A new binuclear mercury(I) complex, [Hg-2(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.
