Neutral Monodentate Ligands Research Articles

Synthesis, Infrared Spectroscopic Characterization and Antimicrobial Studies of Co(III) Dimethylglyoximato Complexes with Aniline and Aniline-derived Axial Ligands

Complexes with cobalt(III) have been used as models in the study of vitamin B12 chemistry. In this study, cobalt(III) complexes with dimethylglyoxime as equatorial ligand and aniline or substituted aniline as well as thiocyanate ion as axial ligands have been synthesized and characterized based on melting point, conductivity, solubility and infrared (IR) spectral studies. The complexes are formulated as [Co(Hdmg)2(B)(SCN)] where Hdmg is dimethylglyoximato, B = aniline (A), 4-bromoaline (4BrA), 2- nitroaniline (2NA), 4-nitroaniline (4NA) or 4-anisidine (4PA). The complexes were formed in low yields (33 – 37 %) except [Co(Hdmg)2(A)(SCN)] which was obtained in significant yield (65 %). The percentage yield of the synthesized cobaloximes follows the order A > 4NA > 4PA > 4BrA = 2NA. They are of various colours, soluble or slightly soluble in the solvents used and have melting points in the range (77 – 120 0C). The data from IR spectra indicated that the coordination compounds coordinated via the nitrogen of the ligands. Further supportive fact of the coordination of the ligands to the metal ions was deduced from the emergence of new bands due to v(M-N) in the metal complexes. In the proposed octahedral coordination sphere of the central cobalt atom, four coordination sites in the equatorial positions are occupied by nitrogen atoms of two dimethylglyoximate monoanions, and the other two sites are occupied by atoms of monodentate neutral ligands and thiocyanate anion. The measured molar conductance showed that the complexes are non-electrolytes, except [Co(Hdmg)2(4BrA)(SCN)] which has conductivity of 149 Scm2 mol-1, hence electrolytic in nature. The in vitro antibacterial potency of the complexes were assayed against some strains of bacteria such as MRSA (Methicillin Resistance Staphylococcus) Staphylococcus aureus, Bacillus subtilis, Streptococcus pneumoniae, and the Gram negative bacteria, Salmonella typhi, Klebsiella pneumoniae, Escherichia coli, and Pseudomonas aeruginosa. The results of the antimicrobial assay uncovered that the complexes have more potency than their free ligands but less than that of the standard drug (Gentamicin)

Strong proton transfer from phenolic ring to imine functionality in 1D azido and dicyanamido bridged Mn(II) coordination polymers: Synthesis, crystal structure and magnetic studies

In this research, two new 1D coordination polymers of Mn(II), [Mn(LH)2(µ1,5-dca)2]n (1) and [Mn(LH)2(µ1,3-N3)(CH3OH)(N3)]n (2) were synthesized and characterized by elemental analysis, spectroscopic methods, single crystal X-ray analysis and magnetic measurements (LH = Schiff base ligand obtained from the reaction of 2-hydroxy-1-naphthaldehyde and 2-amino-5-chloropyridine). These compounds were synthesized by the reaction of LH, MnCl2·4H2O and NaN(CN)2 (for compound 1) or NaN3 (for compound 2) in 1:1:2 M ratio in methanol. The spectroscopic and structural studies indicated that strong intramolecular proton transfer from naphtholic oxygen to the imine nitrogen is occurred in the ligand and due to this; the nitrogen atom of imine functionality is not coordinated to the metal core. As a result, the ligand is coordinated to the metal core as monodentate neutral ligand. The proton transfer process was attributed to the strong electron withdrawing properties of 5-chloropyridine ring. In the structure of compound 1 and 2, the manganese ions are connected to each other through µ1,5-dca and µ1,3-azide bridges, respectively to form 1D coordination polymers. The magnetic measurements showed the presence of antiferromagnetic interactions between Mn∙∙∙Mn cores in both of the obtained 1D coordination polymers, whereat the exchange interaction is an order of magnitude stronger in azido compared to dicyanamido bridged compound (–3.7 cm−1 vs. –0.30 cm−1).

Regioselective interaction of bifunctional o-quinone, annulated with dithiete cycle, and Ni(CO)4. New heterospin bis(o-semiquinonato) nickel complexes

Regioselective activation of dioxolene coordination site was observed in reactions of Ni(CO)4 and bifunctional o-quinone, annulated with dithiete cycle (ditQ). Novel hexacoordinated bis(o-semiquinonato) nickel complexes Ni(ditSQ)2(THF)2 (1), Ni(ditSQ)2(Py)2 (2), Ni(ditSQ)2(2,2′-bpy) (3) and Ni(ditSQ)2(4-NIT-Py)2 (4) (4-NIT-Py = 2-(4-pyridinyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide) were obtained. X-ray diffractometry study revealed a distorted octahedral geometry with trans-arrangement of neutral monodentate ligands for Ni ion. Ferromagnetic metal–ligand and antiferromagnetic ligand–ligand exchange interactions were observed in obtained heterospin systems.

DFT analysis of the interaction between Hg2+ and monodentate neutral ligands using NBO, EDA, and QTAIM.

We report thermodynamic, geometric, and electronic parameters for the interaction between neutral ligands and the [Hg(H2O)]2+ dication, using the B3LYP/6-311 + G(d,p) approach. Gibbs free energies for the interaction were employed to rank the affinity order of the several neutral ligands. To identify the parameters that characterize the affinity between the two fragments, the metal-ligand interaction was analyzed according to the EDA, NBO, and QTAIM decomposition schemes. The phosphine oxide showed the highest affinity for the Hg(H2O)2+ dication, mainly due to the P=O bond polarization. Ligands containing the sulfur atom, characterized by a high covalent component for the metal-ligand interaction, are the following in the interaction order. According to the Gibbs free energy for substitution of one water molecule in the [Hg(H2O)2]2+ complex, the sequence for the affinity order is: phosphine oxide > thioketone > thioesther > lactam > amide > amine > carboxylic acid > thiophene > ketone > esther > thiol > thiocyanate > ammonia > disulfide > aldehyde > ether > haloydrin > alcohol > enol > azide. Graphical abstract Synopsis The interaction between the Hg2+ cation and monodentate ligands containing S, O, or N atoms was evaluated in terms of energetic (bond strength, electrostatic and covalent interactions, donation energy), geometric (metal-ligand distance), electronic (atomic charges, orbital overlap, orbital hybridization) and topologic parameters.

(CF3 )3 Au as a Highly Acidic Organogold(III) Fragment.

The Lewis acidity of perfluorinated trimethylgold (CF3 )3 Au was assessed by theoretical and experimental methods. It was found that the (CF3 )3 Au unit is much more acidic than its nonfluorinated analogue (CH3 )3 Au, and probably sets the upper limit of the acidity scale for neutral organogold(III) species R3 Au. The significant acidity increase on fluorination is in line with the CF3 group being more electron-withdrawing than CH3 . The solvate (CF3 )3 Au⋅OEt2 (1) is presented as a convenient synthon of the unsaturated, 14-electron species (CF3 )3 Au. Thus, the weakly coordinated ether molecule in 1 is readily replaced by a variety of neutral ligands (L) to afford a wide range of (CF3 )3 Au⋅L compounds, which were isolated and characterized. Most of these mononuclear compounds exhibit marked thermal stability. This enhanced stabilization can be rationalized in terms of substantially stronger [Au]-L interactions with the (CF3 )3 Au unit. An affinity scale of this single-site, highly acidic organogold(III) fragment was calculated by DFT methods and experimentally mapped for various neutral monodentate ligands. The high-energy profile calculated for the fluorotropic [Au]-CF3 ⇌F-[Au]←CF2 process makes this potential decomposition path unfavorable and adds to the general stabilization of the fragment.

Synthesis, structure, and biological properties of mixed cobalt(III) dioximates with guanidine derivatives

Two Co(III) dioximates, cyanoguanidine complex {[Na2(µ-H2O)2(L1)2(H2O)2]-[CoIII(DmgH)2(N3)2]} n [CoIII(DmgH)2(N3)2] n (L1 = (H2N)2C=N–C=N) (I) and aminoguanidine complex [H3L2][Co(DmgH)2(N3)2] (H2L2 = H2N–C(=NH)–NH–NH2) (II), were synthesized from the [CoCl(DmgH)2(H2O)] structural unit (DmgH– is the dimethylglyoxime monoanion). The implementation of the synthesis was confirmed by chemical analysis, IR spectroscopy, and X-ray diffraction (CIF files CCDC 1531845 (I), 1531846 (II)). Both compounds are ionic. Compound I consists of cations representing centrosymmetrical 2D coordination polymers, {[Na2(µ-H2O)2(L1)2(H2O)2][CoIII(DmgH)2(N3)2]} n+ n , and monomeric [Co(DmgH)2(N3)2]– anions, while in II, the charge of the [Co(DmgH)2(N3)2]– complex anion is counterbalanced by the organic [H3L2]+ cation. In I, L1 is coordinated to the metal as a monodentate neutral ligand, while in II, H2L2 occurs in the complex as a protonated uncoordinated component. Since L1 in I and H2L2 in II contain functional amine groups able to form intermolecular hydrogen bonds acting as proton donors, the component packing mode in the crystals was analyzed assuming various types of interactions, apart from electrostatic ones. The biological properties of the complexes were tested considering their effect on the biosynthesis of proteases by the micromycete Fusarium gibbosum CNMN FD 12 strain. Culturing the producer on a culture medium containing complex I in the selected optimal concentrations of 5–10 mg/L was found to increase the acid protease activity by 140–150%.

Hydrosilylation of Terminal Alkynes Catalyzed by a ONO-Pincer Iridium(III) Hydride Compound: Mechanistic Insights into the Hydrosilylation and Dehydrogenative Silylation Catalysis

The catalytic activity in the hydrosilylation of terminal alkynes by the unsaturated hydrido iridium(III) compound [IrH(κ3-hqca)(coe)] (1), which contains the rigid asymmetrical dianionic ONO pincer ligand 8-oxidoquinoline-2-carboxylate, has been studied. A range of aliphatic and aromatic 1-alkynes has been efficiently reduced using various hydrosilanes. Hydrosilylation of the linear 1-alkynes hex-1-yne and oct-1-yne gives a good selectivity toward the β-(Z)-vinylsilane product, while for the bulkier t-Bu-C≡CH a reverse selectivity toward the β-(E)-vinylsilane and significant amounts of alkene, from a competitive dehydrogenative silylation, has been observed. Compound 1, unreactive toward silanes, reacts with a range of terminal alkynes RC≡CH, affording the unsaturated η1-alkenyl complexes [Ir(κ3-hqca)(E-CH═CHR)(coe)] in good yield. These species are able to coordinate monodentate neutral ligands such as PPh3 and pyridine, or CO in a reversible way, to yield octahedral derivatives. Further mechanistic asp...

Specific features of the structures of monomeric octahedral d 2-rhenium(V) monooxo complexes with oxygen atoms trans to the oxo ligands: Complexes with monodentate neutral ligands OR trans (OR = DMF, R'OH, L1–L3)

Specific features of the structures of ten mononuclear octahedral rhenium(V) oxo complexes (I–X) with the oxygen atoms of the ligands DMF, R'OH (R' = Me, Et, Pr), and Ln (Ln = ON4C6 ∙ C6H10 (n = 1), O–(C6H3MeCH2NH+Et2) (n = 2), O–(NH+C5H4) (n = 3)) trans to the multiply bonded oxo ligands have been considered. The Re–O(OR)trans bonds in complexes I–VII (OR = DMF, R'OH, L1) are elongated owing to the structural manifestation of the trans influence of multiply bonded oxo ligands. The Re–O–(OR) bonds with a negatively charged oxygen atom in three complexes with zwitterionic ligands L2 (in VIII) and L3 (in IX and X) are either comparable with the standard Re–O(ST) bond length (in IX and X) or strongly shortened as compared with Rе–O(ST) (in complex VIII). In the anionic complex [ReO(MeOH)Cl2(L4)]– (XI), the oxygen atom of the monomeric neutral ligand МеOH is unexpectedly cis to the oxo ligand, while the trans position to =O(oxo) is occupied by the acido oxygen atom of the bidentate chelating monodeprotonated 2-(diphenylphosphonyl) benzoate ligand (L4)–.

Tazarotene copper complexes: Synthesis, crystal structure, DFT and biological activity evaluation

New mononuclear copper(II) complexes of the first topical receptor-selective retinoid drug, Tazarotene (Tz), of the type [Cu(Tz)2X2] (X=Cl (1) and Br (2a)) were synthesized, characterized (elemental analysis, TG, FT IR, UV–Vis, EPR, magnetic susceptibility, molar conductance measurements and single crystal X-ray analysis) and tested for their antimicrobial activities against Staphylococcus aureus and Escherichia coli. Tazarotene behaves as a neutral monodentate ligand via the pyridine nitrogen atom. Complex 1 crystallizes in the monoclinic P21/c space group. The environment around the metal center in 1 could be described as an intermediate between tetrahedral and square–planar geometries. Crystals of the polymeric {[Cu(Tz)(μ-Br)]}n (2b) complex were obtained by the slow evaporation of the reaction filtrate of complex 2a. The distorted tetrahedral environment around Cu(I) is formed from the pyridine N atom of Tz, the S atom of another Tz molecule as well as two bridged bromine atoms, with a Cu…Cu′ distance of 3.327Å. Time-dependent density functional theory calculations were carried out to understand the electronic structure and to explain the related experimental findings. The electronic arrangement, type of hybridization and nature of bonding were obtained from natural bond orbital analysis.

Insights on the UV/Vis, Fluorescence, and Cyclic Voltammetry Properties and the Molecular Structures of ZnII Tetraphenylporphyrin Complexes with Pseudohalide Axial Azido, Cyanato‐N, Thiocyanato‐N, and Cyanido Ligands

AbstractThe syntheses, spectroscopic and photophysical properties, and molecular structures of azido‐ (1), cyanato‐N‐ (2), thiocyanato‐N‐ (3), and cyanido‐ (4) (meso‐tetraphenylporphyrinato)zinc(II) complexes are reported. These species were prepared by using cryptand‐222 to solubilize the pseudohalide salts in organic solvents. The UV/Vis spectra of these zinc metalloporphyrins are solvent‐dependent and exhibit large redshifted Soret bands compared with those of the [Zn(Porph)L] derivatives in which Porph is a meso‐porphyrinato ligand and L is a monodentate neutral axial ligand. The room‐temperature fluorescence spectra of the zinc complexes 1–4 indicate that the Q bands are not very affected by the nature of the axial ligands, and their positions are very close to those of previously reported (meso‐porphyrinato)zinc complexes. The quantum yields of the S1 → So fluorescence of 1–4 range between 2.8 and 5.5 %, and their fluorescence lifetimes are the same (1.7 ns). Cyclic voltammetry investigations on 1–4 show that the characteristic potentials for the reduction and the two first oxidations of the porphyrin ring are not very affected by the nature of the axial ligand. A third irreversible oxidation of the porphyrin ring is observed. Additional anodic irreversible waves are observed for the thiocyanato‐N (3) and cyanido (4) species. The solid‐state molecular structures of 1–4 are the first examples of zinc porphyrin complexes with anionic ligands. The average equatorial zinc–pyrrole N atom (Zn–Np) distances for 1–4 range between 2.083(1) and 2.117(2) Å and are much longer than those of the related pentacoordinate zinc porphyrin complexes with monodentate neutral ligands. As a consequence, the displacement of the Zn2+ cation from the mean 24‐atom plan of the porphyrin core is significant (ca. 0.5 Å), and the porphyrin core is very distorted. The crystal structures of 1–4 are stabilized by weak intermolecular π interactions, C–H···Cg (Cg are the centroids of some six‐membered phenyl rings and five‐membered pyrrole rings). The molecular structure of 1 is further stabilized by weak intermolecular C–H···N hydrogen bonds between one carbon atom of cryptand‐222 and the terminal nitrogen atom of the azido ligand.

Facile formation of homoleptic Au(III) trications via simultaneous oxidation and ligand delivery from [PhI(pyridine)2](2+).

We report the first examples of Au(III) tricationic complexes bound only by neutral monodentate ligands, which are a new class of gold reagents. Oxidative addition to the bis-pyridine Au(I) cation, [Au(4-DMAP)2](+), using a series of dicationic I(III) oxidants of the general form [PhI(L)2](2+) (L = pyridine, 4-DMAP, 4-cyanopyridine) allows ready access to homoleptic and pseudo-homoleptic Au(III) complexes [Au(4-DMAP)2(L)2](3+). The facile oxidative addition of Au(I) species additionally demonstrates the efficacy of PhI(L)2](2+) reagents as halide-free oxidants for Au(I). Comparisons are made via attempts to oxidize NHC-Au(I)Cl, where introduction of the chloride anion results in complex mixtures via ligand and chloride exchange, demonstrating the advantage of using the pyridine-based homoleptic compounds. The new Au(III) trications show intriguing reactivity with water, yielding dinuclear oxo-bridged and rare terminal Au(III)-OH complexes.

Complexes of cis-dioxomolybdenum(VI) and oxovanadium(IV) with a tridentate ONS donor ligand: Synthesis, spectroscopic properties, X-ray crystal structure and catalytic activity

New cis-dioxomolybdenum(VI) and oxovanadium(IV) complexes of the Schiff base, derived from S-methyl dithiocarbazate and 2,3-dihydroxybenzaldehyde (H2dhsm), have been synthesized. The complexes of the type cis-[MoO2(dhsm)] (1a), cis-[MoO2(dhsm)(D)] (1b–1d) [D=neutral monodentate ligand; EtOH, pyridine (py) or imidazole (imz)], [VO(dhsm)(NN)] (2a, 2b) [NN=2,2′-bipyridine (bipy) or 1,10-phenanthroline (phen)] and [VO(dhsm)] (2c) have been isolated, characterized by 1H NMR, IR, UV–Vis and EPR spectral studies and investigated by cyclic voltammetry. The X-ray crystal structure of cis-[MoO2(dhsm)(EtOH)] (1b) has been determined and shows that the complex has a distorted octahedral geometry in which the H2dhsm behaves as a dianionic ONS tridentate ligand coordinating via phenoxide oxygen, hydrazinic nitrogen and thiolate sulfur. The oxomolybdenum(IV) complex [MoO(dhsm)] (1e) has obtained from dioxomolybdenum(VI) complex (1b) by oxo abstraction with PPh3. The reactivity of the complexes toward catalytic oxidation of alcohols in the presence of H2O2 and t-BuOOH as co-oxidants under solvent free conditions is reported.

Activation of Rhenium(I) Toward Substitution in fac-[Re(N,O′-Bid)(CO)3(HOCH3)] by Schiff-Base Bidentate Ligands (N,O′-Bid)

A series of fac-[Re(N,O'-Bid)(CO)3(L)] (N,O'-Bid = monoanionic bidentate Schiff-base ligands with N,O donor atoms; L = neutral monodentate ligand) has been synthesized, and the methanol substitution reactions have been investigated. The complexes were characterized by NMR, IR, and UV-vis spectroscopy. X-ray crystal structures of the compounds fac-[Re(Sal-mTol)(CO)3(HOCH3)], fac-[Re(Sal-pTol)(CO)3(HOCH3)], fac-[Re(Sal-Ph)(CO)3(HOCH3)], and fac-[Re(Sal-Ph)(CO)3(Py)] (Sal-mTol = 2-(m-tolyliminomethyl)phenolato; Sal-pTol = 2-(p-tolyliminomethyl)phenolato; Sal-Ph = 2-(phenyliminomethyl)phenolato; Py = pyridine) are reported. Significant activation for the methanol substitution is induced by the use of the N,O bidentate ligand as manifested by the second order rate constants, with limiting kinetics being observed for the first time. Rate constants (25 °C) (k1 or k3) and activation parameters (ΔHk‡, kJ mol(-1); ΔSk‡, J K(-1) mol(-1)) from Eyring plots for entering nucleophiles as indicated are as follows: fac-[Re(Sal-mTol)(CO)3(HOCH3)] 3-chloropyridine: (k1) 2.33 ± 0.01 M(-1) s(-1); 85.1 ± 0.6, 48 ± 2; fac-[Re(Sal-mTol)(CO)3(HOCH3)] pyridine: (k1) 1.29 ± 0.02 M(-1) s(-1); 92 ± 2, 66 ± 7; fac-[Re(Sal-mTol)(CO)3(HOCH3)] 4-picoline: (k1) 1.27 ± 0.05 M(-1) s(-1); 88 ± 2, 53 ± 6; (k3) 3.9 ± 0.03 s(-1); 78 ± 8, 30 ± 27; (kf) 1.7 ± 0.02 M(-1) s(-1); 86 ± 2, 49 ± 6; fac-[Re(Sal-mTol)(CO)3(HOCH3)] DMAP (k3) 1.15 ± 0.02 s(-1); 88 ± 2, 52 ± 7. An interchange dissociative mechanism is proposed.

ChemInform Abstract: Asymmetric Hydrogenation Using Rhodium Complexes Generated from Mixtures of Monodentate Neutral and Anionic Phosphorus Ligands.

AbstractThis is a study concerning ligand effects and catalyst formation in the asymmetric hydrogenation of olefins.

The Goldilocks principle in action: synthesis and structural characterization of a novel {Cu4(μ3-OH)4} cubane stabilized by monodentate ligands

A {Cu4(μ3-OH)4} compound, where four copper(II) and four μ3-bridging oxygen atoms occupy alternate corners of a slightly distorted cube, has been prepared and structurally characterized. This species, formulated as [Cu4(μ3-OH)4(Htmpz)8](ClO4)4·1.5Et2O (Htmpz = 3,4,5-1H-trimethyl pyrazole), can be classified as belonging to type I Cu4O4 cubane complexes, and is better described as two Cu(II)-(μ-OH)2-Cu(II) units held together by four long Cu-O bonds. The central distorted cubane core is stabilized by neutral monodentate ligands (Htmpz) and perchlorate anions, as demonstrated by single-crystal X-ray structure analysis. The title compound was obtained by hydrolysis of a dinuclear methoxo-bridged species, [Cu(μ-OCH3)(Htmpz)2]2(ClO4)2, which was prepared by reaction of [Cu(Htmpz)4(ClO4)2] with methanol. All these reactions represent a nice example of the Goldilocks principle in action in coordination chemistry, since each single actor (solvent, counteranion, and ligand) has the "just right" electronic, steric or coordinative properties which determine the fate of the final products.

Asymmetric Hydrogenation Using Rhodium Complexes Generated from Mixtures of Monodentate Neutral and Anionic Phosphorus Ligands

A series of monodentate neutral and anionic phosphorus ligands was synthesized and evaluated in the asymmetric rhodium-catalyzed hydrogenation of functionalized olefins by using either catalysts containing identical ligands or catalysts generated from mixtures of two different ligands. We expected that the combination of an anionic ligand with a neutral ligand would favor the formation of hetero over homo bis-ligand complexes due to charge repulsion. NMR spectroscopic studies confirmed that charge effects can indeed shift the equilibrium toward the hetero bis-ligand complexes. In several cases, the combination of a neutral phosphane with an anionic phosphane, one chiral and the other achiral, furnished significantly higher enantioselectivities than analogous mixtures of two neutral ligands. The best results were obtained with a mixture of an anionic phosphoramidite and a neutral phosphoric acid diester. It is supposed that in this case a hydrogen bond between the two ligands additionally stabilizes the hetero ligand combination.

Synthesis and characterization of binary and ternary complexes of Co(II), Ni(II), Cu(II) and Zn(II) ions based on 4-aminotoluene-3-sulfonic acid

Salicylidene (4-aminotoluene-3-sulfonic acid) Schiff base ligand H2L, and its binary and ternary Co(II), Ni(II), Cu(II) and Zn(II) complexes using 8-hydroxyquinoline (8-HOqu) and 2-aminopyridine (2-Ampy) as secondary ligands have been synthesised and characterized via elemental analysis, spectral data (IR, 1H NMR, mass and solid reflectance), molar conductance, magnetic moment, TG–DSC measurements and XRPD analysis. Correlation of all spectroscopic data suggest that H2L ligand acts as monoanionic terdentate ligand with ONO sites coordinating to the metal ions via deprotonated phenolic-O, azomethine-N and sulfonate-O while 2-Ampy behaves as a neutral monodentate ligand via amino group-N and 8-HOqu behaves as a monoanionic bidentate ligand through the ring-N and deprotonated phenolic-O. The thermal behavior of these complexes shows that the coordinated water molecules were eliminated from the complexes at relatively higher temperatures than the hydrated water and there are two routes in removal of coordinated water molecules. All complexes have mononuclear structure and the tetrahedral, square planar or an octahedral geometry have been proposed. The ligand and its complexes have been screened for their antimicrobial activity against Staphylococcus aureus, Bacillus subtilis, Escherichia coli, Salmonella typhimurium, Candida albicans and Aspergillus fumigatus. Among the synthesised compounds, the binary and ternary Ni(II) complexes, (2, 8 and 10) and ternary Zn(II) complex, (12) were found to be very effective against Candida albicans and Bacillus subtilis than all other complexes with MICs of 2 and 8μg/mL, respectively.

New Mn(II), Ni(II), Cd(II), Pb(II) complexes with 2-methylbenzimidazole and other ligands. Synthesis, spectroscopic characterization, crystal structure, magnetic susceptibility and biological activity studies

Synthesis and characterization of Mn(II), Ni(II), Cd(II) and Pb(II) mixed ligand complexes of 2-methylbenzimidazole with other ligands have been reported. The structure of the ligands and their complexes was investigated using elemental analysis, IR, UV–Vis, (1H, 13C) NMR spectroscopy, molar conductivity and magnetic susceptibility measurements. In all the studies of complexes, the 2-methylbenzimidazole behaves as a neutral monodentate ligand which is coordinated with the metal ions through the N atom. While benzotriazole behaves as a neutral bidentate ligand which is coordinated with the Ni(II) ion through the two N atoms. Moreover, the N-acetylglycine behaves as a bidentate ligand which is coordinated with the Mn(II), Ni(II) and Pb(II) ions through the N atom and the terminal carboxyl oxygen atom. The magnetic and spectral data indicate the tetrahedral geometry for Mn(II) complex, irregular tetrahedral geometry for Pb(II) complex and octahedral geometry for Ni(II) complex. The X-ray single crystal diffraction method was used to confirm a centrosymmetric dinuclear Cd(II) complex as each two metal ions are linked by a pair of thiocyanate N=S bridge. Two 2-methylbenzimidazole N-atom donors and one terminal thiocyanate N atom complete a highly distorted square pyramid geometry around the Cd atom. Besides, different cell types were used to determine the inhibitory effect of Mn(II), Ni(II), Cd(II) and Pb(II) complexes on cell growth using MTT assay. Cd(II) complex showed cytotoxic effect on various types of cancer cell lines with different EC50 values.

Palladium β-diiminate chemistry: Reactivity towards monodentate ligands and arylboronic acids

Here we report the synthesis and characterization of a series of palladium β-diiminate complexes. Chloro-bridged dimers [Pd(Ar2nacnac)(μ-Cl)]2 (where [Ar2nacnac]− is [(ArNC(CH3))2CH]− with Ar being aryl substituents) can serve as versatile starting materials, and can be cleaved by neutral monodentate ligands (L) to form mononuclear complexes [Pd(Ar2nacnac)(L)Cl], or engage in unusual transmetallation reactions with boronic acids to form tetrapallada-macrocycles. The reactivity of the tetrapallada-macrocyclic complexes towards L-type ligands, as well as the reactivity of Pd(Ar2nacnac)(L)Cl] complexes towards boronic acids was also explored.

Some new organotin(IV) schiff base adducts: Synthesis, spectroscopic characterization and thermal studies

Three new Schiff base adducts, [SnMe2Cl2(H2cdnaphen)] (1), [SnPh2Cl2(H2cdnaphen)2].C6H6 (2) and [SnBu2Cl2(H2cdnaphen)2] (3) were synthesized by the reaction of SnR2Cl2 (R = Me, Bu and Ph) with a Schiff base ligand, Methyl 2-[2-(2-hydroxynaphthaldimino)ethylamino]-1-cyclopentene-1-dithiocarboxylate (H2cdnaphen). The new products were characterized by elemental analysis, IR, 1H NMR and 119Sn NMR spectroscopies. Spectroscopic data suggest that H2cdnaphen exists predominately in keto-amine tautomeric form and in all complexes acts as a monodentate neutral ligand coordinating with the metal through oxygen atom, while the sulfur atom and imine nitrogen are not involved in coordination with the tin. Thermal decomposition of the complexes was studied through thermogravimetry and the thermodynamic activation parameters were determined by the Coats-Redfern method.