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

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 strikin gly different crystal packing patterns. In NIL, C32H28O2N4S4Ni the geometry around the metal atom is shown to be distorted square planar with a shorte st Ni(1)... S(1A) (ethereal sulfur) contact of 3.547(2) Angstrom in neighbo ring molecules. The coordination configuration about PdL, C32H28O2N4S4Pd, i s square planar with a closest Pd(1)... S(1A) (thiolato) contact of 3.674(1 ) Angstrom in neighboring molecules. The molecular packing of PdL in the un it cell is different from that of Nit, but like a previously reported struc ture of Cut. Unlike Nit and PdL the molecular structure of ZnL, C32H28O2N4S 4Zn, has a C-2 crystallographic axis and the monomer is woven into a polyme ric structure by weak intermolecular S(thiolato)... H interactions of 2.836 Angstrom. 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 C-60 when an aperture is placed in front of the transmission detector, and ca. 2.0 J cm(-2) without an aper ture. The observed optical limiting effects are attributed to both nonlinea r absorption and nonlinear refraction processes.