Synthesis and second-order nonlinear optical properties of new palladium(II) and platinum(II) Schiff-base complexes

The second harmonic generations of the dimeric complexes [M-2(mu-X)(mu-SCnH2n+1)(RC6H3CH=NC6H4R')] (M = Pd, Pt; X = Cl, CH3COO, (R)-CH3CHClCOO; R, R' = NO2 and OC8H17 or N(C4H9)(2); n = 4 or 8) and the monomeric complexes [Pd(RC6H3CH=NC6H4R')L] (L = C5H5 (Cp), CH3COCHCOCH3 (acac)) and [Pd(RC6H3CH=NC6H4R')(CNC6H4R")Cl] (R" = NO2, OCnH2n+1, N(CmH2m+1)(2); n = 4 or 8; m = 1 or 4) have been measured, and the influence of the position of donor and acceptor groups is discussed and compared with that of the free imine ligands. The value of the hyperpolarizability (beta) is raised only when a strong donor group is located in the cyclometalated ring. Moreover, the beta value has been enhanced, too, in the cyclopentadienyl monomer complex by as much as 80% with respect to the beta value of the corresponding free imine. The molecular structure of [Pd-3(mu-Cl)(mu-SC4H9)(N(C4H9)(2)C6H3CH=NC6H4NO2] has been determined by an X-ray diffraction analysis.