Synthesis, structural-bonding-magnetic study, and proton NMR analysis of the temperature-dependent singlet-triplet solution equilibrium of the 46-electron tricobalt tris(pentamethylcyclopentadienyl) dicarbonyl, Co3(.eta.5-C5Me5)3(.mu.3-CO)2: an isolobal analog of the elusive antiaromatic cyclopropenyl monoanion |