Accurate determination of a classic structure in the metal carbonyl field: nonacarbonyldi-iron

Abstract

An equidimensional single crystal of Fe₂(CO)₉ has been used to reinvestigate the molecular structure. The results confirm all the main qualitative features originally reported by Powell and Ewens, and provide the level of accuracy needed for comparison with other structures and for molecular orbital calculations. The molecular symmetry is C_3h(), but there is little deviation from the higher symmetry D_3h(m2). The important molecular dimensions, with their estimated standard deviations in parentheses are: Fe–Fe, 2·523(1)Å; Fe–C (terminal), 1·838(3)Å, Fe–C (bridge), 2·016(3)Å; C–O (terminal), 1·156(4)Å; C–O (bridge), 1·176(5)Å; C(term.)–Fe–C(term.), 96·1 (1)°; Fe–C(bridge)–Fe, 77·6(1)°; Fe–C–O (term.), 177·1 (3)°. Space group: P6₃/m. a= 6·436(1)Å, c= 16·123(2)Å, V= 578·4(2)ų, Z= 1. Of 1064 unique reflections measured with a counter diffractometer, 604 with intensity at least three times the e.s.d. were used to refine the structure (34 parameters) to final discrepancy indices of 0·040 (unit weighted data) and 0·050 (weighted data).