Achieving record-high birefringence in a 3D fluorozincoborate via coplanar alignment of π-conjugated [BO 3 ] units

Two novel fluorozincoborates, Na 6 ZnF 2 B 12 O 24 H 6 and KZn 3 F(BO 3 ) 2 , were designed and synthesized. Notably,KZn 3 F(BO 3 ) 2 possesses the highest birefringence reported to date in the zinc borate family (Δ n cal. = 0.11@546 nm, Δ n exp. = 0.09@546 nm).