Polyoxometalate based hybrids: Synthesis of metal complexes and investigation of their electrochemical, photophysical and biological properties

doi:10.21203/rs.3.rs-1737792/v1

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Polyoxometalate based hybrids: Synthesis of metal complexes and investigation of their electrochemical, photophysical and biological properties

https://doi.org/10.21203/rs.3.rs-1737792/v1

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α-Keggin POM based compounds (KL¹-KL³) were synthesized from the reactions between imine ligands (HL¹-HL³) and α-Keggin-type polyoxometalates and their structures were characterized by various instrumental methods. In addition to other techniques, ¹H(¹³C)NMR methods were also used in the characterization of the azo imine organic ligands (HL¹-HL³). After the Cu²⁺ and Pt²⁺ complexes of the hybrid compounds were synthesized and characterized, their photophysical, electrochemical and antimicrobial properties were investigated. The compounds showed activity against penicillium spp. On the other hand, the KL² POM compound showed the highest antibacterial activity. In the UV-vis spectra of the KL¹, KL² and KL³ POM based compounds in DMF solution, the charge transfer transitions (CT) are observed in the range of 458−453 nm, while ligand-centered π−π* transitions are in the range of 333−316 nm. Among the complexes of hybrid compounds, only the emission values of the KL¹Cu complex in the DMF medium and in the solid state shifted to shorter wavelengths. It was determined that some of the POM based metal complexes showed only metal-centered electrochemical behaviors. In addition, the thermal stability of all compounds was also investigated.

Keggin

hybrid complexes

electrochemical

photophysical

biological

Today, due to the constantly changing needs, the materials needed are required to have both diversity and superior properties. Materials with superior properties are usually possible by combining more than one different material of different types. Polyoxometalates (POMs) continue to attract attention in recent years due to the differences in their structure and chemical properties. In addition to being in the inorganic metal oxide class, these compounds also show properties worth examining in terms of their biological activities[1–5]. Although POMs have high potential for inhibition of various tumor types, their non-specific interactions with biomolecules and their toxicity do not make their clinical use possible. However, the toxicity of hybrid compounds obtained from the reaction of POMs and organic molecules is lower [6, 7]. With the formation of these materials, not only new structures are formed, but also their properties are improved and a material class with superior properties is obtained. For example, hybrid compounds formed by the interaction of metal oxides and organic ligands are not only different in terms of shape, but also in terms of physical and chemical properties. Besides single metal ions and metal carboxylate clusters as the main inorganic components forming hybrid structures, POMs form inorganic-organic hybrid structural motifs, usually POM-based, in high oxidation states (e.g. Mo⁵⁺, Mo⁶⁺, W⁶⁺, V⁵⁺), due to its abundant surface oxygen atoms, they are used as inorganic polydentate ligands to bind with other metal ions or metal-organic moieties via multiple coordination modes [8]. Multifunctional organic ligands with reactive capacity and hybrids obtained from the reaction of POMs have the feature of being used in many different areas. Common uses of hybrids include medicine, magnetic materials, catalysis, energy storage and waste removal. The wide use of hybrids is due to the structural features and diversity of POMs.

It is known that Keggin-based POMs show effective electrocatalytic activity against some compounds. However, since Mo-containing POMs show degradation and instability in a strongly acidic environment, catalysis studies are carried out at low pH [9, 10]. On the other hand, hybrid materials eliminate this disadvantageous situation. Therefore, POM-based hybrids have provided great advantages to material chemistry [11–13]. One of the most used areas of these materials is their preference as electrode material [14, 15].

In the present study, after synthesizing and characterizing three imine compounds (HL¹-HL³) for use in the production of POM based compounds, POM compounds (KL¹-KL³) were obtained from the reaction of Keggin type POM and imine compounds. The Cu²⁺ and Pt²⁺ complexes of the hybrid compounds were obtained and the characterization of all compounds were done by the analytical and spectroscopic methods. Photoluminescence and electronic spectral properties of the compounds in solid and solution form were investigated. In addition, by examining the thermal properties of hybrids and transition metal complexes, information about their thermal stability was obtained. Electrochemical and antimicrobial properties of hybrids (KL¹−KL³) and metal complexes were also investigated.

The materials, preparation methods of all compounds and characterization methods have been given in supplementary file.

The compound α-Keggin heteropolymolybdate used in this study was synthesized according to the known literature method by our group. Structural characterization of this compound was performed by X-ray diffraction method by obtaining single crystals from ethyl alcohol solvent medium and other spectroscopic methods [16]. The obtained POM has the formula H₄[SiMo₁₂O₄₀]·3EtOH. On the other hand, the organic azo-imine ligands [HL¹: 2,2'-((4-((4-aminophenyl)azo)phenyl)imino)bis(ethanol)-3-methoxy salicylidene; HL²: 2,2'-((4-((4-aminophenyl)azo)phenyl)imino)bis(ethanol)-5-methoxy salicylidene; HL³: 2,2'-((4-((4-aminophenyl)azo)phenyl)imino)bis(ethanol)-4-methoxy salicylidene] (Fig. S1) used to obtain hybrid compounds (KL¹-KL³) were also synthesized by our group and characterized spectroscopically, analytically and structurally [17]. The ligands are easily soluble in known polar organic solvents such as EtOH, MeOH, C₃H₆O, DMF because they hydrophilic ends with polar character. Many solvents were tried to synthesize POM-based hybrid compounds (KL¹-KL³) and it was determined that acetone was the most suitable solvent. Therefore, the reaction to obtain POM based compounds was carried out in acetone solvent media. The proposed structures of the obtained POM-based hybrid materials are given in Fig. 1.

FTIR spectra of the organic and POM based compounds were recorded using KBr as a standard and obtained data were given in supplementary file. The spectra of the H₄[SiMo₁₂O₄₀]·3EtOH and POM based compounds KL¹Pt, KL²Pt and KL³Pt are given in Fig. 2. Keggin-based POMs have characteristic FTIR spectral values. In the spectrum of the H₄[SiMo₁₂O₄₀]·3EtOH, the characteristic n(Mo=O), asymmetric n(Mo-O-Mo), symmetric n(Mo-O-Mo) and bridging n(Mo-O-Mo) vibrations are shown at 990, 952, 895, 759 and 530 cm^-1, respectively. It has been determined that there is a hydrogen bond interaction between the α-Keggin type POM and the ethanol molecule [16]. In the spectra of the POM based KL¹-KL³, the bands in the range of 3360-3354 cm^-1 may be assigned to the n(O-H) stretching of the azo-imine ligands.

Vibration bands belonging to the azomethine group n(CH=N) of azo-imine compounds are observed at 1582 cm^-1. The band at 1540 cm^-1 in the KL¹-KL³ POMs may be assigned to the n(N=N) vibration of the azo group. The characteristics n(Mo=O), asymmetric n(Mo-O-Mo), symmetric n(Mo-O-Mo) and bridging n(Mo-O-Mo) vibrations for these compounds were shown as double strong bands in the 990-531 cm^-1 range. In the spectra of the Cu²⁺ and Pt²⁺ complexes, the bands belonging to the n(O-H) stretching were shown in the 3400-3300 cm^-1 range. In the complexes, the azomethine vibrations are in the 1610-1599 cm^-1 range. The shift was an indication of chelation of Cu²⁺ or Pt²⁺ through the imine nitrogen. The vibration band of this group shifted upwards compared to the ligands. The shifts in the vibration bands are generally due to electron transfer from the d-orbitals of the metal to the vacant p* orbital of the azomethine group by back-bonding (metal to ligand) [18]. The characteristic Mo-O vibration bands originating from POM were observed in the range of 1000-531 cm^-1. Shifts in characteristic Mo-O vibrational bands were greater in Pt²⁺ complexes. This may be due to the chemical properties of the metal ions.

UV-Vis absorption and photoluminescence spectral studies for the KL¹-KL³ POMs and their metal complexes were measured in 1x10^-5 M DMF concentration and in the range of 200-850 nm. In addition, the visible reflectance spectra of the POMs and their metal complexes were investigated using CaSO₄ matrices in the 200-900 nm range. Solution and reflectance UV-vis spectra of the POMs complexes KL¹Pt-KL³Pt were shown in Fig. 3. The UV-vis spectra of the other compounds were given in supplementary file (Fig. S2a-d). Moreover, the obtained UV-Vis and photoluminescence spectral data for all compounds were given in Table 1 in supplementary file. The di-ethanol end, which binds to the Keggin POM of the imine ligands, has a flexible structure. Another important point is that only s-electrons are active between imine ligands and POM. The p-electrons of the organic parts in POMs act only on the conjugated system of the imine ligands. This situation affects the electronic transition in the POM structure. In the DMF solution of the KL¹, KL² and KL³ POMs, the absorption bands at 590, 595 and 583 nm can be attributed to the d-d transition with the intervalence bands owing to the electronic transition Mo⁵⁺⋯O⋯Mo⁶⁺ ® Mo⁶⁺⋯O⋯Mo⁵⁺[16], respectively. The maxima absorption bands in the range 493-322 nm range can be assigned to the can be assigned to the (n- π*) of the intra-ligand electronic transitions. In the spectra of the Cu²⁺ complexes, there are two absorption bands in the range of 447-440 and 326-320 nm. While the first of them is due to the n- π* transitions in the ligands, the other could be assigned to ligand-to-metal O(π) ® Mo(dπ) charge transfer transition. The KLⁿPt (n:1-3) complexes have three absorption band in the range of 584-324 nm. The bands in the 584-568 nm range can be attributed to the d-d transition of the Mo-ion. On the other hand, the bands in the 460-455 nm range are due to ligand-centered n- π* transitions. Electronic

transitions in this wavelength range are shifted to longer wavelengths compared (bathochromic shift) to the KLⁿCu complexes. Such electronic shifts confirm the electron transfer between the conjugated organic imine ligands and the a-Keggin POM [19]. The absorption bands at 328 and 324 nm are due to the ligand-to-metal O(π) ® Mo(dπ) charge transfer transition.

The bands in the solid-state spectra of the compounds are generally quite wide and asymmetrical. This situation causes difficulties in understanding of the electronic transitions of the compounds. The wavelengths of the bands of the solid-state electronic transitions of the compounds shifted to longer wavelengths compared to the compounds in the solution medium. In the spectra of the KL¹-KL³, the bands in the range of 680-551 nm may be assigned to the d-d transitions of the Mo ion in a-Keggin POM. While KLⁿPt complexes have absorption bands in the range of 714-694 nm, the bands in this wavelength range are not observed in the spectrum of KLⁿCu complexes. In the spectra of the KLⁿCu and KLⁿPt complexes, the bands in the range of 591-528 nm can be attributed to the d-d transition of the Mo-ion. The absorption band around 460 nm observed in the UV-vis spectrum of KLⁿPt complexes taken in DMF solution was not observed due to the width of the spectrum taken in the solid state. On the other hand, the absorption bands in the range of the 397-313 nm can be assigned to the the ligand-to-metal O(π) ® Mo(dπ) charge transfer transition. The bands in the range of 240-236 nm may be assigned to the s-s* transitions of the imine compounds.

Table 1

UV-Vis and photoluminescence spectral data of a-Keggin POM based hybrids (KL¹-KL³) and their metal complexes.

Compounds	Photoluminescence/(λ_max) UV-Vis/(λ_max)
	Solvent (DMF)
	Excitation	Emission	λ (ɛ)	Reflectance (solid state)
KL¹	533	549	316(0.45x10⁵), 456(0.61x10⁵)	234, 312, 573, 692
KL¹Cu	551	570	320(0.31x10⁵), 440(0.40x10⁵)	240, 312, 551
KL¹Pt	680	697	324(0.14x10⁵), 453(0.17x10⁵), 581(0.05x10⁵)	235, 314, 562, 710
KL²	536	552	333(0.34x10⁵), 458(0.58x10⁵)	232, 311, 556, 705
KL²Cu	575	592	319(0.32x10⁵), 445(0.45x10⁵)	238, 308, 525
KL²Pt	682	697	319(0.37x10⁵), 453(0.63x10⁵), 586(0.08x10⁵)	238, 322, 578, 712
KL³	527	543	318(0.41x10⁵), 453(0.53x10⁵)	235, 315, 552, 697
KL³Cu	581	598	316(0.42x10⁵), 445(0.54x10⁵)	235, 309, 552
KL³Pt	682	697	320(0.37x10⁵), 457(0.57x10⁵), 589(0.10x10⁵)	241, 326, 581, 723

The photoluminescence (excitation and emission) spectra (PL) of the KLⁿ and their Cu²⁺and Pt²⁺ complexes were given in Fig. 4. In the excitation spectra of the KL¹-KL³, the peaks were observed in the 527-536 nm range. On the other hand, the intensity of the excitation band of the KL¹ is the highest. The maximum intensity at 533 nm may be assigned to a charge transfer from the electronic states with low-energy [20,21]. The KL² has minimum intensity at 536 nm. These bands can be attributed to the ligand to metal charge transfer (LMCT) bands [22]. Since the -OCH₃ groups attached to the salicylidene ring in the KL¹ and KL² compounds are in the meta-position, the excitation bands are slightly red-shifted more than the KL³. Because the -OCH₃ groups in the meta-position withdraw s-electrons from the ring with the inductive effect. In the spectra of the Cu²⁺ and Pt²⁺ complexes of the compounds KL¹-KL³, the excitation bands were observed in the range of 683-554 nm. The bands of the Pt²⁺ complexes were shifted to the longer wavelength. In the emission spectra of the KL¹-KL³, the oxygen-to-metal CT (O → Mo) state of the α-Keggin POM lattice were observed in the range of 543-552 nm [23]. It was determined that emission spectral properties of POM-based compounds showed similar behaviours with their excitation spectral properties. In other words, the intensity of the emission peaks of the compounds and the shift of the emission band to the long wavelength were observed in the same way. This can be called the substituent effect. In the spectra of the complexes, while the emission bands of the Pt²⁺ complexes were observed at 697 nm, the bands of the Cu²⁺ complexes were observed in the range of 570-598 nm. The wavelengths of the emission and excitation bands of the Pt complexes did not change depending on the differentiation of the ligands.

The electrochemical properties of the compounds KL¹-KL³ and their metal complexes were investigated in 1.0 × 10⁻³ M DMF-0.1 M Bu₄NBF₄ as supporting electrolyte solution and scan rates at 100, 250 and 500 mVs^-1. The cv curves of the KL¹Pt-KL³Pt complexes were shown in Fig. 5a-c. The electrochemical data of all compounds were given in Table 2. The cv curves of the KL¹-KL³ and their Cu²⁺ metal complexes were given in supplementary file as Fig. S3a-f. The glassy carbon electrode was used as working electrode.

Table 2

Electrochemical data at different scanning rates of a-Keggin POM-based compounds and their Cu²⁺ and Pt²⁺ metal complexes. All the potentials are referenced to Ag⁺/AgCl; where E_pa and E_pcare anodic and cathodic potentials, respectively. ΔE_p= E_pa−E_pc E_1/2 = 0.5 × (E_pa + E_pc).

Compounds	Scan Rates (mV/sn)	*E_pa*	*E_pc*	*E_pa/E_pc*	*E_1/2(*V)	*ΔE_p(*V)
KL¹	100	0.03, 0.88	0.51	1.72	─	0.37
	250	0.06, 0.95	0.47	2.02	─	-041
	500	0.10, 1.07	0.43	2.48	─	-0.33
KL¹Cu	100	0.86	-0.06	10.75	─	0.92
	250	0.87	-0.05	17.40	─	0.92
	500	0.88	-0.03	29.33	─	0.91
KL¹Pt	100	0.14, 0.66, 0.94	0.56, -0.30	1.17	─	0.10
	250	0.15, 0.67, 0.93	0.53, -0.33	1.26	─	0.14
	500	0.16, 0.68, 0.92	0.46, -0.37	1.47	─	0.22
KL²	100	-0.13, 0.75	0.54	1.38	─	0.21
	250	-0.08, 0.89	0.49	1.81	─	0.40
	500	0.09, 1.01	0.44	2.29	─	0.57
KL²Cu	100	0.71	0.28	2.53	─	0.43
	250	0.78	0.20	3.90	─	0.58
	500	0.88	0.09	9.77	─	0.79
KL²Pt	100	0.27, 0.67	0.37, -0.33	1.81	─	0.30
	250	0.28, 0.66	0.35, -0.37	1.88	─	0.31
	500	0.29, 0.65	0.32, -0.41	2.03	─	0.33
KL³	100	-0.08, 0.82	0.49	1.67	─	0.33
	250	-0.04, 0.90	0.44	2.04	─	0.46
	500	0.69	0.27	2.55	─	0.42
KL³Cu	100	0.77	0.19	4.05	─	0.58
	250	0.81	0.14	5.78	─	0.67
	500	0.64	0.38	1.68	─	0.26
KL³Pt	100	0.22, 0.65	0.37, -0.32	1.75	─	0.28
	250	0.21, 0.66	0.36, -0.31	1.83	─	0.30

500

0.30, 0.71

0.39, -0.43

1.82

─

0.32

The electrochemical properties of the α-Keggin heteropolymolybdate compound were investigated in the range of -2.0-(+2.0) V and it was determined that it had alternating redox pairs at some potentials. The redox process of the POM compound is metal-centered [16]. Three anodic and three cathodic peak potentials were observed in this compound. The redox properties of the POM based compounds KL¹-KL³ and their metal complexes were studied in the -1.5-(+1.5) V range. The POM based compounds have two anodic and one cathodic peak potential in the range of -0.13-1.07 and 0.27-0.54 V, respectively. With the increase of scanning speed in positive direction scanning, it causes the anodic peak potential values to increase more positively. On the other hand, the cathodic peak potential values decrease with the increase of scanning speed. In these compounds, the redox processes are irreversible and metal-centered. The Cu²⁺ complexes of the compounds KL¹-KL³ have one anodic peak potential in the 0.71-0.88 V range. Similarly, the cathodic peak potentials of the Cu²⁺ complexes are also one in the -0.06-0.38 V. When the E_paand E_pc values of the Cu²⁺ complexes are compared with the values of KLⁿ compounds, it can be said that the redox processes in the Cu²⁺ complexes are irreversible and in the form of reduction of the Cu²⁺ ion. This redox process can be represented as follows:

The KL²Pt and KL³Pt complexes show the similar electrochemical behaviours in the range of 100-500 mV/s scan rates. That is, the complexes have two E_pa and two E_pc potentials in the range of 0.21-0.71 V and -0.43-0.39 V, respectively. On the other hand, the KL¹Pt complex has three anodic and two cathodic peak potentials in the range of 0.14-0.94 V and -0.37-0.56 V, respectively. When the electrochemical values of Keggin-based POM compounds (KL² and KL³) and KL²Pt and KL³Pt complexes are compared, it is seen that the electrochemical behavior is Pt-centered and as irreversible redox process. Because the electrochemical values in these complexes have shifted towards more negative regions. On the other hand, while the redox process in the KL¹Pt complex is Pt-centered in the range of -0.37-0.68 V, the redox process in the 0.94-0.46 V range is POM-centered. All redox processes for this complex are irreversible. The reduction of the KL¹Pt complex is as follows:

MALDI-TOF method was used for the characterization of a-Keggin POM-based compounds KL¹-KL³ and their Cu²⁺ and Pt²⁺ transition metal complexes. The mass spectral data obtained for the compounds are given in the supplementary file. The MALDI-TOF spectra of the KL¹ and its metal complexes were shown in Fig. 6a-c. No molecular ion peaks could not be obtained for any compound that mass spectra were examined. In the mass spectrum of the compound KL¹, the observed peak at m/z 2.663,38 can be attributed to the fragmentation pattern [M+DHB+Na-3H]⁺. In the spectra of the compounds KL¹ and KL², the peaks at 2.648,803 and 2.644,442 come from the fragmentation patterns [M+DHBA+5H]⁺ and [M+DHBA]⁺, respectively. In the spectra of the POM based Cu²⁺ and Pt²⁺ metal complexes, the molecular ion peaks [M]⁺ belonging to the complexes were not observed. In the Fig. 6b-c, the peaks at the m/z 2.907,790 and 2.933,905 can be attributed to the fragmentation patterns of the KL¹Pt and KL¹Cu complexes, respectively. When the mass spectra of POM-based Cu²⁺ and Pt²⁺ transition metal complexes were examined, better information about the structure has obtained from the spectra of Cu²⁺ complexes.

Thermogravimetric (TG) studies for the KL¹-KL³ and their Cu²⁺ and Pt²⁺ transition metal complexes were done in the nitrogen atmosphere with a heating rate of 10 °C min⁻¹ from 27 °C to 850 °C. The TG curves of the Cu²⁺ complexes have given in Fig. 7. The TG curves of other compounds have given in supplementary file as Fig. S4. The thermal properties of the ethanol solvated α-Keggin heteropolymolybdate compound, which was synthesized and structurally characterized before, were investigated and it was determined that the compound decomposed in four steps [16]. When the thermal curves of the Cu²⁺ complexes in Fig. 7 are examined, it is seen that the complexes decompose in four steps. In the first step, the adsorbed H₂O molecules in the compounds are removed in the temperature range of 50-80 °C. The thermal decomposition in the second step starts at 120 °C and ends at around 210 °C. In this step, the removal of H₂O and Cl^- ions bound to Cu²⁺ ions coordinated to imine compounds takes place. The third step takes place in the temperature range of 386-482 °C, and in this temperature range, the organic ligands HL¹-HL³ are removed from POM-based compounds KL¹-KL³. The last step starts at 535 °C and continues up to 700 °C. Metal oxides such as MoO₂, MoO₃ and CuO have formed in this step. When the thermal curves of Pt²⁺ and Cu²⁺ complexes were compared, it was determined that Pt²⁺ complexes had higher thermal stability than Cu²⁺ complexes.

The antimicrobial properties of POM-based compounds and the transition metal complexes of these compounds were investigated and the results are given in Table S in the supplementary file. All compounds (in 1000 and 2000 ppm concentration) were tested in vitro against to two fungi and five bacterial species by the disc diffusion method. The all compounds (except KL²Cu) showed no inhibition the bacteria tested. Only the compound KL²Cu (in 2000 ppm) showed antibacterial activity (10 mm 100 µL^-1 inhibition zone) to Staphylococcus aureus ATCC 6538 (except for other bacteria tested). Surprisingly the all compounds showed inhibition zones the fungi tested. The results indicated that the all compounds have shown antifungal activity in the range of 10-29 mm 100 µL^-1 inhibition zone to the Penicillium spp. But the all compounds have no shown antifungal activity to Aspergillus niger. Some of the compounds (KL¹Cu, KL¹Pt, KL²Cu, KL³Cu (including 2000 ppm)) have shown antifungal activity in the range of 8-20 mm 100 µL^-1 inhibition zone to the Aspergillus niger. Notable situation here, KL¹Pt (including 2000 ppm) showed the highest antifungal activity against to Penicillium spp. (inhibition zone 29 mm 100 µL^-1). There are differences in the antibacterial and antifungal effects of microorganisms to the compounds, due to the cell wall structure, species and subspecies.

In this study, the organic-inorganic compounds KL¹-KL³ were synthesized from the reaction of azo-imine ligands with amino bis(ethylenehydroxy) ends and α-Keggin POM compound and characterized by spectroscopic methods. The Cu²⁺ and Pt²⁺ metal complexes of the compounds KL¹-KL³ were also obtained and characterized by the FTIR, MALDI-TOF, UV-Vis and photoluminescence methods. The electrochemical and thermal properties of all compounds were investigated. The KLⁿPt complexes from the organic inorganic compounds show the multi-redox processes. But, the redox process of all compounds is irreversible at all potentials. The compounds have the LMCT bands in their UV-Vis spectra. The thermal stabilities of the KLⁿPt complexes are higher than the complexes KLⁿCu. The biological activities of the compounds against bacteria and fungi were investigated and only KL²Cu compound has activity at 2000 ppm against staphylococcus aureus. Many bacteria produce beta-lactamases. These enzymes hydrolyse the beta-lactam ring of the antibiotics, which makes the drug ineffective. On the other hand, all compounds showed activity against the penicillium spp that has mesophilic property.

Acknowledgments

We are grateful to The Scientific & Technological Research Council of Turkey (TUBITAK) (Project number: 115Z065) for the support of this research.

Author Contributions S.A.G. and F.T. did all experimental studies, M.K. and S.T. did the antimicrobial activity studies, M.T. did the study design and wrote the main manuscript text

Declaration

Funding: This work is funded by Scientific & Technological Research Council of Turkey (TUBITAK) (Project number: 115Z065).

Conflict of interest: The authors have no financial or proprietary interests in any material discussed in this article.

Data availability All data generated or analysed during this study are included in this published article.

Ethics approval and consent to participate: The manuscript contains our original work and submitted to only this journal. We will not submit this work elsewhere until a decision made. All authors in the manuscript contributed to this work.

Consent for publication: All authors have authorized the submission of this manuscript.

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Polyoxometalate based hybrids: Synthesis of metal complexes and investigation of their electrochemical, photophysical and biological properties

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