Thioborate materials have been considered for novel infrared nonlinear optical (NLO) materials having large optical nonlinear properties combined with favorable laser damage thresholds and wide transmission ranges from the visible to the mid-infrared regions. In this work, known and new thioborate materials have been investigated that have the potential to overcome the low laser damage thresholds of the NLO chalcopyrite sulfide materials such as AgGaS2 without losing their large nonlinear properties and wide transmission ranges. A new thioborate phase, polycrystalline ZnxBa2B2S5+x (x ≈ 0.2), has been prepared by the reaction of the metal sulfides and B2S3 glass in carbon crucibles sealed inside evacuated silica tubes. It crystallizes in the tetragonal system with unit cell parameters of a = 4.762(4) Å and c = 24.020(7) Å and is based on isolated (BS3)3- structural units. The second harmonic generation (SHG) efficiency determined on powders of ZnxBa2B2S5+x (x ≈ 0.2) is ∼50 times larger than that of α-SiO2. The infrared spectrum shows transparency from 2.5 to 10 μm with absorption bands around 12 μm related to the vibration modes of (BS3)3- units. The UV−visible spectrum shows that it is transparent in the visible region down to ∼350 nm, which is a large improvement over the absorption edge of AgGaS2 at 490 nm.