A single-crystal X-ray structural analysis has confirmed the proposed structure of (CH3N)2Fe3(CO)9, one of several products of the reaction of methyl azide or nitromethane with Fe2(CO)9. This material crystallizes in space group Ci1-PĪ of the triclinic system, with reduced cell constants a = 8.31 (2) Å, b = 8.90 (2) Å, c = 12.79 (3) Å, α = 80° 29’ (10’), β = 108° 27’ (10’), and γ = 111° 29’ (10’). Observed and calculated densities for two molecules per unit cell are 1.89 (2) and 1.90 g/cm3, respectively. The structural determination was based upon 773 independent film data; full-matrix least-squares refinement resulted in a conventional R factor of 6.5%. The crystal structure is made up of discrete (CH3N)2Fe3(CO)9 molecules, in which the iron atoms of three Fe(CO)3 groups are triangularly situated and triply bridged on opposite sides of the Fe-Fe-Fe plane by the two N-CH3 groups. Two of the iron-iron distances (mean 2.462 (7) Å) are of a magnitude indicative of iron-iron bonds, and the third is a nonbonded contact of 3.044 (8) Å. The six iron-nitrogen bond distances are equal within experimental error and have an average value of 1.928 (11) Å. © 1969, American Chemical Society. All rights reserved.