Photochemical reactions of group VIB metal carbonyls with heterocyclic Schiff bases derived from 4-amino -3-hydrazino-5-mercapto-1,2,4-triazole

The new complexes, M(CO)₅(Schiff base) [M?=?Cr; 1, Mo; 2, W; 3, Schiff base?=?4-salicylidenamino-3-hydrazino-5-mercapto-1,2,4-triazole, SAHMT, a; 4-(2-hydroxynaphthylidenamino)-3-hydrazino-5-mercapto-1,2,4-triazole, 2HNAHMT, b; 4-(3-hydroxybenzylidenamino)-3-hydrazino-5-mercapto-1,2,4- triazole, 3HBAHMT, c; 4-(4-hydroxybenzylidenamino)-3-hydrazino-5-mercapto-1,2,4- triazole, 4HBAHMT, d; 4-(5-bromosalicylidenamino)-3-hydrazino-5-mercapto-1,2,4-triazole, 5BrSAHMT, e; were synthesized by photochemical reaction of metal carbonyls M(CO)₆ (M?=?Cr, Mo, W) with new heterocyclic Schiff bases derived from 4-amino-3-hydrazino-5-mercapto-1,2,4-triazole, a–e. The ligands and complexes have been characterized by elemental analysis, EI-mass spectrometry, FT-IR, ¹H and ¹³C-{¹H}-NMR spectroscopy. The spectroscopic studies show that Schiff bases, a–e, are monodentate and coordinate via azomethine N donor to the central metal atom in M(CO)₅(Schiff base) (M?=?Cr, Mo, W).     

Synthetic, structural and biological studies of organotin(IV) complexes of schiff bases derived from pyrrol-2-carboxaldehyde

Some new organotin(IV) complexes having general formulae R₂MCl[L] and R₂M[L]₂ were synthesized by the reactions of Me₂MCl₂ with Schiff bases [5-Mercapto-4-(pyrrolcarboxalideneamino)-s-triazole, 5-Mercapto-3-methyl-4-(2-pyrrolcarboxalideneamino)- s-triazole, 3-Ethyl-5-mercapto-4-(2-pyrrolcarboxalideneamino)-s-triazole] in 1:1 and 1:2 molar ratios. All of the compounds were characterized by elemental analysis, molar conductance, IR, UV, ¹H, ¹³C and ¹¹⁹Sn NMR spectral studies. The IR and ¹H NMR spectral data suggest the involvement of azomethine nitrogen in coordination with the central metal atom. With the help of the above-mentioned spectral studies, penta and hexacoordinated environments around the central metal atoms in the 1:1 and 1:2 complexes, respectively, have been proposed. Finally, the free ligands and their metal complexes were tested in vitro against some pathogenic bacteria and fungi to assess their antimicrobial properties.     

New complexes of Ni(II) and Cu(II) with Schiff bases functionalised with 1,3,4-thiadiazole: spectral,magnetic, biological and thermal characterisation

Schiff bases obtained by the condensation of 2-amino-5-mercapto-1,3,4-thiadiazole with 2,4-pentandione or 1-phenyl-1,3-butandione were synthesized and characterized in order to obtain polydentate ligands HL¹ and HL², respectively. The complexes with these ligands of the type M(L)Cl·nH₂O [(1) M:Ni, L:L¹, n = 0.5; (3) M:Ni, L:L², n = 0.5]; [(2) M:Cu, L:L¹, n = 1; (4) M:Cu, L:L², n = 0] were also synthesized and characterized. The modifications evidenced in IR spectra of complexes were correlated with the presence of monodeprotonate Schiff bases. The electronic spectra display the characteristic pattern of square-planar stereochemistry. The in vitro qualitative and quantitative antimicrobial activity assays showed that the new complexes exhibited variable antimicrobial activity. The thermal analyses have evidenced the thermal intervals of stability and also the thermodynamic effects that accompany them. Schiff bases and complexes have a similar thermal behaviour. Processes as water elimination, melting, chloride anion removal as well as oxidative degradation of the organic ligands were observed.     

Synthesis, physicochemical investigation and biological studies of Zinc(II) complexes with 1,2,4-triazole Schiff bases

A series of metal complexes of Zn(II) have been synthesized with newly synthesized biologically active 1,2,4-triazole Schiff bases derived from the condensation of 3-substituted-4-amino-5-mercapto-1,2,4-triazole with 8-formyl-7-hydroxy-4-methylcoumarin. The structure of the complexes has been proposed in the light of elemental analyses, spectroscopic data (IR, UV-Vis, ¹H NMR and FAB-mass), thermal studies. Electrochemical study of the complexes is also reported. All the complexes are soluble to limited extent in common organic solvents but soluble to larger extent in DMF and DMSO and are non-electrolytes in these two solvent. All these Schiff bases and their complexes have also been screened for their antibacterial (Escherichia. coli, S. aureus, S. pyogenes, P. aeruginosa and Salmonella typhi) and antifungal activities (Aspergillus niger, Aspergillus flavus and cladosporium) by MIC method. The brine shrimp bioassay was also carried out to study their in vitro cytotoxic properties.     

Synthesis and spectroscopic studies of new organotin(IV) complexes with tridentate N- and O-donor Schiff bases

The Schiff bases H₂L¹ and H₂L² have been prepared by the reaction of 2-amino-4-chlorophenol with pyrrole-2-carbaldehyde and 2-hydroxy-1-naphtaldehyde, respectively, and HL³ from reaction of 2-(aminomethyl)pyridine with 2-hydroxy-1-naphtaldehyde. Organotin complexes [SnPh₂(L¹)] (1), [SnPh₂(L²)] (2), [SnMe₂(L²)] (3) and [SnPhCl₂(L³)] (4) were synthesized from reaction of SnPh₂Cl₂ and SnMe₂Cl₂ with these Schiff bases. The synthesized complexes have been investigated by elemental analysis and FT-IR, ¹H NMR and ¹¹⁹Sn NMR spectroscopy. In complexes the Schiff bases are completely deprotonated and coordinated to tin as tridentate ligands via phenolic oxygen, pyrrolic, and imine nitrogens in 1, two phenolic oxygens and imine nitrogen in 2 and 3, and phenolic oxygen, imine and pyridine nitrogens in 4. The coordination number of tin in 1, 2, and 3 is five and in 4 is six.     

Complexes of titanium(IV), vanadium(IV) and tin(IV) with schiff bases derived from 2-(2-aminophenyl)benzimidazole

Summary New titanium(IV), vanadium(IV) and tin(IV) complexes with Schiff bases derived from 2-(2-aminophenyl)benzimidazole with benzaldehyde (L₁) and salicylaldehyde (L₂) have been prepared and have the general formulae MX₄ · 2L (M = Ti, V or Sn; L = L₁ or L₂; X = Cl or Br).All the complexes have been characterized by elemental analyses, magnetic measurements, e.p.r., electronic and i.r. spectral studies. The results show that the Schiff bases act as monodentate ligands. Tentative structures for the complexes are suggested.     

Synthesis,spectral, thermal,solid-state DC electrical conductivity and biological studies of Co(II) complexes with Schiff bases derived from 3-substituted-4-amino-5-hydrazino-1,2,4-triazole and substituted salicylaldehydes

A series of Co(II) complexes have been synthesized with Schiff bases derived from 3-substituted-4-amino-5-hydrazino-1,2,4-triazole and substituted salicylaldehydes. These complexes are insoluble in water but more soluble in DMF and DMSO. The complexes have been characterized by elemental analyses, spectral (IR, UV–Vis, ¹H-NMR, FAB-mass, fluorescence), magnetic, thermal, solid-state DC electrical conductivity and molar conductance data. The molar conductivity values indicate that they are non-electrolytes. The elemental analyses of the complexes suggest a stoichiometry of the type Co · L1–L16 · 2H₂O. The complexes have been considered as semiconductors on the basis of the solid-state DC electrical conductivity data. Fluorescence spectra of one Schiff base and its complex were investigated in various solvents and some of the Schiff bases and their complexes were evaluated for their antimicrobial activities.     

Synthesis, spectroscopic, electrochemical and luminescence studies of ruthenium (II) polypyridyls containing multifunctionalized 1,2,4-triazole as co-ligand

Ruthenium (II) 2,2′-bipyridyl and 1,10-phenanthroline complexes with 4-amino-3-hydrazino-5-mercapto-1,2,4-triazole (LH₂) as co-ligand were synthesised and characterized by elemental analysis, IR, UV/Vis,¹H NMR spectra and FAB-mass data. The electrochemical and luminescent properties of the complexes were also studied.     

Magnetic and spectral properties of nickel(II) complexes of ligands containing O,N, and S donor atoms

Summary Several complexes of nickel(II) with Schiff bases derived from 3-substituted-4-amino-5-mercapto-1,2,4-triazoles (H₂L) have been synthesised. The complexes have a stoichiometry NiL · 2H₂O. The bonding of the ligands has been inferred from i.r. spectroscopy. The ligands preserve the thiol in the complexes. Magnetic moments obtained at room temperature and electronic spectra are consistent with octahedral geometry.     

Synthesis,characterization, DNA cleavage,and in-vitro antimicrobial studies of Co(II), Ni(II), and Cu(II) complexes with Schiff bases of coumarin derivatives

A series of Co(II), Ni(II), and Cu(II) complexes ML?·?3H₂O have been synthesized with Schiff bases derived from 3-substituted-4-amino-5-mercapto-1,2,4-triazole and 5-formyl-6-hydroxy coumarin. The complexes are insoluble in common organic solvents but soluble in DMF and DMSO. The measured molar conductance values in DMF indicate that the complexes are non-electrolytes. In view of analytical, spectral (infrared, UV-Vis, ESR, TG, and FAB-mass), and magnetic studies, it has been concluded that all the metal complexes possess octahedral geometry in which ligand is coordinated to metal through azomethine nitrogen, phenolic oxygen, and sulfur via deprotonation. The Schiff bases and their complexes have been screened for antibacterial (Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa, and Salmonella typhi) and antifungal activities (Aspergillus niger, Aspergillus flavus, and Cladosporium) by the minimum inhibitory concentration method. DNA cleavage is studied by agarose gel electrophoresis.     

Synthesis, structural characterization and electrochemical studies of nickel(II), copper(II) and cobalt(III) complexes of some ONS donor ligands derived from thiosemicarbazide and S-alkyl/aryl dithiocarbazates

Four tridentate ONS ligands, namely 2-hydroxyacetophenonethiosemicarbazone (H₂L¹), the 2-hydroxyacetophenone Schiff base of S-methyldithiocarbazate (H₂L²), the 2-hydroxy-5-nitrobenzaldehyde Schiff base of S-methyldithiocarbazate (H₂L³), and the 2-hydroxy-5-nitrobenzaldehyde Schiff base of S-benzyldithiocarbazate (H₂L⁴), and their complexes of general formula [Ni(HL¹)₂], [ML] (M?=?Ni^II or Cu^II; L?=?L¹, L², L³ and L⁴), [Co(HL)(L); L?=?L¹, L², L³ and L⁴] and [ML(B)] (M?=?Ni^II or Cu^II; L?=?L² and L⁴; B?=?py, PPh₃) have been prepared and characterized by physico-chemical techniques. Spectroscopic evidence indicates that the Schiff bases behave as ONS tridentate chelating agents. X-ray crystallographic structure determination of [NiL²(PPh₃)] and [CuL⁴(py)] indicates that these complexes have an approximately square-planar structure with the Schiff bases acting as dinegatively charged ONS tridentate ligands coordinating via the phenoxide oxygen, azomethine nitrogen and thiolate sulfur atoms. The electrochemical properties of the complexes have been studied by cyclic voltammetry.     

Synthesis,physico-chemical and biological studies on oxovanadium(IV) derivatives of mercaptotriazoles

Summary Complexes of 3-methyl- or 3-ethyl-4-amino-5-thiolato-1,2,4-triazole (LH) and its Schiff base derivatives with oxovanadium(IV), of the types [VOL₂(H₂O)], [VOL₂-(H₂O)] and [VOL(H₂O)₂] (where LH = Schiff bases derived from condensation of LH with benzaldehyde, 2-chlorobenzaldehyde, 4-methoxybenzaldehyde or acetophenone; LH₂ = Schiff bases derived from condensation of LH with salicylaldehyde or o-hydroxyacetophenone) have been prepared and characterized by elemental analyses, electrical conductance, magnetic moments and spectral data. The thermal behaviour of selected complexes was investigated by t.g., d.t.g. and d.s.c. techniques. The antifungal and antiviral activities of the Schiff bases and their corresponding complexes were also investigated.Author to whom all correspondence should be directed.     

Synthesis,spectral, thermal,solid state d.c. electrical conductivity and biological studies of Co(II), Ni(II) and Cu(II) complexes with 3-substituted-4-amino (indole-3-aldehydo)-5-mercapto-1,2,4-triazole Schiff bases

A series of cobalt(II), nickel(II) and copper(II) complexes have been synthesized with Schiff bases derived from 3-substituted-4-amino-5-mercapto-1,2,4-triazole and indole-3-aldehyde in ethanol. These complexes have been characterized by elemental analyses, magnetic, spectroscopic (IR, UV-Vis, H-NMR, ESR, FAB-mass), thermal, electrochemical (CV) and solid state d.c. electrical conductivity studies. The elemental analyses confirm 1 : 2 stoichiometry of the type ML₂·2H₂O (M = Co/Ni) and ML₂ (M=Cu). The complexes are colored solids and non-electrolytes in DMF and DMSO. Magnetic and spectral data suggest octahedral geometry for Co(II) and Ni(II) complexes and square-planar geometry for Cu(II) complexes. The presence of coordinated water in Co(II) and Ni(II) complexes was confirmed by thermal and IR data of the complexes. The complexes are insoluble in water and common organic solvents and decompose at higher temperature. All these ligands and their complexes have also been screened for antibacterial (Bacillus cereus, Staphylococcus aureus, Escherichia coli and Pseudomonas aeruginosa) and antifungal activities (Aspergillus niger and Aspergillus fumigates) by the cup plate method.     

Coordination behaviours of new (bidentate <Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">O</Emphasis>-chelating) Schiff bases towards copper(II) and nickel(II) metal ions: synthesis,characterization, antimicrobial,antioxidant, and DFT studies

Two Schiff bases, HL₁ and HL₂, were synthesized in two different reactions involving 2-hydroxynaphthaldehyde with 2-amino-6-methylbenzothiazole and 2-amino-6-florobenzothiazole respectively. Copper(II) and nickel(II) complexes of the Schiff bases were subsequently prepared in 1:1 metal-to-ligand stoichiometric reactions. The compounds were characterized extensively by ¹H NMR, ¹³C NMR, Dept-90, UV–Vis, and IR spectroscopic techniques, magnetic susceptibility, TGA, DTG, and molar conductivity analysis. The spectroscopic results confirm bidentate nature of the Schiff bases and a four coordinate geometry for all the complexes: [CuL₁ClH₂O], [NiL₁ClH₂O], [Cu(L₂)₂], and [NiL₂ClH₂O]. Quantum chemical studies gave fully optimized geometries of the Schiff bases and metal complexes using the 6-31+g(d,p) basis set. The compounds were studied for their in vitro antibacterial activities against some selected Gram-positive and Gram-negative bacteria, using agar well diffusion. The metal complexes exhibited better antibacterial activities compared to the free ligand due to the effects of chelation, which improved the lipophilicity. Furthermore, the antioxidant potentials of the compounds were ascertained using DPPH radical scavenging and ferrous chelating assay. The copper complexes had the best antioxidant properties of all the tested compounds. The results of the biological analysis were in agreement with the theoretical data from quantum chemical calculations. The study presented biologically active coordination compounds with benzothiazole moiety that could be used as compounds of interest in the drug discovery processes.     

Coordination Chemistry and Spectroscopic Properties of Some Diorganotin(IV) Complexes with S-Donor Schiff Base Ligands

Abstract

Schiff bases S-benzyl- and S-methyl-β-N-(2-hydroxyphenyl)methylene dithiocarbazate (H₂L¹ and H₂L², respectively) and S-benzyl- and S-methyl-β-N-(2-chlorophenyl)methylenedithiocarbazate (HL³ and HL⁴, respectively) were prepared. Then organotin(IV) complexes [SnPh₂(L¹)] (1), [SnMe₂(L¹)] (2), [SnPh₂(L²)] (3), [SnMe₂(L²)] (4), [SnPh₂Cl(L³)] (5), and [SnPh₂Cl(L⁴)] (6) were obtained from the reaction of Schiff bases with SnR₂Cl₂ (R = Ph and Me). The synthesized complexes have been investigated by elemental analysis and IR, ¹H NMR, and ¹¹⁹Sn NMR spectroscopy. Spectroscopic studies show that, in complexes 1–4, the Schiff base acts as a tridentate dianionic ligand and coordinates through the thiol group, imine nitrogen, and phenolic oxygen. The coordination number of tin is five. In complexes 5 and 6, the ligand is monoanionic and unidentate, and coordinated only via the thiol group, and the azomethine nitrogen is not involved in coordination to tin. Therefore the coordination number of tin is four.

GRAPHICAL ABSTRACT      

Synthesis,structures, and urease inhibition of nickel(II), zinc(II), and cobalt(II) complexes with similar hydroxy-rich Schiff bases

Four new nickel(II), zinc(II), and cobalt(II) complexes, [Zn(L¹)₂]?·?H₂O (1), [Ni(L¹)₂]?·?H₂O (2), [Ni(L²)₂] (3), and [Co(L³)₂]?·?H₂O (4), derived from hydroxy-rich Schiff bases 2-{[1-(5-chloro-2-hydroxyphenyl)methylidene]amino}-2-methylpropane-1,3-diol (HL¹), 2-{[1-(2-hydroxy-3-methoxyphenyl)methylidene]amino}-2-ethylpropane-1,3-diol (HL²), and 2-{[1-(5-bromo-2-hydroxyphenyl)methylidene]amino}-2-methylpropane-1,3-diol (HL³) have been synthesized and characterized by elemental analyses, infrared spectroscopy, and single-crystal X-ray determination. Each metal in the complexes is six-coordinate in a distorted octahedral coordination. The Schiff bases coordinate to the metal atoms through the imino N, phenolate O, and one hydroxyl O. In the crystal structures of HL¹ and the complexes, molecules are linked through intermolecular O–H···O hydrogen bonds, forming 1-D chains. The urease inhibitory activities of the compounds were evaluated and molecular docking study of the compounds with the Helicobacter pylori urease was performed.     

Synthesis, spectral characterization, biological and fluorescence studies of lanthanum(III) complexes with 3-substituted-4-amino-5-hydrazino-1,2,4-triazole Schiff bases

Some lanthanum(III) complexes have been synthesized by reacting lanthanum(III) nitrate with Schiff bases derived from 3-substituted-4-amino-5-hydrazino-1,2,4-triazole and substituted salicylaldehydes. All these complexes are soluble in DMF and DMSO and the low molar conductance values observed indicates that they are non-electrolytes. Elemental analyses suggest the complexes have 1:1 stoichiometry of the type La · L · NO₃ · H₂O, and they were characterized further by spectral and thermogravimetric methods. Fluorescence spectra of one of the representative Schiff bases (II) and its lanthanum(III) complex were investigated in various solvents; the complexes were evaluated for their biological activity.     

Catalytic activity of a zirconium(IV) Schiff base complex in facile and highly efficient synthesis of indole derivatives

Eight Schiff base compounds were prepared by condensation of 1-amino-2-propanol with different benzaldehydes in water. One of the Schiff bases, (z)-N-bezylidene-2-hydroxypropane-1-amine (HL¹), was used as a bidentate ligand for preparation of a zirconium complex (Zr(L¹)₂Cl₂). The complex has been used as a catalyst for efficient synthesis of wide variety of indole derivatives in EtOH under mild conditions. The turnover number and reusability of the catalyst indicate that it has high efficiency and is fairly stable under the reaction conditions.     

Triorganotin(IV) Derivatives of Bidentate Schiff Bases: Synthesis and Spectral Studies

Abstract

Reaction of tri-n-butyl tin(IV) chloride with the sodium salt of Schiff bases [salicylidene-2-aminopyridine (sapH), salicylidene-2-amino-4-picoline (sapicH), salicylidene-2-methyl-1-aminobenzene (o-smabH), salicylidene-4-methyl-1-aminobenzene (p-smabH), salicylidene-1- aminobenzene (sabH), salicylidene-3-nitro-1-aminobenzene (snabH)] in MeOH-C₆H₆ mixture in 1:1 molar ratio produced complexes of the type [Buⁿ ₃Sn(sb)] (where sb = Schiff bases). All complexes obtained were characterized by elemental analysis (C, H, N, and Sn), infrared (IR), nuclear magnetic resonance (NMR; ¹H, ¹³C, and ¹¹⁹Sn), and TOF-MS spectroscopic studies. These complexes were found to be monomeric, colored viscous liquids and are soluble in polar solvents (methanol, ethanol, DMSO, and DMF). On the basis of ¹¹⁹Sn NMR observations, a five coordination geometry around tin(IV) atom in these complexes is proposed tentatively.     

Schiff base supported mononuclear organotin(IV) complexes: Syntheses,structures and fluorescence cell imaging

Three mononuclear organotin(IV) complexes supported by Schiff bases have been synthesized. The complexes [(C₆H₅)₂Sn(L)] ( 1 ), [(t‐Bu)₂Sn(L)] ( 2 ) and [(t‐Bu)₂Sn(L')] ( 3 ) (L, L' = deprotonated Schiff bases) were obtained in good yield by the reaction of Schiff bases H ₂ L or H ₂ L′ with corresponding diorganotin dichlorides respectively. All newly synthesized complexes were characterized by means of FT‐IR spectroscopy, elemental analysis and multinuclear (¹H, ¹³C and ¹¹⁹Sn) NMR spectroscopy. In addition, single crystal X‐ray diffraction analyses were employed to establish the solid state molecular structures of these complexes. The structures of 1 – 3 reveal that all complexes are mononuclear with a five‐coordinated tin(IV) centre in it. The absorption and emission properties of all complexes have been investigated. Moreover, cytotoxicity and fluorescence cell imaging studies of theses complexes have been performed.