[Jorge Stolfi]

Lead carbide officially does not exist (indeed lead is believed to be one of the few metals that do not form carbide).  Attempts to obtain it by combining Pb and C directly or by pyrolysis of organinc Pd salts have met with failure.

Yet those failures may mean only that lead carbide is unstable and decomposes below 200-300 C. Indeed there are a couple of dubious reports of a lead acetylide PbC₂ being formed at lower temperatures:

  http://en.wikipedia.org/wiki/Lead_carbide

I wonder if there has been any followup on those reports?

One of the reports claims that a micron-thin layer of PbC₂ was detected at the interface between graphite and a Pb-Bi alloy after very slow cooling. Which might be perhaps the result of trace amounts of some C-containing gas reacting with solid Pb?

The other alleged route, from calcium acetylide CaC₂ + Pb salt, is dubious because CaC₂ is decomposed by water into Ca(OH)₂ and acetylene, which does not ionize.  (Could the "lead carbide" thus formed be just a calcium/lead hydoxide or something of the sort?)

Yet, I wonder whether there is any polar but aprotic solvent (like propylene carbonate) that will dissolve CaC₂ or some other acetylide as a salt Ca²⁺ + C₂^2-, without formation of acetylene; even if only in trace amounts.  That may be enough to test the second PbC₂ claim.

If an unstable lead acetylide does exist, could be formed by electro- or photoexcitation of gaseous mixtures of acetylene and volatile organometallic Pb compounds?

[Jorge Stolfi]

It seems that CaC₂ is quite soluble in certain fused salts, including lithium halides, CaCl₂, BaCl₂, and mixtures thereof:

  W A Barber and C L Sloan (1961) http://pubs.acs.org/doi/abs/10.1021/j100828a025

The lowest temperature reported therein is LiCl-LiF-LiH eutectic, with m.p. 454 °C; it dissolves CaC₂ at about 3% molar.  That is still higher than the melting point of lead (327.46 °C) and hence probably high enough to decompose the hypothetical PbC₂.  (Indeed, that paper reports that attempts to dissolve CaC₂ in molten PbCl₂ resulted in reduction of the latter to metallic Pb.)

So perhaps there are other fused salts (or ionic liquids) that will dissolve CaC₂ at lower temperatures?  Or perhaps other acetylides, such as MgC₂ or Li₂C₂?