CRYSTAL AND MOLECULAR-STRUCTURES OF HFE3(CH3C=NH)(CO)9 AND HFE3(N=CHCH3)(CO)9, ISOMERIC CLUSTER COMPLEXES DERIVED FROM THE REDUCTION OF ACETONITRILE

The complexes HFe3(CH3C=NH)(CO)9 (5a)2 and HFe3(N=CHCH3)(CO)9 (6a)2 have been characterized by low-temperature X-ray crystal structure determination. Molecule 5a crystallizes (in part) in the PI̅ space group with a = 9.276 (3) Å,b = 9.190 (2) Å, c = 9.099 (2) Å, a = 92.40 (2)°, β = 90.79 (2)°, γ = 83.45 (3)°, and V = 770.0 (4) Å3 at -158 °C and Z = 2,Ρobsd25° C = 1.89 g cm-3 and Ρobsd25° C = 1.92 g cm-3. Molecule 6a also crystallizes in the PI̅ space group with a = 13.620(2) Å, b = 7.822 (2) Å, c = 7.554 (1) Å, a = 72.19 (1)°, β = 92.71 (1)°,γ = 89.60 (1)°, and V= 765.2 (2) Å3 at-158 °C;Z = 2, Ρobsd25° C = l.99gcm3, Ρobsd25° C = 2.01 gcm-3. Diffraction data were collected with a Syntex PI automated diffractometer using graphite monochromatized Mo Ka radiation. All atoms including hydrogen atoms were located and refined by standard Patterson, Fourier, and least-squares techniques. The final discrepancy indices are for 5a, Rf = 2.9% and RwF = 4.2% for 4849 independent reflections having 1≥ 3 σ(I) in the range 0° < 2Θ < 65°; for 6a, RF = 4.1% and RwF= 4.8% for 3260 independent reflections havingI≥3σ(I) in the range 0° <2Θ < 60°. In 5a, the iron atoms form a nearly isosceles triangle, Fe(l)-Fe(2) = 2.5173 (7), Fe(l)-Fe(3) = 2.5672 (7), and Fe(2)-Fe(3) = 2.7537 (8) Å. The latter two iron atoms are bridged by a hydrogen atom, Fe(2)-H(FE) = 1.72 (3) Ånd Fe(3)-H(FE) = 1.70 (4) Å. The acetimidoyl group, CH3=NH, is triply bridging on the iron triangle; the carbon-nitrogen distance in this group is 1.344 (2) Å, similar to that of ύ-bonded iminium cations. The degree of bending of the substituents on this group, however, is not pronounced. The acetimidoyl group appears attached to the iron triangle through two a interactions, Fe(2)-N = 1.931 (2) Ånd Fe(3)-C(CN) = 1.933 (2) Å, and oneύ interaction, Fe(l)-N = 2.001 (2) Ånd Fe(l)-C(CN) = 2.096 (2) Å. The closest intermolecular contact, 2.33 Å, is between the acetimidoyl N-H hydrogen atom and a carbonyl oxygen atom of an adjacent molecule. In 6a, the iron atoms approach an equilateral triangle, Fe(l)-Fe(2) = 2.5457 (8), Fe(l)-Fe(3) = 2.5521 (9), and Fe(2)-Fe(3) = 2.5879 (8) Å. The latter two iron atoms are bridged by a hydrogen atom, Fe(2)-H(FE) = 1.59 (6) Ånd Fe(3)-H(FE) =1.71 (6) Å. The ethylidenimido group, N=CHCH3, is triply bridging on the iron triangle. The carbon-nitrogen distance in this group is 1.321 (5) Å, intermediate between σ double and a single carbon-nitrogen bond. The N=CHCH3 group is attached to the iron triangle through two a bonds to the nitrogen atom, Fe(2)-N = 1.878 (3) Ånd Fe(3)-N = 1.877 (3) Å, and a ύ bond displaying a pronounced asymmetry to the third iron atom, Fe(l)-C(CN) = 2.223 (4) Ånd Fe(l)-N = 1.960 (3) Å. The closest intermolecular contact, 2.58 Å, is between the C-H hydrogen atom of the ethylidenimido group and a carbonyl oxygen atom of an adjacent molecule. © 1979, American Chemical Society. All rights reserved.