Anionic Bidentate Ligand Research Articles

Mitochondria-targeted neutral and cationic iridium(III) anticancer complexes chelating simple hybrid sp2-N/sp3-N donor ligands.

Most platinum group-based cyclometalated neutral and cationic anticancer complexes with the general formula [(C^N)2Ir(XY)]0/+ (neutral complex: XY = bidentate anionic ligand; cationic complex: XY = bidentate neutral ligand) are notable owing to their intrinsic luminescence properties, good cell permeability, interaction with some biomolecular targets and unique mechanisms of action (MoAs). We herein synthesized a series of neutral and cationic amine-imine cyclometalated iridium(III) complexes using Schiff base ligands with sp2-N/sp3-N N^NH2 chelating donors. The cyclometalated iridium(III) complexes were identified by various techniques. They were stable in aqueous media, displayed moderate fluorescence and exhibited affinity toward bovine serum albumin (BSA). The complexes demonstrated promising cytotoxicity against lung cancer A549 cells, cisplatin-resistant lung cancer A549/DDP cells, cervical carcinoma HeLa cells and human liver carcinoma HepG2 cells, with IC50 values ranging from 9.98 to 19.63 μM. Unfortunately, these complexes had a low selectivity (selectivity index: 1.62-1.98) towards A549 cells and BEAS-2B normal cells. The charge pattern of the metal center (neutral or cationic) and ligand substituents showed little influence on the cytotoxicity and selectivity of these complexes. The study revealed that these complexes could target mitochondria, cause depolarization of the mitochondrial membrane, and trigger the production of intracellular ROS. Additionally, the complexes were observed to induce late apoptosis and perturb the cell cycle in the G2/M or S phase in A549 cells. Based on these results, it appears that the anticancer efficacy of these complexes was predominantly attributed to the redox mechanism.

Synthesis, characterization, crystal structure, Hirshfeld surface analysis and DFT of 1,2-benzothiazine metal (II) complexes

In the present study, the mononuclear complexes of oxicam precursor with Mn(II), Co(II), Ni(II), Cu(II) and Zn(II) metal ions have been prepared. The UV/Vis, FT-IR, 1H NMR spectroscopies, elemental analysis and magnetic susceptibility measurements were used to confirm successful synthesis of transition metal complexes. The square planar coordination geometry of the Cu(II) complex 5 was confirmed by XRD analysis. The spectroscopic data indicated that two mono anionic bidentate ligands act as chelating agents and attached with metal center via enolate oxygen and carbonyl oxygen of the ester group present in 1,2-benzothiazine. The molar conductance indicated the non-ionic nature of the Mn(II), Co(II), Ni(II), Cu(II) and Zn(II) complexes. The octahedral geometry is proposed for the Mn(II), Co(II) and Zn(II) complexes, respectively and square planar geometry for Ni(II) and Cu(II) complexes is proposed on the basis of obtained data. The reported basis sets with ligand and its Cu(II) complex were used to conduct DFT studies. The synthesis of the targeted compounds was also confirmed by energy gap calculations between HOMO and LUMO. The Hirshfeld surface analysis of the copper complex was carried and 2D contacts were drawn. Furthermore, COX-I and COX-II inhibition studies for the targeted compounds were carried out by applying molecular docking study. The docking results revealed that these molecules have potential to inhibit the cyclooxygenases and may reduce the inflammation in the body.

Catalytic Enantioselective Construction of 6‐4 Ring‐Junction All‐Carbon Stereocenters and Mechanistic Insights

Comprehensive SummaryDeveloping reactions for the synthesis of 6‐6‐4 and 6‐4 carbocyclic scaffolds with a chiral quaternary center at the bridgehead position is highly desired, considering the existence of such skeletons in natural products with biological activities and the potential of using these molecules for downstream studies in chemical biology and medicinal chemistry. Report here is accessing these target skeletons with high chemo‐, regio‐ and enantio‐selectivities through Pd(II)/chiral N,N’‐disulfonyl bisimidazoline (Bim) ligand‐catalyzed asymmetric reaction of yne‐allenones and arylboronic acids. Realization of 6‐6‐4 skeleton with a ring‐junction all‐carbon stereocenter is a one‐step process while synthesizing 6‐4 skeleton is a two‐step process, which begins with intramolecular [2 + 2] reaction of allenes with alkynes, followed by Pd‐catalyzed asymmetric addition of arylboronic acids to cyclic enones generated in the first step. Noteworthy is that chiral Bim ligand as a C2‐symmetric N,N’‐bidentateanionic ligand, designed by us, in coordinating with Pd catalyst was first applied to catalyze asymmetric 1,4‐conjugate addition reaction with the high catalytic performance (the reaction can be carried out in air). DFT calculations have been applied to understand how these reactions take place, the origins of enantioselectivity, and relative reactivities of different substrates.

Hydrogenation of alkenes and alkynes catalysed by NˆO (imino)phenol palladium(II) complexes: Structural, kinetics and chemoselectivity studies

Reactions of 2-(2-methoxyethylimino)ethyl)phenol (HL1), 2-(2-hydroxyethylimino)ethyl)phenol (HL2), 2-(2-aminoethylimino)ethyl)phenol (HL3) and 2-(2-hydroxyethylimino)methyl)phenol (HL4) with [PdCl2(COD)] afforded the neutral palladium complexes [PdCl2(HL1)] (1), [PdCl2(HL2)] (2), [PdCl2(HL3)] (3), [PdCl2(HL4)] (4) respectively. Treatment of complex 1 with PPh3 gave the cationic complex [Pd(HL1)ClPPh3]+ (5), while reactions of 4 with Pd(OAc)2, in the presence of PPh3 and p-TsOH produced the corresponding palladium complex, [Pd(L1) (OTs) (PPh3)] (6). The molecular structure of 4a (derivative of 4) contained two bidentate anionic ligands (L4). Complexes 1–6 formed active catalysts in hydrogenation of alkenes and alkynes, in which the catalytic activities were largely dependent on the pendant donor atom of the ligand motif. Isomerization reactions were dominant in terminal alkenes hydrogenation reactions, while hydrogenation of alkynes to alkanes occurred in two steps via alkene intermediates. Kinetics data were consistent with homogeneous active species. Density functional theory studies supported the hemi-labile nature of the ligands, and offered insights into the catalytic activity trends observed.

Synthesis, characterization and antiproliferative activity of amino- and DMSO complexes of platinum(II) containing l-carnitine

l-Carnitine, a biomolecule able to cross the blood–brain barrier exploiting specific transporters, behaves as mono or bidentate anionic ligand for Pt(II) in the new amino complexes cis-[Pt(l-carnitine-O)2(NH3)2](BF4)2 (1), cis-[PtCl(l-carnitina-O)(NH3)2]BF4 (2), [Pt(l-carnitine-O,O′)(1,2-DACH)]BF4 (3), [Pt(l-carnitine-O)2(1,2-DACH)](BF4)2 (4), and [PtCl(l-carnitine-O)(1,2-DACH)](BF4) (5). Four complexes with DMSO have been also prepared and characterized: the synthetic intermediate [Pt(CO3)(DMSO)2] (6), [Pt(l-carnitine-O,O′)(DMSO)2]BF4 (7), cis-[Pt(l-carnitine-O)2(DMSO)2](BF4)2 (8) and cis-[PtCl(l-carnitine-O)(DMSO)2]BF4, (9).The antiproliferative activity of three representative complexes 1, 5 and 7 has been assayed against three human cancer cell lines A2780, K562 and SKOV3, and it was found comparable to that of the parent active compounds cis-[PtCl2(1,2-DACH)] and cisplatin.

NEW COMPLEXES OF 2-(1H-1, 2, 4-TRIAZOL-3-YL) PYRIDINE WITH Co(II), Cd(II), Rh(III), IONS: SYNTHESIS, STRUCTURE, PROPERTIES AND POTENTIAL APPLICATIONS

Co(II), Cd(II) and Rh(III) complexes with 2-(1H-1,2,4-triazol-3-yl)pyridine (Htzp) as ligand were synthesized and investigated. The neutral mononuclear complexes with a generic [M(tzp)n] structure have been prepared from Htzp and corresponding transition metals chlorides at 2:1 and 3:1, respectively molar ratios in H2O–EtOH. The resulted crystalline complexes were investigated through magnetic and molar conductivity measurements, elemental analysis, FT-IR, mass spectroscopy, thermal analysis, UV-Vis and P-XRD. The experiments indicate that Htzp acts as bidentate anionic ligand, [Co(tzp)2]·1.5H2O and [Cd(tzp)2] are in the tetragonal coordination, whereas six coordinate octahedral [Rh(tzp)3]·H2O complex undergoes a weak tetragonal distortion. In case of Co(II) complex, an interesting feature was revealed through fluorescence spectroscopy, as the fluorescent emission intensity of the free ligand is dependent on the Co(II) solution content. Through complexation, the fluorescence is gradually quenched according to the Co(II) aqueous solution content, which may recommend it as a method of detection of Co(II) presence in waste water.

Charge-Delocalized κ2C,N-NHC-Amine Complexes of Rhodium, Iridium, and Ruthenium

The development of a novel set of complexes bearing an NHC-amine ligand (C-NHC-NH2) is described. M(cod) complexes (M = 1r, Rh) and a Ru complex have been synthesized in which three different coordination modes of the ligand were established: monodentate, neutral bidentate, and anionic bidentate. The anionic bidentate coordination mode of the anionic C-NHC-NH- ligand arises from deprotonation of the amine moiety of the neutral C-NHC-NH2 ligand. Ligand deprotonation proved to be reversible for the Rh and 1r complexes, as was shown by subsequent treatment of the complexes with base and acid. The structural parameters of these differently coordinated ligands were examined, and it was shown that the conjugation of the aniline ring plays a major role in determining the ligand properties. Structural parameters derived from DFT calculations confirm delocalization of the anionic charge over the ligand framework, as is clear from a comparison of the (hypothetical) neutral bidentate complexes [M(cod)(kappa C-2,N-{C-NHC-NH2})](+) with those of the (synthesized) monoanionic complexes [M(cod)(kappa C-2,N-{C-NHC-NH})] (M = Rh, Ir). A similar trend in the structure and bond lengths of the aniline rings was found in the solid-state structure of the novel dimeric complex [(Ru(kappa C-2,N-{C-NHC-NH})(kappa C-2,N-{C-NHC-NH2})Cl)2(mu-Cl)](PF6). The octahedral d5 ruthenium(III) centers in this complex both contain a neutral bidentate C-NHC-NH2 ligand as well as an anionic bidentate ligand. Quite remarkably, the complex is diamagnetic, arising from antiferromagnetic coupling of the two low-spin ruthenium(III) centers over the chloride linker. DFT calculations indeed confirm that the open-shell singlet electronic structure is most stable.

The “Enders Triazole”: A well known molecule, but still a new ligand!!

1,3,4-Triphenyl-1,2,4-triazolium salts have previously been used and described in the literature as precursors for carbenes, which have been reported as organocatalysts and as neutral monodentating N-heterocyclic carbene (NHC) ligands. We now report the synthesis of 1,3,4-tri-phenyl-4,5-dihydro-1H-1,2,4-triazole-5-ylidene-platinum(II)-acetylacetonate where the triazole binds to the metal in a new coordination mode (C^C*) as an anionic bidentate ligand, where the NHC carbene interacts with the platinum center and one of the phenyl rings is cyclometalated. The complex shows phosphorescent emission in the blue region of the visible spectrum at 441 and 465 nm with a quantum yield of 42%. DFT calculations (BP86/6-31G* as well as B3LYP/6-31G*) were found to be well suited to determine the structure of the complex.

Application of neutral d10 coinage metal complexes with an anionic bidentate ligand in delayed fluorescence-type organic light-emitting diodes

A series of heteroleptic coinage metal(I) complexes [Cu(PP)(PS)] 1, [Ag(PP)(PS)] 2, and [Au(PP)(PS)] 3 [PP = 1,2-bis(diphenylphosphino)benzene and PS− = 2-diphenylphosphinobenzenethiolate] were synthesized. X-ray crystallography demonstrated that 1–3 possessed tetrahedral structures containing two types of bidentate ligands, PP and PS−. Photophysical studies and time-dependent density functional theory calculations indicated that the emission from 1–3 in the solid state at room temperature originated from thermally activated delayed fluorescence (TADF). The thiolate ligand with strong electron-donating character (PS−) reduced the contribution from metal orbitals to the highest occupied molecular orbitals of the complexes, decreasing the metal-to-ligand charge-transfer character of the excited states of 1–3. The origin of TADF in 1–3 was attributed to ligand-to-ligand charge-transfer on the basis of molecular orbital calculations. Au(I) complex 3 was unstable in solution because of a rapid ligand exchange reaction, and Ag(I) complex 2 showed limited solubility in organic solvents. Cu(I) complex 1, which exhibited efficient green TADF with a maximum emission wavelength of 521 nm and a quantum yield of 0.52 in the solid state, was used to fabricate TADF-type organic light-emitting diodes via a wet process.

Luminescent Sensor for Carbonate Ion Based on Lanthanide(III) Complexes of 1,4,7,10-Tetraazacyclododecane-1,4,7-Triacetic Acid (DO3A)

Lanthanide(III) complexes of 1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid (H(3)DO3A) are suggested as sensors for sensitive luminescence-based determination of a carbonate anion. Thermodynamic study of association of [Eu(H(2)O)(2)(DO3A)] with bidentate anionic ligands using luminescence spectroscopy reveals an affinity order CO(3)(2-) > oxalate(2-) > picolinate(-) > phthalate(2-) ≈ citrate(3-); presumably as a consequence of an increasing chelate ring size. The ternary [Eu(DO3A)(picolinate)](-) and [Tb(DO3A)(picolinate)](-) complexes show improved photophysical properties due to the antenna effect of the picolinate anion. High quenching effect of carbonate anion and, to a lesser extent also oxalate, enables construction of a linear calibration plot utilizing optimized experimental conditions (e.g. c(LnL) = 0.1 mM, c(picolinate) = 2-5 mM, pH = 7.4, λ(exc) = 286 nm, etc.) for carbonate determination in solution. Both sensors show a comparable sensitivity and the detection limit of about 0.4 mM. In order to improve the photophysical properties of Ln(III) sensor by shift of excitation wavelength about 40 nm to VIS range, the isoquinoline-3-carboxylic acid (IQCA) as antenna ligand was employed instead of picolinic acid. The analysis of commercial samples of European mineral waters was carried out and they were compared to the results obtained by capillary isotachophoresis to confirm there is no inherent (systematic) error to the present analysis. The Ln(III) sensor with IQCA is recommended since it has a better robustness than that with picolinate. The present analytical method is simple and rapid, and it is useful for sensitive determination of bicarbonate/carbonate concentration in water samples under aerobic conditions.

Theoretical Structure–Reactivity Study of Ethylene Insertion into Nickel–Alkyl Bonds. A Kinetically Significant and Unanticipated Role oftransInfluence in Determining Agostic Bond Strengths

Theoretical methods (B3LYP, M06, and CCSD(T)) have been used to study the kinetics and thermodynamics of ethyl migratory insertion in a series of square-planar [(X∧Y)Ni(ethyl)(ethylene)] complexes (X∧Y = anionic bidentate ligand). The results are discussed qualitatively using general trans-influence arguments. When X ≠ Y, the reactions of the two possible isomers have been compared. The results reveal that when one of the coordinating groups exerts a strong trans influence (STI) and the other a weak trans influence (WTI), as in a STI∧WTI chelating ligand such as a phosphino-enolate (P∧O), one of the two isomers has an activation energy for ethylene insertion (i.e., ethyl migration) that is much less than that calculated for symmetrical bidentate ligands of either the WTI∧WTI or STI∧STI types. Specifically, a low activation energy is found when an ethyl group, coordinated trans to the STI group, migrates to the ethylene coordinated trans to the WTI group. The converse pathway in the STI∧WTI system, wherein...

‘2+1’ Tricarbonyltechnetium(I)/tricarbonylrhenium(I) mixed-ligand complexes with methyl thiosalicylate and isocyanide ligands as potential precursors of radiopharmaceuticals

The complexes of [(99m)Tc]-tricarbonyltechnetium(I) and [(188)Re]-tricarbonylrhenium(I), of the '2+1' type, with methyl thiosalicylate as an anionic bidentate ligand and with either tert-butyl 3-isocyanopropionate or glycine-glycine-tyrosine 4-isocyanobutyrate as monodentate ligands, have been prepared on the n.c.a. scale. The complexes exhibit different lipophilicity and high stability in neutral aqueous solutions. Based on the results of the challenge experiment with histidine, cysteine and glutathione the studied complexes might be considered to be promising models for radiopharmaceutical precursors.

Synthesis of Secondary, Tertiary and Quaternary 1,3,5‐Triazapenta‐1,3‐dienes and Their CoII, ZnII, PdII, CuII and BF2 Coordination Compounds

AbstractThe secondary and tertiary 1,3,5‐triazapenta‐1,3‐dienes 2 and 3 are easily obtained by the reaction of N‐imidoyl chlorides with amidines or from ethyl N‐imidoylimidoates 5 and primary amines. In a new synthetic pathway the compounds 5 were prepared by the reaction of imidoates in their protonated or free form with N‐imidoyl chlorides. A quaternary 1,3,5‐triazapenta‐1,3‐diene 4a is obtained by the reaction of the imidoate 5b with pyrrolidine. X‐ray diffraction studies of the tertiary 1,3,5‐triazapenta‐1,3‐diene 3c and its protonated form 3c·HCl allow the comparison of different patterns of intermolecular hydrogen bonding in the solid state. Two equivalents of a secondary 1,3,5‐triazapenta‐1,3‐diene 2 were treated at room temperature after deprotonation with potassium tert‐butoxide with CuCl2, Ni(ClO4)2 or with Pd(ac)2 (without deprotonation) to give the corresponding neutral 2:1 chelate complexes (2a)2·Cu, (2a)2·Ni and (2b)2·Pd, respectively. A fluorescent boron complex 2b·BF2 was obtained by reacting 2b with boron trifluoride–diethyl ether. From the tertiary triazapentadiene 3c and CoCl2 or ZnCl2 the six‐membered 1:1 chelate complexes 3c·CoCl2 and 3c·ZnCl2, respectively, were obtained. In these cases a proton shift from the terminal nitrogen atom of the free ligand to the central nitrogen atom of the complex was observed. Two equivalents of 3c reacted at room temperature with Cu(ac)2 or Pd(ac)2 to form the neutral 2:1 chelate complexes (3c)2·Cu and (3c)2·Pd, respectively. A fluorescent 1:1 boron complex 3c·BF2 was obtained from 3c and boron trifluoride–diethyl ether. In all cases the triazapentadienes act as neutral or anionic bidentate ligands to form six‐membered chelates with the metal ion or the boron centre. Most of the complexes were completely characterized, which included X‐ray crystallography.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

Experimental and computational evidence of solid-state anion–π and π–π interactions in [VO(O2)(L)(pa)]·xH2O complexes (L = picolinate, pyrazinate or quinolinate; pa = picolinamide)

Two new neutral monoperoxidovanadium(V) complexes [VO(O2)(L)(pa)]·xH2O have been synthesized: [VO(O2)(pic)(pa)]·H2O (1) and [VO(O2)(Hquin)(pa)]·2H2O (2) [pic: pyridine-2-carboxylato(1–) or picolinato(1–), Hquin: pyridine-2,3-dicarboxylato(1–) or quinolinato(1–), and pa: picolinamide]. The solid state structures of 1 and 2 feature a typical distorted pentagonal bipyramid coordination polyhedron around the central vanadium atoms. The bidentate anionic ligands are coordinated in two equatorial positions, while the bidentate picolinamide molecule is bound via the aromatic nitrogen and the carboxamide oxygen in one equatorial and one apical position. The experimental geometric parameters were used for a detailed study of intermolecular interactions between the pic–pic and pa–pa aromatic rings in 1. Interestingly, no π–π interactions were observed between the pyridine rings of Hquin or pa in 2, however, the less common anion–π solid-state interactions were found between the pic ligands in 1 and pca [pca = pyrazinecarboxylato(1–)] ligands in the already published structure of the related complex [VO(O2)(pca)(pa)]·H2O (3). The presence of anion–π and π–π interactions in 1 and 3 was confirmed by DFT computations performed on their solid-state structures. Computational results suggested a direct analogy between anion–π and π–π interactions, both being of predominantly electrostatic character.

Cyclic (Amino)[bis(ylide)]carbene as an Anionic Bidentate Ligand for Transition-Metal Complexes

The 3-(triphenylphosphonio)-N-(2,6-diisopropylphenyl)pyrrole reacts with 2 equiv of methyllithium to afford a lithium adduct in which a cyclic (amino)[bis(ylide)]carbene, a novel type of NHC, acts as a 1,4-bidentate ligand via the carbene center and the exocyclic ylidic carbon. This species readily undergoes transmetalation reactions, which allows for the synthesis of a variety of transition-metal complexes.

New Coordination Modes of L‐Ascorbic Acid and Dehydro‐L‐ascorbic Acid as Dianionic Chelating Ligand for Platinum

AbstractA variety of coordination modes of L‐ascorbic acid as an anionic bidentate ligand has been exploited to prepare platinum(II) complexes 1–7 that contain phosphanes or R,R‐dach (1R,2R‐diaminocyclohexane) as neutral ligands in which O2, O3, O5, O6 and C2 act as anionic donating functionalities. An alternative synthetic route to known O2,O3 complexes is proposed, and their solubility in water has been enhanced by introducing PTA (1,3,5‐triaza‐7‐phosphaadamantane) as a neutral ligand. A new coordination mode of ascorbic acid (O2 and O3 protected) as an O5,O6‐diolate chelating ligand has been characterised in solution by NMR spectroscopy and in the solid state by X‐ray crystallography. The first example of a platinum complex that contains dehydroascorbic acid, 7, has also been prepared and its X‐ray crystal structure has been determined. The antiproliferative activity in vitro of complexes 1–7 has been tested, and the best values were obtained for the DHA complex 7, which was found to be more active than cisplatin on both a cisplatin‐sensitive and a cisplatin‐resistant cell line.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

Stereoselective Cyclometalation of Planar Pro-chiral (η6-Arene)tricarbonylchromium Complexes withOC-6-[Ru(CO)2Cl2]n

Ortho-metalation of ligand-appended and planar pro-chiral (η6-arene)tricarbonylchromium complexes has been attempted with octahedral [Ru(CO)2Cl2]n. While amino- and oxazolyl-appended substrates displayed no reactivity, 2-[tricarbonyl(η6-phenyl)chromium]pyridine was readily converted into the corresponding cycloruthenated product consisting of a mixture of chloro-bridged heterotetranuclear dimers, which was analyzed by CPMAS 13C NMR and 2D-DOSY 1H NMR techniques in the solid state and in solution, respectively. The main side-products of this cyclometalation reaction were identified as novel dimers containing a chloro and a hydroxo bridge, according to spectroscopic and X-ray diffraction structural determination. The relative configuration of the produced tetranuclear chloro-bridged (Cr,Ru) dimers was assessed by chemical derivatization into (Cr,Ru) monomers, of which the structures were established by X-ray diffraction analysis. Consistent results as to the stereoselectivity of the cycloruthenation reaction were obtained with 2-ferrocenylpyridine. Further reactivity studies of racemic planar-chiral (Cr,Ru) and (Fe,Ru) dimeric ruthenacycles toward anionic bidentate ligands indicated that chelation of the Ru center was rather stereoselective although probably subject to polytopal rearrangements. It was established that the chelation of the ruthenium(II) center by anionic homobidentate ligands was sensitive to steric hindrance, which favors the coordination of the anionic bidentate ligand at the Ru center in an anti fashion with respect to both Cr(CO)3 and FeCp. This property was applied to the synthesis of the first examples of scalemic ruthenacycles possessing ruthenium-centered and planar chiralities. This study is supported by 12 X-ray diffraction structures of relevant new complexes, among which are two unprecedented examples of chloro,hydroxo-bridged dicarbonylruthenium(II) [C,N] chelates.

Structural characterization of a copper(II) complex containing oxidative cyclization of N-2-(4-picolyl)- N′-(4-methoxyphenyl)thiourea, new ligands of 4-picolylthiourea derivatives and the precursor molecular structure of oxidative cyclization of N-(2-pyridyl)- N′-(4-methoxyphenyl)thiourea

Three new compounds of aryl thiourea derivatives, namely N-2-(4-picolyl)- N′-(4-methoxyphenyl)thiourea ( L1), N-2-(6-picolyl)- N′-(4-methoxyphenyl)thiourea ( L2) and N-2-(4-picolyl)- N′-(4-nitrophenyl)thiourea ( L3), and the new copper(II) complex [Cu(4PicTz4OMePh)(OAC)(EtOH)] ( C1), as a result of oxidative cyclization of the ligand ( L1), were synthesized. In addition, pure precursor ( P1), as the product of the oxidative cyclization of N-(2-pyridyl)- N′-(4-methoxyphenyl)thiourea ( L4), was isolated and characterized. Ligands ( L1) and ( L2) were characterized by 1H and 13C NMR and single crystal X-ray analysis. 1H NMR spectroscopy showed strong hydrogen bonding interactions between N′H-functionalities and the pyridine nitrogen atoms as well as weak intermolecular hydrogen bonding between the thione sulfur and the NH hydrogen. Structural studies of complex ( C1) showed that the copper ion is five-coordinated with a square-pyramidal environment. The oxidative cyclization of ligand ( L1) results in an anionic bidentate ligand in complex ( C1). Both ligand ( L1) and precursor ( P1) crystallize as centrosymmetric dimers.

Crystal structure of lead(ii) acetylacetonate and the structure of the acetylacetone solvated lead(ii) ion in solution studied by large-angle X-ray scattering

The crystal structure of bis(acetylacetonato)lead(II) and the structure of the acetylacetone solvated lead(II) ion in solution have been determined by single-crystal X-ray diffraction and large-angle X-ray scattering (LAXS), respectively. The acetylacetone is deprotonated and acts as a bidentate anionic ligand (acac-) in the solid Pb(acac)2 compound. The lead(II) ion binds four oxygen atoms strongly in a nearly flat pyramidal configuration with Pb-O bond lengths in the range 2.32-2.37 A, and additionally three oxygens from neighboring complexes at 3.01-3.26 A. Acetylacetone acts as a solvent (Hacac) at dissolution of lead(II) trifluoromethanesulfonate forming a pentasolvate with a mean Pb-O bond distance of 2.724(5) A. The 6s2 lone electron pair on the lead(II) ion becomes stereochemically active in the crystalline acetylacetonate complex, while it is inactive in the solvate in solution. The solution was also analysed using IR and 1H NMR spectroscopy.

Modification of Metal Alkoxide Precursors by Organofunctional Bidentate Ligands: Chemical Problems and Opportunities for Materials Syntheses

AbstractFor Abstract see ChemInform Abstract in Full Text.