Adducts of nitric oxide with cobaltous tetraphenylporphyrin and phthalocyanines: Potential nitric oxide sorbents

Article abstract of DOI:10.1016/s0020-1693(97)05964-1

Cobaltous tetraphenylporphyrin (Co(II)TPP) andcobaltous phthalocyanine (Co(II)Pc) complexes were studied in a variety of solvents, including water. The imidazole and nitrosyl adducts were synthesized and characterized by UV-Vis spectrophotometry and electron spin resonance spectroscopy. The imidazole adducts were subsequently exposed to nitric oxide to study the competitive interactions between nitrosyl and imidazole ligands in these cobaltous compounds. This is important, since it has been suggested that aqueous solutions of cobaltous porphyrins and phthalocyanines can serve as denitrification agents when bound to an immobilized imidazole modified silica gel (IMSG) substrate. Our results indicate that while nitric oxide binds both Co(II)TPP and Co(II)Pc in organic solvents in the absence of a bound imidazole ligand, it will not bind when imidazole is axially bound to the cobalt ion. Neither Co(II)TPP nor Co(II)Pc are water soluble and both will dimerize in water. A water soluble NO sorbent which does not dimerize in water would be ideal for removing NO from flue gas streams. The Co(II)PcTs(IMSG) appears to meet these requirements. Preliminary results indicate that aqueous suspensions of Co(II)PcTs(IMSG) are capable of NO removal from a gas stream passed through these suspensions and may thus be suitable candidates for further development as NO sorbents for NO_x abatement.