β-Alanine Zn(II) and Cd(II) coordination complexes with diamondoid frameworks possessing second-order nonlinear optics properties

A complex, [Cd(HL)₄](NO₃)₂ (1) (HL = β-alanine), was synthesized and characterized by X-ray single crystal diffraction method, which crystallized in an acentric space group Fdd2 with supramolecular diamondoid frameworks and its second harmonic generation (SHG) efficiency has been tested. The ligand in complex 1 is electronically neutral. The counter-ion, NO₃^-, interacts with β-alanine ligands by asymmetrical H-bonding connections, which induces the structural polarity of complex 1. Based on our understanding of SHG materials, we predicted and found another new SHG material, [ZnL₂]_n (2) with an acentric space group Cc, although the crystal data of complex 2 has been reported. The possible reasons for complex 2 possessing SHG property were discussed. The analysis about similar and dissimilar influence factors on constructing SHG materials between complex 1 and complex 2 will be useful for synthesizing and finding out more SHG materials.