Compounds with isolated anionic groups often exhibit special linear and nonlinear optical properties and possess potential applications such as birefringence, second harmonic generation and stimulated Raman scattering crystals. In this paper, two new alkali and alkaline earth mixed-metal borates, Li3KB4O8 and LiNa2Sr 8B12O24F6Cl, with isolated (B 12O24)^12- anionic groups have been successfully synthesized by spontaneous crystallization. Their structures were determined by single crystal X-ray diffraction and they both crystallize in the same space group, R3. More interestingly, further structure comparison shows that the discovered anhydrous borates with the (B12O24) ^12- groups also crystallize in the same space group R3, which is related with the local symmetry of the (B12O24) ^12- groups. These structural features suggest that the crystal structures of the family of compounds depend more on their anionic groups. In addition, the property characterizations of the two new borates were investigated by TG-DSC, IR and UV-vis-NIR diffuse reflectance.