Two isostructural ternary acentric sulfides, (1) and (2) were re-investigated to understand the origin of the chemical flexibility of (RE=Y, La−Lu; B=Si, Ge, Sn, Al, Ga; C=monovalent (Ag, Na, Li, etc.), divalent (Mg, Cr, Ni, Zn, etc.), trivalent (Al, In, Ga, etc.), tetravalent (Si, Ge, Sn) and pentavalent (Sb), Ch=S, Se), which consists of ∼444 isostructural compounds. (IV=Si, Ge) were synthesized by a high-temperature salt flux method. The crystal structures of (IV=Si, Ge) are constructed by polyhedra, octahedra, and tetrahedra. The Si1 atom displaces from the center of octahedra with partial occupancy, which can be replaced by various metals, and mainly accounts for the chemical flexibility of the family. The bonding pictures of were studied by electron localization function (ELF) and crystal orbital Hamilton population (COHP) calculations. is evaluated as an indirect semiconductor with a bandgap of 2.4(1) eV measured by UV-Vis. The indirect bandgap of is 1.7(1) eV. (IV=Si, Ge) are not type-I phase-matchable materials. For samples of 47 μm particle size, and own good second harmonic generation (SHG) responses of ∼3.0×AGS and ∼2.8×AGS respectively. and possess high laser damage threshold (LDT) of ∼5.5×AGS and ∼5.2×AGS respectively.