Alkaline earth metals, locations binding

The conclusions from this analysis of carboxylate—metal binding in small structures studied to high resolution are (1) The metal cation generally lies in the plane of the carboxyl group. There are some notable exceptions. Alkali metals and some alkaline earth metals, which ionize readily and form strong bases, appear to have less specific locations of binding. (2) If the distance lies in the range 2.3-2.6 A, it is... 

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