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I would presume that Pyridinium Chlorochromate is not organic soluble due to the relatively strong ionic bonding between the anion and cation on account of their similarly large size. Although the charge on the pyridine is not stabilised by resonance, the charge on the chromium molecule is. Does this weaken the ionic bond enough so that the weak London forces between organic solvent molecules and the ions is enough to pull them apart? Are there other factors at play here?

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    $\begingroup$ Weak London forces? It's soluble in polar solvents, not hexane. $\endgroup$ – Mithoron Dec 19 '19 at 19:05
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Apart from the fact noted by Mithoron that it's soluble in polar organic solvents, we may consider what lattice binding energy the solvation forces must overcome. In a compound like sodium chloride with compact, monatomic ions the lattice forces are too strong for all but the most aggressive solvents (but lithium salts have a way around this problem). With pyridinium chlorochromate (PCC), however, the ions are multiatomic, bulky, and differently shaped as well as having only one charge, so the crystal lattice is only weakly bound compared with sodium chloride. PCC is far from unique; to cite another example, the triangular cyclopropenyl cation was identified through its nmr specta when salts were dissolved in polar solvents.

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    $\begingroup$ The fact that PCC is a protonated salt (of pyridine and the theoretical chlorochromic acid) may also mean that the ionicity is only "partial", with formation of tightly bound neutral pairs in solution in low polarity solvents. A somewhat related case is ethylammonium nitrate (EAN), which is even a room-temperature ionic liquid. and probably has substantial solubility in some organic solvents. Hydrocarbons also have comparatively high solubility in EAN. $\endgroup$ – Nicolau Saker Neto Dec 20 '19 at 16:44
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    $\begingroup$ If you look at my references answer you see that lithium salts are rendered more soluble than heavier alkali metal salts due to ion pairing/association. $\endgroup$ – Oscar Lanzi Dec 20 '19 at 16:46
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    $\begingroup$ I see your point for the lithium salts, but there's a slight subtlety in that simple lithium salts are highly dependent on solvents with good donor atoms to become soluble. For example, lithium iodide has poor solubility in DCM, even though it is relatively polar, and even though LiI is extremely soluble in things like diethyl ether, etc. Lithium favours covalency, as you say, but it needs to bind to a donor solvent to form a tight solvate, which essentially acts as a bulky organic cation. A proton salt like PCC or EAN favours covalency more, and would in principle be less solvent-dependent. $\endgroup$ – Nicolau Saker Neto Dec 20 '19 at 17:06
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    $\begingroup$ Protic cations could also hydrogen bond. That could mean a huge solvent dependency, actually. $\endgroup$ – Oscar Lanzi Dec 20 '19 at 19:57
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    $\begingroup$ I suppose that's true, protic salts just shift the dissolution enhancement (from donor solvents for lithium salts) to solvents capable of supporting hydrogen bonding even if they do not hydrogen bond themselves (which I suppose covers most donor solvents...), and due to the higher covalency of a hydrogen bond (higher polarising power of a proton compared to a lithium cation), dissolution can still be supported in non-donor/weakly polar solvents by forming a strong internal partially covalent hydrogen bond between anion and cation. $\endgroup$ – Nicolau Saker Neto Dec 20 '19 at 21:14

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