Bidentate phosphine-selenoether (P,Se) ligands were synthesized, and their heteroligated Pt(II) complexes were made and studied. The unique "P,S/P,Se" ligand coordination to Pt(II) can be realized via the halide-induced ligand rearrangement reaction. In all cases, the exclusive formation of semi-open heteroligated complexes was achieved as shown by P-31 and Se-77 NMR spectroscopy and from single crystal X-ray diffraction studies. This is the first example of the use of Se-77 NMR spectroscopy to characterize these types of structures through direct observation of the weak-link interaction with the metal center. Heteroligated structure formation is believed to be driven by the relative electron-donating ability of the substituent groups on the seleno or thioether moieties. This effect is studied by comparing the structures of corresponding "P,SMe" and "P,SeMe" complexes bearing a hemilabile "P,SCH2CF3" group, which is less sterically demanding than "P,SPh" but is similar in terms of electron withdrawing ability.