Oxidant-induced hydride abstraction from [Pt(mu-PBu2t)(H)((PBu2H)-H-t)](2) yielding [Pt-2(mu-PBu2t)(2)(H)((PBu2H)-H-t)(2)]C-3(CN)(5) : spectroscopic, crystallographic, and theoretical comparison of the structures of two "Tautomers"