The crystal structure of π-tetracyclo[8,6,0,02,9,03,8]hexadecapenta-4,6,11,13,15-enetricarbonyliron

Abstract

The isomer of Fe(CO)₃C₁₆H₁₆ with m. p. 172° crystallises in the monoclinic system with a= 20·86, b= 6·78, c= 10·99 Å, and β= 94·5°. There are four molecules in the unit cell, space group P2₁/a. A three-dimensional X-ray crystal structure analysis at 153 ± 5°K has shown that the compound has the formula indicated in the title. The iron atom was found from Patterson syntheses, the oxygen and carbon atoms were located unequivocally in difference electron-density syntheses and convincing evidence for the location of the hydrogen atoms was obtained. After refinement by least squares, allowing for anisotropic vibration of the iron atom and eight carbon atoms, and isotropic vibration for the other atoms, R was 0·081.

The iron is co-ordinated by three carbonyl groups, Fe–C = 1·783 Å, CO = 1·16 Å, Fe–C–O = 177·1°, C–Fe–C = 91, 99, and 101° and by four carbon atoms (Fe–C = 2·105 Å) of a six-membered ring in the tetracyclic organic molecule. The remaining two carbon atoms of the six-membered ring form half of one four-membered ring which is fused to another four-membered ring fused in turn to an eight-membered ring. There is one hydrogen atom attached to each carbon atom. Except for the four atoms bonded to iron, the lengths of the carbon–carbon bonds correspond clearly to single or double bonds; the group bonded to iron has carbon–carbon bond lengths of 1·42, 1·41, and 1·46 Å.

For the isomer with m. p. 118°, the crystals are monoclinic a= 9·59, b= 14·28, c= 11·32 Å, and β= 99°, space group P2₁/c.