Molecular Design of Luminescence Ion Probes for Various Cations Based on Weak Gold(I)···Gold(I) Interactions in Dinuclear Gold(I) Complexes

A series of luminescent dinuclear gold(I) complexes with different crown ether pendants, [Au2(P∧P)(S-B15C5)2]
[S-B15C5 = 4‘-mercaptobenzo-15-crown-5, P∧P = bis(dicyclohexylphosphino)methane (dcpm) (1), bis(diphenylphosphino)methane (dppm) (2)] and [Au2(P∧P)(S-B18C6)2] [S-B18C6 = 4‘-mercaptobenzo-18-crown-6, P∧P =
dcpm (3), dppm (4)], and their related crown-free complexes, [Au2(P∧P)(SC6H3(OMe)2-3,4)2] [P∧P = dcpm (5),
dppm (6)], were synthesized. The low-energy emission of the mercaptocrown ether-containing gold(I) complexes
are tentatively assigned as originated from states derived from a S → Au ligand-to-metal charge transfer (LMCT)
transition. The crown ether-containing gold(I) complexes showed specific binding abilities toward various metal
cations according to the ring size of the crown pendants. Spectroscopic evidence was provided for the metal-ion-induced switching on of the gold···gold interactions upon the binding of particular metal ions in a sandwich binding
mode.