Abstract
Complexation reactions of Fe^II^ and Fe^III^ salts with the tridentate ligands 2‐(diphenylphosphanyl)benzaldehyde benzoylhydrazone [(H)PNO] and N‐[2‐(diphenylphosphanyl)benzylidene]‐2‐(2‐pyridyl)ethanamine (PNN) was carried out. For (H)PNO, reaction of a stoichiometric amount of anhydrous FeCl~2~ in the presence of a primary alcohol such as MeOH, EtOH or __n__BuOH gave the mixed‐valence Fe^II^/Fe^III^ paramagnetic complex [Fe{κ^3^‐(H)PNO}~2~]Cl[FeCl~4~], whereas the reaction between FeCl~2~ and a twofold excess of (H)PNO in the presence of AgOTf (OTf = triflate, OSO~2~CF~3~) led to the isolation of the bis‐chelate paramagnetic ferrous complex [Fe{κ^3^‐(H)PNO}~2~][OTf]~2~. A diamagnetic bis‐chelate ferrous complex [Fe{κ^3^‐(PNO)~2~}] was instead obtained from the reaction of FeCl~2~ with a twofold excess of (H)PNO in the presence of NaOMe. In the case of the PNN ligand, the 1:1 reaction with FeCl~2~ gave the neutral paramagnetic trigonal‐bipyramidal complex [Fe(κ^3^‐PNN)Cl~2~]. The X‐ray structures of [Fe{κ^3^‐(H)PNO}~2~]Cl[FeCl~4~], [Fe~2~{κ^3^‐(H)PNO}~2~Cl~6~] and [Fe(κ^3^‐PNN)Cl~2~] are reported, together with CV and magnetic susceptibility measurements and an ab initio study aimed at rationalizing the different stoichiometries and structures observed with the two tridentate ligands. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)