Spectroscopic characterization of tetradentate macrocyclic ligand: its transition metal complexes

Manganese(II), cobalt(II), nickel(II) and copper(II) complexes are synthesized with a novel tetradentate ligand viz. 1,3,9,11-tetraaza-4,8,12,16-tetraoxo-2,6,10,14-tetrathiacyclohexadecane (L) and characterized by the elemental analysis, molar conductance measurements, magnetic susceptibility measurements, electron impact mass, 1H NMR, IR, electronic and EPR spectral studies. The molar conductance measurements of the complexes in DMSO correspond to be nonelectrolytic nature for Mn(II), Co(II) and Cu(II) while 1:2 electrolytes for Ni(II) complexes. Thus these complexes may be formulated as [M(L)X2] and [Ni(L)]X2 (where M: Mn(II), Co(II), and Cu(II) and X = Cl- and NO3-). On the basis of IR, electronic and EPR spectral studies an octahedral geometry has been assigned for Mn(II) and Co(II) complexes, square-planar for Ni(II) whereas tetragonal for Cu(II) complexes. The ligand and its complexes were also evaluated against the growth of bacteria and pathogenic fungi in vitro.     

Rare earth metal complexes bearing thiophene-amido ligand: synthesis and structural characterization

2,6-diisopropyl-N-(2-thienylmethyl)aniline (H2L) has been prepared, which reacted with equimolar rare earth metal tris(alkyl)s, Ln(CH2SiMe3)3(THF)2, afforded rare earth metal mono(alkyl) complexes, LLn(CH2SiMe3)(THF)3 (:Ln=Lu; :Ln=Y). In this process, H2L was deprotonated by one metal alkyl species followed by intramolecular C-H activation of the thiophene ring to generate dianionic species L2- with the release of two tetramethylsilane. The resulting L2- combined with three THF molecules and an alkyl unit coordinates to Y3+ and Lu3+ ions, respectively, in a rare N,C-bidentate mode, to generate distorted octahedron geometry ligand core. Whereas, with treatment of H2L with equimolar Sc(CH2SiMe3)3(THF)2, a heteroleptic complex (HL)(L)Sc(THF) () was isolated as the main product, where the dianionic L2- species bonds to Sc3+ via chelating N,C atoms whilst the monoanionic HL connects to Sc3+ in an S,N-bidentate mode. All complexes have been characterized by NMR spectroscopy and X-ray diffraction analysis.     

Zirconium complexes bearing a tetradentate dipyrrolyl ligand

Using a tetradentate, dianionic ligand several new zirconium complexes have been prepared. These pyrrolyl compounds, unlike their titanium analogues, are inactive in hydrohydrazination catalysis. However, they are quite stable, and their reactivity with H2NR, where R = Ph, C6H11, and NHPh, is reported here. Two of the complexes were characterized by X-ray diffraction.     

Studies on uranyl complexes-III Uranyl complexes of edta

The uranyl complexes of EDTA have been studied by potentiometry ; stability constants of the 1:1 and 2:1 (metal to ligand) chelates have been determined, as well as the respective hydrolysis and polymerization constants. Possible structures for these species are discussed. To account for the abnormally high stability of UO(2)(H(2)O)HL-, hydrogen bonding between a protonated nitrogen atom of the ligand and one oxygen atom of UO(2)(2+) is suggested.     

Novel metal complexes containing a chiral trinitrogen isoindoline-based pincer ligand: in situ synthesis and structural characterization

The first synthesis and characterization of metal coordinated complexes containing in situ prepared chiral trinitrogen 1,3-bis(4,5-dihydrooxazol-2-ylimino)isoindoline-based pincer ligands are reported. Two zinc complexes, isolated as Zn(L)(2), where L = 1,3-bis(4,5-dihydro-4-(R)-phenyloxazol-2-ylimino)isoindoline ((R,R)-5) or 1,3-bis(4,5-dihydro-4-(S)-iso-propyloxazol-2-ylimino)isoindoline ((S,S)-6), respectively, are reported. Complexes Zn((R,R)-5)(2) and Zn((S,S)-6)(2) were prepared in situ through the condensation of phthalonitrile with enantiopure 2-amino-4-(R)-phenyloxazoline ((R)-3) or 2-amino-4-(S)-iso-propyloxazoline ((S)-4) in the presence of ZnCl(2) at 80 °C in dry toluene over 3-4 days. The characterizations of Zn((R,R)-5)(2) and Zn((S,S)-6)(2) in both the solid (X-ray crystallography) and solution (multinuclear NMR spectroscopy) states are reported.     

Novel dinuclear uranyl complexes with asymmetric schiff base ligands: synthesis, structural characterization, reactivity, and extraction studies

The reaction of uranyl nitrate with asymmetric [3O, N] Schiff base ligands in the presence of base yields dinuclear uranyl complexes, [UO2(HL1)]2.DMF (1), [UO2(HL2)]2.2DMF.H2O (2), and [UO2(HL3)]2.2DMF (3) with 3-(2-hydroxybenzylideneamino)propane-1,2-diol (H3L1), 4-((2,3-dihydroxypropylimino)methyl)benzene-1,3-diol (H3L2), and 3-(3,5-di-tert-butyl-2-hydroxybenzylideneamino)propane-1,2-diol (H3L3), respectively. All complexes exhibit a symmetric U2O2 core featuring a distorted pentagonal bipyramidal geometry around each uranyl center. The hydroxyl groups on the ligands are attached to the uranyl ion in chelating, bridging, and coordinate covalent bonds. Distortion in the backbone is more pronounced in 1, where the phenyl groups are on the same side of the planar U2O2 core. The phenyl groups are present on the opposite side of U2O2 core in 2 and 3 due to electronic and steric effects. A similar hydrogen-bonding pattern is observed in the solid-state structures of 1 and 3 with terminal hydroxyl groups and DMF molecules, resulting in discrete molecules. Free aryl hydroxyl groups and water molecules in 2 give rise to a two-dimensional network with water molecules in the channels of an extended corrugated sheet structure. Compound 1 in the presence of excess Ag(NO3) yields {[(UO2)(NO3)(C6H4OCOO)](NH(CH2CH3)3)}2 (4), where the geometry around the uranyl center is hexagonal bipyrimidal. Two-phase extraction studies of uranium from aqueous media employing H3L3 indicate 99% reduction of uranyl ion at higher pH.     

Transition-metal complexes of a bifunctional tetradentate gallium alkoxide ligand

The mixed gallium transition-metal complexes [FeCl[Ga(2)((t)Bu)(4)(neol)(2)]] (1) and [M[Ga(2)((t)Bu)(4)(neol)(2)]], M = Co (2), Ni (3), Cu (4), have been prepared by the reaction of [Ga(2)((t)Bu)(4)(neol-H)(2)] (neol-H(2) = 2,2-dimethyl-propane-1,3-diol) with the appropriate metal halide and Proton Sponge. Compounds 1-4 have been characterized by NMR (3), UV/vis, and IR spectroscopy and magnetic susceptibility (solution and solid state), and their molecular structures have been confirmed by X-ray crystallography. The molecular structure of compounds 1-4 consists of a tetracyclic core formed from two four-membered and two six-membered rings. The central metal atom adopts a square pyramidal (1) or square planar (2-4) geometry. The magnetic susceptibilities for 1, 2, and 4 are as expected for strong ligand field environments. On the basis of spectroscopic and structural data, the [Ga(2)((t)Bu)(4)(neol)(2)](2-) ligand appears to be more flexible than other chelating ligands; this is proposed to be due to the flexibility in the O-Ga-O bond angle.     

Reactions of alkylcobalt complexes containing a tetradentate nitrogen-donating ligand

The reactions of RCo(BDM1,3pn)(H₂O) with light, heat, acids, electrophiles and nucleophiles were studied. (HBDM1,3pn is a mononegative, tetradentate dioxime-diimine ligand formed by condensing 2,3-butanedionemonoxime with 1,3-propanediamine in a 2/1 molar ratio; R = CH₃, C₂H₅, n-C₃H₇, n-C₄H₉, and C₆H₃CH_2-) Pyrolysis and photolysis of the alkyl complexes result in a cobalt(II) complex (anaerobic conditions) along with alkenes and alkanes. The major organic products from solid state pyrolysis at 200°C or photolysis in water are CH₄ (R = CH₃), C₂H₄ (R = C₂H₅), C₃H₆ (R = n-C₃H₇), C₄H₈ (R = n-C₄H₉) and (C₆H₅CH₂)₂ (R = C₆H₅CH₂). No alkyl—cobalt bond cleavage occurs with acids or bases in most cases. Two exceptions are the reactions with 3 M HNO₃ at 25°C and with 1 M NaOH at 52°C. Electrophiles like I₂ cleave the alkyl—cobalt bond forming RI and Co^III (BDM1,3pn)I₂. Nucleophilic reagents (N^-) displace the H₂O trans to the alkyl group to form RCo(BDM1,3pn)(N), but do not dealkylate the alkyl complex under the reaction conditions studied.     

Physical, photophysical and structural properties of ruthenium(II) complexes containing a tetradentate bipyridine ligand

The focus of this report is the synthesis and properties of two new analogues of ruthenium(ii) tris-bipyridine, a monomer and dimer. The complexes contain the ligand 6,6'-(ethan-1,2-diyl)bis-2,2'-bipyridine (O-bpy) which contains two bipyridine units bridged in the 6,6' positions by an ethylene bridge. Crystal structures of the two complexes formulated as [Ru(bpy)(O-bpy)](PF6)2 and [(Ru(bpy)2)2(O-bpy)](PF6)4 reveal structures of lower symmetry than D3 which affects the electronic properties of the complexes as substantiated by density functional theory (DFT) and time dependent density functional theory (TDDFT) calculations. The HOMO lies largely on the ruthenium center; the LUMO spreads its electron density over the bipyridine units, but not equally in the mixed O-bpy-bpy complexes. Calculated Vis/UV spectra using TDDFT methods agree with experimental spectra. The lowest lying triplet excited state for [Ru(bpy)(O-bpy)](PF6)2 is 3MC resulting in a low emission quantum yield and a large chloride ion photosubstitution quantum yield.     

Sigma-borane complexes of iridium: synthesis and structural characterization

Reaction of NaBH4 with (tBuPOCOP)IrHCl affords the previously reported complex (tBuPOCOP)IrH2(BH3) (1) (tBuPOCOP = kappa(3)-C6H3-1,3-[OP(tBu)2]2). The structure of 1 determined from neutron diffraction data contains a B-H sigma-bond to iridium with an elongated B-H bond distance of 1.45(5) A. Compound 1 crystallizes in the space group P1 (Z = 2) with a = 8.262 (5) A, b = 12.264 (5) A, c = 13.394 (4) A, and V = 1256.2 (1) A(3) (30 K). Complex 1 can also be prepared by reaction of BH3 x THF with (tBuPOCOP)IrH2. Reaction of (tBuPOCOP)IrH2 with pinacol borane gave initially complex 2, which is assigned a structure analogous to that of 1 based on spectroscopic measurements. Complex 2 evolves H2 at room temperature leading to the borane complex 3, which is formed cleanly when 2 is subjected to dynamic vacuum. The structure of 3 has been determined by X-ray diffraction and consists of the (tBuPOCOP)Ir core with a sigma-bound pinacol borane ligand in an approximately square planar complex. Compound 3 crystallizes in the space group C2/c (Z = 4) with a = 41.2238 (2) A, b = 11.1233 (2) A, c = 14.6122 (3) A, and V = 6700.21 (19) A(3) (130 K). Reaction of (tBuPOCOP)IrH2 with 9-borobicyclononane (9-BBN) affords complex 4. Complex 4 displays (1)H NMR resonances analogous to 1 and exists in equilibrium with (tBuPOCOP)IrH2 in THF solutions.     

Mixed-ligand uranyl(V) beta-diketiminate/beta-diketonate complexes: synthesis and characterization

The reaction of [UO 2(Ar 2nacnac)Cl] 2 [Ar 2nacnac = (2,6- (i)Pr 2C 6H 3)NC(Me)CHC(Me)N(2,6- (i)Pr 2C 6H 3)] with Na(RC(O)CHC(O)R) (R = Me, Ph, CF 3) in tetrahydrofuran results in the formation of UO 2(Ar 2nacnac)(RC(O)CHC(O)R) (R = Me, 1; Ph, 2; CF 3, 3), which can be isolated in moderate yields. The structures of 1 and 2 have been confirmed by X-ray crystallography, while the solution redox properties of 1- 3 have been measured by cyclic voltammetry. Complexes 1- 3 exhibit reduction features at -1.82, -1.59, and -1.39 V (vs Fc/Fc (+)), respectively, at a scan rate of 100 mV.s (-1). The decrease in the reduction potential follows the electron-withdrawing ability of each beta-diketonate ligand. Chemical reduction of 1 and 2 with Cp* 2Co in toluene yields [Cp* 2Co][UO 2(Ar 2nacnac)(RC(O)CHC(O)R)] (R = Me, 4; Ph, 5), while reduction of 3 with Cp 2Co provides [Cp 2Co][UO 2(Ar 2nacnac)(CF 3C(O)CHC(O)CF 3)] ( 6). Complexes 4- 6 have been fully characterized, while the solid-state molecular structure of 5 has also been determined. In contrast to the clean reduction that occurs with Cp* 2Co, reduction of 1 with sodium ribbon, followed by cation exchange with [NEt 4]Cl, produces [NEt 4][UO 2(Ar 2nacnac)(H 2CC(O)CH(O)CMe)] ( 7) in modest yield. This product results from the formal loss of H (*) from a methyl group of the acetylacetonate ligand. Alternately, complex 7 can be synthesized by deprotonation of 1 with NaNTMS 2 in good yield.     

Spectroscopic characterization and EPR spectral studies on transition metal complexes with a novel tetradentate, 12-membered macrocyclic ligand

Complexes of Cr(III), Mn(II), Co(II), Ni(II) and Cu(II) containing a tetradentate macrocyclic N-donor ligand have been prepared via template reaction of 2,3-pentanedione, ethylene-di-ammine and transition metal ions. The complexes have been characterized on the basis of the elemental analysis, molar conductance, magnetic moment susceptibility, IR, electronic and EPR spectral studies. The complexes are of high spin type and possess four coordinate tetrahedral five coordinate square pyramidal and six coordinated octahedral/tetragonal geometry.     

Design,synthesis and in vitro cytotoxicity of novel dinuclear platinum(II) complexes with a tetradentate carrier ligand

Four novel dinuclear platinum complexes with a tetradentate ligand, (1R,1′R,2R,2′R)‐N¹,N^1′‐(1,2‐phenylenebis(methylene))dicyclohexane‐1,2‐diamine, as the carrier group, have been designed, synthesized and characterized, and their in vitro cytotoxicity against HepG‐2, A549, HCT‐116 and MCF‐7 cell lines evaluated using MTT assay. Results indicate that the targeted dinuclear platinum complexes H1 , H2 , H3 , H4 exhibit significant growth inhibitory properties against HepG‐2, A549 and HCT‐116 cell lines, but none of them show activity against MCF‐7 cell line. Compound H4 shows better antitumor activity than carboplatin against HepG‐2, A549 and HCT‐116 cell lines. Copyright © 2015 John Wiley & Sons, Ltd.     

Preparation and characterization of uranyl complexes with phosphonate ligands

The preparation, spectroscopic characterization and thermal stability of neutral complexes of uranyl ion, UO₂ ²⁺, with phosphonate ligands, such as diphenylphosphonic acid (DPhP), diphenyl phosphate (DPhPO) and phenylphosphonic acid (PhP) are described. The complexes were prepared by a reaction of hydrated uranyl nitrate with appropriate ligands in methanolic solution. The ligands studied and their uranyl complexes were characterized using thermogravimetric and elemental analyses, ESI-MS, IR and UV–Vis absorption and luminescence spectroscopy as well as luminescence lifetime measurements. Compositions of the products obtained dependent on the ligands used: DPhP and DPhPO form UO₂L₂ type of complexes, whereas PhP forms UO₂L complex. Based on TG and DTG curves a thermal stability of the complexes was determined. The complexes UO₂PhP·2H₂O and UO₂(DPhPO)₂ undergo one-step decomposition, while UO₂PhP · 2H₂O is decomposed in a two-step process. The thermal stability of anhydrous uranyl complexes increases in the series: DPhPO < PhP < DPhP. Obtained IR spectra indicate bonding of P–OH groups with uranyl ion. The main fluorescence emission bands and the lifetimes of these complexes were determined. The complex of DPhP shows a green uranyl luminescence, while the uranyl emission of the UO₂PhP and UO₂(DPhPO)₂ complexes is considerably weaker.     

Structural, spectroscopic and redox properties of uranyl complexes with a maleonitrile containing ligand

The reaction of uranyl nitrate hexahydrate with the maleonitrile containing Schiff base 2,3-bis[(4-diethylamino-2-hydroxybenzylidene)amino]but-2-enedinitrile (salmnt((Et(2)N)(2))H(2)) in methanol produces [UO(2)(salmnt((Et2N)2))(H(2)O)] (1) where the uranyl equatorial coordination plane is completed by the N(2)O(2) tetradentate cavity of the (salmnt((Et(2)N)(2)))(2-) ligand and a water molecule. The coordinated water molecule readily undergoes exchange with pyridine (py), dimethylsulfoxide (DMSO), N,N-dimethylformamide (DMF) and triphenylphosphine oxide (TPPO) to give a series of [UO(2)(salmnt((Et(2)N)(2)))(L)] complexes (L = py, DMSO, DMF, TPPO; 2-5, respectively). X-Ray crystallography of 1-5 show that the (salmnt((Et(2)N)(2)))(2-) ligand is distorted when coordinated to the uranyl moiety, in contrast to the planar structure observed for the free protonated ligand (salmnt((Et(2)N)(2))H(2)). The Raman spectra of 1-5 only display extremely weak bands (819-828 cm(-1)) that can be assigned to the typically symmetric O=U=O stretch. This stretching mode is also observed in the infrared spectra for all complexes 1-5 (818-826 cm(-1)) predominantly caused by the distortion of the tetradentate (salmnt((Et(2)N)(2)))(2-) ligand about the uranyl equatorial plane resulting in a change in dipole for this bond stretch. The solution behaviour of 2-5 was studied using NMR, electronic absorption and emission spectroscopy, and cyclic voltammetry. Complexes 2-5 exhibit intense absorptions in the visible region of the spectrum due to intramolecular charge transfer (ICT) transitions and the luminescence lifetimes (< 5 ns) indicate the emission arises from ligand-centred excited states. Reversible redox processes assigned to the {UO(2)}(2+)/{UO(2)}(+) couple are observed for complexes 2-5 (2: E(1/2) = -1.80 V; 3,5: E(1/2) = -1.78 V; 4: E(1/2) = -1.81 V : vs. ferrocenium/ferrocene {Fc(+)/Fc}, 0.1 M Bu(4)NPF(6)) in dichloromethane (DCM). These are some of the most negative half potentials for the {UO(2)}(2+)/{UO(2)}(+) couple observed to date and indicate the strong electron donating nature of the (salmnt((Et(2)N)(2)))(2-) ligand. Multiple uranyl redox processes are clearly seen for [UO(2)(salmnt((Et(2)N)(2)))(L)] in L (L = py, DMSO, DMF; 2-4: 0.1 M Bu(4)NPF(6)) indicating the relative instability of these complexes when competing ligands are present, but the reversible {UO(2)}(2+)/{UO(2)}(+) couple for the intact complexes can still be assigned and shows the position of this couple can be modulated by the solvation environment. Several redox processes were also observed between +0.2 and +1.2 V (vs. Fc(+)/Fc) that prove the redox active nature of the maleonitrile-containing ligand.     

Lanthanide borohydride complexes with an aryloxide ligand: Synthesis, structural characterization and polymerization activity

Reactions of LnCl₃, NaBH₄ and ArONa (Ar = C₆H₂-t-Bu₃-2,4,6) in a molar ratio of 1:3:1 in THF afforded the aryloxide lanthanide borohydrides of (ArO)Ln(BH₄)₂(THF)₂ (Ln = Yb (1), Er (2)). They were characterized by elemental analysis, infrared spectrum and X-ray crystallography. The two complexes are neutral and isostructural. The lanthanide atom is nine-coordinated by an aryloxide ligand, two borohydride ligands and two THF ligands in a trigonal bipyramidal geometry. Both of the BH₄ ligands in each monomeric complex are η³-coordinated. These complexes displayed moderate high catalytic activities for the polymerization of methyl methacrylate. The polymerization temperature had great influence on the catalysis. At about 0 °C, the catalysts showed the polymerization activity best.     

Tin(iv) and lead(iv) complexes with a tetradentate redox-active ligand

The coordination chemistry of a tetradentate redox-active ligand, glyoxal-bis(2-hydroxy-3,5-di-tert-butylanil) (H(2)L), was investigated with the diorganotin(iv) and diphenyllead(iv) moieties. Complexes R(2)SnL (R = Me (), Et (), (t)Bu (), Ph ()) and Ph(2)PbL () have been prepared and characterized. The molecular structures of compounds , and have been determined by single crystal X-ray diffraction. The diamagnetic octahedral complexes bear a tetradentate O,N,N,O redox-active ligand with a nearly planar core. Complexes demonstrate solvatochromism in solution. The CV of complexes reveals four one-electron redox processes. The spin density distribution in the chemically generated cations and anions of was studied by X-band EPR spectroscopy. The experimental data agree well with the results of DFT calculations of electronic structures for , its pyridine adduct ·Py, cation and anion .     

Zirconocene complexes with a biphenyl substituted cyclopentadienyl ligand: synthesis, characterization, and olefin polymerization behavior

Novel zirconocene complexes (1-Biph-3,4-Me₂Cp)₂ZrCl₂ (3), (C₅Me₅)(1-Biph-3,4-Me₂Cp)ZrCl₂ (4), and (C₅H₅)(1-Biph-3,4-Me₂Cp)ZrCl₂ (5) containing a 1-biphenyl-3,4-dimethylcyclopentadienyl ligand (2) have been prepared and their solid state structures were characterized by X-ray diffraction method. The crystal structure of 3 revealed a racemic, C₂-symmetric nature in the solid state. In ethylene polymerization, they all afforded high-density polyethylene with very high activity. Especially, the catalytic properties of 3 were most marked in terms of both polymerization activity and molecular weight of polyethylene among them. They also showed good activity on the polymerization of propylene, but afforded nearly atactic, amorphous polypropylenes with a little higher [mmmm] methyl pentad values by 3 and 4 than that by the most active 5 under the given reaction conditions.     

Synthesis and structural characterization of centrosymmetric multinuclear nickel(II) complexes with neutral tetradentate N6-ligand

A neutral tetradentate ligand L1 [L1?=?3,6-bis(pyrazol-1-yl)-pyridazine] reacts with Ni(ClO₄)₂·6H₂O and undergoes counterion exchange with PF ^?₆ to give di- and tetranuclear complexes [Ni₂(L1)₂(CH₃CN)₄](PF₆)₄·4H₂O (1) and [Ni₄(L1)₄(µ-OH)₄](ClO₄)₄·2H₂O (2), respectively. The presence of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) as base controls the nuclearity of the complex formation. Both complexes were structurally characterized by physicochemical and spectroscopic techniques. Their crystal structures revealed that both complexes are centrosymmetric and adopt slightly distorted octahedral geometry. Complex 1 crystallizes in monoclinic space group C2/c as the Ni(II) center is octahedrally bound to L1 in a trans-isomer arrangement. Complex 2 crystallizes in tetragonal space group I4₁/amd with four L1 and four hydroxy bridging ligands linked to Ni(II) center in cis-isomer arrangement. Cyclic voltammograms of complexes 1 and 2 were measured under Ar and CO₂. Under CO₂, the quasireversible peaks of both complexes become irreversible and a current enhancement occurs under reduction.

     

Divalent nickel,cobalt and copper complexes of a tetradentate N6 macrocyclic ligand

Summary Divalent nickel, cobalt and copper salts react with 2,6-diaminopyridine and acetylacetone to form complexes containing a 16-membered N₆ tetradentate macrocyclic ligand. The complexes are characterised as distorted octahedra of the M(TML)X₂ type where M=nickel(II), cobalt(II) and copper(II); TML=tetradentate macrocyclic ligand and X=Cl, Br, NO₃ or NCS. The ligand coordinates through all the four azomethine nitrogen atoms which are bridged by acetylacetone moieties. Pyridine nitrogen does not participate in coordination, a fact supported by far i.r. studies. The magnetic, electronic and i.r. spectral studies indicate that the complexes have lower symmetries and the amounts of distortion calculated in terms of DT/DQ applying normalised spherical harmonic Hamiltonian theory indicate that these complexes are moderately distored.