LiRb2LaB2O6: a new rare-earth borate with a MOF-5-like topological structure and a short UV cut-off edge

A new rare-earth borate LiRb2LaB2O6 (LB-1) has been synthesized using a high-temperature solution method. Interestingly, it shares its topological structure with the famous porous material MOF-5, which is formed from Zn4O(BDC)3 (BDC = 1,4-benzenedicarboxylate). The nodes [OZn4] and organic linkers [BDC] of MOF-5 are carefully substituted with La3+ rare-earth cations and the inorganic linkers [BO3] and [LiO4], respectively, in order to construct a pure inorganic open framework. LB-1 exhibits good thermal and water stability. Moreover, it possesses a short cut-off edge (<190 nm) and moderate birefringence (exp. 0.040@589.5 nm, cal. 0.038@589.5 nm). Further insights into the cut-off edge were given by first-principles calculations. The factors that influence the birefringence of LB-1 were discussed in view of the spatial arrangement of the [BO3] anionic groups.