Coordination Modes of 9-Methyladenine in cis-Platinum(II) Complexes with Dimethyl(Phenyl)Phosphanes as Ancillary Ligands - Synthesis and Characterization of cis-[PtL2(9-MeAd)(2)](NO3)(2), cis-[PtL2{9-MeAd(-H)}](3)(NO3)(3), and cis-[L2Pt{9-MeAd(-H)}Ptl2](N