Phosphoric acid forms two distinct coordination compounds with manganese salts in aqueous media, a two-dimensional layered structure, [Mn(HPO4).(H2O)(3)], 1, under ambient conditions, and a three-dimensional synthetic mineral, [Mn-5(mu-OH2)(2)(HPO4)(2)(PO4)(2)(H2O)(2)], 2, under hydrothermal procedures, at 120degreesC. In compound 1, the oxygen atom of the doubly deprotonated phosphoric acid interconnects the metal centers to form a layered structure. The neutral hydrophilic layers of 1 are separated by 5.5 Angstrom and may potentially intercalate hydrophilic organic guest molecules. The metal centers in 2 are octahedral and bridged by PO43-, HPO42-, and OH2 groups to form a complex three-dimensional network. XPS analysis on 1 and 2 confirms that manganese exists in the +2 oxidation state. Compound 2 is a poor ion exchanger, but some improvement is observed on partial dehydration. The magnetic properties of both 1 and 2 were studied in detail to examine the amplitude of the magnetic interactions through phosphate ligand bridges. While 1 reveals dominant antiferromagnetic interactions between the spin carriers, a complete investigation of the magnetic properties of 2 revealed its true nature to be a glassy magnet.