Synthesis and Coordination Chemistry of Hexadentate Picolinic Acid Based Bispidine Ligands

The synthesis and CuII, NiII, ZnII, CoII, and GaIII coordination chemistry of the two isomeric hexadentate N5O ligands 6-[[9-hydroxy-1,5-bis­(methoxycarbonyl)-7-methyl-6,8-bis­(pyridin-2-yl)-3,7-diazabicyclo[3.3.1]­nonan-3-yl]­methyl]­picolinic acid (Hbispa1a) and 6-[[9-hydroxy-1,5-bis­(methoxycarbonyl)-7-methyl-2,4-bis­(pyridin-2-yl)-3,7-diazabicyclo[3.3.1]­nonan-3-yl]­methyl]­picolinic acid (Hbispa1b), picolinic acid-appended bispidines, are described. The two ligands are highly preorganized for octahedral coordination geometries and are particularly well suited for tetragonal symmetries, i.e., for Jahn–Teller labile ground states. This is confirmed by all data presented: solid-state structures, solution spectroscopy, electrochemistry, and CuII complex stabilities. Differences in the preorganization of the two isomers for the Jahn–Teller labile CuII centers are thoroughly analyzed on the basis of the crystal structures and an angular-overlap-model-based ligand-field analysis.