Two l-Proline Cadmium Thiocyanates with Moderate Second-Harmonic-Generation Responses and Large Birefringences

Two organic-inorganic cadmium thiocyanates, namely, Cd(SCN)(l-C₅H₈NO₂) (1) and Cd(SCN)₂(l-C₅H₉NO₂) (2), have been synthesized using l-proline as the bridging ligand. The two compounds have double-chain-like and layered structures, respectively. They feature moderate second-harmonic-generation responses (0.33 × KH₂PO₄ for 1 and 1.58 × KH₂PO₄ for 2), wide band gaps (4.68 eV for 1 and 4.59 eV for 2), and large birefringences (0.210 at 546 nm for 1 and 0.295 at 546 nm for 2). The structure-property relationship was explicated by first-principle calculations based on density functional theory.