Synthesis, structure, and stereochemistry of trinuclear metal complexes formed from the phosphorus-based achiral tripodal ligand {P(S)[N(Me)N=CHC₆H₄-o-OH]₃} (LH₃): Luminescent properties of L₂Cd₃·2H₂O

Abstract

Neutral trinuclear metal complexes L₂Cd₃·2H₂O, L₂Mn₃·MeOH, and L₂Zn₃·MeOH were isolated in the reaction between the phosphorus-centered achiral tris(hydrazone) P(S)[N(Me)N=CHC₆H₄-o-OH]₃ (LH₃) and the corresponding divalent metal ions. The trinuclear complexes contain two equivalent terminal metal ions (M_t) and a central metal ion (M_c). The ligand encapsulates M_t in a facial N₃O₃ coordination environment. From the coordination sphere of the two terminal metal ions a pair of phenolic oxygen atoms further coordinate to the central metal ion. The coordination requirements of M_c are completed by the solvents of coordination. The achiral trianionic tripodal ligand (L)^3- induces chirality in the metal complexes. This results in a Δ (clockwise) or Λ (anticlockwise) configuration for the terminal metal ions. The enantiomeric complexes 2-4 (Δ-Δ or Λ-Λ) crystallize as racemic compounds. The supramolecular structures of 2-4 reveal chiral recognition in the solid-state; every molecule with the Δ-Δ configuration interacts stereospecifically, through C-H···S=P bonds, with two Λ-Λ molecules to generate a one-dimensional polymeric chain. Photophysical studies of the diamagnetic trinuclear complexes reveal that the tricadmium complex is luminescent in the solid state as well as in solution. In contrast LH₃ and L₂Zn₃·MeOH are nonluminescent.