Jose Rodriguez García

Metal phosphates represent an important group of materials with established industrial applications that are still attracting special scientific interest, owing to their outstanding physical and chemical properties. In this review, we account on the different synthetic routes and applications of zirconium and titanium phosphates, with a special focus on their application in the medicinal field. While zirconium phosphate has been extensively studied and explored with several reported industrial and medicinal applications, especially for drug delivery applications, titanium phosphates have not yet attracted the deserved attention regarding their established applications. However, titanium phosphates have been the focus of several structural studies with their different polymorphic forms, varied chemical structures, and morphologies. These variations introduce titanium phosphates as a strong candidate for technological and, particularly, biomedical applications.

The structural characterization of Ni_3−xCu_xP₂O₈ (0.0 ≤ x ≤ 3.0) compositions was performed and the colour parameters of these materials measured. Solid solutions with Ni₃P₂O₈, Ni₂CuP₂O₈ and Cu₃P₂O₈ structures were obtained and the compositional range in which they are formed was established. Structural distortion was detected in these solid solutions when x increases from the variation in the unit cell parameters and that of the interatomic distances. Solid solutions with Ni₃P₂O₈ structure are stable at 1200 °C and may be used as ceramic pigments. Changes in the colour of these materials were related to the structural changes. Yellow materials are obtained from Ni_3−xCu_xP₂O₈ solid solutions with a Ni₃P₂O₈ or Ni₂CuP₂O₈ structure and a gradual change from yellow to brown is obtained with the introduction of Cu(II) in the Ni₃P₂O₈ structure, 0.0 ≤ x ≤ 0.7 at 1200 °C.

The hydrothermal synthesis and both the chemical and structural characterization of a diamin iron phosphate are reported. A new synthetic route, by using n-butylammonium dihydrogen phosphate as a precursor, leads to the largest crystals described thus far for this compound. Its crystal structure is determined from single-crystal X-ray diffraction data. It crystallizes in the orthorhombic system (Pnma space group, a = 10.1116(2) Å, b = 6.3652(1) Å, c = 7.5691(1) Å, Z = 4) at room temperature and, below 220 K, changes towards the monoclinic system P2₁/n, space group. The in situ powder X-ray thermo-diffraction monitoring for the compound, between room temperature and 1100 K, is also included. Thermal analysis shows that the solid is stable up to ca. 440 K. The kinetic analysis of thermal decomposition (hydrogenated and deuterated forms) is performed by using the isoconversional methods of Vyazovkin and a modified version of Friedman. Similar values for the kinetic parameters are achieved by both methods and they are checked by comparing experimental and calculated conversion curves.

NH ₄ [Co _{1− y} Ni _y PO ₄ ]·H ₂ O (0 ≤ y ≤ 1) single crystals were fired to prepare Co _{2− x} Ni _x P ₂ O ₇ 0 ≤ x ≤ 2 solid solutions between 800 and 1200°C. The structure of these solid solutions is α‐M ₂ P ₂ O ₇ (M = Co, Ni). The contraction of the unit cell with increasing x confirmed the formation of these solid solutions. The UV–vis–NIR spectra of these solid solutions were consistent with Co( II ) and Ni( II ) ions in the two different crystallographic sites (octahedral site and square pyramidal site) in the α‐M ₂ P ₂ O ₇ structure. Due to their thermal stability, Co _{2− x} Ni _x P ₂ O ₇ (0 ≤ x ≤ 2) solid solutions with α‐M ₂ P ₂ O ₇ structure can be used as a blue, green, brown or yellow ceramic pigment.

H₂O₂-modified carbon nitride chemoselectively photo-oxidises the methyl group of alkylphenoxylate molecule 2-(4-methylphenoxy)ehanol in water medium.

Metal-organic frameworks assembled from Ln(III), Li(I) and rigid dicarboxylate ligand, formulated as [LiLn(BDC)₂(H₂O)·2(H₂O)] (MS1-6,7a) and [LiTb(BDC)₂] (MS7b) (Ln = Tb, Dy, Ho, Er, Yb, Y_0.96Eu_0.04, Y_0.93Tb_0.07, and H₂BDC = terephthalic acid), were obtained under hydrothermal conditions. The isostructural MS1-6 crystallize in monoclinic P2₁/c space group. While, in the case of Tb³⁺ a mixture of at least two phases was obtained, the former one (MS7a) and a new monoclinic C2/c phase (MS7b). All compounds have been studied by single-crystal and powder X-ray diffraction, thermal analyses (TGA), vibrational spectroscopy (FTIR), and scanning electron microscopy (SEM-EDX). The structures of MS1-6 and MS7a are built up of inorganic-organic hybrid chains. These chains constructed from unusual four-membered rings, are formed by edge- and vertex-shared {LnO₈} and {LiO₄} polyhedra through oxygen atoms O3 (vertex) and O6-O7 (edge). Each chain is cross-linked to six neighboring chains through six terephthalate bridges. While, the structure of MS7b is constructed from double inorganic chains, and each chain is, in turn, related symmetrically to the adjacent one through the c glide plane. These chains are formed by infinitely alternating {LiO₄} and {TbO₈} polyhedra through (O2-O3) edges to create Tb–O–Li connectivity along the c-axis. Both MS1-6,7a and MS7b structures possess a 3D framework with 1D trigonal channels running along the a and c axes, containing water molecules and anhydrous, respectively. Topological studies revealed that MS1-6 and MS7a have a new 2-nodal 3,10-c net, while MS7b generates a 3D net with unusual β-Sn topology. The photoluminescence properties Eu- and Tb-doped compounds (MS5-6) are also investigated, exhibiting strong red and green light emissions, respectively, which are attributed to the efficient energy transfer process from the BDC ligand to Eu³⁺ and Tb³⁺.