A spectroscopic and structural examination of the platinum(II) co-ordination chemistry of bis(diphenylphosphino)amine (dppa) and bis(diphenylphosphino)methylamine (dppma) has been made. The complexes [Pt(dppa)Cl2], [Pt(dppma)Cl2], [Pt(dppa)(CN)2], [Pt(dppma)(CN)2], [Pt(dppa)2]2+ and [Pt(dppma)2]2+ as the chloride, iodide and tetrafluoroborate salts, [Pt(Ph2PNPPh2)2], trans-[Pt-(dppa-P)2(CN)2] and [Pt2(µ-dppa)2(CN)2] have been prepared. The solid-state structures of [Pt(dppa)2][BF4]2·MeCN,[Pt(dppma)2][BF4]2 and trans-[Pt(dppa-P)2(CN)2] have been determined by X-Ray crystallography. The crystallographic examination permits a critical evaluation of the nature of the strain in the four-membered rings formed by ligand chelation to a transition-metal centre. Structural and theoretical data suggest that bis(diphenylphosphino)amine chelate complexes should be more strained than the corresponding bis(diphenylphosphino)methane (dppm) complexes. The preference of PtII for binding to dppa rather than dppm implies the formation of a stronger Pt–P bond in complexes of the former ligand.