Two new quaternary sulfides have been synthesized by a high-temperature solid-state routine and flux growth method. The crystal growth process of was elucidated by in situ powder X-ray diffraction and DSC thermal analysis. The millimeter-sized crystals of were grown. K2CoGe3S8 crystallizes in a new structure type in centrosymmetric space group P1 (no. 2) with unit cell parameters of a = 7.016(1) Å, b= 7.770(1) Å, c = 14.342(1) Å, α = 93.80(1)°, β = 92.65(1)°, γ = 114.04(1)°. crystallizes in the structure type and the noncentrosymmetric space group P21 (no. 4) with unit cell parameters of a = 7.1089(5)Å, b = 11.8823(8) Å, c = 16.7588(11) Å, β = 96.604(2)°. There is a high structural similarity between and . The larger volume coupled with higher degrees of distortion of the [FeS4] tetrahedra compared to the [CoS4] tetrahedra accounts for the structure’s shift from centrosymmetric to noncentrosymmetric. The theory simulation confirms that [TS4]T= Co or Fe tetrahedra play a crucial role in controlling the structure and properties of TG(T = Co, Fe). The measured optical bandgaps of and are 2.1(1) eV and 2.6(1) eV, respectively. shows antiferromagnetic ordering at 24 K while no magnetic ordering was detected in . The magnetic measurements also demonstrate the divalent nature of transition metals in TG(T = Co, Fe).