Abstract
In recent years, birefringent crystals have attracted much attention in the field of optical materials and play a significant role in laser technology and optical imaging. However, commercially available birefringent crystals are still relatively scarce and need improvement. Low-dimensional structures and well-oriented anisotropic units are conducive to obtaining excellent birefringent materials. Therefore, it is crucial to utilize a molecular engineering strategy for designing crystal structures. Through screening, the tellurite-nitrate system caught our attention because most of them exhibit low dimensional structures. The structure of Hg(3)(TeO(3))(Te(3)O(7))(NO(3))(2) (HTTN) consists of unprecedented [(Hg(3)Te(4)O(10))(2+)](∞) cationic layers built by a [TeO(3)](2-) triangular pyramid, [(Te(3)O(7))(2-)](∞) chains, and novel [(Hg(3)O(7))(8-)](∞) chains balanced by isolated NO(3) (-) anions. Here, HTTN with multiple functional units was obtained. HTTN has a birefringence value of 0.295 @ 546 nm, which is significantly higher than those of all commercially available birefringent crystals and exhibits the highest value among tellurite-nitrate birefringent crystals. Structural analysis and theoretical calculations reveal that the synergistic interaction between [TeO(3)](2-) (5.19%) and [NO(3)](-) (7.32%) groups and [(Te(3)O(7))(2-)](∞) (36%) and [(Hg(3)O(7))(8-)](∞) (51.49%) chains plays a crucial role in the optical anisotropy of HTTN. This study demonstrates that introducing functional units with high optical anisotropy is an effective strategy for developing high-performance birefringent materials.