EPR and electronic spectral studies on Co(II), Ni(II) and Cu(II) complexes with a new tetradentate [N4] macrocyclic ligand and their biological activity

Cobalt(II), nickel(II) and copper(II) complexes having the general composition M(L)X2 (where M = CO(II), Ni(II) and Cu(II), L = ligand, i.e. 3,4,12,13-tetraketo-2,5,11,14,19,20-hexaazatricyclo[13.3.1.1(6-10)]cosane; 1(19),6,8,10(20),15,17-hexaene and X stands for Cl-; NO3- and SO42-), have been prepared. The structure of the complexes has been elucidated by elemental analysis, molar conductance, magnetic susceptibility measurements, mass, IR, electronic and EPR spectral studies. The magnetic moment measurements of the complexes indicate that the metal ion is in high-spin state. On the basis of IR, electronic and EPR spectral studies an octahedral geometry was assigned for Co(II) and Ni(II) complexes whereas tetragonal geometry for Cu(II) complexes. This ligand and its complexes were also screened against bacteria and pathogenic fungi in vitro.     

The stereochemical diversity of a new SNONS binucleating ligand towards 3d metal ions

A new binucleating ligand containing phenoxide as an endogenous bridging group, 2,6-diformyl-p-cresol bis(2-furanthiocarboxyhydrazone) and its binuclear Co(II), Ni(II), Cu(II) and Zn(II) complexes with chloride ion as an exogenous bridge, have been obtained. The complexes were characterized by elemental analysis, molar conductivities, magnetic moment measurements at room temperature, electronic, IR, 1H-NMR, EPR, FAB spectral studies and thermal data. The copper complex assumes a tetranuclear structure composed of two binuclear units related by a center of symmetry. The dimeric nature of copper(II) complex is supported by FAB. This complex is EPR silent. Room temperature magnetic moment reveals the operation of a significant antiferromagnetic spin exchange between the metal centers. Ligand and its copper and zinc complexes exhibit fluorescence at room temperature in DMF. All the compounds show an appreciable antimicrobial activity.     

Stereochemistry of new nitrogen containing heterocyclic compounds.; X. Supramolecular structures and stereochemical versatility of polymeric complexes

New polymeric complexes of Cu(II), Co(II), Ni(II) and UO2(II) with 5-(2(1)-carboxyphenylazo)-8-hydroxyquinoline (LH2) have been prepared and characterized on the basis of analytical, magnetic, 1H NMR, EPR and electronic spectral studies. Tentative structures for the polymeric complexes are proposed. The important infrared (IR) bands and the main 1H NMR signals are assigned and discussed relative to the molecular structure. EPR spectrum of copper(II) complex has been studied with a view to assigning their stereochemistries. Various EPR parameters have been calculated. Each metal has six-coordinates in an octahedral environment. The ligand acts as a dibasic (bis-bidentate chelating agent coordinating through CN, N=N, COOH and OH groups by replacement of a proton from the two latter groups. Considerable interest has also been focused on the synthesis of the azo compounds and its polymeric metal complex due to its wide potential applications. The thermal decomposition behavior of the complexes is also discussed.     

Spectroscopic, redox and biological activities of transition metal complexes with ons donor macrocyclic ligand derived from semicarbazide and thiodiglycolic acid

A novel macrocyclic Schiff base ligand (2,5,9,12,14,18-hexaoxo-7,16-dithia-1,3,4,10,11,13-hexaazacycloocta-decane (H6L) with N4S2 coordinating sites was prepared by the reaction of the semicarbazide and thiodiglycolic acid. The transition metal complexes with macrocyclic ligand were synthesized and characterized by elemental analyses, magnetic susceptibility measurements, molar conductance, IR, electronic, and EPR spectral studies. Mass, 1H NMR and IR spectral techniques suggest the structural features of macrocyclic ligand. Magnetic and electronic spectral studies suggest an octahedral geometry of complexes. Electrochemical behaviour of cobalt, nickel and copper complexes were determined by cyclic voltammetry. The cyclic voltammogram of the copper complex at room temperature shows a quasi-reversible peaks for Cu(III)-->Cu(II) and Cu(II)-->Cu(I) couples. The macrocyclic ligand and its complexes show growth inhibitory activity against pathogenic bacteria and plant pathogenic fungi A. niger, A. alternata and P. variotii. Most of the complexes have higher activities than that of free ligand.     

Synthesis, spectral characterization and biological activities of Mn(II) and Co(II) complexes with benzyloxybenzaldehyde-4-phenyl-3-thiosemicarbazone

Mn(II) and Co(II) complexes of benzyloxybenzaldehyde-4-phenyl-3-thiosemicarbazone have been synthesized and characterized by the investigations of electronic and EPR spectra and X-ray diffraction. Based on the spectral studies, an octahedral geometry is assigned for the Mn(II) and Co(II) complexes. X-ray powder diffraction studies reveal that Mn(II) and Co(II) complexes have triclinic crystal lattices. The unit cell parameters of the Mn(II) complex are a=11.0469 ?, b=6.2096 ?, c=7.4145 ?, α=90.646°, β=95.127°, γ=104.776°, V=489.7 ?(3) and those of Co(II) complex are a=9.3236 ?, b=10.2410 ?, c=7.8326 ?, α=90.694°, β=99.694°, γ=100.476°, V=724.2 ?(3). When the free ligand and its metal complexes are subjected to antibacterial activity, the metal complexes are proved to be more active than the ligand. However with regard to in vitro antioxidant activity, the ligand exhibits greater antioxidant activity than its metal(II) complexes.     

Synthesis, spectroscopic characterization, electrochemical behaviour, reactivity and antibacterial activity of some transition metal complexes with 2-(N-salicylideneamino)-3-carboxyethyl-4,5-dimethylthiophene

Mn(II), Fe(II), Co(II), Ni(II), Cu(II) and Zn(II) complexes with a potentially tridentate Schiff base, formed by condensation of 2-amino-3-carboxyethyl-4,5-dimethylthiophene with salicylaldehyde were synthesized and characterized on the basis of elemental analyses, molar conductance values, magnetic susceptibility measurements, UV-vis, IR, EPR and NMR spectral data, wherever possible and applicable. Spectral studies reveal that the free ligand exists in a bifunctionally hydrogen bonded manner and coordinates to the metal ion in a tridentate fashion through the deprotonated phenolate oxygen, azomethine nitrogen and ester carbonyl group. On the basis of electronic spectral data and magnetic susceptibility measurements, suitable geometry has been proposed for each complex. The EPR spectral data of the Cu(II) complex showed that the metal-ligand bonds have considerable covalent character. The Ni(II) complex has undergone facile transesterification reaction when refluxed in methanol for a lengthy period. X-ray diffraction studies of Cu(II) complex showed that the complex has an orthorhombic crystal lattice. In view of the biological activity of thiophene derivatives, the ligand and the complexes were subjected to antibacterial screening. It has been observed that the antibacterial activity of the ligand increased on chelation with metal ion.     

Spectroscopic characterization of chromium(III), manganese(II) and nickel(II) complexes with a nitrogen donor tetradentate, 12-membered azamacrocyclic ligand

The complexes of Cr(III), Mn(II) and Ni(II) were synthesized with macrocyclic ligand i.e. 5,11-dimethyl-6,12-diethyl-dione-1,2,4,7,9,10-hexazacyclododeca -1,4,6,10-tetraene. The ligand (L) was prepared by [2+2] condensation reaction of 2,3-pentanedione and semicarbazide hydrochloride. These complexes were found to have the general composition [Cr(L)X(2)]X and [M(L)X(2)] (where M=Mn(II) and Ni(II); X=Cl(-), NO(3)(-), (1/2)SO(4)(2-), NCS(-) and L=ligand [N(6)]). The ligand and its transition metal complexes were characterized by the elemental analysis, molar conductance, magnetic susceptibility, mass, IR, electronic and EPR spectral studies. On the basis of IR, electronic and EPR spectral studies, an octahedral geometry has been assigned for these complexes except sulphato complexes which are of five coordinated geometry.     

Synthesis,spectroscopic characterization,electrochemical behaviour and thermal decomposition studies of some transition metal complexes with an azo derivative

Complexes of manganese(II), cobalt(II), nickel(II), copper(II) and zinc(II) with a novel heterocyclic azo derivative, formed by coupling diazotized 2-amino-3-carbethoxy-4,5-dimethylthiophene with acetylacetone were synthesized and characterized on the basis of elemental analyses, molar conductance, magnetic susceptibility measurements, UV–vis, IR, ¹H NMR and EPR spectral data. Spectral studies revealed that the ligand existed in an internally hydrogen bonded azo-enol form rather than the keto-hydrazone form and coordinated to the metal ion in a tridentate fashion. Analytical data revealed that all the complexes exhibited 1:1 metal–ligand ratio. On the basis of electronic spectral data and magnetic susceptibility measurements, suitable geometry was proposed for each complex. The nickel(II) complex has undergone facile transesterification reaction when refluxed in methanol for a long period. The ligand and the copper(II) complex were subjected to X-ray diffraction study. The electrochemical behaviour of copper(II) complex was investigated by cyclic voltammetry. The thermal behaviour of the same complex was also examined by thermogravimetry.     

EPR, IR and electronic spectral studies on Mn(II), Co(II), Ni(II) and Cu(II) complexes with a new 22-membered azamacrocyclic [N4] ligand

The complexes of transition metal ions with an azamacrocyclic tetradentate nitrogen donor [N4] ligand viz. 2,6,12,16,21,22-hexaaza;3,5,13,15-tetramethyltricyclo[15.3.1.1(7-11)] docosa;1(21),2,5,7,9,11(22),12,15,17,19-decaene (L) have been synthesized. All the complexes were found to have general composition M(L)X2 [where M = manganese(II), cobalt(II), nickel(II) and copper(II) and X = Cl- & NO3-]. All the complexes are characterized by the elemental analysis, molar conductance measurements, magnetic susceptibility measurements, mass, 1H NMR, IR, electronic, EPR spectral and cyclic voltammetric studies. An octahedral geometry was assigned for Mn(II), Co(II) and Ni(II) complexes and tetragonal for Cu(II) complexes. The biological actions of the ligand and complexes have been screened in vitro against many bacteria and pathogenic fungi to study their comparative capacity to inhibit the growth.     

EPR, IR and electronic spectral studies on Ni(II) and Cu(II) complexes with N-donor tetradentate [N4] macrocyclic ligand

Nickel(II) and copper(II) complexes are synthesized with a novel tetradentate macrocyclic ligand, i.e. 2,6,12,16,21,22-hexaaza;3,5,13,15-tetraphenyltricyclo[15,3,1,1(7-11)] docosa;1(21),2,5,7,9,11(22),12,15,17,19-decaene (L) and characterized by the elemental analysis, magnetic susceptibility measurements, mass, (1)H NMR, IR, electronic and EPR spectral studies. All the complexes are non-electrolytic in nature. Thus, these may be formulated as [M(L)X(2)] [M=Ni(II), Cu(II) and X=Cl(-), NO(3)(-) and (1/2)SO(4)(2-)]. Ni(II) and Cu(II) complexes show magnetic moments corresponding to two and one unpaired electron, respectively. On the basis of IR, electronic and EPR spectral studies an octahedral geometry has been assigned for Ni(II) and tetragonal geometry for Cu(II) complexes.     

Structural, spectral and antimicrobial studies of copper(II) complexes of 2-benzoylpyridine N(4)-cyclohexyl thiosemicarbazone

Six new copper(II) complexes of 2-benzoylpyridine N(4)-cyclohexyl thiosemicarbazone (HL) have been synthesized and characterized by different physicochemical techniques like molar conductivity measurements, magnetic studies and electronic, infrared and EPR spectral studies. Five of the complexes have been found to possess the stoichiometry [CuLX], where X = Cl (1), Br (2), NO₃ (3), NCS (4), N₃ (5). The complex prepared from copper sulfate has the composition [Cu₂L₂SO₄] · (H₂O)₂ (6). In all the complexes the deprotonated ligand, L and the anion were found to be coordinated to the Cu(II) ion. The terdentate nature of the ligand is evident from the IR spectra. The metal ligand bonding parameters evaluated from the EPR spectra indicate strong in-plane σ and in-plane π bonding. The magnetic and spectroscopic data indicate a square planar geometry for complexes 1, 3, 4 and 5, while the complexes 2 and 6 are assigned a square pyramidal geometry. Crystal structure of the complex [CuLCl] reveals two molecules per asymmetric unit of a monoclinic lattice, with space group symmetry P2₁/n. The complexes [ CuLBr ₂] (2) and [CuLNCS] (4) crystallized into triclinic lattices with space group . Compound 2 exists as a thiolate bridged copper(II) dimer. The antimicrobial activity of the ligand and the copper complexes were tested against five types of bacteria isolated from clinical samples. The complexes were found to be active against Bacillus sp., Vibrio cholera O1, Staphylococcus aurus and Salmonella paratyphi.     

Synthesis,spectral, and biological studies of transition metal chelates of N-[1-(3-aminopropyl)imidazole]salicylaldimine

Tridentate chelate complexes M[LX?·?2H₂O], where M?=?Co(II), Ni(II), Cu(II), Zn(II), and Cd(II) have been synthesized from the Schiff base L?=?N-[1-(3-aminopropyl)imidazole]salicylaldimine and X?=?Cl. Microanalytical data, UV-Vis, magnetic susceptibility, IR, ¹H-NMR, mass, and EPR techniques were used to confirm the structures. Electronic absorption spectra and magnetic susceptibility measurements suggest square-planar geometry for copper complex and octahedral for other metal complexes. EPR spectra of copper(II) complex recorded at 300?K confirm the distorted square-planar geometry of the copper(II) complex. Biological activities of the ligand and metal complexes have been studied on Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, and Candida albicans by the well diffusion method. The activity data show the metal complexes to be more potent than the parent ligand against two bacterial species and one fungus. The electrochemical behavior of the copper complex was studied by cyclic voltammetry.     

Spectroscopic approach in characterization of chromium(III), manganese(II), iron(III) and copper(II) complexes with a nitrogen donor tetradentate, 14-membered azamacrocyclic ligand

The complexes of Cr(III), Mn(II), Fe(III) and Cu(II) were synthesized with the macrocyclic ligand i.e. 2,3,9,10-tetraketo-1,4,8,11-tetraazacyclotetradecane. The ligand was prepared by the [2 + 2] condensation reaction of diethyloxalate and 1,3-diamino propane. These complexes were found to have the general composition M(L)X3 and M'(L)X2 [where M = Mn(II) and Cu(II), M' = Cr(III) and Fe(III), L = ligand (N4) and X = Cl-, NO3-, 1/2SO4(2-) and [CH3COO-]. The ligand and its transition metal complexes were characterized by the elemental analyses, molar conductance, magnetic susceptibility, mass, IR, electronic, and EPR spectral studies. On the basis of IR, electronic and EPR spectral studies an octahedral geometry has been assigned for Cr(III), Mn(II) and Fe(III) and a tetragonal geometry for Cu(II) complexes.     

Spectroscopic studies on Mn(II), Co(II), Ni(II), and Cu(II) complexes with N-donor tetradentate (N4) macrocyclic ligand derived from ethylcinnamate moiety

Manganese(II), cobalt(II), nickel(II), and copper(II) complexes are synthesized with a novel tetradentate ligand, viz. 1,5,9,13-tetraaza-6,14-dioxo-8,16-diphenylcyclohexadecane (L) and characterized by the elemental analysis, molar conductance measurements, magnetic susceptibility measurements, mass, 1H NMR, IR, electronic, and EPR spectral studies. The molar conductance measurements of the complexes in DMSO correspond to be nonelectrolyte nature for Mn(II), Co(II), and Cu(II) whereas 1:2 electrolytes for Ni(II) complexes. Thus, these complexes may be formulated as [M(L)X(2)] and [Ni(L)]X(2), respectively (where M = Mn(II), Co(II), and Cu(II) and X = Cl- and NO(3-)). On the basis of IR, electronic, and EPR spectral studies an octahedral geometry has been assigned for Mn(II) and Co(II) complexes, square-planar for Ni(II) whereas tetragonal for Cu(II) complexes. The ligand and its complexes were also evaluated against the growth of bacteria and pathogenic fungi in vitro.     

Spectroscopic characterization of tetradentate macrocyclic ligand: its transition metal complexes

Manganese(II), cobalt(II), nickel(II) and copper(II) complexes are synthesized with a novel tetradentate ligand viz. 1,3,9,11-tetraaza-4,8,12,16-tetraoxo-2,6,10,14-tetrathiacyclohexadecane (L) and characterized by the elemental analysis, molar conductance measurements, magnetic susceptibility measurements, electron impact mass, 1H NMR, IR, electronic and EPR spectral studies. The molar conductance measurements of the complexes in DMSO correspond to be nonelectrolytic nature for Mn(II), Co(II) and Cu(II) while 1:2 electrolytes for Ni(II) complexes. Thus these complexes may be formulated as [M(L)X2] and [Ni(L)]X2 (where M: Mn(II), Co(II), and Cu(II) and X = Cl- and NO3-). On the basis of IR, electronic and EPR spectral studies an octahedral geometry has been assigned for Mn(II) and Co(II) complexes, square-planar for Ni(II) whereas tetragonal for Cu(II) complexes. The ligand and its complexes were also evaluated against the growth of bacteria and pathogenic fungi in vitro.     

Synthesis and Biological Evaluation of some 3d Metal Complexes with a Novel Heterocyclic Schiff Base

A heterocyclic Schiff base was prepared by condensing 3‐acetylcoumarin with 2‐amino‐3‐carboxyethyl‐4,5,6,7‐tetrahydrobenzo[b ]thiophene. Such Schiff bases derived from two different heterocyclic moieties are rare and expected to have properties surpassing those of either of the parent compounds in effectiveness of complex formation and biological activities. This ligand formed a series of complexes with manganese(II), cobalt(II), nickel(II), copper(II), and zinc(II) ions. The ligand and the metal complexes were characterized by various physicochemical and spectral studies. These included elemental analysis, molar conductance, magnetic susceptibility, as well as UV–vis, IR, ¹H NMR, ¹³C NMR, and ESR spectral studies. The ESR spectral data adequately supported the covalent nature of the metal–ligand bonds. The ligand possessed a hexagonal crystal structure, but on complexation the crystallinity was lost. The fluorescence spectra of the ligand and its metal complexes in DMSO were also recorded. The ligand and the metal complexes were screened for their antimicrobial activities, and it was observed that the metal complexes are more active than the ligand. The α‐amylase inhibitory activity and the DNA cleavage activity of the ligand and the metal complexes were also examined. in vitro antitumor activity of the copper(II) complex was assayed against human cervical carcinoma cells (HeLa cell line), showing that the complex exhibited promising antitumor activity on the HeLa cell line.     

Spectroscopic studies on Co(II), Ni(II) and Cu(II) complexes with a new macrocyclic ligand: 2,9-dipropyl-3,10-dimethyl-1,4,8,11-tetraaza-5,7:12,14-dibenzocyclotetradeca-1,3,8,10-tetraene

Cobalt(II), nickel(II) and copper(II) complexes containing a tetradentate macrocyclic nitrogen donor ligand i.e. 2,9-dipropyl-3,10-dimethyl-1,4,8,11-tetraaza-5,7:12,14-dibenzocyclotetradeca-1,3,8,10-tetraene have been synthesized and characterized by elemental analysis, molar conductance, magnetic moments, mass, (1)H NMR, IR, electronic and EPR spectral studies. All the complexes are of high spin type and possess four-coordinated tetrahedral, five-coordinated square pyramidal and six-coordinated octahedral/tetragonal geometry. The ligand and its metal complexes were also screened against the growth of some bacteria and plant pathogenic fungi in vitro.     

Studies on DNA cleavage and antimicrobial screening of transition metal complexes of 4-aminoantipyrine derivatives of N2O2 type

A new series of transition metal complexes of Cu(II), Ni(II), Zn(II) and VO(IV), were synthesized from the Schiff base (L) derived from 4-aminoantipyrine, 3-hydroxy-4-nitrobenzaldehyde and acetylacetone. The structural features were arrived from their elemental analyses, magnetic susceptibility, molar conductance, Mass, IR, UV-Vis., ¹H NMR and ESR spectral studies. The data show that the complexes have composition of [ML]X type. The UV-Vis., magnetic susceptibility and ESR spectral data of the complexes suggest a square-planar geometry around the central metal ion except for VO(IV) complex which has square-pyramidal geometry. The redox behavior of copper and vanadyl complexes were studied by cyclic voltammetry. The antimicrobial screening tests were also recorded and gave good results in the presence of metal ion in the ligand system. The nuclease activity of the above metal complexes shows that the copper and nickel complexes cleave DNA through redox chemistry, whereas other complexes are not effective.     

Synthesis,spectroscopic, and antimicrobial studies of the bivalent cobalt,nickel, and copper complexes of thioacetamide

A series of metal complexes of cobalt(II), nickel(II), and copper(II) having the general composition [M(L)₂X₂] with thioacetamide have been prepared and characterized by elemental chemical analysis, molar conductance, magnetic susceptibility measurements, mass, IR, EPR, and electronic spectral studies. The IR spectral data suggests the involvement of sulfur and amino nitrogen in coordination to central metal ion. On the basis of spectral studies, an octahedral geometry has been assigned for the cobalt(II) and nickel(II) complexes whereas tetragonal geometry for copper(II) complexes. Thioacetamide and its metal complexes have been tested in vitro against a number of microorganisms in order to assess their antimicrobial properties.     

Copper(III) and vanadium(IV)-oxo corrolazines

As part of our efforts to develop the transition metal chemistry of corrolazines, which are ring-contracted porphyrinoid species most closely related to corroles, the vanadium and copper complexes (TBP)(8)Cz(H)V(IV)O (1) and (TBP)(8)CzCu(III) (2) of the ligand octakis(para-tert-butylphenyl)corrolazine [(TBP)(8)Cz] have been synthesized. The coordination behavior, preferred oxidation states, and general redox properties of metallocorrolazines are of particular interest. The corrolazine ligand in 1 was shown to contain a labile proton by acid/base titration and IR spectroscopy, serving as a -2 ligand rather than as the usual -3 donor. The oxidation state of the vanadium center in 1 was shown to be +4, in agreement with the overall neutral charge for this complex. The EPR spectrum of 1 reveals a rich signal consistent with a V(IV)(O) (d(1), S = 1/2) porphyrinoid species (g(xx) = 1.989, g(yy) = 1.972, g(zz) = 1.962). The electrochemical analysis of 1 shows behavior closer to that of a porphyrazine than a corrolazine, with a positively shifted, irreversible reduction at -0.65 V (vs Ag/AgCl). Resonance Raman and IR data for 1 confirm the presence of a triply bonded terminal oxo ligand with nu(V(16)O) = 975 cm(-1) and nu(V(18)O) = 939 cm(-1). The copper complex 2 exhibits a diamagnetic (1)H NMR spectrum, indicative of a bona fide square planar copper(III) (d(8), low-spin) complex. Previously reported copper corroles have been characterized as copper(III) complexes which exhibit a paramagnetic NMR spectrum at higher temperatures, indicative of a thermally accessible triplet excited state ([(corrole(*+))Cu(II)]). The NMR spectrum for 2 shows no paramagnetic behavior in the range 300-400 K, indicating that compound 2 does not have a thermally accessible triplet excited state. These data show that the corrolazine system is better able to stabilize the high oxidation state copper center than the corresponding corroles. Electrochemical studies of 2 reveal two reversible processes at +0.93 and -0.05 V, and bulk reduction of 2 with NaBH(4) generates the copper(II) species [(TBP)(8)CzCu(II)](-) (2a), which exhibits an EPR signal typical of a copper(II) porphyrinoid species.