Monoanionic Bidentate Research Articles

Arene-ruthenium complexes with 2-(arylazo)phenol as ancillary ligand: Synthesis, characterization, and utilization in catalytic transfer-hydrogenation

Reaction of 2-(arylazo)phenols (HL-R, where H represents the phenolic proton and, R = CH3, H and Cl) with [{Ru(p-cymene)Cl2}2] in the presence of triethylamine affords a group of three reddish-brown complexes of type [Ru(p-cymene)(L-R)Cl] in good yields. Structure of [Ru(p-cymene)(L-CH3)Cl] has been determined by X-ray crystallography. The 2-(arylazo)phenolate ligand (L-R) is coordinated to the metal center as a mono-anionic bidentate N,O-donor forming five-membered chelate ring. All the complexes are diamagnetic, and show characteristic 1H NMR signals. They also show intense absorptions in the visible and ultraviolet regions, which have been analyzed by TDDFT calculations. Cyclic voltammetry on the complexes shows two successive irreversible oxidations within 1.10–1.40 V versus SCE. The [Ru(p-cymene)(L-R)Cl] complexes are found to serve as efficient catalyst-precursor for the transfer-hydrogenation of aldehydes.

Synthesis, structural and photo-physical studies of transition metal complexes with Mannich bases derived from 2-mercaptobenzimidazole

Two Mannich base ligands, [1-(di-n-butylamine-N-methyl)mercapto-1H-benz-imidazole] (L1) and [1-(diphenylamine-N-methyl)mercapto-1H-benzimidazole] (L2)have been synthesized and further reacted with Co(II), Ni(II), Cu(II) and Zn(II) ionsto afford their respective complexes. The progress of the reaction was monitored by thin layer chromatography. The structural elucidation of Mannich base ligands and their metal complexes was done by Fourier Transform Infrared (FTIR), UV-Visible, Nuclear Magnetic Resonance spectroscopy (1H NMR & 13C NMR) and Atomic absorption spectroscopy (AAS) / Inductively coupled plasma emission spectroscopy (ICPES). FTIR and NMR studies supported the monoanionic bidentate coordination mode of L1 and L2 while tetrahedral geometries of metal complexes were proposed on the basis of AAS/ICP, magnetic moment and electronic spectroscopic data. The synthesized compounds were also investigated for their luminescent behavior which exhibited broad emission bands indicating charge transfer nature of the involved transitions. KEY WORDS: Metal complexes, Mannich bases, 2-Mercaptobenzimidazole, Luminescence Bull. Chem. Soc. Ethiop. 2018, 32(3), 481-490.DOI: https://dx.doi.org/10.4314/bcse.v32i3.7

Cyclometalated Iridium(III) Complexes Containing Benzoxazole Derivatives and Different Ancillary Ligands for Catalytic Oxidation of Toluene

A series of cyclometalated iridium(III) complexes that have the general formula [(C^N)2Ir(NR)(X)] (C^N = monoanionic bidentate cyclometalating ligands; NR = pyridine derivatives; X = Cl− or I−) are designed, prepared, and applied for the transformation of toluene to benzaldehyde using a clean, highly efficient, and environmentally-friendly process. The activation energies that are needed for the catalytic oxidation of toluene when using these complexes as catalysts are quite low: between 22.9 and 30.8 kcal mol−1. The catalytic frequencies (TOF) are fairly high (up to 7.0 × 102 h−1) with excellent reliability, and the turnover number (TON) can reach 4.2 × 103 after 6 h of processing time. Catalytic tests, X-ray absorption near-edge structure (XANES), and kinetic modeling are used to derive detailed insights into the characteristics of the catalysts and their effects on the reactions that are featured in the catalytic oxidation of toluene.

A group of diphosphine-thiosemicarbazone complexes of palladium: Efficient precursors for catalytic C[sbnd]C and C[sbnd]N coupling reactions

Reaction of 4-R-benzaldehyde thiosemicarbazone (denoted in general as HL-R; where H stands for the dissociable acidic proton and R (R = OCH3, CH3, H, Cl and NO2) for the substituent) with [Pd(dppe)(EtOH)2]2+, generated in situ via interaction of [Pd(dppe)Cl2] (dppe = 1,2-bis(diphenylphosphino)ethane) with AgNO3 in hot ethanol, in the presence of triethylamine affords a group of orange complexes of the type [Pd(dppe)(L-R)]NO3. Structures of [Pd(dppe)Cl2] and [Pd(dppe)(L-OCH3)]NO3 have been determined by X-ray crystallography. In the [Pd(dppe)(L-R)]NO3 complexes, the thiosemicarbazone ligands are coordinated to the metal center as monoanionic bidentate N,S-donors forming five-membered chelate rings. The [Pd(dppe)(L-R)]NO3 complexes show intense absorptions in the visible and ultraviolet regions, which have been analyzed by TDDFT calculations. All the [Pd(dppe)(L-R)]NO3 complexes are found to efficiently catalyze Suzuki-type CC and Buchwald-type CN coupling reactions.

Cytotoxicity studies, DNA interaction and protein binding of new Al (III), Ga (III) and In (III) complexes with 5‐hydroxyflavone

We report the synthesis and characterization of three new complexes of the natural flavonoid 5‐hydroxyflavone (primuletin) and Al (III), Ga (III), In (III), respectively. The physico‐chemical properties and structural features of these three novel compounds have been investigated by elemental and thermogravimetric analysis, molar conductance and several spectroscopic techniques, including FT‐IR, UV–Vis and mass spectra. Based on the experimental data, the general chemical formula of the complexes is [M (C15H9O3)3] · nH2O, where M is the cation and n = 2 for Al (III), n = 0 for Ga (III), n = 1, for In (III); each one of the three 5‐hydoxyflavone molecules acts as a monoanionic bidentate chelate ligand in the complexes. DFT calculations further sustain the proposed structures of the complexes. Cytotoxicity was studied using MTS assay on cervical, breast, colon and ovary adenocarcinoma cell lines. The central metal ions exert cytotoxic effects in a disparate manner: Al (III) enhances, while Ga (III) and In (III) decrease the cytotoxicity of the ligand. As a means to investigate the mechanism underlying the cytotoxic effects of the complexes, interactions with calf thymus DNA, human serum albumin and transferrin were also carried out.

Metal-Drug Interactions: Synthesis and Spectroscopic Characteristics, Surface Morphology, and Pharmacological Activity of Ephedrine–HCl Complexes with Mo(V), Nb(V), Ga(III), and Ge(IV)

Four new Mo(V), Nb(V), Ga(III), and Ge(IV) ephedrine complexes, [Mo(Eph)2(Cl)4].Cl, [Nb(Eph)2(Cl)3], [Ga(Eph)2(Cl)3], and [Ge(Eph)2(Cl)2] are synthesized and characterized. Composition and coordination behavior of ephedrine drug towards Mo(V), Nb(V), Ga(III), and Ge(IV) ions are deduced from microanalysis, IR spectra, molar conductance, magnetic and thermal analysis data. These support coordination of the eph ligand in its neutral state. Ephedrine has two powerful chelating sites, OH and NH, that determine its uni- or bidentate mode of action. IR spectra indicate that Mo(V) and Ga(III) coordinate to ephedrine via nitrogen atom of the NH group as a unidentate chelator with six and five coordination geometry, respectively. On the other hand, Eph ligand behaves as a monoanionic bidentate no chelating agent via the NH and deprotonated OH groups in Nb(V) and Ge(IV) complexes. Mo(V) complex demonstrates electrolytic properties, the other complexes are non-electrolytes in DMSO solutions. TG/DTG analysis makes it possible to calculate the number of solvent molecules in and outside the coordination sphere, and estimate stability of the synthesized complexes. The Eph complexes are screened in vitro for antibacterial (Escherichia coli, Pseudomonas aeruginosa, Bacillus subtilis and Staphylococcus aureus) and antifungal (Aspergillus flavus and Candida albicans) activities. Anti-cancer action of the Mo(V) and Ga(III) complexes is assessed against the human hepato cellular carcinoma (HepG-2) tumor cell line (IC50 >1000 μg/mL).

New Five Coordinate Ru(II) Carbonyl Complexes Containing 2‐Aminofluorene Schiff Base Derivatives: Synthesis, Structure and Catalytic Activity

AbstractThe monometallic five coordinated ruthenium(II) Schiff base complexes of the general type [Ru(CO)(EPh3)2(L1−3)]Cl (E=P or As) have been synthesized and characterized by analytical and spectral (FT−IR, UV−Vis and 1H NMR) methods. The electronic spectra of the complexes indicate the presence of intense MLCT transitions in the visible region. The molecular structure of the complex [Ru(CO)(PPh3)2(L3)]Cl 5 was characterized by single crystal X−ray diffraction studies, which revealed that the Schiff base ligands coordinated to the ruthenium(II) ion as mono anionic bidentate (O, N) donor forming six membered chelating rings. Further, the five coordinate [Ru(CO)(PPh3)2(L3)]Cl 5 complex was found efficiently to catalyze the formation of amides from various substituted aldehyde and showing higher catalytic activity in the presence of NH2OH.HCl and NaHCO3 and the yield was up to 97%.

Interaction of triorganotin(IV) moiety with quinolone antibacterial drug ciprofloxacin: Synthesis, spectroscopic investigation, electronic structure calculation, and biological evaluation

AbstractNew triorganotin(IV) derivatives of ciprofloxacin (HL) with general formula R3Sn(L) (where R = Me (1)/Cy (2) and L is the monoanion of ciprofloxacin) have been synthesized and structurally characterized on the basis of elemental analysis, IR, Raman, multinuclear (1H‐, 13C‐ and 119Sn‐) NMR, ESI‐MS, UV‐Visible, and emission spectroscopy. A distorted trigonal bipyramidal geometry around tin has been tentatively proposed for these triorganotin(IV) derivatives in which the ligand may act as monoanionic bidentate coordinating through the Ocarboxylate and Opyridone. The proposed structure has been validated by density functional theory (DFT)‐based electronic structure calculations at B3LYP/6‐31G(d,p)/Def2‐SVP(Sn) level of theory. The atomic charges have been calculated at the selected atoms, and the reactive sites have been assigned on the surface of the molecules through molecular electrostatic potential map. The frontier molecular orbitals and selected conceptual‐DFT‐based global reactivity descriptors have been calculated to obtain an insight into the structure and reactivity behavior of the complexes. A comparative analysis of the experimental vibrational frequencies and simulated harmonic frequencies indicates good correlation between them. The complexes were screened for their in vitro antibacterial activity against two Gram‐positive and five Gram‐negative bacterial strains. The results revealed that both the complexes exhibited promising antibacterial activity against the chosen strains (MIC: 0.062‐0.125 μg/mL).

Combined experimental and theoretical studies on the diorganotin(IV) complexes of sparfloxacin: Synthesis, spectroscopic and DFT studies, and biological activity

New diorganotin(IV) derivatives of sparfloxacin having general formula R2SnCl(L), (where L = monoanion of sparfloxacin (HL) and R = n-Bu (1)/Ph (2)) have been synthesized and structurally characterized by elemental analysis, IR, NMR (1H, 13C, 119Sn), HMQC, ESI-MS, UV–Vis and emission spectroscopy. These investigations suggest that, in these 1:1 monomeric derivatives the sparfloxacin ligand acts as monoanionic bidentate coordinating through the Ocarboxylate and Opyridone, and the polyhedron around tin is intermediate between pseudotetrahedral and cis-trigonal bipyramidal. The proposed structures have been validated by density functional theory (DFT) based electronic structure calculations at B3LYP/6-31G(d,p)/Def2-SVP(Sn) level of theory through the calculation of the atomic charges at the selected atoms, molecular electrostatic potential (MEP) map to assign sites on the surface of the molecules, the selected conceptual-DFT based global reactivity descriptors to obtain an insight into the structure and reactivity behaviour, and the frontier molecular orbital analysis to analyze the nature of frontier orbitals. A comparative analysis of the experimental vibrational frequencies and simulated harmonic frequencies indicates good correlation between them. The simulated UV–Vis spectrum was obtained with time dependent-DFT method in gas phase and in the solvent field with IEFPCM model. The simulated 1H and 13C NMR spectra were obtained by gauge-independent atomic orbital (GIAO) method and the results were in good agreement to the experimental results. The complexes were screened for their in vitro antibacterial activity against two Gram-positive and five Gram-negative bacterial strains. Both the complexes exhibited promising antibacterial activity against all the chosen strains (MIC: 0.062–0.125 μg ml−1).

New triorganotin(IV) complexes of quinolone antibacterial drug sparfloxacin: Synthesis, structural characterization, DFT studies and biological activity

A new series of triorganotin(IV) complexes of sparfloxacin (HL) having general formula R3SnL (where L is the monoanion of sparfloxacin (HL) and R = Me (1)/n‐Bu (2)/Ph (3)/Cy (4)) have been synthesized and characterized by elemental analysis, IR, NMR (1H, 13C, 119Sn), 2D‐HETCOR, ESI‐MS and UV‐Vis studies. These investigations suggest that, in these 1:1 monomeric derivatives the sparfloxacin ligand acts as monoanionic bidentate coordinating through the Ocarboxylate and Opyridone, and the polyhedron around tin is intermediate between pseudotetrahedral and cis‐trigonal bipyramidal, with Opyridone and two organic groups in equatorial plane and the carboxylate oxygen and the third organic group in axial positions. The proposed structures have been validated by density functional theory (DFT) based quantum chemical calculations at B3LYP/6‐31G(d,p)/Def2‐SVP(Sn) level of theory. A detailed electronic structure calculations were performed at this level of theory to calculate atomic charges at the selected atoms, molecular electrostatic potential (MEP) map to assign sites on the surface of the molecules, the selected conceptual‐DFT based global reactivity descriptors to obtain an insight into the structure and reactivity behaviour, and the frontier molecular orbital analysis to analyze the nature of frontier orbitals. All the complexes were screened for their in vitro antibacterial activity against two Gram‐positive and five Gram‐negative bacterial strains. All the complexes exhibited promising antibacterial activity as compared to sparfloxacin against all the chosen strains.

Bis(triazenide), tris(triazenide), and lantern-type of triazenide iron complexes: Synthesis and structural characterization

A commercially available triazine, PhNNN(H)Ph, served as a monoanionic bidentate ligand upon deprotonation using Fe[N(SiMe3)2]2. By simply using different ethereal solvents, the bis(diethylether) and bis(tetrahydrofurane) complexes of Fe[PhNNNPh]2, 1 and 2, can be prepared successfully. The structures of 1 and 2 were confirmed by single crystal X-ray diffraction studies and supported by NMR spectroscopy and elemental analysis. Interestingly, the solid-state structure of 1 exhibits two Et2O ligands coordinated to Fe(II) in a trans manner, whereas 2 shows two THF solvents bound to Fe(II) in a cis fashion. The tris(homoleptic) Fe(III) complex 3 was obtained upon oxidation in air, and the one electron reduced counterpart 4 can be synthesized when treating 3 with KC8. One of the reduced by-products was crystallized and confirmed as a lantern-type diiron complex [Fe2(μ-N,N′-PhNNNPh)4], 5, by single crystal X-ray diffraction. Remarkably, the FeFe bond of 2.1901(4) Å in 5 is among the shortest Fe(II) Fe(II) bond.

Cyclometalated Ru(II)‐NHC Complexes as Effective Catalysts for Transfer Hydrogenation: Influence of Wingtip Group on Catalytic Outcome

AbstractCyclometalated N‐heterocyclic carbene (NHC) based ruthenium benzene complexes of general formula [(η6‐C6H6)Ru(C C)Cl] (C C=1‐butyl‐3‐phenylimidazol‐2‐ylidene 1 a, 1‐isopropyl‐3‐phenylimidazol‐2‐ylidene 1 b and 1‐benzyl‐3‐phenylimidazol‐2‐ylidene 1 c) have been synthesised via C−H activation of 1‐alkyl‐3‐phenylimidazolium salts with [(η6‐C6H6)RuCl2]2 under silver transmetallation condition. All the complexes have been characterized by elemental analysis and spectral methods. The solid‐state structures of the complexes 2 a‐c have been established by a X‐ray single crystal diffraction study which revealed that NHC ligands behaved as mono anionic bidentate C C donors to the Ru(II) center via carbenic carbon and cyclometalated carbon. The newly synthesised ruthenium(II) NHC complexes 2 a‐c have been exploited as potential homogeneous catalysts to the transfer hydrogenation reactions for a broad scope of ketones to alcohols using 2‐propanol as a hydrogen source. The titled complexes worked well with low catalyst loading of 0.2 mol% with maximum conversion of 100% under optimized condition with reference to base, temperature, time, catalyst loading and substrate scope. Besides, the influence of the nature of wingtip group of the NHC ligands on the transfer hydrogenation reaction has also been reported to demonstrate the efficacy of catalyst.

Investigation on biomolecular interactions of nickel(II) complexes with monoanionic bidentate ligands

Reactions of monoanionic bidentate ligands 5-methylsalicylaldehyde (5-msal), 5-bromosalicylaldehyde (5-brsal), 5-nitrosalicylaldehyde (5-nsal) and 2-hydroxy-1-naphthaldehyde (2-hnap) with nickel perchlorate hexahydrate produced nickel(II) complexes 1–4, respectively. Single crystal X-ray analyses of complexes 1 and 2 confirmed bidentate mode of the ligands with O˄O coordination to give square planar geometry around nickel atoms. Complexes 1–4 showed one quasi-reversible redox peak at cathodic region (−0.67 to −0.80 V) and one redox peak at anodic region (+1.08 to +1.44 V) assignable to the Ni(II)/Ni(I) and Ni(II)/Ni(III) redox couples, respectively. The complexes exhibited good bovine serum albumin (BSA) binding abilities with a maximum binding constant of 1.96 × 105 M−1. The binding of complexes with calf thymus DNA (ctDNA) showed that the binding affinity is consistent with an increase in steric bulk of the ligands. The nuclease activity of the complexes showed efficient oxidative cleavage in the presence of hydrogen peroxide as an oxidizing agent. The complexes showed higher zone of inhibition when screened for antimicrobial activity against bacteria and human pathogenic fungi.

Reunderstanding the Fluorescent Behavior of Four-Coordinate Monoboron Complexes Containing Monoanionic Bidentate Ligands.

We demonstrated for the first time that, at temperatures below the melting point of a given polar solvent, the emission of some four-coordinate monoboron complexes containing monoanionic bidentate (NO) ligands shifted to lower wavelengths, but no such shift was observed for studies conducted in nonpolar solvents. This means that the emission from a polar solvent appears at shorter wavelengths if compared with that from a nonpolar solvent when the measurement was performed at low temperatures, a phenomenon totally different from that observed for conventional solvatochromic fluorophores. The finding was rationalized by considering the temperature-dependent conformational relaxation of the tetrahedron monoboron complexes from their local excited (LE) state to their relaxed excited (RE) state. Further studies revealed that variating the structure of the chelating ligands could result in remarkable changes in the fluorescent colors of the monoboron complexes. However, changing the structure of other two monodentate ligands showed little effect upon the fluorescence property of the compounds. Therefore, it is anticipated that the monoboron complexes may be taken as a platform to construct a variety of functional molecular systems via alternating the structure of the chelating ligand and that of the monodentate ligand. As an example, naphthalene was introduced as a monodentate ligand, and independent emissions from naphthalene unit and the other part of the monoboron complex as well as intramolecular energy transfer between them were observed. It is believed that the present work provides a new insight into the monoboron complexes, laying the foundation for them to be explored for developing novel molecular systems.

Monoanionic, Bis(pyrazolyl)methylborate [(Ph3B)CH(3,5-(CH3)2Pz)2)]- as a Supporting Ligand for Copper(I)-ethylene, cis-2-Butene, and Carbonyl Complexes.

The monoanionic bidentate ligand [(Ph3B)CH(3,5-(CH3)2Pz)2)]- has been prepared from lithium bis(pyrazolyl)methanide and triphenylborane. This useful new ligand is closely related to the well-established bis(pyrazolyl)borate and bis(pyrazolyl)methane ligands but has key differences to both analogues as well. The ethylene, cis-2-butene, and carbon monoxide adducts [(Ph3B)CH(3,5-(CH3)2Pz)2]Cu(L) (where L = C2H4, cis-CH3HC═CHCH3, and CO) have been prepared from [(Ph3B)CH(3,5-(CH3)2Pz)2)]Li(THF), copper(I) triflate, and the corresponding coligand. These complexes have been characterized by NMR spectroscopy and X-ray crystallography. In all cases the bis(pyrazolyl) moiety is bound in κ2N fashion with the BPh3 group rotated to sit over the metal center, sometimes coordinating to the metal via phenyl carbons as in [(Ph3B)CH(3,5-(CH3)2Pz)2)]Li(THF) and [(Ph3B)CH(3,5-(CH3)2Pz)2]Cu(CO) or simply hovering above the metal site as in [(Ph3B)CH(3,5-(CH3)2Pz)2)]Cu(C2H4) and [(Ph3B)CH(3,5-(CH3)2Pz)2)]Cu(cis-CH3HC═CHCH3). The 13C and 1H resonances of the ethylene carbon and protons of [(Ph3B)CH(3,5-(CH3)2Pz)2)]Cu(C2H4) appear at δ 81.0 and 3.71 ppm in CD2Cl2, respectively. The characteristic CO frequency for [(Ph3B)CH(3,5-(CH3)2Pz)2]Cu(CO) has been observed at υ̅ 2092 cm-1 by infrared spectroscopy and is lower than that of free CO suggesting moderate M → CO π-back-donation. A detailed analysis of these complexes has been presented herein.

Cyclometalated Iridium(III) Complexes with Ligand Effects on the Catalytic C–H Bond Activation of Toluene

New cyclometalated iridium(III) complexes have been designed, prepared and applied as catalytic systems for the C–H bond activation (CHA) of toluene through a clean, highly efficient, and environmentally friendly process. The complexes have the general formula [(C^N)2Ir(N^O)]. The C^N ligands are the monoanionic bidentate cyclometalating ligands 2‐phenylpyridinato (ppy), 2‐phenylbenzoxazolato (pbo), and 2‐(3.5‐difluorophenyl)benzoxazolato (dfpbo). The (N^O) ligand is also a monoanionic bidentate cyclometalating ligand, namely picolinato (pic). The complexes [(ppy)2Ir(pic)] (1), [(pbo)2Ir(pic)] (2), and [(dfpbo)2Ir(pic)] (3) were structurally characterized by 1H and 13C NMR spectroscopy, FAB‐MS, and X‐ray crystallography. The activation energies for the catalytic CHA oxidation of toluene when using complexes 1–3 as catalysts are quite low, between 14.4 and 25.5 kcal mol–1. The catalytic turnover frequencies (TOFs) are fairly high (up to 4.0 × 103 moltoluene molcatalyst–1 h–1) with excellent reliability and the turnover number (TON) can reach 2.40 × 104 moltoluene molcatalyst–1 after 6 h of reaction time. A combination of catalytic tests, DFT calculations, X‐ray absorption near‐edge structure (XANES) analysis, and kinetic modeling was used to derive detailed insights into the characteristics of the catalysts and their effect on the reactions featured in the CHA oxidation of toluene.

Polypyridyl-hydrazone based Ruthenium(II) complexes: Spectral and computational analysis

New octahedral Ruthenium(II) complexes of the general composition [Ru(bpy)2(L)]Cl containing aroyl hydrazone Schiff base ligands (L) (where bpy=bipyridine, L=4-((E)-(furan-2-carboylimino)methyl)benzoic acid (L1), 4-((E)-(4-methoxybenzoylimino)methyl)benzoic acid (L2) and 4-((E)-(4-nitrobenzoylimino)methyl)benzoic acid (L3)) have been synthesized. All the three complexes have been characterized by various physico-chemical and spectroscopic methods. The molecular structure of L1 and L2 were determined by single crystal X-ray diffraction method. IR study shows that the substituted aroylhydrazone ligands behave as a monoanionic bidentate O and N donors (L) coordinates to ruthenium via the azomethine nitrogen and the deprotonated amide oxygen. Photophysical and electrochemical studies were carried out and the structures of the synthesized complex were optimized using density functional theory (DFT). The molecular geometry, the highest occupied molecular orbital (HOMO), the lowest unoccupied molecular orbital (LUMO) energies and Mulliken atomic charges and molecular electrostatic potential (MEP) of the molecules are determined at the B3LYP method and standard 6-311++G (d,p) basis set starting from optimized geometry.

The synthesis and structural characterization of transition metal coordination complexes of coumarilic acid

The coumarilate (coum−) complexes of CoII(1), NiII(2) CuII(3) and ZnII(4) were synthesized and characterized by elemental analysis, magnetic susceptibility, solid-state UV–Vis, FTIR spectra, thermoanalytical TG–DTG/DTA and single-crystal X-ray diffraction methods. It was found that all of the complex structures have 2 mol (coum−) ligand bonded as monoanionic monodentate in the structures of 1 and 2 while they were coordinated to metal cations as monoanionic bidentate in the complexes 3 and 4. There was not any hydrate water in the metal complexes. The complexes of 1 and 2 have four moles of aqua ligand, and the other complexes have two moles. Thermal decomposition of each complex starts with dehydration, and then the decomposition of organic parts goes. The thermal dehydration of the complexes takes place in one (for the compounds of 2, 3, 4) or two (for the compound 1) steps. The decomposition mechanism and the thermal stability of the complexes under investigation were determined on the basis of their structures. Metal oxides were obtained as the final decomposition product.

Characterization of secondary phosphine oxide ligands on the surface of iridium nanoparticles.

The synthesis of iridium nanoparticles (IrNPs) ligated by various secondary phosphine oxides (SPOs) is described. This highly reproducible and simple method via H2 reduction produces well dispersed, small nanoparticles (NPs), which were characterized by the state-of-the-art techniques, such as TEM, HRTEM, WAXS and ATR FT-IR spectroscopy. In particular, multinuclear solid state MAS-NMR spectroscopy with and without cross polarization (CP) enabled us to investigate the different binding modes adopted by the ligand at the nanoparticle surface, suggesting the presence of three possible types of coordination: as a purely anionic ligand Ir-P(O)R2, as a neutral acid R2P-O-H and as a monoanionic bidentate H-bonded dimer R2P-O-HO[double bond, length as m-dash]PR2. Specifically, the higher basicity of the dicyclohexyl system leads to the formation of IrNPs in which the bidentate binding mode is most abundant. Such cyclohexyl groups are bent towards the edges, as is suggested by the study of 13CO coordination on the NP surface. This study also showed that the number of surface sites on faces available for bridging CO molecules is higher than the number of sites for terminal CO species on edges and apices, which is unexpected taking into account the small size of the nanoparticles. In addition, the IrNPs present a high chemoselectivity in the hydrogenation of cinnamaldehyde to the unsaturated alcohol.

Synthesis and Structural Investigation of New Bio-Relevant Complexes of Lanthanides with 5-Hydroxyflavone: DNA Binding and Protein Interaction Studies.

In the present work, we attempted to develop new metal coordination complexes of the natural flavonoid 5-hydroxyflavone with Sm(III), Eu(III), Gd(III), Tb(III). The resultant hydroxo complexes have been characterized by a variety of spectroscopic techniques, including fluorescence, FT-IR, UV-Vis, EPR and mass spectral studies. The general chemical formula of the complexes is [Ln(C15H9O3)3(OH)2(H2O)x]·nH2O, where Ln is the lanthanide cation and x = 0 for Sm(III), x = 1 for Eu(III), Gd(III), Tb(III) and n = 0 for Sm(III), Gd(III), Tb(III), n = 1 for Eu(III), respectively. The proposed structures of the complexes were optimized by DFT calculations. Theoretical calculations and experimental determinations sustain the proposed structures of the hydroxo complexes, with two molecules of 5-hydroxyflavone acting as monoanionic bidentate chelate ligands. The interaction of the complexes with calf thymus DNA has been explored by fluorescence titration and UV-Vis absorption binding studies, and revealed that the synthesized complexes interact with DNA with binding constants (Kb) ~ 104. Human serum albumin (HSA) and transferrin (Tf) binding studies have also been performed by fluorescence titration techniques (fluorescence quenching studies, synchronous fluorescence spectra). The apparent association constants (Ka) and thermodynamic parameters have been calculated from the fluorescence quenching experiment at 299 K, 308 K, and 318 K. The quenching curves indicate that the complexes bind to HSA with smaller affinity than the ligand, but to Tf with higher binding affinities than the ligand.