Transitional Metal Coordination Polymers: Syntheses, Crystal Structures And Dielectric Properties

Coordination polymers are hybrid materials which are connected by inorganic and organic moieties. The distinguishing features of coordination polymers are various coordination patterns for metal ions, and disignability for ligand molecule structures. All these features lead coordination polymers attracting increasing attention in the field of new-function material, because of the polymers’ abundant structures and multiple functions.Polar solvent molecules play an important part in the formation of coordination polymers, coordinating to the metal ions or acting as the main template of 3D-framework. If polar molecules retained in crystal lattice,they display various dielectric properties, like dielectric relaxation, because they can response to the change of external electric field. Additionally, polar molecules increase the value of dielectric constant for coordination polymers, which is a potentially high-k material. The guest-free polymers will display low-k property for its hollow framework.In this work, we have investigate crystals of three pseudo-polymorphs, Cd(NMIZ)2(glutarate)(1), [(Cd(NMIZ)2(H2O)(glutarate)]·4H2O(2) and [(Cd(NMIZ)2-(H2O)(glutarate)](3), where NMIZ represents N-methylimidazole, through controlling the crystallization temperature. We have carried out measuments like EA, IR, Raman TG and single crystal structure analysis for compounds. In crystal structure of 1, Cd(NMIZ)2 is bridged by glutarate forming 1D coordination polymeric chains. And chains forms 3D molecular crystal via van der Waals force. Compound 2’s structure is similar to the structure of 1. One units of Cd(NMIZ) are linked with another one through glutarate resulting in a chain, and chains are arranged in a 2D layer via van der Waals force. There is one layer of water molecules sandwiched between two coordination polymeric layers. 3 is the intermediate product in the process of losing water molecules of 2. Furthermore, we study the dielectric properties of the three compounds, and find that the dielectric permittivity is related to the amount of water in the lattice with the order 2 > 3 > 1.Among the porous coordination polymers, which are also called metal-organic framework and coomonmly abbrivated to MOFs, there are exsiting some polymers with hydrophobicity porous. These are a kind of low-k materials. In view of that fact, We study one MOFs,which have a triangular prism formed by Cr2+ and isonicotinic acid as nodes. As the existence of trimesic acid, the nodes combine with Zn2+ forming metal-organic framework. We have obtained [Zn3btc2{Cr3O(isonic)6(H2O)2(OH)}]·G through solvothermal reaction, and characterized compounds with elemental analysis and IR spectrum. We synthetize [Zn3btc2{Cr3O(isonic)6(H2O)2(OH)}]·(DMF)15.5(H2-O)8(4) and [Zn3btc2{Cr3O(isonic)6(H2O)2(OH)}]·(DMF)(CH3CN)2.75(H2O)14(5) through handling as-synthetic samples with heating process. And we study the dielectric properties of 4 and 5. All the compounds contains two relaxation steps during two temperature ranges, one is from-60 to 90oC and the other is from-120 to 0 oC, remarked by I and II respectively. We have used Arrhenius law to fit the dielectric data, and obtained activation energy and pre-exponential factor:Ea = 39.70 k J/mol, τ0 = 5.28×10-13 s for relacation I,and Ea = 34.99 k J/mol, τ0 = 1.09×10-15 s for relaxation II. Dielectric relaxation I is related to the orientation of DMF molecules which are confined to little cages, while relaxation II is induced by the orientation of H2 O molecules that are confined to larger porous channels. Compound 5’s dielectric behavior is similar to the 4’s when temperature is higher than-60 oC.