Density Functional Theory Study oftrans-Dioxo Complexes of Iron, Ruthenium, and Osmium with Saturated Amine Ligands,trans-[M(O)2(NH3)2(NMeH2)2]2+ (M=Fe, Ru, Os), and Detection of [Fe(qpy)(O)2]n+ (n=1, 2) by High-Resolution ESI Mass Spectrometry