Bond lengths carboxylate anion

The length of a double bond between any two atoms (e.g., C=C) is almost exactly 0.020 nm less than that for a single bond between the same atoms. If there is resonance, hence only partial double bond character, the shortening is less. For example, the length of the C-C bond in benzene is 0.140 nm the C-O distances in the carboxylate anion are 0.126 nm. 

Carboxylates and other oxo anions have a strong tendency to form polynuclear Cr111 complexes (Section 4.6.5.9.8). A formato complex, [Cr(OCHO)6]3, seems to be the only crystallographically characterized mononuclear Cr111 carboxylate.545 This complex possesses a distorted octahedral geometry, with two Cr—O -C—O units in the sp- and four in the ap-conformation the Cr—O bond lengths are 1.97-1.99 A.545... 

In this paper new results for a similar type of investigation about unsaturated carboxylates are presented and discussed from a similar point of view. The main objectives of this investigation are (1) new confirmation of the formation of a clathrate-like hydrate of tetra-butylammonium unsaturated carboxylates and (2) an examination of the influence of the presence of a double bond in the alkyl group of the carboxylate anion (such as the change in chain length, the decrease in chain flexibility, and the decrease in the number of hydrogen atoms) upon the stability of the hydrate in comparison with the case of the saturated carboxylates briefly summarized above. 

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