Interactions between metal cations and the ionophore lasalocid. Part 13. Structure of 1:1 and 2:1 lasalocid anion–divalent cation complexes in methanol

Abstract

The successive formation of complexes MA⁺ and MA₂ of alkaline-earth cations M²⁺ with lasalocid HA is observable in methanol. Knowing the corresponding formation constants, it was possible to access NMR parameters specific to these two types of species for the four alkaline-earth cations. ¹³C and ¹H chemical shifts are reported for MA⁺ and MA₂; ¹H–¹H coupling constants for MA⁺ only. Experiments at low temperature and experiments using the paramagnetic cation Mn²⁺ determined the coordination sites. All these data show an appreciable variability of coordination in the series of alkaline-earth cations. Computations using the semi-empirical quantum methods AM1 and PM3 and Monte-Carlo simulations in methanol according to BOSS, mainly on MgA⁺ and BaA⁺ fully confirmed these findings.