MOLECULAR MATERIALS CONTAINING DONOR AND ACCEPTOR GROUPS - SYNTHESIS, STRUCTURE AND SPECTROSCOPIC PROPERTIES OF FERROCENYL SCHIFF-BASES

Ferrocenyl Schiff-base derivatives of the form [Fe(eta-C5H5)(eta-C5H4CH=NR)] [R = NCH(C6H4NO2-rho) 1, 7C6H4CN-rho 2, C6H4NO2-rho 3, C6H4F-rho 4, C6H4Cl-rho 5, C6H4Br-rho 6, C6H4NO2-m 7, NH(C6H4NO2-o) 8, NH(C6H4NO2-p) 9 or NH(C6F5) 10], have been prepared from ferrocenecarbaldehyde. Proton, C-13 NMR, UV/VIS and Fe-57 Mossbauer spectroscopic data are presented. A number of these derivatives contain the donor-pi-acceptor-(D-pi-A) structural motif desired for non-linear optical materials. The behaviour of the ferrocenyl moiety as a donor is compared to that of the 4-dimethylaminophenyl group. The UV/VIS spectra of compound 1 showed considerable solvatochromism. As a result of this and its extended donor-pi-acceptor nature, 1 was tested for non-linear optical properties, specifically, second harmonic generation. The results, however, were negative. A single-crystal X-ray study revealed 1 to crystallize in a centrosymmetric space group P2(1)/n, with a = 5.885(1), b = 30.745(3), c = 8.662(1) angstrom, beta = 96.40(2)-degrees and Z = 4. The most striking feature of the molecular structure is the coplanarity of the substituent group with the eta-C5H4 ring of the ferrocenyl moiety. The crystal structure reveals stacks of ferrocenyl, phenyl, phenyl, ferrocenyl moieties with inter-ring distances of 3.529 angstrom between the C5-C6 rings and 3.478 angstrom between the C6-C6 ring planes. The observation of a DAAD in contrast to a DADA stack is discussed.