Non-covalent stacking interactions directing the structural and photophysical features of mono- and dinuclear cyclometalated palladium(ii) complexes.

Abstract

The solution/solid state luminescence properties of selected orthometalated palladium complexes have been investigated in parallel with the relevant structural information provided by their X-ray crystal structures and theoretical calculations. Two cyclometalated backbones with different stacking abilities and a selection of bridging O^O, O^N or N^S ligands comprise the series under study, [{Pd(μ-L) (C^N)}2] (C^N = N-phenylpyrazole (Phpz) ; N-benzylideneaniline (Bza) ; L = acetate (Aco) , succinimidate (succ) , phthalimidate (phthal) , 1-methylimidazoline-2 thionate (Smeimid) ), completed with mononuclear [Pd(C^N)(N-pClPhsal)] (N-pClPhsal = chlorophenylsalycilaldiminate) complexes. New compounds , and were synthesized and the X-ray structures of , , , and have been elucidated in order to examine and compare solid-state Pd(C^N)-Pd(C^N) and ligand-ligand interactions with the rest of the series. The molecular structures of the complexes reveal intramolecular PdPd distances between 2.842 and 2.999 Å and π-π and C-Hπ interactions. All complexes studied show emission in the solid state at room temperature and a relationship is observed between emission energy, the nature of the lowest energy excited state, and metal-metal interactions. DFT calculations are undertaken to gain insight into the relationship between the structure and photophysical properties of the complexes.