Thermally Induced Valence Tautomeric Transition in a Two-Dimensional Fe-Tetraoxolene Honeycomb Network.

A novel tetraoxolene-bridged Fe two-dimensional honeycomb layered compound, (NPr4 )2 [Fe2 (Cl2 An)3 ] ⋅2 (acetone)⋅H2 O (1), where Cl2 Ann- =2,5-dichloro-3,6-dihydroxy-1,4-benzoquinonate and NPr4+ =tetrapropylammonium cation, has been synthesized. 1 revealed a thermally induced valence tautomeric transition at T1/2 =236 K (cooling)/237 K (heating) between Fem+ (m=2 or 3) and Cl2 Ann- (n=2 or 3) that induced valence modulations between [FeIIHS FeIIIHS (Cl2 An2- )2 (Cl2 An.3- )]2- at T>T1/2 and [FeIIIHS FeIIIHS (Cl2 An2- )(Cl2 An.3- )2 ]2- at T<T1/2 . Even in a two-dimensional network structure, the low-temperature phase [FeIIIHS FeIIIHS (Cl2 An2- )(Cl2 An.3- )2 ]2- valence set can be regarded as a magnetic chain-knit network, where ferrimagnetic Δ and Λ chains of [FeIIIHS (Cl2 An.3- )]∞ are alternately linked by the diamagnetic Cl2 An2- . This results in a slow magnetization behavior attributed to the structure acting as a single-chain magnet at lower temperatures.