The reaction of 3,6-bis(2-pyridyl)-1,2,4,5-tetrazine (bptz) with the respective cadmium halides results in the formation of tetranuclear [Cd4(bptz)2(H2O)2(l3-Cl)2(l-Cl)2Cl4] (1), coordination polymer {[Cd(l-bptz) Br2]DMSO}n (2) and mononuclear [Cd(bptz)2I2] (3). To interpret the UV–vis spectra of the compounds measured in the solution phase and also the emission behavior of solid samples, the electronic structures and also electronic spectra of the compounds were studied, respectively, by DFT and TDDFT methods in the free gaseous and solid state. According to our calculations, the synthesized compounds 1, 2 and 3 have an indirect band gap of 1.405, 0.794 and 0.912 eV, respectively. Based on the calculated electronic structures in the solid state, the excitation of the compounds at 450 nm promotes electrons from bptz centered p states (valence bands, VBs) and also halide np states (VBs) to the bptz-p⁄ states (conduction bands, CBs). Moreover, the solid compounds show a narrow emission band at 680 nm due to electron transitions from an excited bptz-p⁄ state (CBs) to the top of the VBs. The compounds were also studied in the solution phase using the 1H NMR spectroscopy method. Also, thermogravimetric analysis (TGA) and differential thermal analysis (DTA) methods were used to determine the thermal stability of the prepared compounds.
