text: Two atoms of this element are coordinated to an arene bridge in a complex with single-molecule magnet properties.
full_question: Two atoms of this element are coordinated to an arene bridge in a complex with single-molecule magnet properties. Stephen Liddle’s group was the first to synthesize a complex containing a triple bond between this element and nitrogen. After determining osmium was too expensive, Fritz Haber proposed using catalysts based on this element which were made moot by iron catalysts. The only molecule shown to have a phi bond is the diatomic form of this element. This element is found in the center of the most commonly studied D8h molecule, which sandwiches this element between a pair of cyclo·octa·tetra·enide rings. A magnesium acetate of this element is a common negative stain for electron microscopy. This element’s hexafluoride undergoes gaseous diffusion or gas centrifugation in order to isolate its lighter isotope, a process known as enrichment. This element most commonly exists as a dioxide, or in a 3:8 ratio with oxygen, which is a form of yellowcake. For 10 points name this actinide whose 235 isotope is the only naturally occurring fissile isotope.
first_sentence: Two atoms of this element are coordinated to an arene bridge in a complex with single-molecule magnet properties.