Crystal Structure of [ 4 ] (1, 1') [ 4 ] (3, 3') [ 3 ] (4, 5')Ferrocenophane and Electronic Spectra of the Relate d Multibridged Ferrocenophanes

Abstract

The crystal structure of slant-bridged [ 4 ] (1, 1') [ 4 ] (3, 3') [ 3 ] (4, 5')ferrocenophane was determined by X-ray diffraction. The compound crystallizes in the monoclinic system, space group A 2/a with unit cell parameters a=21.825(5), b= 8.721(2), c=16.971(4) Å, p103.88(2)°, and z=8. Almost all of the C-C bond lengths and the C-C-C bond angles are in normal ranges. The two cyclopentadienyl (Cp) rings are in a staggard conformation and the dihedral angle between the two rings is 8.7°. The Cp-Fe-Cp distance (3.220 Å)is fairly short in comparison with the ones of tetramethylene-bridged ferrocenophanes.
The electronic absorption spectra of the compound and the related m ultibridged ferrocenophanes have been recorded in tetrahydrofuran and some correlations have been obtained between the d-d absorption band in the visible region and the structural parameters. The band undergoes a progressive hypsochromic shift with increase of the number of the tetramethylene bridges. An approximately linear relationship exists between the hypsochromic shifts of the band and the shortening of the Cp ring-Fe distances. The ring-tilt deformation of the ferrocene moiety also affects the d-d absorption shifts of the multibridged ferrocenophanes. The results are briefly discussed in relation to molecular orbital theory of metallocenes.