Resonance Raman spectroscopy was used to investigate the vibrational properties of the bridging dinitrogen ligand in two different dinuclear zirconium complexes known to contain unusually long N-N bonds. {[(Pr(2)(i)PCH(2)SiMe(2))(2)N] Zr(eta(5)-C5H5)}(2)(mu-eta(1):eta(1)-N-2) (1) has an "end-on" bridging dinitrogen ligand and {[(Pr(2)(i)PCH(2)SiMe(2))(2)N]ZrCl}(2)(mu-eta(2):eta(2)-N-2) (2) has a "side-on" bridging dinitrogen ligand. The nu(N-N) stretching frequency for the mu-eta(1):eta(1)-N-2 complex is observed at 1211 cm(-1) in the solid slate and confirmed by an similar to 40-cm(-1) isotope shift in the N-15(2)-substituted isotopomer. A similar frequency and isotope shift are observed for 1 in toluene, indicating that the mu-eta(1):eta(1)-N-2 structure is preserved in solution. Vibrational assignments for the mu-eta(2):eta(2)-N-2 complex 2 are complicated by the presence of many isotope-sensitive peaks in the solid state. Nevertheless, we propose that the intense peak at similar to 731 cm(-1) corresponds to one of the totally symmetric A(g) modes of the Zr2N2 moiety that is predominantly nu(N-N)in character based on its similar to 22-cm(-1) isotope shift and its strong polarization in THF solution. The majority of the remaining peaks in the resonance Raman spectrum of 2 can be assigned as overtone and combination bands of fundamental modes at 258, 317, and 393 cm(-1) and the nu(N-N) mode at 731 cm(-1) (709 cm(-1) in the N-15 isotopomer). Comparison of solid and solution state data for 2 suggests that the structure of the side-on-bonded N-2 ligand is largely maintained in THF solution. Finally, the vibrational spectroscopic properties of 2 as the dibromo and the mixed bromochloro complex are reported. These complexes all maintain the strong nu(N-N) mode at 709 cm(-1) (N-15 isotopomers) but exhibit changes in the fundamental modes at similar to 300 cm(-1) and, hence, also for the resulting overtone and combination bands. This work has shown that resonance Raman spectra reveal very marked differences and, hence,can be used tb distinguish the two modes of bonding in side-on versus end-on coordinated N-2 complexes of dinuclear transition metals.