Oxidation-induced phase transformations of hybrid tin bromide single crystals enable the occurrence of second-harmonic generation

Phase transformations of tin halide hybrid materials play an important role in the formation of structural diversity and optoelectronic versatility due to the oxidability and instability from Sn2+ to Sn4+. Here, we demonstrate the synthesis, growth, phase transformations and fundamental properties of DMESnBrm (DME2+ = N,N '-dimethylethylenediaminium; m = 4 or 6) and TMDPSnnBr6 (TMDP2+ = 4,4 '-trimethylenedipyridinium; n = 1 or 2) single crystals. Interestingly, both DMESnBr4 and TMDPSn2Br6 single crystals undergo irreversible dissolution-recrystallization-induced phase transformations from Sn2+ to Sn4+ in the HBr-H3PO2 mixed solution when exposed to ambient atmosphere, which easily results in the formation of DMESnBr6 and TMDPSnBr6. In particular, DMESnBr6 crystallizes in the non-centrosymmetric space group P2(1) (no. 4) by single-crystal X-ray diffraction and piezoelectric measurements. The second harmonic generation (SHG) response of DMESnBr6 is about 0.5 times that of potassium dihydrogen phosphate (KDP) with type-I phase matching behaviors. Structural and theoretical analyses show that the SHG effect is attributed to the asymmetrical displacement of {SnBr6} octahedra. The oxidation-induced phase transformation behaviors provide new insights into the design and acquisition of novel Sn-based hybrid optoelectronic materials.

Automated summary

Phase transformations of tin halide hybrid materials have a significant impact on the structural diversity and optoelectronic versatility. Through experiments, it is observed that DMESnBr4 and TMDPSn2Br6 single crystals undergo irreversible phase transformations from Sn2+ to Sn4+ when exposed to ambient atmosphere, resulting in the formation of DMESnBr6 and TMDPSnBr6.