FIGURE 2. Structure and properties of the quantum computer molecule, a perfluorobutadienyl iron complex with the inner two carbons ¹³C-labelled.

Based on the measured J_13C19F values, we concluded that the placement of the iron is as shown, different from that derived in ref. 29 from infrared spectroscopy. The table gives the _i/2 (in Hz) at 11.7 T, relative to a reference frequency of 470 MHz and 125 MHz for ¹⁹F and ¹³C respectively, the longitudinal (T₁, inversion recovery) and transverse (T₂, estimated from a single spin-echo sequence) relaxation time constants (in s), and the J-couplings (in Hz). Ethyl (2-¹³C)bromoacetate (Cambridge Isotope Laboratories, Inc.) was converted to ethyl 2-fluoroacetate by heating with AgF, followed by hydrolysis to sodium fluoroacetate using NaOH in MeOH. This salt was converted to 1,1,1,2-tetrafluoroethane using MoF₆, and was subsequently treated with two equivalents of n-butyl lithium followed by I₂ to provide trifluoroiodoethene. Half of the ethene was converted to the zinc salt, which was recombined with the remaining ethene and coupled using Pd(Ph₃P)₄ to give (2,3-¹³C)hexafluorobutadiene. The end product was obtained by reacting this butadiene with the anion obtained from treating [(-C₅H₅)Fe(CO)₂]₂ with sodium amalgam²⁹. The product was purified with column chromatography, giving a total yield of about 5%. The sample, at 0.88 0.04 mol% in perdeuterated diethyl ether was dried using 3-Å molecular sieves, filtered through a 0.45-m syringe filter, and flame-sealed in the NMR sample tube using three freeze-thaw vacuum degassing cycles. All experiments were performed at 30 °C.