Self-assembly of luminescent platinum-salen Schiff-base complexes

Treatment of K₂PtCl₄ with the MeO-salen Schiff base H₂L [H₂L = N,N′-bis(3-methoxysalicylidene)ethylene- 1,2-diamine] gave the precursor complex PtL, which, upon recrystallization from two different solvent mixtures, afforded different solvate forms of PtL·H₂O (1) and PtL·DMF (2) with different solid-state colors. The self-assembly of the PtL precursor with K₂Pt(CN) ₄ or K₂Pd(CN)₄ leads to the isolation of isostructural compound [K₂(PtL)₂Pt(CN)₄] ·1.5H₂O (3) or [K₂(PtL)₂Pd(CN) ₄]·1.5H₂O (4), respectively. The solid-state structures of 1-4 were established by X-ray crystallography. It is interesting that the helix of the PtL units, along with the other two homochiral helical arrangements of K⁺ and M²⁺ (M = Pt or Pd) ions, can generate a unique "fake" example of a triple-stranded helix in a 1-D helical polymeric chain. Two such triple-stranded helical chains intertwining one another can give rise to a double-stranded helix formed by intermolecular weak C-H⋯N hydrogen-bonding interactions with a long helical pitch of ca. 56 Å. The optical absorption and photoluminescence properties of 1-4 were also examined.