Coexistence of Three Different Spin States in a Cyanido‐Bridged Trinuclear Iron(III) Complex with an Unusual Fe^III to Ligand Charge Transfer

Abstract

We report a trinuclear iron(III) cyanido‐bridged complex trans‐[CpMe3FeIII(dppe)(CN)]2[FeIII(LN4)][PF6]4 (2[PF6]4) as the oxidation product of binuclear complex [CpMe3(dppe)FeIICN‐FeIII(LN4)][PF6] (1[PF6]) (CpMe3=1, 2, 4‐trimethyl‐1,3‐cyclo‐pentadienyl, dppe=1,2‐bis(diphenylphosphino)ethane, LN4=pentane‐2,4‐dione‐bis(S‐methylisothiosemicarbazonato). Complex 1[PF6] possesses an intermediate‐spin five‐coordinated FeIII (S=3/2) which couples antiferromagnetically to the π‐radical ligand (L⋅N4)2− and shows a LMCT (ligand to metal charge transfer) transition from (L⋅N4)2− to FeIII and the FeII→FeIII MMCT transition. Upon oxidation of 1[PF6], (L⋅N4)2− loses one electron to be the strong electron‐attracting ligand (LOxN4)− and the intermediate‐spin five‐coordinated FeIII (S=3/2) becomes a low‐spin six‐coordinated FeIII (S=1/2) in 2[PF6]4. Also interestingly, 2[PF6]4 presents the coexistence of three different spin states (one S=3/2 and two S=1/2) and an uncommon FeIII→(LOxN4)− MLCT transition, confirmed by the experimental results and supported by the TDDFT calculations.