Estimating the energy of noncovalent interactions in a dioxovanadium(V) Schiff base complex: Exploration of its phenoxazinone synthase like activity

Article abstract of DOI:10.1016/j.poly.2017.11.053

A mononuclear dioxovanadium(V) Schiff base complex, [VO₂(L)] {HL = 2-((diethylamino)ethyliminomethyl)-4-bromophenol} has been synthesized and characterized. The importance of noncovalent interactions in the solid state of the complex has been s

Full text of DOI:10.1016/j.poly.2017.11.053

Accepted Manuscript
Estimating the energy of noncovalent interactions in a dioxovanadium(V) Schiff
base complex: Exploration of its phenoxazinone synthase like activity
Snehasish Thakur, Nandita Sarkar, Michael G.B. Drew, Antonio Bauzá,
Antonio Frontera, Shouvik Chattopadhyay
PII:
S0277-5387(17)30781-7
https://doi.org/10.1016/j.poly.2017.11.053
POLY 12955
DOI:
Reference:
Polyhedron
To appear in:
Received Date:
Accepted Date:
26 August 2017
30 November 2017
Please cite this article as: S. Thakur, N. Sarkar, M.G.B. Drew, A. Bauzá, A. Frontera, S. Chattopadhyay, Estimating
the energy of noncovalent interactions in a dioxovanadium(V) Schiff base complex: Exploration of its
phenoxazinone synthase like activity, Polyhedron (2017), doi: https://doi.org/10.1016/j.poly.2017.11.053
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Estimating the energy of noncovalent interactions in a
dioxovanadium(V) Schiff base complex: Exploration of its
phenoxazinone synthase like activity
Snehasish Thakura, Nandita Sarkara, Michael G. B. Drewb, Antonio Bauzác,
Antonio Fronterac,* and Shouvik Chattopadhyaya,*
aDepartment of Chemistry, Inorganic Section, Jadavpur University, Kolkata 700 032, India, E-
mail: shouvik.chem@gmail.com
bSchool of Chemistry, The University of Reading, P.O. Box 224, Whiteknights, Reading RG6
6AD, United Kingdom
cDepartament de Química, Universitat de les IllesBalears, Crta. De Valldemossa km 7.5, 07122
Palma (Baleares), Spain. E-mail: toni.frontera@uib.es.
Abstract
A mononuclear dioxovanadium(V) Schiff base complex, [VO2(L)] {HL = 2-
(diethylamino)ethyliminomethyl)-4-bromophenol} has been synthesized and characterized. The
importance of noncovalent interactions in the solid state of the complex has been studied by
means of DFT and MEP calculations and characterized using Bader’s theory of “atoms in
molecules” (AIM). The complex has been found to show catalytic activity towards the aerial
oxidation of o-aminophenol (OAPH). Kinetics of the reaction has been monitored
spectrophotometrically.
Keywords: Vanadium(V); Schiff base, crystal structure, phenoxazinone synthase like activity.

1. Introduction
Transition-metal based metalloenzymes capable of processing molecular dioxygen under
ambient conditions have received a great deal of attention because they assist the spin-forbidden
interaction between dioxygen and organic matter in various biochemical reactions [1–3].
Analysis of such processes gives us plenty of information for the development of small molecule
catalysts for specific oxidation reactions of organic substances under mild conditions. Vanadium
complexes have been found to act as catalyst precursors in various oxidation reactions like
bromination reactions, epoxidations of alkenes and allylic alcohols, oxidations of sulfides to
sulfoxides and sulfones, hydroxylations of alkanes and arenes, and oxidations of primary and
secondary alcohols to the corresponding aldehydes and ketones [4]. Various vanadium
complexes with a diverse range of ligands have long been investigated for their insulin mimetic
responses [5-6]. The discovery of vanadium in the nitrogen fixation enzyme, nitrogenases also
promoted the interest in the chemistry of model compounds of vanadium with N/O donor ligands
[7-8]. Vanadium containing bromoperoxidase mimicking activities of dioxovanadium(V)
complexes have also been reported in literature [9]. Model studies on metalloenzymes of
vanadium with oxidase (oxygenase) activity are therefore of specific interest for the development
of bioinspired catalysts for oxidation reactions in industrial and synthetic processes.
Phenoxazinone synthase, a multicopper oxidase enzyme, found naturally in the
bacterium, Streptomyces antibioticus, catalyzes the oxidative condensation of o-aminophenol
derivatives into phenoxazinone chromophore [10-11]. This metalloenzyme is known to catalyze
the oxidative coupling of two molecules of a substituted o-aminophenol to the phenoxazinone
chromophore in the final step for the biosynthesis of actinomycin D [12], a naturally occurring
antineoplastic agent, used clinically for the treatment of certain types of cancer [13]. Studies on

the oxidation of o-aminophenol to phenoxazinone by molecular dioxygen in presence of some
mono- and di-nuclear first row transition metal complexes as catalysts have been reported by
several groups [14-17]. However, best to our knowledge, there is no report on phenoxazinone
synthase like activity of any dioxovanadium(V) Schiff base complex till date.
In the present work,
a
tridentate N2O donor Schiff base, HL
=
2-
(diethylamino)ethyliminomethyl)-4-bromophenol, has been used to prepare a mononuclear
pentacoordinated dioxovanadium(V) complex, [VO2(L)]. The structure of the complex has been
confirmed by single crystal X-ray crystallography. The complex has been found to be an
efficient catalyst to perform the aerial oxidation of o-aminophenol to 2-aminophenoxazine-3-one
and could be used as functional model for copper containing enzyme phenoxazinone synthase.
The detailed kinetic study of the catalytic cycle was performed to evaluate various kinetic
parameters, including the turnover number. Supramolecular extended network generated through
weak non-covalent forces (hydrogen and halogen bonding) has also been examined in detail
using several theoretical models, estimating the contribution of each interaction to the formation
of the assembly.
2. Experimental Section
Vanadium(IV) oxide sulphate pentahydrate was purchased from Loba Chemie Pvt Ltd
and was of reagent grade. All other starting materials were commercially available, reagent
grade, and used as purchased from Sigma-Aldrich without further purification.
2.1. Preparation of [VO2(L)]
The tridentate Schiff base ligand, HL, was prepared by refluxing 5-bromosalicylaldehyde
(200 mg, 1 mmol) with N,N-diethyl-1,2-diaminoethane (0.14 mL, 1 mmol) in acetonitrile (10

mL) for ca. 1 h. The ligand was not isolated and was directly used for the preparation of the
complex. Vanadium(IV) oxide sulphate pentahydrate (253 mg, 1 mmol) was dissolved in
acetonitrile (10 mL). The solution was then added into the acetonitrile solution (20 mL) of HL
and the resulting solution was then refluxed for ca. 3 h. A yellow crystalline product was
separated out on cooling in open atmosphere and collected by filtration. It was recrystalized from
acetonitrile solution to obtain X-ray quality single crystals.
Yield: 274 mg (72%); Anal. Calc. for C13H18VBrN2O3 (F.W = 381.13) C, 40.97; H, 4.76;
N, 7.35%. Found: C, 40.9; H, 4.7; N, 7.4%; FT-IR (KBr, cm-1): 1632 (νC=N), 936, 855 (νV=O).
UV–Vis, λmax (nm), [εmax (L mol-1 cm-1)] (CH3CN): 212 (1.633×105), 295 (1.53×105), 421
(3.1×103). Magnetic moment = Diamagnetic.
2.2. Physical measurement
Elemental analyses (carbon, hydrogen and nitrogen) were performed using a Perkin
Elmer 240C elemental analyzer. IR spectrum in KBr (4500-500 cm-1) was recorded with a Perkin
Elmer Spectrum Two spectrophotometer. Electronic spectrum (800-200 nm) was recorded in
acetonitrile on a PerkinElmer Lambda 35 UV–Vis spectrophotometer. X-ray diffraction pattern
of powdered sample was obtained on a Bruker D8 instrument with Cu K (= 0.15418 Å)
radiation. The magnetic susceptibility measurement was performed with an EG and PAR
vibrating sample magnetometer, model 155 at room temperature (300 K) in a 5000 G magnetic
field, and diamagnetic corrections were performed using Pascal's constants.
2.3. X-ray crystallography
A suitable single crystal was picked and mounted on a glass fiber, and diffraction
intensities were measured with an Oxford Diffraction X-Calibur diffractometer, equipped with

Mo Kα radiation ( = 0.71073 Å, 50 kV, 40 mA) at 150 K. Data collection and reduction was
performed with the Oxford Diffraction Crystalis system. The structure of the complex was
solved by direct method and refined by full-matrix least squares on F2, using the SHELX-97
package [18]. The absorption correction type is empirical with ABSPACK program of Oxford
Diffraction Ltd. Non-hydrogen atoms were refined anisotropically. The hydrogen atoms were
placed in their geometrically idealized positions and constrained to ride on their parent atoms.
Programs used: SHELXL-97 [18], PLATON [19], WINGX [20], ORTEP [21], and MERCURY
[22]. Significant crystallographic data are summarized in Table 1. Selected bond lengths and
bond angles are gathered in Tables 2 and 3.
2.4. Kinetic study: catalytic activity of the complex
The kinetic study for the phenoxazinone synthase like activity was monitored
spectrophotometrically due to the increase of the formation of the product 2-aminophenoxazine-
3-one at λmax ~ 430 nm. The experiment was carried out in a standard UV-quartz cuvette (light-
path length of 1 cm) in acetonitrile at 25°C under aerobic conditions for 1h and 40mins. In the
experiment, 10-4 M solution of the complex in acetonitrile was added to solutions with varying
concentrations (10-3 M to 10-2 M) of substrate (o-aminophenol) in acetonitrile. In the above case,
complex: substrate ratio should be ≥ 1:10 to maintain pseudo-first order condition to determine
the dependency of rate on the substrate concentration and various kinetic parameters. The rate of
the reaction was derived from the initial rate method.
2.5. Theoretical methods
The calculations of the noncovalent interactions were carried out using the
TURBOMOLE version 7.0 [23] using the M06-2X/def2-TZVP level of theory. To evaluate the

interactions in the solid state, the crystallographic coordinates have been used. This procedure
and level of theory have been successfully used to evaluate similar interactions [24-27]. The
interaction energies were computed by calculating the difference between the energies of isolated
monomers and their assembly. The interaction energies were corrected for the Basis Set
Superposition Error (BSSE) using the counterpoise method [28].
3. Results and discussion
3.1. Synthesis
The tridentate Schiff base ligand, HL, was prepared by the condensation of 5-
bromosalicylaldehyde with N,N-diethyl-1,2-diaminoethane, following the literature method [29].
The Schiff base, HL, was reacted with vanadium(IV) oxide sulphate pentahydrate in acetonitrile
to prepare a pentacoordinated dioxovanadium(V) complex, [VO2(L)]. In this case, the
deprotonation of the Schiff base is favoured by the hydroxide ions produced by the reduction of
O2 during the areal oxidation of vanadium(IV) to vanadium(V). Formation of the complex is
shown in Scheme 1.
Scheme 1: Synthesis of the ligand and the complex

3.2. Description of structure of [VO2(L)]
X-ray crystal structure determination reveals that the complex crystallizes in monoclinic
space group P21/n. A perspective view of the complex along with the selective atom numbering
scheme is shown in Figure 1. The vanadium(V) center is five-coordinated. The basal plane is
composed of one imine nitrogen atom, N(19), one amine nitrogen atom, N(22), one phenoxo
oxygen atom, O(11), of a deprotonated Schiff base ligand and an oxo group, O(2). The apical
position is occupied by a second oxo group, O(1).
The extent of distortion of a square pyramidal geometry toward a trigonal bipyramidal
geometry can be measured by the value of Addison parameter (τ) which is defined as (α–β)/60°,
where α and β are the two largest angles subtended at the vanadium center (For an ideal square
pyramidal geometry τ is 0 and for an ideal trigonal bipyramidal geometry τ is 1) [30]. The τ
value for the complex is 0.38, indicating a severely distorted square pyramidal coordination
around the vanadium(V) center. The deviation of all the coordinating atoms, N(19), N(22), O(11)
and O(2), in the basal plane from the mean plane passing through them are -0.277(2) Å, 0.123(2)
Å, 0.107(2) Å and -0.343(2) Å for the complex. The vanadium(V) center lies 0.493(2) Å from
the mean plane of the basal atoms in the direction of the apical oxo group, O(1). The V(1)-O(1)
and V(1)-O(2) distances are 1.621 and 1.623 Å respectively, indicating they are typical V=O
double bonds [31]. The coordinate bond lengths in the complex are comparable with the bond
lengths of reported dioxovanadium(V) complexes with similar Schiff base ligands [32].
The hydrogen atom, H(25A), attached with C(25), is involved in C–H···π interaction
with a symmetry related (1-x,1-y,-z) phenyl ring [C(12)-C(13)-C(14)-C(15)-C(16)-C(17)] to
form a supra molecular dimer (Figure 2). The details of geometric features of C–H···π
interaction are given in Table 4.

3.3. Theoretical Study of noncovalent interactions
The theoretical study mainly focused on relevant hydrogen bonding and halogen bonding
interactions observed in the solid state architecture of the complex, as shown in Figure 3a. The
MEP surface of the complex has been computed to investigate the most positive and negative
regions of the molecule in order to rationalize the interactions observed in the solid state. The
MEP surface is given in Figure 3b and it can be observed that the most negative region is located
at the oxygen atoms (–55 kcal/mol) and the most positive one at the iminic hydrogen atom (+38
kcal/mol). The aromatic hydrogen atoms of the ligand are also positive (+16 kcal/mol).
Moreover, it is interesting to note the presence of an σ-hole at the bromine atom (+14 kcal/mol),
thus it is suitable for establishing directional halogen bonding interactions with electron rich
atoms.
Figure 3a shows a fragment of the X-ray structure where the formation of an infinite 1D
supramolecular chain governed by halogen bonding interaction is highlighted. These 1D chains
interact with adjacent chains forming a 2D sheet by means of hydrogen bonding interactions (see
Figure 3c) and also C-H···π interactions (see Figure 2). The interaction energies of both
hydrogen bonding and halogen bonding interactions have been evaluated using the models
shown in Figure 3c,d. It can be observed that the hydrogen bonding dimer is energetically more
favourable (ΔE1 = –7.7 kcal/mol) that the halogen bonded dimer (ΔE2 = –2.8 kcal/mol). In the
former several symmetrically related hydrogen bonds are established thus explaining the larger
interaction energy compared to the latter where only one halogen bond is formed.
The Bader’s theory of atoms-in-molecules has been used to further confirm the existence
of the noncovalent interactions described above. The existence of a bond critical point (CP) and
bond path connecting two atoms is an unambiguous evidence of interaction. The distributions of

critical points and bond paths for both hydrogen bonded and halogen bonded dimers of 1 are
shown in Figure 4. It can be observed that the hydrogen bonded dimer (Figure 4a) is
characterized by the presence of six bond CPs (red spheres) and bond paths connecting the
hydrogen atoms to the oxygen atoms. Moreover, the hydrogen bonding network is also
characterized by several ring CPs (yellow spheres) as a consequence of the formation of several
supramolecular rings. The halogen bonding interaction is characterized by the presence of one
CP and bond path connecting the bromine atom to the oxygen atom, thus confirming the
existence of the halogen bonding. The distribution also reveals the formation of two ancillary
hydrogen bonded interactions between the C–H bonds of the methyl groups and the bromine
atom that also contribute to the formation of the 1D supramolecular chain in the solid state of the
complex.
3.4. IR, electronic spectra and magnetic moment
In the IR spectrum of the complex, strong and sharp band at 1632 cm-1 due to the
azomethine (C=N) group has been routinely noticed [33]. Strong bands at 936 cm-1 and 855 cm-1
in the complex may be assigned to symmetric and asymmetric ν(O=V=O) vibrations of cis-VO2
groups [34-35]. The values agree satisfactorily with similar dioxovanadium(V) Schiff base
complexes.
Electronic spectrum of the complex in acetonitrile displays absorption band at 388 nm.
This band may be assigned as a ligand-to-metal charge transfer (LMCT) transition originating
from the pπ orbital on the phenolate oxygen to the empty d orbitals of the vanadium(V) [31]. A
more intense band at 246 nm in the complex may be assigned as intraligand π-π* transition [36].

Magnetic susceptibility measurements show that the complex is diamagnetic which is quite
obvious for vanadium(V) [37].
3.5. X-ray diffraction of powdered sample
The experimental XRD pattern of the powdered bulk material is in good agreement with
the simulated XRD pattern from single crystal X-ray diffraction results, indicating consistency of
the bulk sample. The simulated pattern of the complex was calculated from the single crystal
structural data (Cif) using the CCDC Mercury software.
3.6. Hirshfeld Surface analysis
Hirshfeld surfaces of the complex are illustrated in Figure 5A. The intermolecular
interactions appear as distinct spikes in the 2D fingerprint plots (Figure 5B). This decomposition
of fingerprint plots enables separation of contributions from different interaction types, which
overlap in the full fingerprint.
3.7. Kinetic study: Oxidation of o-aminophenol (phenoxazinone synthase like activity)
The catalytic ability of the complex, towards the oxidation of o-aminophenol to 2-
aminophenoxazine-3-one (phenoxazinone synthase like activity), was monitored. The gradual
increase of peak (characteristic of the phenoxazinone absorption) intensity at ~430 nm implies
the catalytic conversion of o-aminophenol (OAP) to 2-aminophenoxazine-3-one in aerobic
conditions. The time dependent spectral profile of the complex is shown in Figure 6.
The ESI-MS positive spectroscopy was performed for 1:50 mixture (in molar proportion)
of the complex with the substrate o-aminophenol. The peak at m/z = 213.9629 arises due to
[phenoxazinone-H]+ which confirms the completion of catalytic cycle. Another important peak

obtained at m/z = 587.1485, is for [VO2(HL)(OAP)(CH3CN)(H2O)K]+. On the basis of this mass
spectroscopic data, a probable reaction mechanism is given in scheme 2. The ESI-MS spectra are
given in Figures 7-8.
Scheme 2: The probable mechanistic pathway for the formation of 2-aminophenoxazine-3-one
from o-aminophenol
3.8. Rationalization of kinetic parameters
In the kinetic studies, the Briggs-Haldane scheme is used, which considers the formation
and dissociation reactions of the enzyme-substrate complex, ES, and its decomposition reaction,
forming the products and regenerating the enzyme.

Applying this kinetic scheme to the steady state approximation for the concentration of
the enzyme-substrate adducts the famous Michaelis-Menten equation for the initial reaction rate
was obtained (equation 1).
V (time-1) = Vmax [S]/([S] + KM) - - - - - - - - (1)
Plot of Eq. 1 for kinetic studies of air oxidations of o-aminophenol catalyzed by the
complex show rectangular hyperbolic nature which finally tends towards a saturation curve. This
proofs the first order rate kinetics followed by the substrates. The initial rate constants, V
(min−1), are obtained directly from the slope of the plot of log[(A∞−A0)/(A∞−At)] vs. time which
is a straight line passing through origin. According to the Eq. 1, the limiting rate at high substrate
concentration [S]0 is designated as Vmax (Vmax = kcat[E]0)
On the other hand, rearrangement of Eq. 1, produces Hanes equation (Eq. 2). In this case, [S]/V
vs. [S] are plotted.
[S]/V = [S]/Vmax + KM/ Vmax - - - - - - - - - - (2)
Eadie-Hofstee equation (Eq. 3) is sometimes used in biochemistry for a graphical representation
of enzyme kinetics. In this case, V/ [S] vs. V is plotted.
V = Vmax - KM (V/[S]) - - - - - - - - - - - (3)
All the above equations was used to determine the kinetic parameters, Vmax i.e maximum
reaction velocity, KM i.e. Michaelis constant and Kcat i.e. turnover number. All related plots of

the catalytic activity by the complex are shown in Figure 9. All kinetic parameters values are
given in Table 5.
4. Conclusion
In summary, a mononuclear dioxovanadium(V) Schiff base complex, [VO2(L)] {HL = 2-
(diethylamino)ethyliminomethyl)-4-bromophenol} has been synthesized and characterized by X-
ray crystallography. Formation of O···Br halogen bonding interaction has been studied using
DFT calculations and characterized using the Bader’s theory of “atoms-in-molecules”. The
presence of an σ-hole at the bromine atom has been confirmed using the MEP surface. The
catalytic efficiency of the complex was assessed by following conventional Michaelis-Menten
enzymatic kinetics. The complex is found to show phenoxazinone synthase like activity (i.e
conversion of o aminophenol to 2-aminophenoxazine-3-one).
Acknowledgments
S.T thanks the DST, India, for awarding a Junior Research Fellowship (IF160359). N.S.
thanks the UGC, India, for awarding a Junior Research Fellowship (Sr. No. 2061410290, Ref.
No.: 22/06/2014(i)EU-V, dated 7.08.2015). A. F. and A. B. gratefully acknowledge the financial
support of this work by the MINECO of Spain (project CTQ2014-57393-C2-1-P, FEDER funds).
We thank the CTI (UIB) for free allocation of computer time. M. G. B. D thanks the University
of Reading and the EPSRC (U. K.) for funds for the diffractometer.
Appendix A. Supplementary data
CCDC 1551853 contains the supplementary crystallographic data for the complex. This
data can be obtained free of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.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
[1] E. I. Solomon, T. C. Brunold, M. I. Davis, J. N. Kemsley, S. K. Lee, N. Lehnert, F. Neese, A.
J. Skulan, Y. S. Yang, J. Zhou, Chem. Rev. 100 (2000) 235-350.
[2] E. I. Solomon, R. Sarangi, J. S. Woertink, A. J. Augustine, J. Yoon, S. Ghosh, Acc. Chem.
Res. 40 (2007) 581-591.
[3] E. G. Kovaleva, J. D. Lipscomb, Nat. Chem. Biol. 4 (2008) 186-193
[4] A. G. J. Ligtenbarg, R. Hage, B. L. Feringa, Coord. Chem. Rev. 237 (2003) 89-101
[5] H. Sakurai, K. Fujii, H. Watanabe, H. Tamura, Biochem. Biophys. Res. Commun. 214
(1995) 1095-1101.
[6] M. Melchior, K. H. Thompson, J. M. Jong, S. J. Rettig, E. Shuter, V. G. Yuen, Y. Zhou, J. H.
McNeill, C. Orvig, Inorg. Chem. 38 (1999) 2288-2293.
[7] J. M. Arber, B. R. Dobson, R. R. Eady, P. Stevens, S. S. Hasnain, C. D. Garner, B. E. Smith,
Nature 325 (1987) 372-374.
[8] C. E. McKenna, J. R. Benemann, T. G. Traylor, Biochem. Biophys. Res. Commun. 41 (1970)
1501-1508.
[9] C. Chen, Q. Sun, D.-X. Ren, R. Zhang, F.-Y. Bai, Y.-H. Xing, Z. Shi, CrystEngComm 15
(2013) 5561-5573.
[10] C. E. Barry, P. G. Nayar, T. P. Begley, Biochemistry 28 (1989) 6323-6333.

[11] E. E. Golub, J. S. Nishimura, J. Bacteriol. 112 (1972) 1353-1357.
[12] C. E. Barry, P. G. Nayar, T. P. Begley, J. Am. Chem. Soc. 110 (1988) 3333-3334.
[13] I. Cs. Szigyártó, T. M. Simándi, L. I. Simándi, L. Korecz, N. Nagy, J. Mol. Catal. A: Chem.
251 (2006) 270–276
[14] T. M. Simándi, L. I. Simándi, M. Győr, A. Rockenbauer, Á. Gömöry, Dalton Trans. (2004)
1056-1060.
[15] L. I. Simándi, T. Barna, S. Németh, J. Chem. Soc., Dalton Trans. (1996) 473-478.
[16] I. C. Szigyártó, T. M. Simándi, L. I. Simándi, L. Korecz, N. Nagy, J. Mol. Catal. A: Chem.
251 (2006) 270-276.
[17] A. Panja, P. Guionneau, Dalton Trans. 42 (2013) 5068-5075.
[18] G. M. Sheldrick, Acta Crystallogr. Sect. A: Found. Crystallogr. 64 (2008) 112-122.
[19] A. L. Spek, ActaCryst. D65 (2009) 148-155.
[20] J. L. Farrugia, J. Appl. Cryst. 45 (2012) 849-854.
[21] M. N. Burnett, C. K. Johnson, ORTEP-3: Oak Ridge Thermal Ellipsoid Plot Program for
Crystal Structure Illustrations, Report ORNL-6895, Oak Ridge National Laboratory, Oak Ridge,
TN, USA, 1996.
[22] C. F. Macrae, I. J. Bruno, J. A. Chisholm, P. R. Edgington, P. McCabe, E. Pidcock, L. R.
Monge, R. Taylor, J. van de Streek, P. A. Wood, J. Appl. Crystallogr. 41 (2008) 466-470.
[23] R. Ahlrichs, M. Bär, M. Häser, H. Horn, C. Kölmel, Chem. Phys. Lett. 162 (1989) 165-169.

[24] A. Bauzá, A. Terrón, M. Barceló-Oliver, A. García-Raso, A. Frontera, Inorg. Chim. Acta
452 (2016) 244-250.
[25] D. Sadhukhan, M. Maiti, G. Pilet, A. Bauzá, A. Frontera, S. Mitra, Eur. J. Inorg. Chem. 11
(2015) 1958-1972.
[26] M. Mirzaei, H. Eshtiagh-Hosseini, Z. Bolouri, Z. Rahmati, A. Esmaeilzadeh, A.
Hassanpoor, A. Bauzá, P. Ballester, M. Barceló-Oliver, J. T. Mague, B. Notash, A. Frontera,
Cryst. Growth Des. 15 (2015) 1351-1361.
[27] P. Chakraborty, S. Purkait, S. Mondal, A. Bauzá, A. Frontera, C. Massera, D. Das,
CrystEngComm 17 (2015) 4680-4690.
[28] S. F. Boys, F. Bernardi, Mol. Phys. 19 (1970) 553-555.
[29] K. Ghosh, A. Banerjee, S. Roy, A. Bauzá, A. Frontera, S. Chattopadhyay, Polyhedron 112
(2016) 86-95.
[30] A. W. Addison, T. N. Rao, J. Reedijk, J. van Rijn, G. C. Verschoor, J. Chem. Soc., Dalton
Trans. (1984) 1349.
[31] G. Asgedom, A. Sreedhara, J. Kivikoski, E. Kolehmainen, C. P. Rao, J. Chem. Soc., Dalton
Trans. (1996) 93-97.
[32] L. M. Mokry, C. J. Carrano, Inorg. Chem. 32 (1993) 6119-6121.
[33] K. Nakamoto, Infrared Spectra of Inorganic and Coordination Compounds, fourth ed.
Wiley, New York, 1986.
[34] E. Kwiatkowski, G. Romanowski, W. Nowicki, M. Kwiatkowski, K. Suwińska, Polyhedron
26 (2007) 2559-2568.
[35] G. Romanowski, M. Wera, Polyhedron 29 (2010) 2747-2754.
[36] M. R. Maurya, A. Kumar, M. Abid, A. Azam, Inorg. Chim. Acta 359 (2006) 2439-2447.

[37] T. Ghosh, B. Mondal, T. Ghosh, M. Sutradhar, G. Mukherjee, M. G. B. Drew, Inorg. Chim.
Acta 360 (2007) 1753-1761.
Table 1: Crystal data and refinement details of the complex
Formula
Formula Weight
Temperature(K)
Crystal system
Space group
a(Å)
C13H18VBrN2O3
381.13
150
Monoclinic
P21/n
14.0920(8)
6.9610(3)
15.2756(8)
107.255(6)
1431.01(1)
4
b(Å)
c(Å)
β(deg)
V
Z
dcalc(g cm-3)
μ(mm-1)
1.769
3.493
F(000)
768
Total Reflections
Unique Reflections
9502
4144
Observed data [I > 2 σ (I)]
No. of parameters
R(int)
3373
183
0.047
R1, wR2 (all data)
R1, wR2 [I > 2 σ (I)]
0.0598, 0.1140
0.0437, 0.1037

Table 2: Selected bond lengths (Å) for the complex.
Bond lengths (Å)
V(1)-O(1)
V(1)-O(2)
V(1)-O(11)
V(1)-N(19)
V(1)-N(22)
1.621(2)
1.623(2)
1.918(2)
2.146(2)
2.203(2)
Table 3: Selected bond angles (°) for the complex.
Bond angles (°)
O(1)-V(1)-O(2)
O(1)-V(1)-O(11)
O(1)-V(1)-N(19)
O(1)-V(1)-N(22)
O(2)-V(1)-O(11)
O(2)-V(1)-N(19)
O(2)-V(1)-N(22)
O(11)-V(1)-N(19)
O(11)-V(1)-N(22)
N(19)-V(1)-N(22)
110.70(1)
103.20(1)
113.62(1)
93.82(1)
97.13(1)
134.56(1)
90.75(1)
82.32(9)
157.22(9)
76.67(8)

Table 4: Geometric features (distances in Å and angles in ) of the C–H···π interactions obtained
for the complex.
C–H···Cg(Ring)
H···Cg C–H···Cg (°) C···Cg (Å)
2.62 157 3.530(3)
C(25)–H(25A)···Cg(3)a
a
Symmetry transformations: = 1-x,1-y,-z Cg(3) = Center of gravity of the ring [C(12)–C(13)–
C(14)–C(15)–C(16)–C(17)]
Table 5: Kinetic parameters of phenoxazinone synthase like activity of the complex at 25°C in
CH3CN
Enzyme kinetic
plots
Vmax
KM
Kcat
Michaelis-Menten
Plot
6.3x10-4M min-1
2.91x10-3(M)
378 h-1
Hanes-Woolf
plot
6.28x10-4M min-1
2.92x10-3(M)
376.8 h-1
Eadie-Hofstee
plot
5.458x10-4M min-1 2.65x10-3(M)
327.48 h-1

Figure 1: Perspective view of the complex with selective atom numbering scheme.
Figure 2: Supramolecular dimer in the complex, generated through C–H∙∙∙π interactions.
Selected atoms have been omitted for clarity.

Figure 3: (a) Partial view of the X-ray structure of the complex (hydrogen atoms omitted). (b)
MEP surface of the complex with indication of the energetic values in selected point of the
surface (isosurface at 0.002 a.u.) (c,d) theoretical models used to evaluate the noncovalent
interactions
Figure 4: Distribution of bond and ring (red and yellow spheres) critical points in two dimers of
the complex.

Figure 5: (A) Hirshfeld surfaces mapped with dnorm (top), shape index (middle) and curvedness
(bottom) of the complex; (B) 2D Fingerprint plot of the complex shows proportions of
O···H/H···O and C···H/H···C interactions comprise 20.8% and 18.0% of total surface of the
complex.

Figure 6: The spectral profile showing the growth of 2-aminophenoxazine-3-one at ~430 nm
upon addition of (10-2 M) o-aminophenol to the complex (10−4 M) in CH3CN
Figure 7: The magnified ESI-MS spectrum of 1:50 molar proportion mixture of the complex and
o-aminophenol (0-230 m/z range)

Figure 8: The magnified ESI-MS spectrum of 1:50 molar proportion mixture of the complex and
o-aminophenol (538-600 m/z range)

Figure 9: (a) Michaelis-Menten plot; (b) Hanes-Woolf plot and (c) Eadie-Hofstee plot of the
complex in CH3CN medium for oxidation of o-aminophenol.

A mononuclear dioxovanadium(V) Schiff base complex has been synthesized and
characterized. Noncovalent interactions have been explored by means of DFT and MEP
calculations and characterized using Bader’s theory of “atoms in molecules” (AIM). The
complex shows catalytic activity towards the oxidation of o-aminophenol to 2-
aminophenoxazine-3-one.