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

According to spectrophotometric data, the reaction of trans-[Ru(NH3)(4)P(OEt)(3)(H2O)](2+) with NO2- in alkaline medium (CH+ < 10(-9) mol L-1) occurs on two steps. In the first, both the nitro (trans-[Ru(NH3)(4)P(OEt)(3)(NO2)](+)) and nitrito (trans-[Ru(NH3)(4)P(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, K-N, of trans-[Ru(NH3)(4)P(OEt)(3)(NO2)](+) (5.2 +/- 0.6) x 10(3) M-1 (pH 11.0; mu = 0.3 mol L-1 NaCF3COO; T = (25 +/- 0.2) degrees 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)(4)P(OEt)(3)(NO2)](+), was (1.2 +/- 0.3) x 10(-1)s(-1)(pH 10.9; mu = 0.3 mol L-1 NaCF3COO; T= (25+/- 0.2) degrees C). Trans-[Ru(NH3)(4)P(OEt)(3)NO2](+) was quantitatively converted into the trans-[Ru(NH3)(4)P(OEt)(3)NO](3+) in acid solutions (CH+ > 10(-5) mol L-1; k(obs) = 2.2 x 10(-3) s(-1) at pH 4). However the inverse conversion was not quantitative. (c) 2007 Elsevier Ltd. All rights reserved.