Sr[B(OH)4](IO3) and Li4Sr5[B12O22(OH)4](IO3)2: two unprecedented metal borate-iodates showing a subtle balance of enlarged band gap and birefringence.

Two unprecedented metal borate-iodates, Sr[B(OH)4](IO3) (SBIO) and Li4Sr5[B12O22(OH)4](IO3)2 (LSBIO), were synthesized via the strategy of introducing (IO3)- into borates. In particular, the LSBIO possessed a new B12O26 fundamental building block (FBB). The two compounds integrated the advantages of both pure iodates and borates, showing enlarged band gaps and birefringence. Moreover, diverse B-O FBBs achieved the modulation of birefringence. This work reported the first two examples of borate-iodates.