The reaction of inosine-5′-monophosphate acid (IMPH2) with hydrated magnesium chloride MgCl2•6H2O gives complexes of the type Mg(IMP)•5H2O and Mg2(IMP)3•15H2O. The FT-IR spectra of Mg(IMP)•5H2O in the region 1800–400 cm−1 showed marked similarities with that of the structurally characterized N7-bound Ni(IMP)•5H2O and Co(IMP)•5H2O complexes, while Mg2(IMP)3•15H2O exhibited distinct spectral similarities with the known Cd2(IMP)3•12H2O and Ca(IMP)•6.5H2O compounds, where a direct metal–phosphate and metal–sugar binding as well as metal–N7-coordination has been shown crystallographically. The Mg(II) ion in Mg(IMP)•5H2O is N7-bound with an indirect metal–phosphate and metal–carbonyl interaction through a coordinated water molecule and in the Mg2(IMP)3•15H2O compound it binds directly to the phosphate and to the sugar moiety as well as to the N7-site of the purine ring system.