Hg3(TeO3)2(NO3)2 and Hg3(Te2O5)2(NO3)2: The First Two Hg‐Based Tellurite Nitrate Unit‐Mixed Crystals with Large Optical Anisotropy

Abstract Birefringent materials are highly demanded for high‐performance polarized optics. Herein, the first two examples of mercury‐based tellurite nitrates, Hg 3 (TeO 3 ) 2 (NO 3 ) 2 and Hg 3 (Te 2 O 5 ) 2 (NO 3 ) 2 , are reported by the multiple functional group strategy. Both crystals feature a 2D layered structure and large birefringence of 0.120@546 and 0.117@546 nm, respectively. The synergistic effect of tellurite oxygen groups, mercury oxygen groups, and [NO 3 ] − groups isconfirmed to be responsible for their large birefringence. In addition, the quantitative analysis of different functional groups indicates that their arrangement can also significantly affect their contribution to the overall birefringence. Overall, this work not only enriches new compound systems but also provides potential birefringent materials and an effective strategy for exploring new birefringent crystals.