Non-linear optical absorption of [{Ni(mnt)2}2]2− and its unique counter ion, a disodium triple-decker dication [Na2(benzo-15-crown-5)3(H2O)2]2+

Reaction of NiCl2·6H2O and Na2[mnt] (mnt=maleonitriledithiolate) in CH3OH at room temperature leads to Ni(II) dithiolato complex [Ni(mnt)2]2−. An oxidation process of [Ni(mnt)2]2− affords [{Ni(mnt)2}2]2− and yields solid crystalline product [Na2(benzo-15-crown-5)3(H2O)2][{Ni(mnt)2}2] (1) in the presence of benzo-15-crown-5. X-ray diffraction analyses revealed that in solid state the dianions of 1 pack as columns and the counter ions are discrete disodium triple-decker dications. A non-linear absorption coefficient β of 2.4 cm GW−1 was recorded at 1064 nm for 1 in acetonitrile solution with a concentration of 1.0×10−4 mol l−1.