Synthesis, characterization, crystal structure, and reactivity of heterobimetallic dioxovanadium(V) complexes containing multidentate hydrazone ligands

Article abstract of DOI:10.1080/00958972.2017.1380194

Two new heterobimetallic complexes of the composition [(VO₂)₂(μ₃-slsch){Na₂(μ-H₂O)₂(H₂O)₂}]_n (1) and [(VO₂)₂(μ₃-npsch){Na₂(μ-H₂O)₂(H₂O)₂}(DMF)]_n (2) were obtained by reaction of the ligand and vanadium pentoxide in a 1:1 molar ratio in methanol in the presence of Na₂CO₃ (2 equivalents). The complexes obtained were characterized using various spectroscopic studies. The structures of both the complexes were established by single crystal X-ray crystallographic study. We have also explored the catalytic behavior of the complexes in oxidative bromination of phenol red, which is the bio-inspired reaction catalyzed by an enzyme haloperoxidase.

Full text of DOI:10.1080/00958972.2017.1380194

Journal of Coordination Chemistry
ISSN: 0095-8972 (Print) 1029-0389 (Online) Journal homepage: http://www.tandfonline.com/loi/gcoo20
Synthesis, characterization, crystal structure, and
reactivity of heterobimetallic dioxovanadium(V)
complexes containing multidentate hydrazone
ligands
Sunshine D. Kurbah, Arvind Kumar, O. Sanentiba Ozukum, Ibanphylla
Syiemlieh & Ram A. Lal
To cite this article: Sunshine D. Kurbah, Arvind Kumar, O. Sanentiba Ozukum, Ibanphylla
Syiemlieh & Ram A. Lal (2017): Synthesis, characterization, crystal structure, and reactivity of
heterobimetallic dioxovanadium(V) complexes containing multidentate hydrazone ligands, Journal
of Coordination Chemistry, DOI: 10.1080/00958972.2017.1380194
To link to this article: http://dx.doi.org/10.1080/00958972.2017.1380194
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Date: 16 September 2017, At: 02:30

Publisher: Taylor & Francis
Journal: Journal of Coordination Chemistry
DOI: http://doi.org/10.1080/00958972.2017.1380194
Synthesis, characterization, crystal structure, and reactivity of
heterobimetallic dioxovanadium(V) complexes containing
multidentate hydrazone ligands
SUNSHINE D. KURBAH†, ARVIND KUMAR‡, O. SANENTIBA OZUKUM†, IBANPHYLLA SYIEMLIEH†
and RAM A. LAL*†
†
‡
Centre for Advanced Studies, Department of Chemistry, North-Eastern Hill University, Shillong-793022, India
Department of Chemistry, Faculty of Science and Technology, The University of West-Indies, St. Augustine,
Trinidad and Tobago
Two new heterobimetallic complexes of the composition [(VO ) (μ -slsch){Na (μ-
2
2
3
2
H O) (H O) }] (1) and [(VO ) (μ -npsch){Na (μ-H O) (H O) }(DMF)] (2) were obtained by
2
2
2
2
n
2 2
3
2
2
2
2
2
n
reaction of the ligand and vanadium pentoxide in a 1:1 molar ratio in methanol in the presence of
Na CO (2 equivalents).The complexes obtained were characterized by using various
2
3
spectroscopic studies.The structures of both the complexes wereestablishedby singlecrystal
X-ray crystallographic study. We have also explored the catalytic behavior of the complexesin
oxidative bromination of phenol red, which is the bio-inspired reaction catalyzed by an enzyme
haloperoxidase.
Keywords: Crystal structure; Heterobimetallic; Reactivity; Dioxovanadium(V)
1
. Introduction
Oxo-bridged units have been found to be one of the most important structural motifs in the
chemistry of first-row transition metals, particularly those complexes containingvanadium
[1],manganese [2] andiron [3].Many metalloproteins and metalloenzymes in which µ-oxo-
bridged motifs are incorporated at their active sites have been found to carry out a wide range of
functions in biological systems.These enzymes containing homobinuclear (FeII/IV) and
*
Corresponding author. Email: ralal@rediffmail.com
1

heterobinuclear (FeII/CuII) active sites are capable of activating dioxygen molecules by a variety
of complex mechanisms involving a putative µ-hydroxo species as a key intermediate
responsible for the oxidation of a wide range of organic substrates [4-10].Such compounds with
ancillary bridging ligands play a crucial role in biological systems during dioxygen activation by
a host of metalloenzymes. The tetra-manganese water oxidase enzyme of the green plant
photosystem II is also believed to contain an oxo-bridged active site [11, 12] and the
involvement of a V-O-V dimer in the biology of vanadium is suspected on the basis of
spectrochemical evidence [13]. Such efficient use of µ-oxido species as catalyst by mother
nature in biological systems has made chemists interested in using similar species as an effective
catalyst [14, 15].
Homobimetallic compounds dominate this area, even though the potential number of
heterometallic pairings significantly outnumbers the former. A synthetic roadblock to expanding
heterometallic systems is the inherent challenge of selectively assembling different transition
metals together with other metals. This is of particular interest in the field of molecular host
guest chemistry, coordination polymers and molecular magnets.
In view of the diverse importance of µ-oxo-bridged heterodinuclear compounds andtheir
utility in catalysis and biomimetic studies, we focused our intentionto develop new
methodsforsynthesizingnew heterobimetallic µ-oxo-bridged vanadium complexes by choosing
polyfunctional ligand family ofsuccinoyldihydrazones.Further, these ligands possesseight
binding sites which can bind to vanadium and other metal centersindifferentcoordination modes.
The protonation state of these ligands on complexation plays an important role since it offers the
opportunity of fine tuning properties such as electrochemical, photophysical and catalytic.
Hence, in this manuscript we report our initial explorations in the coordination chemistry
of the ligandsH slsch and H npsch with vanadium, which can have the tendency to form µ-oxo-
4
4
bridged heterobimetallic complexes with other metals. The synthetic and structural studies
demonstrate the versatility of H slsch and H npschto act as a supporting ligand for generating
4
4
asymmetric dinuclear complexes comprisingof sodium and vanadium ions. This work provides
usthe foundation for future reactivity and mechanistic work.
2

2
. Experimental
Solvents were reagent grade and used as received. Other chemicals were E-Merck, Himediaand
equivalent grades.
2
.1. Physical measurements
Vanadium was determined by a standard literature procedure [16]. C, H and N were determined
by microanalytical methods using a Perkin-Elmer 2400 CHNS/O Analyzer 11. Infrared spectra
-1
(
figures S1 and S2) in the range 4000-450 cm were recorded as KBr discs by using a BX-
1
13
III/FTIR Perkin Elmer spectrophotometer. The H NMR and C NMR spectra were recorded on
a Bruker Avance II spectrometer at 400 and 100 MHz in DMSO-d solution using TMS as an
6
internal standard. Electronic spectra were recorded on a Perkin-Elmer Lambda-25
spectrophotometer. Cyclic voltammograms were recorded on a CH Electrochemical Analyzer
using a standard three-electrode assembly (glassy-carbon working, Pt wire auxiliary, SCE
reference) and 0.1 M NBu ClO as supporting electrolyte. Mass spectra of the complexes were
4
4
recorded on a Water ZQ-4000 Micromass Spectrometer. Gas Chromatographic (GC) analysis
was performed on a Bruker 430-GC Gas Chromatograph equipped with a 30m × 0.32mm ×
0
.5 μm HP-Innowax capillary column and flame ionization detector (FID).
2
.2. X-ray crystallography diffraction
Single crystals of 1 and 2 were obtained by slow evaporation from water/DMF solutions after a
few days. Intensity data for the compounds were measured using an Xcalibur Eos Gemini
diffractometer equipped with monochromated MoK radiation ((λ = 0.71073 Å) source. The
α
CrysAlis PRO, Agilent, 2013 software packages were used for data collection and reduction
[17a]. In all cases, absorption corrections based on multiscans were applied [17b]. The structure
2
was solved by direct methods and refined on F by a full matrix least squares [17c] procedure
2
2 2
2 2 1/2
based on all data minimizing R = Σ || F | - |F ||/Σ |F |, wR = [Σ [w (F – F ) ]/Σ (F ) ] and S =
0
c
0
0
c
0
2
2 2
1/2
[
Σ [(F – F ) /(n–p)] . SHELXT-2014 and SHELX-2014 were used for structure solutions and
0 c
refinements [17d]. All non-hydrogen atoms were refined anisotropically, whereas the hydrogen
atom positions were placedat a calculated distance and refined freely in the final refinement.
Crystal data and structure refinement parameters of 1 and 2 are in table 1.
3

2
2
.3. Synthetic procedures
.3.1. General procedure for synthesis of ligandsH slsch and H npsch.Ligand preparation
4
4
involves two steps. In the first step it involved condensation of diethyl succinate with hydrazine
hydrate in 1:2.5 molar ratio in ethanol to give succinoyldihydrazide. In the second step,
condensation of succinoyldihydrazide (2 g, 13.70 mmol) with 2-hydroxy-1-benzaldehyde
(3.68 g, 30.16 mmol) and 2-hydroxy-1-naphthaldehyde (5.19 g, 30.16 mmol) gave the desired
ligands H slsch and H npsch in moderate yield.
4
4
2
.3.2. Bis(2-hydroxy-1-benzaldehyde)succinoyldihydrazone, H slsch.Yield: 5.281 g (47%).
4
M.p: 225-227 C (lit [17. (c)]: 300°C),Color: white. Anal (%), Calcd for C H N O (MW:
1
8
18
4
4
3
54.37): C, 61.01; H, 5.12; N, 15.81; Found: C, 60.68; H, 5.15; N, 15.65.
2
.3.3. Bis(2-hydroxy-1-naphthaldehyde)succinoyldihydrazone, H npsch. Yield: 5.281g
4
(47%). M.p: 245-247 C (lit [17. (d)] 254°C, Color: yellow.Anal (%), Calcd for
C H N O (MW: 454.49): C, 68.71; H, 4.88; N, 12.33; Found: C, 68.71; H, 4.88; N, 12.33.
2
6
22
4
4
2
.4. General procedure for synthesis of complexes 1 and 2
A suspension of vanadium pentoxide (0.2 g, 1 mmol) in methanol solution was added dropwise
to a solution containing H slsch (0.35 g, 1 mmol; for 1) and H npsch (0.39 g, 1 mmol; for 2) in
4
4
1
:1 molar ratio at room temperature. The reaction mixture was refluxed for 40 min, then cooled
to room temperature, followed by addition of sodium carbonate (0.22 g, 2 mmol) and stirred well
until the brown solution turned yellow. The yellow solution was allowed to stand at room
temperature for 1 h, until the precipitate settled. The mixture was filtered, washed three times
with warm methanol(5 mL each time), collected and dried over CaCl to obtain the desired
2
complexes 1 and 2. Single crystal of 1 and 2 were obtained by slow evaporation of DMF
solutions at ambient temperature within a fortnight.
2
.4.1. [Disodium (di (μ-aquo) (μ -bis-(2-hydroxybenzylidene) succinohydrazide)
3
(
bis(dioxidovanadate(V)]:[(VO ) (μ -slsch)(Na (μ-H O) ] ·4H O (1). Yield: 0.57 g (75%).
2 2 3 2 2 2 n 2
M.p: >300 C;Color: Yellow. Anal (%), Calcd for C H N NaO V (MW 757.4 g/mol): C,
1
8
40
4
20
2
-1
2
8.54; H, 5.32; N, 7.40; Found: C, 28.73; H, 5.30; N, 7.49. IR data (cm , KBr): 3426 (vs br)
4

ν(OH), 1571, 1550, 1478, 1450, 1356, 1290, 1216, 1154, 1031, 954, 900, 761, 725, 626, 579,
1
4
84, 469. H NMR (400 MHz, DMSO-d ,Me Si): δ (ppm): 7.02-7.86 (m, 8H, Ar-H), 8.3 (s, 2H,
6
4
1
3
C(H)=N), 2.5 (s, 4H, (-CH ). C NMR (100 MHz, DMSO-d ,Me Si): 174.27, 163.15, 153.56,
2
6
4
1
31.76, 131.28, 118.59, 118.21, 115.52, 40.72 ppm. Electronic spectrum, [λmax, nm]: CH CN
3
solution, λmax (nm): 323 nm, 417 nm.
2
.4.2. [Disodium (di (μ-aquo)(μ -bis-(2-hydroxynaphthalen-1-yl)methylene)
3
succinohydrazide (bis(dioxidovanadate(V)]:[(VO ) (μ -npsch)(Na (μ-H O) (H O) )(DMF)]
n
2
2
3
2
2
2
2
2
(2). Yield: 0.65 g (72%). M.p: >300 °C; Color: Light brown. Anal (%), Calcd for
C H N Na O V (MW 900.59 g/mol): C, 42.68; H, 4.92; N, 9.33; Found: C, 42.68; H, 4.92;
3
2
44
6
2
15
2
-1
N, 9.33. IR data (cm , KBr): 3461 (vs br) ν(OH), 1604, 1558, 1455, 1399, 1352, 1335, 1196,
1
9
42, 921, 822, 746, 588, 538, 510. H NMR (400 MHz, DMSO-d ,Me Si): δ (ppm): 7.02-7.86
6
4
(
m, 12H, Ar-H), 8.3 (s, 2H, C(H)=N), 2.5 (s, 4H, (-CH ). (100 MHz, DMSO-d ,Me Si): 174.35,
2 6 4
1
64.93, 150.55, 133.64, 132.89, 128.62, 127.45, 126.72, 122.74, 122.61, 120.10, 109.77, 40.05
ppm. Electronic spectrum, [λmax, nm]: CH CN solution, λ (nm): 371 nm, 421 nm.
3
max
2
2
.4.3. Oxidative bromination of phenol red. Oxidative bromination was carried out using 1 and
at room temperature. In a typical experiment, vanadium(V) complexes were dissolved in
CH CN/H O in a 3:7 ratioand added to a solution containing KBr (0.24g, 2 mmol), phenol red
3
2
(
0.35g, 1 mmol) and 30% H O (10 ml). After 4 minutes the solution turned red,following the
2 2
addition of 70% HClO (0.5 mmol) it was stirred for 1 h. An additional 0.5 mmol was added to
4
the reaction mixture at every 30 minute interval. The reaction mixture was then extracted, dried
over anhydrous Na SO and purified by column chromatography to get the product.
2
4
3
3
. Results and discussion
.1. Synthesis and spectral characteristics
The ligands (hydrazone = H slsch, H npsch) under study (figure 1) were prepared according to a
4
4
1
13
literature report [18]and were characterized by melting point, IR, H NMR and C NMR
spectroscopies; characterization details are presented in the Experimental section. Complexes 1
and 2of the composition [(VO ) (μ -slsch)(Na (μ-H O) )(H O) ] ·4H O (1) and[(VO ) (μ -
2
2
3
2
2
2
2
2 n
2
2 2
3
npsch){Na (μ-H O) (H O) }(DMF)] (2)were synthesized in good yield (scheme 1).
2
2
2
2
2
n
5

Scheme 1. Schematic diagram showing preparation of complexes.
The complexes are insoluble in common organic solvents such as MeOH, EtOH, CH Cl , CHCl ,
2
2
3
CCl , ether, acetone and benzene,sparingly soluble in acetonitrile and readily soluble in
4
DMF/DMSO. The analytical data obtained for both the complexesare in agreement with the
proposed structural formula.
3
.2. UV-Vis spectra
The UV-vis spectra of 1 and 2 were recorded in acetonitrile solutions with concentration of
-5
-1
1
0 mol L . The electronic spectra show two absorption bands at 323 nm and 388 nm (for 1)
figure S3) and 326 nm and 413 nm (for 2) (figure S4). The strong absorption bands at 323 nm
and 321 nm are due to an intra-ligand transition, most probably,-* whereas the bands at
88 nm and 392 nm are assigned to LMCT arising from transfer of charge from the p-orbital of a
phenolate-oxygen to an empty d-orbital of the vanadium(V) center [20].
(
3
1
13
3
.3. H NMR and C NMRspectra
1
13
In order to confirm the coordination modes of the ligand to the metal center, H and C NMR
1
13
spectroscopieswere employed. The H NMR and C NMRspectra ofthe free ligandsand
complexes were recordedin DMSO-d (figures S5-S8) using TMS as an internal standard
6
reference, and the details of the dataare given in the Experimental section. The free
ligandsexhibit a resonance at δ=11.72 ppm, δ=11.30 ppm, δ = 10.18 ppm and 10.15 ppm which
are assigned to –OH and -NH groups. These signals disappeared confirming deprotonation of
both the -OH and –NH protonsupon complexation (figures S5 and S6).The coordination mode of
1
3
the ligand to the metal ion was also studied by coordination-induced C NMR chemical shifts.
6

The azomethine carbons in both ligands appear at 167.55 ppm and 168.28 ppm, whereas,upon
1
3
complexation, C NMR spectra show upfield shifts to 163.15 and 164.93 ppm with Δδ = 2-3
ppm (figures S7 and S8) in both the complexes. The coordination of enol oxygencarbons C8 and
C12 were indicated by downfield shifts with Δδ = 1-2 ppm.The signals of aromatic carbon atoms
appearedat the expected positionsin both the ligands and complexes with slight shifts in their
positions.
3
.4. Electrochemical studies
The electrochemical studies were carried out for both the heterobimetallic complexes in DMF
solution using TBAP (0.1 M) as supporting electrolyte at a scan rate of 100 mV. Complex
1
(figure S9) shows four quasi-reversible redox couples with peak potential differences>50 mV.
Towards the positive scan, redox couples with E = ±0.23 V and E = ±1.42 V were observed.
1
/2
1/2
The first redox couple at E = +0.23 V (process at potential E = +0.34 V) is attributed to the
1
/2
metal oxidation (M2+/3+), while the second redox process at E = +1.42 V is assigned to the
1
/2
oxidation of the ligand. The negative scan also shows two quasi-reversible redox couples,the first
redox couple at E = -0.52 V and the other one at E = -1.02 V. The second redox couple with
1
/2
1/2
E = -1.02 V is attributed to the metal reduction (M+5/+4) which is in agreement to the literature
1
/2
report [21]. The first couple at E = -0.52 V is assigned to the reduction of the
1
/2
ligand.Similarly,2 (figure S10) shows three quasi-reversible redox couples with peak
potentials> 90 mV. In the positive scan, the redox couples with E = ±0.31 V and E = ±1.2 V
1
/2
1/2
are attributed to metal oxidation (M2+/3+) and ligand oxidation, respectively. In the negative
potential scan, the quasi-reversible redox couple at E = -1.01 V is assigned to metal reduction
1
/2
(
M+5/+4), and a peak at E = -0.47 V is due to ligand oxidation. Electrochemical studies of both
1/2
+
complexes show similar results;these similarities arise due to the presence of [(VO ) ] in the
2
2
structural units of both the complexes, which is also confirmed by other spectroscopies studies.
3
.5. Crystal structure description
The asymmetric unit of 1 (figure 2) and 2 (figure 3) is composed of one vanadium(V) ion, one
sodium ion, half of the ligand moiety, one oxido atom and three aqua ligands, whereas in 2, one
additional solvent molecule (dimethylformamide) is present. Both of the complexes are arranged
into [(VO ) (L)] units that are interconnected through the differently bound oxido-
2
2
2
7

sodiummoieties, [Na (μ-O)] in 1 and [Na (μ-H O) ] in 2, resulting in the formation of distinct
2
2
2
3
one-dimensional heterobimetallic networks.
Complex 1 crystallizes in the triclinic space group P-1. The asymmetric unit of the
complex [(VO ) (μ -slsch)] consists of one vanadium ion, one terminal oxido ion (O3), one
2
2
3
2
bridging oxido ion (O4) and one-half tetra-deprotonated ligand in the transoid conformation,
shown in figure2. The bridging oxygen (O4) forms a linker to the sodium ion forming a M-O-M
core, in which the sodium ionis bonded by four water molecules. The ligand coordinates to the
metal centers in tridentate fashion through the azomethine nitrogen (N1), phenolic oxygen (O1)
and carbonyl oxygen atom, the fourth and fifth positionsare occupied by oxido (O3) and bridging
oxido (μ-O4) in both the arm of the ligand. The transoid basal position of the complexes consists
of two oxygens and one azomethine nitrogen, whereas the apical position consists of the bridging
V-O. The V-O bond lengths (table S1) range from1.617(3) Å [V-O4], 1.652(3) Å [V=O3],
1
2
.907(3) Å [V-O1] to 1.972(2) Å [V-O2] whereas the V-N bond length of the azomethine is
.131(3) Å, larger than that of the average V-O bond length by 0.344Å. The trans angles in the
complex are O1-V1-O2 (152.29(12) and O3-V1-N1 (140.27(13), with τ = 0.2 (table S1). Hence,
the geometry around the vanadium center can be described as distorted square pyramidal.The
values of bond lengths and angles around the vanadium ion found in the present study are in
agreement with those reported in the literature [22].Another interesting property of the complex
is the presence of sodium ions together with one μ-O4 group and two water molecules. The
sodium center consists of two μ-O4 at the axial positions [Na1-O4, 2.377(3)] andfour water
1
molecules at the equatorial sites [Na1-O5, 2.405(3), Na1-O6 , 2.450(4) Å], resulting in the
formation of a six-coordinate [Na-O ] octahedral geometry around the sodium ion.Na-O bond
6
lengths are similar to those found in other hetero-metallic Na-V compounds [22]. Therefore, the
ligand in the complex acts in a μ [O-N-O] bridging mode [N O ] which binds to two vanadium
3
2
4
ions forming [(VO ) L], together with two bridging sodium ions from oxygen (O4) ions [μ-O4]
2
2
forming a tetra-metallic [V Na (μ -slsch)] fragment with metal separation of 8.972 Å
2
2
3
1
1
[
V1…V1 ], 14.291 Å [Na1…Na1 ] and 3.747 Å [Na1…V1]. Therefore, the synthesized complex
consists of two different metal ions [V Na ] with different geometrical arrangements, in which
2
2
two vanadium ions adopt five-coordinate distorted square pyramidal geometry whereas for the
sodium ions, a regular octahedral geometry has been observed. In addition, four water molecules
are present in the complex; these water molecules can be best described as lattice water forming
8

inter- and intra-molecular hydrogen bonding with the complex, which together construct a
(VO ) (μ -L)Na (μ-O4) (H O) }]·4H O unit. The presence of two μ-O4 bridging oxido ions
[
2
2
3
2
2
2
4
2
generates a more complex structure which is interconnected to another part of the fragment
molecules, resulting in the formation of an infinite one dimensional ladder like metal-organic
chain (figure 4). Further extension of the 1D coordination network results in a 3D
supramolecular assembly (figure 5).
In 2 (figure 3), the asymmetric unit bears similar [(VO ) (μ -L)] blocks which are
2
2
3
structurally identical to 1, but different through one coordinated solvent molecule
(dimethylformamide) which coordinates to sodium ions and two bridging water molecules
(
μ-H- O) compared to 1. The ligand coordinates to the metal center and participates in complex
2
formation through O, N, O donor atoms with oxygen and nitrogen of the azomethine at the basal
position, whereas the fourth equatorial position is occupied by oxygen atom (O3) and the axial
position by one bridging oxido O4 [μ-O4]. The bridging oxido [μ-O4] provide a linkage to
sodium ions, together with one terminal water and three bridging water molecules resulting in
the formation of six-coordinate, distorted octahedral sodium ions.
The vanadium-oxygen (V-O) bond lengths are1.912(15) Å [V1-O1], 1.957(14) Å
[
V1-O2] and V=O bond lengths are 1.609(15) Å [V=O4], 1.645(15) Å [V=O3], whereas the V-N
bond length is 2.108(17) Å, closer to that of the average V-O, V=O and V-N bond length of 1
table S1). The trans angles in 2 are O1-V1-O2, 148.67(6) and O3-V1-N1, 142.56(7) with τ =
.1(table S1). However, the main distinct features of 2 consist of sodium ions bonded to three
bridging aqua ligands along with one H O and DMF together forming a more complex structure
(
0
2
[
[Na (μ-H O) (H O) ]. The coordination geometry around the vanadium(V) center can be
2 2 3 2 2
described as slightly distorted square pyramidal. Hence, the ligand in the complex acts in a
μ [O-N-O] bridging mode [N O ] which binds to two vanadium ions forming [(VO ) npsch],
3
2
4
2 2
together with two bridging sodium ions from oxygen atom [μ-O4] forming tetra-metallic
1
[
V Na (μ -npsch)] fragments with metal-metal separation of 9.457 Å [V1…V1 ], 3.368 Å
2
2
3
1
[
Na1…Na1 ], and 3.748 Å [Na1…V1]. Complex 2 consists of two different metal ions [V Na ]
2
2
with different geometrical arrangement, in which two vanadium ions adopt five-coordinate
distorted square pyramidal geometry whereas in the case of two sodium ions, a distorted
octahedral geometry has been observed; together both vanadium and sodium ions construct
[
(VO ) (μ -L) Na (μ-O4) (H O) }]·4H O unit. The Na-O, V-O, V-N bond lengths and bond
2 2 3 2 2 2 4 2
9

angles around the two metal ions match the values reported in the literature [22].The presence of
bridging aqua [μ-H O] ligands generates a more complex structure which is interconnected to
2
another sodium ion, resulting in the formation of an infinite one-dimensional coordination
network (figure 5). The 3D supramolecular assembly (figure 4) of 2is constructed considering
together the presence of inter- and intra-molecular hydrogen bonding.
3
.6. Crystal packing diagram
Crystal packing diagrams of 1 and 2 areshown in figure 4.Complex 1 crystallized in triclinic
(space group P-1) with Z = 1 and 2crystallized in monoclinic (space group I2/n) with Z = 4. The
3
unit cell volume and density at ambient temperature (291.93-295.7) are d = 1.603 g/cm , V =
3
3
3
7
82.30(15) Å for 1 and d = 1.513 g/cm , V = 3945.0(5) Å for 2. The unit cell length and cell
angles in 1 are a = 7.258(9) Å, b = 10.381(12) Å, c = 10.831(9) Å, α = 95.321(8)°, β =
1
9
00.093(9)°, γ = 100.885(10)° and for 2, a = 24.162(2) Å, b = 6.164(3) Å, c = 27.158(17) Å, α =
0°, β = 102.757(7)°, γ = 90°. Complexes 1 and 2 have different packing arrangements. The
complete fragment of the ligand along with vanadium and sodium ions results ina 1D
arrangement in 1. In 2, the complex packing results into three parallel 1D arrangements.The
packing efficiency of complexes are 68.09% for 1 and 67.51% for 2; the packing index of 2 is
slightly lower compared to 1.
1
0

3
.7. Reactivity of dioxovanadium(V) complexes with H O
2 2
H2O
H2O
Na
H2O
O
H2O
H2O
H2O
H2O
Na
O
O
H2O
V
O
O
O
O
V
O
N
O
N
H O
O
2
2
N
N
N
O
N
O
O
V
N
N
O
O
O
O
V
Na
O
Na
O
O
O
O
O
V
O
V
O
O
O
H O
2
2
N
N
N
O
N
N
V
N
N
N
O
O
V
O
O
O
O
O
O
H O Na H O
H2O Na H2O
2
2
O
O
N
O
N
O
OH2
OH2
OH2
OH2
Na
N
Na
2
N
H O
H O
2
Scheme 2. Schematic diagram showing reaction of 1 and 2 with H O .
2
2
The reaction of [(VO ) (μ -slsch){Na (μ-H O) (H O) }] (1) and[(VO ) (μ -
2
2
3
2
2
2
2
2
n
2 2
3
npsch){Na (μ-H O) (H O) }] (2)with H O in acetonitrile solution was studied using UV/Vis
2
2
2
2
2
n
2
2
spectroscopy. In 1, initially we observed a decrease in absorbance at 385 nm upon addition of
H O and the changes observed result in the presence of one isosbestic point at 340 nm, whereas
2
2
the band at 312 nm shows a bathochromic shift to 320 nm (figure 6A). The absorbance decreases
with increase in H O concentration. Similarly, in 2 upon addition of H O , the solution showed a
2
2
2
2
similar trend and the changes observed resulted in the presence of two isosbestic points at
73 nm and 438 nm. Further, after addition of the H O solution, the series of spectra (figure 6B)
3
2
2
show a gradual decrease at 413 nm and the appearance of a more intense band at 326 nm. These
changes indicate that in both of the complexes the peroxo group reacts with the metalcenter. The
changes in the electronic spectra in both the complexes were attributed to the formation of
V
corresponding V O-(O ) species and hence the results obtained are consistent with the reported
2
literature [23].
1
1

3
.8. Mimetic activity of dioxovanadium(V) complexes with 3,5-di-tert-butylcatechol
OH
OH
O
O
complex
Scheme 3. Schematic diagram showing catalytic oxidation of 3,5-di-tert-butylcatecholto 3,5-di-
tert-butylquinone by 1 and 2.
The oxidation of catechol to quinones catalyzed by binuclear copper complexes in the
presence of O is one of the most important biochemical transformations [24]. In our study,
2
catalytic oxidation of 3,5-di-tert-butylcatechol to 3,5-di-tert-butylcyclohex-4-ene-1,2-dione using
our newly synthesized complex [(VO ) (μ -slsch){Na (μ-H O) (H O) }] (1) in acetonitrile
2
2
3
2
2
2
2
2
n
solution was monitored by employingUV/Vis spectroscopy.In a typical experiment, 100 µL of
-4
the complex in acetonitrile solution (1×10 M) was transferred to a 1 cm path-lengthcell. The
-2
reaction was initiated by the addition of 3,5-di-tert-butylcatechol (1×10 M) solution.
Absorbance vs wavelength plots were generated from each experiment, which were recorded
every 5 minutes in the region of 300-700 nm of the electronic spectrum (figure 7). The reaction
mixture changed color after 2 minutesupon addition of 3,5-di-tert-butylcatechol. This change
indicates the coordination of the substrate to the vanadium center. This is also evident from the
strong intense absorptionbandsappearing at 554 nm, which is characteristic of charge transfer
bands in vanadium complexes containing catecholate ligands [25]. These bands also increase in
intensity on subsequent addition of 3,5-di-tert-butylcatechol, indicating the formation of non-
innocent complexes with vanadium(V), during the course of the reduction of the vanadium
center from V(V)  V(IV). Many vanadium-catechol containing compounds have been reported
and often they are not stable towards internal redox reactions, indicating the formation of
o-benzoquinones from these systems.The completion of the reactions was determined
-1
-1
spectrophotometrically by monitoring the increase in absorbance at 400 nm (e = 1600 M cm )
as a function of time, which is the characteristic absorption band of 3,5-di-tert-butylcyclohex-4-
ene-1,2-dione.The product was purified by column chromatography and the yield of 3,5-di-tert-
1
2

-1
butylcyclohex-4-ene-1,2-dionewas 62% with a turnover frequency of 20.66 h , which are
comparable to the literature reported values for other model systems[26].The productwas also
1
13
1
confirmed by H and C NMR spectroscopy. Yield: 62%. H NMR (400 MHz, CDCl ): 6.93 (d,
3
1
3
1
H, J = 2.28 Hz), 6.21(d, 1H, J = 1.52Hz), 1.26 (s, 9H), 1.22 (s, 9H) ppm; C NMR (100 MHz,
CDCl ): d 181.26, 180.17, 163.46, 150.07, 133.60, 122.22, 36.16, 35.61, 29.34, 28.01 ppm.
3
3
.9. Oxidative bromination activity of complexes 1 and 2
Br
O
O
S
S
O
O
KBr, HClO , 30%H O
4
2
2
O
O
HO
HO
complex
Br
Br
Br
HO
HO
Scheme 4. Schematic diagram showing oxidative bromination of phenol red to bromo-phenol
blue catalyzed by 1 and 2.
+
Dioxovanadium complexes containing VO moiety have been found to be promising
2
candidates for catalyzing oxidative bromination of organic substrates, such as tri-
methoxybenzene, salicylaldehyde and phenol [27]. The reactions,in which vanadium
haloperoxidases act as catalyst,take place in the presence of H O and bromide.In our study,
2
2
taking into an account the importance of vanadium haloperoxidase enzymes, we investigated the
oxidative bromination of phenol red usingour newly synthesized complexes [(VO ) (μ -
2
2
3
slsch){Na (μ-H O) (H O) }] (1) and[(VO ) (μ -npsch){Na (μ-H O) (H O) }] (2),as catalyst
2
2
2
2
2
n
2 2
3
2
2
2
2
2
n
precursor in the presence of H O , HClO and KBr.During this process, 1 and 2react with two
2
2
4
-
equivalents of H O , forming bis-(peroxo) [(VO ) ] species(which readily oxidize
2
2
2 2
bromide)resulting in the formation of a hydroperoxo intermediate. The oxidized bromine species
-
-
Br , Br or, most likely, HOBrwere then trapped by the organic substrate (phenol red) which
2
3
resultedin a color change of the solution from yellow to blue, which indicated formation of the
brominated product phenol blue [28].The crude product was extracted, dried over anhydrous
sodium sulfate, the solution filtered and the solvent evaporatedunder reduced pressure to obtaina
1
3

red powder. The product was purified using column chromatography. The brominated product
1
1
obtained was also confirmed by H NMR spectroscopy. Color: light red powder; yield: 57%. H
NMR (400 MHz, CDCl ): 7.87-8.09 (m, 4H), 9.10 (s, 2H), 7.55 (s, 4H).
3
4
. Conclusion
We have synthesized two new heterobimetallic complexes of the following
compositions,[(VO ) (μ -slsch){Na (μ-H O) (H O) }] (1) and[(VO ) (μ -npsch){Na (μ-
2
2
3
2
2
2
2
2
n
2 2
3
2
H O) (H O) }] (2),using V O as the starting material and polyfunctional hydrazone ligand. For
2
2
2
2
n
2
5
testing the feasibility of the complexes as catalyst precursors for oxidative bromination reaction
that are catalyzed by haloperoxidase enzyme, we performed experiments using phenol red as a
substrate for bromination. The oxidative bromination results obtained are similar comparedto
literature reports, producing phenol blue in moderate yield as a brominated product. In addition,
we have also extended our work for the catalytic oxidation of 3,5-di-tert-butylcatechol to 3,5-di-
tert-butylcyclohex-4-ene-1,2-dione using 1 as catalyst.The results obtained are in agreement with
the literature report;the catalyst is efficient for accelerating the reaction in good yield. We will
continue to explore the efficiency of vanadium complex as a catalyst for further application.
Appendix A. Supplementary data
The cif files of [(VO ) (μ -slsch){Na (μ-H O) (H O) }] (1) and [(VO ) (μ -npsch){Na (μ-
2
2
3
2
2
2
2
2
n
2 2
3
2
H O) (H O) }] (2) were deposited with the Cambridge Crystallographic Data Centre (1497273
2
2
2
2
n
and 1497295). These data can be obtained via https://summary.ccdc.cam.ac.uk/structure-
summary-form, Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ,
UK; Fax: (+44) 1223-336-033; E-mail: deposit@ccdc.cam.ac.uk. Supplementary data related to
this article can be found in the online version.
Acknowledgements
Authors would like to thank to the Head, SAIF, North-Eastern Hill University, Shillong-793022,
1
13
India for providing H and C NMR spectra. Sunshine D. Kurbah would like to thank UGC-
NFST New Delhi, India, for awarding fellowship.
1
4

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[
1
6

Graphical abstract
1
7

A. Disalicylaldehydesuccinoyldihydrazone (H slsch)
4
B.Bis(2-hydroxy-1-naphthaldehyde)succinoyldihydrazone (H npsch)
4
Figure 1. Structural formula of the ligands used in this study and their numbering scheme.
1
8

A
B
Figure 2. Crystal structure of 1 showing the asymmetric unit (A) and complete fragment (B).
1
9

A
B
Figure 3. Crystal structure of 2 showing the asymmetric unit (A) and complete fragment (B).
2
0

Figure4. ORTEP drawing and polyhedral representation of an infinite one-dimensional structure
of [(VO ) (μ -slsch){Na (μ-H O) (H O) }] (1) and[(VO ) (μ -npsch){Na (μ-H O) (H O) }] (2),
2
2
3
2
2
2
2
2
n
2 2
3
2
2
2
2
2
n
V by dark blue polyhedral, Na by light blue polyhedral.
2
1

A
B
Figure5. Crystal packing diagram of 1(A) and 2(B) viewed along their geometrical a- and b-axis.
2
2

A
B
Figure 6. Spectral changes observed during the reaction of H O with [(VO ) (μ -slsch){Na (μ-
2
2
2 2
3
2
H O) (H O) }] (1) A and[(VO ) (μ -npsch){Na (μ-H O) (H O) }] (2) B. The spectra were
2
2
2
2
n
2 2
3
2
2
2
2
2
n
-2
-5
recorded upon the dropwise addition of a 2×10 M H O solution to a 1.32×10 M solution of 1
2
2
and 2in CH CN (10 mL).
3
2
3

0.30
0.25
0.20
0
100
200
time (min)
A
B
Figure 7. (a) Change in spectral pattern for the reaction of 1 with 3,5-DTBC in CH CN after
3
observing the reaction for 6 h. (b) A plot of absorbance vs time.
2
4

Table 1. Crystal data and structure refinement parameters of 1 and 2.
1
2
CCDC No.
1497295
1497273
Empirical formula
C H N O NaV
C H N O VNa
1
8
40
4
20
2
16 21
3
7.5
Formula weight
757.41
450.29
Temperature/K
291.93(10)
Triclinic
P-1
295.7(2)
Crystal system
Monoclinic
Space group
I2/a
a/Å
7.2582(9)
24.162(2)
b/Å
10.3808(12)
10.8313(9)
95.321(8)
100.093(9)
100.885(10)
782.30(15)
1
6.1642(3)
c/Å
27.1577(17)
α/°
90
β/°
102.757(7)
γ/°
90
Volume/Å3
3945.0(5)
Z
8
μ/mm-1
0.700
0.571
Reflections collected
Independent reflections
Data/restraints/parameters
Final R indexes [I>=2σ (I)]
Final R indexes [all data]
5653
7229
3487/0/247
1.060
3010/0/282
1.084
R1 = 0.0622, wR2 = 0.1783
R1 = 0.0713, wR2 = 0.1897
R1 = 0.0312, wR2 = 0.0760
R1 = 0.0366, wR2 = 0.0789
2
5