Syntheses, Structures, and Properties of [Mn2(.mu.-O)2(.mu.-O2CCH3)(fac-bpea)2](ClO4)2 and Two Halide-Ligated Dioxo-Bridged Dimers Derived Therefrom: [Mn2(.mu.-O)2X2(mer-bpea)2](ClO4)2 (X = F, Cl)