Solid-State Nonlinear Optical Properties of Mononuclear Copper(II) Complexes with Chiral Tridentate and Tetradentate Schiff Base Ligands

• Main Authors: Luca Rigamonti, Alessandra Forni, Elena Cariati, Gianluca Malavasi, Alessandro Pasini
• Format: Article
• Language: English
• Published: MDPI AG 2019-11-01
• Series: Materials
• Subjects: chiral diamines; template synthesis; mononuclear copper(ii) complexes; schiff base ligands; nonlinear optics; kurtz–perry powder technique
• Online Access: https://www.mdpi.com/1996-1944/12/21/3595

Salen-type metal complexes have been actively studied for their nonlinear optical (NLO) properties, and push-pull compounds with charge asymmetry generated by electron releasing and withdrawing groups have shown promising results. As a continuation of our research in this field and aiming at solid-state features, herein we report on the synthesis of mononuclear copper(II) derivatives bearing either tridentate N₂O Schiff bases L^{(a&#8722;c)&#8722;} and pyridine as the forth ancillary ligand, [Cu(L^a&#8722;c)(py)](ClO₄) (<b>1a</b>&#8722;<b>c</b>), or unsymmetrically-substituted push-pull tetradentate N₂O₂ Schiff base ligands, [Cu(5-A-5&#8242;-D-saldpen/chxn)] (<b>2a</b>&#8722;<b>c</b>), both derived from 5-substituted salicylaldehydes (sal) and the diamines (1<i>R</i>,2<i>R</i>)-1,2-diphenylethanediamine (dpen) and (1<i>S</i>,2<i>S</i>)-1,2-diaminocyclohexane (chxn). All compounds were characterized through elemental analysis, infrared and UV/visible spectroscopies, and mass spectrometry in order to guarantee their purity and assess their charge transfer properties. The structures of <b>1a</b>&#8722;<b>c</b> were determined via single-crystal X-ray diffraction studies. The geometries of cations of <b>1a</b>&#8722;<b>c</b> and of molecules <b>2a</b>&#8722;<b>c</b> were optimized through DFT calculations. The solid-state NLO behavior was measured by the Kurtz&#8722;Perry powder technique @1.907 &#181;m. All chiral derivatives possess non-zero quadratic electric susceptibility (<i>&#967;</i>⁽²⁾) and an efficiency of about 0.15&#8722;0.45 times that of standard urea.