A series of new acetylide complexes of the type [Fe(η5-C5H5)(P down curve sign P)(p-C≡CC6H4R)] (P down curve sign P = DPPE (=l,2-bis(diphenylphosphino)ethane), (P)-PROPHOS (=R)-(+)-l,2-bis(diphenylphosphino)propane), R = NO2, C6H4NO2, (Z)-C(H)=C(H)C6H4NO2, (E)-C(H)=C(H)C6H4NO2) have been synthesized by halide abstraction from the precursors [Fe(η5-C5H5)(P down curve sign P)(I)] and fully characterized. Quadratic hyperpolarizabilities (β) for the complexes have been determined by hyper-Rayleigh scattering at 1064 nm. The influence on the nonlinear response of acetylide chain length in proceeding from 4-nitrophenylethynyl to 4-nitrobiphenylethynyl and 4-nitro-(E)-stibenylethynyl has been studied, revealing values of the first hyperpolarizabilities among the highest reported for organometallic molecular materials. Comparisons on the nonlinear efficiencies are drawn with the related well-known families of compounds [Ru(η5-C5H5)-(PR3)2(p -C≡C-(aryl)-NO2)] and [Fe(η5-C5H5)(P down curve sign P)(p-N≡C-(aryl)-NO2)]+. Cubic hyperpolarizabilities (γ) determined by Z-scan at 800 nm are consistent with an increase in γupon replacing Ru by the more easily oxidizable Fe and upon chain-lengthening the delocalizable π-bridging unit (proceeding from 4-C6H4 to (E)-4,4′-C6H4CH=CHC6H4). X-ray crystallographic structures of complexes [Fe(η5-C5H5(DPPE)(p-C≡CC6H 4NO2)] and [Fe(η5C5H5)(DPPE)((E)-p-C≡CC6 H4C(H)=C(H)C6H4NO2)] were studied in order to investigate the existence of π-back-donation suggested by spectroscopic and electrochemical data. Crystal packing was analyzed with the aim of assessing the alignment of the molecules in the lattice and hence suggesting the magnitude of NLO properties at the macroscopic level.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Organic Chemistry
- Inorganic Chemistry