Uranyls are hexavalent compounds of uranium of the type UO22+ with a O-U-O bond angle of 180° (trans) that is taken for granted. A cis-uranyl therefore was a surprising find as reported by Paul B. Duval et al. of the University of Missouri-Columbia in an Angewandte Chemie (VIP) article in 2007(DOI).
However Michel Ephritikhine et al. of CEA Saclay (the French Atomic Energy Commission) now allege in the same journal that news was too good to be true (DOI).
In a very simple reaction the Missouri people added uranyl acetate to a stirred suspension of monocarboxylated ferrocene (fcc) in dichloromethane (Note added: as to the why of this combination the article is not specific) and after evaporation reddish-orange crystals appeared in a 83% chemical yield.
The reaction product was identified as a coordination polymer of alternating ferrocene units connected to uranyl group through the carbocylic acid group and connected to the next unit via a newly formed carbon-carbon bond. X-ray crystallography revealed the cis-uranyl configuration and as another novelty the reaction was found to reversible simply by adding glacial acetic acid.
The CEA people on the other hand, repeating the procedure only found some red crystals among an orange powder and dark materials but ultimately isolated what they believe is (UO2(fcc)2(L)2)·L with L solvent pyridine or methanol in about 80% yield which is basically uranyl acetate with the acetate groups replaced by ffc and water by solvent. Nothing remarkable really, no bent O-U-O bonds and no reversible CC bond formation.
The reaction is seemingly simple but the findings of both groups are miles apart and they cannot be both a little bit right. The Angewandte post office should expect Missouri mail right about.....now!