Carboxylato Bridged Cyclic SBUs as Robust Features in a Series of Cu(II) Coordination Polymers and Halogen•••Halogen Interactions in Crystal Packing

Four new pyridine/meta-substituted halopyridine appended coordination polymers (CPs) {[Cu(ip)(6)(py)(6)]center dot 2CH(3)OH}(n) (1), [Cu(ip)(2)(3-Clpy)2](n) (2), [Cu(ip)(2)(3-Brpy)(2)](n) (3), and [Cu(ip)(2)(3-Ipy)2](n) (4) (py = pyridine, 3-Clpy = 3chloropyridine, 3-Brpy = 3-bromopyridine, 3-Ipy = 3-iodopyridine, and H(2)ip = isophthalic acid) have been synthesized by a diffusion method. The compounds are structurally characterized by the single crystal X-ray diffraction technique, and supramolecular interactions are studied by geometrical and density functional theory calculations. The study reveals that the compounds 1-3 form a two-dimensional (2D) coordination polymeric structure with carboxylato bridged dimeric Cu(II) cyclic secondary building units. However, a cyclic supramolecular synthon involving four halogen (X = Cl, Br) atoms has been observed in 2 and 3. This cyclic halogen synthon combined with a pyridine ring forms a (pi center dot center dot center dot pi)+X center dot center dot center dot X+(pi center dot center dot center dot pi) mega-synthon, which dictates the dimensionality of 2D CPs into a three-dimensional (3D) network. However, compound 4 with a larger I atom does not show such interactions and forms a 1D tape structure.