This paper reports the syntheses and crystal structures of a manganese and a uranyl phosphonate based on 1,4,7-triazacyclononane-1,4,7-triyl-tris(methylenephosphonic acid), namely, Mn-3{C9N3H18(PO3)(3)}(H2O)(6)*center dot 1.5H(2)O (1) and UO2{C9N3H19(PO3H)(3)}-H2O (2). Compound 1 shows a unique layer structure where the hydrophobic triazacyclononane moieties all reside on one side of the inorganic backbone of the manganese phosphonate layer while the hydrophilic coordinated water molecules reside on the other side. In compound 2, the triazacyclononane moieties are immobilized on the inorganic backbone of the uranyl phosphonate chains. The magnetic properties of compound 1 and the ion exchange properties of compound 2 have been studied.