Metal node design is crucial for obtaining structurally diverse coordination polymers (CPs) and metal-organic frameworks with desirable properties;h owever,F e II ions are exclusively six-coordinated. Herein, we present ac yanidebridged three-dimensional (3D) CP,F ePd(CN) 4 ,bearing fourcoordinate Fe II ions,which is synthesized by thermal treatment of at wo-dimensional (2D) six-coordinate Fe II CP,F e-(H 2 O) 2 Pd(CN) 4 •4 H 2 O, to remove water molecules.A tomicresolution transmission electron microscopyand powder X-ray and neutron diffraction measurements revealed that the FePd-(CN) 4 structure is composed of atwo-fold interpenetrated PtS topology network, where the Fe II center demonstrates an intermediate geometry between tetrahedral and square-planar coordination. This four-coordinate Fe II center with the distorted geometry can act as athermo-responsive flexible node in the PtS network.

Two-dimensional Hofmann-type coordination polymers of type Mn­(H2O)2[Pd­(CN)4]·xH2O (1· x H 2 O; x = 0, 1, and 4), Mn­(H2O)­(MeOH)­[Pd­(CN)4]·2MeOH (2·2MeOH), and Mn­(MeOH)2[Pd­(CN)4]·MeOH (3·MeOH) have been synthesized. The homosolvent-bound 1·4H 2 O, 1·H 2 O, and 3·MeOH polymers consist of undulating layer structures, whereas the structure of heterosolvent-bound 2·2MeOH consists of “Janus-like” flat layers in which water-bound and MeOH-bound-sides are present. 1·4H 2 O and 1·H 2 O exhibited anisotropic two-dimensional thermal expansions involving structural transformations of the undulating layers; one layer axis expands while the other contracts. 2·2MeOH exhibits anisotropic thermal expansion in which the flat layers shift sideways as the temperature is increased, with colossal interlayer expansion occurring (αc = +200 MK–1 over 140–180 K, αc = +165 MK–1 over 200–280 K). 3·MeOH also showed colossal interlayer expansion (αc = +216 MK–1) together with expansion of the undulating layers.

Metal node design is crucial for obtaining structurally diverse coordination polymers (CPs) and metal-organic frameworks with desirable properties;h owever,F e II ions are exclusively six-coordinated. Herein, we present ac yanidebridged three-dimensional (3D) CP,F ePd(CN) 4 ,bearing fourcoordinate Fe II ions,which is synthesized by thermal treatment of at wo-dimensional (2D) six-coordinate Fe II CP,F e-(H 2 O) 2 Pd(CN) 4 •4 H 2 O, to remove water molecules.A tomicresolution transmission electron microscopyand powder X-ray and neutron diffraction measurements revealed that the FePd-(CN) 4 structure is composed of atwo-fold interpenetrated PtS topology network, where the Fe II center demonstrates an intermediate geometry between tetrahedral and square-planar coordination. This four-coordinate Fe II center with the distorted geometry can act as athermo-responsive flexible node in the PtS network.