Synthesis of New Cobalt(III) Meso-Porphyrin Complex, Photochemical, X-ray Diffraction, and Electrical Properties for Photovoltaic Cells

The present work describes the preparation and characterization of a new cobalt(III) porphyrin coordination compound named (chlorido)(nicotinoylchloride)[meso-tetra(para-chlorophenyl)porphyrinato]cobalt(III) dichloromethane monosolvate with the formula [Co^III(TClPP)Cl(NTC)]·CH₂Cl₂ (4). The single-crystal X-ray molecular structure of 4 shows very important ruffling and waving distortions of the porphyrin macrocycle. The Soret and Q absorption bands of 4 are very red-shifted as a consequence of the very distorted porphyrin core. This coordination compound was also studied by fluorescence and cyclic voltammetry. The efficiency of our four porphyrinic compounds-the H₂TClPP (1) free-base porphyrin, the [Co^II(TClPP)] (2) and [Co^III(TClPP)Cl] (3) starting materials, and the new Co(III) metalloporphyrin [Co^III(TClPP)Cl(NTC)]·CH₂Cl₂ (4)-as catalysts in the photochemical degradation was tested on malachite green (MG) dye. The current voltage of complexes 3 and 4 was also studied. Electrical parameters, including the saturation current density (J_s) and barrier height (ϕ_b), were measured.

Insight into the preferential N-binding versus O-binding of nitrosoarenes to ferrous and ferric heme centers

Nitrosoarenes (ArNOs) are toxic metabolic intermediates that bind to heme proteins to inhibit their functions. Although much of their biological functions involve coordination to the Fe centers of hemes, the factors that determine N-binding or O-binding of these ArNOs have not been determined. We utilize X-ray crystallography and density functional theory (DFT) analyses of new representative ferrous and ferric ArNO compounds to provide the first theoretical insight into preferential N-binding versus O-binding of ArNOs to hemes. Our X-ray structural results favored N-binding of ArNO to ferrous heme centers, and O-binding to ferric hemes. Results of the DFT calculations rationalize this preferential binding on the basis of the energies of associated spin-states, and reveal that the dominant stabilization forces in the observed ferrous N-coordination and ferric O-coordination are dπ-pπ* and dσ-pπ*, respectively. Our results provide, for the first time, an explanation why in situ oxidation of the ferrous-ArNO compound to its ferric state results in the observed subsequent dissociation of the ligand.

Synthesis, crystal structures and spectroscopic characterization of Co(II) bis(4,4′-bipyridine) with meso-porphyrins α,β,α,β-tetrakis(o-pivalamidophenyl) porphyrin (α,β,α,β-TpivPP) and tetraphenylporphyrin (TPP)

The reaction of the starting materials [ Co II ( Porph )] (Porph = α,α,α,α-tetrakis(o-pivalamidophenyl)porphyrin (TpivPP) and the meso-tetraphenylporphyrin (TPP)) with an excess of 4,4′-bipyridine in chlorobenzene leads to the creation of two cobalt(II) derivatives: [ Co II (α,β,α,β- TpivPP )(4,4′- bpy )2]· C 6 H 5 Cl · C 6 H 14(1) and [ Co II ( TPP )(4,4′- bpy )2]·2 bpy (2). These compounds have been characterized by UV-vis, IR, 1 H NMR and MALDI-TOF spectroscopy. The proton NMR spectra of (1) and (2) clearly indicated that these derivatives are paramagnetic while the UV-vis data confirmed creation of a new six-coordinated or penta-coordinated Co ( II )-meso-porphyrin complexes by displaying red shifted Soret bands. The determined X-ray structures of (1) and (2) show that in the solid state these species are considered as coordination polymers which consist of 1D chains of alternating [ Co II ( Porph )] and 4,4′-bipyridine molecules located at the axial positions of the cobalt(II) coordination sphere. The coordination geometry of Co ( II ) in (1) and (2) is octahedral; the porphyrin (TpivPP or TPP) acts as a tetradentate chelating ligand with four nitrogen atoms from the pyrrole moieties occupying the equatorial positions along the porphyrin core. The N -donor atoms of the 4,4′-bipyridine create the axial ligands. It is noteworthy that for complex (1) the starting porphyrin is the α,α,α,α-TpivPP atropisomer but the final coordination polymer contains the α,β,α,β-TpivPP conformer.

Synthesis and solid-state molecular structures of bis- and mono-nitrosobenzene complexes of ruthenium porphyrins

Bis-nitrosobenzene complexes of the form (por)Ru(PhNO)2 (por = TPP, TTP; TPP = tetraphenylporphyrinato dianion, TTP = tetratolylporphyrinato dianion) have been prepared in good yields from the reaction of the (por)Ru(CO) precursor with excess PhNO in dichloromethane. The IR spectra of the complexes (as KBr pellets) displayed new bands at ~1348 cm–1, due to υNO. The solid-state molecular structure of (TPP)Ru(PhNO)2 was determined by single-crystal X-ray diffraction, and revealed that the PhNO ligands are bound to the Ru center via the N-binding mode. Reactions of the (por)Ru(PhNO)2 complexes with excess 1-methylimidazole gave the mono-nitrosobenzene complexes (por)Ru(PhNO)(1-MeIm). The IR spectra revealed a lowering of υNO in these mononitrosobenzene derivatives by ~27 cm–1, a feature consistent with the replacement of one π-acid PhNO ligand with the more basic 1-MeIm ligand. The solid-state molecular structure of (TPP)Ru(PhNO)(1-MeIm) reveals, in addition to the N-binding of the PhNO ligand, an essentially parallel arrangement of the C-N-O (of PhNO) and imidazole planes; this is in contrast with the (TPP)Ru(PhNO)2 complex, in which the C-N-O planes (of PhNO) are essentially perpendicular.Key words: nitroso, X-ray, ruthenium, porphyrin, imidazole.