One-dimensional mercury(II) halide coordination polymers of 3,6-bis(2-pyridyl)-1,2,4,5-tetrazine ligand: Synthesis, crystal structure, spectroscopic and DFT studies

Three new coordination polymers, [Hg(μ-bptz)X₂]_n (X=Cl (1), Br (2)) and [Hg₂(μ-bptz)(μ-I)₂I₂]_n (3) (bptz=3,6-bis(2-pyridyl)-1,2,4,5-tetrazine) were synthesized. X-ray structural analysis indicated that compounds 1 and 2 are composed of one-dimensional (1D) linear chains while the compound 3 has 1D stair-stepped structure. The electronic band structure along with density of states (DOS) calculated by the DFT method indicates that compound 1 and 2 are direct band gap semiconductors; however, compound 3 is an indirect semiconductor. The linear optical properties of the compounds are also calculated by DFT method. According to the DFT calculations, the observed emission band of the compounds in solid state is due to electron transfer from an excited bptz-π* state (CBs) to the top of VBs. ¹H NMR spectra of the compounds indicate that, in solution phase, the compounds don't decompose completely. Thermal stability of the compounds is studied using TG, DTA methods. - Graphical abstract: Synthesis, crystal structure and emission spectra of [Hg(μ-bptz)X₂]_n (X=Cl and Br) and [Hg₂(μ-bptz)(μ-I)₂I₂]_n are presented. The electronic band structure and linear optical properties of the compounds are calculated by the DFT method. - Highlights: • Three 1D Hg(II) halide coordination polymers with bptz ligand have been prepared. • The structures of the compounds are determined by single crystal XRD. • DFT calculations show that [Hg(μ-bptz)X₂]_n (X=Cl and Br) have a direct band gap. • DFT calculations show that [Hg₂(μ-bptz)(μ-I)₂I₂]_n has an indirect band gap. • The compounds show an intraligand electron transfer emission band in solid state.