Four new compounds, K(2.4)Ga(2.4)M(1.6)Q(8) (M = Si, Ge; Q = S, Se), were successfully synthesized via a reactive flux method. All compounds crystallize in the tetragonal system of space group I4/mcm, and belong to the Tl2Se2 structure type (Pearson symbol t/16). The isostructural scaffold of the compounds feature [(Ga-0.6/M-0.4) Q(4/2)] one-dimensional chains separated by K+ ions. The chains are composed of edge-sharing [(Ga-0.6/M-0.4) Q(4/2)] tetrahedrons. Powder and glass samples were synthesized from solid state reactions with different annealing processes. The transport properties of crystalline K2.4Ga2.4Ge1.6S8 and K2.4Ga2.4Ge1.6Se8 were determined from optical absorption measurements to be wide band gap semiconductors (Eg = 3.5 eV for K2.4Ga2.4Ge1.6S8 and 2.7 eV for K2.4Ga2.4Ge1.6Se8). A red shift of the band gap energy in the glass samples was observed. K2.4Ga2.4Ge1.6S8 glass showed a wide transparent range from 0.6 mu m to 10 mu m and a high soften-temperature of 533 degrees C. First-principles calculations fitted well with the optical measurements, indicating that the Ge substitution is beneficial for narrowing the band gap.