GAYLANI, KILNER, FRENCH, PICK AND WALLWORK 259After preliminary X-ray photography, lattice parameters were refined from 16 reflections with 11 ° < 0 < 14 ° and about 3300 X-ray intensities were measured on a Hilger & Watts computer-controlled, four-circle diffractometer up to 0 = 25 ° using a 0/20 scan technique in the range -11 ___ h ___ 9, -12 ___ k ___ 12, 0 < 1 <_ 12. Of these, 3067 were regarded as significant [I> 3tr(/)]. No corrections were made for absorption, in view of the low absorption coefficient and small crystal size (maximum dimension ca 0.5 mm). The structure was solved by the heavyatom Patterson method, and refined by least-squares calculations (on F), using anisotropic thermal parameters, to a final R value of 0.032, wR = 0.044. H atoms were included in calculated positions with fixed isotropic thermal parameters, and not refined. A weighting scheme of the form of a four-term Chebyshev polynomial was applied in the last few cycles of refinement (235 parameters refined). A/trmax = 0"14. The CRYSTALS system of programs was employed.Discussion. A drawing of the molecular structure showing the atomic numbering scheme is given in Fig. 1. Table 1 gives the atomic coordinates and Ueq values for the non-H atoms and Fig. 2 shows the crystal structure projected along the b axis.*The bond distances and angles found for the present complex (Table 2) centres, and the substituent at the skeletal C atom. The skeletal NCN angle is generally lower (108.0 °) when the latter substituent is methyl, than when it is phenyl (usually 110-112°), except for the case where each N atom substituent is CH(CH3)C6Hs. Also for this acetamidinato complex the Mo atom is positioned, within experimental error, in the skeletal NCN plane whereas for the chiral complexes dihedral angles up to 5.7 ° occur. The planes of the phenyl rings of the present complex are twisted so that two ortho-H atoms lie below the plane containing the metal and skeletal NCN atoms, whereas the methyl C atom lies above this plane, thus minimizing repulsion. The packing of the molecules in the crystal is in layers parallel to (10T), with adjacent molecules within the layers in opposite orientations.We thank the Science and Engineering Research Council for supplying the X-ray diffractometer. Abstract.[FeSn(CsHs)(C6Hs)3(CO)(CO2){P(C6-H5)3}], Mr = 805.27, orthorhombic, Pbca, a =
