myo-Inositol hexakisphosphate (InsP 6 ) interacts strongly with cations, forming soluble complexes and solids, both of which are biologically relevant. We have recently reported advances in this area, showing the importance of the interaction with Mg 2+ and Ca 2+ . We now extend the data to Sr 2+ and Ba 2+ , which behaved similarly to Mg 2+ and Ca 2+ , but giving even less soluble systems. We also describe the interactions with Li + , Na + , K + , Mg 2+ , Ca 2+ , Sr 2+ , and Ba 2+ in a non-interacting medium: these depended strongly on cation charge but only weakly on ionic radius within each series. In addition, we probed structural aspects of InsP 6 compounds with alkaline earth cations, by means of IR and Raman spectroscopy of the solids and computational calculations on the 1:1 complexes of Mg 2+ . Both approaches suggested direct and multidentate phosphate-metal coordination. In [Mg(H 2 L)(H 2 O) 3 ] 8À , three oxygen atoms from two phosphate groups and three water molecules were predicted to form a roughly octahedral coordination shell; alternate or vicinal phosphate groups were predicted to chelate Mg 2+ depending on whether InsP 6 is in the 5-axial/1-equatorial or the 1-axial/5-equatorial conformation, respectively.