Responsive Four‐Coordinate Iron(II) Nodes in FePd(CN)4.

Metal node design is crucial for obtaining structurally diverse coordination polymers (CPs) and metal–organic frameworks with desirable properties; however, FeII ions are exclusively six‐coordinated. Herein, we present a cyanide‐bridged three‐dimensional (3D) CP, FePd(CN)4, bearing four‐coordinate FeII ions, which is synthesized by thermal treatment of a two‐dimensional (2D) six‐coordinate FeII CP, Fe(H2O)2Pd(CN)4⋅4 H2O, to remove water molecules. Atomic‐resolution transmission electron microscopy and powder X‐ray and neutron diffraction measurements revealed that the FePd(CN)4 structure is composed of a two‐fold interpenetrated PtS topology network, where the FeII center demonstrates an intermediate geometry between tetrahedral and square‐planar coordination. This four‐coordinate FeII center with the distorted geometry can act as a thermo‐responsive flexible node in the PtS network. [ABSTRACT FROM AUTHOR]