Review: Natural oxalates and their analogous synthetic complexes

Metal oxalates, commonly classified as organic minerals, are widely distributed in Nature, occurring in mineral deposits or as biominerals in plants, fungi, and lichens or in the form of deposits, of different kinds, in animal tissues. Eighteen natural species of this type have so far been reported and investigated. In the first part of this review we give an overview on the general characteristics of these minerals, including also some comments on their environmental effects. The central part of the review is devoted to the discussion of synthetic oxalates, analogous to the natural species, including the usual procedures employed for their synthesis and the thorough analysis of their crystallographic and structural peculiarities. The thermal, spectroscopic, and magnetic properties of these complexes are also discussed in detail. Some comparisons with related coordination compounds are also made along the text.