Design and Synthesis of Mixed Valent Coordination Networks Containing Pyridine Appended Terpyridyl, Halide, and Dicarboxylates

The ability of 4′-(4-pyridyl)-2,2′:6′,2″-terpyridine (L), which contains a chelating center as well as an exodentate center for coordination, to form mixed-valent coordination polymers together with bromide and organic dicarboxylates as bridges has been explored with Cu­(I), Cu­(II), Co­(II), and Ni­(II) metal salts using hydrothermal reactions. The mixed-valent complexes containing Cu­(I) and Cu­(II) with L were formed only when the organic anions are glutarate (GA) or 1,3-dicarboxylate (BDC). The glutarate-containing complex exhibits a double helix in which the opposite handed helices interact with each other via π–π interactions between the two L-units. In the case of the BDC-containing complex, the Br– joins the two Cu­(I) and Cu­(II) centers to form a one-dimensional (1D) network containing Cu2L2Br2 boxes. The HBDC units, which are connected to the above-mentioned 1D network, extend the dimensionality of the network to a three-dimensional (3D) network through catemeric -COOH interactions. The presence of succinate (SA) or biphenyl 2,6,2′,6′-tetracraboxylate (TCA) produced the complexes containing only Cu­(II) but not Cu­(I). The SA acts as a bridge between two Cu­(II) centers to form one-dimensional chains containing Cu2L2SA2 boxes. On the other hand, the presence of TCA resulted in the formation of a 1D chain of CuL without TCA inclusion in the crystal lattice. The reactions of L in the presence of BDC with Ni­(II) and Co­(II) resulted in the formation of similar 1D isomeric chains containing ML units. All the six complexes were characterized by single crystal X-ray diffraction, IR, and diffuse reflectance spectroscopy studies. The mixed valence complexes were characterized by cyclic voltammetry.