Synthesis and characterization of coordination complexes and polymers for second order nonlinear optics

The second order nonlinear optical properties of the compounds Fe(SALEN)(pyridyl)X, where SALEN = N,N{dollar}spprime{dollar}-ethylenebis(salicylaldiminato) anion and {dollar}rm X = Fsp-, Clsp-, Brsp-, Isp-, Nsb3sp-, NCSsp-{dollar} were examined. Complexes where X is a halide exhibited weak to moderate second harmonic generation (SHG) intensities with the chloride complex having a powder {dollar}chisp{lcub}(2){rcub}{dollar} value of 0.20 x urea. The other halide complexes had {dollar}chisp{lcub}(2){rcub}{dollar} values of 0.06-0.10 x urea. Considerable enhancement of SHG intensity was demonstrated by the azide complex (X = N{dollar}sb3sp-),{dollar} which has a {dollar}chisp{lcub}(2){rcub}{dollar} value of 2 x urea but the thiocyanate analog did not exhibit any second order optical properties. The crystal structure of the azide compound was determined by X-ray diffraction and shows that the complex is octahedrally coordinated with the SALEN ligand binding to the four equatorial sites. One of the axial sites is occupied by a nitrogen atom of the azide and the other site is coordinated to the pyridyl nitrogen. This complex has two molecular dipoles; one along the axial position and the other along the equatorial plane. The equatorial dipole results from the electronic donation from the phenolic oxygen to the imine nitrogen of the SALEN and lies on the plane of the macrocycle. The axial dipole encompasses the azide, the metal center and the pyridine; lying along the axial positions. The nonlinear optical properties of this complex may result from either the equatorial, axial or the vectorial sum of these two molecular dipoles.; Metal Schiff's base complexes were designed to crystallize as polar coordination polymers in the solid state. A series of 4-(pyridyl) carboxylic acids and 4-(pyridyl) sulfonic acids were reacted with Mn(SALEN)Br to give the corresponding Mn(SALEN) carboxylate and sulfonate complexes respectively. These compounds were characterized by elemental analysis, FTIR (mid and far) and fast atom bombardment (FAB) mass spectroscopy. Room temperature magnetic susceptibility measurements showed that most of the complexes have magnetic moments close to the spin-only value of 4.90 B.M. for a high spin d{dollar}sp4{dollar} system. X-ray crystallography showed that four of these complexes crystallize as an infinite chain coordination polymer. The Mn atoms are octahedrally coordinated with the SALEN ligand filling four equatorial sites, an oxygen atom of the acid occupying one axial site, and a pyridyl nitrogen of an adjacent molecule occupying the trans axial site. This bonding pattern is repeated to give a polymer with head-to-tail alignment along the backbone. Similar analyses on the corresponding Cr and Fe analogs of the Mn coordination polymers are also consistent with the formation of infinite chain polymers.; In contrast, the reaction between Mn(SALEN)Br with 4-(cyanophenyl)glycine gives a compound whose crystal structure consists of a mixture of the monomer (H{dollar}sb2{dollar}O)Mn(SALEN)(4-(cyanophenyl)glycinate) and a Mn(SALEN)(4-(cyanophenyl)glycinate) polymer; the latter consists of adjacent Mn(SALEN) moieties bridged by a single carboxylate unit in a syn-anti conformation with no head-to-tail alignment.