d,17q
presence of two distinct VO moieties in solution.
A
(−CH
)
3
representative spectrum is shown in Figure S1. Another new
2
−1
band observed in solution at around 820−823 cm was
tentatively assigned to the ν(V−O−V)
1.11−1.04 ppm (−CH
3
12b,17f,18b,24c,30
13
mode,
The C NMR spectra of 1−4 in DMSO also showed two
sets of bands with an approximate ratio of 1:1; the second set of
bands (blue) disappeared upon the addition of a small amount
which was not observed in the spectra of 1−4 in the solid state.
These observations indicate that at least two distinct species
may exist in solution. The IR spectra in solution depict many
features already observed in the solid state, corresponding to
the mononuclear complexes, as well as features that probably
correspond to the simultaneous formation of the corresponding
dinuclear complexes as second species.
1
of EtOH, as in the case of the H NMR spectrum. The
13
representative C NMR spectra of 1 are included in Figure S3.
Further characterization of the vanadium(V) complexes was
51
obtained by measuring their V NMR spectra in solution;
namely, the 51V NMR chemical shift values δ( V) of the
compounds recorded in MeCN−DMSO (10:1) were obtained
to access their behavior/speciation upon modification of the
composition of the solutions (Scheme 1 and Table 3). The
assignment of the resonances was done by considering both the
experiments described below and the results of the DFT
calculations carried out; the latter also demonstrate a weak
51
Electronic Spectroscopy. The electronic spectral data of
−4 are summarized in the Experimental Section, and a
representative spectrum is shown in Figure S2. Each displays
1
four strong absorption bands in CHCl in the wavelength range
3
4
4
35−235 nm. The lower-energy absorptions in the range 435−
20 nm are ascribed to the ligand-to-metal charge-transfer
51
transitions, while the higher-energy absorptions in the range
dependence of the V chemical shift on the solvent nature.
The 51V NMR spectral data of these complexes show strong
resonances at δ −548 (1), δ −554 (2), δ −500 (3), and δ −511
3
40−235 nm are likely to be due to ligand-centered
12b,30
transitions.
The electronic spectra depict similar features
F
DOI: 10.1021/acs.inorgchem.6b01001
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Inorganic Chemistry
Article
1
Figure 2. H NMR spectra of complex 1 in DMSO-d : (A) full range; (B) aromatic region; (a) before the addition of EtOH; (b) after the addition of
6
EtOH.
calc
calc
ppm (4) in DMSO-d :MeCN-d (1:10), values within those
formation of 1·DMSO (δV = −570 ppm), 1·MeCN (δV
=
6
1
calc
normally found for vanadium(V) complexes containing O/N-
−579 ppm), and 1·EtOH (δV = −587 ppm) adducts from 1
and the corresponding solvent is significantly endergonic (by
13.1, 16.0, and 13.9 kcal/mol, respectively, in terms of the
Gibbs free energy in solution). Thus, we do not expect the
formation of these species to be favorable. Cartesian atomic
coordinates (in Å) of the calculated equilibrium structures, for
DMSO taken as the solvent, for the calculations of the bulky
solvent effect are summarized in Table S1.
1
,8,31,32
donor sets.
Table 3 summarizes the data of experimental and calculated
V NMR chemical shifts obtained. Namely, it depicts data
5
1
concerning the solvent-dependent behavior of the 51V NMR
spectra. If coordination of a solvent molecule (DMSO, MeCN,
or EtOH) to vanadium in the monomeric complexes 1−4 is
considered, theoretical DFT calculations indicate that the
G
DOI: 10.1021/acs.inorgchem.6b01001
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Inorganic Chemistry
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Table 3. Summary of the Experimental 1V NMR Data (δV,
5
is observed [Figure 3A(b)]. After ca. 6 h, a clear major species
calc
ppm) and DFT Calculations (δV , ppm, in parentheses, for
DMSO solutions if not Stated Otherwise): See the Text and
Scheme 1
shows up at −536 ppm, and the resonance at −576 ppm is
V
again detected. Probably most V -hnal-abhz complexes
decomposed with time upon the addition of EtOH, with the
resonance at −536 ppm being compatible with those reported
V
V
M -M (dinuclear
2−
31
MV
−548 (−566), (−568), (−568),
species)
for vanadate ethanol esters (ROVO ) or vanadates, whose
3
33
compound
δV may vary with the pH and probably also slightly with the
nature of the solvent.
a
b
1
−576 (−587, −573)
c
(
−566)
Complex 2 in MeCN−DMSO depicts a resonance at −554
1
1
1
2
3
4
4
4
·DMSO
·EtOH
·MeCN
(−570)
(−587)
(−579)
calc
ppm [Figure 3B(a)]. The corresponding δ
= −553 ppm
V
supports its assignment to 2. The resonance measured at δ =
V
−
594 ppm is tentatively assigned to the corresponding species
-2 (Scheme 1). The signal at δV = −594 ppm almost
−554 (−553)
−500 (−529)
−511 (−539), (−539)
(−543)
−594
−522
−549 (−566)
V
V
2
c
disappears upon the addition of EtOH [Figure 3B(b)], and
after 6 h, only a resonance at −533 ppm is detected. Again we
tentatively assign this resonance to vanadates or vanadate
·DMSO
·EtOH
(−561)
ethanol esters (ROVO32 ).
−
31,33
The V NMR spectrum of 3
51
a
Geometry optimization with DMSO as the solvent, and single-point
NMR calculations with MeCN as the solvent. Geometry optimization
with DMSO as the solvent, and single-point NMR calculations with
EtOH as the solvent. Both geometry optimization and NMR
b
dissolved in MeCN−DMSO depicts a single resonance at −500
ppm (Figure 4A), which we assign to 3 (Scheme 1); for this
c
calculations with EtOH as the solvent.
The 51V NMR spectrum of 1 (ca. 4.0 mM) dissolved in
MeCN−DMSO has a major resonance at −548 ppm, a minor
one at −576 ppm, and one/two other very minor peaks [Figure
3A(a)]. Complex 1 (Scheme 1) probably corresponds to the
Figure 4. 51V NMR spectra of a 4.0 mM solutions of (A) 3 and (B) 4:
(a) in MeCN:DMSO (10:1); (b) solutions of part a after 6 h; (c)
solutions of part b after 12 h.
species, δVcalc = −529 ppm. After ca. 6 h, this peak decreases in
intensity and a major resonance appears at −522 ppm, which
V
3
we tentatively assign to the corresponding [{V O(L )} -μ-O]
(
2
V
V
species 3 -3 ; Scheme 1). After 12 h, several other minor
peaks are detected; these may correspond to vanadate ethanol
2
−
−
esters (ROVO and ROVO H ) and/or to vanadates (V , V ,
3
3
1
2
31,33
Figure 3. 51V NMR spectra of 4.0 mM solutions of (A) 1 and (B) 2:
a) in MeCN:DMSO (10:1); (b) solutions of part a after the addition
or V4).
In the case of 4 dissolved in MeCN−DMSO, it depicts a
resonance at δ = −511 ppm (Figure 4B), which may be
(
of a few drops of EtOH; (c) solutions of part b after 6 h.
V
calc
assigned to 4 (Scheme 1); for this species in DMSO, δ
=
V
−
539 ppm. After ca. 6 h, this peak disappears, and two other
calc
resonance at −548 ppm; this agrees reasonably with a δ
resonances are detected: a major one at −526 ppm and a minor
one at −549 ppm. We tentatively assign the resonance at −526
V
value of −566 ppm (Table 3). The minor species observed in
V
V
4
V
V
Figure 3A(a) at −576 ppm may tentatively be assigned to 1 -
ppm to the corresponding [{V O(L )} -μ-O] (species 4 -4 ;
2
V
V
V
V
V
1
1
·DMSO and 1 -1 ·MeCN; in fact, the dinuclear complex 1 -
Scheme 1) and the one at −549 ppm to vanadates or vanadate
ethanol esters (ROVO3 ).
disappears.
calc
2− 31,33
(Scheme 1) corresponds to calculated δV values of −587
After 12 h, the latter resonance
and −573 ppm.
1
13
Upon the addition of a few drops of EtOH, all minor peaks
in Figure 3A(a) disappear and only the one at δ = −548 ppm
In agreement with the IR in solution, the NMR ( H, C, and
51
V) data also indicate that at least two species exist in a
V
H
DOI: 10.1021/acs.inorgchem.6b01001
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Inorganic Chemistry
Article
DMSO/MeCN−DMSO solution (either immediately or after a
monomeric species would link V centers of the monomeric
complexes. We also exclude the possibility of such a phenolate-
linked chain structure; if phenolate was coordinated to the V
center in the minor species, a phenolate ligand to vanadium
metal charge-transfer band would have disappeared when a
small amount of EtOH was added to the chloroform solution of
complexes 1−4. However, there were no such recognizable
changes in the UV−vis spectra of complexes 1−4 in the
chloroform solution after the addition of a small amount of
EtOH. Additionally, theoretical DFT calculations demonstrate
that such a dinuclear species 4−4b probably does not exist in
solution because all attempts to locate the corresponding
minimum on the potential energy surface resulted in the
formation of two separate monomers of 4.
few hours), and whatever the nature of the second species
V
V
(
here identified as M -M ), it converts back to its monomeric
V
form M in the presence of a small amount of EtOH.
Alkoxides often form dinuclear complexes, so one of the
possible structures for the dinuclear species is the formation of
34
an alkoxido-bridged dimer. However, we could exclude the
possibility of an ethoxido-bridged dinuclear complex as the
second species because there is only one set of bands for a
coordinated ethoxido moiety. If the second species is an
ethoxido-bridged dimer, there should be another set of bands
for two bridging ethoxido groups, and as a six-coordinated
complex, the VO stretching should have been found at lower
1
2c
frequency.
Additionally, theoretical DFT calculations in-
dicate that the Gibbs free energy of formation of such dinuclear
species 4−4a from two monomers of 4 (taken as
representative, Scheme 2) is highly endergonic in both
Finally, another of the plausible structures for the second
species formed in solution is a dinuclear μ-oxido complex.
From the IR results in solution, there was a significant change
in the VO stretches of complexes 1−4 in a chloroform/
DMSO solution compared to that of the monomeric species in
the solid state, and another new band that may correspond to
a
Scheme 2. Formation of Dimeric Complex 4-4a
1
2b,30
the ν(V−O−V)
mode is observed. This indicates that,
along with monomeric species, the complexes may exist as an
isolated dinuclear μ-oxido (second species) in solution, as
12f,30
reported in other recent publications.
On the basis of the above results, the mentioned solution
behavior of 1−4 should be ascribed to the equilibria in Scheme
3
existing in chloroform/DMSO/MeCN−DMSO containing a
small amount of water, which also explains the simultaneous
presence of the two species M (monomer, isolated in the solid
V
V
V
state and characterized by single-crystal XRD) and M -M
second species, proposed as a dinuclear μ-oxido complex) in
solution.
(
Even though no water molecules were observed in the crystal
structures of 1−4, possible proton sources may come from
solvents used in the IR and NMR experiments or from water
molecules in air that were probably adsorbed on the surface of
the particles of the complexes. The role of water as well as of
the free EtOH molecules for the existence of the above
equilibria was inferred from the presence of the band at ∼3.73
a
The calculated Gibbs free energy of the reaction in DMSO solution is
indicated. The molecular formula of 4-4b, for which no minimum was
found in the calculation, is also shown (see the text).
(
br) ppm for water and the sharp peaks at ∼3.47 and ∼1.07
ppm from the protons of free, nonligated EtOH in DMSO-d .
6
DMSO and EtOH solutions (ΔG values are +35.0 and +32.4
kcal/mol, respectively). So, we may exclude the possibility of
such alkoxido-bridged dimers as the second species.
Other possible structures for second species are a chain
structure in which a O phenolate atom of the neighboring
s
In some cases (2 and 3), the water peak is assigned, and in
other cases (1 and 4), it is not clearly detected. However, these
equilibria could be shifted more to the left by the addition of a
few drops of EtOH, which was reflected in the change in the
Scheme 3. Schematic Diagram for the Interconversion of Monomeric and Dinuclear Species in Solution, Taking Complex 4 as
a
Representative
a
The ΔG values calculated using different functionals are indicated in kilocalories per mole.
s
I
DOI: 10.1021/acs.inorgchem.6b01001
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
NMR spectrum of [V O(OEt)(L1−4)] upon the addition of
EtOH.
V
and 4, rather similar MS results were obtained (Figures S4−
S6). For 1, 2, and 4, the peak corresponding to the mass of the
mononuclear ion is predominant (100%), whereas for 3, it is
the opposite: the peak corresponding to the mass of the
dinuclear μ-oxido ion is the predominant one. This difference
in the behavior of 3 may be attributed to the absence of any H-
bond-acceptor atom as the second substituent on the phenyl
ring of the coordinated ligand, which diminishes the possibility
of any intramolecular hydrogen bonding. The results of mass
spectrometry give strong evidence in favor of the formation of
μ-oxidodioxidodivanadium complexes as the second species in
all systems.
These conclusions are supported by DFT calculations, which
indicate that the Gibbs free energy of formation of a dinuclear
complex of 4 shown in Scheme 3 is only +2−3 kcal/mol in a
DMSO solution. Such low positive values suggest that (i) the
dinuclear complex may be easily formed in a DMSO solution in
a noticeable amount, (ii) the monomer is still the predominant
form in solution, in agreement with the higher intensity of its
signal in the 51V NMR spectra compared to that of the
dinuclear complex, and (iii) the addition of even a small
amount of EtOH should efficiently shift this equilibrium toward
monomeric structures, again in agreement with the experiment.
Therefore, we can conclude that, in a DMSO/MeCN−DM-
SO solution in the presence of EtOH, compounds 1−4 partly
retain the structure in which they are present in the solid state,
Redox Properties. The redox properties of compounds
V
[V O(OEt)(L)] (1−4) were studied by CV in MeCN using
[NBu ][BF ] as the electrolyte. The cyclic voltammograms of
4
4
the complexes display quasi-reversible cathodic waves in the
V
V
V
IV
and the other second species, M -M , which were also present
in solution, may be reconverted into the mononuclear one, M .
Complexes M -M exhibit the characteristic spectroscopic
properties of the dinuclear μ-oxido species, similar to those of
the dinuclear μ-oxido complex reported in two of our recent
range of 0.27−0.44 V (vs SCE), assigned to the V → V
V
reduction processes (Figure S7).
V
V
When compound 2 is left in the electrolyte solution for about
1 h, a shift in the potential to lower values (by ca. 0.11 V) of the
cathodic wave is observed (Figure 6). The potential of the new
1
2f,30
publications.
ESI-MS. Complexes 1−4 in a DMSO solution gave two
peaks at m/z ∼400−385 and ∼784−754 in the ESI-MS
(
negative mode) spectrum. The lower mass peak corresponds
V
−
to the mononuclear complex anion, [V O L] , isolated in the
2
solid state, and for the other peak, we propose it corresponds to
V
IV
−
the molecular anion [V V O (L) ] of their dinuclear μ-oxido
3
2
species formed in solution. The representative ESI-MS
spectrum for 2 is depicted in Figure 5. For complexes 1, 3,
Figure 6. Cyclic voltammograms of 2 (---) immediately after
dissolution and () after 1 h in the electrolyte solution and (•••)
V
5
5
of [(V OL ) O] (H L = 2-furoylazine of 2-hydroxy-1-acetonaph-
2
2
3
0
thone) in [NBu ][BF ]/MeCN (0.10 M) solutions.
4
4
wave is well in the range of that of the dinuclear μ-
5
V
V
5
oxidovanadium(V) compound [L (O)V OV (O)L ] previ-
5
ously reported for a complex with a similar ligand (L , where
H L = 2-furoylazine of 2-hydroxy-1-acetonaphthone). In
5
30
2
Figure 6, for comparative purposes, the cyclic voltammogram of
V
5
[
(V OL ) O] is also included; the similarity of the cyclic
2
5
V
V
5
voltammograms of [L (O)V OV (O)L ] and 2 (after standing
ca. 1 h in the electrolyte solution) further confirms the
V
V
feasibility of the formation of 2 -2 in solutions of 2.
Chronocoulometry of 1−4 and Subsequent EPR
Studies. In MeCN, compounds 1−4 partly convert into the
monooxido-bridged divanadium(V,V) complexes M -M ,
which most probably correspond to the precursors for
monooxido-bridged divanadium(IV,V) compounds.
V
V
With the purpose of elucidating whether the mixed-valence
V
IV
V
IV
species [{V V O (L) }-μ-O] (designated as M -M , where M
2
2
=
1, 2, 3, or 4) could be obtained from complexes 1−4, CPE
Figure 5. ESI-MS spectrum of complex 2 in DMSO: m/z 387.08
V
2
−
(
100%, [V O (L )] , MW = 387.02) and 758.05 (30%,
was undertaken at potentials selected according to the values
measured by CV for the reduction of each complex (Table 4).
2
V
IV
2
−
[
V V O (L ) ] , MW = 758.48).
3 2
J
DOI: 10.1021/acs.inorgchem.6b01001
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Inorganic Chemistry
Article
Table 4. Spin Hamiltonian Parameters Obtained from 4.0
mM Solutions of the Reduced Forms of Compounds 1−4 in
MeCN and Those Calculated by Simulation of the
with both unrelaxed and optimized geometries, the spin density
is mostly localized at one of the V centers (0.95−1.10 e; Figure
8). The negative spin density values at the bridging O atom and
Experimental First-Derivative EPR Spectra Recorded at 77 K
and DFT-Calculated Values for the Dinuclear Species
−4
−
V
IV
V
IV
V
IV
V
IV
[
{VO(L1 )} -μ-O] (1 -1 , 2 -2 , 3 -3 , and 4 -4 ),
2
IV
1−4
−
−
−
−
Monomeric [V O(OEt)(L )] (Designated by 1 , 2 , 3 ,
−
IV
1−4
and 4 ), and [V O(L )(EtOH)] (Designated by 1′, 2′, 3′,
a
and 4′) Compounds
4
4
E1/2red
A (×10
A , A (×10
z
x
y
−1
−1
complex (4 mM)
gz
cm
)
gx, gy
cm
)
(V)
b
1
1.950
163.8
159.5
1.981
58.2
0.37
0.44
0.44
1
V-1IV (DFT
55.0, 56.5
52.0, 52.5
58.2, 61.4
calculations)
1 −
(DFT
156.5
163.4
calculations)
1
′ (DFT
calculations)
b
2
2
1.949
165.5
160.6
1.949
59.8
V-2IV (DFT
56.0, 57.3
calculations)
2−
(DFT
157.4
164.4
53.2, 53.4
59.3, 62.3
calculations)
2
′ (DFT
calculations)
b
3
3
3
(species i)
1.951
1.952
165.8
167.6
160.1
1.981
1.981
57.9
b
(species ii)
58.2
V-3IV (DFT
54.8, 58.3
V
IV
V
IV
calculations)
Figure 8. Spin-density distribution in 1 -1 and 4 -4 with unrelaxed
3−
(A), partially optimized (B), and fully optimized (C) geometries.
(DFT
156.4
163.4
50.9, 53.2
57.2, 62.8
calculations)
3
′ (DFT
oxido ligands (−0.01 to −0.11 e) indicate some spin
polarization and delocalization between the V and O atoms.
All of these data suggest that both vertical and adiabatic
reductions affect only one metal center and lead to the
formation of a mixed-valence complex.
calculations)
b
4
4
4
(species i)
1.951
1.950
165.1
167.0
159.0
1.980
1.980
58.7
0.27
b
(species ii)
59.4
V-4IV (DFT
53.6, 57.5
calculations)
4−
In contrast, in the monoreduced compound [{VO(han-
(DFT
156.0
163.2
50.4, 53.0
57.0, 62.5
−
V
IV
calculations)
abhz)} -μ-O] (4 -4 ) with unrelaxed geometry, the spin
2
4
′ (DFT
density is localized at both metal centers (ca. 0.60 e for each of
the V atoms; Figure 8), indicating that the vertical reduction
(i.e., that occurring at the initial moment before the geometry
relaxation) equally affects both V atoms. In the partially
calculations)
a
The column on the right displays the experimental E1/2red (vs SCE)
b
obtained by CV studies. From EPR spectra recorded after one-
electron reduction for each of the two V centers present in solution.
V
V
IV
optimized structure of 4 -4 with the frozen V−O
bonds
bridge
and the V−O−V angle, the spin density is also delocalized
The chronocoulometric processes were undertaken until the
charge supplied reached the value calculated for transfer of half
an electron per mole of original complex (Q = 1/2nFc); then it
was interrupted, and a sample of the electrolyzed solution was
collected and frozen for EPR studies.
between two V atoms (ca. 0.67 e for each of the V atoms).
V
IV
However, the fully optimized complex 4 -4 corresponds to
the mixed-valence species with the spin electron density
concentrated at one V center (1.08 e). Therefore, the adiabatic
reduction (i.e., that allowing the geometry relaxation) affects
only one V center and leads to the formation of a mixed-
valence complex.
In accordance with DFT calculations, the lowest unoccupied
V
molecular orbital (LUMO) of the dinuclear [{V O(L)} -μ-O]
compounds [{V O(hnal-abhz)} -μ-O] (1 -1 ) and [{V O-
2
V
V
V
V
2
These results also indicate that the spin delocalization
between two V atoms is determined by the geometry of the V−
O−V fragment. Taking into account that the energy difference
V
V
(
han-abhz)} -μ-O] (4 -4 ) is centered at the V atoms, oxido
2
ligands, and bridging O atom (Figure 7). In the singly reduced
V
IV
−
V
IV
complex [V O(hnal-abhz)−O−V O(hnal-abhz)] (1 -1 ),
V
IV
between the partially and fully optimized structures of 4 -4 is
only 2.2 kcal/mol, structural changes leading to delocalization
of the spin density between two V atoms can occur easily in a
V
IV
solution of 4 -4 at room temperature due to thermal motion.
All of these results correlate with the EPR data, indicating 8-line
V
IV
patterns at both 77 K and room temperature for 1 -1 , while
V
IV
for 4 -4 , an 8-line pattern at 77 K and a 15-line pattern at
room temperature were obtained.
The EPR spectra of the solutions containing the electro-
V
V
V
V
V
IV
−
Figure 7. Plots of the LUMO of the 1 -1 and 4 -4 complexes.
reduced species [{V V O (L) }-μ-O] were measured in
2 2
K
DOI: 10.1021/acs.inorgchem.6b01001
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Inorganic Chemistry
Article
5
1
liquid (at room temperature) as well as frozen (77 K) MeCN.
The EPR spectra of frozen solutions of 3 and 4 after one-
electron electroreduction for each of the two V centers indicate
the presence of (at least) two species in solution. The frozen
of a single, unpaired electron to two equivalent V nuclei (2nI
+ 1 = 15 for two 51V centers with I = / ). These EPR spectra
are indicative of delocalization of the unpaired electron over
both metal centers; therefore, the generation of mixed-valence
7
2
1
9
IV
V
solution EPR spectra were simulated, and the spin
Hamiltonian parameters thereby obtained are included in
V −O−V species is confirmed by EPR. Rather similar EPR
18b
spectra were reported by Dinda et al.
groups.
and some other
5
1
17c,o,18a
Table 4. The DFT calculated values of the V hyperfine
28
coupling constants are in reasonable agreement with the
experimental values (Table 4). Additionally, calculations
Interestingly, in the ESI-MS (negative mode) obtained for
1−4, important peaks with m/z values closely corresponding to
one-electron reduction of the dinuclear M -M complexes were
detected. This confirms the plausibility and propensity of
V
V
demonstrate noticeable differences of the |A | value for the
z
IV
−
reduced mononuclear structures (i) [V O(OEt)(L)]
−
4
−1
IV
V
V
V
IV
[
[
(
(156.0−157.4) × 10 cm ] and (ii) [V O(L)(EtOH)]
formation of both the M -M and M -M species in these
−4
−1
(163.2−164.4) × 10 cm ] and dinuclear structure [{VO-
systems.
−
−4
−1
V
IV
L)} -μ-O] [(159.0−160.6) × 10 cm ].
The formation of mixed-valence V −O−V species is clearly
2
V IV V IV
The room temperature (300 K) X-band EPR spectra of
demonstrated in these experiments for 3 -3 and 4 -4 for the
V
IV
V
IV
complexes 1 and 2 (thus, 1 -1 and 2 -2 ) after electro-
spectra at 77 K. It is noteworthy that the calculated A values
z
V
IV
IV
−
reduction exhibited an 8-line pattern (Figures 9 and S8). In
for the distinct reduced complexes M -M , V O(OEt)(L)
−
IV
(
M ), and V O(L)(EtOH) (M′) differ significantly. The
observed A values obtained in the cases of 3 and 4 upon
z
calc
reduction mostly differ from these Az values, with 3′ and 4′
being those that correspond to closer values, while the A values
z
obtained for 1 and 2 upon reduction are quite close to those of
1
′ and 2′ (differences of less than 1%).
CONCLUSIONS
Four substituted hydrazones H L
condensation of aroylhydrazines and naphthol derivatives and
characterized. When each of the H2L
■
1
−4
were prepared by the
2
1
−4
compounds was
V
reacted with the vanadium(V) precursor NH V O , the
4
3
V
monomeric [V O(OEt)(L)] complexes 1−4 were obtained
and characterized in the solid state and in solution by
1
13
51
spectroscopic techniques (IR, UV−vis, H, C, and
NMR, and ESI-MS). Single-crystal XRD analysis of 1, 3, and
4 confirmed coordination of each of the (L
V
Figure 9. First-derivative EPR spectra of 1 in MeCN after CPE (upon
passing the amount of charge corresponding to one-electron reduction
V
1−4 2−
for each of the two V centers present): (a) spectrum at room
)
ligands with a
temperature; (b) spectrum of the solution frozen at 77 K. An 8-line
pattern is obtained at room temperature. The spin Hamiltonian
O N binding set, each corresponding to a distorted square
2
V
pyramidal geometry around the V center [τ values of 0.25 (1),
parameters obtained for the spectrum at 77 K are in Table 4; the A
1−4
iso
0.33 (3), and 0.19 (4)], where the O,N,O-donor atoms of L
value for the spectrum at room temperature is 93.2 × 10−4 cm .
−1
and the O ethoxido atoms constitute satisfactory O N basal
3
planes.
V
these cases, the unpaired electron is localized on one of the V
centers. In a frozen solution (77 K), the EPR spectra also
exhibit patterns corresponding to a localized V O species.
However, in the cases of 3 and 4, the EPR spectra at room
temperature exhibit a 15-line pattern centered around g = 2.00,
with Aiso of ca. 48 and 50 G (Figure 10). This corresponds to
the g values and hyperfine pattern anticipated for delocalization
The structurally characterized [V O(OEt)(L)] compounds
transform in solution into the corresponding monooxido-
bridged divanadium(V,V) compounds. Formation of the
dinuclear μ-oxido species [{V O(L )} -μ-O] generated in
situ in solution was confirmed by several spectroscopic
techniques (IR and H, C, and V NMR) as well as by
ESI-MS and DFT calculations. For example, in the case of
IV
V
1−4
2
1
13
51
Figure 10. First-derivative EPR spectra measured for solutions of 3 and 4 in MeCN after CPE (upon passing the amount of charge corresponding to
V
one-electron reduction for each of the two V centers present): (a) spectra at room temperature; (b) spectra of the solutions frozen at 77 K. In both
cases, a 15-line pattern is obtained at room temperature. The spin Hamiltonian parameters obtained for the spectra at 77 K are in Table 4; the A
iso
values for the spectra at room temperature are 48 × 10−4 cm (for 3) and 50 × 10 cm (for 4).
−1
−4
−1
L
DOI: 10.1021/acs.inorgchem.6b01001
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
compound 4, DFT allowed one to predict that its Gibbs free
energy of formation of a dinuclear complex, 2[V O(OEt)(L )]
Notes
V
4
The authors declare no competing financial interest.
V
4
+
H O ⇆ [(V OL ) -μ-O] + 2EtOH, is only +2−3 kcal/mol in
2
2
a DMSO solution, supporting the proposal that the dinuclear
ACKNOWLEDGMENTS
V
V
■
complex 4 -4 may be easily formed in a DMSO solution in a
noticeable amount and that the addition of even a small
amount of EtOH should be enough to shift this equilibrium
towards its monomeric form, in agreement with what was
Funding for this research was provided by the Department of
Science and Technology, India [Grants SR/WOS-A/CS-145/
2
011 (to S.P.D.), SR/FT/CS-016/2008 (to R.D.), and SB/FT/
1
13
51
CS-100/2013 (to A.K.)]. R.D. thanks Prof. H. Reuter, Prof. M.
Nethaji, and Prof. S. Chattopadhyay for assistance with XRD
analysis. J.C.P. thanks the Portuguese Foundation for Science
and Technology [Grants UID/QUI/00100/2013, RECI/QEQ-
QIN/0189/2012, RECI/QEQ-MED/0330/2012, and SFRH/
BPD/90976/2012 (to A.K.)].
observed in NMR ( H, C, and V) experiments.
The 8-line EPR pattern observed in the EPR spectra at 77 K
of the electrolyzed solutions of 1−4 showed that upon
reductive transfer of half an electron per mole to complexes,
V
IV
there was a reduction of V to V . In the cases of the
reductions with solutions of 3 and 4, a 15-line EPR pattern was
recorded at room temperature, which indicates that the
unpaired electron is extensively delocalized between the two
V centers in the formed mixed-valence complex. In contrast,
upon similar reductive transfer with solutions of 1 and 2, an 8-
line EPR pattern was obtained at room temperature. It is
REFERENCES
■
(
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1
−2
−
plausible that mixed-valence compounds [{VO(L )} -μ-O]
2
formed but, in these two cases, with the unpaired electron
localized on one of the V atoms. DFT calculations globally
allowed rationalization of the data obtained for several systems.
IV
Moreover, the DFT-calculated A values for the proposed V -
z
(
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containing species are in reasonable agreement with the
experimental ones.
(
Further supporting the formation in solution of dinuclear
V
V
V
IV
M -M species and their propensity to form M -M
(
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V
IV
expected for oxido-bridged M -M complexes.
The crystallographic data for the structural analysis of 1, 3,
and 4 have been deposited with the Cambridge Crystallo-
graphic Data Centre (CCDC 1471661 for 1, CCDC 1471662
for 3, and CCDC 1471663 for 4). A copy of this information
may be obtained free of charge from the CCDC, 12 Union
Road, Cambridge CB2 1EZ, U.K. [Tel. +44 (0) 1223 762911;
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ASSOCIATED CONTENT
Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.inorg-
chem.6b01001.
■
*
S
IR spectra of 3 (Figure S1), UV−vis spectrum of 2
1
3
(
Figure S2), C NMR spectra of complex 1 (Figure S3),
ESI-MS spectra of complexes 1, 3, and 4 (Figures S4−
S6), cyclic voltammograms of 1−4 (Figure S7), EPR
spectra of 2 (Figure S8), Cartesian atomic coordinates
M. S.; Barreiro, E. J.; Lima, L. M.; Varela, J.; Gonzal
H.; Moreno, V.; Pessoa, J. C.; Gambino, D. Eur. J. Med. Chem. 2013,
2, 20−27. (h) Fernandez, M.; Varela, J.; Correia, I.; Birriel, E.;
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M.; Gambino, D. Dalton Trans. 2013, 42, 11900−11911.
9) Rehder, D.; Costa Pessoa, J.; Geraldes, C.; Castro, M.; Kabanos,
́
ez, M.; Cerecetto,
(
Table S1) (PDF)
6
́
X-ray crystallographic data in CIF format for 1 (CIF)
X-ray crystallographic data in CIF format for 3 (CIF)
X-ray crystallographic data in CIF format for 4 (CIF)
́
(
T.; Kiss, T.; Meier, B.; Micera, G.; Pettersson, L.; Rangel, M.;
Salifoglou, A.; Turel, I.; Wang, D. JBIC, J. Biol. Inorg. Chem. 2002, 7,
AUTHOR INFORMATION
■
3
(
84−396.
Corresponding Authors
10) Dash, S. P.; Pasayat, S.; Bhakat, S.; Roy, S.; Dinda, R.; Tiekink,
*E-mail: joao.pessoa@ist.utl.pt (J.C.P.).
E-mail: rupamdinda@nitrkl.ac.in (R.D.).
E. R.; Mukhopadhyay, S.; Bhutia, S. K.; Hardikar, M. R.; Joshi, B. N.;
Patil, Y. P.; Nethaji, M. Inorg. Chem. 2013, 52, 14096−14107.
(
*
Author Contributions
11) (a) Sutradhar, M.; Pombeiro, A. J. L. Coord. Chem. Rev. 2014,
The manuscript was written through contributions of all
authors. All authors have given approval to the final version of
the manuscript.
2
65, 89−124. (b) Galloni, P.; Conte, V.; Floris, B. Coord. Chem. Rev.
2015, 301−302, 240−299. (c) Honzicek, J.; Vinklar
Acta 2015, 437, 87−94.
́
ek, J. Inorg. Chim.
M
DOI: 10.1021/acs.inorgchem.6b01001
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