Europium compounds are compounds formed by the lanthanide metal europium (Eu). In these compounds, europium generally exhibits the +3 oxidation state, such as EuCl3, Eu(NO3)3 and Eu(CH3COO)3. Compounds with europium in the +2 oxidation state are also known. The +2 ion of europium is the most stable divalent ion of lanthanide metals in aqueous solution.无机化学丛书. pp 187-188. 1.2.3 氧化态及电极电势. Many europium compounds fluoresce under ultraviolet light due to the excitation of electrons to higher energy levels. Lipophilic europium complexes often feature acetylacetonate-like ligands, e.g., Eufod.
Properties of europium compounds
Formula Color Crystal structure Space group No EuBr2 white SrBr2 P4/n 85 EuBr3 grey PuBr3 Cmcm 63 EuCl2 white PbCl2 Pnma 62 EuCl3 yellow UCl3 P63/m 176 EuF2 dark yellowish fluorite Fmm 225 EuF3 white LaF3 Pnma 62 EuI2 yellow monoclinic P21/c 14 EuI3 colorless BiI3 R 148 EuH2 dark red PbCl2 Pnma 62 Eu(OH)2 pale yellow orthorhombic P21am 26 Eu(OH)3 pale pink《无机化学丛书》. 第七卷 钪 稀土元素. 易宪武 等主编. 科学出版社. P168~171. (2)氢氧化物 hexagonal P63/m 176 EuO violet fluorite Fmm 225 Eu2O3 white monoclinic C2/m 12 EuS black fluorite Fmm 225 EuSe black fluorite Fmm 225 EuTe black fluorite Fmm 225 EuSO4 white orthorhombic Pnma 62 Eu2(SO4)3 white monoclinic C2/c 15
Chalcogenides
Oxides
Europium(II) oxide can be obtained by the reduction of europium(III) oxide with metallic europium at high temperatures. It has a rock-salt structure, is a deep red solid, and is ferromagnetic at 77 K. It has the potential to become a magnetic refrigeration material (ΔSmag=−143 mg/cm3 K，50 kOe).无机化学丛书. pp 200-203. 2. 氧族化合物; pp 215. 3. 氧化物及氢氧化物. Europium(II) sulfide is also ferromagnetic, but europium(II) telluride is antiferromagnetic. The mixed valence oxide Eu3O4 of europium can be obtained by reducing europium(III) oxide with a reducing agent in a hydrogen atmosphere, such as:
2 Eu2O3 + 2 EuOCl + 2 LiH → 2 Eu3O4 + 2 LiCl + H2↑
Europium(III) oxide is the most stable oxide of europium, a light pink solid with a high melting point, which can be obtained by the thermal decomposition of europium(III) nitrate. It reacts with water to give EuOOH.Batsanov, S. S.; Deribas, A. A.; Kustova, G. N. Reaction of rare earth metal oxides with water. Zhurnal Neorganicheskoi Khimii, 1967. 12 (9): 2283-2286. . The reaction of soluble europium salts with ammonia or sodium hydroxide can precipitate hydroxide Eu(OH)3, but in the presence of polyhydroxyl compounds (such as glucose), the precipitation is incomplete.
Eu(H2O) and Eu(H2O)2 complexes can be obtained by the reaction of metallic europium in solid argon with water. Eu(H2O) is rearranged to obtain HEuOH, which is further decomposed into EuO and H2; Eu(H2O)2 is decomposed into Eu(OH)2 and H2.
Other chalcogenides
Europium(III) sulfide can be obtained by the decomposition of Eu(Et2NCS2)3 then at 500~600 °C.Kuzmina, N. P.; Ivanov, R. A.; Paramonov, S. E.; Martynenko, L. I. Volatile lanthanide diethyldithiocarbamates as precursors for lanthanide sulfide film deposition. Proceedings - Electrochemical Society, 1997. 97 (25). 880-885. . Europium(III) sulfide can also be obtained by the decomposition of the thiocyanate Eu(NCS)3;Grizik, A. A.; Eliseev, A. A.; Borodulenko, G. P.; Tolstova, V. A. Low-temperature form of Ln2S3 (Ln = europium, samarium, or gadolinium). Zhurnal Neorganicheskoi Khimii, 1977. 22 (2): 558-559. . Its two crystal forms, α-type and γ-type, belong to orthorhombic and cubic crystal systems, respectively. Europium(II) sulfide is prepared by sulfiding the oxide at temperatures sufficiently high to decompose europium(III) oxide:
Eu2O3 + 3 H2S → 2 EuS + 3 H2O + S
The selenides, europium(III) selenide and europium(II) selenide, and tellurides, europium(II) telluride and europium(III) telluride, are also known. They can generally be prepared by reacting europium with selenium or tellurium in a vacuum ampoule at a high temperature. Europium(II) selenide can also be obtained by heating europium(II) oxalate with an excess of selenium.
Europium oxysulfide is obtained by reacting europium(III) oxide in a carbon disulfide/argon/low-pressure oxygen stream. It is a solid of the triclinic crystal system, with the space group Pm1, and its optical band gap is 4.4 eV. Europium oxyselenide and europium oxytelluride can be prepared by reacting europium(III) oxide with selenium or tellurium at 600 °C.Sadovskaya, O. A.; Yarembash, E. I.; Eliseev, A. A. Europium oxychalcogenides. Izvestiya Akademii Nauk SSSR, Neorganicheskie Materialy, 1974. 10 (11): 2076-2077. . The oxyselenide is heated in air and oxidized to oxyselenite.Markku Leskela. Thermal stability and infrared absorption spectrum of europium oxyselenide (Eu2O2Se). Finnish Chemical Letters, 1980 (6): 173-176. . A similar reaction occurs with oxytelluride to give Eu2TeO6.
Halides
Europium metal reacts with all the halogens: 2 Eu + 3 X2 → 2 EuX3 (X = F, Cl, Br, I) This route gives white europium(III) fluoride (EuF3), yellow europium(III) chloride (EuCl3), gray europium(III) bromide (EuBr3), and colorless europium(III) iodide (EuI3). Europium also forms the corresponding dihalides: yellow-green europium(II) fluoride (EuF2), colorless europium(II) chloride (EuCl2) (although it has a bright blue fluorescence under UV light), colorless europium(II) bromide (EuBr2), and green europium(II) iodide (EuI2).Holleman, A. F.; Wiberg, E. "Inorganic Chemistry" Academic Press: San Diego, 2001. p. 1706, .
Europium can form all four trihalides. They are strong electrolytes in water, and all but the fluoride are soluble in water. Anhydrous europium trihalides can be prepared by reacting oxides or the halides' hydrates:无机化学丛书. pp 210-215. 2. 卤素化合物 Eu2O3 + 6 NH4Cl → 2 EuCl3 + 3 H2O + 6 NH3↑ EuCl3·6H2O + 6 SOCl2 → EuCl3 + 6 SO2↑ + 12 HCl↑ Among them, europium(III) iodide can only be obtained by reacting europium(III) oxide and hydroiodic acid.Emel'yanov, V. I.; Kuznetsova, L. I.; Abramova, L. V.; Ezhov, A. I. Systems Eu2O3-HI-H2O and EuI3-HI-H2O at 25°C. Zhurnal Neorganicheskoi Khimii, 1997. 42(8): 1394-1396.
In addition, europium can also form all four dihalides. They can generally be prepared by reducing the corresponding europium trihalide with hydrogen gas or europium:
2 EuX3 + H2 → 2 EuX2 + 2 HX
Europium(II) iodide can also be obtained by direct treating the reagent with ammonium iodide. Of the dihalides, EuF2 and EuI2 are yellow, and EuCl2 and EuBr2 are white, although when irradiated by ultraviolet light, EuCl2 has a bright blue fluorescence.
Pnictides
Europium(III) nitride is a black solid that can be prepared by the reaction of metallic europium in a stream of ammonia in corundum boats in fused quartz tubes at 700 °C:
2 Eu +2 NH3 → 2 EuN + 3 H2
In this reaction, the europium is oxidized and the hydrogen in the ammonia is reduced. Europium(III) nitride shows Van Vleck paramagnetism and crystallises in the rock salt structure. Thin films of rare earth nitrides, including europium(III) nitride, tend to form oxides in the presence of oxygen. Europium(III) phosphide can be produced from a solution of europium metal in liquid ammonia with phosphine at -78 °C. This produces hydrogen and first Eu(PH2)2 is formed, but it then decomposes to EuP and PH3. It crystallises cubically like NaCl. Pure europium(III) phosphide also shows Van Vleck paramagnetism. Europium(II) diarsenide, Eu2As2, is unique which it contains the ion instead of the As3- ion, unlike other lanthanide arsenides. It crystallizes in the distorted Na2O2 structure, similar to nickel arsenide, and is produced from reacting europium and arsenic at 600 °C. Other arsenides, antimonides and bismuthides of europium are also known.
Organoeuropium compounds
Organoeuropium compounds are a class of organic metal compounds containing Eu-C bonds. The cyclopentadienyl complexes of europium were studied in the early stage. They can be prepared by the reaction of sodium cyclopentadienide and anhydrous europium halide in tetrahydrofuran, such as:无机化学丛书. pp 338. 2.3.7 稀土元素有机化合物. EuCl3 + 3 C5H5Na → (C5H5)3Eu + 3 NaCl EuI2 + 2 (C5HiPr4)Na → (C5HiPr4)2Eu + 2 NaI Europium bis(tetraisopropylocene) is an orange-red solid that can be melted at 165 °C. The complex of cyclononatetraene and europium(II) can be prepared by a similar method, and its toluene solution emits blue-green fluorescence at 516 nm, compared with other organic europium(II) sandwich complexes (about 630 nm) with a clear blue shift.
In addition to the preparation of organo-europium compounds by metathesis reaction, metal europium can also be directly involved in the reaction, such as the reaction of europium and pentamethylcyclopentadiene to generate light orange bis(pentamethylcyclopentadiene) europium; and the reaction between cyclooctatetraene and europium gives the pale green cyclooctatetraene europium.
Other compounds
Europium(II) sulfate is the sulfate of divalent europium, which can be obtained by electrolysis of europium sulfate solution with mercury as the cathode, or by reducing europium(III) chloride with zinc amalgam, and then reacting with sulfuric acid.无机化学丛书. pp 203. 3. Ln2+的水溶液体系. It reacts with sodium carbonate or ammonium oxalate to obtain europium(II) carbonate and europium(II) oxalate, respectively:
EuSO4 + Na2CO3 + xH2O → EuCO3·xH2O + Na2SO4 EuSO4 + (NH4)2C2O4(saturated) + H2O → EuC2O4·H2O + (NH4)2SO4
Europium(III) sulfate can be directly obtained by reacting europium(III) oxide and dilute sulfuric acid, and crystallized, and dehydration of hydrate can obtain the anhydrous form. Europium(III) sulfate is soluble in water, and its octahydrate has a solubility of 2.56 g at 20 °C.无机化合物合成手册. pp 258-259. 819 硫酸盐. Europium(III) sulfite (Eu2(SO3)3·nH2O，n=0, 3, 6Koskenlinna, Markus; Niinisto, Lauri. Lanthanoid sulfites. III. Preparation and properties of two isomorphous series of lanthanoid sulfite hydrates. Finnish Chemical Letters, 1975. (3-4): 83-88. .) and its basic salt (EuOHSO3·4H2O) are known, and heating the sulfite in a carbon monoxide atmosphere will dehydrate to obtain the anhydrous form, and after Eu2O2SO4, finally obtain the oxysulfide Eu2O2S.
Europium(II) hydroxide can be obtained by reacting metallic europium with sodium hydroxide.H. Baernighausen. Lattice constants and space group of the isotypic compounds Eu(OH)2·H2O, Sr(OH)2·H2O, and Ba(OH)2·H2O. Zeitschrift fuer Anorganische und Allgemeine Chemie, 1966. 342 (5-6): 233-239. ISSN: 0044-2313. Europium(II) hydroxide belongs to the orthorhombic crystal system. It decomposes to form europium(III) hydroxide, a pale pink solid that reacts with acids and produces europium(III) salts. It can be prepared by reacting europium with water, or by reacting europium(III) nitrate with hexamethylenetetramine at 95 °C or with ammonium hydroxide.
Europium(III) nitrate can be obtained by reacting europium(III) oxide and nitric acid and crystallizing. The crystal is dried with 45~55% sulfuric acid to obtain hexahydrate.高胜利, 刘翊纶, 杨祖培. 稀土硝酸盐的制法、性质及结构 . 稀土, 1990 (4): 23-28. Its anhydrous form can be obtained by the reaction of europium oxide and dinitrogen tetroxide, while heating the hydrate can only obtain the basic salt EuONO3.无机化合物合成手册. pp 260-261. 820 硝酸盐. Europium(III) phosphate can be obtained by reacting europium(III) chloride and diammonium hydrogen phosphate (or europium(III) oxide and 5 mol/L phosphoric acid), and its white monohydrate precipitates from solution. It loses water at 600~800 °C, and changes from a hexagonal phase with water to an anhydrous monoclinic phase. Europium(III) oxide reacts with arsenic pentoxide to obtain europium(III) arsenate, which is a colorless crystal with a xenotime structure.