Synthesis and electrochemical and EPR investigations of the 48/49-electron [(.eta.5-C5H4Me)MnFe2(.eta.5-C5H5)2(.mu.-CO)2(.mu.-NO)(.mu.3-NO)]n series (n = 0, 1-): stereochemical-bonding analysis of the redox-generated change in geometry of a triangular mixed-metal cluster