Crystal Engineering of 6-Carboxy-4-aryl-2,2′-bipyridine Complexes: Potent Chelators with Intrinsic Intermolecular Affinity

Abstract

Herein we report the coordination chemistry and structural properties of two multifunctional terdentate 2,2′-bipyridine derivatives 4- and 3-(4-nitrophenyl)-2,2′-bipyridine-6-carboxylate, L1/L2, respectively. We report eight new coordination complexes with CdII, CoII, and CoIII, and study their behavior in the crystalline phase with the view of establishing L1 and L2 as robust and functional chelators for use in extended metallosupramolecular systems. The divalent complexes [Cd(L1)2]·H2O 1, [Cd(L2)2] 2, [Co(L1)2] 5, and [Co(L2)2] 7 are mononuclear complexes with distorted octahedral coordination geometries dictated by the two meridionally coordinated L1/L2 ligands. Also reported are two trivalent byproducts [Co(L1)2]NO3 6 and [Co(L2)2]NO3 8 which were formed in trace quantities during the initial screening of complexes 5 and 7, respectively. The extended structures of these complexes are dominated by substantial intermolecular interactions, including anion···π hole interactions. Modification of the reaction conditions from 1 and 2 gives two closely related trinuclear cluster species [Cd3(L1)3(NO3)2(DMF)4]NO3 3 and [Cd3(L2)3(NO3)2(DMF)4]NO3·DMF 4, in which three cadmium ions, with pentagonal bipyramidal coordination geometries, form disc-shaped assemblies with L1/L2, which undergo further weak interactions between neighboring complexes in the crystalline state. With these outcomes L1 and L2 are established as exciting new building blocks for metallosupramolecular assemblies involving d-block metal ions.