Pb 2 BO 3 Cl: A Tailor‐Made Polar Lead Borate Chloride with Very Strong Second Harmonic Generation

A meticulously designed, polar, non‐centrosymmetric lead borate chloride, Pb 2 BO 3 Cl, was synthesized using KBe 2 BO 3 F 2 (KBBF) as a model. Single‐crystal X‐ray diffraction revealed that the structure of Pb 2 BO 3 Cl consists of cationic [Pb 2 (BO 3 )] + honeycomb layers and Cl − anions. Powder second harmonic generation (SHG) measurements on graded polycrystalline Pb 2 BO 3 Cl indicated that the title compound is phase‐matchable (type I) and exhibits a remarkably strong SHG response, which is approximately nine times stronger than that of potassium dihydrogen phosphate, and the largest efficiency observed in materials with structures similar to KBBF. Further characterization suggested that the compound melts congruently at high temperature and has a wide transparency window from the near‐UV to the mid‐IR region.