Crowded Bis-(M-salphen) [M = Pt(II), Zn(II)] Coordination Architectures: Luminescent Properties and Ion-Selective Responses

For
binuclear luminescent host systems, cooperativity between metal–organic
moieties becomes feasible with regards to photophysical properties
and sensing behavior. A new class of conformationally rigid binuclear
platinum­(II) and zinc­(II) complexes bearing tetradentate aromatic
Schiff base (salphen) ligands with limited rotational freedom has
been prepared and characterized, and the molecular structure of a
(Pt-salphen)2 derivative has been determined by X-ray crystallography.
Their UV–vis absorption and emission properties have been investigated
and are tentatively ascribed to different excited states depending
on the metal and the extent of intramolecular π-stacking interactions.
Colorimetric and phosphorescent responses by the bis-Pt­(II) complexes
in the presence of selected metal ions have been observed. The nature
of the host–guest interactions has been examined by quantitative
binding studies, mass spectrometry and DFT calculations, and through
comparisons with control complexes.