Organocobaloximes with Mixed Dioxime Equatorial Ligands: A Convenient One-Pot Synthesis. X-ray Structures and Cis−Trans Influence Studies

Synthesis and Characterization of Chloridobis(dimethylglyoximato)4-(2-ferrocenylvinyl)pyridinecobalt(III): A New Heterobinuclear Cobaloxime

The synthesis of a new heterobinuclear cobaloxime with 4-(2-ferrocenylvinyl)pyridine, fcvpy, is reported. The complex [CoCl(dmgH)2(fcvpy)], where dmgH2is dimethylglyoxime and dmgH is dimethylglyoximato, has been characterized by1H-NMR, UV-Vis, cyclic voltammetry, and elemental analysis. The cyclic voltammogram of this complex shows a fc/fc+reversible wave at +0.58 V versus Ag/AgCl, one irreversible wave,Epc= −0.54 V versus Ag/AgCl, assigned to the reduction of Co(III) to Co(II), and two quasireversible processes at −1.02 V and −1.10 V versus Ag/AgCl associated with the reduction of Co(II). The complex showed ferrocene-ligand charge transfer bands at 334 nm and 505 nm. TDDFT/B3LYP/6-31G(d) calculations support this assignation.

Synthesis and characterization of novel organocobaloximes as potential catecholase and antimicrobial activity agents

An asymmetric, potentially bidentate dioxime ligand (H₂L) was formed by condensation of 4-biphenylchloroglyoxime and napthyl-1-amine. Two equivalents of H₂L were reacted with CoCl₂  · 6H₂O under appropriate conditions with deprotonation of the dioxime ligand. A series of new organocobaloxime derivatives of the type [CoR(HL)₂Py], [CoRL₂PyB₂F₄], and [CoRL₂Py(Cu(phen))₂] (H₂L = 4-(napthyl-1-amino)biphenylglyoxime; phen = 1,10-phenathroline; R = izopropyl and benzyl; Py = pyridine) were synthesized. The products were characterized by elemental analysis, molar conductance, FT-IR, ¹H NMR, and magnetic susceptibility measurements. Catecholase-like activity properties of all complexes were also studied. All complexes are catalysts for the oxidation of 3,5-di-tert-butylcatechol to 3,5-di-tert-butyl-1,2-benzoquinone in methanol. Antimicrobial activity studies of H₂L and the six complexes were carried out on standard strains (human pathogenic) of bacteria (Staphylococcus aureus, methicillin-resistant S. aureus (MRSA), Bacillus cereus, Enterococcus faecalis, Streptococcus pneumoniae, Listeria monocytogenes, Bacillus subtilis, Escherichia coli, Pseudominas aeruginosa, Salmonella typhi) and the yeast Candida albicans. The compounds showed a significant inhibition of the growth of the Gram-positive bacteria tested. Among the tested microorganisms, S. aureus was the most sensitive strain, especially to H₂L and its complexes.

Catalytic hydrogen evolution from a covalently linked dicobaloxime

A dicobaloxime in which monomeric Co(III) units are linked by an octamethylene bis(glyoxime) catalyzes the reduction of protons from p-toluenesulfonic acid as evidenced by electrocatalytic waves at -0.4 V vs. the saturated calomel electrode (SCE) in acetonitrile solutions. Rates of hydrogen evolution were determined from catalytic current peak heights (k(app) = 1100 ± 70 M(-1) s(-1)). Electrochemical experiments reveal no significant enhancement in the rate of H(2) evolution from that of a monomeric analogue: The experimental rate law is first order in catalyst and acid consistent with previous findings for similar mononuclear cobaloximes. Our work suggests that H(2) evolution likely occurs by protonation of reductively generated Co(II)H rather than homolysis of two Co(III)H units.

Kinetics of the reduction of 4-amino and 4-cyanopyridinechlorocobaloximes by iron(II)

Cobaloximes such as trans[Co(dmgH) 2(Py-NH2)Cl] and trans- [Co(dmgH) 2(Py-CN)Cl], where, dmgH = dimethylglyoximato anion, Py-NH 2 = 4-aminopyiridne and Py-CN = 4-cyanopyridine, were prepared and characterized by elemental analysis, UV-VIS, IR and NMR spectroscopy. The kinetics of iron(II) reduction of the complexes were studied spectrophotometrically at 300 nm in 2% (v/v) DMSO-H2O medium at 27?0.1?C and I = 0.25 M (LiClO4) at various hydrogen ion concentrations in the range 2.5 x 10-4 to 5.0x10-2 M under pseudo-first-order conditions using an excess of the reductant. The inverse dependence of rate on [H+] suggests an equilibrium between the protonated and unportonated forms of the complexes, the protonated form reacting slower than the unprotonated form. Computation of the data enabled the evaluation of the rate constants for the protonated and unprotonated from of the complexes, leading to an evaluation of the protonation constant for the complexes. .

Platinum(II) Complexes with Pyridyl Azolate-Based Chelates: Synthesis, Structural Characterization, and Tuning of Photo- and Electrophosphorescence

A new series of luminescent platinum(II) azolate complexes with a formula of [Pt(NwedgeN)(2)], in which NwedgeN = mppz (1), bppz (2a), bzpz (2b), bmpz (2c), bqpz (2d), fppz (3a), hppz (3b), bptz (4), hptz (5), were synthesized, and their photophyscial properties were examined. Single-crystal X-ray diffraction studies of 2c and 3b revealed a planar molecular geometry, in which the NwedgeN chelates adopt a trans configuration and show notable interligand C-H...N hydrogen bonding within the complex. Interesting intermolecular interactions were observed in the solid state. Complex 2c formed a slipped-stack structure with a Pt...Pt separation distance of 6.432 Angstroms, while complex 3b showed a columnar stacking with the molecules oriented in an alternating order in relation to the chain axis, giving a much reduced Pt...Pt distance of 3.442 Angstroms. The lowest absorption band for all complexes revealed strong state mixings between the singlet and triplet (MLCT and intraligand pipi) manifolds. Complexes 1 and 2 showed mixed (3)MLCT and (3)pipi phosphorescence in fluid solution. While radiationless deactivation was apparently dominant for complexes 3-5 in solution, resulting in rather weak emission, strong phosphorescence was observed in the room-temperature solid state with the peak wavelength being significantly red shifted compared to that in solution. The emission nature has been tentatively assigned to be (3)MMLCT in character. OLED devices with a multilayer configuration of ITO/NPB/CBP:2a/BCP/Alq(3)/LiF/Al were successfully fabricated using a CBP layer doped with various amount of 2a, ranging from 6 to 100%, as the emitting layer. A substantial red shift with increasing doping concentrations was observed in electroluminescence. With a neat film of 2a, the device showed a green emission with lambda(max) at 556 nm and an external QE of approximately 1.6% at a driving current of 20 mA. Similarly, for the device using a neat film of 3a, an electroluminescence centered at 616 nm with a slightly reduced external QE of approximately 2.1% was recorded. Aggregation of platinum(II) complexes in the solid state was proposed to account for the large red-shift in electroluminescence.

Interplay between Intra- and Interligand Charge Transfer with Variation of the Axial N-Heterocyclic Ligand in Osmium(II) Pyridylpyrazolate Complexes: Extensive Color Tuning by Phosphorescent Solvatochromism

The rational design and syntheses of a new series of Os(II) complexes with formula [Os(fppz)(2)(CO)(L)] (1: L=4-dimethylaminopyridine; 2: L = pyridine; 3: L = 4,4'-bipyridine; 4: L = pyridazine; 5: L = 4-cyanopyridine), bearing two (2-pyridyl)pyrazolate ligands (fppz) together with one carbonyl and one N-heterocyclic ligand at the axial positions are reported. Single-crystal X-ray diffraction studies of, for example, 2 reveal a distorted octahedral geometry in which both fppz ligands reside in the equatorial plane with a trans configuration and adopt a bent arrangement at the metal center with a dihedral angle of approximately 23 degrees , while the carbonyl and pyridine ligands are located at the axial positions. Variation of the axial N-heterocyclic ligand leads to remarkable changes in the photophysical properties as the energy gap and hence the phosphorescence peak wavelength can be tuned. For complexes 1 and 2 the solvent-polarity-independent phosphorescence originates from a combination of intraligand (3)pi-pi* ((3)ILCT) and metal-to-ligand charge transfer transitions ((3)MLCT). In sharp contrast, as supported by cyclic voltammetry measurements and theoretical calculations, complexes 3--5 exhibit mainly ligand-to-ligand charge transfer (LLCT) transitions, resulting in a large dipolar change. The phosphorescence of complexes 3--5 thus exhibits a strong dependence on the polarity of the solvent, being shifted for example, from 560 (in C(6)H(12)) to 665 nm (in CH(3)CN) and from 603 (in C(6)H(12)) to 710 nm (in CH(3)CN) for complexes 3 and 5, respectively. The results clearly demonstrate that a simple, straightforward derivatization of the axial N-heterocyclic ligand drastically alters the excitation properties per se from intraligand charge transfer (ILCT) to LLCT transitions. The latter exhibit remarkable LLCT phosphorescence solvatochromism so that a broad range of color tunability can be achieved.