Remarkable Disparity of Second Harmonic Generation Response in Two Inorganic–Organic Hybrid Metal Thiocyanates

Colorless crystals of Cd(SCN)₂(l-C₅H₉NO₂)₂ (1) and Zn(SCN)₂(l-C₅H₉NO₂)₂ (2) were obtained by a solvent evaporation method. Compound 1 has a chainlike structure crystallized in the polar space group P2₁, while compound 2 features a monomeric structure crystallized in the polar space group C2. The second harmonic generation (SHG) responses of the two metal thiocyanates are 0.5 and 3.1 times that of KH₂PO₄, respectively. Theoretical calculation results reveal that the strong SHG response of compound 2 stems from the cooperative effect between the linear thiocyanate groups and terminal l-proline ligands.