Deuterium kinetic isotope effects are widely used in chemical and biological research. Deuterium thermodynamic effects on the aqueous synthesis of inorganic materials, however, seem-not to have been recognized. Here we report that the simple replacement of H2O with D2O in the synthesis of a solid-state manganese complex results in a new structurally and magnetically distinct phase. When iron oxides are synthesized, the relative amount of the mineral phases obtained in H2O vs D2O is different. The morphology and magnetic properties of the iron core of the iron storage protein ferritin are likewise different when mineralization is carried out in heavy water. The formation of extra inorganic solids, change in the ratio of two phases or alteration of a single phase morphology in D2O suggest that new inorganic and bioinorganic metal complexes might be obtained by using the thermodynamic isotope effect.