Syntheses, Crystal Structures, And Properties Of Tetracyanometallate-based Coordination Polymers

This paper reviews the development in the field of porous coordination polymers as gas storage materials, then a series of Hofmann-type cyano-bridged coordination polymers have been synthesized by self-assembly using [M'(CN)4]2- (M' = Ni, Pd, Pt) as building blocks. The structures and properties of these coordination polymers have also been studied.Single crystals of a 2D (two-dimensional) Hofmann-type coordination polymer Mn(H2O)2[Ni(CN)4]·4H2O (1) and powder samples of M(H2O)2[Ni(CN)4]·xH2O (M = Mn, Fe, Co, Ni, Cd) have been obtained by self-assembly using [Ni(CN)4]2? as building block and transition metal ions M2+ (M = Mn, Fe, Co, Ni, Cd). 1 belongs to Orthorhombic system, space group Cmcm. M and Ni centers are connected by cyano-bridges alternately, forming infinite 2D corrugated sheets in an ABAB packing mode. VT-PXRD (Variable temperature X-ray diffraction) and TG (Thermogravimetry) analysis indicate that all these coordination polymers have a stable mediate phase after dehydration, which can be used as precursors for the construction of 3D Hofmann-type coordination polymers.A 3D Hofmann-type coordination polymer Mn(L)[Ni(CN)4] (L = pyrazine) has been synthesized by inserting ligand into 2D layers using Mn(H2O)2[Ni(CN)4] as precursor. The coordination polymers M(L)[Ni(CN)4] (M = Mn, Fe; L = pyrazine) have also been synthesized using quick mixing method for comparison. The results of adsorption experiments show that these coordination polymers all exhibit some adsorption property for N2 and H2, and synthetic methods and metal ions have influence on the adsorption properties.A series of 2D Hofmann-type coordination polymer M(DMF)2[M'(CN)4] (M = Mn, Fe, Co, Ni, Cu, Zn, Cd; M' = Ni, Pd, Pt) have been synthesized using DMF as solvent. DMF is a strong ligand which can coordinate to metals preferentially than other bridged organic ligands and can even substitute the macrocyclic ligands which have already connected with metals. SC-XRD (Single-crystal X-ray diffraction) analysis reveals that these coordination polymers belong to Monoclinic system, space group C2/m. M and Ni centers are connected by cyano-bridges alternately, forming infinite 2D corrugated sheets in an ABAB packing mode. The DMF molecules coordinated to M are in trans-form. TG analysis indicates that these coordination polymers may lose DMF molecules and form relatively stable mediate products. VT-XRD and VT-Raman (Vaiable temperature Raman) results show that the framework of Zn(DMF)2[Ni(CN)4] begins to collapse with the loss of DMF molecules. Temperature dependence of cell parameters for Zn(DMF)2[Ni(CN)4] has been studied by in situ SC-XRD method and the result shows that it has a positive thermal expansion coefficient.Three 3D porous coordination polymers with PtS-type topology ZnM'(CN)4 (M' = Ni, Pd, Pt) have been obtained unexpectedly by using [M'(CN)4]2-(M = Ni, Pd, Pt) and transition metal ion Zn2+ as"square-planar"building blocks. Three coordination polymers are isostructural and belong to tetragonal system, space group P4(2)/mcm. Zn and M' centers are in tetrahedral and square-planar geometry, respectively. Both centers are connected by cyano-bridges alternately, forming 3D PtS-type topology with two-fold interpenetration. VT-PXRD and TG analysis indicate that ZnNi(CN)4 has higher stability and no solvent molecules are involved in the structure. The result of adsorption/desorption experiments shows that ZnNi(CN)4 has low N2 and H2 adsorption properties due to the interpenetration in the structure.