Studying the structure of metal-organic polymers using in-house powder X-ray diffraction data: structural transformations induced by thermal treatment

Abstract

Abstract The use of X-ray powder diffraction for the structure determination of inorganic, organic and metal-organic compounds has grown impressively over the last ten years. In supramolecular chemistry, the knowledge of the three-dimensional structure of a material is essential for the discussion of its macroscopic behaviour, and as a result the design of new functionalized materials. The ab initio crystal structure determination of previously unknown metal-organic compounds is still rare but is a field of high interest and activity. Here we describe the formation of 1D coordination polymers and the phase transformation processes that lead to the formation of 3D polymers on heating, accompanied by colour changes. The reaction of pyrazine-2,5-dimethyl-3,6-dicarboxylic acid with first row transition metal salts lead to the formation of coordination polymers always in the form of microcrystalline powders. With manganese and nickel salts isostructural 1D coordination polymers were obtained. With zinc chloride and copper chloride isomorphous 1D coordination polymers were obtained. The thermal decomposition of the nickel and copper polymers were studied and it was shown that on the loss of the coordinated water molecules new 3D coordination polymers could be obtained. In both the 1D and 3D coordination polymers the metal atoms have octahedral geometry in N2O4 environments. The crystal structures of all six complexes have been determined from powder X-ray diffraction data. Crystal data: (1) crystal symmetry monoclinic [space group P21/c, a = 7.4645(1), b = 8.9472(2), c = 7.6166(1) Å, β = 92.198(2)°]; (2) crystal symmetry orthorhombic [space group Pmna, a = 7.4060(2), b = 7.1857(2), c = 9.0661(2) Å]; (3) crystal symmetry monoclinic [space group P21/c, a = 6.9376(9), b = 7.1306(12), c = 8.5852(20) Å, β = 113.299(18)°]; (4) crystal symmetry orthorhombic [space group Pbcn, a = 9.0593(2), b = 7.4410(1), c = 14.6697(2) Å]; (5) crystal symmetry orthorhombic [space group Pbcn, a = 8.9727(1), b = 7.2354(1), c = 15.0444(2) Å]; (6) crystal symmetry monoclinic [space group P21/c, a = 6.9133(4), b = 7.9927(6), c = 8.2084(6) Å, β = 110.066(6)°].