This element is sandwiched between two (*) cyclopentadienyls ["cyclo"-"penta"-dye-EE-nuls] in the first known metallocene.
This metal is the central atom in a redox couple containing a deep blue salt with a BF4Â– counterion ["counter"- "ion"] whose voltage is 0.64 volts with respect to the hydrogen electrode. This element was the central atom in a compound made in a failed synthesis of fulvalene ["FULL-vuh-leen"] whose structure was deduced independently by Woodward and Fischer. In that compound, this element coordinates two ligands with hapticity 5 and appears to be an orange powder. This element is sandwiched between two (*) cyclopentadienyls ["cyclo"-"penta"-dye-EE-nuls] in the first known metallocene. Aluminum reacts with this element's oxide in the typical thermite reaction. Cytochromes contain a cofactor consisting of this element coordinated to a porphyrin ring which also appears in myoglobin and hemoglobin. For 10 points, name this element whose oxide is rust.
This metal is the central atom in a redox couple containing a deep blue salt with a BF4Â– counterion ["counter"- "ion"] whose voltage is 0.64 volts with respect to the hydrogen electrode.
iron [prompt on Fe]