One pot synthesis of two cobalt(iii) Schiff base complexes with chelating pyridyltetrazolate and exploration of their bio-relevant catalytic activities

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One pot synthesis of two cobalt(III) Schiﬀ base

complexes with chelating pyridyltetrazolate and

exploration of their bio-relevant catalytic

activities†

Cite this: RSC Adv., 2018, 8, 28216

b

Kousik Ghosh,^aAbhisek Banerjee,^aAntonio Bauza,

Antonio Frontera

*

´

a

*

and Shouvik Chattopadhyay

Two new cobalt(III) tetrazolato complexes [Co(L¹)(PTZ)(N₃)] (1) and [Co(L²)(PTZ)(N₃)] (2) {where H₂L¹¼ 2((3-

(methylamino)propylimino)methyl)-6-methoxyphenol, H₂L²¼ 2((3-(dimethylamino)propylimino)methyl)-

6-ethoxyphenol and HPTZ ¼ 5-(2-pyridyl)tetrazole}, have been synthesized via in situ 1,3-dipolar

cycloaddition reaction of 2-cyanopyridine and sodium azide in the presence of cobalt(^II) nitrate

hexahydrate and respective Schiﬀ bases in the open atmosphere. The structures of both complexes have

been conﬁrmed by single crystal X-ray diﬀraction studies. Features of noncovalent interactions in the

solid state of both complexes have been studied by means of DFT and MEP calculations and

characterized using Bader's theory of “atoms in molecules” (AIM). These complexes act as biomimetic

catalysts promoting the aerobic oxidation of 3,5-di-tert-butylcatechol (3,5-DTBC) to the corresponding

o-benzoquinone at room temperature. The reaction follows Michaelis–Menten enzymatic reaction

kinetics with turnover numbers of ꢀ0.030 s^ꢁ1in an acetonitrile–methanol (2 : 1) mixture. Both

complexes are also reactive towards aerobic oxidation of o-aminophenol in acetonitrile–methanol (2 : 1)

Received 9th April 2018

Accepted 16th July 2018

DOI: 10.1039/c8ra03035a

rsc.li/rsc-advances

with turnover numbers ꢀ0.095 s^ꢁ1

.

copper(^II), di-nickel(II) and manganese(II/III) containing func-

tional models of these metalloenzymes have been shown to

mediate such catechol oxidation.⁷Phenoxazinone synthase,

another multicopper oxidase enzyme, is known to catalyze the

oxidative condensation of two molecules of a substituted o-

aminophenol to the phenoxazinone chromophore.⁸Many

transition metal complexes of Schiﬀ bases have been showing to

have the ability to mimic these two enzyme.⁹Focusing to

cobalt(^III) Schiﬀ base complexes, extensive attention into their

metallo-organic and coordination chemistry arises from their

synthetic accessibility, fascinating structural features and

diverse range of applications in photochemistry,¹⁰electro-

chromism,¹¹and catalysis.¹²They also have signicant biolog-

ical applications.¹³Cobalt(III) Schiﬀ base complexes have been

used as precursor for the synthesis of Co₃O₄nanoparticles via

thermal decomposition method.¹⁴

The chemistry of tetrazoles and their complexes, on the other

hand, has received great attention now-a-days¹⁵for their wide

range of applications in coordination chemistry,¹⁶medicinal

chemistry¹⁷and material science.¹⁸Although several synthetic

methods have been reported so far, synthesis by 1,3-dipolar

cycloaddition of cyanopyridine/cyanopyrazines and metal

coordinated azide is probably the best method.¹⁹However,

although few metal tetrazolate complexes containing Schiﬀ

bases as blocking ligands exist in literature,²⁰best to our

Introduction

Transition metals are known to play various signicant roles in

living systems.¹They are present in many metalloenzymes and

metalloproteins and the roles of these enzymes and proteins are

primarily dependant on these metal ions.²If the metal ions are

removed from these enzymes, the corresponding apo-enzymes

are found to lose their catalytic activity, either partially or

completely.³The group of enzymes that is capable of processing

molecular oxygen under ambient conditions has attracted the

attention of synthetic inorganic chemists and they designed

many catalysts acting as mimics of various oxidase enzymes.⁴

Mimics of these oxidase metalloenzymes are of particular

interest for the development of bio-inspired catalysts for

oxidation reactions.⁵For example, atmospheric dioxygen is

used by catechol oxidase, a type-3 di-copper enzyme, for the

oxidation of catechols to ortho-quinones.⁶A variety of di-

^aDepartment of Chemistry, Inorganic Section, Jadavpur University, Kolkata, 700032,

India. E-mail: shouvik.chem@gmail.com; Tel: +913324572147

b

´

Departament de Quımica, Universitat de les IllesBalears, Crta. De Valldemossa km

7.5, 07122 Palma (Baleares), Spain. E-mail: toni.frontera@uib.es

† Electronic supplementary information (ESI) available: CCDC 1548132 and

1548133 contain the supplementary crystallographic data for

1 and 2

respectively. For ESI and crystallographic data in CIF or other electronic format

see DOI: 10.1039/c8ra03035a

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knowledge there is no report for the synthesis of any cobalt(III) (y_C–H), 2015 (y_N3), 1616 (y_C]N), 1468 (y_tetrazolate), 1442 (y_tetrazolate).

tetrazolate complexes with Schiﬀ base coligands. Keeping this UV-Vis, l_max(nm), [3_max(dm³mol^ꢁ1cm^ꢁ1)] (CH₃CN), 710 (3.02

in mind, we plan to synthesize and characterize few cobalt(^III) ꢂ 10²), 352 (9.85 ꢂ 10³), 240 (5.20 ꢂ 10⁴). Magnetic moment:

tetrazolato complexes with Schiﬀ base co-ligands. Supramolec- 0.098 BM (diamagnetic).

ular extended networks generated through weak non-covalent

forces (hydrogen bonding and C–H/p interaction) have also Crystallographic data collection and renement

been examined in detail using several theoretical models at the

‘Bruker SMART APEX II’ diﬀractometer equipped with graphite-

DFT-D3 level, estimating the contribution of each interaction to

the formation of the assembly. Finally, catechol oxidase and

phenoxazinone synthase like activities of both cobalt(^III) tetra-

zolato complexes have been explored.

˚

monochromated Mo K_aradiation (l ¼ 0.71073 A) was used for

data collection from suitable single crystals of both complexes.

Direct methods were used to solve the molecular structures and

full-matrix least squares on F²were used to rene the structures

using SHELX-2014 package.²¹Non-hydrogen atoms were rened

with anisotropic thermal parameters. The hydrogen atoms were

placed in their geometrically idealized positions and con-

strained to ride on their parent atoms. Multi-scan empirical

absorption corrections were applied to the data using the

program SADABS.²²Details of the crystallographic data and

renement details of both complexes are given in Table 1.

Experimental section

Materials

All starting materials were commercially available, reagent

grade, and used as purchased from Sigma-Aldrich without

further purication. The reactions and all manipulations of the

samples were carried out under aerobic conditions.

Caution!!! Metal complexes containing azides and organic

ligands are potentially explosive. Only a small amount of the

material should be prepared and they should be handled with

care. The experimental work is safe with the proper precautions.

Details of instrumentation

Elemental analyses (carbon, hydrogen and nitrogen) were per-

formed using a Perkin Elmer 240C elemental analyzer. IR

spectra in KBr (4500–500 cm^ꢁ1) were recorded with a Perkin

Elmer Spectrum Two spectrophotometer. Electronic spectra in

acetonitrile–methanol (2 : 1) mixture were recorded on a SHI-

MADZU UV-1700(E) Pharma Spec UV-Vis spectrophotometer.

Steady-state photoluminescence spectra in acetonitrile–meth-

anol (2 : 1) mixture were obtained with a Shimadzu RF-5301PC

spectrouorometer at room temperature. Time-dependent

photoluminescence spectra were recorded using a Hama-

matsu MCP photomultiplier (R3809) and were analyzed using

IBHDAS6 soware. The cyclic voltammetry experiments were

performed in DMF solution containing tetrabutylammonium

perchlorate (TBAP) as supporting electrolyte using glassy

carbon, Ag/Ag+ (nonaqueous) and platinum wire as working,

Preparations

Preparation of [Co(L¹)(PTZ)(N₃)] (1). A methanol solution of

(20 mL) N-methyl-1,3-diaminopropane (0.11 mL, 1 mmol) and 3-

methoxysalicylaldehyde (152 mg, 1 mmol) was reuxed for ca.

1 h to form a Schiﬀ base, HL¹. A methanol solution (5 mL) of 2-

cyanopyridine (1 mmol, 105 mg) was then added to it, followed

by the addition of a methanol solution (5 mL) of cobalt(^II)

nitrate hexahydrate (1 mmol, 291 mg) with constant stirring. A

solution of sodium azide (1 mmol, 65 mg) in methanol-water

was added to it and the stirring was continued for additional

2 h. A dark brown crystalline material was started to separate

out on standing the resulting solution at room temperature. It

was collected by ltration and dissolved in acetonitrile. Dark

brown single crystals, suitable for X-ray diﬀraction started to

separate aer ca. 7 days.

Table 1 Crystal data and reﬁnement details of complexes 1 and 2

1

2

Yield: 347 mg (ꢀ74%); based on cobalt(^III). Anal. calc. for

Formula

C

₁₈H₂₁CoN₁₀O₂

C₂₀H₂₅CoN₁₀O₂

496.43

Monoclinic

P2₁/c

16.1282 (4)

7.7871 (2)

18.6891 (5)

104.133 (1)

1.449

0.794

1032

31 148

3995

3493

298

0.031

0.0325, 0.0745

0.0271, 0.0714

0.199, ꢁ0.227

C

₁₈H₂₁CoN₁₀O₂(FW ¼ 468.38): C, 46.12; H, 4.48; N, 29.89%.

Found: C, 46.2; H, 4.4; N, 29.9%. FT-IR (KBr, cm^ꢁ1): 3182 (y_N–H),

2990–2890 (y_C–H), 2022 (y_N3), 1632 (y_C]N), 1472 (y_tetrazolate), 1446

(y_tetrazolate). UV-Vis, l_max(nm), [3_max(dm³mol^ꢁ1cm^ꢁ1)]

(CH₃CN), 670 (1.12 ꢂ 10²), 345 (6.16 ꢂ 10³), 240 (3.95 ꢂ 10⁴).

Magnetic moment: 0.095 BM (diamagnetic).

Formula weight

Crystal system

Space group

468.38

Monoclinic

P2₁/c

7.9648 (3)

7.9932 (3)

31.0201 (11)

96.409 (2)

1.585

0.915

968

25 838

3491

3158

280

0.04

0.0607, 0.1219

0.0547, 0.1194

0.683, ꢁ0.919

˚

a (A)

˚

b (A)

˚

c (A)

b (^ꢃ)

Preparation of [Co(L²)(PTZ)(N₃)] (2). Complex 2 was prepared

using a similar method as that used for complex 1 except that

HL²was used instead of HL¹. HL²was synthesized by reuxing

d(calc.) [g cm^ꢁ3

]

m [mm^ꢁ1

F(000)

]

a

methanol solution of N,N-dimethyl-1,3-diaminopropane

Total reections

Unique reections

Observed data [I > 2s(I)]

No. of parameters

R (int)

(0.125 mL, 1 mmol) and 3-ethoxysalicylaldehyde (166 mg, 1

mmol) for ca. 1 h. X-ray quality dark brown single crystals

started to grow from acetonitrile solution aer ca. 7 days.

Yield: 360 mg (ꢀ72%); based on cobalt(^III). Anal. calc. for

R1, wR2 (all data)

R1, wR2 [I > 2 s(I)]

Residual electron density (e A

C

₂₀H₂₅CoN₁₀O₂(FW ¼ 496.43): C, 48.35; H, 5.04; N, 28.20%.

ꢁ3

Found: C, 48.4; H, 5.0; N, 28.3%. FT-IR (KBr, cm^ꢁ1): 3000–2928

˚

)

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Scheme 1 In situ formation of tetrazolate via 1,3-dipolar cycloaddition reaction.

reference and auxiliary electrodes respectively at ambient similar interactions.²⁹The interaction energies were computed

temperature (300 K) with no trace of decomposition as reected by calculating the diﬀerence between the energies of isolated

in the smooth curve, in the potential range from ꢁ2 to +2 V and monomers and their assembly. The interaction energies were

were uncorrected for junction contribution. The magnetic corrected for the Basis Set Superposition Error (BSSE) using the

susceptibility measurements were done with an EG & PAR counterpoise method.³⁰The molecular electrostatic potential

vibrating sample magnetometer, model 155 at room tempera- surfaces were computed using the SPARTAN soware.³¹The

ture and diamagnetic corrections were made using Pascal's Bader's “atoms-in-molecules” analysis was performed at the

constants. X-ray diﬀraction of the powder samples were per- same level of theory, using the AIMAll program.³²

formed on a Bruker D8 instrument with Cu K_aradiation (l ¼

˚

1.54184 A). Electrospray ionization mass spectra were recorded

using Waters QTOF Micro YA263 mass analyzer. Electron

paramagnetic resonance (EPR) spectra were recorded in stan-

Kinetics of the catalytic oxidations of 3,5-DTBC and o-

aminophenol

dard quartz EPR tubes using JEOL JES-FA200 X-band

spectrometer.

With the aim of study the catechol oxidase and phenoxazinone

synthase mimicking activity of cobalt(^III) tetrazolato complexes,

10^ꢁ4M solution of each complex in acetonitrile–methanol

(2 : 1) mixture was treated with at least ten equivalents of

substrate solution separately (3,5-DTBC for catechol oxidase

mimicking activity and o-aminophenol for phenoxazinone

synthase mimicking activity) under aerobic conditions at room

temperature. All catalytic reactions were monitored spectro-

photometrically for ꢀ2 h in the wavelength range 300–500 nm.

In the catalytic oxidations of 3,5-DTBC and o-aminophenol the

Hirshfeld Surface analysis

Hirshfeld surfaces²³and the ngerprint²⁴(2D) plots were

calculated using Crystal Explorer.²⁵The details could be found

in many previous papers.^26,27

Theoretical methods

The calculations of the noncovalent interactions were carried increase in the absorbance as a function of time around 401 and

out using the TURBOMOLE version 7.0 (ref. 28) using the BP86- 433 nm respectively, conrms the formation of corresponding

D3/def2-TZVP level of theory. To evaluate the interactions in the chromophores. In addition, to check the rate dependency on

solid state, the crystallographic coordinates were used. This catalyst concentration, similar sets of experiments were per-

procedure and level of theory was successfully used to evaluate formed at a xed concentration of substrate with variable

Scheme 2 Synthetic route to complexes 1 and 2.

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Table 2 Selected bond lengths (A˚) of complexes 1 and 2

1

2

Co(1)–O(1)

Co(1)–N(1)

Co(1)–N(1Z)

Co(1)–N(2)

Co(1)–N(3)

Co(1)–N(7)

1.871(2)

2.002(3)

1.952(3)

1.911(3)

1.955(3)

1.981(3)

1.8651(14)

2.0720(15)

1.9521(16)

1.9076(17)

1.9419(15)

1.9911(15)

tetrazolate was prepared in situ by 1,3-dipolar cycloaddition of 2-

cyanopyridine and azide (Scheme 1).³⁴

The complexes were prepared in situ by the reaction of

cobalt(^II) nitrate hexahydrate, 2-cyanopyridine and sodium

azide with the corresponding Schiﬀ base ligands (HL¹for 1 and

HL²for 2) under stirring condition using methanol as solvent.

Cobalt(^II) is readily oxidised to cobalt(III) by aerial oxygen in

presence of strong eld Schiﬀ base ligands, as was also observed

in similar complexes.³⁵Cobalt(II) is quite stable in aqueous (or

Fig. 1 ORTEP presentation of complex 1 (ellipsoids are drawn at the

40% probability level) with selected atom-numbering scheme.

amounts of catalyst concentrations. Rate of the reactions was

derived from the initial rate method, and the average initial rate

over three independent measurements was recorded.

2+

methanol) medium and remains as high spin Co(L)₆(L ¼

H₂O, CH₃OH), which assumes a pale pink colour. The electronic

conguration of this species is t⁵_2ge_g². On adding a strong eld

ligand, the spin state changes to LS with concomitant change in

the electronic conguration to t⁶_2ge_g¹. If the strong eld ligand

produces suﬃcient strong eld, 10 Dq becomes very high. This

leads to severe destabilization of the e_gelectron, which, in turn,

is responsible for the easy removal of this electron, leading to

the oxidation of cobalt(^II) to cobalt(III).

Results and discussion

Synthesis

In current investigation, two Schiﬀ base ligands HL¹and HL²

were used as blocking ligands to prepare two mononuclear

cobalt(^III) tetrazolato complexes. HL¹was synthesized by the

1 : 1 condensation of N-methyl-1,3-diaminopropane with the 3-

methoxysalicylaldehyde whereas, HL²was synthesized by

similar 1 : 1 condensation of N,N-dimethyl-1,3-propanediamine

with 3-ethoxysalicylaldehyde in methanol following the litera-

ture method.³³The ligands were not isolated and the yellow

coloured methanol solutions were used directly for the

synthesis of cobalt(^III) complexes. On the other hand, the

We have repeated the reaction under N₂atmosphere, but no

complex could be isolated. The formation of both complexes is

shown in Scheme 2.

Description of crystal structures

[Co(L¹)(PTZ)(N₃)] (1) and [Co(L²)(PTZ)(N₃)] (2). Both

complexes crystallize in the monoclinic space group P2₁/c. The

structures consist of discrete mononuclear units in each of

which cobalt(^III) exhibits similar coordination environment.

The perspective views of complexes 1 and 2 together with

Table 3 Selected bond angles (^ꢃ) of complexes 1 and 2

1

2

O(1)–Co(1)–N(1)

O(1)–Co(1)–N(1Z)

O(1)–Co(1)–N(2)

O(1)–Co(1)–N(3)

O(1)–Co(1)–N(7)

N(1)–Co(1)–N(1Z)

N(1)–Co(1)–N(2)

N(1)–Co(1)–N(3)

N(1)–Co(1)–N(7)

N(1Z)–Co(1)–N(2)

N(1Z)–Co(1)–N(3)

N(1Z)–Co(1)–N(7)

N(2)–Co(1)–N(3)

N(2)–Co(1)–N(7)

N(3)–Co(1)–N(7)

86.56(12)

93.19(12)

92.00(12)

168.01(12)

87.57(12)

173.85(14)

85.18(14)

93.94(13)

97.44(13)

88.69(13)

87.58(13)

88.69(13)

99.98(13)

177.31(14)

80.48(13)

90.60(6)

89.33(6)

91.15(6)

168.59(6)

87.67(6)

179.27(7)

88.19(7)

92.72(6)

96.19(6)

91.08(7)

87.48(6)

84.53(6)

99.85(7)

175.47(7)

81.12(6)

Fig. 2 ORTEP presentation of complex 2 (ellipsoids are drawn at the

40% probability level) with selected atom-numbering scheme.

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Fig. 3 MEP surfaces of complexes 1 (a) and 2 (b) with indication of the energetic values in selected point of the surface (isosurface at 0.002 a.u.).

selected atom-numbering schemes are shown in Fig. 1 and 2 a terminal azide in the axial positions. It is to be noticed here

respectively. In each complex, cobalt(^III) is in a distorted octa- that in each case, the Schiﬀ base is occupying one facial posi-

hedral environment being coordinated by the phenoxo oxygen tion. Thus the important point may be the bending of the Schiﬀ

atom, O(1), the amine nitrogen atom, N(1), and the imine base. In the equatorial plane, pyridyltetrazolate and Schiﬀ base

nitrogen atom, N(2), from the deprotonated Schiﬀ base ligand moieties are not co-planar, but they form dihedral angles of

{(L¹)^ꢁfor complex 1 and (L²)^ꢁfor complex 2} and two additional 32.65⁰(in 1) and 43.19⁰(in 2). Azide moieties are diﬀerently

nitrogen atoms, N(3) and N(7), from 2-pyridyltetrazolate, (PTZ)^ꢁoriented in the coordination sphere of the two complexes that

in the equatorial plane and by the amine nitrogen atom, N(1) of lead to diﬀerent packing patterns in their solid state structures.

the tridentate Schiﬀ base and another nitrogen atom, N(1Z) of The bond lengths and bond angles of the complexes (given in

Fig. 4 (a) Crystal packing of 1 (hydrogen atoms omitted); (b and c) theoretical models used to evaluate the noncovalent interactions (distances in

A˚); (d) distribution of bond and ring (red and yellow spheres) critical points in one dimer of complex 1.

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Fig. 5 (a) Crystal packing of 2 (hydrogen atoms omitted); (b and c) theoretical models used to evaluate the noncovalent interactions (distances in

A˚); (d and e) distribution (partial views) of bond, ring and cage (red, yellow and green spheres) critical points in two dimers of complex 2.

Fig. 6 Hirshfeld surfaces mapped with d_norm(left-side), shape index (middle) and curvedness (right-side).

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Fig. 7 Fingerprint plots of 1 (left-side) and 2 (right-side): full and resolved into H/H, C/H/H/C, N/H/H/N contacts showing the percentages

of contacts contributed to the total Hirshfeld surface area of both complexes. Surfaces in the right hand columns highlight the relevant surface

patches associated with the speciﬁc contacts in the total Hirshfeld surface area of complexes 1 and 2.

Table

4 The details data of the photoluminescence and time-

from the bond angles, which deviate from the ideal values of 90^ꢃ

(for the cis angles) or 180^ꢃ(for the trans angles). The Co(III)–

resolved photoluminescence decays of complexes 1 and 2

Absorption

(nm)

Emission

(nm)

Time

(ns)

N_iminedistances are shorter than the Co(III)–N_amineones, due to

Complexes

c²

the diﬀerent hybridization of nitrogen atoms. This is a common

phenomenon observed in many other cobalt(^III) Schiﬀ base

complexes.³⁶The saturated six member chelate rings, Co(1)–

N(1)–C(2)–C(3)–C(4)–N(2) (for complex 1) and Co(1)–N(1)–C(3)–

C(4)–C(5)–N(2) (for complex 2) are present in chair conforma-

1

2

240

350

380

7.24

7.91

1.042081

1.067222

tions with puckering parameters^37aq ¼ 0.674(3) A, q ¼ 13.3(3), f

˚

Tables 2 and 3, respectively) are comparable with previously

reported octahedral cobalt(^III) Schiﬀ base complexes.^20c,34The

distortion of the octahedral geometry can be easily observed

ꢃ

˚

¼ 352.2(15) (for complex 1) and q ¼ 0.6724(18) A, q ¼ 12.55(17),

f ¼ 4.8(8)^ꢃ(for complex 2).

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directionality of the interaction (hydrogen bond) indicates that

the hydrogen atom is pointing to the p instead of the s-elec-

trons of the pseudohalide. The hydrogen bonded dimer pres-

ents stronger interaction energy in agreement to the MEP

surface, since the interaction of N–H and tetrazole is very

favored electrostatically. The C–H/p interaction described in

˚

Fig. 4c (2.91 A to one C atom of the ring) is similar to that

previously highlighted by N. Nishio in the crystal structure of

37b

˚

levopimaric acid (2.94 A to one carbon atom) and also in

phenyl-substituted tetrahydroisoquinoline derivatives (2.86

37c

˚

A). Similar C–H/p interactions have also been commonly

described in supramolecular assemblies of several complexes,

reported in previous journals.^37d,eThe Bader's theory of atoms-

in-molecules was used to further conrm the existence of the

CH/p interactions. 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 the dimer of complex 1 are shown in Fig. 4d. It

can be observed that the conventional C–H/p(phe) interaction

is characterized by the presence of two bond CPs (red spheres)

and bond paths connecting two hydrogen atoms to the phenyl

ring. Moreover, the unconventional C–H/p(azide) interaction

is characterized by the presence of a bond CP and bond path

connecting the hydrogen atom to a nitrogen atom of the ligand,

thus conrming the existence of the interaction.

A fragment of the crystal packing of complex 2 is shown in

Fig. 5a, where the formation of 2D layers is highlighted.

Complex 2 forms self-assembled dimers governed by hydrogen

bonding and p–p stacking interactions (see black and red

dashed lines, respectively, Fig. 5b). This self-assembled dimer

interacts with the adjacent one by means of C–H/p interac-

tions (see Fig. 5d) involving the p-systems of phenyl and azide

moieties, as previously observed in complex 1. The interaction

energies of both assemblies were evaluated using the models

shown in Fig. 5b and d. It can be observed that the self-

assembled hydrogen bonding dimer is energetically very favor-

able (DE₃¼ ꢁ17.5 kcal mol^ꢁ1) due to the formation of several

hydrogen bonds. The interaction energy of the other dimer

Fig. 8 Cyclic voltammogram of complex 1 in DMF medium. Inset

shows the voltammogram in between ꢁ2 to 0 V.

Theoretical study of noncovalent interactions

We have focused our attention to the study of relevant hydrogen

bonding and C–H/p interactions observed in the solid state

architecture of both complexes. At rst, the MEP surfaces of

both complexes were computed to investigate the most positive

and negative regions in order to rationalize the interactions

observed in their crystal packing. The MEP surfaces are given in

Fig. 3 and it can be observed that the most negative region is

located at the nitrogen atoms of the tetrazole ring in both

complexes (ꢁ60 kcal mol^ꢁ1) and the most positive one at the

NH group in complex 1 (+50 kcal mol^ꢁ1) and at the hydrogen

atoms of the coordinated N(CH₃)₂group in 2 (+29 kcal mol^ꢁ1).

The nitrogen atoms of the azide are also present in strongly

negative MEP values. Therefore interactions involving the NH/

N(CH₃)₂groups as hydrogen bond donors and tetrazole/azide as

acceptors are electrostatically favored.

A fragment of the crystal packing of complex 1 is shown in

Fig. 4a, where the formation of 2D layer is highlighted. In one

direction the chain is governed by hydrogen bonding interac-

tions (Fig. 4c) and in the perpendicular direction the molecules

interact by means of C–H/p interactions (Fig. 4b). The inter-

action energies of both assemblies were evaluated using the

models shown in Fig. 4c. It can be easily observed that the

hydrogen bonding dimer is energetically more favorable (DE₂¼

governed by C–H/p interactions is more modest (DE₄

¼

ꢁ7.7 kcal mol^ꢁ1). In complex 2 the conventional aromatic ring

involved in the C–H/p(phe) interaction belongs to the PTZ

ligand instead to the Schiﬀ-base ligand. In addition, two H-

atoms of the N(CH₃)₂group interact with p-system of the

˚

azide (2.8 A). The distributions of critical points and bond paths

for the dimers of 2 are shown in Fig. 5c and e. In the self-

assembled dimer, it can be observed that each hydrogen

bonding interaction is characterized by the presence of one

bond CPs (red spheres) and bond path that connects the

hydrogen atom to the nitrogen atom of the tetrazole ring

ꢁ14.1 kcal mol^ꢁ1) than the dimer (DE₁¼ ꢁ4.7 kcal mol^ꢁ1

)

governed by CH/p interactions. In the latter, two diﬀerent p-

˚

systems are involved, the conventional aromatic ring (at 2.82 A

to the ring centroid) and the p-system of the azide, since the

Table 5 Cyclic voltammetry data (V) for both complexes in DMF medium (scan rate 25 mV s^ꢁ1

)

E_1/2

Complexes

E_III/II

E_II/III

DE_III4II

E_II/I

E_I/II

DE_II4I

E_{1/2 II4I}

III4II

1

2

ꢁ0.70

ꢁ0.62

ꢁ0.38

ꢁ0.30

0.32

ꢁ0.54

ꢁ0.46

ꢁ1.80

ꢁ1.81

ꢁ1.84

ꢁ1.44

0.04

0.37

ꢁ1.82

ꢁ1.63

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(Fig. 5c). The interaction is further characterized by the pres-

ence of a ring CP (yellow sphere) due to the formation of

a supramolecular ring. Moreover, the p/p interaction is

characterized by the presence of a bond CP and bond path

interconnecting two nitrogen atoms of the tetrazole rings, thus

conrming the existence of the interaction. Finally, in Fig. 5e it

is shown the distribution of CPs for the C–H/p assembly. It

can be observed that the conventional C–H/p(phe) interaction

is characterized by the presence of two bond CPs (red spheres)

and bond paths connecting two hydrogen atoms of the methyl

groups to the phenyl ring and tetrazole rings. Moreover, the

unconventional C–H/p(azide) interaction is characterized by

the presence of two bond CPs and bond paths connecting two

hydrogen atoms of the N(CH₃)₂group to two N-atoms of the

pseudohalide.

Hirshfeld surface analysis

Fig. 9 Time resolved UV-Vis spectral proﬁles indicating the increment

of 3,5-DTBQ peak at ꢀ400 nm upon addition of 10^ꢁ2M 3,5-DTBC to

the 10^ꢁ4M of complex 1 in acetonitrile–methanol (2 : 1) mixture at

room temperature.

The Hirshfeld surfaces of the two complexes, mapped over

d_norm(range of ꢁ0.1 to 1.5 A), shape index and curvedness, are

˚

illustrated in Fig. 6. The dominant interaction between N/H/

H/N atoms can be seen in the Hirshfeld surfaces as red spots

on the d_normsurface in Fig. 6. Other visible spots in the

Hirshfeld surfaces correspond to mainly C/H/H/C and H/H

contacts. Additionally, the 2D ngerprint plots (Fig. 7) illustrate

the diﬀerence between the intermolecular interaction patterns

and the relative contributions (in percentage) for the major

intermolecular interactions associated with the complex. In the

2D ngerprint plot (Fig. 7) intermolecular interactions appear

as distinct spikes. The ngerprint plots can also be decomposed

to emphasize selected atoms pair close contacts. This decom-

position enables separation of contributions from diﬀerent

interaction types, which overlap in the full ngerprint. Relative

contributions to the Hirshfeld surface area for the various

intermolecular contacts of both complexes are shown in Fig. S1

(ESI†).

in the IR spectra of both complexes.⁴⁰The bands at 1446,

1472 cm^ꢁ1(for 1) and 1444, 1469 cm^ꢁ1(for 2) are due to the

tetrazolate moiety and also observed in other tetrazolate-based

metal complexes in previous reports.⁴¹IR spectra of complexes 1

and 2 are given in Fig. S4 and S5 respectively (ESI†).

The electronic spectra (200–900 nm) of the complexes are

similar to each other in acetonitrile–methanol (2 : 1) mixture at

room temperature. Usually low-spin octahedral cobalt(^III)

complexes show two broad absorption bands at low energy

1

region due to spin allowed A_1g/ T_1gand A_1g/ T_2gtran-

sitions.⁴²In the present case, complexes 1 and 2 show broad

X-ray diﬀraction of powdered sample

The X-ray diﬀraction patterns of the powdered samples are in

excellent agreement with those simulated from single crystal X-

ray diﬀraction, conrming the purity of the bulk samples. The

simulated patterns of the complexes were calculated from the

single crystal structural data using the CCDC Mercury soware.

Experimental and simulated powder XRD patterns of complexes

1 and 2 are given in Fig. S2 and S3 respectively (ESI†).

Spectral and magnetic properties

The IR spectrum of complex 1 exhibits a moderately strong

band at 3182 cm^ꢁ1, which may be ascribed to the N–H

stretching vibration. No such band is observed in case of

complex 2, because of the absence of N–H bond in it. The bands

in the range of 3000–2900 cm^ꢁ1due to alkyl C–H stretching

vibrations are routinely noticed in IR spectra of both

complexes.³⁸Sharp bands at 2021 and 2015 cm^ꢁ1indicate the

presence of monodentate azide coligand in the IR spectra of

complexes 1 and 2, respectively.³⁹The distinct bands at

Fig. 10 Time resolved UV-Vis spectral proﬁles indicating the incre-

ment of o-aminophenoxazine-3-one peak at ꢀ433 nm upon addition

of 10^ꢁ2M o-aminophenol to the 10^ꢁ4M of complex 1 in acetonitrile–

ꢀ1625 cm^ꢁ1due to the azomethine (C]N) groups are noticed methanol (2 : 1) mixture at room temperature.

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Fig. 11 Michaelis–Menten plot (a), Lineweaver–Burk plot (b), Hanes plot (c) and Eadie–Hofstee plot (d) of complex 1 for catalytic oxidation of

3,5-DTBC in acetonitrile–methanol (2 : 1) mixture at room temperature.

absorption bands at 670 nm and 710 nm, respectively, attrib-

utable to one of the two expected transitions for any low-spin

cobalt(^III) in octahedral geometry, as mentioned above.⁴³The

intense absorption bands of the complexes, at around 350 nm

may be assigned as charge transfer transitions from the coor-

dinated ligands to the cobalt(^III) centers (LMCT).^44aHigh energy

absorption bands around 240 nm in both complexes may be

assigned to intra ligand p–p* transition.^44bElectronic spectra of

1 and 2 are given in Fig. S6 and S7 respectively (ESI†).

Both complexes show strong photoluminescence upon the

irradiation of ultraviolet light. Upon excitation at around

240 nm, complex 1 emits at 350 nm whereas complex 2 emits at

380 nm. The excited state mean lifetimes of complexes 1 and 2

are 7.24 ns and 7.91 ns, respectively (Table 4) Photo-

luminescence spectra and time dependent photoluminescence

decay prole of both complexes is shown in Fig. S8–S10 (ESI†).

Room temperature magnetic susceptibility measurements

show that both complexes are diamagnetic as expected for low-

spin cobalt(^III) complexes.^45a

Electrochemical studies

By scanning in the negative direction initiated at 0.00 V, two

reduction peaks are observed. The starting reduction peaks

corresponding to Co(^III) / Co(II) reduction processes are

observed at about potential ꢁ0.70 and ꢁ0.62 V for complexes 1

and 2 respectively. Similarly the subsequent reduction peaks

of complexes 1 and 2 are observed at ꢁ1.80 and ꢁ1.81 V

respectively, which indicate Co(^II) / Co(I) transformation. The

corresponding oxidation peaks are observed during the

reverse scan process. The oxidation of Co(^I) / Co(II) is sug-

gested by the presence of the peaks at ꢁ1.84 and ꢁ1.44 V for

complexes 1 and 2 respectively. Co(^II) / Co(III) oxidation

processes are observed at ꢁ0.38 and ꢁ0.30 V for complexes 1

and 2 respectively. The cyclic voltammogram of complex 1 is

shown in Fig. 8. The quasi-reversible redox reaction may be

rationalized by the expected structural changes by elongation

of axial bond lengths or losing of axial ligands because of the

addition of one electron to d_zorbital and vice versa.^45b

Repeated scans lead to nearly superposable cyclic voltammo-

grams, which suggest all three oxidation states of cobalt are

2

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Fig. 12 Michaelis–Menten plot (a), Lineweaver–Burk plot (b), Hanes plot (c) and Eadie–Hofstee plot (d) of complex 1 for catalytic oxidation of

OAPH in acetonitrile–methanol (2 : 1) mixture at room temperature.

markedly stable. The reduction peak potentials are strongly

depend on donor strength of the coordinate ligands. Presence

good electron withdrawing groups such as 5-(2-pyridyl)tetra-

zole and azide causes more electron aﬃnity on cobalt center

and so a more negative cathodic peak than cobalt Schiﬀ base

complexes.^45cThe results of cyclic voltammetry also closely

resemble that of the similar reported complexes, which serve

as further evidences for similar structural and electronic

properties.^45b–dThe detailed cyclic voltammetry data (V) for

both complexes are given in Table 5.

Catechol oxidase mimicking activity

The catechol oxidase mimicking activity of both complexes was

investigated with model substrate 3,5-DTBC. Among the diﬀerent

catechols used in catechol oxidase model studies, 3,5-DTBC is the

most widely used substrate because of its low redox potential for

the quinone–catechol couple, which makes it easy to be oxidized

to the corresponding quinone (3,5-DTBQ), and its bulky substit-

uents help to stop further oxidation reactions, such as ring

opening etc. The product (3,5-DTBQ) is signicantly stable and it

exhibits a strong absorption around 400 nm. So, catechol oxidase

mimicking activity and the respective reaction kinetics can be

easily followed by UV-visible spectroscopy by following the

appearance of the characteristic absorption of the 3,5-DTBQ. The

band intensity around 400 nm is gradually increased as a func-

tion of time, suggesting cobalt(^III) tetrazolato complexes are

capable of exhibiting prominent bio-mimetic catalytic activity

related to catechol oxidase. Time resolved UV-Vis spectral proles

indicating the increment of 3,5-DTBQ characteristic peak of

complex 1 is shown in Fig. 9. It was found that in the absence of

catalyst, no catalytic oxidation of the substrate occurs.

Catalytic activity and kinetic study

The catalytic experiments were conducted in aerobic condition

at room temperature with model substrates 3,5-di-tert-butylca-

techol (3,5-DTBC) for catechol oxidase like activity and OAPH (o-

aminophenol) for phenoxazinone synthase like activity. Whole

catalytic activity was performed in acetonitrile–methanol (2 : 1)

mixture because of very good solubility of the complexes,

substrates and their products. No additional base was added in

the reaction medium.

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Scheme 3 Proposed mechanistic pathway for the aerial oxidation of 3,5-DTBC catalyzed by complexes 1 and 2.

oxidative condensation of o-aminophenol catalyzed by the

complexes was investigated by monitoring the increase of the

absorption peak around 433 nm, characteristic of the phenox-

azinone chromophore. The spectral scan for both complexes

reveal the progressive increase of peak intensity at ca. ꢀ433 nm

suggesting catalytic oxidation of o-aminophenol in aerobic

condition. The time dependent spectral change for the period of

2 h aer the addition of o-aminophenol to the acetonitrile–

Phenoxazinone synthase mimicking activity

It is generally agreed phenoxazinone synthase catalyzes the

penultimate step in the biosynthesis of the antibiotic actino-

mycin D by Streptomyces antibioticus, where oxidative conden-

sation of o-aminophenol substituents occurs. Therefore, o-

aminophenol is used as model substrate for investigating phe-

noxazinone synthase mimicking activity of both complexes. The

Scheme 4 Proposed mechanistic pathway for the aerial oxidation of o-aminophenol catalyzed by complexes 1 or 2.

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Table 8 A comparison of catechol oxidase mimicking activity of previously reported cobalt based complexes^a

Complexes

Solvent

V_max(M s^ꢁ1

)

K_M(M)

k_cat(h^ꢁ1

)

Ref.

[Co^III(HL³)₂](OAc)$H₂O

CH₃OH

CH₃CN

DCM

CH₃CN

CH₃OH

CH₃CN : DMF

CH₃CN : CH₃OH

(3.36 ꢄ 0.339) ꢂ 10^ꢁ5

(5.99 ꢄ 0.198) ꢂ 10^ꢁ5

(4.06 ꢄ 0.571) ꢂ 10^ꢁ5

1.02 ꢂ 10^ꢁ7

(7.38 ꢄ 0.597) ꢂ 10^ꢁ4

(4.90 ꢄ 0.597) ꢂ 10^ꢁ4

(1.25 ꢄ 0.229) ꢂ 10^ꢁ3

5.20 ꢂ 10^ꢁ3

1210

2160

1460

14.7

26.4

379

741

270

222

150

47a

[Co^II₃(L⁴)(OAc)₂(CH₃OH)₂]$2CHCl₃

[Co^II₃(L⁴)(OAc)₂(H₂O)₂]

47b

47c

47d

1.83 ꢂ 10^ꢁ7

7.09 ꢂ 10^ꢁ3

[Co^II₃L⁵₂(m-L⁵)₂(m-OH₂)₂(CF₃CO₂)₂]

[Co^II₇(m-L⁵)₆(m-OMe)₆]Cl₂

[Co^II₂L⁶]$3H₂O

(10.54 ꢄ 0.742) ꢂ 10^ꢁ7

(20.59 ꢄ 0.988) ꢂ 10^ꢁ7

4.50 ꢂ 10⁴

(24.55 ꢄ 0.072) ꢂ 10^ꢁ5

(43.23 ꢄ 0.098) ꢂ 10^ꢁ5

9.76 ꢂ 10²

[Co^II₂L⁷]$4H₂O

3.70 ꢂ 10⁴

8.57 ꢂ 10²

[Co^II₂L⁸]$5H₂O

2.50 ꢂ 10⁴

5.47 ꢂ 10²

[(Co^III₂(H₂L⁹)₂(OAc)₂)]$CH₃OH

[Co^II₃Co^III₃(HL¹⁰)₂(H₂L¹⁰)₂(OAc)₂]

$9CH₃OH$H₂O

(1.33 ꢄ 0.136) ꢂ 10^ꢁ7

(8.70 ꢄ 1.470) ꢂ 10^ꢁ3

79.75

72.2

47e

47f

1.20 ꢂ 10^ꢁ5

5.60 ꢂ 10^ꢁ3

Co^II(OAc)₂$4H₂O

CH₃CN : CH₃OH

CH₃OH Tris–HCL

buﬀer

9.30 ꢂ 10^ꢁ8

1.00 ꢂ 10^ꢁ2

32

0.9

1.14

7.02

47g

47h

[Co^II₂(L¹¹)Cl₂](ClO₄)₂$5H₂O {at pH 7.3}

[Co^II₂(L¹¹)Cl₂](ClO₄)₂$5H₂O {at pH 7.6}

[Co^II₂(L¹¹)Cl₂](ClO₄)₂$5H₂O {at pH 8.0}

[Co^III(phen)₂(Cl)₂]⁺

2.50 ꢂ 10^ꢁ8

2.47 ꢂ 10^ꢁ3

3.16 ꢂ 10^ꢁ8

2.51 ꢂ 10^ꢁ3

1.95 ꢂ 10^ꢁ7

2.77 ꢂ 10^ꢁ3

CH₃OH

CH₃CN

CH₃OH

DMF

CH₃OH

DMF

CH₃OH

CH₃CN

CH₃OH

CH₃CN

DMF

2.68 ꢂ 10^ꢁ5

1.77 ꢂ 10^ꢁ3

965

47i

47j

47k

[Co^IIICo^IIL¹²(N₃)₃]$0.5CH₃CN$0.27H2O

(7.93 ꢄ 0.631) ꢂ 10^ꢁ7

(1.18 ꢄ 0.214) ꢂ 10^ꢁ3

114.24

21.408

29.700

24.353

20.054

45.38

482.16

447

45.9

42.9

212.6

188.0

191.3

142

85

99

10.0

11.2

5020

122.83

466.74

113.00

113.83

[Co^IIICo^II(HL¹³)₂(H₂O)

5.946 ꢂ 10^ꢁ4

8.815 ꢂ 10^ꢁ3

(HOCH₂CH₃)]Cl$2H₂O

8.25 ꢂ 10^ꢁ4

2.014 ꢂ 10^ꢁ4

[Co^IIICo^II₂(H₂L¹⁴)₂(L²)Cl₂]$3H₂O

6.764 ꢂ 10^ꢁ4

8.972 ꢂ 10^ꢁ3

5.57 ꢂ 10^ꢁ5

12.00 ꢂ 10^ꢁ4

[Co^IIICo^IIL¹⁵(N₃)₃]$CH₃CN

(3.152 ꢄ 0.695) ꢂ 10^ꢁ7

(3.348 ꢄ 0.858) ꢂ 10^ꢁ6

1.24 ꢂ 10^ꢁ4

(1.576 ꢄ 0.702) ꢂ 10^ꢁ3

(3.011 ꢄ 1.227) ꢂ 10^ꢁ3

2.45 ꢂ 10^ꢁ3

47l

[Co^II₂(L¹⁶H)(H₂O)₂(OAc)₂](OAc)₂

[Co^II₂(L¹⁷)(H₂O)₂(OAc)₂](OAc)

[Co^II₂(L¹⁸)(H₂O)₂(OAc)₂](OAc)

[Co^IIICo^IIIL¹⁹(N₃)₄]$6H₂O

[Co^IIICo^IIIL²⁰(N₃)₄]$3.5H₂O

[Co^IIICo^IIL²¹(N₃)₃]$H₂O

47m

1.28 ꢂ 10^ꢁ5

1.78 ꢂ 10^ꢁ3

1.19 ꢂ 10^ꢁ5

2.39 ꢂ 10^ꢁ3

(1.477 ꢄ 0.259) ꢂ 10^ꢁ6

(1.306 ꢄ 0.268) ꢂ 10^ꢁ6

(1.328 ꢄ 0.329) ꢂ 10^ꢁ6

(1.967 ꢄ 0.113) ꢂ 10^ꢁ6

(1.195 ꢄ 0.010) ꢂ 10^ꢁ6

(1.382 ꢄ 0.065) ꢂ 10^ꢁ6

(6.967 ꢄ 0.858) ꢂ 10^ꢁ8

(7.80 ꢄ 0.592) ꢂ 10^ꢁ8

(1.45 ꢄ 1.24) ꢂ 10^ꢁ4

3.412 ꢂ 10^ꢁ6

(1.678 ꢄ 0.578) ꢂ 10^ꢁ3

(3.300 ꢄ 1.045) ꢂ 10^ꢁ3

(4.523 ꢄ 1.578) ꢂ 10^ꢁ3

(1.89 ꢄ 0.059) ꢂ 10^ꢁ3

(1.44 ꢄ 0.008) ꢂ 10^ꢁ3

(1.65 ꢄ 0.048) ꢂ 10^ꢁ3

(1.26 ꢄ 0.328) ꢂ 10^ꢁ3

(1.24 ꢄ 0.208) ꢂ 10^ꢁ3

(1.90 ꢄ 0.880) ꢂ 10^ꢁ3

2.553 ꢂ 10^ꢁ4

47n

47o

47p

cis-[Co₃L²₂²(MeOH)₂(N₃)₂(m_1,1-N₃)₂]

trans-[Co₃L²₂²(H₂O)₂(N₃)₂(m_1,1-N₃)₂]$(H₂O)₂

[Co₃L²₂³(N₃)₃(m_1,3-N₃)]

[Co^IIIL²⁴(N₃)₂(H₃O⁺)]$2MeOH

[Co^IIIL²⁴(NCS)(H₂O)]$DMF$H₂O

[Co^III(L²⁵)₂](ClO₄)₃

CH₃OH

CH₃CN

CH₃CN : CH₃OH

47q

47r

[Co^III(L²⁶)(L²⁷)(N₃)]

[Co^III(L²⁸)(L²⁹)(NCS)]

12.965 ꢂ 10^ꢁ6

6.834 ꢂ 10^ꢁ4

[Co^III(L¹)(PTZ)(N₃)]

(3.139 ꢄ 0.453) ꢂ 10^ꢁ6

(1.198 ꢄ 0.089) ꢂ 10^ꢁ6

This work

[Co^III(L²)(PTZ)(N₃)]

(3.162 ꢄ 0.415) ꢂ 10^ꢁ6

(1.047 ꢄ 0.623) ꢂ 10^ꢁ6

a

Where, H₂L³¼ N-(2-hydroxyethyl)-3-methoxysalicylaldimine; H₄L⁴¼ condensation product of 2,3-dihydroxynaphthalene-1,4-dicarbaldehyde and

2-[O-(1-ethyloxyamide)]oxime-4,6-dibromophenol; HL⁵¼ 2-{(3-ethoxypropylimino)methyl}-6-methoxyphenol; H₂L⁶¼ 1 : 2 condensation product of

1,2,4,5-tetra-amino benzene and 2-hydroxy benzaldehyde; H₂L⁷¼ 1 : 2 condensation product of 1,2,4,5-tetra-amino benzene and 2,4-dihydroxy

benzaldehyde; H₂L⁸¼ 1 : 2 condensation product of 1,2,4,5-tetra-amino benzene and 2-hydroxy naphthaldehyde; H₄L⁹¼ 3,5-di-tert-butyl-2-

hydroxybenzylideneamino)-2-(hydroxymethyl)propane-1,3-diol; H₄L¹⁰

¼

2-(3,5-di-tert-butyl-2-hydroxybenzylideneamino)-2-(hydroxymethyl)

propane-1,3-diol; L¹¹¼ N,N,N⁰,N⁰-tetrakis(2⁰-benzimidazolylmethyl)-1,4-diethylene amino glycol ether; phen ¼ 1,10-phenanthroline; H₂L¹²¼ [2 +

2] condensation product of 2,6-diformyl-4-methylphenol and 2,2-dimethyl-1,3-diaminopropane; H₃L¹³¼ 3-[(2-hydroxy-benzylidene)-amino]-

propane-1,2-diol; H₃L¹⁴

¼

3-[(2-hydroxy-3-methoxy-benzylidene)-amino]-propane-1,2-diol; H₂L¹⁵

¼

[2 + 2] condensation of 4-ethyl-2,6-

diformylphenol and 2,2⁰-dimethyl-1,3-diaminopropane; HL¹⁶¼ 2,6-bis(N-ethylpiperazine-iminomethyl)-4-methyl-phenolato; HL¹⁷¼ 2,6-bis(2-

ethylpyridine-iminomethyl)-4-methyl-phenolato; HL¹⁸

¼

2,6-bis(N-ethylpiperidine-iminomethyl)-4-methyl-phenolato; H₂L²²

¼

N,N⁰-

bis(salicylidene)-1,3-propanediamine;

H₂L²³

¼

N,N⁰-bis(2-hydroxybenzyl)-1,3-propanediamine;

H₂L²⁴

¼

N,N⁰-ethylenebis(3-

ethoxysalicylaldiimine); L²⁵¼ condensation product of 1,3-propanediamine and 2-benzoylpyridine; HL²⁶¼ 2((2(piperidin-1-yl)ethylimino)

methyl)-6-ethoxyphenol; HL²⁷

pentanedione.

¼

1-acetyl-2-naphthol; HL²⁸

¼

2-((3(dimethylamino)propylimino)methyl)-6-methoxyphenol; HL²⁹

¼

2,4-

methanol (2 : 1) mixture of complex 1 is depicted in Fig. 10. It

should be noted at this point that a blank experiment without

catalyst (complex) does not show signicant growth of the band

at ꢀ433 nm, characteristic of phenoxazinone chromophore, in

an identical reaction condition.

Kinetic parameters and explanation of the turnover numbers

Michaelis–Menten model is an important tool to treat this type

of saturation rate dependency on the concentration of the

substrate. The Michaelis–Menten equation:

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Table 9 A comparison of phenoxazinone synthase mimicking activity of previously reported cobalt based complexes^a

Complexes

Solvent

V_max(M s^ꢁ1

)

K_M(M)

k_cat(h^ꢁ1

)

Ref.

47q

48a

48b

[Co^III(L²⁵)₂](ClO₄)₃

CH₃OH

CH₃CN

(1.27 ꢄ 0.915) ꢂ 10^ꢁ4

(1.42 ꢄ 0.985) ꢂ 10^ꢁ4

(2.13 ꢄ 0.412) ꢂ 10^ꢁ6

(3.84 ꢄ 0.847) ꢂ 10^ꢁ3

(6.04 ꢄ 1.04) ꢂ 10^ꢁ4

(9.66 ꢄ 0.198) ꢂ 10^ꢁ3

4590

5120

153.60

[Co^III₂Co^IIL²₂³(m₂-C₆H₅CO₂

(C₆H₅CO₂^ꢁ)₂]$(CH₃CN)₂

)

ꢁ

2

[Co^III(L³⁰)(N₃)₂]$0.5CH₃CN

[Co^III(L³⁰)(NCS)₂]$0.5H₂O

CH₃OH

CH₃CN

3.00 ꢂ 10^ꢁ7

1.35 ꢂ 10^ꢁ2

54.0

48.6

26.1

8.37

2.70 ꢂ 10^ꢁ7

1.24 ꢂ 10^ꢁ2

[Co(HL³⁰)₂][Co(NCS)₄]$NCS

[Co(L³⁰)₂]₂[Co(NCO)₄]

4.65 ꢂ 10^ꢁ8

8.87 ꢂ 10^ꢁ3

1.45 ꢂ 10^ꢁ7

1.02 ꢂ 10^ꢁ2

[Co^III(L³¹)₂(L³²)₂]-Cl$8H₂O

[Co^III(HL³³)₂](OAc)$H₂O

1.70 ꢂ 10^ꢁ7

6.08 ꢂ 10^ꢁ3

30.6

48c

48d

48e

(7.87 ꢄ 0.541) ꢂ 10^ꢁ4

3.19 ꢂ 10^ꢁ8

(4.31 ꢄ 0.775) ꢂ 10^ꢁ4

6.785 ꢂ 10^ꢁ4

28 300

11.48

27.90

13.752

20.37

33.26

30.09

23.04

3.36

6.37

8.28

13.68

7.38

4.10

247.2

257.4

77.52

72.12

166.64

626.40

355.28

351.68

[Co^IIIL³⁴(L³⁵)2]ClO₄$MeOH$H₂O

[Co^IIIL³⁴(L³⁶)₂Na(ClO₄)₂]$0.5H₂O

[Co^III₂(L³⁷)₂(m-L³⁸)₂Cl₂]Cl₂$2H₂O

[Co^III(L³⁹)(N₃)₃]

7.75 ꢂ 10^ꢁ8

2.356 ꢂ 10^ꢁ3

1.91 ꢂ 10^ꢁ7

1.57 ꢂ 10^ꢁ3

9f

46b

(5.66 ꢄ 0.32) ꢂ 10^ꢁ8

(9.24 ꢄ 0.52) ꢂ 10^ꢁ8

(8.60 ꢄ 0.09) ꢂ 10^ꢁ8

(6.40 ꢄ 0.08) ꢂ 10^ꢁ8

(1.87 ꢄ 0.06) ꢂ 10^ꢁ8

(3.54 ꢄ 0.06) ꢂ 10^ꢁ8

(4.60 ꢄ 0.08) ꢂ 10^ꢁ8

(3.80 ꢄ 0.31) ꢂ 10^ꢁ7

(2.05 ꢄ 0.22) ꢂ 10^ꢁ7

(1.14 ꢄ 0.05) ꢂ 10^ꢁ7

6.73 ꢂ 10^ꢁ6

(7.12 ꢄ 0.72) ꢂ 10^ꢁ3

(8.58 ꢄ 0.96) ꢂ 10^ꢁ3

(1.01 ꢄ 0.15) ꢂ 10^ꢁ2

(1.47 ꢄ 0.16) ꢂ 10^ꢁ2

(1.01 ꢄ 0.14) ꢂ 10^ꢁ2

(1.28 ꢄ 0.15) ꢂ 10^ꢁ2

(1.32 ꢄ 0.17) ꢂ 10^ꢁ2

(2.0 ꢄ 0.30) ꢂ 10^ꢁ2

(1.9 ꢄ 0.30) ꢂ 10^ꢁ2

(1.6 ꢄ 0.90) ꢂ 10^ꢁ2

5.08 ꢂ 10^ꢁ4

[Co^III(L⁴⁰)(N₃)₃]

[Co^III₂(L⁴¹)₂(m-O₂)](ClO₄)₄$2CH₃CN

[Co^III₂(L⁴²)₂(m-O₂)](ClO₄)₄

[Co^II(L⁴³)(CH₃CN)](ClO₄)₂

[Co^II(L⁴⁴)(H₂O)](ClO₄)₂

[Co^II(L⁴⁵)(H₂O)](ClO₄)₂

[Co^II(L⁴⁶)Cl(H₂O)]Cl$H₂O

[Co^II(L⁴⁶)(NCS)₂]

48f

48g

[Co^II(L⁴⁷)Cl₂]

[Co^III(L⁴⁸)(L⁴⁹)(N₃)]

48h

[Co^III(L⁴⁸)(L⁴⁹)(NCS)]

[Co^III(L⁵⁰)(L⁵¹)(N₃)]

CH₃CN

CH₃CN : CH₃OH

7.15 ꢂ 10^ꢁ6

5.75 ꢂ 10^ꢁ4

2.153 ꢂ 10^ꢁ6

1.613 ꢂ 10^ꢁ5

45

[Co(L⁵²)(L⁴⁹)(N₃)]

2.003 ꢂ 10^ꢁ6

1.565 ꢂ 10^ꢁ5

[Co^III(L²⁶)(L²⁷)(N₃)]

4.629 ꢂ 10^ꢁ6

0.676 ꢂ 10^ꢁ4

47r

[Co^III(L²⁸)(L²⁹)(NCS)]

[Co^III(L¹)(PTZ)(N₃)]

17.400 ꢂ 10^ꢁ6

3.238 ꢂ 10^ꢁ4

(9.869 ꢄ 0.906) ꢂ 10^ꢁ6

(199.682 ꢄ 18.486) ꢂ 10^ꢁ4

This work

[Co^III(L²)(PTZ)(N₃)]

(9.769 ꢄ 1.248) ꢂ 10^ꢁ6

(101.684 ꢄ 5.708) ꢂ 10^ꢁ4

a

Where, HL³⁰¼ condensation product of N,N-dimethyldipropylenetriamine and o-vanillin; H₂L³¹¼ 3,5,6-tribromo-4-pyridiniumcatechol; L³²

¼

pyridine; H₂L³³¼ N-(2-hydroxyethyl)-3-methoxysalicylaldimine; H₂L³⁴¼ N,N⁰-bis(3-methoxysalicylidehydene)cyclohexane-1,2-diamine); L³⁵¼ 4-

aminopyridine; L³⁶¼ 1-methylimidazole; L³⁷¼ 2-aminomethylpyridine; L³⁸¼ 2-iminomethylpyridine anion; L³⁹¼ bis(2-pyridylmethyl)amine;

L⁴⁰¼ (2-pyridylmethyl)(2-pyridylethyl)amine; L⁴¹¼ 1 : 2 condensation product of 3,3⁰-bisaminopropylamine and 2-pyridinecarboxaldehyde; L⁴²

¼ 1 : 2 condensation product of 3,3⁰-bisaminopropylamine and 2-acetylpyridine; L⁴³¼ 1 : 2 condensation product of diethylenetriamine and 2-

pyridinecarboxaldehyde; L⁴⁴¼ 1 : 2 condensation product of 3,3⁰-bisaminopropylamine and 6-methyl-2-pyridinecarboxaldehyde; L⁴⁵¼ 1 : 2

condensation product of 3,3⁰-diamino-N-methyldipropylamine and 6-methyl-2-pyridinecarboxaldehyde; L⁴⁶¼ N,N⁰-bis(pyridin-2-ylmethylene)-2,2-

dimethylpropane-1,3-diamine; L⁴⁷¼ N,N⁰-bis(6-methylpyridin-2-ylmethylene)-2,2-dimethylpropane-1,3-diamine; HL⁴⁸¼ 2-(3-(dimethylamino)

propyliminomethyl)-6-ethoxyphenol; HL⁴⁹¼ 1-benzoylacetone; HL⁵⁰¼ 2((2(2-hydroxyethylamino)ethylimino)methyl)-6-ethoxyphenol, HL⁵¹¼ 2-

acetyl-1-naphthol; HL⁵²¼ 1((2(diethylamino)ethylimino)methyl)naphthalen-2-ol.

V_max½Sꢅ

V

V ¼

(1)

V ¼ V_maxꢁ K_M

(4)

K_Mþ ½Sꢅ

½Sꢅ

where, V ¼ initial rate; [S] ¼ concentration of the substrates; K_M

¼ Michaelis–Menten constant for the metal complex and V_max

¼

All these equations are used to analyze a variety of kinetic

parameters, including turnover number (k_cat) and specicity

constant (k_cat/K_M) for catechol oxidase and phenoxazinone

synthase mimicking activity of synthesized complexes. Kinetic

parameters like V_maxand K_Mwere calculated by the analysis of

entire experimental data. The turnover number value (k_cat) is

obtained by dividing the V_maxby the concentration of the

catalyst (complex) used. Fig. 11 and 12 represent the Michaelis–

Menten plot, Lineweaver–Burk plot, Hanes plot and Eadie–

Hofstee plot of complex 1 for catalytic oxidation of 3,5-DTBC

and OAPH, respectively. Similarly, the Michaelis–Menten plot,

Lineweaver–Burk plot, Hanes plot and Eadie–Hofstee plot of

complex 2 for catalytic oxidation of 3,5-DTBC and OAPH are

maximum initial rate attained for a particular concentration of

the metal complex in the presence of a large excess of the

substrate.

On the other hand, rearrangement of Michaelis–Menten

equation produces Lineweaver–Burk equation (eqn (2)), Hanes

equation (eqn (3)) and Eadie–Hofstee equation (eqn (4)).

1

K_M

1

¼

þ

(2)

V

V_max½Sꢅ V_max

½Sꢅ

½Sꢅ K_M

¼

þ

V_maxV_max

(3)

V

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Fig. 13 ESI-MS positive spectrum of 1 : 50 mixture of complex 1 and 3,5-DTBC in acetonitrile–methanol (2 : 1) mixture at room temperature.

given in Fig. S11 and S12 (ESI†), respectively. Tables 6 and 7

The catalytic activity depends on the interaction between

contain all kinetic parameters of the complexes for catechol substrate and catalyst. Higher the interaction between substrate

oxidase and phenoxazinone synthase like activity, respectively. and catalyst higher the k_catvalues (Tables 6 and 7). Both

In order to calculate kinetic parameters more accurately, several complexes have comparable turnover numbers. Similar types of

enzyme kinetic plots have been used. More or less similar tentative catalytic cycles have also been proposed by several

kinetic parameters have been obtained in all cases and this other groups.⁴⁶

indicates the accuracy of the experimental results. The k_catvalue

A detailed literature survey with cobalt based model

suggest that both complexes are very eﬀective catalyst for the complexes for catechol oxidase and phenoxazinone synthase

conversation of 3,5-DTBC to 3,5-DTBQ and o-aminophenol to 2- mimicking activities has shown that several factors may aﬀect

aminophenoxazine-3-one.

their catalytic activity, such as the oxidation state of the metal,

coordination geometry around the metal center, metal–metal

distance, ligand exibility, exogenous bridging ligand etc.^47,48All

these cobalt based model complexes showing catechol oxidase

and phenoxazinone synthase mimicking activity are gathered in

Tables 8 and 9 respectively along with several kinetic parame-

ters such as K_M, V_maxand k_cat. As the turnover numbers (k_cat

values) of both complexes fall in between the range, they may be

considered as moderate catalysts.

Origin and mechanistic pathway of catalytic activity

Based on the above experimental results, it is clear that both

complexes are very reactive towards the catechol oxidase and

phenoxazinone synthase mimicking activity. Schemes 3 and 4

represent possible mechanism for catalytic conversation of 3,5-

DTBC to 3,5-DTBQ and o-aminophenol to 2-aminophenoxazine-

3-one, respectively. It is easily understandable that at initial step

of the catalytic cycles, the tetrazole moiety and/or monodentate

azide co-ligand were replaced by the substrate, thereby forming

Experimental and theoretical proof

^{a substrate–catalyst adduct. Hence it may be stated that the}behind proposed mechanistic

replacement of tetrazole moiety and/or monodentate azide co-

ligand initiated the catalytic cycles. This substrate–catalyst

adduct yields a substrate radical in the rate determining step.

pathways

Experimental proof

Finally, quinone chromophore was formed from this substrate

Electrospray ionization mass spectral analysis. The electro-

radical via a number of oxidative dehydrogenation processes.

spray ionization mass spectral analysis (ESI-MS positive) of

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Fig. 14 ESI-MS positive spectrum of 1 : 50 mixture of complex 1 and o-aminophenol in acetonitrile–methanol (2 : 1) mixture at room

temperature.

complex 1 in presence of substrate (3,5-DTBC for catechol of complex 1 in acetonitrile–methanol (2 : 1) mixture is given in

oxidase mimicking activity and o-aminophenol for phenox- S13 (ESI†). Peak around m/z ꢀ 477 indicates the formation of

azinone synthase mimicking activity) in acetonitrile–methanol [Co-L¹-N₃-OCH₃-2(CH₃CN)-K]⁺(loss of tetrazole moiety) which is

(2 : 1) mixture were recorded to get inside the catalytic cycles. the initial step of catalyses. The proposed mechanistic pathways

Complex 1 was taken as a model complex. ESI-MS positive (Schemes 3 and 4) are therefore justied by the mass spectral

spectra of a 1 : 50 mixture of the complex 1 with 3,5-DTBC and analysis.

o-aminophenol were recorded separately aer 5 min of mixing

Electron paramagnetic resonance spectral analysis. Electron

in acetonitrile–methanol (2 : 1) mixture and the results are paramagnetic resonance spectroscopy is a very helpful tool to

depicted in Fig. 13 and 14, respectively. The most attention- monitor the generation of radical intermediate during catalytic

grabbing observation from the mass spectral study is the cycles. As radical is formed as an intermediate species in our

appearance of peaks related to substrate–catalyst intermediate proposed mechanistic pathways, EPR measurements at room

species. For catechol oxidase and phenoxazinone synthase temperature have been performed on the mixture of the

mimicking activity of the complex 1, mass peaks around m/z ꢀ complex 1 with 3,5-DTBC and o-aminophenol separately.

501 indicate the substrate–catalyst intermediate species, [Co-L¹- Fig. 15(a) and (b) illustrate the EPR spectra of the mixture

(3,5-DTBC)-H]⁺and [Co-L¹-N₃-(OAPH)-CH₃OH-K]⁺, respectively. containing complex 1 and 3,5-DTBC/o-aminophenol, respec-

These peaks verify that the catalytic cycles proceed through tively in acetonitrile medium. Both the EPR spectra is domi-

a stable substrate–catalyst intermediate formation.

nated by an isotropic signal around g_isoꢀ 2.00 (for instance, g_iso

In presence of 3,5-DTBC, the mass spectrum exhibits a peak ¼ 1.974 in case of 3,5-DTBC and g_iso¼ 1.973 in case of o-ami-

at m/z ¼ 243.0899 corresponding to quinone sodium aggregate nophenol), with a peak-to-peak line width of ca. 20 G. The g

[3,5-DTBQ-Na]⁺, conrming the catechol oxidase mimicking value of the signal is very much closed to 2.0023 (value for a free

activity of complex 1. On the other hand, in presence of o- electron⁴⁹), a value that is characteristic for organic radicals,

aminophenol a peak appears at m/z ¼ 215.0353 which corre- such as a phenoxyl-type radical.⁵⁰Hence it can be concluded

sponds the formation of [phenoxazinone-H]⁺. This conrms that cobalt(^III) tetrazolato complexes are capable of oxidizing

phenoxazinone synthase mimicking activity of the complex. 3,5-DTBC and o-aminophenol through a radical pathway, as

Electrospray ionization mass spectral analysis (ESI-MS positive) shown in Schemes 3 and 4, respectively.

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Fig. 15 EPR spectra of acetonitrile solution of complex 1 (10^ꢁ4M) at 77 K immediately after addition of (a) 3,5-DTBC or (b) o-aminophenol.

Fig. 16 (a) DFT optimized geometry of the complex between the 3,5-DTBC substrate and cobalt(III) metal center. (b) Spin density plot of the

cobalt(II) complex (upon SET). (c) DFT optimized geometry of the complex between the OAPH substrate and cobalt(III) metal center. H-atoms

omitted for clarity. Distances in A˚.

shown in Scheme 4 (see Fig. 16c). The substrate is mono-

coordinated to cobalt, and the NH₂group is H-bonded to the

Theoretical proof

Catechol oxidase and phenoxazinone synthase mimicking

activities have been extensively analyzed previously by theoret-

ical studies.^{9g,46c,47o,51}Therefore, we have mainly focused in the

theoretical study to analyze the energetic features of the

supramolecular interactions and how they inuence the crystal

packing. However, in an eﬀort to give some theoretical support

to the mechanism and species proposed in the ESI-MS experi-

ments, we have computed both cobalt(^III) and cobalt(II) inter-

mediates proposed in Scheme 3 using DFT calculations (BP86-

D3/def2-TZVP). The fully optimized geometries and spin

density analysis of the cobalt(^II) complex have been given in

Fig. 16. The catechol is doubly coordinated to the cobalt(^III) with

similar Co/O distances. Upon the single electron transfer, the

spin density plot reveals that the unpaired electron is equally

distributed in both O-atoms and also the aromatic ring. The

spin density at the cobalt(^II) atom is 2.7 e, thus conrming the

cobalt(^II) oxidation state, with some spin density delocalized

into the ligand (to the atoms directly bonded to cobalt). Finally,

we have also optimized using DFT calculations the proposed

complex [Co-L¹-N₃-(OAPH)-CH₃OH] as the rst mechanistic step

˚

MeOH group (O/N distance 2.67 A).

Concluding remarks

Two new cobalt(III) tetrazolato complexes with Schiﬀ bases and

azide co-ligands have been synthesized under non-

hydrothermal and non-microwave reaction conditions using

a simple in situ 1,3-dipolar cycloaddition reaction. The simple

domino synthesis of these complexes therefore opens a new

convenient synthetic route for such types of cobalt(^III) tetrazo-

lato complexes with Schiﬀ base and azide as co-ligands. The

structures of the complexes were conrmed by single crystal X-

ray diﬀraction technique. The formation of hydrogen bonding

and C–H/p interactions have been studied using DFT calcu-

lations. Catechol oxidase and phenoxazinone synthase

mimicking activity of the complexes have been studied spec-

trophotometrically. Due to the similarity of molecular struc-

tures, the complexes show comparable results as far as catechol

oxidase and phenoxazinone synthase activity.

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¨

T. Weyhermuller, T. K. Paine, S. Mukherjee and

Conﬂicts of interest

C. Mukherjee, Biol. Chem., 2005, 386, 1023–1033.

6 (a) F. T. Ferre, J. A. L. C. Resende, J. Schultz, A. S. Mangrich,

R. B. Faria, A. B. Rocha and M. Scarpellini, Polyhedron, 2017,

123, 293–304; (b) A. Panja, N. C. Jana, S. Adak and

K. Pramanik, Inorg. Chim. Acta, 2017, 459, 113–123; (c)

A. T. Fiedler and A. A. Fischer, J. Biol. Inorg Chem., 2017,

22, 407–424; (d) H. Yang, J. Zha, P. Zhang, Y. Qin, T. Chen

and F. Ye, Sens. Actuators, B, 2017, B247, 469–478; (e)

N. Sarkar, P. K. Bhaumik and S. Chattopadhyay,

Polyhedron, 2016, 115, 37–46.

7 (a) F. Zippel, F. Ahlers, R. Werner, W. Haase, H. F. Nolting

and B. Krebs, Inorg. Chem., 1996, 35, 3409–3419; (b)

T. Kurahashi and H. Fujii, J. Am. Chem. Soc., 2011, 133,

8307–8316; (c) P. Setha, M. G. B. Drew and A. Ghosh, J.

Mol. Catal. A: Chem., 2012, 365, 154–161; (d) M. Mondal,

P. M. Guhaa, S. Giri and A. Ghosh, J. Mol. Catal. A: Chem.,

2016, 424, 54–64; (e) C. Fernandes, A. Neves,

A. J. Bortoluzzi, A. S. Mangrich, E. Rentschler,

B. Szpoganicz and E. Schwingel, Inorg. Chim. Acta, 2001,

320, 12–21.

There are no conicts to declare.

Acknowledgements

K. G. expresses his gratitude to UGC, India, for awarding

a Senior Research Fellowship (Sr. No. 2121410149; Roll No.:

132586; Ref. No.: 21/12/2014(ii)EU-V; Dated: 25.08.2015). Crys-

tallographic data were collected at the DST-FIST, India funded

Single Crystal Diﬀractometer Facility at the Department of

Chemistry, Jadavpur University. A. F. and A. B. gratefully

acknowledge the nancial 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.

Notes and references

1 (a) Y. Fu, F.-M. J. Chang and D. P. Giedroc, Acc. Chem. Res.,

2014, 47, 3605–3613; (b) H. Zhu, J. Fan, B. Wang and X. Peng,

Chem. Soc. Rev., 2015, 44, 4337–4366; (c) T. McKee and

J. R. McKee, Biochemistry: An Introduction, McGraw-Hill

Companies, Inc., China Science Press, New York, 2nd edn,

8 (a) M. L. Roes-Hill, C. Goodwin and S. Burton, Trends

Biotechnol., 2009, 27, 248–268; (b) C. E. Barry, P. G. Nayar

and T. P. Begley, Biochemistry, 1989, 28, 6323–6333; (c)

A. W. Smith, A. Camara-Artigas, M. Wang, J. P. Allen and

W. A. Francisco, Biochemistry, 2006, 45, 4378–4387.

´

1999; (d) C. S. Bonnet and E. Toth, Future Med. Chem.,

2010, 2, 367–384; (e) C. K. Mathews and K. E. Van Holde,

Biochemistry,

The

Benjamin/Cummings

Publishing

Company, Inc., Menlo Park, 2nd edn, 1996; (f) J. J. Braymer

and D. P. Giedroc, Curr. Opin. Chem. Biol., 2014, 19, 59–66;

9 (a) I. A. Koval, P. Gamez, C. Belle, K. Selmeczi and J. Reedijk,

Chem. Soc. Rev., 2006, 35, 814–840; (b) R. Than,

A. A. Feldmann and B. Krebs, Coord. Chem. Rev., 1999, 182,

211–241; (c) C. Gerdemann, C. Eicken and B. Krebs, Acc.

Chem. Res., 2002, 35, 183–191; (d) K. Selmeczi, M. Reglier,

M. Giorgi and G. Speier, Coord. Chem. Rev., 2003, 245, 191–

201; (e) N. Sarkar, M. Das and S. Chattopadhyay, Inorg.

Chim. Acta, 2017, 457, 19–28; (f) A. Panja and

P. Guionneau, Dalton Trans., 2013, 42, 5068–5075; (g)

N. Sarkar, K. Harms, A. Frontera and S. Chattopadhyay,

New J. Chem., 2017, 41, 8053–8065.

´

(g) C. Bleriot, M. Gault, E. Gueguen, P. Arnoux, D. Pignol,

M. A. M. Berthelota and A. Rodrigue, Metallomics, 2014, 6,

1400–1409.

2 (a) D. A. Quist, D. E. Diaz, J. J. Liu and K. D. Karlin, J. Biol.

Inorg Chem., 2017, 22, 253–188; (b) M. Can, F. A. Armstrong

and S. W. Ragsdale, Chem. Rev., 2014, 114, 4149–4174; (c)

H.-J. Thierse, S. Helm, M. Pink and H. U. Weltzien, J.

Immunol. Methods, 2007, 328, 14–20; (d) M. M. Bernardo,

S. Brown, Z. H. Li, R. Fridman and S. Mobashery, J. Biol.

Chem., 2002, 277, 11201–11207; (e) P. A. Lindahl and 10 (a) S. Kumar, D. N. Dhar and P. N. Saxena, J. Sci. Ind. Res.,

M. J. Moore, Biochemistry, 2016, 55, 4140–4153.

3 (a) M. Hoaraua, C. Hureaua, E. Gras and P. Faller, Chem. Soc.

Rev., 2016, 308, 445–459; (b) T. Ye, X. Bai, X. Jiang, Q. Wu,

2009, 68, 181–187; (b) T. Suzuki, T. Moriya, R. Endo and

N. Iwasaki, Polym. Chem., 2017, 8, 761–768; (c)

U. Schatzschneider, Eur. J. Inorg. Chem., 2010, 1451–1467.

S. Chen, A. Qu, J. Huang, J. Shenc and W. Wu, Polym. 11 (a) R. Bikas, H. H. Monfared, T. Lis and M. Siczek, Inorg.

Chem., 2016, 7, 2847–2857; (c) R. L. D'Ordine, R. S. Linger,

C. J. Thai and V. J. Davisson, Biochemistry, 2012, 51, 5791–

5803; (d) E. L. Kovrigin and J. P. Loria, Biochemistry, 2006,

45, 2636–2647.

4 (a) J. Fritsch, O. Lenz and B. Friedrich, J. Bacteriol., 2011, 193,

2487–2497; (b) K. S. Hewitson, L. A. McNeill, J. M. Elkins and

C. J. Schoeld, Biochem. Soc. Trans., 2003, 31, 510–515; (c)

P. A. Cobine, F. Pierrel and D. R. Winge, Biochim. Biophys.

Acta, 2006, 1763, 759–772.

5 (a) K. Ladomenou, G. Charalambidis and A. G. Coutsolelos,

Inorg. Chim. Acta, 2010, 363, 2201–2208; (b) S. K. Dey and

A. Mukherjee, Coord. Chem. Rev., 2016, 310, 80–115; (c)

A. A. Vernekar, T. Das, S. Ghosh and G. Mugesh, Chem.–

Asian J., 2016, 11, 72–76; (d) T. Ueno, Angew. Chem., Int.

Ed., 2010, 49, 3868–3869; (e) P. Chaudhuri, K. Wieghardt,

Chem. Commun., 2012, 15, 151–155; (b) A. H. Kianfar,

¨

M. Sedighipoor, G. Mohammadnezhad, H. Gorls, W. Plass

and M. Roushani, J. Iran. Chem. Soc., 2017, 14, 313–322; (c)

S. K. Gupta, N. Sen, J. A. Ganaie, R. J. Butcher and

J. P. Jasinski, J. Coord. Chem., 2017, 70, 3147–3170; (d)

H. Iranmanesh, M. Behzad, G. Bruno, H. A. Rudbari,

H. Nazari, A. Mohammadi and O. Taheri, Inorg. Chim. Acta,

2013, 395, 81–88.

12 (a) S. Shit, D. Saha, D. Saha, T. N. G. Row and C. Rizzoli,

Inorg. Chim. Acta, 2014, 415, 103–110; (b) A. Nishinaga,

T. Yamada, H. Fujisawa, K. Ishizaki, H. Ihara and

T. Matsuura, J. Mol. Catal., 1988, 48, 249–264; (c)

K. Maruyama, Y. Murakami, K. Yoda, T. Mashino and

A. Nishinaga, J. Chem. Soc., Chem. Commun., 1992, 1617–

1618.

28234 | RSC Adv., 2018, 8, 28216–28237

View Article Online

Paper

RSC Advances

´

13 (a) A. Biswas, L. K. Das, M. G. B. Drew, G. Aromı, P. Gamez

and A. Ghosh, Inorg. Chem., 2012, 51, 7993–8001; (b)

P. Kavitha, M. R. Chary, B. V. V. A. Singavarapu and

K. L. Reddy, J. Saudi Chem. Soc., 2016, 20, 69–80; (c)

F. Kelleher, J. McGinley, V. McKee and U. Sheridan,

Polyhedron, 2012, 33, 289–296; (d) Z.-H. Sun, L.-B. Meng

and H. Lin, Acta Crystallogr., Sect. C: Cryst. Struct.

Commun., 2009, E65, m280.

N. Shahabadi, S. Kashanian and F. Darabi, Eur. J. Med. 21 (a) G. M. Sheldrick, Acta Crystallogr., Sect. A: Fundam.

Chem., 2010, 45, 4239–4245.

Crystallogr., 2008, 64, 112–122; (b) G. M. Sheldrick,

SHELXS-97 and SHELXL-97: Program for Structure Solution,

14 (a) A. D. Khalaji, M. Nikookar, K. Fejfarova and M. Dusek, J.

Mol. Struct., 2014, 1071, 6–10; (b) A. D. Khalajia, R. Rahdaria,

F. Ghariba, J. S. Matalobos and D. Das, J. Ceram. Process.

¨

University of Gottingen, Institute fur Anorganische

Chemieder Universitat, Gottingen, Germany, 1997.

Res., 2015, 16, 486–489; (c) L. Ka-Ahmadi and 22 G. M. Sheldrick, SADABS: Soware for Empirical Absorption

¨

L. Shirmohammadzadeh, J. Nanostruct. Chem., 2017, 7,

179–190.

15 (a) Q. Yang, X. Song, W. Zhang, L. hou, Q. Gong, G. Xie,

Correction, University of Gottingen, Institute fur

Anorganische Chemieder Universitat, Gottingen, Germany,

1999-2003.

Q. Wei, S. Chen and S. Gao, Dalton Trans., 2017, 46, 2626– 23 (a) M. A. Spackman and D. Jayatilaka, CrystEngComm, 2009,

2634; (b) A. Mrowiec, A. Jurowska, M. Hodorowicz and

J. Szklarzewicz, Dalton Trans., 2017, 46, 4030–4037; (c)

A. Gualandi, E. Matteucci, F. Monti, A. Baschieri,

N. Armaroli, L. Sambri and P. G. Cozzi, Chem. Sci., 2017, 8,

1613–1620.

11, 19–32; (b) F. L. Hirshfeld, Theor. Chim. Acta, 1977, 44,

129–138; (c) H. F. Clausen, M. S. Chevallier,

M. A. Spackman and B. B. Iversen, New J. Chem., 2010, 34,

193–199; (d) M. A. Spackman and P. G. Byrom, Chem. Phys.

Lett., 1997, 267, 215–220.

16 (a) C. C. Du, J. Z. Fan, X. F. Wang, S. B. Zhou and D. Z. Wang, 24 (a) A. L. Rohl, M. Moret, W. Kaminsky, K. Claborn,

J. Mol. Struct., 2017, 1133, 348–357; (b) X.-L. Wang, T.-J. Li,

A.-X. Tian and N. Xu, Inorg. Chim. Acta, 2016, 443, 78–85;

(c) J. Yang, J. Wang, B. Wei, L. Shen, Y.-T. Min,

H.-J. Cheng, Y. Xu, J. Huang, C.-C. Wang, X. Zhang,

M.-L. Wu, Q.-Y. Li and G.-W. Yang, Transition Met. Chem.,

2016, 41, 35–43; (d) M. Taheriha, M. Ghadermazi and

J. J. McKinnon and B. Kahr, Cryst. Growth Des., 2008, 8,

4517–4525; (b) A. Parkin, G. Barr, W. Dong, C. J. Gilmore,

D. Jayatilaka, J. J. McKinnon, M. A. Spackman and

C. C. Wilson, CrystEngComm, 2007, 9, 648–652; (c)

M. A. Spackman and J. J. McKinnon, CrystEngComm, 2002,

4, 378–392.

V. Amani, J. Mol. Struct., 2016, 1107, 57–65; (e) L. Shen1, 25 S. K. Wolﬀ, D. J. Grimwood, J. J. McKinnon, D Jayatilaka,

M. J. Cao, F. F. Zhang, Q. Wu, L. Y. Zhao, Y. M. Lu,

Q. Y. Li, G. W. Yang, B. Wei and J. H. Zou, Transition Met.

Chem., 2016, 41, 125–131.

M. A. Spackman, Crystal Explorer 2.0; University of Western

Australia: Perth, Australia, 2007. http://

hirshfeldsurfacenet.blogspot.com/.

17 (a) R. Imai, S. Komeda, M. Shimura, S. Tamura, 26 (a) A. Bhattacharyya, S. Roy, J. Chakraborty and

S. Matsuyama, K. Nishimura, R. Rogge, A. Matsunaga,

I. Hiratani, H. Takata, M. Uemura, Y. Iida1, Y. Yoshikawa,

J. C. Hansen, K. Yamauchi, M. T. Kanemaki and

K. Maeshima, Sci. Rep., 2016, 6, 24712; (b) S. Kuwata and

T. Ikariya, Chem. Commun., 2014, 50, 14290–14300; (c)

S. Chattopadhyay, Polyhedron, 2016, 112, 109–117; (b)

´

S. Roy, T. Basak, S. Khan, M. G. B. Drew, A. Bauza,

A. Frontera and S. Chattopadhyay, ChemistrySelect, 2017, 2,

9336–9343; (c) T. Basak, K. Ghosh and S. Chattopadhyay,

Polyhedron, 2018, 146, 81–92.

´

¨

G. E. Buchel, I. N. Stepanenko, M. Hejl, M. A. Jakupec, 27 A. Bhattacharyya, A. Bauza, A. Frontera and

B. K. Keppler and V. B. Arion, Inorg. Chem., 2011, 50, 7690–

7697; (d) B. C. Losantos, A. A. Krokhin, I. N. Stepanenko, 28 R. Ahlrichs, M. Bar, M. Haser, H. Horn and C. Kolmel, Chem.

S. Chattopadhyay, Polyhedron, 2016, 119, 451–459.

¨

R. Eichinger, M. A. Jakupec, V. B. Arion and B. K. Keppler,

Inorg. Chem., 2007, 46, 5023–5033.

Phys. Lett., 1989, 162, 165–169.

´

29 (a) A. Bauza, A. Terron, M. Barcelo-Oliver, A.Garcıa-Raso and

18 (a) P. Neves, A. B. Lysenko, A. C. Gomes, M. Pillinger,

I. S. Gonçalves and A. A. Valente, Catal. Lett., 2017, 147,

A. Frontera, Inorg. Chim. Acta, 2016, 452, 244–250; (b)

´

D. Sadhukhan, M. Maiti, G. Pilet, A. Bauza, A. Frontera

¨

1133–1143; (b) L. Peters, R. Frohlich, A. S. F. Boyd and

and S. Mitra, Eur. J. Inorg. Chem., 2015, 11, 1958–1972; (c)

M. Mirzaei, H. Eshtiagh-Hosseini, Z. Bolouri, Z. Rahmati,

A. Esmaeilzadeh, A. Hassanpoor, A. Bauza, P. Ballester,

A. Kra, J. Org. Chem., 2001, 66, 3291–3298; (c) M. Das,

S. Chatterjee, K. Harms, T. K. Mondal and

S. Chattopadhyay, Dalton Trans., 2014, 43, 2936–2947.

´

M. Barcelo-Oliver, J. T. Mague, B. Notash and A. Frontera,

19 (a) B. G. Mukhopadhyay, S. Mukhopadhyay, M. F. C. G. da

Silva, M. A. J. Charmier and A. J. L. Pombeiro, Dalton

Trans., 2009, 4778–4785; (b) A. Hantzsch and A. Vagt, Justus

Cryst. Growth Des., 2015, 15, 1351–1361; (d) P. Chakraborty,

´

S. Purkait, S. Mondal, A. Bauza, A. Frontera, C. Massera

and D. Das, CrystEngComm, 2015, 17, 4680–4690.

Liebigs Ann. Chem., 1901, 314, 339–369; (c) R. Nasani, 30 S. F. Boys and F. Bernardi, Mol. Phys., 1970, 19, 553–555.

M. Saha, S. M. Mobin and S. Mukhopadhyay, Polyhedron, 31 Spartan ’10, v. 1.1.0, Wavefunction Inc, Irvine CA,

2013, 55, 24–36.

20 (a) M. Das, K. Harms and S. Chattopadhyay, Dalton Trans., 32 T. A. Keith, AIMAll (Version 17.01.25), Gristmill Soware,

2014, 43, 5643–5647; (b) R.-J. Xu, D.-W. Fu, J. Dai, Overland Park KS, USA, 2013.

Y. Zhang, J.-Z. Ge and H.-Y. Ye, Inorg. Chem. Commun., 33 (a) S. Roy, K. Harms and S. Chattopadhyay, Polyhedron, 2015,

www.wavefun.com.

2011, 14, 1093–1096; (c) A. D. Bond, A. Fleming, J. Gaire,

91, 10–17; (b) A. Bhattacharyya, P. K. Bhaumik, P. P. Jana and

RSC Adv., 2018, 8, 28216–28237 | 28235

View Article Online

RSC Advances

Paper

S. Chattopadhyay, Polyhedron, 2014, 78, 40–45; (c) W.-J. Lian, 45 (a) K. Ghosh, K. Harms and S. Chattopadhyay, Polyhedron,

X.-T. Wang, C.-Z. Xie, H. Tian, X.-Q. Song, H.-T. Pan, X. Qiao

and J.-Y. Xu, Dalton Trans., 2016, 45, 9073–9087.

34 M. Das, K. Harms, B. N. Ghosh, K. Rissanen and

S. Chattopadhyay, Polyhedron, 2015, 87, 286–292.

2017, 123, 162–175; (b) A. Bottcher, T. Takeuchi,

K. I. Hardcastle, T. J. Meade and H. B. Gray, Inorg. Chem.,

1997, 36, 2498–2504; (c) A. A. Khandar, B. Shaabani,

F. Belaj and A. Bakhtiari, Polyhedron, 2006, 25, 1893–1900;

(d) M. Salehi and M. Hasanzadeh, Inorg. Chim. Acta, 2015,

426, 6–14.

35 (a) S. Chattopadhyay, G. Bocelli, A. Musatti and A. Ghosh,

´

Inorg. Chem. Commun., 2006, 9, 1053–1057; (b) L. Pogany,

ˇ

´

ˇ

´

J. Moncol, M. Gal, I. Salitros and R. Boca, Inorg. Chim. 46 (a) M. Das, B. N. Ghosh, A. Bauza, K. Rissanen, A. Frontera

Acta, 2017, 462, 23–29; (c) K. Ghosh, A. Banerjee, S. Roy,

and S. Chattopadhyay, RSC Adv., 2015, 5, 73028–73039; (b)

A. Panja, M. Shyamal, A. Saha and T. K. Mandal, Dalton

Trans., 2014, 43, 5443–5452; (c) N. Sarkar, K. Harms,

´

A. Bauza, A. Frontera and S. Chattopadhyay, Polyhedron,

2016, 112, 86–95.

´

¨

36 (a) J. Muller, C. Wurtele, O. Walter and S. Schindler, Angew.

Chem., Int. Ed., 2007, 46, 7775–7777; (b) D. Bandyopadhyay,

M. Layek, M. Fleck, R. Saha and C. Rizzoli, Inorg. Chim.

Acta, 2017, 461, 174–182; (c) H. A. Rudbari, M. R. Iravani,

A. Bauza, A. Frontera and S. Chattopadhyay,

ChemistrySelect, 2017, 2, 2975–2984; (d) M. Mitra,

T. Kundu, G. Kaur, G. Sharma, A. R. Choudhury, Y. Singh

and R. Ghosh, RSC Adv., 2016, 6, 58831–58838.

V. Moazam, B. Askari, M. Khorshidifard, N. Habibi and 47 (a) M. Mitra, P. Raghavaiah and R. Ghosh, New J. Chem.,

G. Bruno, J. Mol. Struct., 2016, 1125, 113–120.

2015, 39, 200–205; (b) X.-Y. Li, L. Chen, L. Gao, Y. Zhang,

S. F. Akogun and W.-K. Dong, RSC Adv., 2017, 7, 35905–

35916; (c) T. S. Mahapatra, D. Basak, S. Chand, J. Lengyel,

M. Shatruk, V. Bertolasic and D. Ray, Dalton Trans., 2016,

45, 13576–13589; (d) M. I. Ayad, Arabian J. Chem., 2016, 9,

S1297–S1306; (e) S. K. Dey and A. Mukherjee, New J. Chem.,

2014, 38, 4985–4995; (f) S. K. Dey, P. Mitra and

A. Mukherjee, Cryst. Growth Des., 2015, 15, 706–717; (g)

S. K. Dey and A. Mukherjee, J. Mol. Catal. A: Chem., 2015,

407, 93–101; (h) J.-H. Qiu, Z.-R. Liao, X.-G. Meng, L. Zhu,

Z.-M. Wang and K.-B. Yu, Polyhedron, 2005, 24, 1617–1623;

(i) D. Dey, A. B. Roy, A. Ranjani, L. Gayathri,

S. Chandraleka, D. Dhanasekaran, M. A. Akbarsha,

C.-Y. Shen, H.-L. Tsai, M. Maji, N. Kole and B. Biswas, J.

Chem. Sci., 2015, 127, 649–661; (j) L. Mandal, S. Sasmal,

H. A. Sparkes, J. A. K. Howard and S. Mohanta, Inorg.

Chim. Acta, 2014, 412, 38–45; (k) R. Modak, Y. Sikdar,

S. Mandal and S. Goswami, Inorg. Chem. Commun., 2013,

37, 193–196; (l) S. Majumder, S. Mondal, P. Lemoine and

S. Mohanta, Dalton Trans., 2013, 42, 4561–4569; (m)

A. Banerjee, A. Guha, J. Adhikary, A. Khan, K. Manna,

S. Dey, E. Zangrando and D. Das, Polyhedron, 2013, 60,

102–109; (n) L. Mandal and S. Mohanta, Dalton Trans.,

2014, 43, 15737–15751; (o) A. Hazari, L. Kanta Das,

R. M. Kadam, A. Bauza, A. Frontera and A. Ghosh, Dalton

Trans., 2015, 44, 3862–3876; (p) P. Chakraborty and

S. Mohanta, Inorg. Chim. Acta, 2015, 435, 38–45; (q)

A. K. Maji, A. Chatterjee, S. Khan, B. K. Ghosh and

R. Ghosh, J. Mol. Struct., 2017, 1146, 821–827; (r) K. Ghosh,

K. Harms and S. Chattopadhyay, ChemistrySelect, 2017, 2,

8207–8220.

37 (a) D. Cremern and J. A. Pople, J. Am. Chem. Soc., 1975, 97,

1354–1358; (b) N. Nishio, Phys. Chem. Chem. Phys., 2011,

13, 13873–13900; (c) H. Suezawa, T. Yuzuri, Y. Kohno,

Y. Yamaguchi and M. Asami, Bull. Chem. Soc. Jpn., 2010,

83, 802–808; (d) M. Nishio, Y. Umezawa, J. Fantini,

M. S. Weiss and P. Chakrabarti, Phys. Chem. Chem. Phys.,

2014, 16, 12648–12683; (e) M. Nishio, J. Mol. Struct., 2012,

1018, 2–7.

38 (a) M. A. Spackman and P. G. Byrom, Chem. Phys. Lett., 1997,

267, 215–220; (b) S. Roy and S. Chattopadhyay, Inorg. Chim.

Acta, 2015, 433, 72–77; (c) M. Das and S. Chattopadhyay,

Polyhedron, 2013, 50, 443–451; (d) T. Basak, K. Ghosh,

´

C. J. Gomez-Garcıa and S. Chattopadhyay, Polyhedron,

2018, 146, 42–54.

39 (a) B. K. Shaw, M. Das, A. Bhattacharyya, B. N. Ghosh, S. Roy,

P. Mandal, K. Rissanen, S. Chattopadhyay and S. K. Saha,

RSC Adv., 2016, 6, 22980–22988; (b) P. Schmid, M. Maier,

¨

H. Pfeiﬀer, A. Belz, L. Henry, A. Friedrich, F. Schonfeld,

K. Edkins and U. Schatzschneider, Dalton Trans., 2017, 46,

13386–13396.

40 (a) M. Das, B. K. Shaw, B. N. Ghosh, K. Rissanen, S. K. Saha

and S. Chattopadhyay, RSC Adv., 2015, 5, 46869–46872; (b)

M. Das, K. Harms, B. N. Ghosh, K. Rissanen and

S. Chattopadhyay, Polyhedron, 2015, 87, 286–292; (c) S. Roy,

´

K. Harms, A. Bauza, A. Frontera and S. Chattopadhyay,

Polyhedron, 2017, 121, 199–205; (d) K. Ghosh, K. Harms,

´

A. Bauza, A. Frontera and S. Chattopadhyay, Dalton Trans.,

2018, 47, 331–347.

41 (a) P. K. Bhaumik, S. Roy, K. Harms and S. Chattopadhyay,

Polyhedron, 2014, 81, 168–179; (b) S. Bhattacharya, S. Roy

and S. Chattopadhyay, J. Coord. Chem., 2016, 69, 915–925.

42 S. Chattopadhyay, M. G. B. Drew and A. Ghosh, Eur. J. Inorg.

Chem., 2008, 1693–1701.

48 (a) A. Hazari, A. Das, P. Mahapatra and A. Ghosh, Polyhedron,

˜

2017, 134, 99–106; (b) A. Panja, N. C. Janaa and P. Brandao,

New J. Chem., 2017, 41, 9784–9795; (c) A. Panja and

A. Frontera, Eur. J. Inorg. Chem., 2018, 924–931; (d)

M. Mitra and R. Ghosh, Indian J. Chem., Sect. A: Inorg., Bio-

inorg., Phys., Theor. Anal. Chem., 2016, 55A, 681–685; (e)

M. Mahato, D. Mondal and H. P. Nayek, ChemistrySelect,

2016, 1, 6777–6782; (f) A. Panja, Dalton Trans., 2014, 43,

7760–7770; (g) A. Panja, Polyhedron, 2014, 80, 81–89; (h)

43 A. Kufelnicki, S. V. Tomyn, Y. S. Moroz, M. Haukka,

´

J. J. Rosinska and I. O. Fritsky, Polyhedron, 2012, 33, 410–416.

44 (a) M. Galini, M. Salehi, M. Kubicki, A. Amiri and

A. Khaleghian, Inorg. Chim. Acta, 2017, 461, 167–173; (b)

A. H. Kianfar, W. A. K. Mahmood, M. Dinari,

M. H. Azarian and F. Z. Khafri, Spectrochim. Acta, Part A,

2014, 127, 422–428.

´

K. Ghosh, S. Roy, A. Ghosh, A. Banerjee, A. Bauza,

28236 | RSC Adv., 2018, 8, 28216–28237

View Article Online

Paper

RSC Advances

A. Frontera and S. Chattopadhyay, Polyhedron, 2016, 112, 6–

17.

M. L. Kuznetsov, M. F. C. Guedes da Silva and

A. J. L. Pombeiro, Chem.–Eur. J., 2011, 17, 11882–11892.

49 P. H. Rieger, in Electron Spin Resonance: Analysis and 51 (a) P. Chakraborty, J. Adhikary, B. Ghosh, R. Sanyal,

´

Interpretation; Royal Society of Chemistry, Cambridge, U.K.,

2007.

S. K. Chattopadhyay, A. Bauza, A. Frontera, E. Zangrando

and D. Das, Inorg. Chem., 2014, 53, 8257–8269; (b) P. Adak,

´

50 (a) K. Ghosh, M. G. B. Drew and S. Chattopadhyay, Inorg.

Chim. Acta, 2018, 482, 23–33; (b) A. Biswas, L. K. Das,

B. Ghosh, A. Bauza, A. Frontera, A. J. Blake, M. Corbella,

C. D. Mukhopadhyay and S. K Chattopadhyay, RSC Adv.,

2016, 6, 86851–86861; (c) S. Dasgupta, I. Majumder,

´

M. G. B. Drew, G. Aromı, P. Gamez and A. Ghosh, Inorg.

´

Chem., 2012, 51, 7993–8001; (c) R. Wanke, L. Benisvy,

P. Chakraborty, E. Zangrando, A. Bauza, A. Frontera and

D. Das, Eur. J. Inorg. Chem., 2017, 133–145.

RSC Adv., 2018, 8, 28216–28237 | 28237

Article Doi

One pot synthesis of two cobalt(iii) Schiff base complexes with chelating pyridyltetrazolate and exploration of their bio-relevant catalytic activities

DOI: 10.1039/c8ra03035a

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