Molecular quadratic non-linear optical properties of dipolar trans-tetraammineruthenium(II) complexes with pyridinium and thiocyanate ligands

Seven new complex salts trans-[Ru-II(NCS)(NH3)(4)(L-A)][PF6](2) [L-A = N-methyl-4,4'-bipyridinium (MeQ(+)) 1, N-methyl-2,7-diazapyrenium (Medap(+)) 2, N-methyl-4-[trans-2-(4-pyridyl)ethenyl]pyridinium (Mebpe(+))3, N-phenyl-4,4'-bipyridinium (PhQ(+))4, N-phenyl-4-[trans-2-(4-pyridyl) ethenyl] pyridinium (Phbpe(+))5, N-(4-acetylphenyl)- 4,4'bipyridinium (4-AcPhQ(+))6, or N-(2-pyrimidyl)-4,4'- bipyridinium (2-PymQ(+))7] have been prepared. The electronic absorption spectra of 1-7 display intense, visible metal- to- ligand charge- transfer (MLCT) bands, the energies (E-max) of which decrease in the order 2 > 1 > 3 > 4 > 6 > 5 > 7, as the electron-accepting ability of L-A increases. The E-max values generally correlate with cyclic voltammetric and H-1 NMR data.