Bis-silyl substituted ferrocenylenes, including dicyanovinyl electron-withdrawing groups, as potential non-linear optical materials

1,1′-Bis-silylferrocenylenes (p-XC6H4SiMe2-C5H4)2Fe, X=Br (1), CHO (2), CHC(CN)2 (3) have been synthesized and characterized by NMR and Mössbauer spectroscopy, single crystal X-ray diffraction and electrochemistry. Complex 1 crystallizes in the centrosymmetric space group P21/n whereas 3 forms in the non-centrosymmetric group Cc. The latter complex exhibits a chain-like structure in the solid state via CH⋯N intermolecular hydrogen bonding. The hyperpolarizability of 3 is significantly greater than the related mono-silylferrocene complex (C5H5)Fe(C5H4SiMe2C6H4CHC(CN)2) while Mössbauer spectroscopy exhibits negligible charge transfer between the cyano groups and the ferrocenylene iron center.