Preparation, structural, spectroscopic, thermal and DFT characterization of cadmium(II) complexes with quinaldic acid

Cadmium(II) complex with quinaldic acid (quinH), [Cd(quin)₂(H₂O)₂] (1), was prepared by the reaction of cadmium(II) acetate and quinaldic acid in water-ethanol mixture, while another cadmium(II) complex, [Cd(quin)₂(DMSO)₂] (2), was prepared by the recrystallization of 1 in DMSO. Both complexes were characterized by IR spectroscopy and TGA/DTA methods. The crystal structure of 2 was determined by X-ray structure diffraction analysis. Cadmium(II) ion is octahedrally coordinated by two N,O-bidentate quinaldate ligands in equatorial and by two DMSO molecules in axial positions. Only weak intermolecular C-H···O hydrogen bonds and π-π stacking interactions as packing forces are present in the crystal structure of 2. The theoretical investigations included geometry optimizations of both complexes at DFT level (B3LYP and mPW1PW91 functionals) and calculations of vibrational frequencies. Calculated and experimental IR spectra were compared and characteristic bands assigned. The electronic properties of the complexes were investigated by the NBO analysis. Thermogravimetric studies showed the initial loss of two coordinated water molecules in 1 and of DMSO in 2 and then complete decomposition of quinaldate ligands for both 1 and 2.     

Synthesis, structural, spectroscopic and thermal characterization of cobalt complexes with 3- and 6-methylpicolinic acid. Voltammetric and spectrophotometric study in solution

Cobalt complexes of 3- and 6-methylpicolinic acid, namely [Co(3-Mepic)₃] (1) and [Co(6-Mepic)₂(H₂O)₂] · 2H₂O (2) were prepared and characterized by spectroscopic methods (IR, UV-Vis, NMR), their molecular and crystal structures were determined by X-ray crystal structure analysis and their thermal stability by TGA/DTA methods. Square-wave voltammetry showed that on mercury electrode the oxidation of 2 requires higher potential than the oxidation of complex anion [Co(3-Mepic)₃]⁻, the most probable product of the reduction of 1. The reduction of 1 and the oxidation of 2 depend on the kinetics of electron transfer and the electrode material. X-ray structural analysis revealed octahedral coordination polyhedron in both 1 and 2 and the same N,O-chelated coordination mode for both ligands. ¹³C, ¹H and ¹⁵N NMR spectroscopy confirmed that coordination mode of 3-methylpicolinic acid in 1 in DMSO solution. UV-Vis spectrophotometric measurements were used to study the complexation of cobalt with 3- and 6-methylpicolinic acid in aqueous solution and to determine the composition of the formed complexes by Job method of continuous variation. The stoichiometry of the complex with 3-methylpicolinic acid is 2:3, while it is 2:3 and 3:2 for the complex with 6-methylpicolinic acid, indicating the possibility of the formation of more than one complex species.     

Synthesis, characterization and in vitro cytotoxicity studies of platinum(IV) complexes with thiouracil ligands

Reactions of [PtMe₃(bpy)(Me₂CO)][BF₄] (2) with the thionucleobases 2-thiouracil (s²Ura), 4-thiouracil (s⁴Ura) and 2,4-dithiouracil (s²s⁴Ura) resulted in the formation of complexes of the type [PtMe₃(bpy)(L-κS)][BF₄] (L = s²Ura, 3; s⁴Ura, 4; s²s⁴Ura, 5). The complexes were characterized by NMR spectroscopy (¹H, ¹³C, ¹⁹⁵Pt), IR spectroscopy as well as microanalyses. The coordination through the C4S groups (4, 5) was additionally confirmed by DFT calculations, where it was shown that these complexes [PtMe₃(bpy)(L-κS⁴)]⁺ (L = s⁴Ura, s²s⁴Ura) are about 5.8 (4b) and 3.3 kcal/mol (5b), respectively, more stable than the respective complexes, having thiouracil ligands bound through the C2X groups (X = O, 4a; S, 5a). For [PtMe₃(bpy)(s²Ura-κS²)][BF₄] (3) no preferred coordination mode could be assigned solely based on DFT calculations. Analysis of NMR spectra showed the κS² coordination. In vitro cytotoxic studies of complexes 3−5 on nine different cell lines (8505C, A253, FaDu, A431, A549, A2780, DLD-1, HCT-8, HT-29) revealed in most cases moderate activities. However, 3 and 5 showed significant activity towards A549 and A2780, respectively, possessing IC₅₀ values comparable to those of cisplatin. Cell cycle perturbations and trypan blue exclusion test on cancer cell line A431 using [PtMe₃(bpy)(s²s⁴Ura-κS⁴)][BF₄] (5) showed induction of apoptotic cell death. Furthermore, the reaction of [PtMe₃(OAc-κ²O,O′)(Me₂CO)] (6) with 4-thiouracil yielded the dinuclear complex [(PtMe₃)₂(μ-s⁴Ura_-H)₂] (7), which has been characterized by microanalysis, NMR (¹H, ¹³C, ¹⁹⁵Pt) and IR spectroscopy as well as ESI mass spectrometry. X-ray diffraction analysis of crystals yielded in an isolated case exhibited the presence of a hexanuclear thiouracilato platinum(IV) complex, possessing each three different kinds of methyl platinum(IV) moieties and 4-thiouracilato ligands. This exhibited the ability of 4-thiouracil platinum(IV) complexes to form multinuclear complexes.     

Syntheses, characterization and antimicrobial activity of the first complexes of Zn(II), Cd(II) and Co(II) with N-benzyloxycarbonylglycine: X-ray crystal structure of the polymeric Cd(II) complex

For the first time, complexes of Zn(II), Cd(II) and Co(II) (1-3) with N-benzyloxycarbonylglycine have been synthesized and characterized. The complexes adopt tetrahedral, pentagonal-bipyramidal and octahedral geometry, respectively. The structure of the polymeric cadmium complex was resolved by single crystal X-ray analysis. The cadmium ion has a distorted pentagonal-bipyramidal coordination formed by two water molecules and two N-benzyloxycarbonylglycinato ligands (N-Boc) coordinated in different fashions, one as bidentate and the second connecting three cadmium atoms. In a rather complicated 2D supramolecular structure, the phenyl rings interact mutually exclusively by the CH?π interactions.Investigation of the antimicrobial activity of the obtained complexes and N-benzyloxycarbonylglycine revealed that the ligand does not inhibit the growth of Candida albicans, whereas the newly synthesized complexes suppress the growth of this human fungal pathogen.     

Interaction of copper(II) complexes with bis(p-nitrophenyl)phosphate: Structural and spectral studies

When the complexes [Cu(L1)(H₂O)](ClO₄)₂1, where L1 = 4-methyl-1-(pyrid-2-ylmethyl)-1,4-diazacycloheptane, and [Cu(L2)Cl₂] 2, where L2 = 4-methyl-1-(quinol-2-ylmethyl)-1,4-diazacycloheptane are interacted with one/two equivalents of bis(p-nitrophenylphosphate, (p-NO₂Ph)₂PO₂, BNP), no hydrolysis of BNP is observed. From the solution the adducts of copper(II) complexes [Cu₂(L1)₂((p-NO₂Ph)₂PO₂)₂]-(ClO₄)₂3 and [Cu(L2)((p-NO₂Ph)₂PO₂)₂]·H₂O 4 have been isolated and structurally characterised. The X-ray crystal structure of 3 contains two Cu(L1) units bridged by two BNP molecules. The Cu···Cu distance (5.1 Å) reveals no Cu-Cu interaction. On the other hand, the complex 4 is mononuclear with Cu(II) coordinated to the 3N ligand as well as BNP molecules through phosphate oxygen. The trigonality index (τ, 0.37) observed for 4 is high suggesting the presence of significant trigonal distortion in the coordination geometry around copper(II). The complexes are further characterized by spectral and electrochemical studies.     

Equilibrium and structural studies on Co(II), Ni(II), Cu(II) and Zn(II) complexes with N-(2-benzimidazolyl)methyliminodiacetic acid: crystal structures of Ni(II) and Cu(II) complexes

Combined pH-metric, UV-Vis, ¹H NMR and EPR spectral investigations on the complex formation of M(II) ions (M=Co, Ni, Cu and Zn) with N-(2-benzimidazolyl)methyliminodiacetic acid (H₂bzimida, hereafter H₂L) in aqueous solution at a fixed ionic strength, I=10⁻¹ mol dm⁻³, at 25 ± 1 °C indicate the formation of M(L), M(H₋₁L)⁻ and M₂(H₋₁L)⁺ complexes. Proton-ligand and metal-ligand constants and the complex formation equilibria have been elucidated. Solid complexes, [M(L)(H₂O)₂] · nH₂O (n=1 for M = Co and Zn, n=2 for M = Ni) and {Cu (μ-L) · 4H₂O}_n, have been isolated and characterized by elemental analysis, spectral, conductance and magnetic measurements and thermal studies. Structures of [Ni(L)(H₂O)₂] · 2H₂O and {Cu(μ-L) · 4H₂O}_n have been determined by single crystal X-ray diffraction. The nickel(II) complex exists in a distorted octahedral environment in which the metal ion is coordinated by the two carboxylate O atoms, the amino-N atom of the iminodiacetate moiety and the pyridine type N-atom of the benzimidazole moiety. Two aqua O atoms function as fifth and sixth donor atoms. The copper(II) complex is made up of interpenetrating polymeric chains of antiferromagnetically coupled Cu(II) ions linked by carboxylato bridges in syn-anti (apical-equatorial) bonding mode and stabilized via interchain hydrogen bonds and π-π stacking interactions.     

Stereospecific ligands and their complexes. V. Synthesis, characterization and antimicrobial activity of palladium(II) complexes with some alkyl esters of (S,S)-ethylenediamine-N,N′-di-2-propanoic acid

Three new ligands and their palladium(II) complexes of general formula [PdCl₂(R₂-S,S-eddp)] (R = n-propyl, n-butyl and n-pentyl) have been synthesized and characterized by microanalysis, infrared and ¹H and ¹³C NMR spectroscopy. Antimicrobial activity of these ligands and complexes was tested by microdilution method and both minimal inhibitory and microbicidal concentration were determined. These tested complexes demonstrated the significant antifungal activity against pathogenic fungi Aspergillus flavus and Aspergillus fumigatus. On the other hand, these complexes demonstrated moderate antibacterial activity.     

Nickel(II) and copper(II) complexes of Schiff base ligands containing N4O2 and N4S2 donors with pyrrole terminal binding groups: Synthesis, characterization, X-ray structures, DFT and electrochemical studies

A series of hexadentate ligands, H₂L^m (m = 1−4), [1H-pyrrol-2-ylmethylene]{2-[2-(2-{[1H-pyrrol-2-ylmethylene]amino}phenoxy)ethoxy]phenyl}amine (H₂L¹), [1H-pyrrol-2-ylmethylene]{2-[4-(2-{[1H-pyrrol-2-ylmethylene]amino}phenoxy)butoxy]phenyl}amine (H₂L²), [1H-pyrrol-2-ylmethylene][2-({2-[(2-{[1H-pyrrol-2-ylmethylene]amino}phenyl)thio]ethyl}thio)phenyl]amine (H₂L³) and [1H-pyrrol-2-ylmethylene][2-({4-[(2-{[1H-pyrrol-2-lmethylene]amino}phenyl)thio]butyl}thio) phenyl]amine (H₂L⁴) were prepared by condensation reaction of pyrrol-2-carboxaldehyde with {2-[2-(2-aminophenoxy)ethoxy]phenyl}amine, {2-[4-(2-aminophenoxy)butoxy]phenyl}amine, [2-({2-[(2-aminophenyl)thio]ethyl}thio)phenyl]amine and [2-({4-[(2-aminophenyl)thio]butyl}thio)phenyl]amine respectively. Reaction of these ligands with nickel(II) and copper(II) acetate gave complexes of the form ML^m (m = 1−4), and the synthesized ligands and their complexes have been characterized by a variety of physico-chemical techniques. The solid and solution states investigations show that the complexes are neutral. The molecular structures of NiL³ and CuL², which have been determined by single crystal X-ray diffraction, indicate that the NiL³ complex has a distorted octahedral coordination environment around the metal while the CuL² complex has a seesaw coordination geometry. DFT calculations were used to analyse the electronic structure and simulation of the electronic absorption spectrum of the CuL² complex using TDDFT gives results that are consistent with the measured spectroscopic behavior of the complex. Cyclic voltammetry indicates that all copper complexes are electrochemically inactive but the nickel complexes with softer thioethers are more easily oxidized than their oxygen analogs.     

Structural and equilibrium studies on mixed ligand complexes of Co(II), Ni(II), Cu(II) and Zn(II) with N-(2-benzimidazolyl)methyliminodiacetic acid and typical N, N donor ligands

Mixed ligand complexes: [Co(L)(bipy)] · 3H₂O (1), [Ni(L)(phen)] · H₂O (2), [Cu(L)(phen)] · 3H₂O (3) and [Zn(L)(bipy)] · 3H₂O (4), where L²⁻ = two -COOH deprotonated dianion of N-(2-benzimidazolyl)methyliminodiacetic acid (H₂bzimida, hereafter, H₂L), bipy = 2,2′ bipyridine and phen = 1,10-phenanthroline have been isolated and characterized by elemental analysis, spectral and magnetic measurements and thermal studies. Single crystal X-ray diffraction studies show octahedral geometry for 1, 2 and 4 and square pyramidal geometry for 3. Equilibrium studies in aqueous solution (ionic strength I = 10⁻¹ mol dm⁻³ (NaNO₃), at 25 ± 1 °C) using different molar proportions of M(II):H₂L:B, where M = Co, Ni, Cu and Zn and B = phen, bipy and en (ethylene diamine), however, provides evidence of formation of mononuclear and binuclear binary and mixed ligand complexes: M(L), M(H₋₁L)⁻, M(B)²⁺, M(L)(B), M(H₋₁L)(B)⁻, M₂(H₋₁L)(OH), (B)M(H₋₁L)M(B)⁺, where H₋₁L³⁻ represents two -COOH and the benzimidazole N₁-H deprotonated quadridentate (O⁻, N, O⁻, N), or, quinquedentate (O⁻, N, O⁻, N, N⁻) function of the coordinated ligand H₂L. Binuclear mixed ligand complex formation equilibria: M(L)(B) + M(B)²⁺ ? (B)M(H₋₁L)M(B)⁺ + H⁺ is favoured with higher π-acidity of the B ligands. For Co(II), Ni(II) and Cu(II), these equilibria are accompanied by blue shift of the electronic absorption maxima of M(II) ions, as a negatively charged bridging benzimidazolate moiety provides stronger ligand field than a neutral one. Solution stability of the mixed ligand complexes are in the expected order: Co(II) < Ni(II) < Cu(II) > Zn(II). The Δ log K_M values are less negetive than their statistical values, indicating favoured formation of the mixed ligand complexes over the binary ones.     

Copper(II) complexes with unsymmetrical pentadentate ed3a-type diamino-tricarboxylate ligands. Crystal structures, configurational analysis and DFT study of complexes

The O-O-N-N-O-type pentadentate ligands H₃ed3a, H₃pd3a and H₃pd3p (H₃ed3a stands ethylenediamine-N,N,N′-triacetic acid; H₃pd3a stands 1,3-propanediamine-N,N,N′-triacetic acid and H₃pd3p stands 1,3-propanediamine-N,N,N′-tri-3-propionic acid) and the corresponding novel octahedral or square-planar/trigonal-bipyramidal copper(II) complexes have been prepared and characterized. H₃ed3a, H₃pd3a and H₃pd3p ligands coordinate to copper(II) ion via five donor atoms (three deprotonated carboxylate atoms and two amine nitrogens) affording octahedral in case of ed3a³⁻ and intermediate square-pyramidal/trigonal-bipyramidal structure in case of pd3a³⁻ and pd3p³⁻. A six coordinate, octahedral geometry has been established crystallographically for the [Mg(H₂O)₆][Cu(ed3a)(H₂O)]₂ · 2H₂O complex and five coordinate square-pyramidal for the [Mg(H₂O)₅Cu(pd3a)][Cu(pd3a)] · 2H₂O. Structural data correlating similar chelate Cu(II) complexes have been used for the better understanding the pathway: octahedral → square-pyramidal ↔ trigonal- bipyramid geometry. An extensive configuration analysis is discussed in relation to information obtained for similar complexes. The infra-red and electronic absorption spectra of the complexes are discussed in comparison with related complexes of known geometries. Molecular mechanics and density functional theory (DFT) programs have been used to model the most stable geometric isomer yielding, at the same time, significant structural data. The results from density functional studies have been compared with X-ray data.     

Supramolecular cobalt(II)-pyridine-2,5-dicarboxylate complexes with isonicotinamide, 2-amino-3-methylpyridine and 2-amino-6-methylpyridine: Syntheses, crystal structures, spectroscopic, thermal and antimicrobial activity studies

The mer-[Co(pydca)(H₂O)₃(ina)]·H₂O (1), (2a3mpyH)₂[Co(pydca)₂(H₂O)₂]·2H₂O (2) and (2a6mpyH)₂[Co(pydca)₂(H₂O)₂]·2H₂O (3) complexes (H₂pydca: pyridine-2,5-dicarboxylic acid, ina: isonicotinamide, 2a3mpy = 2-amino-3-methylpyridine and 2a6mpy = 2-amino-6-methylpyridine) were synthesised and characterised by elemental analysis, magnetic and spectroscopic measurements (UV-Vis and IR spectra) and single crystal X-ray diffraction technique. The thermal behaviour of the complexes was also studied by simultaneous thermal analysis techniques (TG, DTG and DTA). In complex 1, Co(II) ion was coordinated by one bidentate pydca, one isonicotinamide and three aqua ligands to generate a CoN₂O₄ distorted octahedral geometry. Complexes 2 and 3 crystallise in the triclinic system and space group and the structures consist of one complex anion [Co(pydca)₂(H₂O)₂]²⁻, two protonated aminomethylpyridinium cations, ampyH⁺ and two crystal water molecules. In the anions, the Co(II) ions have a distorted octahedral configuration and are coordinated by two bidentate pydca and two trans-aqua ligands. The pydca ligand is coordinated to the Co(II) by both the heterocyclic N atom and the adjacent carboxylate group O atom, creating a chelate ring, while protonated ampy ions behave as counter ion.     

Coordination versatility of 1,3-bis[3-(2-pyridyl)pyrazol-1-yl]propane: Co(II) and Ni(II) complexes

The ligand 1,3-bis[3-(2-pyridyl)pyrazol-1-yl]propane (L⁸) has afforded six-coordinate monomeric and dimeric complexes [(L⁸)Co^II(H₂O)₂][ClO₄]₂ (1), [(L⁸)Ni^II(MeCN)₂][BPh₄]₂ (2), [(L⁸)Ni^II(O₂CMe)][BPh₄] (3), and . The crystal structures of 1, 2 · MeCN, 3, and 4 revealed that the ligand L⁸ is flexible enough to expand its coordinating ability by fine-tuning the angle between the chelating fragments and hence folds around cobalt(II)/nickel(II) centers to act as a tetradentate chelate, allowing additional coordination by two trans-H₂O, cis-MeCN, and a bidentate acetate affording examples of distorted octahedral , , and coordination. The angles between the two CoN₂/NiN₂ planes span a wide range 23.539(1)° (1), 76.934(8)° (2), and 69.874(14)° (3). In contrast, complex 4 is a bis-μ-1,3-acetato-bridged (syn-anti coordination mode) dicobalt(II) complex [Co?Co separation: 4.797(8) Å] in which L⁸ provides terminal bidentate pyridylpyrazole coordination to each cobalt(II) center. To our knowledge, this report provides first examples of such a coordination versatility of L⁸. Absorption spectral studies (MeCN solution) have been done for all the complexes. Complexes 1-3 are uniformly high-spin. Temperature-dependent (2-300 K) magnetic studies on 4 reveal weak ferromagnetic exchange coupling between two cobalt(II) (S = 3/2) ions. The best-fit parameters obtained are: Δ (axial splitting parameter) = −765(5) cm⁻¹, λ (spin-orbit coupling) = −120(3) cm⁻¹, k (orbital reduction factor) = 0.93, and J (magnetic exchange coupling constant) = +1.60(2) m⁻¹.     

pH - Specific synthesis, spectroscopic, and structural characterization of an assembly of species between Co(II) and N,N-bis(phosphonomethyl)glycine. Gaining insight into metal-ion phosphonate interactions in aqueous Co(II)-organophosphonate systems

Cobalt involvement in chemical and metallobiological processes entails largely unknown reactivity pathways with a variety of ligands. Such ligands include phosphonate and carboxylate-containing metal ion binders. In an attempt to investigate the nature and properties of species arising from aqueous interactions between Co(II) and N,N-bis(phosphonomethyl)-glycine (H₅NTA2P), reactions between the two led to an assembly of species in (NH₄)₄[Co(H₂O)₆][(H₂O)₂Co(HNTA2P)Co(NH₃)₂(H₂O)₃]₂[Co(NTA2P)(H₂O)₂]₂ · 10H₂O · 1.36CH₃CH₂OH (1) at pH ∼ 5.5. The analytical, spectroscopic and X-ray data on 1 reveal mononuclear and dinuclear complexes of Co(II) surrounded by oxygens, belonging to terminal carboxylates, phosphonates and bound water molecules, and nitrogen atoms from coordinated ammonia and H_xNTA2P^q− (x = 1, q = 4; x = 0, q = 5) ligands. Worth noting is the variable protonation state of the bound diphosphonate ligand and its ability to bridge two Co(II) centers with ostensibly differing coordination spheres. The assembly of three Co(II) species of variable nuclearity and composition attests to the importance of pH-specific conditions, under which “capturing” of more than one species can be achieved for a given Co(II):H₅NTA2P stoichiometry in the presence of ammonia. Collectively, 1 provides a rare glimpse of a “slice” of the aqueous speciation of the binary Co(II)-H₅NTA2P system, while its lattice composition projects key structural features in Co(II)-carboxyphosphonate materials.     

Identification of cis/trans isomers of bis(acetylacetonato)nickel(II) complexes in solution based on electronic spectra

Electronic spectra of Ni(acac)₂ were studied in acetone, DMF, and some other solvents for the purpose of identifying the cis/trans isomers from the spectra (acac⁻ = acetylacetonate anion). The spectral components were investigated in the spin-allowed transition bands, and a relationship was found between the spectral pattern and the cis/trans isomers. According to this relationship, it was concluded that the cis isomer was formed in DMF and in N-methylformadide, whereas the trans isomer was formed in acetone and in pyridine. Based on the DFT computation, the cis-[Ni(acac)₂(DMF)₂] was found to be stabilized by intramolecular hydrogen bonds between acetylacetonate and DMF.     

Syntheses, stereochemistry, reactivity, and some properties of sulfur-bridged cobalt(III)-cadmium(II) polynuclear complexes derived from mononuclear cobalt(III) complex with d-penicillaminate

A reaction of the octahedral bidentate metalloligand, trans(N)-[Co(d-pen)₂]⁻ (d-pen=d-penicillaminate) with Cd(NO₃)₂ or Cd(ClO₄)₂ gave a novel S-bridged trinuclear complex, [Cd(H₂O){Co(d-pen)₂}₂] (1). In this complex molecule, the central Cd atom is surrounded by four S atoms from two [Co(d-pen)₂]⁻ units and one O atom of a H₂O molecule to form a distorted five-coordinated geometry. Each of two terminal [Co(d-pen)₂]⁻ units takes an approximately octahedral geometry and has a similar trans(N) geometry to that of the starting material. On the other hand, the reaction of trans(N)-[Co(d-pen)₂]⁻ with CdCl₂ in the molar ratio of 1:1 gave an S-bridged dinuclear complex, [CdCl{Co(d-pen)₂}(H₂O)_m]·nH₂O (m+n=4) (2). The reactivity of trans(N)-[Co(d-pen)₂]⁻ toward CdCl₂ is significantly influenced by the ratio of two components, and the formation of a similar trinuclear species to 1 is also suggested under the condition with excess amount of trans(N)-[Co(d-pen)₂]⁻. Some spectrochemical properties of these complexes are also discussed in relation to their structures.     

Pyrrole-substituted tridentate complexes of Ru(II): Spectroscopy, electrochemistry, photosensitization and the role of orbital mixing

One-step syntheses are reported of 4′-(pyrrol-2-yl)-2,2′;6′,2″-terpyridine, 4-(pyrrol-2-yl)-2,6-di(pyrazol-2-yl)pyridine and of their homoleptic Ru(II) complexes, in good to very good yields. DFT calculations confirmed that the pyrrole rings lay coplanar with the tridentate cores and constituted effective π-donors, but also showed that the properties of the Ru(II) complexes defied classical analyses based on localized metal- or ligand-centred orbitals. The low-potential electrochemical oxidations led to electropolymerization but were not purely pyrrole-centred. The low-energy electronic spectral absorptions were not purely metal-to-ligand charge transfer (MLCT) in character, but resulted from mixed metal-to-ligand and intraligand transitions. The complexes’ photosensitization abilities showed that the pyrrole groups were beneficial to the survival of the photoexcited states, albeit not as much as p-tolyl groups.     

Synthesis, characterization, spectroscopic and electrochemical properties of trans,trans,trans-bis(triphenyl phosphine) bis(aroyl hydrazonato)ruthenium(II) complexes

Four ruthenium (II) complexes of general formula Ru(PPh₃)₂(L)₂ have been synthesized and characterized. The spectroscopic and cyclic voltammetric studies of these complexes are also reported. X-ray crystal structure determination of two of the complexes reveal that Ru(II) occupies trans,trans,trans-(t,t,t) N₂O₂P₂ centrosymmetric octahedral environments, with the ligand pair occupying the equatorial plane. ³¹P NMR confirms the presence of two trans-PPh₃ groups in all the complexes. The transformation of the complexes in dichloromethane solution is studied by spectrophotometry and ³¹P NMR spectroscopy.     

Syntheses, characterization, and DFT investigation of new mononuclear acetonitrile- and chloro-ruthenium(II) terpyridine complexes

A series of mononuclear acetonitrile complexes of the type [Ru(CH₃CN)(L)(terpy)]²⁺ {L = phen (1), dpbpy (3), and bpm (5)}, and their reference complexes [RuCl(L)(terpy)]⁺ {L = phen (2), dpbpy (4), and dpphen (6)} were prepared and characterized by electrospray ionization mass spectrometry, UV-vis spectroscopy, and cyclic voltammograms (CV). Abbreviations of the ligands (Ls) are phen = 1,10-phenanthroline, dpbpy = 4,4′-diphenyl-2,2′-bipyridine, bpm = 2,2′-bipyrimidine, dpphen = 4,7-diphenyl-1,10-phenanthroline, bpy = 2,2′-bipyridine, and terpy = 2,2′:6′,2″-terpyridine. The X-ray structures of the two complexes 2 and 3 were newly obtained. The metal-to-ligand charge transfer (MLCT) bands in the visible region for 1, 3, and 5 in acetonitrile were blue shifted relative to those of the reference complexes [RuCl(L)(terpy)]⁺. CV for all the [Ru(CH₃CN)(L)(terpy)]²⁺ complexes showed the first oxidation wave at around 0.95 V, being more positive than those of [RuCl(L)(terpy)]⁺. The time-dependent-density-functional-theory approach (TDDFT) was used to interpret the absorption spectra of 1 and 2. Good agreement between computed and experimental absorption spectra was obtained. The DFT approach also revealed the orbital interactions between Ru(phen)(terpy) and CH₃CN or Cl⁻. It is demonstrated that the HOMO-LUMO energy gap of the acetonitrile ligand is larger than that of the Cl⁻ one.     

Synthetic, structural and spectroscopic studies of complexes derived from the copper(II) perchlorate/succinamic acid/N,N′-donor tertiary reaction systems

The use of succinamic acid (H₂sucm) in Cu(ClO₄)₂·6H₂O/N,N′-donor [2,2′-bipyridine (bpy), 1,10-phenanthroline (phen), 4,4′-dimethyl-2,2′-bipyridine (dmbpy), 4,4′-bipyridine (4,4′-bpy)] reaction mixtures yielded compounds [Cu₂(Hsucm)₃(bpy)₂](ClO₄)·0.5MeOH (1·0.5MeOH), [Cu₂(Hsucm)(OH)(H₂O)(bpy)](ClO₄)₂ (2), [Cu₄(Hsucm)₅(dmbpy)₄]_n(ClO₄)_3n·nH₂O ·0.53nMeOH (3·nH₂O·0.53nMeOH), [Cu₂(Hsucm)₂(dmbpy)₂(H₂O)₂](ClO₄)₂·2H₂O (4·2H₂O), [Cu₂(Hsucm)₂(phen)₂(H₂O)₂](ClO₄)₂·1.8MeOH (5·1.8MeOH), [Cu₂(Hsucm)₂(phen)₂(MeOH)₂](ClO₄)₂·MeOH (6·MeOH) and [Cu(Hsucm)₂(H₂O)(4,4′-bpy)]_n (7). The succinamate(−1) ligand exists in five different coordination modes in the structures of 1-7, i.e. the common syn, syn μ₂-κO:κO′ in 1-6, the μ₂-κ²O in 1, the μ₂-κ²O:κO′ in 1, the μ₃-κ²O:κ²O′ in 3, and the monodentate κO in 7. The primary amide group of Hsucm⁻ remains uncoordinated and participates in intra- and intermolecular hydrogen bonding interactions leading to interesting crystal structures. Characteristic IR bands of the complexes are discussed in terms of the known structures and the coordination modes of the Hsucm⁻ ligands. The thermal decomposition of representative complexes was monitored by TG/DTG and DTA measurements.     

Novel cobalt(II) complexes with pyridyl/ether or pyridyl/thioether ligands. The conversion of pyridyl/thioether cobalt(II) complex to pyridyl/sulfinato cobalt(III) compound

Two new cobalt(II) complexes of symmetric hexadentate mixed-ligand N,O [1,12-bis(2-pyridyl)-5,8-dioxa-2,11-diazadodecane (pydado)] and N,S [1,12-bis(2-pyridyl)-5,8-dithia-2,11-diazadodecane (pydadt)] donor atoms have been synthesized as perchlorate salts. The crystal structures show that [Co(pydado)](ClO₄)₂ · H₂O (1) crystallizes in the triclinic space group and [Co(pydadt)](ClO₄)₂ (2) crystallizes in the monoclinic space group P2_1/c. The cation [Co(pydado)]²⁺ is pseudo-octahedral with the two pyridyl groups in trans position. However, in [Co(pydadt)]²⁺ complex, the size of thioether sulfur atoms imposes a distorted octahedral geometry; the pyridyl groups and the sulfur atoms are in trans position. The reaction of the complex 2 and hydrogen peroxide resulted to the oxidation of Co^II into Co^III and the thioether groups of the ligand to sulfinate groups with elimination of the central ethylenic group of pydadt. Thus, complex 2 was converted to bis[3-(2-pyridylmethylamino)ethanesulfinate] cobalt(III) complex (3) {[Co(pynso)₂](ClO₄) · 0.5H₂O}. The X-ray crystal structure reveals that the compound 3 crystallizes in the triclinic space group with the same donor atoms (N_pyridyl, N_amine and S) belonging to the two ligands in cis-position. In aqueous solution, the stability constants of the Co(II) chelates with these two ligands, determined by potentiometry, show the formation of [Co(LH)]³⁺ and [CoL]²⁺ species in all cases. The chelating power of pydadt ligand is slightly greater than that of pydado.