Geometric control of Cu, Ni and Pd complexes in the solid state via intramolecular H-bonding interactions

In this article, we describe the synthesis and characterization of a family of copper, nickel and palladium complexes bound by bidentate ligands derived from ortho-phenylenediamine that contain tunable H-bond donors. The crystal structures of the reduced dianionic metal complexes (formulated as [MII(L2-)2]2-) depict intramolecular H-bonding interaction between the two ligand scaffolds. Variations on the primary (Cu, Ni, Pd), secondary (H-bonding donor) and tertiary coordination sphere (solvent of crystallization and countercation), led to the isolation of the metal complexes in square-planar (SP) and/or twisted pseudo-tetrahedral geometry (TW). A detailed structural analysis of the complexes in the solid state revealed that the intramolecular H-bonding interactions can be altered by disrupting the bonds between the countercation, solvent of crystallization and the ligand scaffold, which leads to changes in the geometry of the complexes (SP or TW). DFT calculations are in agreement with our experimental observations, in which the Cu complexes were found to favor twisted geometries while the Ni and Pd complexes favored square-planar geometries.