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

In this paper, we use bidentate ligand and transition metals to construct series of 3D Hoffman-type coordination polymers by self-assembly using [M'(CN)₄]2- (M'= Ni, Pd, Pt) as building blocks. Then a series of tetracyanometallate-based coordination polymers have been synthesized. The strutures and some properties of these compounds have been characterized.Two three-dimensional Hofmann-type coordination polymers Zn(L)[M(CN)₄]·nH₂O { L = N-(4-pyridyl)isonicotinamide, M = Ni, n = 3, (1); M = Pt, n = 2, (2) } which are formed through axial bridging of the in-planes by the bidentate N-(4-pyridyl)isonicotinamide, where the in-plane is formed by transition metal ions Zn²⁺ and building block of [M(CN)₄]2- (M = Ni, Pt). The two coordination polymers 1 and 2 are isomorphic and they belong to Monoclinic system, space group P21/m. PXRD (Powder X-ray diffraction) and TG (thermogravimetric) analysis indicate that 1 and 2 are stable. The result of adsorption/desorption experiments shows that crystals of 1 and 2 can not adsorb neither N2 nor H₂ basically after rubbing. But the powder of 1 has low N2 and H₂ adsorption properties.Accidentally, a 3D porous coordination polymer with PtS-type topology ZnNi(CN)₄ (3) has been obtained in the solution which is used to synthesize 1. A new crystal ZnNi(CN)₄·CH3CN (4) in PtS-type topology can be obtained when the ligand L is not add in the solution which is used to synthesize 1. The frameworks of 3 and 4 are unstable, they start to transform when they leave the mother liquid. The transformed powder of 3 and 4 can't adsorb any gas because there are no longer porous structures.Two 2D Hofmann-type coordination polymer Mn(phen)M(CN)₄ {phen = 1,10–phenanthroline, M = Ni (5), Pd (6) } have been synthesized using phen as bridged ligand by slow diffusion. The two coordination polymers 5 and 6 are isomorphic, and they all belong to Monoclinic system, space group C2/c. Owing to the common N,N-endo-bidentate coordination of phen, the plane formed by [M(CN)₄]2- and Mn²⁺ is getting contorteder. Different ligands such as bpba { bpba = N,N'-bis(4-pyridirecarboxmide)-1,4-benzene }, L, bpy ( bpy = 4,4'-bipyridine) and different transition metal ions ( Zn²⁺, Mn²⁺ ) are selected to construct the other Hofmann-type coordination polymers. Unexpectedly, analogues of the Hofmann clathrates [Zn(bpba)(H₂O)₂]Ni(CN)₄·3H₂O (7), [Mn(L)(H₂O)₂]Ni(CN)₄·H₂O (8), [Zn(bpy)(H₂O)₂]Ni(CN)₄ (9) are obtainted. In the structures of the three coordination polymers, two of four cyanide groups are coordination to other atoms. In the structures of 7 and 8, the bridging cyanide groups are at the para positions, while they are at consecutive positions in the structures of 9. This results in two different kinds of frameworks. The former is 2D layered framework while the latter is 3D pillared layer framework. The result of host-guest properties for 7 indicate that the adsorption and desorption of H₂O is reversible, basically.