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

A series of anionic chromium(III) thiocyanato complexes with metal crown et her cations have been prepared and characterized These complexes have the f orm [Crown-M](2)(+) [Cr(NCS)(5)(H2O)](2-) and [Crown-M](3)(+)[Cr(NCS)(6)](3 -), where M=Na+, K+, or NH4+ and crown represents the crown ether. The crow n 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(DM F) or in acetonitrile, and they release thiocyanate slowly, k=(0.71-2.67)x1 0(-9) mol/(L s) in acetonitrile in the dark. Photoanation of thiocyanate wa s observed for the complexes in DMF and in acetonitrile. The quantum yields of thiocyanate release in DMF and in acetonitrile are reported. The quantu m yields were in the range 0.05 to 0.52 mol einstein(-1) and were solvent a nd wavelength dependent. In general, larger quantum yields were observed in DMF than in acetonitrile. The photoreaction mechanism is discussed. (C) 19 99 Elsevier Science Ltd. All rights reserved.