An estimate of the enthalpy change associated with the substitution of H20 in (NH3)5RuOH22+by NO+(aq) has been made by thermochemical measurements on a cycle of reactions, which includes the reaction of (NH3)5RuOH22+with N02-(aq) and which involves the assumption that the heat of dissolution of NOBF4(s) to produce NO+(aq) + BF4-(aq) is close to the heat of dissolution of csbf4(s). The chemistry is complicated because the reaction of (NH3)5RuOH22+with N02-ultimately produces trans-[(NH3)4Ru(OH)NO]3+rather than [(NH3)5RuNO]3+. Reasonably good estimates of the enthalpy changes of the reactions needed for the cycle to close on [(NH3)5RuNO]3+ can be made, and when these are combined with the experimental results, they yield as ΔH° for the reaction of interest -52 kcal mol-1. We believe that this result is accurate to within 5 kcal, and the conclusion that the reaction of NO+(aq) with Ru(II) is more exothermic than that of the isoelectronic CO(aq) (-38.2 ± 1.2 kcal mol-1) seems safe. The assumption as to the heat of solution of NOBF4(s) and csbf4(s) is validated by the finding that the enthalpy change for the formation of 2H+ + N02-by the reaction of NO+(aq) with water, -10.6 ± 0.5 kcal mol-1, which can be calculated from our results, lies between upper and lower limits set by the work of others.
All Science Journal Classification (ASJC) codes
- Physical and Theoretical Chemistry
- Inorganic Chemistry