Kinetic study of ferrous nitrosyl complexes

The formation and dissociation rate constants and equilibrium constants for the reversible binding of NO to Fe/sup II/(H/sub 2/O)/sub 5/, Fe/sup II/(cit), Fe/sup II/(acac)/sub 2/, and Fe/sup II/(EDTA) in aqueous solution are reported (cit = citrate, acac = acetylacetonate, EDTA = ethylenediaminetetraacetate). The constants were determined (at 25/sup 0/C) as follows: Fe/sup II/(H/sub 2/O)/sub 5/NO, k/sub 1/ = 7.1 x 10/sup 5/ M/sup -1/ s/sup -1/, k/sub /sup -1// = 1.5 x 10/sup 3/ s/sup -1/, K = 470 M/sup -1/; Fe/sup II/(cit)NO, k/sub 1/ = 4.4 x 10/sup 5/ M/sup -1/ s/sup -1/, k/sub -/sub 1// = 6.6 x 10/sup 2/ s/sup -1/, K = 670 M/sup -1/; Fe/sup II/(acac)/sub 2/NO, k/sub 1/ = 4.0 x 10/sup 2/ M/sup -1/ s/sup -1/, k//sup -//sub 1// = 24 s/sup -1/, K = 17 M/sup -1/; Fe/sup II/(EDTA)NO, k/sub 1/ greater than or equal to 6.0 x 10/sup 7/ M/sup -1/ s/sup -1/, k/sub -/sub 1// greater than or equal to 60 s/sup -1/. The visible spectra of the complexes are also reported.