A novel compound with four mixed anions, Y₈O(OH)₁₅(CO₃)₃Cl, exhibiting an infrequent three-dimensional (3-D) inorganic cationic framework, has been successfully designed and synthesized by introducing π-conjugated planar triangular CO₃ groups and chloride anions into a rare earth oxide system, which exhibits good balance among its wide UV transmission range, large second harmonic generation (SHG) coefficient and suitable birefringence to meet the phase-matching condition, indicating that the titled compound is a promising short-wave UV nonlinear optical material.