Comparison of the co-ordinative behaviour of calcium(II) and magnesium(II) from crystallographic data

Abstract

Known crystal structures of calcium(II) and magnesium(II) complexes containing water, alcohols, ethers, carboxylates, halides, pseudohalides, carbonyl compounds, phosphates and polyphosphate as ligands have been examined in order to compare the co-ordinative behaviour of the two cations. A quantative assessment of the differences in the co-ordination numbers, the co-ordinative bond distances and the geometry of co-ordination to a typical ligand such as carboxylate has been carried out by systematic analysis of the crystallographic data. The observed higher flexibility of the calcium(II) complexes is explained in terms of (i) dimensions of the naked cations, (ii) dependence of the co-ordinative bond strengths on their lengths and (iii) second co-ordination sphere interactions.