Photochemical synthesis and structural characterization of (η-C5Me5)3Mo3(CO)4(μ2-H)(μ3-O): an unprecedented 46-electron trimolybdenum cluster containing a localized monoprotonated Mo---Mo double bond

Irradiation of the 30-electron Mo₂(η⁵-C₅Me₅)₂(CO)₄ and Re₂(CO)₁₀ in toluene solution (containing H₂O) afforded (in 1–2% yields) a novel triangular metal cluster, (η⁵-C₅Me₅)₃Mo₃(CO)₄(η₂-H)(η₃-O) (1), which was characterized by a single-crystal X-ray diffraction study. Compound 1, of pseudo C_s-m symmetry, has a triangulo-Mo₃(η₃-O) core with composite Mo---H---Mo and Mo---Mo electron-pair bonds along one unusually short edge (2.660(1) Å) and Mo--- electron-pair bonds along the other two edges (2.916(1) and 2.917(1) Å). The edge-bridged hydride ligand, which displays a characteristic high-field proton NMR resonance at δ −17.79 ppm, was not found from the crystallographic determination but was located via a quantitative potential-energy-minimization method. This procedure unambiguously established that the optimized hydrogen position, which corresponds to a distinct coordination site with identical Mo---H distances of 1.85 Å, is the only one that can be sterically occupied by a metal-bound hydride ligand. This 46-electron species is the first electron-deficient trimolybdenum cluster containing a monoprotonated Mo---Mo double bond; its existence is attributed to ligand overcrowding due to the bulky pentamethylcyclopentadienyl rings. Black (η⁵- C₅Me₅)₃Mo₃(CO)₄(η₂-H)(η₃-O) · 1/2THF crystallizes with two formula species in a triclinic unit cell of P1 symmetry with a 8.603(4), b 11.115(4), c 19.412(11) Å, 80.69(4)°, β 101.10(4)°, and γ 98.88(3)° at −40° C. Least-squares refinement (RAELS with 221 variables) of one independent Mo₃ molecule and a centrosymmetrically-disordered THF molecule converged at R₁(F) 5.62%, R₂(F 6.88% for 8460 independent diffractometry data (I₀ ρ 3σ(I₀ collected at −40° C with Mo-K radiation     

H NMR Spectra and electronic structure of binuclear niobocene and titanocene containing fulvalene ligands

¹H NMR spectra of binuclear metallocene hydride complexes, (η⁵ : η⁵-C₁₀H₈)(C₅H₅)₂M₂(μ-H)₂ (M = Nb, 20°C and Ti, (−60 to +25°C), were studied. The Nb complex is diamagnetic and gives a high resolution spectrum. The coordination of bridging hydride H atoms provides Nb atoms with complete 18 electron configuration. In its ground state, the Ti complex is also diamagnetic (the spectrum at −60°C agrees to that) in spite of only 17 electron configuration of each Ti atom. However, the population of the excited triplet state in the case of the Ti complex is appreciable at temperatures higher than −30°C, the proton resonance lines being shifted downfield and significantly broadened as compared with the spectrum at −60°C.     

Structure cristalline et conformation en solution aqueuse de la carnosine (β-alanyl-L-histidine)

Carnosine (β-alanyl-L-histidine) is a biologically active molecule involved in muscular metabolism. It crystallises in the C; space group with a = 24.725 Å b = 5,427 Å c = 8,004 Å β = 100,2° (Z = 4)

In the crystal, acid and basic groups are engaged in hydrogen bonds whose strength is evaluated through IR frequencies. Molecular conformation in the solid state is defined by τ₁ = /t-177° τ₂ = −38° φ = −96° ψ = +131° χ₁ = 181° χ₂₁ = 62°

NMR study of carnosine in aqueous solution indicates that rotation about CH₂-CH₂ is free and that the other angles take the following values: Ø −150° or −90° and X₁ = 165° or 315°. Infrared and Raman spectra suggest that τ₂ undergoes small changes when going from crystal to solution while ψ is close to +150°.     

Hydrothermal syntheses and crystal structures of bimetallic cluster complexes [{Cd(phen)2}2V4O12]·5H2O and [Ni(phen)3]2[V4O12]·17.5H2O

The hydrothermal reactions of vanadium oxide starting materials with divalent transition metal cations in the presence of nitrogen donor chelating ligands yield the bimetallic cluster complexes with the formulae [{Cd(phen₂)₂V₄O₁₂]·5H₂O (1) and [Ni(phen)₃]₂[V₄O₁₂]·17.5H₂O (2). Crystal data: C₄₈H₅₂Cd₂N₈O₂₂V₄ (1), triclinic. a=10.3366(10), b=11.320(3), c=13.268(3) Å, =103.888(17)°, β=92.256(15)°, γ=107.444(14)°, Z=1; C₇₂H₁₃₁N₁₂Ni₂O_29.5V₄ (2), triclinic. a=12.305(3), b=13.172(6), c=15.133(4), =79.05(3)°, β=76.09(2)°, γ=74.66(3)°, Z=1. Data were collected on a Siemens P4 four-circle diffractometer at 293 K in the range 1.59° <θ<26.02° and 2.01°<θ<25.01° using the ω-scan technique, respectively. The structure of 1 consists of a [V₄O₁₂]⁴⁻ cluster covalently attached to two {Cd(phen)₂}²⁺ fragments, in which the [V₄O₁₂]⁴⁻ cluster adopts a chair-like configuration. In the structure of 2, the [V₄O₁₂]⁴⁻ cluster is isolated. And the complex formed a layer structure via hydrogen bonds between the [V₄O₁₂]⁴⁻ unit and crystallization water molecules.     

The X-ray analysis of dihydroheliangine monochloroacetate

In connection with heliangine, extracted from leaves of Helianthus tuberosus L., the crystal structure of dihydroheliangine monochloroacetate, C₂₂H₂₉C₇Cl, has been determined by X-ray methods. The tetragonal unit cell with dimensions, A = 13·77, C = 11·95 Å, contains four molecules, the space group being P4₁ - C₄² or P4₃ - C₄⁴. Using a three-dimensional Patterson function and minimum functions, a majority of atomic positions were determined. Further elucidation of the structure was continued by alternative application of successive least squares treatment and Fourier syntheses. The structure thus determined is fully consistent with the chemical results obtained by Morimoto et al. The final R-value is 0·134 (using 1680 data with sin² θ/λ² < 0·20) or 0·152 (using 2419 data with sin²θ/λ² < 0·27).     

Order parameters of the mesogenic core in two nematic liquid crystals containing a four-unit link

A series of compounds containing a four-unit link, 4'-n-alkylphenyl-4-n-hexyloxycinnamates, has been synthesized, and their mesomorphic behaviour has been determined. The orientational ordering of two compounds in this series has been studied in detail by 2D carbon-13 nuclear magnetic resonance with variable angle sample spinning. The carbon-proton dipolar coupling constants were obtained and the order parameters were calculated for different molecular segments (two phenyl rings, the central link containing an ethylenic motif, and the methylene carbons of the alkoxy chain). The temperature dependence of the local order parameters of each fragment were determined using these data and C-13 chemical shifts which were measured as a function of temperature. In these non-rigid molecules, the ratio between the order parameters of the two phenyl rings was found to be temperature dependent. The ring bearing the double bond is more ordered at low temperatures compared to the ring bearing the short alkyl chain, but this behaviour is reversed near the clearing point. The position of the major axis of the rigid core was calculated from the order parameter of one ring and the order parameter of the ethylenic link. It was found that this major axis forms a constant angle with respect to the para axis of the phenyl ring connected to the ethylenic group. On the other hand, the angle of this major axis with respect to the para axis of the phenyl ring connected to the carboxylic group is temperature dependent, varying from 11° at T/T_NI = 0·92 to 7° at T/T_NI = 0·98.     

Studies of π-bonding perturbation in the tungsten-nitrogen multiple bond of isopropylimido tungsten(VI) complexes: The crystal and molecular structures of [W(NCHMe2)Cl4]2·C6H6 and [W(NCHMe2)Cl5][NEt4]

¹³C NMR chemical shift data for the -carbon (δ) of a variety of tungsten isopropylimido complexes indicate that the extent to which the nitrogen lone pair participates in multiple bonding to tungsten depends on the form of the complex and the ligands involved. The structures of [W(NCHMe₂)Cl₄]₂·C₆H₆ (1a) and [W(NCHMe₂)Cl₅][NEt₄] (7) which show widely different δ values, have been determined by single-crystal X-ray diffraction methods. Crytals of 1a are triclinic space group P , with a = 6.394(2), b = 8.890(3), c = 11.205(2) Å and = 109.95(2)°, β = 98.91(2)°, γ = 93.96(2)°; crystals of 7 are orthorhombic, space group Pnma, with a = 13.667(5), b = 15.152(2), c = 9.432(2) Å. Both structures were solved by Patterson and Fourier methods and refined to an R value of 0.050 for 1325 observed data of 1a and to an R value of 0.050 for the 1157 observed data of 7. Complex 1a is dimeric with a W---N bond length of 1.697(12) Å and complex 7 is monomeric with a longer W---N bond length of 1.763(16) Å. Comparison of the W---Cl bond lengths and correlations with π-bonding to make an 18-electron count, indicates that the W---N bond lengths differ in the two complexes as a result of overall π-bonding requirements.     

Studies on organolanthanide complexes : LXIII. Synthesis, spectroscopic and X-ray crystallographic characterization of new early organolanthanide, organoyttrium hydride and organoholmium hydroxide complexes

Organolanthanide chloride complexes [(CH₃OCH₂CH₂C₅H₄)₂Ln(μ-Cl)]₂ (Ln = La, Pr, Ho and Y) react with excess NaH in THF at 45°C to give the dimeric hydride complexes [(CH₃OCH₂CH₂C₅H₄)₂Ln(μ-H)]₂, which have been characterized by IR, ¹H NMR, MS and XPS spectroscopy, elemental analyses and X-ray crystallography. [(CH₃OCH₂CH₂C₅H₄)₂Y(μ-H)]₂ crystallizes from THF/n-hexane at −30°C, in the triclinic space group P1 with a = 8.795(2) Å, b = 11.040(1) Å, c = 16.602(2) Å, = 93.73(1)°, β = 91.82(1)°, γ = 94.21(1)°, D_c = 1.393 gcm⁻³ for Z = 2 dimers. However, crystals of [(CH₃OCH₂CH₂C₅H₄)₂Ho(μ-OH)]₂ were obtained by recrystallization of holmium hydride in THF/n-hexane at −30°C, in the orthorhombic space group Pbca with a = 11.217(2) Å, b = 15.865(7) Å, c = 17.608(4) Å, D_c = 1.816 gcm⁻³ for Z = 4 dimers. In the complexes of yttrium and holmium, each Ln atom of the dimers is coordinated by two substituted cyclopentadienyl ligands, one oxygen atom and two hydrogen atoms (for the Y atom) or two hydroxyl groups (for the Ho atom) to form a distorted trigonal bipyramid if the C(η⁵)-bonded cyclopentadienyl is regarded as occupying a single polyhedral vertex.     

New aspects of the reaction of silver(I) cations with the ethylenediaminetetraacetate ion

The highly neutralized ethylenediaminetetraacetate (EDTA) titrant (95–99% as Y⁴⁻ anion) precipitates with Ag⁺ cations to form the Ag₄Y species, in aqueous medium, which is well characterized from conductometric titration, thermal analysis and potentiometric titration of the silver content of the solid. The precipitate dissolves in excess Y⁴⁻ to form a complex, AgY³⁻. Equilibrium studies at 25°C and ionic strength 0.50 M (NaNO₃) have shown from solubility and potentiometric measurements that the formation constant (95% confidence level) β₁ = (1.93 ± 0.07) × 10⁵ M⁻¹ and the solubility products are K_S0 = [Ag +]⁴[Y⁴⁻] = (9.0 ± 0.4) × 10⁻¹⁸ M⁵ and K_S1 = [Ag +]³[AgY³⁻] = (1.74 ± 0.08) × 10⁻¹² M⁴. The presence of Na⁺, rather than ionic strength, markedly affects the equilibrium; the data at ionic strength 0.10 M are: β₁ = (1.19 ± 0.03) × 10⁶ M⁻¹, K_S0 = (1.6 ± 0.4) × 10⁻¹⁹ M⁵ and K_S1 = (1.9 ± 0.5) × 10⁻¹³ M⁴; at ionic strength tending to zero; β₁ = (1.82 ± 0.05) × 10⁷ M⁻¹, K_S0 = (2.6 ± 0.8) × 10⁻²² M⁵ and K_S1 = (5 ± 1) × 10⁻¹⁵ M⁴. The intrinsic solubility is 2.03 mM silver (I) in 0.50 M NaNO₃. Well-defined potentiometric titration curves can be taken in the range 1–2 mM with the Ag indicator electrode. Thermal analysis revealed from differential scanning calorimetry a sharp exothermic peak at 142°C; thermal gravimetry/differential thermal gravimetry has shown mass loss due to silver formation and a brown residue, a water-soluble polymeric acid (decomposition range 135–157°C), tending to pure silver at 600°C, consistent with the original Ag₄Y salt.     

Effect of iron concentration on the thermal behaviour of γ-Mn2O3

Samples of γ-Mn₂O₃ with various iron contents are obtained by co-precipitation from appropriate amounts of manganese sulphate and ferric nitrate solutions by a concentrated (2.5 N) boiling solution of sodium hydroxide. Thermal analysis, X-ray diffraction and IR spectroscopy of the specimens reveal that the presence of iron in γ-Mn₂O₃ up to 15 to 25 at.% leads to formation of a single phase γ-Mn₂O₃ solid solution, which is partly reduced to Mn₃O₄ around 680 °C and finally transforms to the -Mn₂O₃ phase on heating at or above 950 °C. With increasing iron concentration beyond 25 at.%, the formation of a ferrite phase has been detected in addition to the γ-Mn₂O₃ solid solution. However, this ferrite phase is thermally unstable and breaks down on heating around 600°C.     

The organic ligands as template: the synthesis, structures and properties of a series of the layered structure rare-earth coordination polymers

A series of new 2D-layered structural rare-earth coordination polymers with the general formal [Ln(C₈H₄O₅)(H₂O)₅]·(H₂O)·(C₈H₄O₅)_1/2 (Ln=Eu for (1); Gd for (2); Tb for (3); Dy for (4); and Er for (5)) have been yielded by hydrothermal synthesis. The coordination polymers crystallize in monoclinic space group C/2c with a=19.838(16), b=10.529(8), c=17.752(14) Å, β=107.503(14)° for (1), with a=19.823(7), b=10.552(4), c=17.762(6) Å, β=107.443(6)° for (2), with a=19.770(4), b=10.519(2), c=17.698(4) Å, β=107.52(3)° for (3), with a=19.632(2), b=10.492(2), c=17.617(3) Å, β=107.470(12)° for (4), with a=19.648(7), b=10.480(3), c=17.598(6) Å, β=107.502(6)° for (5), respectively. And the metal ions (Ln³⁺) are located in nine-member coordination environment. The carboxyl groups from 5-hydroxyisophthalate chelate the metal ions to form 1D helical cation chains. It is interesting that these helical cation chains are arranged to form 2D anion–cation layers by the uncoordinated ligands' anions as template. And the luminescence properties of the rare-earth ions are studied in the paper.     

Solid state synthesis and characterization of iron（Ⅱ） pyrophosphate Fe2P2O7

Offwhite pure Fe_2P_2O_7 was synthesized through solid phase reaction using Fe_2O_3 and NH_4H_2PO_4 in argon atmosphere.The reaction products of Fe_2O_3 and NH4_H_2PO_4 at a series of temperatures from 400 to 900℃were characterized by XRD.Comparison and analysis of XRD patterns of resultant products indicated well-crystallized Fe_2P_2O_7 could be obtained over 630℃and Fe_2P_2O_7 prepared at 700℃was triclinic in cell type.Comparison of the cell parameters proved that the as-prepared Fe_2P_2O_7 belonged toβ- Fe_2P_2O_7 in crystal phase and SEM showed its size distribution was 0.5-2μm.     

Reactions of tetrakis(trifluoromethyl) diphosphine and bis(trifluoromethyl) phosphine with ruthenium carbonyl clusters; X-ray structure of tetraruthenium carbonyl cluster derivatives

Reaction of [Ru₃(CO)₁₂ with (CF₃)₂P---P(CF₃)₂ in p-xylene at 140°C yielded the compounds [Ru₄(CO)₁₃{μ-P(CF₃)₂}₂] (1), [Ru₄(CO)₁₄{μ-P(CF₃)₂}₂] (2) and [Ru₄(CO)₁₁{μ-P(CF₃)₂}₄] (3). Reaction with [(μ-H)₄Ru₄(CO)₁₂] under similar conditions yielded [(μ-H)₃Ru₄(CO)₁₂{μ-P(CF₃)₂}] (4). All four compounds have been characterised by X-ray crystallography. The fluxional behaviour of the hydrides in 4 has also been studied by variable-temperature NMR spectroscopy. Compounds 1, 2 and 4 were also obtained from the reactions of Ru₃(CO)₁₂ with (CF₃)₂PH in dichloromethane at 80°C.     

Study of the N2 bΠu state via 1 + 1 multiphoton ionization

Medium-resolution spectra of the N₂ b¹Π_u-X¹Σ_g⁺ band system were recorded by 1 + 1 multiphoton ionization. In the spectra we found different linewidths for transitions to different vibrational levels in the b ¹Π_u state: Δν₀ = 0.50 ± 0.05 cm⁻¹, Δν₁ = 0.28 ± 0.02 cm⁻¹, Δν₂ = 0.65 ± 0.06 cm⁻¹, Δν₃ = 3.2 ± 0.5 cm⁻¹, Δν₄ = 0.60 ± 0.07 cm⁻¹, and Δν₅ = 0.28 ± 0.02 cm⁻¹. From these linewidths, predissociation lifetimes τ_ν were obtained: τ₀ = 16 ± 3 ps, τ₁ > 150 ps, τ₂ = 10 ± 2 ps, τ₃ = 1.6 ± 0.3 ps, τ₄ = 9 ± 2 ps, and τ₅ > 150 ps. Band origins and rotational constants for the b ¹Π_uν = 0 and 1 levels were determined for the ¹⁴N₂ and ¹⁴N¹⁵N molecules.     

Spectrophotometric study and analytical application of the reaction between manganese(II) and 4-(2-pyridylazo)resorcinol

A highly sensitive method for spectrophotometric determination of manganese(II) with 4-(2-pyridylazo)resorcinol (PAR) as reagent is described. The molar absorptivity of the complex was found to be 8.65 ± 0·04 x 10⁴. The stability constant of the ML₂ complex was found to be log β₂ = 15·6. Beer's law is obeyed within the range 0·02–0·5 μg of Mn/ml. An application of this reaction for analytical purposes is described.     

Zwitterionic titanoxanes {Cp[η-C5H4B(C6F5)3]Ti}2O and {(η-PrC5H4)[η-1,3-PrC5H3B(C6F5)3]Ti}2O as catalysts for cationic ring-opening polymerization

Zwitterionic titanoxanes {Cp[η⁵-C₅H₄B(C₆F₅)₃]Ti}₂O (I) and {(η⁵-ⁱPrC₅H₄)[η⁵-1,3-ⁱPrC₅H₃B(C₆F₅)₃]Ti}₂O (II), which contain two positively charged Ti(IV) centres in the molecule, are able to catalyse the ring-opening polymerization of -caprolactone (-CL) in toluene solution and in bulk. The process proceeds with a noticeable rate even at room temperature and accelerates strongly on raising the temperature to 60 °C. The best results have been obtained on carrying out the reaction in bulk. Under these conditions, the use of I as a catalyst (-CL:I = 1000:1) gives at 60 °C close to quantitative yield of poly--CL with the molecular mass of 197 000. An increase in the -CL:I ratio to 6000:1 increases the molecular mass of poly--CL to 530 000. Tetrahydrofuran (THF) is also polymerized under the action of I albeit with a lesser rate. However, the molecular mass of the resulting poly-THF can reach rather big values under optimal conditions (up to 217 000 at 20 °C and the THF:I ratio of 770:1). A rise in the reaction temperature from 20 to 60 °C results here to a decrease in the efficiency of the process. Titanoxane II is close to I in its catalytic activity in the -CL polymerization but it is much less active in the polymerization of THF. Propylene oxide (PO), in contrast to -CL and THF, gives with I only liquid oligomers in wide temperature and PO:I molar ratio ranges (−30 to +20 °C, PO:I = 500–2000:1). γ-Butyrolactone and 1-methyl-2-pyrrolidone are not polymerized under the action of I at room temperature. The reactions found are the first examples of catalysis of the cationic ring-opening polymerization by zwitterionic metallocenes of the group IVB metals.     

Strahlenchemie von alkoholen—IX Die UV-photolyse (λ = 185 nm) von methanol in flüssiger phase

The UV photolysis (λ = 185 nm) of liquid methanol yields hydrogen, glycol, formaldehyde, methane and traces of ethane in quantum yields of 0·83, 0·78, 0·058, 0·05 and 0·002 resp. (related to φ(H₂) = 0·4 of the ethanol-actinometer (5 mole/1 in water)). The isotopic distribution of the hydrogen (85% HD) formed in the photolysis of CH₃OD shows, that as in the gasphase² the scission of the O---H-bond (1) is the major process. CH₃OH + hv (λ = 185 nm) → CH₃O^• + H^• (1)

In methanoi-water mixtures (nearly all the light of the wavelength λ = 185 nm is absorbed by methanol) the quantum yields of hydrogen, glycol, methane and ethane are greatly reduced, while the formaldehyde yield remains unaffected. In 1 molar solution φ(H₂) = 0·42, φ(glycol) = 0·32 and φ(CH₄) = 6 x 10⁻⁴ is obtained. Ethane cannot be detected.     

Structures of propionaldehyde, butyraldehyde, and pivalaldehyde complexes of the chiral rhenium fragment [(η-C5H5)Re(NO)(PPh3)]

The crystal structures of propionaldehyde complex (RS,SR)-(η⁵-C₅H₅)Re(NO)(PPh₃)(η²-O=CHCH₂CH₃)]⁺ PF₆⁻ (1b⁺ PF₆^s−; monoclinic, P2₁/c (No. 14), a = 10.166 (1) Å, b = 18.316(1) Å, c = 14.872(2) Å, β = 100.51(1)°, Z = 4) and butyraldehyde complex (RS,SR)-[(η⁵-C₅H₅)Re(NO)(PPh₃)(η²-O=CHCH₂CH₂CH₃)]⁺ PF₆⁻ (1c⁺PF₆⁻; monoclinic, P2₁/a (No. 14), a = 14.851(1) Å, b = 18.623(3) Å, c = 10.026(2) Å, β = 102.95(1)°, Z = 4) have been determined at 22°C and −125°C, respectively. These exhibit C O bond lengths (1.35(1), 1.338(5) Å) that are intermediate between those of propionaldehyde (1.209(4) Å) and 1-propanol (1.41 Å). Other geometric features are analyzed. Reaction of [(η⁵-C₅H₅)Re(NO)(PPh₃)(ClCH₂Cl)]⁺ BF₄⁻ and pivalaldehyde gives [(η⁵-C₅H₅)Re(NO)(PPh₃)(η²-O=CHC(CH₃)₃)]⁺BF₄⁻ (81%), the spectroscopic properties of which establish a π C O binding mode.     

Thermal stability of osmium mixed oxides I. CaOsO3 decomposition products: A new orthorhombic phase Ca2Os2O7

The thermal decomposition of CaOsO₃ by differential thermal analyses, thermogravimetry and X-ray powder diffraction has been studied. In nitrogen CaOsO₃ decomposes at 880 ± 10°C into CaO, osmium metal and oxygen due to the reaction CaOsO₃ → CaO + Os + O₂. In static air the decomposition occurs in three stages: 2CaOsO₃ + 1/2O₂ → Ca₂Os₂O₇ (in region 775–808°C), Ca₂Os₂O₇ → Ca₂Os₂O_6,5 + 1/4O₂ (at a temperature interval of 850–1000°C) and in the third stage Ca₂Os₂O_6,5 → 2CaO + OsO₄ ÷ 1/4 O₂ (at 1005 ± 5°C). The first intermediate Ca₂Os₂O₇ is isostructural with orthorhombic Ca₂Nb₂O₇ and its cell parameters are: a₀ = 3.745 Å, b₀ = 25.1 Å, c₀ = 5.492 Å, Z = 4, space group Cmcm or Cmc2. Ca₂Os₂O₇ exhibits metallic conductivity and its electrical resistivity is 4.6 × 10⁻² ohm-cm at 296K.     

The system CePO4–K3PO4

The phase diagram of the system CePO₄–K₃PO₄ has been determined based on investigations by differential thermal analysis, X-ray powder diffraction, IR spectroscopy and optical microscopy. The system contains only one intermediate compound K₃Ce(PO₄)₂, which melts incongruently at (1500±20)°C. This compound is stable down to room temperature and exhibits a polymorphic transition at 1180°C. It was confirmed that the low-temperature form β-K₃Ce(PO₄)₂ crystallizes in a monoclinic system, space group P2₁/m with unit cell parameters a=9.579 (5), b=5.634 (6), c=7.468 (5) Å; =γ=90°, β=90.81 (3)°; V=403.083 Å³.