Dioxomolybdenum (VI) Compounds of Macrocyclic Schiff base Ligands: Preparation, Characterization and Antibacterial activity

Using di-2-furanylethanedione and 5-bromo-3-methylbenzene-1,2-diamine we prepared a monomeric [MoO 2 (SL)] with a Schiff base, as well as 4 different compounds using the formulation [MoO 2 (MSL). We investigate how [MoO 2 (SL)] reacts with 1,3-diketones. Several characterizations are discussed in this article, including molar conductance measurement, elemental analysis, UV-Vis, IR, NMR, and thermal measurements. Molybdenum has a six-coordination number. All five MoO 2 (VI) compounds have distorted octahedral arrangements. Molybdenum octahedra have four N-atoms and two oxidized O-atoms.Against S. aureus and S. typhi , all synthesized compounds showed moderate activity. The chelation hypothesis is used to define the progression of the antibacterial task.

Metalloproteins and enzymes contain positions of metal that can be modelled by Schiff base compounds in the bioinorganic field 21 .In comparison to the isolated ligand, the anticancer activity of various Schiff bases is greater for that particular metal compound [22][23][24][25][26][27][28][29] .Additionally, they remain fascinated by chemistry reactions and consumer electronics memory storage gadgets.
Extreme density ligands in transition metal compounds have different configurations and coordination numbers 30,31 .The multiple oxidation states of molybdenum can allow it to be adaptable in this aspect.A coordination number may also range from 4 to 8 32 .Schiff base edifices can be produced for homogeneous and heterogeneous reactions by linking molybdenum compounds with ligands containing hetero atoms (N,O and S) [33][34][35][36][37][38][39] .There are a number of biological applications that can be achieved by MoO 2 (VI) compounds because they have multidentate ligands.[MoO 4 ] 2- can readily be acquired in aqueous solution as Mo(VI).Solution concentration and pH can determine the concentration of the [MoO 4 ] 2-ion.A template for oxygen transfer has been shown to exist in the form of the [MoO 4 ] 2-ion.It has been shown that their oxygen transfer properties have a negative effect on the molybdenum oxotransferase mechanism [40][41][42][43] .It is known that several redox enzymes are fully oxidized.A cisdioxomolybdenum moiety is associated with their active sites in such cases [44][45][46] .
Molybdenum is the only transition metal considered as a biometal that is essential for pathogenic microorganisms found in human, animal and vegetation pathogens 47,48 .The biological and catalytic properties of Mo(VI) coordinate chemistry make it an active area of scientific research [49][50][51][52] .A molybdenum molecule sets up the physiological functions of oxomolybdoenzymes [53][54][55] .It might be useful as a chelating agent since di-2-furanylethanedione is versatile.There could be Schiff base condensation between diamines and di-2-furanylethanedione due to its reactive carbonyl groups.In order to synthesize macrocyclic ligands, di-2-furanylenedione plays an essential role.
Di-2-furanylethanedione has denticity ligands, which can be synthesized from reaction of diamine with di-2-furanylethanedione under certain conditions.Through metal template impact, the synthesized compound undergoes cyclization with 1,3-diketones.It is possible to prepare and characterize them, and TGA, nmr, ir, UV-Vis spectroscopy, molar conductivity measurements, and elemental analysis have all supported their provisional structures.

Physical Measurements and Analytical Methods
In Arunachal Pradesh, India, CHN analysers were used at important CRFs, including NERIST, Nirjuli, Itanagar, to examine C,H and N in the compounds.Nitrogen is assessed using Kjeldahl's method for synthesized compounds.Using a gravimetric technique, molybdenum was measured after decay of the compound 56 .As barium sulfate was developed as a method for estimating sulfur, sulfur estimation progressed 57 .In addition to sulfuric acid baths, general methods were used for determining uncorrected melting factors.A Labinda-UV 3000+ UV/Vis spectrophotometer at UPTTI Kanpur, U.P., India was used to compute the electronic absorption spectra of the compounds utilizing ethanol.At Indian Institute of Technology Kanpur, we recorded the infrared spectra of MoO 2 (VI) compounds in KBr using Perkin-Elmer Spectrum models 10.03.06 and 18.03.06spectrophotometers.On the JMM ECS-400 (JEOL) spectrometer, proton ( 1 H NMR) spectra of MoO 2 (VI) compounds were obtained.An analysis of the temperature distribution of the [MoO 2 (SL)] compound was carried out using the TG/DTA-SDT Q600 V 20.9 Built 20, USA thermal analyzer under a nitrogen atmosphere at temperatures between 50-900°C at a10°C min -1 heating rate.

Preparation of molybdenum(VI) compounds containing ligands that result from condensation of di-2-furanylethanedione and 5-bromo-3methylbenzene-1,2-diamine with 1,3-diketones.
Schemes 1, 2 and 3 show how to synthesize [MoO 2 (MSL)].Drop-wise addition of molybdenyl acetylacetonate (1.6307 g, 5 mmol) in ethanol (50 mL) was followed by the addition of di-2-furanylethanedione (0.9506 g, 5 mmol) in 50 mL ethanol and 5-bromo-3-methylbenzene-1, 2-diamine (2.0106 g, 10 mmol) in 50 mL ethanol.The solution turns brown after 3 h of slight reflux in the reaction mixture.After filtering, ethanol was used to wash the solid product, and silica gel was used to isolate the solid under vacuum.In order to check the purity of the compound, the TLC method was used.As a result, the yield increased to 48% (type A). 3D structures of the Schiff base ligand (SL) and parent compound [MoO 2 (SL)] are given in Figure 1 and 2. Where,  According to elemental analysis (Table 1), metal and ligand are in a 1:1 stoichiometry.

Antibacterial activity assay
Several bacterial strains were tested in vitro for their antibacterial activity, including S. aureus, B. subtilis, E. aerogene and S. typhi utilizing an agar-well diffusion process [58][59][60] .Antibacterial activity of Doxycycline became the same as that of other antibiotics.Agar media were drilled with 6 mmdiameter holes using a metallic borer.All bacterial suspensions were adjusted to a density of 3x10 5 colony-forming units per mL.Agar was expanded with standardized suspensions.In the examined sample, 300 g mL -1 of the produced compounds were dissolved in 1% DMSO.Each well was filled with the examined samples.DMSO and Doxycycline (0.05%) were packed in the rest of the wells.Upon incubation at 355°C for 30 h growth inhibition is tested.

Infrared spectra
T h r o u g h a n i n -s i t u p r o c e d u r e , dioxomolybdeum(VI) was produced by refluxing a mixture of di-2-furanylethanedione, 5-bromo-3-methylbenzene-1,2-diamine, and molybdenyl acetylacetonate in aqueous ethanol in a 1:2:1 ratio, which resulted in macrocyclic compounds as shown in the scheme.Several infrared bands were observed for the isolated ligands and the MoO 2 (VI) compounds.Table 2 highlights these bands.A macrocyclic compound with N-atoms of the group azomethine bonded to molybdenum has been demonstrated by lowering C=N absorption frequencies [61][62][63][64] .In isolated ligands, >C=N absorption appears at 1665 cm -1 in spectrum bands between 1610-1650 cm -161-63 .It could be assigned to the Mo-N vibration around 490-570 cm -1 , which is not related to free ligands 65 .Di-2-furanylethanedione forms a strong bond with diamines due to the presence of two >C=N bands around 1710 cm -1 66,67 .Dioxomolybdeum(VI) compounds and their isolated ligands exhibit compound infrared spectra due to various ring vibrations and C-H vibrations.An asymmetric (N-H) and symmetric (N-H) wide band is targeted at 3430 and 3060 cm -1 , respectively.There is no difference between [MoO 2 (SL)] and [MoO 2 (MSL)] because the NH group is absent.This implies the NH group is not involved in the bonding process 68 .Among dioxomolybdenum(VI) compounds, d-orbital is used most often for bonding, forming preferentially cis-dioxo groups.In dioxomolybdenum(VI) c o m p o u n d s , c i s -[ M o O 2 ] 2 + d e m o n s t r a t e s asymmetric and symmetric stretching vibrations at 896-910 cm -1 and 962-970 cm -1 as a result of C 2V symmetry 69 .There are two infrared spectral bands at these wavelengths that are associated with n asym(O=Mo=O) and n sym(O=Mo=O) vibrations respectively [69][70][71][72][73][74][75][76] .In comparison to n sym(O=Mo=O) , n asym(O=Mo=O) vibrations are lower 77,78 .On the outer coordination sphere, the acetylacetonate group can be observed in the bands around 1555-1570 cm -1 and 1465-1482 cm -1 , which correspond to the C=O and C=C vibrations, respectively 79 .The macrocyclic compounds exhibit an equal pattern of infrared spectral bands.A method of cyclizing 1,3-diketones by containing amino groups on the carbonyl group, the asymmetrically and symmetrically stretching vibrations of terminal amino groups disappear 79,80 .In the range of 4000-400 cm -1 , all spectra were recorded with KBr

H NMR spectra
All NMR signals are given in Table 3.All MoO 2 (VI) compounds as well as the ligand were analyzed using 1 H NMR in DMSO-D 6 .It is possible that SL contains signal because of NH 2 at δ (5.32), which is also found in [MoO 2 (SL)], at δ (7.20) but not in other macrocyclic compounds, which suggests the presence 1,3-diketones that are present in cyclization [84][85][86] .For isolated ligands and molybdenum compounds, the ten protons are multiplets within the range δ (7.84-6.53).About δ 7.25 peaks appeared for the protons of aromatic rings.In the preparation of the macrocyclic compound, two types of azomethine are offered which appear to result in these chemical shifts.It is possible that peak at δ 2.33 is be due to CH 3 attached to an aryl group.

UV-Visible spectra
These spectra were measured in ethanol, and they are consistent with the strength energy level scheme suggested by the tetradentate tetraaza ligand and dixomolybdenum(VI) compounds [81][82][83] .Tetradentate ligands and dixomolybdenum(VI) compounds exhibit similar spectra.With the Mo(VI) ion having no d-electron, it is no longer expected to show pure d-d absorption bands.All molybdenum compounds can also be explained as charge transfer transitions between their nitrogen and molybdenum d-orbitals [N(π)→d(Mo)].A dioxomolybdenum(VI) compound containing nitrogen donor atoms exhibits homogeneous UV-Vis spectra.Strong absorption bands during the UV-Vis spectrum of those compounds is identified at 292 nm and at 311 nm, which may be attributed to intraligand transitions and n→π*/π→π* transitions.The band between 380 nm and 395 nm appears to be caused by N(π)→d(Mo).Transition 2 B 2 → 2 A 1 (d xy →d x2-y2 ) may be covered within other bands and is ideal to facilitate charge transfer between the molybdenum LUMO and the ligand HOMO.Energy level schemes for these compounds have been provided by Ballhausen-Gray diagrams.Each compound's electronic spectrum has an octahedral distortion 87 .

Magnetic and molar conductance measurements
As for d 0 configuration, it is not necessary to mention that dioxomolybdenum(VI) compounds are diamagnetic.Due to the absence of electrons in d-orbitals, no d-d transitions are determined for those compounds.The molar conductivities (Λ M ) of all molybdenum compounds in DMF at the ca. 10 -3 M endorse 1:1 sort electrolytes.Those compounds have molar conductance ranging from 90 to 110 Ω -1 cm 2 mol -1 .As predicted by the schemes, the molar conductance values on top of the compounds of dioxomolybdenum(VI) type (A) and macrocyclic type (B) suggest tentative shapes.

Thermogravimetric analyses
Thermogravimetric curve (TG Curve) of the compound presented in Fig. 3 reveals that the compound has decomposed in one step.At a temperature of 279 ν about 83% weight loss has been observed which is due to loss of Schiff ligand and acetylacetonate moiety (calculated weight 83.1%).At 281, the residue left is 16.3% which corresponds to MoO 3 .Weight percent left at 324 is 14.48 and is attributed to MoO 2 .antimicrobial activity.It was tried against a variety of bacteria, including S. aureus, B. subtilis, E. aerogenes, and S. typhi, using the synthesized dioxomolybdenum(VI) compounds.Chelation hypothesis can be used to explain the improvement of dioxomolybdenum(VI) compounds' antibacterial properties 79,80 .A doxycycline remedy is used as the reference material.Many of the compounds were found to have low or modest activity against S. aureus and S. typhi.
Using Eq 1 as a starting point, we calculate the percentage of inhibition effect based on the positive control.

CONCLUSION
These compounds haven't been crystallized yet, so their crystal structures are unavailable.The [MoO 2 (SL)] and [MoO 2 (MSL)] compounds can be represented using the above elemental and spectral studies.The antibacterial activity of these compounds has been tested.We demonstrate the formation of dioxin derivatives from dioxomolybdenum(VI) Schiff bases.The Schiff base condensation was confirmed using a flexible chelator with two carbonyl groups, di-2-furanylethanedione.As a result of their reaction with 1,3-diketones, macrocyclic products are formed.Distorted octahedron surrounding Mo.Di-2furanyledione and diamines are used to condense Schiff bases in ethanol medium.Tetradentate bonds are formed between azomethine nitrogen atoms and metal ions in Schiff bases.One metal ion is present in each ligand molecule.Compounds prepared have been shown to have six coordinated distorted octahedral shapes and a mononuclear six coordination.

ACKNOWLEDGMENT
It would be appreciated if the authors could thank the BoM-Secretary, D.A-V.Post-Graduate College, Kapur for the opportunity to look at the work in a laboratory setting.Fortuitously, UPTTI Kanpur India supplies analytical facilities.

Fig. 3 .
Fig. 3. TG thermograph of [MoO 2 (SL)] Antibacterial activity A s c a n b e s e e n i n Ta bl e 4 , t h e dioxomolybdenum(VI) compounds exhibit