Crystal structures, molecular packing and picosecond optical limiting properties of quadridentate Schiff base divalent metal complexes derived from S-benzyl dithiocarbazate

Abstract

The neutral divalent metal complexes ML [H₂L=1,4-bis(2′-formylphenyl)-1,4-dioxabutane bis(S-benzyl dithiocarbazate); M=Ni, Pd and Zn] show strikingly different crystal packing patterns. In NiL, C₃₂H₂₈O₂N₄S₄Ni the geometry around the metal atom is shown to be distorted square planar with a shortest Ni(1)···S(1A) (ethereal sulfur) contact of 3.547(2) Å in neighboring molecules. The coordination configuration about PdL, C₃₂H₂₈O₂N₄S₄Pd, is square planar with a closest Pd(1)···S(1A) (thiolato) contact of 3.674(1) Å in neighboring molecules. The molecular packing of PdL in the unit cell is different from that of NiL, but like a previously reported structure of CuL. Unlike NiL and PdL the molecular structure of ZnL, C₃₂H₂₈O₂N₄S₄Zn, has a C₂ crystallographic axis and the monomer is woven into a polymeric structure by weak intermolecular S(thiolato)···H interactions of 2.836 Å. The picosecond optical limiting properties of ML [M=Cu(II), Ni(II), Pd(II) and Zn(II)] were investigated. The limiting threshold for PdL is ca. 0.9 J cm⁻², comparable to that of C₆₀ when an aperture is placed in front of the transmission detector, and ca. 2.0 J cm⁻² without an aperture. The observed optical limiting effects are attributed to both nonlinear absorption and nonlinear refraction processes.