Dinuclear fused salen complexes of group-10 metals: Peculiarity of the crystal structure and near-infrared luminescence of a bis(Pt-salen) complex

Dinuclear fused salen complexes with Ni, Pd, and Pt nuclei were synthesized, and their crystal structures were determined. In the crystal structure of the Pt complexes, the molecules were virtually planar and formed a closely stacked dimer every two molecules, whose Pt—Pt interatomic distance was 3.43 Å. The absorption spectra of the dinuclear salen complexes were similar to each other both in solution and in the solid state. The dinuclear Pt complex exhibited photoluminescence, presumably related to the π-conjugated system of the naphthalene ring, both in solution and in the solid state. The low-energy emission, corresponding to a longer wavelength compared to that of analogous mononuclear complexes, ranged to the near-infrared region, suggesting that the naphthalene ring is perturbed by the adjoining chelate rings as if these moieties formed a fused aromatic ring system.