Aspects of nitrite association with trans-[Ru(NH3)4P(OEt)3H2O]2+

According to spectrophotometric data, the reaction of trans-[Ru(NH3)4P(OEt)3(H2O)]2+ with NO2- in alkaline medium (CH+<10-9molL-1) occurs on two steps. In the first, both the nitro (trans-[Ru(NH3)4P(OEt)3(NO2)]+) and nitrito (trans-[Ru(NH3)4P(OEt)3(ONO)]+) isomers are formed. In the second step, the nitrito isomer is converted into the nitro form. Under equilibrium conditions and using pyrazine as auxiliary ligand, the formation constant, KN, of trans-[Ru(NH3)4P(OEt)3(NO2)] + (5.2 ± 0.6) × 103 M−1 (pH 11.0; μ = 0.3 mol L−1 NaCF3COO; T = (25 ± 0.2) °C) was measured using the Indicator Colorimetric Method. The spectrophotometrically measured specific rate constant for the equation of the nitrite ligand in trans-[Ru(NH3)4P(OEt)3(NO2)]+, was (1.2 ± 0.3) × 10−1 s−1(pH 10.9; μ = 0.3 mol L−1 NaCF3COO; T = (25 ± 0.2) °C). Trans-[Ru(NH3)4P(OEt)3NO2]+ was quantitatively converted into the trans-[Ru(NH3)4P(OEt)3NO]3+ in acid solutions (CH+>10-5molL-1; kobs = 2.2 × 10−3 s−1 at pH 4). However the inverse conversion was not quantitative.

trans-[Ru(NH3)4P(OEt)3(H2O)]2+ is known to reacts with nitrite ions in alkaline media (pH > 10) yielding trans-[Ru(NH3)4P(OEt)3(NO2)]+, KN = (5.2 ± 0.6) × 103 M−1 ((25 ± 0.2) °C), which releases the nitrite ligand, k−N = (1.2 ± 0.03) × 10−1 s−1. The nitro compound, in acid environment, undergoes quantitative conversion to the corresponding nitrosyl complex (kobs = 2.2 × 10−3 s−1 at pH 4).Figure optionsDownload as PowerPoint slide