Six new nonlinear optical (NLO) chromophores with pyrazinyl-pyridinium electron acceptors have been synthesized by complexing a known pro-ligand with electron donating {Ru-II(NH3)(5)}(2+) or trans-{Ru-II(NH3)(4)(py)}(2+) (py = pyridine) centers. These cationic complexes have been characterized as their PF6- salts by using various techniques including electronic absorption spectroscopy and cyclic voltammetry. The visible d -> pi* metal-to-ligand charge-transfer (MLCT) absorptions gain intensity on increasing the number of Ru-II centers from one to two, but remain at constant energy. One or two Ru-III/II redox processes are observed which are reversible, quasi-reversible, or irreversible, while all of the ligand-based reductions are irreversible. Molecular first hyperpolarizabilities beta have been determined by using hyper-Rayleigh scattering (HRS) at 1064 nm, and depolarization studies show that the NLO responses of the symmetric species are strongly two-dimensional (2D) in character, with dominant "off-diagonal" beta(zyy) components. Stark (electroabsorption) spectroscopic measurements on the MLCT bands also allow the indirect determination of estimated static first hyperpolarizabilities beta(0). Both the HRS and the Stark-derived beta(0) values increase on moving from mono- to bimetallic complexes, and substantial enhancements in NLO response are achieved when compared with one-dimensional (1D) and 2D monometallic Ru-II ammine complexes reported previously.