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The structure and absolute configuration of the thioamido complex (-)s,s-($-CsH5)Mo(C0)$3C(CH3)NR with R' = (S)CH(CH,)(C,H,) have been determined by single-crystal X-ray diffraction. The substance crystallizes in the orthorhombic system; space group P212121 with cell constants of a = 8.314(l), b = 9.020(l), and c = 22.352(2) A, and 2 = 4 molecules/unit cell. The absolute configuration was determined using Bijvoet's method. Refinement of the data using the anomalous scattering contributions of MO and S yields a final R(F) = 0.036 for 2715 independent reflections having 1 > 3a(I). The distorted square pyramidal coordination of the MO atom is defined by two carbonyl carbons and the S and N atoms of the thioamido ligand occupying the four basal plane sites and the five carbons of the $-&Hs ligand in the axial position. The Mo-ligand distances and most of the bond lengths and angles within the ligands are normal and compare closely with those of recent structure determinations. However, the distances and angles within the thioacetamide ligand show, distinctly, the effect of chelate binding to the MO atom. In particular, the angles at the central thioacetamide c&bon differ markedly from those of free thioacetamide and monodentate, S-bound metal thioacetamido complexes. The MO atom is 1.041 a above the plane formed by the four basal ligands. The conformation of the (S)-cr-phenylethyl group with respect to the ligand plane, defined by the thio-For part IV see ref. 1. also part IL of the series Optically active transition metal compleses (Part XLVIII see ref. 2).

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Crystal structure analysis shows that the molecules of a bis(tricarbony1iron) complex of 3,a-dimethylstyrene consist of two, linked, planar tricarbonylironisoprene units, inclined to one another a t an angle of 37.4O. SAREL et al.'have prepared two isomeric tricarbonyliron complexes of 3,a-dimethylstyrene. Chemical properties and spectroscopic data show that these complexes do not have any aromatic character, trapping of Kekulb structures being inierred. To test this proposal we have determined the crystal structure of one of them.