Crystal structures of trans-acetyl­dicarbon­yl(η⁵-cyclo­penta­dien­yl)(di­methyl­phenyl­phosphane)molybdenum(II) and trans-acetyl­dicarbon­yl(η⁵-cyclo­penta­dien­yl)(ethyl­diphenyl­phosphane)molybdenum(II)

The crystal structures of the title compounds are compared, showing mol­ecular parameters that reflect the relative steric pressure of their respective phosphine ligands. Their supra­molecular properties are distinct but in both cases are organized around short C—H...O contacts involving the acetyl ligands.