Synthesis, characterization, and photochemistry of the supramolecules formed from chromium(III) thiocyanato anion associated with crown ethers

Abstract

A series of anionic chromium(III) thiocyanato complexes with metal crown ether cations have been prepared and characterized. These complexes have the form [Crown-M] 2 +[Cr(NCS) 5(H 2O)] 2− and [Crown-M] 3 +[Cr(NCS) 6] 3−, where M=Na +, K +, or NH 4 + and crown represents the crown ether. The crown ethers are 15-crown-5, B-15-crown-5, 18-crown-6, DB-18-crown-6, and DB-24-crown-8, where B- and DB- stand for benzo- and dibenzo-, respectively. The complexes are stable for at least 20 h in the dark in dimethylformamide(DMF) or in acetonitrile, and they release thiocyanate slowly, k=(0.71–2.67)×10 −9 mol/(L s) in acetonitrile in the dark. Photoanation of thiocyanate was observed for the complexes in DMF and in acetonitrile. The quantum yields of thiocyanate release in DMF and in acetonitrile are reported. The quantum yields were in the range 0.05 to 0.52 mol einstein −1 and were solvent and wavelength dependent. In general, larger quantum yields were observed in DMF than in acetonitrile. The photoreaction mechanism is discussed.