Ba₃(C₄H₄O₅)₂(OH)₂: A Novel Short‐Wavelength Alkaline Earth Metal 2‐Hydroxybutanedioate

Abstract With the continuous development of optical science and technology, there are higher requirements for the versatility and multi‐application scenarios of optical devices. Organic–inorganic hybrid birefringent crystals have attracted much attention due to their high flexibility in molecular design and assembly. In this work, an alkaline earth metal 2‐hydroxybutanedioate Ba 3 (C 4 H 4 O 5 ) 2 (OH) 2 crystallizing in the C 2/ c space group is synthesized by the hydrothermal method. Its unit cell parameters are a = 20.0584(7) Å, b = 7.4499(3) Å, c = 9.5087(3) Å, and β = 96.808(2) °. Ba 3 (C 4 H 4 O 5 ) 2 (OH) 2 polycrystalline powder is characterized in detail by Fourier transform infrared (FTIR) absorption spectroscopy, UV–vis–NIR diffuse reflectance spectroscopy, and simultaneous thermal analysis. In addition, theoretical analyses are carried out using first‐principles calculations and Hirshfeld surface analysis. The theoretical birefringence of Ba 3 (C 4 H 4 O 5 ) 2 (OH) 2 is calculated to be 0.1 @546 nm. At the same time, UV–vis–NIR diffuse reflectance and band structure calculations show that Ba 3 (C 4 H 4 O 5 ) 2 (OH) 2 has an indirect bandgap of 5.11 eV with a UV cutoff edge of 203 nm. By leveraging the complementary attributes of organic and inorganic materials, Ba 3 (C 4 H 4 O 5 ) 2 (OH) 2 stands out as a promising UV birefringent candidate.