New oxidovanadium(V) complexes of the cation [VO]3+: Synthesis, structural characterization and DFT studies

Article abstract of DOI:10.1016/j.poly.2012.01.015

5-Tert-butyl-(3-(1,3-dihydroxy-2-(hydroxymethyl)propan-2-ylimino)methyl) -2-hydroxybenzaldehyde (L₁), (4-tert-butyl-2-(1,3-dihydroxy-2- (hydroxymethyl)propan-2-ylimino)methyl)-6-(dimethoxymethyl) phenol (L ₂) and (2-(1,3-dihydroxy-2-

Full text of DOI:10.1016/j.poly.2012.01.015

Polyhedron 36 (2012) 21–29
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Polyhedron
journal homepage: www.elsevier.com/locate/poly
New oxidovanadium(V) complexes of the cation [VO]3+: Synthesis, structural
characterization and DFT studies
a
a,
b
Davi Fernando Back a, , Cristiéli Rossini Kopp , Gelson Manzoni de Oliveira , Paulo Cesar Piquini
⇑
⇑
a Departamento de Química, Universidade Federal de Santa Maria (UFSM), LMI, Camobi, 97105-900 Santa Maria, RS, Brazil
b Departamento de Física, Universidade Federal de Santa Maria (UFSM), Camobi, 97105-900 Santa Maria, RS, Brazil
a r t i c l e i n f o
a b s t r a c t
Article history:
5-Tert-butyl-(3-(1,3-dihydroxy-2-(hydroxymethyl)propan-2-ylimino)methyl)-2-hydroxybenzaldehyde
(L1), (4-tert-butyl-2-(1,3-dihydroxy-2-(hydroxymethyl)propan-2-ylimino)methyl)-6-(dimethoxymethyl)
phenol (L2) and (2-(1,3-dihydroxy-2-(hydroxymethyl)propan-2-ylimino)methyl)-6-methoxyphenol (L3),
react with vanadyl acetylacetonate to give the vanadium(V) complexes [VO(L1-3H+)]2ꢀdmso, [VO(L2-
3H+)]2 and [VO(L3-3H+)]2ꢀdmso. All complexes present the vanadium(V) center as the less common
[VO]3+ cation. The structural features of the title compounds, specially the occurrence of supramolecular
assemblies supported by bifurcated and trifurcated hydrogen bonding are discussed, as well as DFT stud-
ies and HOMO–LUMO energy gaps. Calculated spatial maps of the Fukui functions, f+(r) and fꢁ(r), are also
presented and discussed.
Received 1 December 2011
Accepted 12 January 2012
Available online 20 January 2012
Keywords:
Vanadium(V) complexes
Compounds of the VO3+ cation
DFT studies on vanadium(V) complexes
Ó 2012 Elsevier Ltd. All rights reserved.
1. Introduction
reported in the understanding of the rules of vanadium-bromoper-
oxidase [18], in the molecular mechanism of vanadium transport
Vanadium(IV) occurs as the highly stable vanadyl dication
[VO]2+ or as vanadium dioxide, VO2. While vanadium(V) is well
known as [VO2]+, the existence of [VO]3+ has been reported many
times [1–6]. Oxidovanadium compounds with unlike oxidation
states have been extensively studied in different fields of bioinor-
ganic chemistry: the intriguing discovery that some nitrogenases
display a cofactor in which molybdenum is replaced by vanadium
or iron has stimulated widespread research into nitrogenase [7,8];
vanadium plays also an important role in the halogenation of or-
ganic substrates [9], and in the natural occurring Amavadin (shown
in Fig. 1), a vanadium-containing anion found in three species of
poisonous Amanita mushrooms: A. muscaria, A. regalis and A. velat-
ipes, first extracted in 1972 [10]. The tunichromes, in turn, consti-
tute a series of vanadium compounds isolated from the blood cells
of the ascidians, marine invertebrates [11].
Vanadium-containing compounds have also revealed a great
potential as inhibitors of chemically-induced tumors in test ani-
mals and cell cultures in vitro, being efficient, for example, in the
treatment of leukemia, breast adenocarcinoma and Ehrlich tumors
in murines, as well as in human lung, breast, ovarian, testicular, re-
nal, gastrointestinal, nasopharyngeal and HEp-2 carcinomas [13–
17]. Mimetic complexes of dioxidovanadium(V), VOþ2 have been
in ascidians [19] and, more recently, as highly efficient and reus-
able catalyst [20].
Schiff bases, in the other hand, have been used extensively as
ligands in the coordination chemistry [21,22]. These compounds
can show a highly suitable applicability regarding antitumor activ-
ities [23], photochromism [24] and thermochomism [25] by proton
displacement between the hydroxyl O atom and the imine N atom.
Specifically 2-hydroxy Schiff base ligands are of interest, mainly
due to the existence of O–Hꢀ ꢀ ꢀN and N–Hꢀ ꢀ ꢀO hydrogen bonds as
models for the study of keto–enol tautomerism [26–28]. Structur-
ally, Schiff bases derived from salicylaldehyde generally exist in
the phenol-imine form [29,30], and sometimes enamine or keto
tautomer, and a zwitterionic structure with a longer N+–H bond
[31]. Tris(hydroximethyl)amino methane (TRIS) has been widely
used in biochemistry and molecular biology as a component of
buffer solutions [32]. More recently, TRIS has been used also in
medicine against metabolic acidosis in acute lung injury [32].
Therefore, we have focused our attention in studies on the coor-
dination chemistry of vanadium(V) with such ligands. The present
work describes a new synthetic route for the preparation of three
new complexes of vanadium(V), as well as their structural charac-
terization, spectroscopy, and treatment in the view of the density
functional theory (DFT). The title compounds of this work are not
unusual because of their syntheses or even due to structural specif-
ities. They flee from known standards with respect to oxidovanadi-
um compounds, since, as we will see, vanadium(V) appears in form
⇑
Corresponding authors. Tel.: +55 55 3220 8868; fax: +55 55 3220 8031.
E-mail addresses: daviback@gmail.com (D.F. Back), manzonideo@smail.ufsm.br
(G. Manzoni de Oliveira).
0277-5387/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2012.01.015

22
D.F. Back et al. / Polyhedron 36 (2012) 21–29
stirred by 1 h under Ar atmosphere. The yellow precipitate was re-
moved by filtration. The slow evaporation of the mother solution
yielded yellow crystals. Yield: 84%.
Properties: yellow crystals. Melting point: 182–184 °C. Anal.
Calc. C, 65.36; H, 5.83; N, 16.34. Found: C, 65.02; H, 5.39; N,
CH3
N
HOOC CH
16.46%. IR (KBr, cmꢁ1): 3440 [shoulder,
m
(OꢁH)]; 2959 [weak,
OH
m
(CꢁH)]; 1680 [strong,
m
(C@O)]; 1638 [strong, (C@N)]; 1237
m
[middle,
m
(CꢁN)]; 1051 [strong, (CꢁO)alkoh].
m
HOOC CH
1H NMR (400 MHz, DMSO-d6): d 10.37 (s, 1H, CHO); 8.61 (s, 1H,
CHN); 7.78 (d, 1H, 1JHH = 3 Hz, ar); 7.73 (d, 1H, 1JHH = 3 Hz, ar); 4.97
(br, 3H, OH); 3.68 (s, 6H, CH2); 1.27 (s, 9H, CH3).
CH3
Fig. 1. Structure of Amavadin, reported by Garner et al. [12].
2.5. Synthesis of 4-tert-butyl-2-(1,3-dihydroxy-2-(hydroxymethyl)
propan-2-ylimino)methyl)-6-(dimethoxymethyl) phenol (L2)
of the uncommon cation [VO]3+, instead of the more frequent
dioxidovanadium species [VO2]+.
TRIS (0.121 g, 1 mmol), dissolved in 10 ml of anhydrous metha-
nol, was mixed with 0.103 g (0.5 mmol) of 5-(1,1-dimethylethyl)-
2-hydroxy-1,3-benzenedicarboxaldehyde. The bright yellow solu-
tion was stirred by 1 h under Ar atmosphere. After evaporation
of the solvent the oily product was recrystallized in a mixture of
methanol with 5% DMSO, resulting a yellow solid. Yield: 78%.
Properties: oily, yellow-orange substance. Anal. Calc. C, 65.36; H,
5.83; N, 16.34. Found: C, 65.02; H, 5.39; N, 16.46%. IR (KBr, cmꢁ1):
2. Experimental
2.1. X- ray crystallography
Data were collected with a Bruker APEX II CCD area-detector
diffractometer and graphite-monochromatized Mo K
a radiation.
The structures of 1, 2 and 3 were solved by direct methods using
SHELXS-97 [33]. Subsequent Fourier-difference map analyses yielded
the positions of the non-hydrogen atoms. Refinements were car-
ried out with the SHELXL-97 package [34]. All refinements were
made by full-matrix least-squares on F2 with anisotropic displace-
ment parameters for all non-hydrogen atoms. Hydrogen atoms
were included in the refinement in calculated positions. Drawings
were made with the DIAMOND for Windows [35]. Crystal data and
more details of the data collections and refinements are contained
in Table 1.
3396 [sh,
m
(OꢁH)]; 2956 [w,
m
(NCꢁH)]; 1634 [s,
m(C@N)]; 1236 [m,
m(CꢁN)]; 1049 [s,
m
(CꢁO)alkoh]. 1H NMR (400 MHz, DMSO-d6): d
8.56 (s, 1H, CHN); 7.50 (s, 1H, ar); 7.33 (s, 1H, ar); 5.58 (s, 1H,
CH); 4.59 (br, 3H, OH); 3.64 (s, 12H, CH2 + OCH3); 1.27 (s, 9H, CH3).
2.6. Synthesis of (2-(1,3-dihydroxy-2-(hydroxymethyl)propan-2-
ylimino)methyl)-6-methoxyphenol (L3)
L3 was prepared starting from o-vanillin, with basis on litera-
ture methods [3]. TRIS (0.121 g, 1 mmol), dissolved in 10 ml of
anhydrous methanol, was mixed with 0.150 g (1 mmol) of o-vanil-
lin. The bright yellow solution was stirred by 1 h under Ar atmo-
sphere. The slow evaporation of the solvent led to the formation
of a crystalline yellow solid. Yield: 93%.
2.2. Physical measurements
IR spectra were measured as KBr pellets on a Shimadzu FTIR-
spectrometer in the 4000–400 cmꢁ region. 1H NMR spectra for
1
the ligands 1 and 2 were acquired on a Bruker DPX 400 (1H at
400.13 MHz) in DMSO-d6/TMS (DMSO, dimethyl sulfoxide; TMS,
tetramethylsilane) solutions at 298 K. Abbreviations used for the
reported 1H NMR spectra are as follows: s, singlet; d, doublet and
br, broad.
Properties: yellow crystalline substance. Anal. Calc. C, 56.47; H,
6.66; N, 5.49. Found: C, 56.42; H, 6.69; N, 5.46%. IR (KBr, cmꢁ1):
3375 [sh,
m
(OꢁH)]; 2959 [w,
m
(CꢁH)]; 1638 [s,
m(C@N)]; 1237 [m,
m(CꢁN)]; 1051 [s,
m
(CꢁO)alkoh].
2.7. Synthesis of [VO(L1-3H+)]2ꢀdmso (1)
2.3. Computational details
L1 (0.2 mmol, 61.8 mg) was dissolved in 8 ml of methanol and
mixed with 0.1 mmol (27.9 mg) of 95% vanadyl acetylacetonate.
The mixture was stirred for 1.5 h at 100 °C. The precipitate was re-
moved by filtration and after few days the solvent evaporation
yielded orange crystals. Yield: 45%.
Properties: deep yellow, irregular crystals. Melting point: 182–
184 °C. Anal. Calc. for C18H26NO7SV (451.40): C, 65.36; H, 5.83; N,
16.34. Found: C, 65.02; H, 5.39; N, 16.46%. IR (KBr, cmꢁ1): 3431
First principles calculations based on the density functional the-
ory (DFT) have been performed using the GAUSSIAN 09 package [36].
The hybrid B3LYP functional was employed to the exchange and
correlation functional [37], and the molecular orbitals were de-
scribed using the 6-31+G(d,p) basis set [38]. Infrared vibrational
frequency calculations have been performed for the isolated mole-
cules forming the molecular crystals at the geometries directly ta-
ken from the crystallographic X-ray data. These non-optimized
geometries are determined not to be true local minima. Geometry
optimizations were then performed and the obtained geometries
were verified to exhibit only real infrared frequencies. The HOMO
and LUMO orbitals of each studied molecule at the equilibrium
geometries are then visualized using the GaussView 5 package
[39].
[sh,
(C@N)]; 1243 [m,
O)alkoh]; 955 [m,
(C@O2)sym].
m
(O–H)]; 2924 [w,
(C–N)ꢀ]; 1045 [m, d(S@O)dmso]; 1018 [s,
(V@O)alkoh]; 750 [w, (V@O2)ass]; 560 [m,
m
(C–H)]; 1678 [s,
m
(C@O)]; 1630 [s,
m
m
m
m
(C–
m
m
2.8. Synthesis of [VO(L2-3H+)]2 (2)
L2 (0.1 mmol, 40 mg) was dissolved in 8 ml of methanol and
mixed with 0.1 mmol (27.9 mg) of 95% vanadyl acetylacetonate.
The mixture was stirred for 2 h at 100 °C. The precipitate was re-
moved by filtration and after 45 days the solvent evaporation
yielded orange crystals. Yield: 20%.
Properties: orange, blade-forming crystals. Melting point: 182–
184 °C. Anal. Calc. for C18H26NO7V (419.34): C, 65.36; H, 5.83; N,
2.4. Synthesis of 5-tert-butyl-3-(1,3-dihydroxy-2-(hydroxymethyl)
propan-2-ylimino)methyl)-2-hydroxybenzaldehyde (L1)
TRIS (0.121 g, 1 mmol), dissolved in 10 ml of anhydrous metha-
nol, was mixed with 0.206 g (1 mmol) of 5-(1,1-dimethylethyl)-2-
hydroxy-1,3-benzenedicarboxaldehyde. The yellow solution was

D.F. Back et al. / Polyhedron 36 (2012) 21–29
23
Table 1
Crystal data and structure refinement for 1, 2 and 3.
Complex
1
2
3
Empirical formula
Formula weight
T (K)
Radiation, k (Å)
Crystal system
Space group
Unit cell dimensions
a (Å)
C
18H26NO7SV
C18H26NO7V
419.34
293(2)
0.71073
monoclinic
P21/c
C14H20NO7SV
397.31
293(2)
0.71073
monoclinic
P21/c
451.40
293(2)
0.71073
triclinic
ꢀ
P1
10.2553(11)
11.3306(11)
11.4504(12)
65.105(6)
15.9166(9)
10.7581(6)
11.8319(6)
11.9998(2)
11.6888(2)
12.4056(2)
b (Å)
c (Å)
a
(°)
b (°)
67.165(6)
98.348(4)
110.4500(10)
c
(°)
64.966(6)
1057.25(19)
2, 1.418
0.606
472
V (Å3)
2004.54(19)
4, 1.390
1630.39(5)
4, 1.619
Z, calculated density (g cmꢁ3
)
Absorption coefficient (mmꢁ1
F(000)
)
0.533
0.773
880
824
Crystal size (mm)
h range (°)
Index ranges
0.278 ꢂ 0.160 ꢂ 0.127
2.63–27.16
12 6 h 6 13
14 6 k 6 14
14 6 l 6 14
18244
0.256 ꢂ 0.193 ꢂ 0.088
2.57–25.76
19 6 h 6 19
13 6 k 6 12
14 6 l 6 14
15323
0.164 ꢂ 0.133 ꢂ 0.075
1.81–27.13
15 6 h 6 15
14 6 k 6 14
15 6 l 6 15
14943
Reflections collected
Reflections unique
Completeness to theta max.
Absorption correction
4647 [Rint = 0.0426]
98.9%
3797 [Rint = 0.0974]
98.9%
3594 [Rint = 0.0714]
99.9%
Maximum and minimum transmission
Refinement method
0.9652 and 0.9359
full-matrix
0.9325 and 0.8643
full-matrix
0.9608 and 0.8639
full-matrix
least-squares on F2
4647/0/262
least-squares on F2
3797/18/280
least-squares on F2
3594/0/225
Data/restraints/parameters
Goodness-of-fit (GOF) on F2
1.080
1.002
1.056
Final R indices [I > 2
R indices (all data)
r
(I)]
R1 = 0.0661, wR2 = 0.1741
R1 = 0.0914, wR2 = 0.1915
0.635 and 0.827
R1 = 0.0591, wR2 = 0.1205
R1 = 0.1313, wR2 = 0.1481
0.298 and 0.250
R1 = 0.0458, wR2 = 0.1130
R1 = 0.0803, wR2 = 0.1408
0.547 and ꢁ0.482
Largest difference peak and hole (e Åꢁ3
)
16.34. Found: C, 65.02; H, 5.39; N, 16.46%. IR (KBr, cmꢁ1): 3440 [sh,
m
(OꢁH)]; 2957 [w,
1108 [s,
(CꢁO)hemiacetal]; 1054 [s,
(V@O)alkoh]; 670 [w, (V@O2)ass]; 567 [m, m(C@O2)sym].
m
(NCꢁH)]; 1625 [s,
m
(C@N)]; 1292 [m,
m
(CꢁN)ꢀ];
m
m
(CꢁO)alkoh]; 964 [m,
m
m
2.9. Synthesis of [VO(L3-3H+)]2ꢀdmso (3)
Complex 3 was prepared with basis on literature methods [9].
L3 (0.1 mmol, 40 mg) was dissolved in 10 ml of methanol together
with 0.1 mmol (27.9 mg) of 95% vanadyl acetylacetonate. The mix-
ture was stirred for 1 h at 80 °C. The precipitate was removed by
filtration and after 20 days the solvent evaporation yielded dark-
brown crystals. Yield: 35%.
Properties: dark-brown crystalline substance. Melting point:
179ꢁ181 °C. Anal. Calc. for C14H20NO7SV (397.31): C, 43.57; H,
4.74; N, 3.91. Found: C, 44.02; H, 4.39; N, 3.69%. IR (KBr, cmꢁ1):
3431 [sh,
m
(OꢁH)]; 2924 [w,
m
(CꢁH)]; 1630 [s,
m
(C@N)]; 1296 [m,
m
m
(CꢁN)]; 1052 [m, d(S@O)dmso]; 1018 [s,
m
(CꢁO)alkoh]; 955 [m,
(V@O)alkoh]; 750 [w,
m(V@O2)ass].
Fig. 2. Molecular structure of complex 1 with 50% thermal (by DIAMOND [35])
ellipsoids. Symmetry operations used to generate equivalent atoms: (#) 1 ꢁ x, 1 ꢁ y,
ꢁz. For clarity, the hydrogen atoms are omitted.
3. Results and discussion
3.1. Structure
six, giving a distorted octahedral geometry. This fact can be con-
firmed from the analysis of the angles formed between the atoms
O4–V–O2, O5–V–N1 and O1–V–O4#, which are, respectively,
170.83(15)°, 167.38(11)° and 153.02(11)°.
The distances of the V–O bonds around the atoms of vanadium
(O2, O1, O4, O5 and O#4) range from 1.601(5) (the double bond
character of the vanadyl oxygen) to 2.276(6) Å. On the other hand,
the distance of the V–N1 bond is 2.130(9) Å. The values found are
Fig. 2 exhibits the dimeric arrangement with an inversion cen-
ter of the binuclear complex [VO(L1-3H+)]2ꢀdmso (1). Each poly-
dentate ligand L1 contributes with five coordination sites: two
oxygen atoms ꢁ one of them with a bridge function ꢁ from the
twofold deprotonated molecule of TRIS, a nitrogen (imine) bond
and a deprotonated phenolic oxygen atom, as can be seen in
Fig. 2. Thus, the two metal centers have a coordination number

24
D.F. Back et al. / Polyhedron 36 (2012) 21–29
Table 2
Selected bond lengths (Å) and angles (°) for the compounds 1, 2 and 3.
Complex 1
Complex 2
Bond lengths and angles
VꢁO2
1.601(3)
1.789(2)
1.885(2)
1.894(2)
2.131(3)
2.276(2)
1.408(4)
1.427(4)
2.276(2)
1.406(5)
1.323(4)
1.194(5)
1.285(4)
1.491(4)
1.521(3)
1.766(5)
1.789(6)
VꢁO1
1.590(3)
1.781(3)
1.851(3)
1.899(3)
2.118(3)
2.386(3)
1.430(4)
2.386(3)
1.323(5)
1.417(4)
0.8200
VꢁO5
VꢁO5
VꢁO1
VꢁO2
VꢁO4
VꢁO4
VꢁN
VꢁN
VꢁO4#1
O5ꢁC25
O4ꢁC24
O4ꢁV#1
O3ꢁC23
O1ꢁC1
VꢁO4#1
O4ꢁC24
O4ꢁV#1
O2ꢁC1
O3ꢁC23
O3ꢁH3
O6ꢁC61
NꢁC21
NꢁC22
O7ꢁC61
O6ꢁC61
NꢁC21
1.411(5)
1.286(5)
1.486(5)
1.382(5)
NꢁC22
O7ꢁS
C18ꢁS
C17ꢁS
O2ꢁVꢁO5
O2ꢁVꢁO1
O5ꢁVꢁO1
O2ꢁVꢁO4
O5ꢁVꢁO4
O1ꢁVꢁO4
O2ꢁVꢁN
99.96(12)
101.25(12)
96.01(11)
98.05(12)
99.00(11)
153.04(11)
92.30(12)
167.39(11)
84.39(11)
76.16(10)
170.84(11)
86.72(10)
84.14(10)
74.55(10)
80.78(10)
105.45(10)
118.0(3)
O1ꢁVꢁO5
O1ꢁVꢁO2
O5ꢁVꢁO2
O1ꢁVꢁO4
O5ꢁVꢁO4
O2ꢁVꢁO4
O1ꢁVꢁN
101.83(14)
104.04(15)
97.05(12)
99.58(13)
94.91(12)
150.63(12)
90.41(13)
166.52(14)
85.26(12)
77.30(12)
170.96(12)
85.23(11)
73.95(11)
80.42(11)
82.06(11)
106.05(11)
119.4(3)
O5ꢁVꢁN
O5ꢁVꢁN
O1ꢁVꢁN
O2ꢁVꢁN
O4ꢁVꢁN
O4ꢁVꢁN
O2ꢁVꢁO4#1
O5ꢁVꢁO4#1
O1ꢁVꢁO4#1
O4ꢁVꢁO4#1
NꢁVꢁO4#1
VꢁO4ꢁV#1
C21ꢁNꢁC22
C21ꢁNꢁV
C22ꢁNꢁV
O1ꢁVꢁO4#1
O5ꢁVꢁO4#1
O4ꢁVꢁO4#1
O2ꢁVꢁO4#1
NꢁVꢁO4#1
VꢁO4ꢁV#1
C21ꢁNꢁC22
C21ꢁNꢁV
C1ꢁO2ꢁV
Fig. 3. Section of the extended one-dimensional chain of the complex 1. Symmetry
operations used to generate equivalent atoms: (#) 2 ꢁ x, 1 ꢁ y, ꢁz. For clarity, the
hydrogen atoms not involved in secondary bonds (dashed lines) are omitted.
Table 3
128.2(2)
113.6(2)
126.3(3)
137.3(3)
Secondary interactions: lengths (Å) and angles (°) for complex 1.
(D–Hꢀ ꢀ ꢀA)a
D–H (Å)
Hꢀ ꢀ ꢀA (Å)
Dꢀ ꢀ ꢀA (Å)
D–Hꢀ ꢀ ꢀA (°)
Complex 3
O2ꢀ ꢀ ꢀH18c–C18
O2#ꢀ ꢀ ꢀH18b–C18
H25b#ꢀ ꢀ ꢀO6@C51
H24a#ꢀ ꢀ ꢀO6@C51
0.960(7)
0.960(6)
0.914(4)
0.970(5)
2.451(9)
2.484(11)
2.607(4)
2.685(13)
2.342(14)
3.432(16)
3.347(15)
3.507(17)
154.40(34)
169.21(33)
152.99(43)
142.99(24)
Bond lengths and angles
VꢁO1
VꢁO4
VꢁO2
VꢁO5
VꢁN
1.603(2)
1.783(2)
1.871(2)
1.914(2)
2.128(3)
2.270(2)
1.504(3)
1.776(4)
1.294(4)
a
D, donor; A, acceptor.
VꢁO5#1
SꢁO7
SꢁC13
NꢁC8
oxide molecule. Fig. 3 allows the visualization of intermolecular
O2ꢀ ꢀ ꢀH–C secondary interactions in the ab plane, between the
atoms O2ꢀ ꢀ ꢀH18c–C18 and C18–H18bꢀ ꢀ ꢀO2#. The O2(#)ꢀ ꢀ ꢀH–C an-
gles and distances confirm that these intermolecular bonds sup-
port the growth of a supramolecular assembly of complex 1
along the crystallographic a axis (see Fig. 3, symmetry transforma-
tions used to generate equivalent atoms: (#) 2 ꢁ x, 1 ꢁ y, ꢁz). The
comparison of hydrogen secondary bonds for compound 1 is
shown in Table 3.
In addition to these intermolecular interactions involving the
solvate molecules, it is noteworthy that also along the a axis there
is an expressive number of further bifurcated hydrogen bonding, as
shown in Fig. 4 [40–44]. These secondary bonds are of electrostatic
nature, but sometimes their nature can undergo variations.
According to Desiraju and Steiner [44], for supramolecular organi-
zations the directionality of the connection depends on the donor
and the receiver, as is shown in Scheme 1.
O1ꢁVꢁO4
O1ꢁVꢁO2
O4ꢁVꢁO2
O1ꢁVꢁO5
O4ꢁVꢁO5
O2ꢁVꢁO5
O1ꢁVꢁN
100.20(12)
102.14(12)
97.99(10)
97.61(11)
97.40(10)
152.31(10)
90.78(12)
167.89(11)
84.54(10)
75.91(10)
169.73(11)
85.98(9)
84.96(9)
73.31(9)
82.44(9)
106.69(9)
127.6(2)
O4ꢁVꢁN
O2ꢁVꢁN
O5ꢁVꢁN
O1ꢁVꢁO5#1
O4ꢁVꢁO5#1
O2ꢁVꢁO5#1
O5ꢁVꢁO5#1
NꢁVꢁO5#1
VꢁO5ꢁV#1
C8ꢁNꢁV
The supramolecular organization depicted in Fig. 4 exemplifies
the parameters shown in Scheme 1: for strong hydrogen bonds, the
directionality of the receiver matches the geometry of the product
obtained by the covalent bond of a hypothetical proton transfer
reaction [45,46].
within the range of bond lengths of V–N and V–O expected, accord-
ing to data of the literature [9]. Some selected bond lengths and an-
gles of 1, 2 and 3 are resumed in Table 2.
The molecule has numerous hydrogen interactions, some of
them being associated with the solvate molecule of dimethylsulf-
The adequate knowledge of the nature of hydrogen bonds and
of the acceptor–receiver concept can provide a good basis for the

D.F. Back et al. / Polyhedron 36 (2012) 21–29
25
Fig. 4. Bifurcated hydrogen interactions in complex 1. Symmetry operations used to generate equivalent atoms: (#) 1 + x, ꢁ1 + y, z. For clarity, the hydrogen atoms not
involved in secondary bonds (dashed lines) are omitted.
inversion center of complex 1 was observed. The double, covalent
VꢁO1 bond presents shorter distance (1.590(2) Å) than the
coordinative ones VꢁO5 (1.781(1)), VꢁO2 (1.851(4)), VꢁO4
(1.899(1)), VꢁO4# (2.386(3)) and VꢁN (2.118(1) Å). This causes a
distortion of the octahedral geometry of the vanadium(V) ion. The
axial angle NꢁVꢁO5 measures 166.52°, thus, the binuclear complex
2 presents the same geometry of complex 1, a distorted octahedral
Scheme 1. Supramolecular arrangements and the geometric parameters for the
configuration. In the case of complex 2, an interesting difference
was observed in the substituted aldehyde (O6, see Fig. 2), with the
formation of an acetal (C61, see Fig. 5).
hydrogen bond according to Desiraju and Steiner [44] (D, donor; R, receiver).
The formation of an acetal group from the reaction between the
aldehyde and methanol was confirmed by the 1H NMR experi-
ments. By comparing the 1H NMR spectra of complexes 1 and 2
it is possible to observe in the spectrum of 2 the vanishing of the
signal at 10.37 ppm for the aldehyde (present in the spectrum of
1), and the appearance of a signal at 5.58 ppm for the CH group
of the acetal. Furthermore, it has been also recorded an intensive
signal at 3.64 ppm, corresponding to 12H, regarding the two meth-
oxyl signals (6H) of each ligand.
understanding of supramolecular assemblies and the crystal
engineering of this kind of compound. Specifically, supramolecular
synthons [47] based upon bifurcated and trifurcated hydrogen
bonds involving these acceptor groups have been successfully
described.
The dimeric structure of [VO(L2-3H+)]2 (2), shown in Fig. 5, is
similar to that of compound 1. The coordination of L2 with VO3+
occurs through the deprotonated oxygen atoms O2, O5,
l-O4 and
l-O4#, as well as the nitrogen of the neutral imino ligand. The same
Fig. 5. A representation of the molecular structure of complex 2, generated by reflection of the asymmetric unit. Symmetry transformations used to generate equivalent
atoms: # 1 ꢁ x, 2 ꢁ y, 1 ꢁ z. For clarity, the hydrogen atoms are omitted.

26
D.F. Back et al. / Polyhedron 36 (2012) 21–29
OH OH
OH OH
HO
H
O R
N
H
OH
O
HO
N
H
OH
O
HOR
H
H
R = alkyl
prototropism
OH OH
OH OH
H
H
HO
H
HO
N
H
OH
O
O R
N
OH
O
O R
H
H
H
RO
H
Fig. 6. Molecular structure of the complex 3. For clarity, the DMSO molecule is not
displayed. Symmetry transformations used to generate equivalent atoms: # ꢁx, ꢁy,
2 ꢁ z. For clarity, the hydrogen atoms are omitted.
Hemiacetal
OH OH
OH OH
R
O
HO
N
H
OH
R
R
O
HO
N
OH O
H
H
H
H2O
OR
Acetal
Scheme 2. Proposed mechanism for the formation of the acetal group in complex 2.
Hemiacetals result from addition of an alcohol’s hydroxyl group
to the carbon in the C@O bond. This kind of organic substituent
represents an example of the dynamic covalent chemistry (DCC)
and results from the introduction into molecules of bonds formed
through reversible chemical reactions. To expand the possibilities
of DCC it is necessary to explore other reversible reactions with
controllable formation efficiency and exchange kinetics [48]. The
hemiacetal groups are important species because they are efficient
organic ligands for the achievement of a wide variety of 3d-metal
clusters of high nuclearity with interesting optical and magnetic
properties, as well as for the synthesis of actinide complexes. We
propose the mechanism described further in Scheme 2 for the
obtainment of this organic functions in complex 2 [49,50].
Fig. 7. DIAMOND plot of complex
3 with the atom numbering. The thermal
ellipsoids are drawn at 50% probability level. Symmetry code for the generated
atoms: # x, 0.5 ꢁ y, ꢁ0.5 + z; # 2 ꢁx, 0.5 + y, 1.5 ꢁ z. For clarity, the hydrogen atoms
not involved in secondary bonds (dashed lines) are omitted.
In [VO(L3-3H+)]2ꢀdmso (3), whose structure is depicted in Fig. 6,
the V–O and V–N distances are not in disagreement with these dis-
tances in other analogue compounds: the V–O distances are
1.603(2) {V–O1}, 1.871(2) {V–O2}, 1.784(2) {V–O4}, 1.914(2) {V–
Fig. 7. Table 4 resumes the intermolecular secondary interactions
of 3.
l-O5} and 2.270(2) Å {V–l-O5#}, while the V–N distance is
2.129(5) Å (symmetry transformations used to generate equivalent
atoms: # ꢁx, ꢁy, 2 ꢁ z). Complex 3 exhibits also a dinuclear (di-
meric) oxidovanadium(V) structure, having an inversion center.
Both vanadium atoms are in the center of distorted octahedral
environments. From the three CH2OH groups, one is free and the
other two are bound to the metal center after deprotonation.
The single structure illustrated in Fig. 6 seems to be very similar
to the other examples discussed in this work, but if we compare
the hydrogen interactions between the VꢁO1 fragment and the
neighboring molecules, it becomes clear that, unlike the first exam-
ple, we have now the contribution of hydrogen bonds not only
from the DMSO solvate, but also from CꢁH units, yielding a typical
example of trifurcated hydrogen interactions [40,41], as shown in
3.2. DFT calculations
Fig. 8 shows the highest occupied (HOMO) and the lowest unoc-
cupied (LUMO) molecular orbitals of the complexes 1, 2 and 3. It
can be clearly seen that, independently of the substituent at the
ortho position of the benzene ring (aldehyde, hemiacetal, and o-
vanillin), the frontier orbitals present similar character. The Ci
point group symmetry of these molecules is also reflected at these
(frontier) orbitals. The HOMO levels show greater contributions of
p-like orbitals at the benzene rings at both sides of the molecule
centers, with smaller contributions from p-orbitals at the N and
O atoms close to the benzene rings. On the other hand, the LUMO

D.F. Back et al. / Polyhedron 36 (2012) 21–29
27
Table 4
electrons, f(r) is the Fukui function, with
g
and S being the global
Secondary interactions: lengths (Å) and angles (°) for complex 3.
hardness an global softness of the system. From the equation above,
one can see that the Fukui function is given as the derivative of the
electronic density with respect to the total number of electrons for a
fixed external potential
(DꢁHꢀ ꢀ ꢀA)
DꢁH (Å)
0.960(5)
0.929(4)
0.991(3)
Hꢀ ꢀ ꢀA (Å)
2.574(2)
2.476(3)
2.540(3)
Dꢀ ꢀ ꢀA (Å)
3.418(5)
3.228(5)
3.524(4)
DꢁHꢀ ꢀ ꢀA (°)
146.77(28)
138,24(23)
172.24(28)
O1ꢀ ꢀ ꢀH13b#–C13#
O1ꢀ ꢀ ꢀH8#–C8#
O1ꢀ ꢀ ꢀH12b#2 –C12#2
ꢀ
ꢁ
@
q
@N
ðrÞ
fðrÞ ¼
;
mðrÞ
while the global hardness (the negative electronegativity) is defined
by
orbitals are concentrated in the center of the molecules. The great-
er contributions of the LUMO orbitals come from d-orbitals of the
vanadium atoms, with further significant contributions from the
p-like orbitals of the O atoms around the V atoms. Such frontier
orbitals characterize a ligand–metal CT transition for these kinds
of compounds.
ꢀ
ꢁ
@N
g
¼
¼ ꢁv
;
@
l
mðrÞ
where
v
is the electronegativity.
The calculated HOMO–LUMO energy gaps are: 3.43 eV
(361.88 nm), 3.45 eV (359.78 nm), and 3.26 eV (380.75 nm), for
the molecules containing aldehyde (1), hemiacetal (2), and methox-
yl (of o-vanillin) (3) as substituents at the benzene rings, respec-
tively. The closeness of the calculated gaps for the three
molecules, all in the UV region, is related to the character of the fron-
tier orbitals, which do not depend directly of the substituents.
The local version of the Hard and Soft Acids and Bases principle
[51] has been used to investigate the nucleophilic and electrophilic
centers of the three studied complex molecules. According to the
conceptual density functional theory [52], the regioselective reac-
tivity of a chemical system can be given by the local softness,
S(r), which can be defined as [53]
For chemical reactions in which the system exchanges an elec-
tron, the derivatives defining f(r) and
g can be calculated by finite
differences as
fþðrÞ ¼ qm;Nþ1ðrÞ ꢁ qm;NðrÞ;
fꢁðrÞ ¼ qm;NðrÞ ꢁ qm;Nꢁ1ðrÞ;
I ꢁ A
g
¼
2
with I and A being the vertical ionization potential and electron
affinity, respectively.
The Fukui functions f+(r) and fꢁ(r) will give the regions at which
the molecular system is most able to accommodate the addition
and removal of an electron, respectively. Hence, large values of
f+(r) will indicate the molecular regions most susceptible to nucle-
ophilic attacks, while large fꢁ(r) values will be associated with re-
gions susceptible to electrophilic attacks.
ꢀ
ꢁ
ꢀ
ꢁ
@
q
ðrÞ
@N
fðrÞ
SðrÞ ¼
¼
fðrÞ ¼
¼ SfðrÞ;
@
l
@
l
g
mðrÞ
mðrÞ
We have performed total energy calculations for the three stud-
ied molecules at three different charge states, i.e., neutral, singly
positively and negatively charged. All these calculations were
where
potential
q
(r) represents the electronic density,
l is the chemical
m
(r) is the external potential, N is the total number of
Fig. 8. Highest occupied (HOMO) in left column and the lowest unoccupied molecular orbitals (LUMO) in right column of the molecules, respectively, for compounds 1, 2 and
3.

28
D.F. Back et al. / Polyhedron 36 (2012) 21–29
Fig. 9. The calculated maps of the Fukui functions, f+(r) and fꢁ(r). The highest values at the f+(r) maps, at the left column show the most reactive sites for nucleophilic attacks,
i.e., the electrophilic centers of these molecules, whereas the highest values at the fꢁ(r) maps, at the right column, show the nucleophilic centers of these molecules.
performed at the equilibrium geometries of the neutral charge
state of the molecules. From these calculations we determined I
are other nucleophilic centers located at the C atoms near the butyl
groups for the molecules containing the aldehyde and hemiacetal
groups, and at the O atoms close to the o-vanillin group for the mol-
ecule containing this specific chemical group. It must be pointed out
that comparison between experimentally determined and theoret-
ically predicted quantities like IP (ionization potential) and EA (elec-
tronic affinity) would give a better account of the degree of accuracy
of the used theoretical approach. However, we would like to stress
that the experimental samples are crystals, not isolated molecules,
and although they are molecular crystals, the crystalline environ-
ment will certainly influence the experimental values for work
functions and electron affinities. It means that IPs and EAs obtained
from calculations for isolated molecules would be of low predictive
value in our case. Actually, one possible theoretical approach capa-
ble to take into account the influence of crystal fields on the proper-
ties of molecules in molecular crystals would be the use of
polarizable continuum models (PCM) [54]. It would require the
determination of the PCM parameters for each of the crystalline
environments involving each molecular unit in the molecular crys-
tals (which would be seen as continuum media). This, however,
would be out of the scope of this paper. Furthermore, even if we
decided to show the calculated vertical IP and EA values for each iso-
lated molecule (which is an easy task once the equilibrium struc-
tures are already determined), we would need to compare them
with results from direct and inverse photoemission spectroscopy
measurements. Unfortunately, these techniques are not available
in our laboratory nowadays.
and A, and consequently
g, as well as spatial maps of the Fukui
functions f (r) (that are similar to the s (r) maps).
The calculated values for the vertical ionization potentials/elec-
tronic affinities are 7.58/2.04, 6.92/1.37 and 6.79/1.29 eV, resulting
also very similar global hardness values: 2.77, 2.78 and 2.75 eV for
the molecules containing aldehyde, hemiacetal and methoxyl (o-
vanillin), respectively (complexes 1, 2 and 3). These global hard-
ness values suggest that these three molecules will act similarly
against electrophilic, nucleophilic or radical attacks.
The calculated maps of the Fukui functions, f+(r) and fꢁ(r), are
shown in Fig. 9. The highest values at the f+(r) maps, at the left col-
umn of Fig. 9, show the most reactive sites for nucleophilic attacks,
i.e., the electrophilic centers of these molecules, whereas the high-
est values at the fꢁ(r) maps, at the right column of Fig. 9, show the
nucleophilic centers of these molecules.
The f+(r) maps show that the spatial localization of active electro-
philic centers of these molecules resemble the respective LUMO
orbitals, i.e., these molecules tend to receive electrons mainly
through the V atoms, with smaller contributions from the O atoms
close to the V atoms at the molecules. The nucleophilic centers of
these molecules shown at the fꢁ(r) maps, on the other hand, do
not have the same information as the respective HOMO orbitals.
Contrarily to the HOMO orbitals, which have great contributions
from the benzene rings, the nucleophilic centers are located at the
O atoms that connect the V atoms and the benzene rings. There

D.F. Back et al. / Polyhedron 36 (2012) 21–29
29
[12] R.E. Berry, E.M. Armstrong, R.L. Beddoes, D. Collison, S.N. Ertok, M. Helliwell,
C.D. Garner, Angew. Chem., Int. Ed. 38 (1999) 795.
4. Conclusions
[13] K.B. Garbutcheon-Singh, M.P. Grant, B.W. Harper, A.M. Krause-Heuer, M.
Manohar, N. Orkey, J.R. Aldrich-Wright, Curr. Top. Med. Chem. 11 (2011) 521.
[14] G.G. Nunes, A.C. Bonatto, C.G. Albuquerque, A. Barison, R.R. Ribeiro, D.F. Back,
A.V.C. Andrade, E.L. Sá, F.O. Pedrosa, J.F. Soares, E.M. Souza, J. Inorg. Biochem.
(2011), doi:10.1016/j.jinorgbio.2011.11.019.
[15] R. Liasko, T.A. Kabanos, S. Karkabounas, M. Malamas, A.J. Tasiopoulos, D.
Stefanou, P. Collery, A. Evangelou, Anticancer Res. 18 (1998) 3609.
[16] A. Evangelou, S. Karkabounas, G. Kalpouzos, M. Malamas, R. Liasko, D.
Stefanou, A.T. Vlahos, T.A. Kabanos, Cancer Lett. 119 (1997) 221.
[17] A. Papaioannou, M. Manos, S. Karkabounas, R. Liasko, V. Kalfakakou, I. Correia,
A. Evangelou, J. Costa Pessoa, T.A. Kabanos, J. Inorg. Biochem. 98 (2004) 959.
[18] M.P. Waller, K.R. Geethalakshmi, M. Buhl, J. Phys. Chem. B 112 (2008) 5813.
[19] S.A. Taghavi, M. Moghadam, I. Mohammadpoor-Baltork, S. Tangestaninejad, V.
Mirkhani, A.R. Khosropour, V. Ahmadi, Polyhedron 30 (2011) 2244.
[20] J.P. Gaffney, A.M. Valentine, Biochemistry 48 (2009) 11609.
[21] D. Sadhukhan, A. Ray, G. Rosair, L. Charbonnière, S. Mitra, Bull. Chem. Soc. Jpn.
84 (2) (2011) 211.
We have described the synthesis and the structural characteriza-
tion, together with DFT studies, of the three new oxidovanadium(V)
complexes of the cation [VO]3+, [VO(L1-3H+)]2ꢀdmso (1), [VO(L2-
3H+)]2 (2) and [VO(L3-3H+)]2ꢀdmso (3), where L are different Schiff
bases ligands (see Section 2). The reactions reported in this work
corroborate also earlier literature statistics [55,56], that dibasic tri-
dentate ligands prefer dimeric vanadium complexes. The oxidation
of the starting reagent [VO]2+ from IV to V, assuming the chelated
form [VO]3+, can be explained also with basis in results obtained
by Rao [9], according to which the final presence of VO2 or VO3+
+
dinuclear complexes depends upon the reaction conditions: vana-
dium exists in acidic solutions as VO2+, and in highly alkaline med-
ium as tetrahedral VO43ꢁ [57]. It has been reported the formation of
VO3+ and VO2+ using the same ligand, under different experimental
conditions, but without any X-ray structure [58]. Reactions per-
formed [9] in neutral medium between VO(acac)2 and H3Ly
(L = Schiff base ligand holding alkoxo group(s); Ly = L2, L7, L8) gave
as products [VOLy]2, also, dimers of the core VO3+. The synthesis of
a large variety of alkoxo-bound oxidovanadium(V) complexes using
Schiff bases as ligands resulted in VO3+ and VO2+ complexes, and the
studies on their interconversions have shown that the addition of
[22] A.T. Chaviara, P.J. Cox, R.M. Papi, K.T. Papazisis, D. Zambouli, A.H. Kortsaris, D.A.
Kyriakidis, C.A. Bolos, J. Inorg. Biochem. 98 (8) (2004) 1271.
[23] X. Qiao, Z.Y. Ma, C.Z. Xie, F. Xue, Y.W. Zhang, J.Y. Xu, Z.Y. Qiang, J.S. Lou, G.J.
Chen, S.P. Yan, J. Inorg. Biochem. 105 (5) (2011) 728.
[24] I. Yilmaz, H. Temel, H. Alp, Polyhedron 27 (2008) 125.
[25] E. Hadjoudisa, A. Rontoyiannib, K. Ambroziakc, T. Dziembowskac, I.M.
Mavridis, J. Photochem. Photobiol. A: Chem. 162 (2004) 521.
[26] K. Uzarevic, M. Rubcic, V. Stilinovic, B. Kaitner, M. Cindric, J. Mol. Struct. 984
(2010) 232.
[27] G. Türkoglu, H. Berber, H. Dal, C. Ögretir, Spectrochim. Acta, Part A 79 (2011)
1573.
[28] P. Fita, E. Luzina, T. Dziembowska, D. Kopec, P. Piatkowski, Cz. Radzewicz, A.
Grabowska, Chem. Phys. Lett. 416 (2005) 305.
[29] D.M. Boghaei, M. Gharagozlou, Spectrochim. Acta, Part A 67 (2007) 944.
[30] J. Vanco, J. Marek, Z. Trávnícek, E. Racanská, O. Sajlenová, J. Muselík, J. Inorg.
Biochem. 102 (2008) 595.
[31] R. Fernando Martínez, Ma. Ávalos, R. Babiano, P. Cintas, J.L. Jiménez, M.E. Light,
J.C. Palacios, Eur. J. Org. Chem. (2011) 3137.
[32] S.S. Harsha, D. Grischkowsky, J. Phys. Chem. A 114 (2010) 3489.
[33] G.M. Sheldrick, SHELXS-97: Program for Crystal Structure Solution, University of
Göttingen, Germany, 1997.
[34] G.M. Sheldrick, SHELXL-97: Program for Crystal Structure Refinement, University
of Göttingen, Germany, 1997.
[35] K. Brandenburg, DIAMOND 3.1a. 1997–2005, Version 1.1a. Crystal Impact GbR,
Bonn, Germany.
small amounts of acid converts VO2 to VO3+, but the reverse does
+
not happen in the presence of base [9].
The results of DFT calculations show that the distribution of the
electron density in the title complexes is very similar, also if com-
pared with other molecules already synthesized by us. Such equal-
itarian distribution of electron density may reveal, among other
consequences, a tendency for inhibition of the biological activity
of certain enzymes, such as acetylcholine. This performance, how-
ever, deserves further systematic studies, before one can make any
statements about it.
[36] M.J. Frisch, G.W. Trucks, H.B. Schlegel, G.E. Scuseria, M.A. Robb, J.R. Cheeseman,
G. Scalmani, V. Barone, B. Mennucci, G.A. Petersson, H. Nakatsuji, M. Caricato,
X. Li, H.P. Hratchian, A.F. Izmaylov, J. Bloino, G. Zheng, J.L. Sonnenberg, M.
Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y.
Honda, O. Kitao, H. Nakai, T. Vreven, J.A. Montgomery Jr., J.E. Peralta, F. Ogliaro,
M. Bearpark, J.J. Heyd, E. Brothers, K.N. Kudin, V.N. Staroverov, R. Kobayashi, J.
Normand, K. Raghavachari, A. Rendell, J.C. Burant, S.S. Iyengar, J. Tomasi, M.
Cossi, N. Rega, J.M. Millam, M. Klene, J.E. Knox, J.B. Cross, V. Bakke, C. Adamo, J.
Jaramillo, R. Gomperts, R.E. Stratmann, O. Yazyev, A.J. Austin, R. Cammi, C.
Pomelli, J.W. Ochterski, R.L. Martin, K. Morokuma, V.G. Zakrzewski, G.A. Voth,
P. Salvador, J.J. Dannenberg, S. Dapprich, A.D. Daniels, O. Farkas, J.B. Foresman,
J.V. Orti, J. Cioslowski, D.J. Fox, GAUSSIAN 09, Revision A.02, Gaussian, Inc.,
Wallingford, CT, 2009.
[37] A.D. Becke, J. Chem. Phys. 98 (1993) 1372.
[38] G.A. Petersson, A. Bennett, T.G. Tensfeldt, M.A. Al-Laham, W.A. Shirley, J.
Mantzaris, J. Chem. Phys. 89 (1988) 2193.
[39] Roy Dennington, Todd Keith, John Millam, GaussView, Version 5, Semichem
Inc., Shawnee Mission KS, 2009.
[40] D.F. Back, G. Manzoni de Oliveira, M. Hörner, F. Broch, Polyhedron 31 (2012) 558.
[41] L. Checinska, S.J. Grabowski, M. Malecka, J. Phys. Org. Chem. 16 (2003) 213.
[42] L.S. Glass, B. Nguyen, K.D. Goodwin, C. Dardonville, W.D. Wilson, E.C. Long,
M.M. Georgiadis, Biochemistry 48 (2009) 5943.
Acknowledgements
Brazilian Research Councils CNPq and FAPERGS-Fundação de
Amparo à Pesquisa do Estado do Rio Grande do Sul Edital No.
003/2009 and Edital No. 002/2011.
Appendix A. Supplementary data
CCDC 856023, 856024, 856025 contain the supplementary
crystallographic data for this paper. These data can be obtained
free of charge via http://www.ccdc.cam.ac.uk/conts/retriev-
ing.html, 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.
References
[43] P. Sharma, M. Chawla, S. Sharma, A. Mitra, RNA 16 (2010) 942.
[44] G.R. Desiraju, T. Steiner, Structural Chemistry and Biology: The Weak
Hydrogen Bond (International Union of Crystallography – Monographs on
Crystallography), Oxford University Press, 2001.
[1] J. Chakravarty, S. Dutta, S.K. Chandra, P. Basu, A. Chakravorty, Inorg. Chem. 32
(1993) 4249.
[45] S.J. Grabowski, J. Phys. Org. Chem. 17 (2004) 18.
[46] J.C. Mareque Rivas, L. Brammer, Inorg. Chem. 37 (1998) 4756.
[2] S. Mondal, S. Dutta, A. Chakravorty, J. Chem. Soc., Dalton Trans. (1995) 1115.
[3] J. Chakravarty, S. Dutta, A. Dey, A. Chakravorty, J. Chem. Soc., Dalton Trans.
(1994) 557.
[4] T.A. Kabanos, A.D. Keramidas, A. Papaioannou, A. Terzis, Inorg. Chem. 33 (1994)
845.
[5] A.D. Keramidas, A.B. Papaioannou, A. Vlahos, T.A. Kabanos, G. Bonas, A.
Makriyannis, C.P. Rapropoulou, A. Terziz, Inorg. Chem. 35 (1996) 357.
[6] V.A. Nikolakis, P. Stathopoulos, V. Exarchou, J.K. Gallos, M. Kubicki, T.A.
Kabanos, Inorg. Chem. 49 (2010) 52.
[7] T. Lovell, R.A. Torres, W.-G. Han, T. Liu, D.A. Case, L. Noodleman, Inorg. Chem.
41 (2002) 5744.
ˇ
´
[47] D. Drahonovsky, J.-M. Lehn, J. Org. Chem. 74 (2009) 8428.
[48] C. Villiers, P. Thuéry, M. Ephritikhine, Polyhedron 29 (2010) 1593.
[49] K. Funabiki, Y. Itoh, Y. Kubota, M. Matsui, J. Org. Chem. 76 (2011) 3545.
[50] T.J. Przystas, T.H. Fife, J. Am. Chem. Soc. 103 (1981) 4884.
[51] R.G. Parr, R.G. Pearson, J. Am. Chem. Soc. 105 (1983) 7512.
[52] P. Geerlings, F. De Proft, W. Langenaeker, Chem. Rev. 103 (2003) 1793.
[53] W.T. Yang, R.G. Parr, Proc. Natl. Acad. Sci. USA 82 (1985) 6723.
[54] P.K. Nayak, N. Periasamy, Org. Electron. 10 (2009) 1396.
[55] A. Syamal, K.S. Kale, Inorg. Chem. 18 (1979) 992.
[56] C.J. Carrano, C.M. Nunn, R. Quan, J.A. Bonadies, V.L. Pecoraro, Inorg. Chem. 29
(1990) 944.
[57] F.A. Cotton, G. Wilkinson, Advanced Inorganic Chemistry, fourth ed., Wiley-
Interscience Publications, 1980.
[8] R.R. Eady, Chem. Rev. 96 (1996) 3013.
[9] G. Asgedom, A. Sreedhara, J. Kivikoski, J. Valkonen, E. Kolehmainen, C.P. Rao,
Inorg. Chem. 35 (1996) 5674.
[10] E. Bayer, H.Z. Kneifel, Z. Naturforsch. B 27 (1972) 207.
[11] S.W. Taylor, B. Kammerer, E. Bayer, Chem. Rev. 97 (1997) 333.
[58] J.A. Bonadies, C.J. Carrano, J. Am. Chem. Soc. 108 (1986) 4088.