Oxocarbon anions

All of these oxocarbon anions are aromatic according to simple molecular orbital calculations. The aromatic stabilization of the anion is apparently responsible for the fact that squaric acid (HjC O,) is about as strong as sulfuric acid.104 There is a considerable and growing body of knowledge of the chemistry of these systems, but most of it is probably more appropriate to a discussion of organic chemistry.105... 

Fig. 16.35 Cyclic oxocarbon anions (a) squonttc (b) croconutc (c) rhodizonale.

Note that oxalic acid containing carbon in a comparable oxidation stale but not aromatic has a Ki approximately equal to A for squsne and sulfuric acids, and Kj for oxalic odd is three orders of masraiude smaller. For a difference of opinion coneeraing the aromaticity of the oxocarbon anions, see Aihura. J. J. Am. Chem. Soc. 1981.I0S. 1633-1635... 

The oxides of carbon include the very stable and abundant CO and CO2, the unstable but isolable C3O2, and more complicated carbon oxides derived from organic backbones by removal of all hydrogen, for example, C12O9, from the complete dehydration of meUitic acid (benzenehexacarboxyhc acid). Oxocarbon anions, C 0 , with apparent aromatic properties are also known. The properties of these carbon-oxygen compounds are sununarized below. 

Oxocarbon anions, C 0 (3 < n < 6), are derived from the cyclic dihydroxy compounds depicted in Figure 3. Deltic and squaric acids are made by hydrolysis of suitable cyclopropene and cyclobutene derivatives (Figure 4). Much milder conditions (e.g. n-butanol in diethyl ether) are... 

Uranium(Vl) strongly bonds squarate (1), second in strength only to Fe(III) among the metal cations studied, and likewise rhodizonate (3), second only to Cu(II) , again among the metals of interest, which did not include Fe(III). The order of binding strength of the various metals to these oxocarbon anions remains unexplained. 

The deconstruction of the potassium croconate crystal allows us to recognize the analogies with another member of the family of oxocarbon anions, rubidium rodizhonate Rb2C606. The crystals possess some remarkable... 

We next turned our attention to oxo-anions bearing divergent hydrogen-bond accepting sites as effective building components, and among the most suitable molecular species for this purpose are the whole series of monocyclic oxocarbon anions. 

Oxocarbon anions are frequently used as photoreceptors, organic semiconductors, and in nonlinear optical applications [20]. Rhodizonate salts 4 are widely used as analytical reagents for metal salts, typical examples being lead traces in forensics, to analyze radium in drinking water and to identify iron and barium [21]. Rhodozinate 4 is also interesting because of its luminescent properties [21, 22]. 

---