Praseodymium(III) Nitrate Hexahydrate: Structure, Doping & MOF Synthesis
Praseodymium(III) nitrate hexahydrate iscommonly used in the production of electronic components, including ceramiccapacitors, magnetic bubble memories, and photochromic glass. Its uniqueoptical and electrical properties, such as its high dielectric constant andrefractive index, make it a desirable material in the electronics industry. Itis also used as a praseodymium source for the preparation of other praseodymiumcompounds. Praseodymium(III) nitrate hexahydrate can be used as: A dopant to fabricate dye-sensitized solar cells. The addition of rare earth enhances the power conversion efficiency of solar cells by narrowing the band gap of photoanode materials; A precursor to synthesize high entropy lanthanide oxysulfides (wide band gap semiconductors); To synthesize functionalized UV-emitting nanocomposite for photodynamic cancer therapy; To fabricate Pr-doped MoO3 thinfilms for gas sensing applications.
Redetermination of Praseodymium(III) nitrate hexahydrate
The structure of the title compound, Praseodymium(III) nitrate hexahydrate, was redetermined. The structure models derived from the previous determinations were confirmed, but now with all H atoms unambiguously located, revealing a complex O—H⋯O hydrogen-bonding network, extending throughout the whole structure. In the title compound, the coordination environment of the PrIII atom can best be described as a distorted bicapped square antiprism defined by three bidentate nitrate anions and four water molecules. Additionally, two lattice water molecules are observed in the crystal packing. The title compound is isotypic with several other lanthanide-containing nitrate analogues. The title compound was serendipitously obtained in low yield as a product of an experiment aimed at obtaining a PrIII-containing coordination polymer, with dicarboxylate ligands as the connecting moiety, following an earlier successful synthesis of a vanadium metal-organic framework with the same type of linkers (Liu et al., 2012). In the synthesis, 0.1 mmol Praseodymium(III) nitrate hexahydrate, along with 0.3 mmol dicarboxylic acid and four drops of 0.6 M aqueous HNO3 was dissolved in 5 ml of a 1:1 mixture of 1:1 MeOH/H2O. After seven days of heating the mixture to 363 K, the title compound was isolated as colourless crystals, suitable for single-crystal X-ray diffraction analysis.[1]
Optical Properties of Pr-Doped CeO2
A series of Pr-doped CeO2 was prepared with different molar concentrations of Pr cation through a solvothermal method combined with subsequent calcination in air, in which Ce(NO3)3∙6H2O served as cerium source, whereas Praseodymium(III) nitrate hexahydrate served as dopant. Typically, appropriate amounts of Ce(NO3)3∙6H2O and Pr(NO3)3∙6H2O with a total of 4.0 mmol were dissolved in a mixed solution of 25 mL ethylene glycol and 5 mL distilled water, and then the above-mentioned mixed solution was decanted into a 50 mL Teflon-lined stainless steel autoclave and sealed. After maintaining the solution at 200 °C for 24 h, the precursor powders were collected by centrifugation and washed with distilled water and ethanol, and then dried in air at 60 °C for 24 h. Finally, a series of Pr-doped CeO2 powders was obtained by subsequent calcination in air at 500 °C for 2 h. The as-prepared Pr-doped CeO2 powders with different molar concentrations of Pr were labeled as 1% Pr-doped CeO2, 2% Pr-doped CeO2, 3% Pr-doped CeO2, 4% Pr-doped CeO2, 5% Pr-doped CeO2 and 6% Pr-doped CeO2. Similarly, the undoped CeO2 powders were also prepared following the same procedure as control; however, in the absence of Praseodymium(III) nitrate hexahydrate, it was labeled as Undoped CeO2.[2]
Pr-doped CeO2 with different doping levels was prepared from Ce(NO3)3∙6H2O and Praseodymium(III) nitrate hexahydrate by solvothermal method without any additional reagents, in which the mixed solution of ethylene glycol and distilled water was employed as a solvent. The influences of Pr-doping on phase composition, crystal structure and morphology were investigated, as well as Pr valence and oxygen vacancy defects. The Pr cations entered into the CeO2 crystal lattice with normal trivalence and formed a Pr-CeO2 solid solution based on the fluorite structure. The larger trivalent Pr was substituted for tetravalent Ce in the CeO2 crystal and compensated by oxygen vacancy defects, which caused the local lattice expansion of the crystal lattice. Moreover, the Pr-doped CeO2 solid solutions exhibited visible color variation from bright cream via brick red to dark brown with the increasing of Pr contents. The degradation of AO7 dye was also investigated using a domestic medical ultraviolet lamp; the removal efficiency of AO7 by 1% and 2% Pr-doped CeO2 approached 100%, much higher than 66.2% for undoped CeO2.
Metal−Organic Framework Structures of Ce(III) and Pr(III) with Pyridine-2,6-dicarboxylic Acid
Standard hydrothermal conditions used for the synthesis of 1 afforded solids not suitable for X-ray crystallography. We adopted a different approach where 1 mmol of Praseodymium(III) nitrate hexahydrate and 2 mmol of pyridine-2,6-dicarboxylic acid (pdcH2) were taken in 5 mL of water in a Teflon-lined autoclave. The autoclave was heated under autogenous pressure to 180° C for 3 days and then left to cool to room temperature (RT). On allowing the filtrate from the reaction to evaporate at RT, pale green rectangular parallelepipeds of [Pr(pdc)(pdcH)2H2O]0·4H2O could be isolated in ∼65% yield. Anal. Calcd for C14H19N2O14Pr: C, 28.98; H, 3.30; N, 4.83%. Found: C, 29.06; H, 3.38; N, 4.76%. Ce(NO3)3·6H2O or Praseodymium(III) nitrate hexahydrate and pyridine-2,6-dicarboxylic acid form a linear coordination polymeric structure under hydrothermal conditions. Hexameric water clusters join these linear chains through bonding to the metal ions. Other coordinated water and the carboxylate oxygen form an intricate array of hydrogen bonding resulting in a 3D network where each metal ion shows 9-coordination with an approximate D3 symmetry. Dimeric water clusters are also located in the void spaces. In the structure containing Pr(III), the water dimers are hydrogen-bonded to the hexamers, whereas in the Ce(III) structure, the dimers and the hexamers are far apart.[3]
References
[1]Decadt R, Van Der Voort P, Van Driessche I, Van Deun R, Van Hecke K. Redetermination of [Pr(NO₃)₃(H₂O)₄]·2H₂O. Acta Crystallogr Sect E Struct Rep Online. 2012 Jul 1;68(Pt 7):i59-i60. doi: 10.1107/S1600536812028024. Epub 2012 Jun 27. PMID: 22807700; PMCID: PMC3393143.
[2]Xu Y, Wu P, Wu M, Gu Y, Yu H, Ding Z. Solvothermal Synthesis, Structural Characterization and Optical Properties of Pr-Doped CeO2 and Their Degradation for Acid Orange 7. Materials (Basel). 2022 Oct 7;15(19):6953. doi: 10.3390/ma15196953. PMID: 36234294; PMCID: PMC9572288.
[3]Ghosh SK, Bharadwaj PK. Coexistence of water dimer and hexamer clusters in 3D metal-organic framework structures of Ce(III) and Pr(III) with pyridine-2,6-dicarboxylic acid. Inorg Chem. 2003 Dec 15;42(25):8250-4. doi: 10.1021/ic034976z. PMID: 14658875.
