Heteronuclear Complexes Derived from trans-a2PtL2 (a = NH3 or CH3NH2, L = 2-Pyridonate). Distorted Coordination Geometries of All Three Metals in trans-[a2PtL2CuL2Pt(a2)]2+ and an Extraordinary Short Hydrogen Bond in trans-[a2PtL(LH)]+