Bifunctional Dinuclear Complexes Based on Iminodiacetate and 1,2-Di(4-pyridyl)ethylene: Crystal Structures, Vapochromism, and Iodine Adsorption

Two dinuclear complexes, namely, [Ni-2(IDA)(2)(dpe)(H2O)(4)]-(H2O)(6) (1) and [Cu-2(IDA)(2)(dpe)(H2O)(2)] (2) (IDA(2-) = iminodiacetate and dpe = 1,2-di(4-pyridyl)ethylene) were synthesized and structurally characterized. The Ni(II) center in 1 exhibits octahedral geometry, but the Cu(II) center in 2 shows distorted square pyramidal geometry. Both metal centers are coordinated by IDA(2-) via a chelating mode (kappa(3)-O,N,O) and linked by mu(2)-dpe, forming a dinuclear complex. Three dimensional (3D) supramolecular architectures of 1 and 2 are considerably different that arise from the influence of flexible ligands with different metal centers. Interestingly, a robust, but flexible, 3D supramolecular framework of 1 contains 1D channels along the c-axis, which is filled by six water molecules. Complex 1 exhibits a reversible thermally induced structural transformation with chromotropism upon dehydration and rehydration processes, whereas 2 exhibits a nonreversible process. In addition, 1 and its activated form 1a (1 was heated at 90 degrees C to remove all lattice water) and anhydrous form 1b (1 was heated at 200 degrees C) display vapochromic behavior after exposure to a variety of saturated amine vapors that were confirmed by FT-IR, solid-state UV-vis, and X-ray absorption spectroscopy (XAS), TGA, and PXRD techniques. Moreover, the activated form la exhibits an excellent iodine adsorption in hexane with the removal efficiency of 98.8%. The encapsulated iodine can be also released into an acetonitrile solution.