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

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