Hydrazine Nitrogen Research Articles

Phenolate-thiazole based reversible “turn-on” chemosensor for the selective detection of carbonate anion: X-ray crystallography, DFT/TDFT, and cell study

A new phenolate-thiazole derivative (L) has been synthesized and structurally characterized.The chemo-sensing activity of L is detected by the naked eye for the aqueous carbonate anion in the pH range of 4 to 8. The selective ‘turn-on’ fluorescence occurs through the formation of a stable intermediate L∙CO32–(1) following the PET mechanism. The limit of detection (LOD) is found 0.18 µM based on the absorbance-based assay.The quinonoid form of bromophenol unit binds strongly with CO32– through thiazole nitrogen and hydrazinic nitrogen. Further, the selective holding of CO32– anion over other planar tetranuclear anions (e.g., SO32–, NO3–) happens with several intra and intermolecular hydrogen bonds as envisaged by the DFT/TDFT study. The formation mechanism of L∙CO32– is proposed based on experimental and theoretical studies. The biological experiments (MTT and cell imaging)reveal the non-cytotoxicity nature of L and the biocompatible uptake of L mostly in the cytoplasm at physiological pH.

Preparation of new organo-ruthenium(II) complexes and their nucleic acid/albumin binding efficiency and in vitro cytotoxicity studies.

Hetero-bimetallic ruthenium(II) complexes (PRAFIZ and PRBFIZ) containing acetyl ferrocene (AFIZ)/benzoyl ferrocene isonicotinic hydrazone ligands (BFIZ) were synthesized and characterized by various spectral and analytical techniques. The structure of acetyl ferrocene isonicotinic hydrazone (AFIZ) and the complex PRBFIZ was confirmed by X-ray crystallography. The hydrazide ligands coordinated in a bidentate monobasic fashion using their N1 hydrazinic nitrogen and enolic oxygen atoms. The binding interactions of the ligands and complexes were examined using Calf-Thymus DNA (CT-DNA) and bovine serum albumin (BSA). Scanning Electron Microscopic (SEM) experiments clarified the efficient binding interaction of the ligands and complexes with BSA. The results of in vitro cytotoxicity studies on MDA-MB-261 breast cancer cells and A549 human lung cancer cells and cell morphological analysis results through staining assays clearly indicated the cytotoxic nature of the complexes.

Copper-Catalyzed Glutathione Oxidation is Accelerated by the Anticancer Thiosemicarbazone Dp44mT and Further Boosted at Lower pH

Glutathione (GSH) is the most abundant thiol in mammalian cells and plays a crucial role in maintaining redox cellular homeostasis. The thiols of two GSH molecules can be oxidized to the disulfide GSSG. The cytosolic GSH/GSSG ratio is very high (>100), and its reduction can lead to apoptosis or necrosis, which are of interest in cancer research. CuII ions are very efficient oxidants of thiols, but with an excess of GSH, CuIn(GS)m clusters are formed, in which CuI is very slowly reoxidized by O2 at pH 7.4 and even more slowly at lower pH. Here, the aerobic oxidation of GSH by CuII was investigated at different pH values in the presence of the anticancer thiosemicarbazone Dp44mT, which accumulates in lysosomes and induces lysosomal membrane permeabilization in a Cu-dependent manner. The results showed that CuII-Dp44mT catalyzes GSH oxidation faster than CuII alone at pH 7.4 and hence accelerates the production of very reactive hydroxyl radicals. Moreover, GSH oxidation and hydroxyl radical production by CuII-Dp44mT were accelerated at the acidic pH found in lysosomes. To decipher this unusually faster thiol oxidation at lower pH, density functional theory (DFT) calculations, electrochemical and spectroscopic studies were performed. The results suggest that the acceleration is due to the protonation of CuII-Dp44mT on the hydrazinic nitrogen, which favors the rate-limiting reduction step without subsequent dissociation of the CuI intermediate. Furthermore, preliminary biological studies in cell culture using the proton pump inhibitor bafilomycin A1 indicated that the lysosomal pH plays a role in the activity of CuII-Dp44mT.

Heteroleptic silver(I), nickel(II), and copper(II) complexes of N4‐substituted thiosemicarbazones and ciprofloxacin: Theoretical, in vitro anti‐proliferative, and in silico molecular modeling and pharmacokinetics studies

In this study, a series of new heteroleptic silver(I), nickel(II), and copper(II) complexes of the type [M(L1–3)(Cfx)n] (1–9), where L1–3 = N4‐substituted thiosemicarbazones (TSCs), Cfx = ciprofloxacin, M = Ag(I), Ni(II), or Cu(II), and n = 1 or 2, have been synthesized and characterized by spectral methods. The spectral data of the complexes suggest bidentate behavior of the TSC ligand, which coordinate with metal ion through thione sulphur and hydrazine nitrogen atoms, and neutral bidentate behavior of the ciprofloxacin drug that coordinates with metal ion through pyridone oxygen and one of the carboxylate oxygen atoms. The structural properties of the silver(I) complexes (1–3) were studied by density functional theory calculations, which indicate the distorted tetrahedral geometry with lower energy gap for complex 3. All the heteroleptic complexes were screened for their in vitro anti‐proliferative activity against four cancerous (lung [A549], estrogen negative [MDA‐MB‐231], estrogen positive [MCF‐7] and Henrietta's cancer cells [HeLa]), and one non‐cancerous (non‐tumorigenic human breast epithelial cell line [MCF‐10a]) cell lines by MTT reduction assay. The obtained results revealed the lower activity of silver(I) complexes and higher activity of copper(II) complexes against the tested cancer cell lines. The complexes 6 and 9 induce apoptosis in MDA‐MB‐231 cells, which was evidenced by acridine orange/ethidium bromide staining method. The molecular docking studies revealed hydrogen bonding and hydrophobic interactions between the complexes and the epidermal growth factor receptor. The in silico analysis of the complexes for Lipinski's “rule of five” and absorption, distribution, metabolism, and excretion properties predicted the drug‐likeness of the synthesized complexes.

α-(1,2,3-Triazolyl)-acetophenone: Synthesis and theoretical studies of crystal and 2,4-dinitrophenylhydrazine cocrystal structures

The crystal structures of cocrystal of 1-phenyl-2-(4-phenyl-[1,2,3]triazol-1-yl)-ethanone/2,4-dinitrophenylhydrazine (PPTE/DNPH) and 1-phenyl-2-(4-phenyl-[1,2,3]triazol-1-yl)-ethanone, namely α-(1,2,3-triazolyl)-acetophenone, were determined by X-ray diffraction analyses. Cocrystal PPTE/DNPH presented important N−H···O hydrogen bonds between carbonyl group from acetophenone moiety with hydrazine nitrogen atom of dinitrophenylhydrazine. This interaction helps to join the coformer molecules 1-D chains, shaping the crystal packing and supramolecular network. The results are in accordance with the solid behavior of compounds, as evidenced from Hirshfeld surface analysis and QTAIM/NCI index. Theoretical studies of molecular and electronic properties indicate a reactivity modulation by cocrystal PPTE/DNPH in relation to coformer compounds.

Crystal structure of N′-[2-(benzo[d]thiazol-2-yl)acetyl]benzohydrazide, an achiral compound crystallizing in space group P1 with Z = 1

In the molecule of the title compound, C16H13N3O2S, one hydrazinic nitrogen atom is essentially planar, but the other is slightly pyramidalized. The torsion angle about the hydrazinic bond is 66.44 (15)°. Both hydrazinic hydrogen atoms lie antiperiplanar to the oxygen of the adjacent carbonyl group. The molecular packing is a layer structure determined by two classical hydrogen bonds, N—H...O=C and N—H...Nthiazole. The space group is P1 with Z = 1, which is unusual for an achiral organic compound.

SYNTHESIS, CHARACTERIZATION AND ANTIMICROBIAL SCREENING OF SOME MIXED LIGAND COMPLEXES OF DIOXOURANIUM

Abstract Complexes of Nicotinic hydrazide (NH) and isonicotinic acid hydrazide (INH) with uranylnitrate and uranylacetate were prepared; [UO2(NH)2(NO3)2]nH2O 1, [UO2(INH)2(NO3)2]nH2O 2, [UO2(NH)2(CH3COO)2]nH2O 3 and [UO2(INH)2(CH3COO)2] nH2O 4 and characterized. They recorded melting points ranging between 154 – 189 oC and shows non electrolytic character in solution indicating the ligands and complexes are neutral compounds. IR and uranium elemental analysis revealed mixed ligand complexes where the hydrazide ligands show bidentate coordination through the carbonyl oxygen and the hydrazinic nitrogen leading to the formation of a 5-membered chelate with uranium(VI) ion. All complexes adopt octahedral geometry with two nitrate and acetate ions respectively occupying the fifth and sixth coordination sites of the complexes via unidentate mode of coordination. Electronic spectral studies display spectra bands between 320 – 350 nm and 400 – 500 nm in the spectra of the complexes due to intraligand and charge transfer transitions respectively. Antimicrobial studies revealed that [UO2(NH)2(NO3)2] and [UO2(INH)2(NO3)2] exhibited a fair inhibition of the growth of S. aureus. All other compounds did not display antimicrobial action against all the organisms tested. The complex compounds are stable recommending the ligands can find application in uranium spectroanalysis and in pollution remediation.

Synthesis, Characterization, and Crystal Structures of a Thiosemicarbazone Ligand and Its Silver(I) Complex

Thiosemicarbazone ligand 4Hbatsc = 4-hydroxybenzaldehyde-thiosemicarbazone and its silver(I) complex [Ag(PPh3)3(4Hbatsc)]NO3 were synthesized and characterized by elemental analysis (CHN), FT-IR spectroscopy, and single-crystal X-ray diffraction. The triclinic unit cell of 4H-ba-tsc (space group P-1) contains two independent molecules. Each of the two independent molecules is almost planar, with the sulfur atom (S1/S2) and the hydrazine nitrogen atom (N6/N4) in the E position concerning the C3-N5/C4-N4. The title complex is a triclinic P-1 mononuclear complex with the silver(I) ion coordinated in a distorted tetrahedral geometry by one S atom of 4H-ba-tsc and three P atoms of three PPh3. The complex involves the 4H-ba-tsc thiosemicarbazone ligand in an S monodentate binding mode. Besides, the thermal behavior of the complex was studied using thermogravimetry in order to evaluate its thermal stability and thermal decomposition pathway. Finally, nanoparticles of the complex were prepared in an ultrasonic bath.

Photophysical, electrochemical and TD-DFT studies of Ni(II) and Mn(II) complexes of N′-(2-methylfuran-3-carbonyl)hydrazine carbodithioic acid ethyl ester

Two new complexes [Ni(Hmfchce)2(py)2] (1) and [Mn(Hmfchce)2(o-phen)] (2) with [N′-(2-methylfuran-3-carbonyl)hydrazine]-carbodithioic acid ethyl ester (H2mfchce) have been synthesized which contain o-phenanthroline (o-phen)/pyridine (py) as coligand. The ligand and its metal complexes have been characterized by elemental analyses, IR, magnetic susceptibility and single crystal X-ray diffraction data. Complexes 1 and 2 crystallize in orthorhombhic system with space group ‘Pbca’ and ‘Pbcn’, respectively. In complex 1, nickel centre is coordinated through one hydrazine nitrogen atom, one carbonyl oxygen of two units of ligand and two pyridine nitrogen atoms. The manganese center in complex 2 is coordinated in a N4O2 core by two uininegative bidentate ligands using hydrazine nitrogen (after loss of proton) and carbonyl oxygen and two nitrogen atoms of o-phen. In both complexes, the metal ion adopts a distorted octahedral geometry. Complexes 1 and 2 are fluorescent materials which exhibit an emission at 291 and 285 nm, respectively upon excitation at 263 and 251 nm. The course of the thermal degradations of complexes 1 and 2 have been investigated by TGA which indicate that metal oxide is formed as the final residue in both complexes. The metal complexes, [Ni(Hmfchce)2(py)2] (1) and [Mn(Hmfchce)2(o-phen)] (2) were immobilized on glassy carbon electrodes using Nafion® (Nf). The modified electrodes have been characterized by cyclic voltammetry in 0.1 M KOH. Complexes 1 and 2 have efficient activity towards electrochemical water oxidation in the 0.1 M KOH. The simulated spectra of the two complexes 1 and 2 are characterized by excited states with ligand-to-ligand charge-transfer (LLCT) and ligand-to-metal charge-transfer (LMCT) character.

Numerical Simulation of Ignition Process for the Monomethyl Hydrazine–Nitrogen Tetroxide Thrusters

The numerical simulation of the ignition process of the monomethyl hydrazine–nitrogen tetroxide attitude-control thrusters is difficult because of the complex hypergolic gas–liquid chemical reaction between the propellants. To calculate the thruster ignition delay accurately, a 36-step gas-phase chemical kinetics model and a one-step finite-rate liquid-phase hypergolic reaction are proposed. These chemical mechanisms are integrated into the Euler–Lagrange-based transient spray combustion simulation platform. The calculated ignition pressure curve of a 2 kN thruster coincides well with that from the experiment. The numerical and experimental ignition delays are 2.4 and 3.1 ms, respectively. A parameter study shows that the liquid-phase reaction at the propellant impingement points consumes 22–44% propellant and provides energy to heat the gas mixtures, which is essential for a successful gas-phase ignition. The lower limit of ignition delay was estimated as 1.5 ms under design restrictions for most thrusters.

Computational Mechanistic Study of [MoFe3S4] Cubanes for Catalytic Reduction of Nitrogenase Substrates.

Molybdenum-dependent nitrogenase is the most active biological catalyst for dinitrogen reduction. This reaction is catalyzed by a [MoFe7S9C] cofactor (FeMoco). FeMoco can be described as a double-cubane, with [MoFe3S3] and [Fe4S3] parts, bound via an interstitial carbide and three bridging sulfides. Model compounds have been synthesized since early studies of the enzyme and Coucouvanis and co-workers demonstrated that [MoFe3S4] cubanes are active catalysts for many substrates catalyzed by nitrogenase. These reactions include hydrazine reduction to ammonia and cis-dimethyldiazene reduction to methylamine. Experiments implicated molybdenum as the binding site but the mechanisms have not been studied by theoretical calculations before. Here we present a DFT study of the catalytic reaction mechanisms of hydrazine and cis-dimethyldiazene reduction with a [MoFe3S4] cubane. Like in the experiments, molybdenum is revealed as the likely substrate binding site, likely due to the labile ligand on Mo.For the hydrazine mechanism, a reduction event is centered on Fe, specifically on the Fe antiferromagnetically coupled to the mixed-valence pair. After protonation of the distal hydrazine nitrogen, the N-N bond can be cleaved to yield NH3 and a Mo-bound -NH2 intermediate. This is followed by another protonation/reduction step to give an -NH3 intermediate, and finally substituted by thesubstrate to complete the cycle. The computed mechanisms shed light on the bimetallic cooperativity in these systems where the reduction steps are localized on Fe while the substrate binds to Mo and the reductions require only a free coordination site (onMo) and a favorable reduction event (to Fe). Although both substrates easily displace the weakly bound acetonitrile ligand, one reduction event is required for hydrazine activation and N-N bond cleavage to give an integer-spin -NH2 intermediate. An integer-spin -NH2 intermediate has been observed as a common intermediate for the enzyme reduction of hydrazine and diazene, suggesting a possible link to the enzyme chemistry.

Molecular modeling, spectroscopic and structural studies on newly synthesized ligand N-benzoyl-2-isonicotinoylhydrazine-1-carboxamide

The new ligand N-benzoyl-2-isonicotinoylhydrazine-1-carboxamide (BIsoH) was synthesized and characterized by FTIR, 1H NMR, Mass and UV–Vis spectra. The spectral data indicated that BIsoH exists of keto-form. To shed more light on structure of the BIsoH, Quantum chemical calculations of the geometrically optimized structure, spectral data (IR, 1H NMR and UV–Vis) and Natural Bond Orbital (NBO) analysis have been carried out by DFT/B3LYP method. The structural parameters bond lengths, angles, and dihedral angles, displayed good agreement with the x-ray data of analogue molecules. Good agreement observed between the experimental and DFT computed IR and 1H NMR spectral data. The electronic spectrum, in DMSO, compared with TD-DFT calculations to explore the nature and contribution of the molecular orbitals into the observed transitions. The NBO data revealed that, the E(2) values for the electron density transfer of the hydrazinic nitrogen atoms lone pair to the anti-bonding molecular orbit of the carbonyl groups are 37.07 and 30.75 kJ/mol. HOMO-LUMO energy gap and Mulliken atomic charges are also calculated and properly presented.

Azapeptide Synthesis Methods for Expanding Side-Chain Diversity for Biomedical Applications.

Mimicry of bioactive conformations is critical for peptide-based medicinal chemistry because such peptidomimetics may augment stability, enhance affinity, and increase specificity. Azapeptides are peptidomimetics in which the α-carbon(s) of one or more amino acid residues are substituted by nitrogen. The resulting semicarbazide analogues have been shown to reinforce β-turn conformation through the combination of lone pair-lone pair repulsion of the adjacent hydrazine nitrogen and urea planarity. Substitution of a semicarbazide for an amino amide residue in a peptide may retain biological activity and add benefits such as improved metabolic stability. The applications of azapeptides include receptor ligands, enzyme inhibitors, prodrugs, probes, and imaging agents. Moreover, azapeptides have proven therapeutic utility. For example, the aza-glycinamide analogue of the luteinizing hormone-releasing hormone analogue Zoladex is a potent long-acting agonist currently used in the clinic for the treatment of prostate and breast cancer. However, the use of azapeptides was hampered by tedious solution-phase synthetic routes for selective hydrazine functionalization. A remarkable stride to overcome this bottleneck was made in 2009 through the introduction of the submonomer procedure for azapeptide synthesis, which enabled addition of diverse side chains onto a common semicarbazone intermediate, providing a means to construct azapeptide libraries by solution- and solid-phase chemistry. In brief, aza residues are introduced into the peptide chain using the submonomer strategy by semicarbazone incorporation, deprotonation, N-alkylation, and orthogonal deprotection. Amino acylation of the resulting semicarbazide and elongation gives the desired azapeptide. Since the initial report, a number of chemical transformations have taken advantage of the orthogonal chemistry of semicarbazone residues (e.g., Michael additions and N-arylations). In addition, libraries have been synthesized from libraries by diversification of aza-propargylglycine (e.g., A3 coupling reactions, [1,3]-dipolar cycloadditions, and 5-exo-dig cyclizations) and aza-chloroalkylglycine residues. In addition, oxidation of aza-glycine residues has afforded azopeptides that react in pericyclic reactions (e.g., Diels-Alder and Alder-ene chemistry). The bulk of these transformations of aza-glycine residues have been developed by the Lubell laboratory, which has applied such chemistry in the synthesis of ligands with promising biological activity for treating diseases such as cancer and age-related macular degeneration. Azapeptide analogues of growth hormone-releasing peptide-6 (His-d-Trp-Ala-Trp-d-Phe-Lys-NH2, GHRP-6) have for example been pursued as ligands of the cluster of differentiation 36 receptor (CD36) and show promising activity for the development of treatments for angiogenesis-related diseases, such as age-related macular degeneration, as well as for atherosclerosis. Azapeptides have also been employed to make a series of conformationally constrained second mitochondria-derived activator of caspase (Smac) mimetics that exhibit promising apoptosis-inducing activity in cancer cells. The synthesis of cyclic azapeptide derivatives was used to make an aza scan to study the conformation-activity relationships of the anticancer agent cilengitide, cyclo(RGDf-N(Me)V), and its parent counterpart cyclo(RGDfV), which exhibit potency against human tumor metastasis and tumor-induced angiogenesis. Innovations in the synthesis and application of azapeptides will be presented in this Account, focusing on the creation and use of side-chain diversity in medicinal chemistry.

Synthesis, structural characterization, electrochemical studies and DFT calculations on nickel(II) complexes of N-picolinoyl-N′-benzothioylhydrazide and 5-(pyridine-4-yl)-2H-1,2,4-triazole-3-thione

Two Ni(II) complexes, [Ni(pbth)2] and [Ni(ptt)2(en)2] {Hpbth = N-picolinoyl-N′-benzothioylhydrazide, Hptt = 5-(pyridine-4-yl)-2H-1,2,4-triazole-3-thione} have been synthesized and characterized by physico-chemical and spectroscopic methods. [Ni(pbth)2] contains a pair of N-picolinoyl-N′-benzothioylhydrazide ligands coordinated via their thione sulfur, pyridyl nitrogen and hydrazinic nitrogen atoms, forming two C2N2Ni and two CSN2Ni five-membered chelate rings. The intermediate compound 1-isonicotinoyl-3-thiosemicarbazide is converted to 5-(pyridine-4-yl)-2H-1,2,4-triazole-3-thione in the presence of ethanolic NaOH, giving the complex [Ni(ptt)2(en)2] in which the ptt ligands coordinate through their triazole ring nitrogen atoms, while four more nitrogens from two ethylenediamine ligands complete the octahedral structure. The crystal structures of the complexes involve various types of intermolecular extended hydrogen bonds, forming supramolecular frameworks. Cyclic voltammetry studies of both complexes show quasi-reversible redox behavior. Density Functional Theory electronic structure calculations corroborate our experimental findings.

Molecular Interactions in an α-Chitin/Hydrazine Complex: Dynamic Hydrogen Bonds and Improvement of Polymeric Crystallinity

The high-resolution structure of an α-chitin/hydrazine complex has been determined to reveal the molecular interactions between hydrazine molecules and chitin chains. The complexation with guest hydrazine molecules improves the crystallinity of α-chitin from the original form, so that the primary hydroxyl group is clearly located in the gt position on the chitin chains arranged in an antiparallel manner in contrast to the original α-chitin structure which has the disorder between gt and gg positions. During the complexation process, α-chitin chains translate by c/4 to incorporate hydrazine molecules. Molecular dynamics calculations based on the refined structure show that hydrazine nitrogen atoms are disordered with competing hydrogen bonds. These observations suggest a mechanism for the structural conversion of polysaccharides to their crystal solvate forms during penetration by amine molecules.

Polymeric, dimeric and monomeric Mn(II) complexes derived from [N′-(pyridine-4-carbonyl)-hydrazine]-carbodithioic acid methyl ester and 1-isonicotinoyl-4-phenyl-3-thiosemicarbazide: Syntheses, crystal structure and thermal analysis

The new Mn(II) polymeric complexes [Mn(pot)2(H2O)2]n (1) {pot−=5-(4-pyridyl)-1,3,4-oxadiazole-2-thione} and [Mn(ttfa)(μ-pchcm)]n (3) {Hpchcm=[N′-(pyridine-4-carbonyl)-hydrazine]-carbodithioic acid methyl ester}, from the precursor [Mn(ttfa)2(bpy)] (2) {Httfa=thenoyltrifluoroacetone}, as well as [Mn(ipt)2(o-phen)] (4) and [Mn(ttfa)2(ppta)2](ppta) (5) {ppta=N-phenyl-5-(4-pyridyl)-1,3,4-thiadiazol-2-yl-amine}, obtained from 1-isonicotinoyl-4-phenyl-3-thiosemicarbazide (Hipt) using o-phen and Httfa, are described. The ligand and complexes have been characterized by various physicochemical methods. The reaction of Hpchcm with Mn(OAc)2·4H2O in the presence of Httfa afforded an uniform two-dimensional Mn(II) coordination polymer, [Mn(pot)2(H2O)2]n (1), in which the cyclized ligand is bonded through the oxadiazole and pyridyl ring nitrogen atoms. During complexation, 1-isonicotinoyl-4-phenyl-3-thiosemicarbazide is converted to N-phenyl-5-(pyridine-4-yl)-1,3,4-thiadiazol-2-amine (ppta) in complex 5, where the Mn(II) center is bonded by two ttfa anions and two cyclized ppta ligands via pyridyl nitrogen atoms in axial positions. The crystal structure of complex 4 reveals that the ligand is uncyclized, bonded to the Mn(II) center as ON uninegative bidentate, through the deprotonated hydrazinic nitrogen and carbonyl oxygen atoms. The complexes have a distorted octahedral geometry around the metal center. Hpchcm acts as a multidentate ligand bonding through the Npy, Nhy, O and S atoms, producing five and six membered chelate rings in complex 3 and forming a network structure. The thermal behavior of the ligand Hpchcm and complexes 1, 2 and 3 have been studied which show that the complexes undergo two/three stages of decomposition and finally yield MnO as the residue.

Synthesis, structural characterization, and catalytic reactivity of a new molybdenum(VI) complex containing 1,3,4-thiadiazole derivative as a tridentate NNO donor ligand

A new cis-dioxo molybdenum(VI) complex was obtained by reaction of 2,4-dihydroxybenzylidene(5-N,N-methylphenylamino-1,3,4-thiadiazol-2-yl)hydrazone as ligand and [MoO2(acac)2] in methanol and was characterized by elemental analyses, 1H NMR, IR, and electronic spectroscopic studies. The complex was also analyzed by single-crystal X-ray diffraction. The structure determination revealed a distorted octahedral coordination geometry around molybdenum in which the tridentate NNO donor (L2–) is bonded to [MoO2]2+ through phenolic oxygen, hydrazinic nitrogen, and thiadiazole nitrogen. The sixth coordination site is occupied by a weakly bonded methanol. The complex was tested as a catalyst for homogeneous epoxidation of olefins using tert-butyl hydrogen peroxide as an oxidant. In the homogeneous catalytic system, the reactions are efficiently carried out with high yields and selectivity.

Hydrolysis of hydrazido-oxalic acid leading to the formation of hydrazinium cadmium hydrazido-oxalate/uranium oxalate species with a polymeric structure

A series of new metal hydrazido-oxalates with the formula [M(Hox)2(H2O)2]·nH2O, where M=Co (1), Ni (2) and Zn (3); Hox=hydazido-oxalate; n=0 (Co), 1 (Ni) and 5 (Zn), as well as (N2H6)0.5[Cd(Hox)2]NO3 (4) and the hydrazinium uranyl oxalate (N2H6)[(UO2)2(C2O4)3]·2H2O (5) were synthesized. Among the five synthesized compounds, the structures of 1, 4 and 5 were characterized by single crystal X-ray diffraction. The hydrazinium cation and oxalate anions generated in the synthesis were derived from hydrazido-oxalic acid, which is present in compounds 4 and 5. The structure of compound 1 consists of an octahedral coordination around cobalt, arising from two chelating (N,O) acid hydrazide ligands, coordinating through the carbonyl oxygen and hydrazinic nitrogen atoms in a cis-fashion, and two monodentate water molecules. It is interesting to note that the anionic carboxylate moieties are not involved in the coordination. Unlike cobalt, the anhydrous cadmium compound (4) consists of a hydrazinium (+2) cation, nitrate anion and a neutral cadmium hydrazido-oxalate complex. In this complex, the Cd(II) site has a coordination number of eight, comprising of six oxygen atoms and two nitrogen atoms with four adjacent hydrazido-oxalates. Thus, the polyhedral arrangement around the cadmium atoms is connected by hydrazido-oxalate groups to form a 2D framework [Cd(Hox)2], with tunnels and a square grid cross-section in two directions which form a cavity at their intersection. The structure of compound 5 consists of a two-dimensional network of uranyl and oxalate ions that form hexagonal rings. Specifically, the oxalate ions are tetradentate, each bridging two uranyl ions which are coordinated by three oxalate groups, and this results in a distorted hexagonal bipyramidal environment for the uranium atoms.

Trinuclear supramolecular Zn(II) complexes derived from N′-(pyridine carbonyl) hydrazine carboperthioates: Synthesis, structural characterization, luminescent properties and metalloaromaticity

Novel trinuclear Zn(II) complexes [Zn3(μ-4-pchcp)2(py)4] (1) and [Zn3(μ-3-pchcp)2(py)4] (2) have been isolated containing N′-(pyridine-4-carbonyl) and (N′-pyridine-3-carbonyl) hydrazine carboperthioate ligands which have been generated from potassium N′-(pyridine-4-carbonyl) and (N′-pyridine-3-carbonyl) hydrazine carbodithioates by in situ S–S coupling. In both complexes, the middle Zn(II) center has four coordinate tetrahedral arrangement bonded through two hydrazinic nitrogens and two sulfur atoms from two perthio ligands. This center mimic structurally a model compound for the zinc finger protein in which zinc is coordinated by two nitrogen atoms of the histidine and two sulfur atoms of the cysteine of the amino acid residue arranged in a tetrahedral fashion. Both terminal Zn(II) centers have five coordination with τ=0.57, characteristic of a geometry close to trigonal bipyramidal coordinated by one carbonyl oxygen, one hydrazinic nitrogen, one sulfur from perthio ligand and two nitrogens of pyridine which act as secondary ligand. In both complexes, ortho-CH bonds from the pyridine or pyridyl part of the ligand produce CH⋯π interactions with the metal chelate rings. The molecular geometry of complexes is symmetrical, which is a consequence of the four CH⋯π (chelate ring) interactions working cooperatively. We report here the self-assembly of two supramolecular structures based on similar trimeric Zn(II) units that are built from 4 and 3-substituted pyridyl ligands coordinated to Zn(II) ions. In the solid state, the supramolecular structures can be controlled by the pyridyl substituent via intermolecular interaction such as CH⋯S, π⋯π stacking and CH⋯π interactions. Complex 1 is a fluorescent material with maximum emission at 470nm at an excitation wavelength of 347nm.

A multiprotic indole-based thiocarbohydrazone in the formation of mono-, di- and hexa-nuclear metal complexes

A new thiocarbohydrazone (LH4) derived from indole-7-carbaldehyde was synthesized and reacted with NiII, PdII, PtII, CuI and AgI salts to bind the metals in various coordination fashions, forming complexes with different nuclearities. The reaction with CuCl in the presence of PPh3 produced a dinuclear CuI complex with the formula [Cu2Cl2(LH4)2(PPh3)2], in which LH4 binds the metals as a neutral μ2-S-donor ligand. The reaction of the thiosemicarbazone with AgI resulted in the formation of a hexanuclear complex featuring an Ag6S6 core. The ligand in this complex is monoanionic and uses the sulfur and a hydrazinic nitrogen atom in binding to the metals. The reaction of LH4 with [MCl2(PPh3)2] (M=NiII, PdII and PtII) at room temperature yielded complexes of the type [M(LH2)(PPh3)]. The thiocarbohydrazone in these complexes takes advantage of one indole N atom donor to act as a dianionic NNS tridentate ligand. A modification of the conditions of the reaction with the PdII salt led to the formation of the dinuclear complex [Pd2Cl(LH)(PPh3)3]. In this molecule, the thiocarbohydrazone is triply deprotonated and chelates one metal center by its dianionic NNS pocket, while coordinating the second metal ion through a hydrazinic N atom. The structure of the molecules was studied by X-ray crystallography and NMR spectroscopy.