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.