Layered Uranyl Phosphonates Encapsulating Co(II)/Mn(II)/Zn(II) Ions: Exfoliation into Nanosheets and Its Impact on Magnetic and Luminescent Properties

Abstract

Layered heterometallic 5f-3d uranyl phosphonates can exhibit unique luminescent and/or magnetic properties, but the fabrication and properties of their 2D counterparts have not been investigated. Herein we report three heterobimetallic uranyl phosphonates, namely, [(UO 2 ) 3 M(2-pmbH) 4 (H 2 O) 4 ] • 2H 2 O [MU, M=Co(II), CoU; Mn(II), MnU; Zn(II), ZnU; 2-pmbH 3 = 2-(phosphonomethyl)benzoic acid]. They are isostructural and display two-dimensional layered structures where the M(II) centers are encapsulated inside the windows generated by the diamagnetic uranyl phosphonate layer. Each M(II) has an octahedral geometry filled with four water molecules in the equatorial positions and two phosphonate oxygen atoms in the axial positions. The uranium atoms adopt UO 7 pentagonal bipyramidal and UO 6 square bipyramidal geometries. The lattice and coordination water molecules can be released by thermal treatment and reabsorbed in a reversible manner, accompanied with changes of magnetic dynamics. Interestingly, the bulk samples of MU can be exfoliated in acetone via freezing and thawing processes forming nanosheets with single-layer or two-layer thickness (MU-ns). Magnetic studies revealed that the CoU and MnU systems exhibited field-induced slow magnetization relaxation at low temperature. Compared with crystalline CoU, the magnetic relaxation of the CoU-ns aggregates is significantly accelerated. Moreover, photoluminescence measured at 77 K showed slight red-shift of the five characteristic uranyl emission bands for ZnU-ns in comparison with those of the crystalline ZnU. This work gives the first examples of 2D materials based on 5f-3d heterometallic uranyl phosphonates and illustrates the impact of dimension reduction on their magnetic/optical properties.

Regulating the Porosity of Uranyl Phosphonate Frameworks with Quaternary Ammonium: Structure, Characterization, and Fluorescent Temperature Sensors

“…The UV–vis spectra of the three compounds show two strong and broad absorption peaks at 200–450 nm (Figure ). The strong peaks at around 320 nm are assigned to ligand-to-metal (from equatorial electron-donating atom to uranium ion) charge transfer (LMCT) . The slightly weaker broad peaks at around 420 nm are caused by the Laporte forbidden LMCT transition from the O 2p orbital to the U 5f/6p orbital. , Multiple peaks caused by the typical vibration fine structure of uranyl compounds appear at around 420 nm in UPF-107 and 108 (393.56, 406.04, 415.40, and 427.87 nm for UPF-107 and 406.83, 417.74, 429.42, and 442.64 nm for UPF-108 ). , …”

A homochiral hexagadolinium phosphonate cluster with a large magnetocaloric effect

“…Organophosphonic acid ligand has a versatile coordination mode, which can make metal organophosphonate coordination polymers with 0D, 1D, 2D and 3D structures through the coordination of various metal ions, which has potential application prospects in ion exchange, catalysis, optics, biology and magnetic. [33][34][35][36][37][38][39][40][41][42] However, Among the numerous metal phosphonates reported so far, many are layered materials, while lanthanide clusters based on phosphonates are limited, chiral phosphonates lanthanide clusters are extremely scarce. In this context, we chose a chiral amino acid phosphonic acid as ligand to react with the rare earth metal Gd(III) salt at room temperature, obtaining a new homochiral gadolinium phosphonate cluster R-[Gd 6 (pmhpH) 1a).…”