Abstract A new borate chloride, Li2B5O8Cl, has been obtained. It exhibits complicated interpenetrating 3D B–O frameworks composed of the functional building block (FBB) [B5O10], enriching the structural diversity of B–O configurations. The theoretical study indicates that the birefringence is estimated to be 0.026 at 1064 nm. Meanwhile, the structure-property relationships were analyzed through the first-principles calculation with a bandgap of 5.737 eV for GGA and 6.880 eV for HSE06, and the electronic properties of each group are analyzed by the density of states (DOS).