Abstract A series of four-coordinate air stable and water soluble cis- and trans-Pt(II) and Pd(II) complexes containing two PTA or DAPTA ligands (PTA=1,3,5-triaza-7-phosphaadamantane; DAPTA=3,7-diacetyl-1,3,7-triaza-5-phosphabicyclo[3.3.1]nonane) with the general formulas, [PtR2(PTA)2], [M(Me)X(PTA)2], [Pt(Et)X(PTA)2], [MR2(DAPTA)2], [MX2(DAPTA)2], and [M(Me)X(DAPTA)2] (where M=Pt or Pd; R=Me, Et, CCR (R=Ph, SiMe3); X=Cl, Br, I) were prepared by ligand displacement starting from [M(R)2(COD)], [M(R)(X)(COD)] or precursors or metathesis reactions utilizing [MCl2(PR3)2] precursors in good yields (63%–90%). The complexes were characterized by multinuclear NMR, IR, MS, and elemental analysis experiments and in some cases by X-ray crystallography studies. Complexes, cis-[PtMe2(PTA)2] (cis-1), trans-[Pt(Me)Cl(PTA)2] (trans-3a), trans-[PtCl2(PTA)2] (trans-4), trans-[Pt(CCPh)2(PTA)2] (trans-6), and trans-[PtI2(DAPTA)2] (trans-13c) were characterized by X-ray crystallography. The molecular structures reveal, in general, distorted square planar geometries at the metal center. For the DAPTA complexes, both syn- and anti-conformations of the DAPTA rings were observed depending upon the nature of the groups at the metal center.