IUPAC name of the complex, K3FeCN6 is

CN-…cyanido or cyano(preferably cyanido)…uninegative ligand ;Oxidation state of iron is “+3” ;Counter ion is potassium ion and while naming the counter ion  prefixes like di, tri…should not be used;Complex ion is an anion, it should be written after name of cation;While naming the complex, ligands are named first (in alphabetical order with proper prefixes) followed by metal ion with its oxidation state as roman number in parenthesis;While naming the metal ion of an anionic complex the suffix “ate” is used;