The sulfur coordination polymer catena-poly[zinc(II)-μ-bis[5-(methylsulfanyl)-2-sulfanylidene-2,3-dihydro-1,3,4-thiadiazol-3-ido-κN:S]], [Zn(CHNS)] or [ZnMTT], constructed from Zn ions and 5-methylsulfanyl-1,3,4-thiadiazole-2-thione (HMTT), was synthesized successfully and structurally characterized. [ZnMTT] crystallizes in the tetragonal space group I-4 (No. 82). Each MTT ligand (systematic name: 5-methylsulfanyl-2-sulfanylidene-2,3-dihydro-1,3,4-thiadiazol-3-ide) coordinates to two different Zn ions, one via the thione group and the other via a ring N atom, with one Zn atom being in a tetrahedral ZnS and the other in a tetrahedral ZnN coordination environment. These tetrahedral ZnS and ZnN units are alternately linked by the organic ligands, forming a one-dimensional chain structure along the c axis. The one-dimensional chains are further linked via C-H...N and C-H...S hydrogen bonds to form a three-dimensional network adopting an ABAB-style arrangement that lies along both the a and b axes. The three-dimensional Hirshfeld surface analysis and two-dimensional (2D) fingerprint plots confirm the major interactions as C-H...S hydrogen bonds with a total of 35.1%, while 7.4% are C-H...N hydrogen-bond interactions. [ZnMTT] possesses high thermal and chemical stability and a linear temperature dependence of the bandgap from room temperature to 270 °C. Further investigation revealed that the bandgap changes sharply in ammonia, but only fluctuates slightly in other solvents, indicating its promising application as a selective sensor.