Role of Cobalt(III) Cationic Complexes in the Self-Assembling Process of a Water Soluble Porphyrin

Under moderate acidic conditions, the cationic (+3) complexes ions tris(1,10-phenanthroline)cobalt(III), [Co(phen)3]3+, and hexamminecobalt(III), [Co(NH3)6]3+, efficiently promote the self-assembling process of the diacid 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin (H2TPPS4) into J-aggregates. The growth kinetics have been analyzed according to a well-established autocatalytic model, in which the rate determining step is the initial formation of a nucleus containing m porphyrin units (in the range 2–3), followed by a stage whose rate constant kc evolves as a power of time. The observed catalytic rate constants and the extent of J-aggregation increase on increasing the metal complex concentration, with the phen complex being the less active. The UV/Vis extinction spectra display quite broad envelops at the J-band, especially for the amino-complex, suggesting that electronic dipolar coupling between chromophores is operative in these species. The occurrence of spontaneous symmetry breaking has been revealed by circular dichroism and the measured dissymmetry g-factor decreases on increasing the aggregation rates. The role of these metal complexes on the growth and stabilization of porphyrin nano-assemblies is discussed in terms of the different degree of hydrophilicity and hydrogen bonding ability of the ligands present in the coordination sphere around the metal center.

Preparation, Structure and Thermolysis Characteristics of Ammonia Borane

Ammonia borane (NH3BH3, AB) is an excellent source of hydrogen(19.6 wt %) for fuel cell applications. In this paper, pure ammonia borane is successfully prepared by using amino complex for ammonia complex Ag(NH3)2Cl as new ammonia source, and sodium borohydride (NaBH4) as boron source. The composition and constitution of the products are measured by XRD and FT-IR. The thermolysis of ammonia borane is significant for its practical application. Boric acid plays a role in improving ammonia borane hydrogen performance. The effects of different mass ratio of boric acid and ammonia borane on dehydrogenation are tested by XRD, TG/DTA and TPD-MS. The results show that boric acid can decrease the first level dehydrogenation temperature of ammonia borane decrease to about 85°C (working temperature of PEMFC). What’s more, the onset temperature of AB’s thermolysis can decrease to about 60°C when the mass ratio of ammonia borane and boric acid is equal to 3:1. This makes ammonia borane be more suitable for the application in on-board hydrogen storage system.

Nano Sized Pd Particles In A SiO2 Matrix By Sol-Gel Processing

ABSTRACTPd colloid containing Ormocers (organically modified ceramics) have been prepared from Pd amino complexes of the type Pd[NH2CH2CH2NH(CH2)3Si(OMe)3]2ac2 by hydrolysis and condensation (sol-gel reaction) of the silane together with Si(OEt)4 and Si(OEt)3(CH2)3OCH2CHCH2O. The amino complex formation is necessary to avoid spontaneous reduction and uncontrolled colloid formations in the liquid phase. This synthesis route leads to Pd colloid containing powders and coatings on glass. By thermal curing (temperatures up to 500 °C) using different atmospheric conditions (N2, Ar, H2/N2) brown to deep black coatings on glass with transmission values from 80 to 0 % can be obtained. The average particle size can be controlled by varying the molar ratio of the used Pd salt (Pd(ac)2) and the aminosilane.