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On page 88 and 89 of this document, the author laments that $\ce{OClF5}$ has still not been discovered. He says it would be "just about the ultimate possible storable oxidizer" (for rockets).

(Note: it's pages 88 and 89 as labeled by the writing on the page, not the pdf metadata.)

The text seems a little dated. Has anyone ever found/produced any $\ce{OClF5}$? A related compound, $\ce{OClF3}$, was made in 1970 (footnote on page 89). So this seems to indicate that one of those weird loopy pairs of electrons can be jammed/bonded with an atom of oxygen.

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  • $\begingroup$ In ClF5 there's an axial lone pair so your compound may be possible. $\endgroup$ – Mithoron Jul 25 '15 at 11:58
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    $\begingroup$ The isoelectronic ClF6+ ion is known, but you have to hit ClF5 pretty hard, with PtF6 or [KrF][AsF6] according to Housecroft and Sharp. Greenwood and Earnshaw say "F5ClO has been claimed but the report could not be confirmed", but doesn't give the reference. $\endgroup$ – Ian Bush Jul 25 '15 at 13:27
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Yes there has been experimental evidence published. Reaction of CIF5, with OF2: Preparation and Properties of Chlorine Oxide Trifluoride and the Existence of Chlorine Oxide Pentafluoride, Angewandte Chemie, Internation Edition, vol. 11, pages 1094-5, purports to show a series on F-19 NMR spectra of the compound, at temperatures ranging from 34 to -76 degrees C.

The series shows a relatively sharp peak at 34 degrees C, which progressively broadens and shifts upon cooling to until about -40, upon which further cooling sharpens to a peak with much different chemical shift than the room temperature peak. The authors conclude that at room temperature there is fast exchange among the 5 F atoms, and at low temperature 4 equivalent equatorial F atoms are observed, while the peak for the axial F atom is too broad to be observed.

However, the above claim is considered refuted by "Chlorine Oxyfluorides" Advances in Inorganic Chemistry and Radiochemistry vol. 18, pages 319-98.

See On the XeF+/H2O System: Synthesis and Characterization of the Xenon(II) Oxide Fluoride Cation, FXeOXeFXeF+ J. Am. Chem. Soc., vol. 131, pages 13474–89 for further discussion and references:

Chlorine oxide pentafluoride, ClOF5, would be the highest performing earth-storable, liquid rocket-propellant oxidizer. Although the synthesis of ClOF5 had been claimed in 1972,(1) this claim was subsequently refuted.(2) Continued efforts to prepare this compound by oxidative fluorination of substrates such as ClOF3(3-5) or ClOF4−(6, 7) have failed because the oxygen ligand is more easily oxidized than the central chlorine atom. This failure prompted a search for alternate synthetic approaches, such as the reaction of ClF5 with an oxidative oxygenator. Potential candidates for oxidative oxygenators include hypofluorous acid, HOF, a well-known unstable compound,(8, 9) and its protonated form, the H2OF+ cation,(10, 11) if indeed it should exist.

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