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Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: richard on July 30, 2007, 08:42:49 PM

Title: Formation Constant for Isothiocyanatoiron(III) ion
Post by: richard on July 30, 2007, 08:42:49 PM

Is there a known value for the formation constant of [FeNCS]²⁺?  The equilibrium equation is Fe³⁺ + NCS^- <==> FeNCS²⁺.

Title: Re: Formation Constant for Isothiocyanatoiron(III) ion
Post by: Borek on July 31, 2007, 02:43:11 AM

Fe³⁺ + SCN^- <-> FeSCN²⁺; log K = 3.02
Fe³⁺ + 2SCN^- <-> Fe(SCN)₂⁺; log K = 4.64
Fe³⁺ + 3SCN^- <-> Fe(SCN)₃; log K = 5.0
Fe³⁺ + 4SCN^- <-> Fe(SCN)₄^-; log K = 6.3
Fe³⁺ + 5SCN^- <-> Fe(SCN)₅^2-; log K = 6.2
Fe³⁺ + 6SCN^- <-> Fe(SCN)₆^3-; log K = 6.1


Edit: Sorry, after pasting the data I realized you asked about isothio... No idea where to find them.

Title: Re: Formation Constant for Isothiocyanatoiron(III) ion
Post by: AWK on July 31, 2007, 03:26:01 AM

SCN- anion forms mainly tiocyanate complexes. Only in crystals sometimes mixed complexes FeSCN and FeNCS happen