Hemilability and nonrigidity in a series of mixed P, PS donor ligands has been studied in the complexes [Pd (P, PS) Cl2],[Pd (η3-C3H5)(P, PS)][SbF6], and [Rh (cod)(P, PS)][SbF6](P, PS= Ph2P-QP (S) Ph2). The effect of bite angle, the rigidity of the ligand backbone, and the role of the ancillary ligands are discussed.