A three-dimensional X-ray diffraction study has been made of crystals of triphenyltin tetracarbonyltriphenyl-phosphinemanganese. These have the space group P21/n with a= 10·45, b= 26·48, c= 12·65 Å, β= 99° 34′, and four molecules in the cell. The molecule has been shown to contain a covalent bond between the tin and manganese atoms. The tin, manganese, and phosphorus atoms lie almost on a straight line defining the major axis of a distorted octahedron with manganese at its centre; Sn–Mn = 2·627 Å, Mn–P = 2·27 Å. The four carbonyl groups define the central plane of the octahedron: Mn–C(av.)= 1·79 Å, C–O(av.)= 1·15 Å. The Sn–C and P–C bonds are arranged tetrahedrally with respect to the major axis in an eclipsed conformation; Sn–C(av.)= 2·17 Å, P–C(av.)= 1·83 Å. The crystal packing appears to determine the distorted shape of the molecule.