Structural, spectral and theoretical study of the coordination of 3,6-bis(2-pyridyl)tetrazine ligand with zinc(II) and mercury(II)

We report the synthesis and single crystal X-ray structures of three zinc(II) and mercury(II) coordination polymers (1D-zigzag-{[Zn(mu-BPTZ)Cl-2]center dot DMSO}(n) (1), 1D-zigzag-{[Zn(mu-BPTZ)Br-2]center dot CH3CN}(n) (2) and 2D-herringbone [Hg-2(mu-BPTZ)(mu-CN)(2)(CN)(2)](n) (3)) and a binuclear 3D-supramolecular coordination compound of mercury(II), [Hg-2(mu-BPTZ)(SCN)(4)] (4), with 3,6-di(pyridin-2-yl)-1,2,4,5-tetrazine (BPTZ) ligand. The compounds are characterized by elemental analysis and by FT-IR, H-1 NMR spectroscopies. Stability of syn and anti conformers of BPTZ and the energy barrier for converting the isomers was calculated by DFT method. 1 and 2 are isostructural coordination polymers in which the zinc(II) ion has a distorted octahedral coordination environment N4X2 (X: Cl (1), Br (2)). The coordination environment of mercury(II) ion in 3 (with N3C2 donor set) and 4 (with N2S2 donor set) is close to square-pyramidal and seesaw geometries, respectively. The binuclear [Hg-2(mu-BPTZ)(SCN)(4)] units in 4 are linked via Hg center dot center dot center dot center dot center dot center dot Nthiocyanate interactions to form a 3D-supramolecular coordination network. In addition, all coordination modes of BPTZ derivatives, reported in crystal structure database (CSD), were extracted and discussed.