Rich diversity of single-ion magnet features in the linear OCu(III)O(-) ion confined in the hexagonal channels of alkaline-earth phosphate apatites.

Following our recent discovery of slow spin relaxation in the unique [OCu(III)O](-) anion located in the apatite-type pigment A10(PO4)6(CuxOH1-x-y)2, where A = Sr, we present the magnetic behavior of this anion for the cases of A = Ca and Ba, which provides evidence for a cation field impact on the properties of a single-ion magnet molecular anion.