Six-coordinate Octahedral Geometry Research Articles

Spectral, XRD, SEM and biological properties of new mononuclear Schiff base transition metal complexes

Six new transition metal complexes derived from the reaction of 4 ( 4 -(dimethylamino) benzylideneamino) benzoic acid and Mn(II), Fe(II), Co(II), Ni(II), Cu(II) and Zn(II) cations, were prepared, isolated and characterized by a range of spectral and analytical methods including UV/Vis, FT IR, NMR, MS, powder XRD, TGA and SEM. The complexes were formed with the deprotonation of the ligand and presented typical six-coordinated octahedral geometry. In addition, the biological activity was evaluated by conducting in vitro anti-bacterial, anti-fungal and anti-leishmanial screenings. All the complexes were found more active than the ligand, while complex 7 revealed biological significance. Six new mononuclear transition metal complexes were synthesized with Schiff base ligand i.e. 4 ( 4 -(dimethylamino) benzylideneamino) benzoic acid in 1:2 molar stoichiometry. Analytical data obtained proved the deprotonation of the ligand in distorted octahedral geometry. Zn(II) complex proved an interesting biological significance during the in vitro anti-bacterial and anti-fungal screenings. • Mononuclear transition metal Schiff base complexes were synthesized. • Solution structures were determined using UV/Vis and NMR. • Solid structure analysis was carried out via FT IR, XRD, and SEM. • Excellent anti-leishmanial activity

Surface modification of anatase nanoparticles with fused ring salicylate-type ligands (3-hydroxy-2-naphthoic acids): a combined DFT and experimental study of optical properties

The surface modification of nanocrystalline TiO2 particles (45 Å) with salicylate-type ligands consisting of an extended aromatic ring system, specifically 3-hydroxy-2-naphthoic acid, 3,5-dihydroxy-2-naphthoic acid and 3,7-dihydroxy-2-naphthoic acid, was found to alter the optical properties of nanoparticles in a similar way to salicylic acid. The formation of the inner-sphere charge-transfer (CT) complexes results in a red shift of the semiconductor absorption compared to unmodified nanocrystallites and a reduction in the band gap upon the increase in the electron delocalization when including an additional ring. The investigated ligands have the optimal geometry for binding to surface Ti atoms, resulting in ring coordination complexes of a salicylate-type (binuclear bidentate binding-bridging) thus restoring the six-coordinated octahedral geometry of surface Ti atoms. From both absorption measurements in methanol/water = 90/10 solutions and steady-state quenching measurements of modifier fluorescence upon binding to TiO2 in aqueous solutions, stability constants in the order of 10(3) M(-1) have been determined at pH 2 and pH 3. Fluorescence lifetime measurements, in the presence and absence of colloidal TiO2 nanoparticles, indicated that the fluorescence quenching process is primarily static quenching, thus proving the formation of a nonfluorescent CT complex. The binding structures were investigated by using FTIR spectroscopy. Quantum chemical calculations on model systems using density functional theory (DFT) were performed to obtain the vibrational frequencies of charge transfer complexes, and the calculated values were then compared with the experimental data.

Synthesis, Structural Characterization, and Antimicrobial Activity Evaluation of New Binuclear Niobium(V) Tartrate Complexes with Biologically Important Drugs

The new binuclear niobium(V) complexes of the type [[NbO(L)C4H4O6]2C4H4O6] (where L = DMH, IMH, IPH, FPH, TMT) were prepared with biologically important drugs and characterized by using elemental analysis; IR, 1H-NMR, and UV-Vis spectral studies, and thermogravimetric analysis. The molar conductance measurement of all the complexes in DMF solution corresponds to 1 : 1 electrolytic nature. All complexes were of the pure diamagnetic character and were found to have six-coordinate octahedral geometry. The antimicrobial activity of these complexes has been screened against two Gram-positive and two Gram-negative bacteria. Antifungal activity against two different fungi has been evaluated and compared with controls. All the complexes inhibit the growth of both Gram-positive and Gram-negative bacteria to a competent level.

Poly[[bis{μ2-N2,N6-bis[(pyridin-3-yl)methyl]pyridine-2,6-dicarboxamide}dichloridonickel(II)]N,N-dimethylformamide tetrasolvate

In the title compound, {[NiCl(2)(C(19)H(17)N(5)O(2))(2)]·4C(3)H(7)NO}(n), the Ni(II) atom is located on an inversion centre and is in a six-coordinated octahedral geometry, formed by four pyridine N atoms from four N(2),N(6)-bis[(pyridin-3-yl)methyl]pyridine-2,6-dicarboxamide (BPDA) ligands occupying the equatorial plane and two chloride anions at the axial sites. The bidentate bridging BPDA ligands link the Ni(II) atoms into a two-dimensional corrugated grid-like flexible layer with a (4,4)-connected topology, which consists of left- and right-handed helical chains sharing the common Ni(II) atoms. Investigation of the thermal stability shows that the network is stable up to 573 K.

Synthesis and crystal structures of two three-dimensional vanadium polyoxoanion-bridged macrocyclic metal complexes

The reactions of transition metal macrocyclic complexes [ML](ClO4)2 (L = 5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane, M = Ni, Cu) with NH4VO3 under hydrothermal conditions gave two coordination polymers, namely [NiL]2[V6O17] and [CuL]2[V6O17]. Single-crystal X-ray diffraction analyses indicated that the central Ni(II)/Cu(II) atom displays a distorted six-coordinate octahedral coordination geometry by coordination with four nitrogen atoms of L, and two oxygen atoms of [VO4] tetrahedrons. Compounds [NiL]2[V6O17] and [CuL]2[V6O17] show three-dimensional structures, which are constructed through the connections of dodecanuclear [V12O32]4− rings with [NiL]2+ in [NiL]2[V6O17], and [V8O22] n 4n− chains with [CuL]2+ in [CuL]2[V6O17], respectively, generating one-dimensional channels.

Synthesis, Structural Characterization and Antimicrobial Activity Evaluation of Manganese(II) Complexes with BiologicallyImportant Drugs

The mononuclear Mn(II) complexes of the type [Mn(L)n(H2O)2Cl2] (where n= 1 or 2) were prepared with biologically important drugs viz. Clomiphene citrate (CPC), Imipramine hydrochloride (IMH), Diphenylpyraline hydrochloride (DPH), Embramine hydrochloride (EBH), and Dothiepin hydrochloride (DOT), and characterized by using elemental analysis, infra-red (IR), UV-visible spectra, X-ray powder diffraction studies and thermogravimetric analysis. The molar conductance measurement of all the complexes in DMF solution corresponds to non-electrolytic nature. All complexes were of the high-spin type and found to have six-coordinate octahedral geometry. The antimicrobial activity of these complexes has been screened against two gram-positive and two gram-negative bacteria. Antifungal activity against two different fungi has been evaluated and compared with standard drug. All the complexes inhibit the growth of both gram positive and gram negative bacteria to competent level.

Synthesis, characterization and antimicrobial activities of some metal(II) amino acids’ complexes

Metal(II) coordination compounds of glycine and ph-enylalanine were synthesized and characterized using infrared and electronic spectroscopic, and magnetic susceptibility measurements. The complexes were tested for antimicrobial activity against Bacillus subtilis, Staphylococcus aureus, Methicillin Resistant Staphy-lococcus aureus (MRSA), Escherichia coli, Pseudo-monas aeruginosa, Proteus vulgaris and Candida albicans. The stoichiometric reaction between the metal (II) ions and ligands in molar ratio M:L (1:3) [where M = Mn, Co, Ni, Cu and Cd; L= glycine; phenylalanine] resulted in the formation of five-coordinate square pyramidal dinuclear geometry for both copper complexes and six-coordinate octa-hedral geometry for the other complexes. The spectroscopic and magnetic moment data suggested that the ligands coordinated via both their amino and carboxylate ion moieties. The complexes demonstrated better activities against one or more of the tested microbes than acriflavine, the standard drug used.

Surface modification of anatase nanoparticles with fused ring catecholate type ligands: a combined DFT and experimental study of optical properties

Surface modification of nanocrystalline TiO(2) particles (45 Å) with catecholate-type ligands consisting of an extended aromatic ring system, i.e., 2,3-dihydroxynaphthalene and anthrarobin, was found to alter the optical properties of the nanoparticles in a similar way to modification with catechol. The formation of inner-sphere charge-transfer (CT) complexes results in a red shift of the semiconductor absorption compared to unmodified nanocrystallites and the reduction of the band gap upon the increase of the electron delocalization on the inclusion of additional rings. The binding structures were investigated by FTIR spectroscopy. The investigated ligands have the optimal geometry for binding to surface Ti atoms, resulting in ring coordination complexes of catecholate type (binuclear bidentate binding-bridging) thus restoring the six-coordinated octahedral geometry of surface Ti atoms. From the Benesi-Hildebrand plot, stability constants in methanol/water = 90/10 solutions at pH 2 of the order 10(3) M(-1) have been determined. Quantum chemical calculations on model systems using density functional theory (DFT) were performed to obtain vibrational frequencies of charge transfer complexes, and the calculated values were compared with the experimental data.

Template synthesis, spectroscopic studies, antimicrobial, nematicidal and pesticidal activities of chromium(III) macrocyclic complexes

A new series of Cr(III) macrocyclic complexes have been synthesized by template condensation of ligands 2-[4-chloro-2-(2-oxo-1,2-diphenyl-ethylideneamino)-phenylimino]-1,2-diphenyl-ethanone (ML1) and 2-[4-fluro-2-(2-oxo-1,2-diphenyl-ethylideneamino)-phenylimino]-1,2-diphenyl-ethanone (ML2) respectively, with appropriate diamines i.e. 1,2-phenylenediamine, 4- chloro 1,2-phenylenediamine and 4-fluro- 1,2-phenylenediamine in the presence of CrCl3.6H2O. The ligands and their complexes have been characterized on the basis of elemental analyses, molecular weight determinations, conductance and magnetic susceptibility measurements and spectral studies including IR, ESR, electronic spectra and X-ray powder diffraction studies. On the basis of these studies, a six-coordinated octahedral geometry has been proposed for all these complexes. The newly synthesized ligands and their complexes have been screened for their antimicrobial, nematicidal and pesticidal activities. The results are indeed positive.

Synthesis, structural characterization and antimicrobial activity evaluation of metal complexes of sparfloxacin

The synthesis and characterization of binary Cu(II)- ( 1), Co(II)- ( 2), Ni(II)- ( 3), Mn(II)- ( 4), Cr(III)- ( 5), Fe(III)- ( 6), La(III)- ( 7), UO 2(VI)- ( 8) complexes with sparfloxacin ( HL 1 ) and ternary Cu(II)- ( 9), Co(II)- ( 10), Ni(II)- ( 11), Mn(II)- ( 12), Cr(III)- ( 13), Fe(III)- ( 14), La(III)- ( 15), UO 2(VI)- ( 16) complexes with sparfloxacin ( HL 1 ) and dl-alanine ( H 2 L 2 ) complexes are reported using elemental analysis, molar conductance, magnetic susceptibility, IR, UV–Vis, thermal analysis and 1H-NMR spectral studies. The molar conductance measurements of all the complexes in DMF solution correspond to non-electrolytic nature. All complexes were of the high-spin type and found to have six-coordinate octahedral geometry except the Cu(II) complexes which were four coordinate, square planar and U- and La-atoms in the uranyl and lanthanide have a pentagonal bipyramidal coordination sphere. The antimicrobial activity of these complexes has been screened against two Gram-positive and two Gram-negative bacteria. Antifungal activity against two different fungi has been evaluated and compared with reference drug sparfloxacin. All the binary and ternary complexes showed remarkable potential antimicrobial activity higher than the recommended standard agents. Ni(II)- and Mn(II) complexes exhibited higher potency as compared to the parent drug against Gram-negative bacteria.

Synthesis, characterization, reactivity, and electrochemical studies of manganese(IV) complexes of bis(2-hydroxy-1-naphthaldehyde)adipoyldihydrazone

Manganese(IV) complexes [MnIV(npah)(H2O)2] (1) and [MnIV(npah)(A)2] · nH2O (where A = py (2), 2-pic (3), 3-pic (4), 4-pic (5)) and MnIV(npah)(NN)] (NN = bpy (6) and phen (7)) have been synthesized from bis(2-hydroxy-1-naphthaldehyde)adipoyldihydrazone in methanol. The composition of the complexes has been established by elemental analyses. Complex 3 has been characterized by mass spectral data also. Structural assessment of the complexes has been based on data from molar conductance, magnetic moment, electronic, electron paramagnetic resonance, and infrared (IR) spectral studies. Molar conductances of the complexes in DMSO suggest non-electrolytes. Magnetic moment and EPR studies suggest +4 oxidation state for manganese in these complexes. Electronic spectral studies suggest six-coordinate octahedral geometry around the metal ions. IR spectra reveal that H4npah coordinates to the metal in enol form. Reaction of the complexes with benzyl alcohol and SO2 has been investigated. Cyclic voltammetric studies of the complexes have also been carried out.

Synthesis, Characterization and X-Ray Crystal Structure of the Tri Aqua (3-Hydroxy-5-Hydroxymethyl-2-Methylpyridine-4-Carboxaldehyde-3-Methylisotiosemicarbazone: k3, O3, N7, N10) Ni(II) Nitrate

The title complex triaqua (3-hydroxy-5-hydroxymethyl-2-methylpyridine-4-carboxaldehyde-3-methylisothiosemicarbazone-k3,O3,N7,N10)Ni(II) nitrate ([Ni(PLITSC)(H2O)3](NO3)2, 1) represents the second transition metal complex incorporating an isothiosemicarbazide-pyridoxal based Schiff base that has been crystallographically characterized. Complex 1 crystallizes in a P21/n space group, with lattice constants: a = 11.2254(1) A, b = 12.9941(2) A, c = 12.8663(2), β = 96,7713(5)°, V = 1863.64(4) A3, Z = 4, F(000) = 1016, R 1 = 0.0681, wR 2 = 0.1201. The central Ni(II) cation is found in a six-coordinate octahedral geometry formed by the tridentate Schiff base ligand PLITSC and three water molecules. The identity of 1 was further confirmed by elemental analysis, IR spectra, and conductometric and magnetochemical measurements. The coordination sphere of the Ni(II) cation in the green, paramagnetic complex [Ni(C10H14N4O2S1)(H2O)3](NO3)2 (1, Fig. 1), which crystallizes in P21/n space group, consists of three water molecules and a single tridentate ligand (Schiff base) obtained from isothiosemicarbazide and pyridoxal (pyridoxal is 3-hydroxy-5-hydroxymethyl-2-methylpyridine-4-carboxaldehyde) moieties.

Synthesis and Characterization of Some Nickel(II) and Copper(II) Complexes of 2-substituted-4,4,4-trifluoro1-(2-thienyl)butane-1,3-dione (TTAH), their 2,2′ -Bipyridine and 1,10-Phenanthroline Adducts and X-Ray Structure of (2,2′ -Bipyridine)Bis(4,4,4-trifluoro-1-(2-thienyl)butane-1,3-dionato)Nickel(II)

The nickel(II) and copper(II) complexes of 2-substituted-4,4,4-trifluoro-1-(2-thienyl)butane-1,3-dione (R-TTAH) and their 2,2′ -bipyridine and 1,10-phenanthroline adducts have been prepared and characterized by microanalysis, conductance, magnetic and spectral measurements. The conductance data in nitromethane indicate that the compounds are non-electrolytes except for [Cu(Phen)2TTA](TTA) and [Ni(Phen)3](TTA)2, which are 1:1 and 1:2 electrolytes respectively. The room temperature magnetic moments suggest that they are magnetically dilute compounds while the electronic spectral (solid and solution) bands of the ligands shifted upon chelation. The infrared spectra showed the different shifts of the carbonyl frequencies and a six-coordinate octahedral geometry formed by coordination of the nickel(II) ion through four oxygen atoms of the 4,4,4-trifluoro-1-(2-thienyl)butane-1,3-dione (TTAH) and two nitrogen atoms of the bipyridine was established for (2,2′ -bipyridine)bis{4,4,4-trifluoro-1-(2-thienyl)butane-1,3-dionato}nickel(II) using X-ray crystallography.

Preparation, Characterization, and Catalytic Properties of Ruthenium(II) Nitrosyl Complexes with α-Diimine Ligands

Reactions of Ru(NO)Cl3·5H2O with α-diimines have yielded new Ru(II) complexes fac-[(N−N)Ru(NO)Cl3] [N−N = R′N═C(R)C(R)═NR′, R = Me, R′ = 2,6-dimethylphenyl, ligand a; 1; R = Me, R′ = 2,6-diisopropylphenyl, ligand b, 2; R = H, R′ = 2,6-diimethylphenyl, ligand c, 3; R = H, R′ = 2,6-diisopropylphenyl, ligand d, 4; R = H, R′= 2,6-cyclohexyl, ligand e, 5], mer-[(N−O)Ru(NO)Cl3] [N−O = (E)-1-(4-amino-3,5- diisopropylphenyl)-2-(2,6-diisopropylphenylimino)ethanone; 6], and cis-[(N−N)2RuCl2] [N−N = e; 7]. An unprecedented N,O ligand was formed from ligand d in 6, as revealed by its X-ray crystal structure. Molecular structures of 1, 2, 4, and 7 have also been determined by X-ray crystallography. 1, 2, and 4 exhibit six-coordinate octahedral geometry around the central Ru atom, which is ligated by two nitrogen atoms from the α-diimine ligand, three chlorine atoms in the facial configuration, and the nitrogen atom of the NO ligand. Studies of catalytic properties of 1−5 show they are efficient catalyst precursors for the transfer hydrogenation of ketones. 3−5 also exhibit catalytic activities in atom transfer radical polymerization of styrene.

Bis-N-heterocyclic carbene ruthenium(II) carbonyl complexes: Synthesis, structural characterization and catalytic activities in transfer hydrogenation of ketones

In this contribution, the synthesis and characterization of eight ruthenium(II) carbonyl complexes supported by chelating alkane-bridged bis-N-heterocyclic carbene ligands are reported. The products obtained are analyzed using infrared and NMR spectroscopies. The molecular structures of four metal complexes were determined by X-ray crystallography, which exhibit the six-coordinate octahedral geometry with two carbene carbon atoms from the bidentate Bi-NHCs, two carbonyl groups and two chlorine atoms in the trans(Cl)–cis(CO) configuration. All these complexes show catalytic activities in transfer hydrogenation of ketones.

New Hybrid Properties of TiO2 Nanoparticles Surface Modified With Catecholate Type Ligands

Surface modification of nanocrystalline TiO2 particles (45 Å) with bidentate benzene derivatives (catechol, pyrogallol, and gallic acid) was found to alter optical properties of nanoparticles. The formation of the inner-sphere charge–transfer complexes results in a red shift of the semiconductor absorption compared to unmodified nanocrystallites. The binding structures were investigated by using FTIR spectroscopy. The investigated ligands have the optimal geometry for chelating surface Ti atoms, resulting in ring coordination complexes (catecholate type of binuclear bidentate binding–bridging) thus restoring in six-coordinated octahedral geometry of surface Ti atoms. From the Benesi–Hildebrand plot, the stability constants at pH 2 of the order 103 M−1 have been determined.

Restriction of apical coordination in the square-planar nickel(II) complexes of meso-1,5,8,12-tetramethyl-1,4,8,11-tetraazacyclotetradecane with axially oriented C-methyl groups

Crystal structures of nickel(II) complexes coordinated with cyclam-type macrocyclic tetraamine, meso-1,5,8,12-tetramethyl-1,4,8,11-tetraazacyclotetradecane ( L) in two complex salts 1 and 2 have been determined by single-crystal X-ray crystallographic analysis. Complexes in both salts adopted trans-III structure, but the C-methyl groups of L adopted equatorial configuration in 1, while axial in 2. Complex 2 is the first example of complex of cyclam-type tetraamine with only axially oriented C-methyl groups. Complex in 1 adopted six-coordinated octahedral geometry with two water molecules occupying two apical sites, while in 2, apical sites were vacant resulting in four-coordinated square-planar geometry. UV–Vis spectra in various solutions also revealed the formation of octahedral six-coordinated complex for 1 but not for 2. Network of hydrogen bonds involving chloride ion, water, and N–H of L was present in crystals of both 1 and 2. Convenient synthetic paths for 1 and 2 are also presented.

Surface Modification of Colloidal TiO2 Nanoparticles with Bidentate Benzene Derivatives

Surface modification of nanocrystalline TiO2 particles (45 A) with bidentate benzene derivatives, that is, 2-hydroxybenzoic acid, 2,5-dihydroxybenzoic acid, 2,3-dihydroxybenzoic acid, 3,4-dihydroxybenzoic acid, and catechol was found to alter optical properties of nanoparticles. The formation of the inner-sphere charge transfer (CT) complexes results in a red shift of the semiconductor absorption compared to unmodified nanocrystallites. The binding structures were investigated by using FTIR spectroscopy. The investigated ligands have the optimal geometry for chelating surface Ti atoms, resulting in ring coordination complexes (catecholate or salycilate type of binuclear bidentate binding), thus restoring six-coordinated octahedral geometry of surface Ti atoms. From the Benesi−Hildebrand plot, the stability constants at pH 2 of the order 103 M−1 have been determined.

Synthesis, characterization and ethylene oligomerization and polymerization of 2-( 1H-2-benzimidazolyl)-6-(1-(arylimino)ethyl)pyridylchromium chlorides

A series of N^N^N tridentate chromium complexes ( C1– C6) bearing 2-( 1H-2-benzimidazolyl)-6-(1-(arylimino)ethyl)pyridine derivatives was synthesized and characterized by elemental and spectroscopic analysis along with single-crystal X-ray crystallography. X-ray crystallographic analyses reveal chromium complex C1 as a distorted six-coordinated octahedral geometry. On treatment with modified methylaluminoxane (MMAO), the chromium complexes exhibited high activities for ethylene oligomerization (up to 1.50 × 10 6 g mol −1 (Cr) h −1) and polymerization (up to 2.06 × 10 6 g mol −1 (Cr) h −1) at 10 atm ethylene pressure. Various reaction parameters were investigated in detail, and less steric hindrance and electron-withdrawing substituents of ligands enhance the catalytic activities of their chromium complexes.

A new C2-symmetric diaza-crown ether–Cu II mononuclear complex containing 1,2,3-triazole ligands

A novel C 2-symmetric lariat ether containing two [1,2,3]triazolo-ligands as sidearms was prepared via a click chemistry approach from known N, N′-dipropargyl-4,13-diaza-18-crown-6 ( 1). The ligand ( 2) readily forms a stable 1:1-complex with cupric perchlorate. A single crystal structure of the centro-symmetric mononuclear complex ( 3) could be determined. The Cu II center displays a distorted six-coordinated octahedral geometry where two triazoles and two pivot nitrogens constitute the basal plane. The axial positions are occupied by two oxygens of the crown ether part. The cyclic voltammograms of a DMF solution of the complex showed two redox processes in our experimental conditions.