Photoluminescent 3D Lanthanide–Organic Frameworks Based on 2,5-Dioxo-1,4-piperazinylbis(methylphosphonic) Acid Formed via in Situ Cyclodehydration of Glyphosates

Hydrothermal reactions of lanthanide
nitrates with glyphosate have
resulted three new isostructural 3D lanthanide–organic frameworks,
Ln­(NO3)­(H2L) [Ln = Eu (1), Tb (2), Gd (3); H4L = 2,5-dioxo-1,4-piperazinylbis­(methylphosphonic)
acid], with good yields, where H4L as a new ligand was
formed via in situ cyclodehydration of original ligand glyphosates
during the hydrothermal reaction. The compounds were thoroughly characterized
by IR, UV–vis, elemental analysis, single-crystal X-ray diffraction
analysis, powder X-ray diffraction analysis, and thermogravimetric/differential
thermal analysis (TG-DTA). Three compounds display 3D 6,6-connected
open frameworks with 413·62 topology possessing
1D channels in which NO3– anions act
as troglodytes by chelating Ln3+ centers. The TG-DTA study
of the compounds showed remarkable thermal stability up to 380 °C.
Under room temperature UV-light irradiation, the Eu3+ and
Tb3+ compounds showed the corresponding characteristic
Ln3+ intra 4fn emission peaks.
The triplet energy level (21882 cm–1) of the ligand
(H4L) was determined from the emission spectrum of its
Gd3+ compound at 77 K. The emission lifetimes (1.54 ms
of 5D0 for compound 1 and 1.98
ms of 5D4 for compound 2) and absolute
emission quantum yields (10.1% for compound 1 and 5.9%
for compound 2) were also determined.