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It is important to establish and clarify the relationship between stereochemically active lone pairs and birefringence, since it is one of the significantly effective routes to explore birefringent crystals by introducing Sn‐centered polyhedra with stereochemically active lone pairs. Herein, four tin(II)‐based ternary halides A3SnCl5 and ASn2Cl5 (A=NH4 and Rb) have been synthesized successfully. The experimental birefringence of Rb3SnCl5 and RbSn2Cl5 is larger than or equal to 0.046 and 0.123@546 nm, respectively. Through investigating the alkali or alkaline‐earth metal tin(II)‐based ternary halides, the structure‐performance relationship has been concluded between stereochemically active lone pairs and optical anisotropy. It is beneficial to the analysis and prediction of birefringence in tin‐based halides and provides a guide for exploring tin(II)‐based optoelectronic functional materials. [ABSTRACT FROM AUTHOR]

Exploring non π‐conjugated phosphate birefringent crystal with a large birefringence has been a great challenge. Herein, based on the unique two‐dimensional layered structure in KBe2BO3F2 (KBBF), two new compounds, Sn2PO4I and Sn2BO3I, were designed and synthesized successfully, maintaining the layer structural feature and enhancing the optical anisotropy of crystals. In particular, the birefringence of Sn2PO4I is larger than or equal to 0.664 @546 nm, which is largest among the reported borates and phosphates, even surpassing commercial birefringent crystals YVO4 and TiO2. This work indicates that a breakthrough in birefringence of inorganic compound was achieved. Also, it provides a guiding idea for exploring large birefringence materials in the future. [ABSTRACT FROM AUTHOR]

A material with a large birefringence is needed for optical systems, and borate is a good choice as an excellent birefringent material. Herein, we report two borates BaMIV(BO3)2 (MIV = Ti, Sn), in which the [TiO6] and [SnO6] units have similar coordination environments. Moreover, the experimental birefringence of BaTi(BO3)2 is equal to or larger than 0.169 at 546 nm measured by using a polarizing microscope, which mainly originates from the high-density and parallel arrangement of the isolated [BO3] groups. This discovery indicates that BaTi(BO3)2 can be a promising ultraviolet birefringent material. [ABSTRACT FROM AUTHOR]

The first tin (II) borate bromide, Sn2B5O9Br (SBOB), as an outstanding bifunctional material with excellent linear and nonlinear optical (NLO) performance is synthesized successfully. As far as it is known, it exhibits the largest birefringence among the reported borates (0.439 at 546 nm), even over famous birefringent materials YVO4 and TiO2. Meanwhile, it also owns a strong second harmonic generation (SHG) response of 2.4 times that of KH2PO4. Theoretical calculations display that its incredible optical properties mainly originate from the extremely intensive stereochemical activity lone pair (SCALP) of [SnO7Br2] polyhedra, which results in the enhancement of birefringence and SHG response, increasing to 2.6‐ and 4.8‐fold, respectively, from Sn2B5O9Cl (SBOC) to SBOB. These perceptions will guide and accelerate the exploration of excellent birefringence and NLO materials in tin (II)‐based compound. [ABSTRACT FROM AUTHOR]

The simple binary fluoride α‐SnF2 is shown to be an excellent birefringent material with outstanding birefringence, about 14 times that of MgF2. Furthermore, it exhibits a shorter UV cutoff edge and easy crystal growth at ambient temperature compared to YVO4 and TiO2. A novel theoretical calculation mode was established to analyze the stereochemical‐activity lone‐pair (SCALP) contribution to the birefringence (SCB) based on the SCALP′s strength and arrangement, and it was found that the large birefringence of α‐SnF2 mainly benefits from well‐aligned [SnF5] polyhedra with a strong SCALP. The exploration of the α‐SnF2 birefringent crystal points out the direction of the future search for excellent birefringent materials. [ABSTRACT FROM AUTHOR]

Two new isostructural alkali metal hydroxyborates, AB11O16(OH)2 (A = K and Cs), with two-dimensional (2D) interpenetrating [B11O18(OH)2]∞ layers have been successfully obtained. The calculated birefringences of KB11O16(OH)2 and CsB11O16(OH)2 are 0.104 and 0.100 at 546 nm, respectively. Moreover, KB11O16(OH)2 exhibits a short DUV cutoff edge (195 nm). [ABSTRACT FROM AUTHOR]

The excellent birefringent materials are needed for optical systems. Herein, we reported a new compound, the first tin borate chloride, Sn2B5O9Cl (SBOC) with a large birefringence (0.168 at 546 nm) measured by the polarizing microscope. Its birefringence is 16 times that of the isostructural Ba2B5O9Cl (BBOC) compound (0.010@ at 546 nm). The results show that the birefringence enhancement originates mainly from the Sn2+ polyhedra. We propose that the birefringence can be enlarged by substituting the alkaline‐earth metal cation by the Sn2+ cation in the isostructural borate with small birefringence. This strategy will guide the discovery of large birefringent materials in the future. [ABSTRACT FROM AUTHOR]