The zero-order waveplates, the essential materials in altering the polarization state of optical waves, are significant in polarimetry and the laser industry. Restricted by birefringence and absorption edge, few materials can have moderately small birefringence (Delta n < 0.01) and a deep-ultraviolet (DUV; lambda < 200 nm) transparency range. We used the B3O3F6 unit for designing the zero-order waveplate material, which is composed of three BO2F2 tetrahedra interconnected by corner sharing. Here we obtained a new Cs3B3O3F6 compound with the isolated B3O3F6 unit by a high-temperature solution method, which has the DUV cutoff edge and suitable birefringence (0.0069 at 532 nm) based on the experimental and computational results. This demonstrates that the isolated B3O3F6 unit is a potential group, which favors the search for suitable compounds for DUV zero-order waveplate materials.