We report the synthesis and characterization of new ruthenium and rhenium nucleosides [Ru(tolyl-acac)2(IMPy)-T] (tolyl-acac = di(p-methylbenzonatemethane), IMPy = 2'-iminomethylpyridine, T = thymidine) (5) and [Re(CO)(3)(IMPy)-T]Cl (9), respectively. Structural analysis of 9 shows that the incorporation of this metal complex causes minimal perturbation to the sugar backbone and the nucleobase. Eletrochemical (5, E-1/2 = 0.265 V vs NHE; 9, E-1/2 = 1.67 V vs NHE), absorption (5, lambda(max) = 600, 486 nm; 9, lambda(max) = 388 nm), and emission (9, lambda(max) = 770 nm, pi = 17 ns) data indicate that 5 and 9 are suitable probes for DNA-mediated ground-state electron-transfer studies. The separation and characterization of diastereoisomers of 5 and bipyridyl-based ruthenium nucleoside [Ru(bpy)(2)(IMPy)-T](2+) (7) are reported.