Crystal structures of trans-acetyl-dicarbon-yl(η5-cyclo-penta-dien-yl)(1,3,5-tri-aza-7-phosphaadamantane)molybdenum(II) and trans-acetyl-di-carbon-yl(η5-cyclo-penta-dien-yl)(3,7-diacetyl-1,3,7-tri-aza-5-phosphabi-cyclo-[3.3.1]nona-ne)molyb-den-um(II).

The title compounds, [Mo(C5H5)(COCH3)(C6H12N3P)(CO)2], (1), and [Mo(C5H5)(COCH3)(C9H16N3O2P)(C6H5)2))(CO)2], (2), have been prepared by phosphine-induced migratory insertion from [Mo(C5H5)(CO)3(CH3)]. The mol-ecular structures of these complexes are quite similar, exhibiting a four-legged piano-stool geometry with trans-disposed carbonyl ligands. The extended structures of complexes (1) and (2) differ substanti-ally. For complex (1), the molybdenum acetyl unit plays a dominant role in the organization of the extended structure, joining the mol-ecules into centrosymmetrical dimers through C-H⋯O inter-actions with a cyclo-penta-dienyl ligand of a neighboring mol-ecule, and these dimers are linked into layers parallel to (100) by C-H⋯O inter-actions between the molybdenum acetyl and the cyclo-penta-dienyl ligand of another neighbor. The extended structure of (2) is dominated by C-H⋯O inter-actions involving the carbonyl groups of the acetamide groups of the DAPTA ligand, which join the mol-ecules into centrosymmetrical dimers and link them into chains along [010]. Additional C-H⋯O inter-actions between the molybdenum acetyl oxygen atom and an acetamide methyl group join the chains into layers parallel to (101).