A series of two-dimensional lanthanide-organic materials (LnOFs), [Ln(H
3NMP)]·1.5H
2O [Ln
3+ =La
3+ (
1), Pr
3+ (
2), Nd
3+ (
3), Sm
3+ (
4), or Eu
3+ (
5); H
3NMP
3- is a residue of nitrilotris(methylenephosphonicacid)], has been isolated as microcrystalline powders from hydrothermal synthesis and characterized byhigh-reso
lution laboratory and synchrotron powder X-ray diffraction (PXRD), solid-state NMR, FTIRand FT Raman spectroscopies, CHN elemental analysis, thermogravimetry, scanning electron microscopy,and energy dispersive analysis of X-ray spectroscopy. The crystal structure of [Pr(H
3NMP)]·1.5H
2O (
2)has been solved from a combined study of ab initio methods using high-reso
lution PXRD data and high-reso
lution solid-state NMR techniques performed on [La(H
3NMP)]·1.5H
2O (
1) (
13C,
15N,
31P CPMASand 2D
1H-
1H/
31P HOMCOR/HETCOR). The structure contains a single lanthanide center which doesnot have water molecules in its first coordination sphere. This Ln
3+ center acts as the node of a neutra
lundulated two-dimensional network,
2[Pr(H
3NMP)], having a (4,4) topology, which close packs alongthe [100] direction of the unit cell (adjacent layers are related by inversion). Water molecules ofcrystallization occupy the interlayer spaces, and a one-dimensional water c
luster (spiral chain topology)is confined to the channels formed by the packing of adjacent layers. Removal of these water molecules(investigated by variable-temperature PXRD) leads to a new crystalline phase with a smaller interlayerspace. The material partially reabsorbs water from the surrounding environment, originating the parentphase. This dehydration/rehydration process has also been monitored by photo
luminescence (PL)spectroscopy, revealing that the presence of water in the interlayer spaces does not affect much the PLproperties of [Eu(H
3NMP)]·1.5H
2O (
5).