Mono, di and trinuclear photo-luminescent cadmium(II) complexes with N2O and N2O2 donor salicylidimine Schiff bases: Synthesis, structure and self assembly

Reactivity of Nitric Oxide and Nitrosonium Ion with Copper(II/I) Schiff Base Complexes: Mechanistic Aspects of Imine C═N Bond Cleavage and Oxidation of Pyridine-2-aldehyde to Pyridine-2-carboxylic Acid

Four Schiff base ligands of the general formulas [6-(R)-2-pyridyl-N-(2'-methylthiophenyl)methylenimine] (^RL1) and 6-p-chlorophenyl-2-pyridyl-N-(2'-phenylthiophenyl)methylenimine (^RL2), where R = H, Me, p-ClPh, and their bis-ligand copper(II) and copper(I) complexes, 1-4 and 1'-4', respectively, were synthesized and characterized. The reactivities of 1-4 with nitric oxide (NO) gas and of 1'-4' with solid NOBF₄ (NO⁺) were examined in dry acetonitrile in the presence and absence of water (H₂O). The results revealed that, in the absence of H₂O, complexes 1-4 (or 1'-4') reacts with NO (or NOBF₄), leading to imine C═N bond cleavage of both (or one) Schiff base(s) that generates 2 (or 1) equiv of 2-(methyl/phenyl)thiobenzenediazonium perchlorates (5/6) and the corresponding picolaldehyde (^RPial) via a copper nitrosyl of a {CuNO}¹⁰-type intermediate. In the presence of H₂O, the in situ formed ^RPial get oxidized to the corresponding picolinic acid (^RPicH) via an in situ formed LCu^IOH intermediate (LCu^I + HO-NO → LCu^IOH + NO⁺; L = ^RL1/^RL2/^RPic^- and ν_O-H of Cu^IOH = 3650 cm^-1) and subsequently produces, with the aid of NO⁺ oxidant, the picolinate-ligated copper(II) complexes (i) [(^HPic)₂Cu] (7), [(^MePic)₄Cu₃(NO₃)₂]_n·H₂O (8·H₂O), or [(^ClPhPic)₂Cu] (9) when NO reacts with 1-4 or (ii) [(^RPic)Cu^II(^RL1/^RL2)]⁺ when NO⁺ reacts with 1'-4'. The Cu^II to Cu^I reduction of [(^RPic)Cu^II(^RL1/^RL2)]⁺ is essential for C═N cleavage of the remaining ^RL1/^RL2 Schiff base; excess NO can do it. The X-ray structures (1, 1', 3', 5, 7, and 8) and spectroscopic results revealed the role of Cu^II/I, NO, NO⁺, and H₂O, shedding light on the mechanism of C═N bond cleavage and the oxidation of pyridine-2-aldehyde to pyridine-2-carboxylic acid. The reaction of 1 with ¹⁵NO revealed that the terminal N of the N₂⁺ group of 5 originates from ¹⁵NO [ν_{¹⁴N¹⁴N-} = 2248 cm^-1 and ν_{¹⁵N¹⁴N-} = 2212 cm^-1].

Synthesis of New Naphthyl Aceto Hydrazone-Based Metal Complexes: Micellar Interactions, DNA Binding, Antimicrobial, and Cancer Inhibition Studies

In the present study, naphthyl acetohydrazide (HL) ligand was prepared and used for the synthesis of new six amorphous transition metal (Co(II), Ni(II), Cu(II), Zn(II), Pb(II), Cd(II)) complexes. All the compounds were characterized by elemental analysis, UV-vis, FT-IR, ¹H- and ¹³C-NMR, and Matrix-Assisted Laser Desorption Ionization (MALDI). The solubilization study was carried out by estimating the interaction between the metal complexes with surfactants viz. sodium stearate (SS) and Cetyltrimethylammonium bromide (CTAB). UV-Visible spectroscopy was employed to determine partitioning and binding parameters, whereas electrical conductivity measurements were employed to estimate critical micellar concentration (CMC), the extent of dissociation, and free energy of micellization. The CT-DNA interaction of synthesized compounds with DNA represents the major groove binding. The synthesized ligand and metal complexes were also tested against bacterial and fungal strains and it has been observed that Cu(II) complex is active against all the strains except Candida albicans, while Cd(II) complex is active against all bacterial and fungal strains except Pseudomonas. Among all compounds, only the Pd(II) complex shows reasonable activity against cervical cancer HeLa cell lines, representing 97% inhibition.

Theoretical insights on the encapsulated hydronium ion mediated supramolecular assembly of nickel(ii) Schiff base complexes: strong hydrogen bonding interaction due to charge transfer from the lone pair of oxygen to the antibonding orbital of the O–H bond

Strong hydrogen bonding interactions are observed in a hydronium ion trapped nickel(ii) Schiff base complex. The energetics regarding these interactions which provide the stability to the supramolecular structure are analysed by DFT calculations.

DFT study on the redox behavior of two dioxovanadium(v) complexes with N2O donor Schiff base ligands and their use in catalytic oxidation ofortho-aminophenol

Solution phase redox behavior of two vanadium(v) Schiff base complexes was checked. The results agree well with DFT calculations. Both complexes exhibited good catalytic efficiency for the conversion ofo-aminophenol to 2-aminophenoxazine-3-one.

A combined experimental and computational study on supramolecular assemblies in hetero-tetranuclear nickel(ii)-cadmium(ii) complexes with N2O4-donor compartmental Schiff bases

Two new hetero-tetranuclear nickel(ii)/cadmium(ii) complexes, a cubane [(CH₃CO₂)₂Ni₂(L¹)₂Cd₂(NCS)₂] (1) and a linear tetramer [(DMSO)₂NiL²Cd(NCS)(μ_1,3-SCN)Ni(DMSO)L²Cd(NCS)₂] (2) {where H₂L¹ = N,N'-bis(3-methoxysalicylidene)propane-1,3-diamine and H₂L² = N,N'-bis(3-ethoxysalicylidene)propane-1,3-diamine are potential octadentate compartmental Schiff bases}, were synthesized and characterized. The structures of both complexes were confirmed by single crystal X-ray diffraction studies. Complex 1 contained a Ni₂Cd₂O₄ cubane core, whereas complex 2 featured an end-to-end thiocyanate-bridged tetranuclear moiety. Furthermore, complex 1 showed C-HH-C interactions, whereas a unique Sπ interaction was observed in complex 2. Theoretical studies were performed using several computational tools such as NBO and AIM analyses. Both complexes showed photoluminescence in DMSO medium at room temperature upon irradiation with ultraviolet light. The lifetimes of the excited states were ∼27 ns.

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

Two new cobalt(iii) tetrazolato complexes [Co(L¹)(PTZ)(N₃)] (1) and [Co(L²)(PTZ)(N₃)] (2) {where H₂L¹ = 2((3-(methylamino)propylimino)methyl)-6-methoxyphenol, H₂L² = 2((3-(dimethylamino)propylimino)methyl)-6-ethoxyphenol and HPTZ = 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⁻¹ in an acetonitrile–methanol (2 : 1) mixture. Both complexes are also reactive towards aerobic oxidation of o-aminophenol in acetonitrile–methanol (2 : 1) with turnover numbers ∼0.095 s⁻¹.

Two cobalt(iii) tetrazolato complexes have been synthesized and characterized. Noncovalent interactions have been analysed by DFT and MEP calculations and characterized using Bader's theory of AIM. Both complexes catalyze the aerial oxidation of 3,5-DTBC and OAPH.

Formation of a water-mediated assembly of two neutral copper(ii) Schiff base fragments with a Cu2(NCS)4moiety: exploration of non-covalent C–H⋯π(bimetallo ring) interactions

The energetic features of dimer formation and water encapsulation in an interesting copper(ii) Schiff base complex, [(CuL)₂⊂(H₂O)][Cu₂(μ_1,3-NCS)₂(NCS)₂], have been studied using DFT calculations.

Thiocyanate mediated structural diversity in phenol based "end-off" compartmental ligand complexes of group 12 metal ions: Studies on their photophysical properties and phosphatase like activity

The reaction of a pentadentate compartmental ligand LH, namely 4-tert-Butyl-2,6-bis-[(2-pyridin-2-yl-ethylimino)-methyl]-phenol, with group 12 metal ions (Zn^II, Cd^II, Hg^II) followed by addition of NaSCN afforded one discrete dinuclear complex [Zn₂(L)(SCN)₃](1), and two polymeric 1D species [Cd_2.5(L)(SCN)₃(AcO)]_n (2) and [Hg₂(L)(SCN)₃]_n (3). All the complexes have been structurally characterized by single crystal X-ray diffraction. The crystal structure of the complexes reveals different coordination modes of thiocyanate anion that affect the different topology detected in the compounds: the anions are μ¹-NCS and μ^1,1-NCS connected in complex 1, while μ^1,3-NCS bridging mode is observed in 2, and μ¹-SCN and μ^1,3-NCS in 3. The polymeric Hg complex of the bicompartmental ligand system here reported is unprecedented. Detail study of their photophysical properties including the phosphorescence spectra at 77K has been done. Phosphatase like activity of all the three complexes has been performed in DMSO-H₂O medium and their activity follows the order of 1>2>>3.

Importance of C–H⋯π interactions in stabilizing the syn/anti arrangement of pendant alkoxy side arms in two manganese(iv) Schiff base complexes: exploration of catechol oxidase and phenoxazinone synthase like activities

Two manganese(iv) complexes have been prepared and characterized. Both complexes exhibit catechol oxidase and phenoxazinone synthase like activities.