Molecular materials containig donor and acceptor groups. Synthesis, structure and spectroscopic properties of ferrocenyl Schiff bases

Abstract

Ferrocenyl Schiff-base derivatives of the form [Fe(η-C5H5)(η-C5H4CHNR)][R = NCH(C6H4NO2-p)1, C6H4CN-p2, C6H4NO2-p3, C6H4F-p4, C6H4Cl-p5, C6H4Br-p6, C6H4NO2-m7, NH(C6H4NO2-o)8, NH(C6H4NO2-p)9 or NH(C6F5)10], have been prepared from ferrocenecarbaldehyde. Proton, 13C NMR, UV/VIS and 57Fe Mössbauer spectroscopic data are presented. A number of these derivatives contain the donor–π-acceptor-(D–π-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–π-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 P21/n, with a= 5.885(1), b= 30.745(3), c= 8.662(1)Å, β= 96.40(2)° and Z= 4. The most striking feature of the molecular structure is the coplanarity of the substituent group with the η-C5H4 ring of the ferrocenyl moiety. The crystal structure reveals stacks of ferrocenyl, phenyl, phenyl, ferrocenyl moieties with inter-ring distances of 3.529 Å between the C5–C6 rings and 3.478 Å between the C6–C6 ring planes. The observation of a DAAD in contrast to a DADA stack is discussed.