Electrochemical and spectroscopic investigation of redox processes for labile metal dithiocarbamate complexes

Although metal dithiocarbamate complexes have been studied extensively, there is in sate cases a distinct lack of data concerning redox properties and the products thereof. This is particularly true for complexes of the late transition and main group metals which are important in agriculture, industry, and chemical analysis. Hence, using electrochemical techniques, the redox behaviour of dithiocarbamate complexes of zinc, cadmium, mercury, lead, and tellurium has been examined. The products of oxidation and reduction have also been characterized by spectroscopic techniques (NMR, EPR, UV, and IR), mass spectrometry, conductivity, and Where possible, crystallographic study of an isolated compound. The species studied were without exception labile with the result that electrochemistry at mercury electrodes was influenced by the great stability of the mercury dithiocarbamate (Hg(RR’dtc) 2) complexes. Investigation of the latter showed that oxidative processes in the presence of mercury led to a new class of expounds: polymeric mercury dithiocarbamato cations. Oily one of these could be isolated as a solid, with the formula [Hg5(RR’dtc) 8](C104)2 For R=R’=ethyl the crystal structure was determined. For other metal dithiocarbamates the electrochemical behaviour at mercury electrodes in many ways paralleled that of the mercury analogues. Thus oxidative processes involved oxidation of electrode mercury to form mixed metal cationic species. Polarographic reduction led to the metal amalgam, usually via formation of mercury dithiocarbamate. Electrochemical studies at inert electrode materials such as platinum yielded distinctly different responses, with both oxidation and reduction being more difficult. Oxidation products at platinum electrodes gave identical polarographic responses to those firm mercury electrodes due to rapid interaction of the former with electrode mercury. The results are in sharp contrast to much of the previous work on transition metal dithiocarbamates for which electrochemical redox processes are often metal based arid not explicated by interaction with the electrode material.

Antimicrobial and toxicological studies of some metal complexes of 4-methylpiperazine-1-carbodithioate and phenanthroline mixed ligands

A few mixed ligand transition metal carbodithioate complexes of the general formula [M(4-MPipzcdt)_x(phen)_y]Y (M = Mn(II), Co(II), Zn(II); 4-MPipzcdt = 4-methylpiperazine-1-carbodithioate; phen = 1,10-phenanthroline; x = 1 and y = 2 when Y = Cl; x = 2 and y = 1 when Y = nil) were synthesized and screened for their antimicrobial activity against Candida albicans, Escherichia coli, Pseudomonas aeruginosa,Staphylococcus aureus and Enterococcusfaecalis by disk diffusion method. All the complexes exhibited prominent antimicrobial activity against tested pathogenic strains with the MIC values in the range <8-512 μgmL-1. The complexes [Mn(4-MPipzcdt)₂(phen)] and [Co(4-MPipzcdt)(phen)₂]Cl inhibited the growth of Candida albicans at a concentration as low as 8 µgmL^-1.The complexes were also evaluated for their toxicity towards human transformed rhabdomyosarcoma cells (RD cells). Moderate cell viability of the RD cells was exhibited against the metal complexes.

Electrostatic forces induce poly(vinyl alcohol)-protected copper nanoparticles to form copper/poly(vinyl alcohol) nanocables via electrospinning

Copper/poly(vinyl alcohol) (PVA) nanocables have been successfully obtained by electrospinning a PVA-protected copper nanoparticle solution. The molar ratio of copper ions to PVA (in terms of VA repeating units) plays an important role in the formation of copper/PVA nanocables. The average diameter of the copper cores and PVA shells is about 100 and 400 nm, respectively. The structures of the copper/PVA nanocables are characterized by transmission electron microscopy (TEM) and their formation is confirmed by scanning electron microscopy (SEM).

Structural characterization of rare intramolecularly (1,4-Te· · ·N) bonded diorganotellurides and their monomeric complexes with mercury(II) halides: metal assisted C-H· · ·X (Hg) interactions leading to supramolecular architecture

Monomeric tellurides 4-RC₆H₄(SB)Te [SB = 2-(4,4'-N0₂C₆H₄CH=NC₆H₃-Me); R = H, 1a; Me,1b; OMe, 1c], which incidentally represent the first example of a telluride with 1,4-Te···N intramolecular interaction, have been prepared and characterized by solution and solid-state ¹²⁵Te NMR, ¹³C NMR and X-ray crystallography. Interplay of weak C-H···O and C-H-··π{ interactions in the crystal lattice of 1b and1c are responsible for the formation of supramolecular motifs. These tellurides undergo expected oxidative addition reactions with halogens and interhalogens and also interact coordinatively with mercury(II) halides to give 1:2 complexes, HgX₂[4-RC₆H₄(SB)Te]₂ (X = CI, R = H, 2a; Me, 2b; OMe, 2c and X = Br, R = H, 3a; Me, 3b; and OMe, 3c) with no sign of Te-C bond cleavage, as has been reported for some 1,5-Te·· ·N(O) intramolecularly bonded tellurides. The complexes 2a and 3c are the first structurally characterized monomeric 1:2 adducts of mercury(II) halides with Te ligands. The 1,4-Te···N intramolecular interactions in the solid-state are retained in the complexes highlighting simultaneously the Lewis acid and base character of the Te(lI) atom. Packing of molecules in the crystal lattice of 2a
and 3c reveals that non-covalent C-H· . ·Cl/Br interactions involving metal-bound halogen atoms possess significant directionality and in
combination with coordinative covalent interactions may be of potential use in creating inorganic supramolecular synthons.

Evaluation of selected platinum group metal complexes as chemiluminescence reagents

This research extends the investigations into the chemiluminescence and electrochemiluminescence of platinum group metal reagents and their applications. The effect of the chemical nature of tris(2,2'-bipyridyl)ruthenium(II) and selected analogues on the chemiluminescence reaction is further explored, and this chemistry is extended to include novel iridium(III) and osmium(II) based chemiluminescence reagents.

New perspectives on the annihilation electrogenerated chemiluminescence of mixed metal complexes in solution

Preliminary explorations of the annihilation electrogenerated chemiluminescence (ECL) of mixed metal complexes have revealed opportunities to enhance emission intensities and control the relative intensities from multiple luminophores through the applied potentials. However, the mechanisms of these systems are only poorly understood. Herein, we present a comprehensive characterisation of the annihilation ECL of mixtures of tris(2,2′-bipyridine)ruthenium(ii) hexafluorophosphate ([Ru(bpy)3](PF6)2) and fac-tris(2-phenylpyridine)iridium(iii) ([Ir(ppy)3]). This includes a detailed investigation of the change in emission intensity from each luminophore as a function of both the applied electrochemical potentials and the relative concentrations of the two complexes, and a direct comparison with two mixed (Ru/Ir) ECL systems for which emission from only the ruthenium-complex was previously reported. Concomitant emission from both luminophores was observed in all three systems, but only when: (1) the applied potentials were sufficient to generate the intermediates required to form the electronically excited state of both complexes; and (2) the concentration of the iridium complex (relative to the ruthenium complex) was sufficient to overcome quenching processes. Both enhancement and quenching of the ECL of the ruthenium complex was observed, depending on the experimental conditions. The observations were rationalised through several complementary mechanisms, including resonance energy transfer and various energetically favourable electron-transfer pathways.

Complexes of the tripodal nitrilotrimethylenetrisphosphonic (H6L) and P,P',P''-triphenylnitrilotrimethylenetrisphosphinic (H3L) acids with the copper(II) ion. Synthesis and charaterization of [Hpy][Cu(H3L)(H2O)] and [Cu(HL)(py)]2.2Me2CO

The complexes [Hpy][Cu(H₃L)(H2O)] 1 (L⁶ = nitrilotrimethylenetrisphosphonate) and [Cu(HL°)(py)]₂·2Me₂CO 2 [(L°)³ = P,P,P" -triphenylnitrilotrismethylenetrisphosphinate)] have been isolated and characterized by X-ray crystallography, near IR-visible spectroscopy and magnetic measurements. The structure determination has shown the complexes to be constituted by monomeric and dimeric units respectively. In the monomer the metal atom is surrounded by the phosphonate ligand and a water molecule, with a geometry between a trigonal bipyramid and a square pyramid. The two copper atoms in the dimer are held together by an arm of the tripod ligand, with a pyridine molecule as additional ligand, and display octahedral geometry. The presence of monomeric and dimeric species in aqueous solutions of 1 and 2 has been shown by ESMS studies. The formation in water solution of the dimer [{Cu(H₃L)}₂]^2-, as a minor species, has been supported by potentiometric measurements, whereas only the monomeric anion [CuL°] has been ascertained to be present. In general the ligand H₃L° forms less stable copper(II) complexes than H₆L.

Beryllium (II) complexes of the klaui tripodal ligand cyclopentadienyltris (diethylphosphito-P) cobaltate(-)

The interactions of the beryllium(II) ion with the cyclopentadienyltris(diethylphosphito-P)cobaltate monoanion, L^-, have been investigated, in aqueous solution, by synthetic methods, potentiometry, ESMS, and ¹H, ³¹P, and ⁹Be NMR spectroscopy. L^- has been found able to displace either two or three water molecules in the beryllium(II) coordination sphere, to form mononuclear, dinuclear, and trinuclear derivatives, in which the metal ion is pseudotetrahedrally coordinated. The species [BeL(H₂O)]⁺ and [Be₂L₂(μ-OH)]⁺ have been identified in solution while complexes of formula BeL₂ and [Be₃L₄](ClO₄)₂ have been isolated as solid materials. The species [BeL(OPPh₂)]⁺, closely related to [BeL(H₂O)]⁺, has been characterized in acetone solution and isolated as tetraphenylborate salt. The structure of the unusual trimeric complex [Be₃L₄]²⁺ has been elucidated by an unprecedented 2D ⁹Be-³¹P NMR correlation spectrum showing the presence of a single central beryllium nucleus and two equivalent terminal beryllium nuclei. The three beryllium centers are held together by four cobaltate ligands, which display two different bonding modes: two ligands are terminally linked with all the three oxygen donors to one terminal beryllium, and the other two bridge two metal centers, sharing the oxygen donors between central and terminal beryllium atoms.

Synthesis and structural diversity of rare earth anthranilate complexes

Four structural classes have been established for rare earth anthranilates, which have been prepared from the lanthanoid chloride or triflate and anthranilic acid (anthH) followed by pH adjustment to 4. [La(anth)3]n is a polymeric complex with nine coordinate lanthanum and bridging tridentate (O,O,O′) anthranilate ligands, whereas [Nd(anth)3(H2O)3] · 3H2O is monomeric with nine coordinate neodymium and solely chelating (O,O) anthranilate groups. Both chelating (O,O) and bridging bidentate (O,O′) ligands are observed in dimeric [Er2(anth)6(H2O)4] · 2H2O, in which erbium is eight coordinate and the water ligands are in a trans arrangement. A polymer is observed for [Yb(anth)3(H2O)]n with solely bridging bidentate (O,O′) ligands and seven coordination for ytterbium. The NH2 groups of the anthranilate ligands are not coordinated to the metal but is unusually involved in hydrogen-bond networks with water molecules for Ln = Er, Yb.

Synthesis, X-ray structure and electrochemical characterization of palladium(II) bearing ferrocenyldiphenylphosphine complexes

Four new complexes, [PdX(κ2-2-C6R4PPh2)(PPh2Fc)] [X = Br, R = H (1), R = F (2); X = I, R = H (3), R = F (4)], containing ferrocenyldiphenylphosphine (PPh2Fc) have been prepared and fully characterised. The X-ray structures of complexes trans-1, cis-2 and cis-4, and that of a decomposition product of 4, [Pd(κ2-2-C6F4PPh2)(μ-I)(μ-2-C6F4PPh2)PdI(PPh2Fc)] (5), have been determined. These complexes show a distorted square planar geometry about the metal atom, the bite angles of the chelate ligands being about 69°, as expected. The cis/trans ratio of 1–4 in solution is strongly dependent on solvent. The new complexes and the uncoordinated PPh2Fc ligand were electrochemically characterised by cyclic and rotating disk voltammetry, UV-visible spectroelectrochemistry, and bulk electrolysis in dichloromethane and acetonitrile. In both cases, oxidation occurs at both the ferrocene and phosphine centres, but the complexes oxidise at more positive potentials than uncoordinated PPh2Fc; subsequently, the metal–phosphorus bond is cleaved, leading to free PPh2Fc+, which undergoes further chemical and electrochemical reactions.

Novel dithiolene complexes incorporating conjugated electroactive ligands

A series of new metal (M) dithiolene complexes bearing terthiophene (3, 12, M = Ni; 4, M = Pd; 5, 6, M = Au) and 2,5-bis(para-methoxyphenyl)thiophene units (14, M = Ni; 15, 16, M = Au; 17, M = Pd) have been synthesised in 38–99% yield. The electrochemical properties of the materials have been characterised by cyclic voltammetry and UV-vis spectroelectrochemistry. The nickel complexes possess low oxidation potentials (−0.12 to −0.25 V vs Ag/AgCl) due to the electron-rich dithiolene centres and all complexes display ligand-based redox activity. The terthiophene derivatives have been polymerised by electrochemical oxidation to give stable films with, in the case of poly(3), broad absorption characteristics. Charge transfer materials have been isolated from 14 and 16 with conductivities in the range 9 × 10⁻⁶ to 7 × 10⁻⁸ S cm⁻¹.

Annihilation electrogenerated chemiluminescence of mixed metal chelates in solution : Modulating emission colour by manipulating the energetics

We demonstrate the mixed annihilation electrogenerated chemiluminescence of tris(2,2′-bipyridine)ruthenium(ii) with various cyclometalated iridium(iii) chelates. Compared to mixed ECL systems comprising organic luminophores, the absence of T-route pathways enables effective predictions of the observed ECL based on simple estimations of the exergonicity of the reactions leading to excited state production. Moreover, the multiple, closely spaced reductions and oxidations of the metal chelates provide the ability to finely tune the energetics and therefore the observed emission colour. Distinct emissions from multiple luminophores in the same solution are observed in numerous systems. The relative intensity of these emissions and the overall emission colour are dependent on the particular oxidized and reduced species selected by the applied electrochemical potentials. Finally, these studies offer insights into the importance of electronic factors in the question of whether the reduced or oxidized partner becomes excited in annihilation ECL. This journal is