Second-order non-linear optical properties of Fe(SALEN) complexes

The second-order non-linear (NLO) properties of the set of compounds iron (III) [N,N'-ethylenebis(salicylaldiminato)(pyridyl)(X), [Fe(SALEN)(pyridyl)X], where X = F-, Cl-, Br-, I, N-3(-), NCS- were examined. Complexes where X is a halide or thiocyanate exhibited weak SHG intensities (0.05-0.2 x urea). Considerable enhancement of SHG intensity was demonstrated by the azide complex (X = N-3(-)), which has a powder SHG efficiency twice that of urea. Complexes of the form Fe(SALEN)(N-3)(B), where B = 4-aminopyridine and 4-dimethylaminopyridine, did not demonstrate any second-order NLO properties. The X-ray crystal structure of 1 shows it crystallizes in the hexagonal space group P6(5) with a = 17.480(2), c = 12.513(3) Angstrom, and Z = 6. The iron 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. The non-linearity in this material originates from charge-transfer transitions in both the SALEN ligand, and the pyridyl-Fe pi-system. Copyright (C) 1996 Elsevier Science Ltd.