Structures and Nonlinear Optical Properties of Two Acentric Borates with Cubic Cage-like Frameworks

Two new acentric borates, Li2Sr0.5[B3(BO3)4] (1) and Na4[Al3(BO3)4]·Cl (2), with cage-like frameworks constructed by BO3 and TO4 (T = B (1), Al (2)) units, were hydrothermally synthesized. The 3D anionic frameworks of 1 and 2 are built by two types of isostructural B–O and Al–B–O cages, respectively, and are further interpenetrated by polyhedral cubic unit (pcu) cationic frameworks. Both compounds not only feature novel interpenetrating pcu anionic and cationic frameworks, which are rarely observed in borate structural chemistry, but also exhibit moderate second harmonic generation (SHG) responses and a short cutoff edge, indicating their potential as deep ultraviolet nonlinear optical (NLO) crystals.