A new binuclear mercury(I) complex, [Hg2(L)2(NO3)2] (L= (4-nitrophenyl)pyridin-2-ylmethyleneamine), 1, has been synthesized and characterized by CHN analyses, IR, UV–vis spectroscopy and X-ray crystal structure analysis. The complex contains a metal–metal bonded core, [Hg–Hg]2?, in which a single bidentate imine ligand is coordinated to each mercury atom. The Hg atoms have an additional interaction with the oxygen atom of the NO3 - ion. Theoretical studies show that the interaction energy between the two {Hg(L)NO3} fragments is about 45–59 kcal/mol depending on the level of calculation. The Mayer-Mulliken and Wiberg bond indices (WBI) for Hg–Hg bond at different levels of theory are about 0.75–0.88 and 0.60–0.70, respectively, and are significantly larger than that for Hg–N and Hg–O bonds. The NBO calculations by using different methods and basis sets also show that the S character in Hg–Hg bond is very large (94.65–97.81 %). All above data for this complex are compared with those for linear Hg2X2 (X = F,Cl, Br, I, Ph) complexes. Interestingly, the bond order for Hg–Hg bond in complex 1 is comparable with that for Hg2F2 and larger than those in above linear complexes. This is consistent with the experimental data indicating that the Hg–Hg bond in 1 is shorter than that in all above complexes, except Hg2F2.
