Palladium clusters Pd<Subscript>4</Subscript>(SR)<Subscript>4</Subscript>(OAc)<Subscript>4</Subscript> and Pd<Subscript>6</Subscript>(SR)<Subscript>12</Subscript> (R = Bu,Ph): Structure and properties

The structures of the Pd₄(SBu)₄(OAc)₄ (I) and Pd₆ (SBu)₁₂ (II) palladium clusters are determined by the X-ray diffraction method. For cluster I: a = 8.650(2), b = 12.314(2), c = 17.659(4) Å, α = 78.03(3)°, β = 86.71(2)°, γ = 78.13(3)°, V = 1800.8(7) ų, ρcalcd = 1.878 g/cm³, space group P \(\bar 1\), Z = 4, N = 3403, R = 0.0468; for structure II: a = 10.748(2), b = 12.840(3), c = 15.233(3) Å, α = 65.31(3)°, β = 70.10(3)°, γ = 72.91(3)°, V = 1767.4(6) ų, ρ calcd = 1.605 g/cm³, space group P \(\bar 1\), Z = 1, N = 3498, R = 0.0729. In cluster I, four Pd atoms form a planar cycle. The neighboring Pd atoms are bound by two acetate or two mercaptide bridges (Pd…Pd 2.95–3.23 Å, Pd…Pd angles 87.15°–92.85°). In cluster II, the Pd atoms form a planar six-membered cycle with Pd···Pd distances of 3.09–3.14 Å, the PdPdPd angles being 118.95°–120.80°. The Pd atoms are linked in pairs by two mercaptide bridges. The formation of clusters I and II in solution is proved by IR spectroscopy and calorimetry. Analogous clusters are formed in solution upon the reaction of palladium(II) diacetate with thiophenol.     

Synthesis and crystal structure of a Cu(II) complex Cu<Subscript>2</Subscript>(Endc)<Subscript>2</Subscript>(Bipy)<Subscript>2</Subscript> and its photoluminescence properties

A novel Cu(II) complex Cu₂(Endc)₂(Bipy)₂ has been synthesized by the reaction of Cu(NO₃)₂ · 3H₂O, Endc (endo-norbornene-cis-5,6-dicarboxylic acid), and Bipy (2,2-bipyridine) at room temperature. Elemental analysis, IR spectra, and X-ray single-crystal diffraction were carried out to determine the composition and crystal structure. Crystal data for this complex: triclinic, P \(\bar 1\) with a = 9.0373(10), b = 10.1637(11), c = 10.5574(12) Å, α = 65.78(1)°, β = 72.32(2)°, β = 73.23(2)°, Z = 1, V = 827.46(16) ų, ρ _c = 2.160 g/cm³, F(000) = 410.0, R = 0.0483 and wR = 0.0958 independent reflections for 4468 observed ones (I > 2 σ(I)).The Cu²⁺ ion is coordinated by two nitrogen atoms from the Bipy molecule and three oxygen atoms from two Endc, giving a distorted squarepyramidal coordination geometry. Two neighboring Cu²⁺ ions are bridged by a pair of bimonodentate carboxyl groups of different Endc acids, giving a centrosymmetrical binuclear structure which a Cu…Cu distance of 3.2946 Å. The photoluminescence properties of the complex were studied at room temperature. The complex displays an obvious photoluminescent emission upon excitation at 390 nm in the solid state.     

Synthesis and structure of [UO<Subscript>2</Subscript>(C<Subscript>2</Subscript>O<Subscript>4</Subscript>){CONH<Subscript>2</Subscript>N(CH<Subscript>3</Subscript>)<Subscript>2</Subscript>}<Subscript>2</Subscript>]

The single crystals of [UO₂(C₂O₄){CONH₂N(CH₃)₂}₂] were synthesized and studied by X-ray diffraction. The crystals are monoclinic, a = 7.461(2) Å, b = 8.828(2) Å, c = 11.756(2) Å, β = 107.21(3)°, space group Pc, Z = 2, R = 2.94%. The structure comprises infinite chains [UO₂(C₂O₄){CONH₂N(CH₃)₂}₂] extended along [001] and corresponding to the AT¹¹M ₂ ¹ crystallochemical group (A = UO ₂ ²⁺ , T¹¹ = C₂O ₄ ^2? , M¹ = N,N-CONH₂N(CH₃)₂) of uranyl complexes. The chains are connected into a three-dimensional framework by hydrogen bonds involving the oxygen atoms of oxalate and uranyl ions and the N,N-dimethylcarbamide methyl groups.     

Organometallic coordination polymers based on silver carboxylates: [AgCF<Subscript>3</Subscript>CO<Subscript>2</Subscript>(2,3-Et<Subscript>2</Subscript>Pyz)] and [AgCF<Subscript>3</Subscript>CO<Subscript>2</Subscript>(Bpeta)]

Coordination polymers [AgCF₃CO₂(2,3-Et₂Pyz)](I)(2,3-Et₂Pyz-C₈H₁₂N₂) and [AgCF₃CO₂(Bpeta)] (II) (Bpeta is 4′4-bipyridylethane, C₁₂H₁₂N₂) are synthesized. Their structures are determined. The crystals of compound I are monoclinic, space group P2(1)/n, a = 7.185(1), b = 14.754(1), c = 12.317(1)Å, β = 97.09(1)°, V = 1295.7(2) ų, ρ_calcd = 1.831 g/cm³, Z = 4. Structure I consists of infinite chains of doubled polymeric chains joined by silver carboxylate dimers [[Ag₂(CF₃CO₂)₂(Et₂Pyz)₂]_∞. The coordination polyhedron of Ag⁺ is a distorted tetrahedron. The crystals of compound II are orthorhombic, space group Pbca, a = 13.555(3), b = 13.991(3), c = 16.449(3) Å, V = 3119.5(11) ų, ρ_calcd = 1.725 g/cm³, Z = 8. Doubled polymeric chains with the Ag…Ag bond (3.16 Å) are also formed in structure II. Supramolecular layers are formed in the structure due to the weak π-π-stacking interaction between the aromatic groups of chains. The CF₃CO ₂ ^? anion is weakly bound to Ag⁺ (Ag-O_avg 2.790 Å).     

Synthesis and crystal structure of a 1D coordination polymer [Cd(NITpPy)<Subscript>2</Subscript>(N(CN)<Subscript>2</Subscript>)<Subscript>2</Subscript>)]<Subscript><Emphasis Type="Italic">n</Emphasis></Subscript>

A novel one-dimensional chain complex [Cd(NITpPy)₂(N(CN)₂)₂)] _n (NITpPy = 2-(4′-pyridyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide) has been synthesized and characterized structurally. It crystallizes in the triclinic space group P \(\bar 1\) with a = 7.1742(13), b = 9.4913(17), c = 13.208(2) Å, α = 71.020(2)°, β=87.308(2)°, γ = 70.503(2)°, V = 799.8(3) ų, C₂₈H₃₂CdN₁₂O₄, Mr = 713.06, Z = 1, ρ _c = 1.48 g/cm³, μ(MoK _α) = 0.736 mm^?1, F(000) = 364, R = 0.0275 and wR = 0.0605 for 2702 observed reflections with I > 2σ(I). The crystal structure consists of infinite chains of [Cd(NITpPy)₂(N(CN)₂)₂)] units linked by dicyanamide anions [N(CN)₂]^?. Each Cd²⁺ ion is six-coordinated with the geometry of a distorted octahedron.     

Supramolecular 2D structure of [Co(2-Me-Pyz)<Subscript>2</Subscript>(H<Subscript>2</Subscript>O)<Subscript>4</Subscript>](NO<Subscript>3</Subscript>)<Subscript>2</Subscript>

The complex [Co(2-Me-Pyz)₂(H₂O)₄](NO₃)₂ is synthesized and its structure is determined. The crystals are monoclinic: space group P2₁/n, a = 10.685(2) Å, b = 6.837(1), c = 12.515(3) Å, β = 91.84(3)°, V = 913.8(3) ų, ρ_calcd = 1.042 g/cm ³, Z = 2. The Co²⁺ ion (in the inversion center) is coordinated at the vertices of the distorted octahedron by two nitrogen atoms of methylpyrazine and four oxygen atoms of the water molecules (Co(1)–N(1) 2.180(3), average Co(1)–O(w) 2.079(3) Å, angles at the Co atom 87.9(1)–92.1(1)°). Supramolecular pseudometallocycles are formed in the structure through the O(w)–H…N(1) hydrogen bonds between the coordinated H₂O molecules and the terminal nitrogen atoms of the 2-methylpyrazine molecules. Their interaction results in the formation of supramolecular layers joined by the NO₃ groups into a three-dimensional framework.     

Synthesis and crystal structure of two complexes [Cu<Subscript>2</Subscript>(NiL)<Subscript>2</Subscript>Cl<Subscript>4</Subscript>] and [Cd<Subscript>2</Subscript>(CuL)<Subscript>2</Subscript>Cl<Subscript>4</Subscript>]

Macrocyclic and supermolecular complexes [Cu₂(NiL)₂Cl₄] (I) and [Cd₂(CuL)₂Cl₄] (II) (H₂L = 2,3-dioxo-5,6,14,15-dibenzo-1,4,8,12-tetraazacyclo-pentadeca-7,13-diene) have been synthesized and structurally determined by X-ray diffraction and IR spectrum. Complex I crystallizes in the monoclinic system with P2₁/n group, a = 10.9019(15), b = 14.3589(19), c = 12.4748(17) 0A, β = 108.645(2)°, Z = 4. Complex II crystallizes in the monoclinic system with P2₁/n group, a = 10.9784(16), b = 14.580(2), c = 12.8904(18) Å, β = 109.339(2)°, Z = 4.     

Preparation,crystal structure and mechanism of thermal decomposition of complex [Dy(<Emphasis Type="Italic">p</Emphasis>-MOBA)<Subscript>3</Subscript>Phen]<Subscript>2</Subscript>

1,10-Phenanthrolinetris(4-methoxybenzoate)dysprosium, Dy(p-MOBA)₃Phen (where p-MOBA = p-methoxybenzoate and Phen = 1,10-phenanthroline), (I) has been synthesized. The complex was characterized by various techniques including elemental analysis, UV, IR, XRD, molar conductance, and TG-DTG. The crystals consist of binuclear molecules and monoclinic, space group P2 ₁/n: a = 14.143(6) Å, b = 17.550(7) Å, c = 14.493(6) Å, β = 117.357(4)°, Z = 2, ρ _c = 1.655 g cm^?3, F(000) = 1588; R ₁ = 0.0176, wR ₂ = 0.0455. In the complex, each Dy³⁺ ion is nine-coordinate to one 1,10-phenanthroline molecule, one bidentate chelating carboxylate group, and four bridging carboxylate groups in which the carboxylate groups are bonded to the Dy³⁺ ions in three modes: bridging bidentate, bridging tridentate, and chelating bidentate. The thermal decomposition mechanism of I has been determined on the basis of thermal analysis. In addition, the lifetime equation at a weight-loss of 10% was deduced as lnτ = ?28.8361 + 19478.37/T by isothermal thermogravimetric analysis.     

Organic-inorganic hybrid perovskite (C<Subscript>6</Subscript>H<Subscript>5</Subscript>(CH<Subscript>2</Subscript>)<Subscript>2</Subscript>NH<Subscript>3</Subscript>)<Subscript>2</Subscript>CdCl<Subscript>4</Subscript>: Synthesis,structural and thermal properties

The present research work reports the study on crystal structure, vibrational spectroscopy and thermal analysis of organic-inorganic hybrid compound (C₆H₅(CH₂)₂NH₃)₂CdCl₄. Single crystals of bis(phenethylammonium)tetrachlorocadmate (C₆H₅(CH₂)₂NH₃)₂CdCl₄ (PEA–Cd) were obtained by diffusion at room temperature. This compound crystallizes in the orthorhombic space group C2cb with unit cell parameters a = 7.4444(2) Å, b = 38.8965(3) Å, c = 7.3737(2) Å and Z = 4. Single crystal structure has been solved and refined to R = 0.036 and wR = 0.092. The structure consists of an extended [CdCl₄]^2– network and two [C₆H₅(CH₂)₂NH₃]⁺ cations to form a two-dimensional perovskite system. The infrared (IR) spectrum of the title compound was recorded at room temperature. Differential scanning calorimetry (DSC) was used to investigate the phase transition; this compound exhibits a reversible single solid-solid phase transition.     

Crystal Structure of [UO<Subscript>2</Subscript>SO<Subscript>4</Subscript>{(CH<Subscript>3</Subscript>)HNCONH(CH<Subscript>3</Subscript>)}<Subscript>2</Subscript>]

The single crystals of [UO₂SO₄{(CH₃)HNCONH(CH₃)}₂] (I) were synthesized and studied by X-ray diffraction. The crystals are monoclinic, a = 6.847(1) Å, b = 14.259(3) Å, c = 14.297(3) Å, β = 93.451(4)°, space group P2₁/n, Z = 4. The main structural units of crystals I are ribbons whose composition coincides with the composition of the compound. The crystal chemical formula of the complex is AT³M ₂ ¹ (A = UO ₂ ²⁺ ).     

Crystal structures of <Emphasis Type="Italic">trans</Emphasis>-[Re<Subscript>6</Subscript>S<Subscript>8</Subscript>(CN)<Subscript>2</Subscript>L<Subscript>4</Subscript>] complexes,L = pyridine or 4-methylpyridine

The structures of three novel octahedral rhenium cluster compounds [Re₆S₈(CN)₂(py)₄]·H₂O (1), [Re₆S₈(CN)₂(4-Mepy)₄] (2), [Re₆S₈(CN)₂(4-Mepy)₄]·4-Mepy (3) (py = pyridine, 4-Mepy = 4-methylpyridine) are determined by X-ray crystallography. Crystal data are: C2/m space group, a = 14.813(1) Å, b = 14.772(1) Å, c = 9.2122(6) Å, β = 119.085(2)°, V = 1761.7(2) ų, d _x = 3.318 g/cm³, R = 0.0585 (1); I4₁/amd space group, a = 16.0018(3) Å, c = 14.7186(5) Å, V = 3768.81(16) ų, d _x = 3.169 g/cm³, R = 0.0489 (2); P2₁/c space group, a = 9.0452(4) Å, b = 15.8065(7) Å, c = 15.2951(6) Å, β = 103.700(2)°, V = 2124.57(16) ų, d _x = 2.957 g/cm³, R = 0.0245 (3). Molecular cluster complexes interact via π-π stacking affording 3D frameworks in 1 and 2 and chains in 3.     

Structure and some properties of [UO<Subscript>2</Subscript>CrO<Subscript>4</Subscript>{CH<Subscript>3</Subscript>CON(CH<Subscript>3</Subscript>)<Subscript>2</Subscript>}<Subscript>2</Subscript>]

A new complex [UO₂CrO₄{CH₃CON(CH₃)₂}₂] (I) was studied by thermal analysis, IR spectroscopy, and X-ray crystallography. The crystals are monoclinic: a = 13.8108(11) Å, b = 8.6804(7) Å, c = 13.0989(10) Å, β = 104.777(1)°, V = 1518.4(2) ų, space group P2₁/c, Z = 4, R = 2.39%. The structure of I contains infinite chains of the [UO₂CrO₄{CH₃CON(CH₃)₂}₂] composition running along [001]; the complex belongs to the AT¹¹M¹ ₂ crystal-chemical group (A = UO ₂ ²⁺ , T¹¹ = CrO ₄ ^2? , M¹ = CH₃CON(CH₃)₂) of uranyl complexes. The chains are linked into a three-dimensional framework due to hydrogen bonds between oxygen atoms of chromate ions and hydrogen atoms of methyl groups of the dimethylacetamide.     

Three- and four-coordinated silver(I) ions in the coordination polymers [Ag(Me<Subscript>4</Subscript>Pyz)<Subscript>2</Subscript>]PF<Subscript>6</Subscript> and [Ag(2,3-Et<Subscript>2</Subscript>Pyz)<Subscript>2</Subscript>]PF<Subscript>6</Subscript>

The coordination polymers [AgPF₆(Me₄Pyz)₂] (I) and [AgPF₆(2,3-Et₂Pyz)₂] (II) were synthesized, and their structures were determined. Crystals of I are monoclinic, space group C2/c, a = 10.213(2) Å, b = 16.267(3) Å, c = 12.663(3) Å, β = 92.90(3)°, V = 2102.1(7) ų, ρ_calcd = 1.660 g/cm³, Z = 4. The structure of I is built of polymeric zigzag [Ag(C₈H₁₂N₂)] _∞ ⁺ chains and octahedral [PF₆] anions. The coordination polyhedron of the Ag⁺ ion is a flat triangle. Crystals of II are tetragonal, space group P \(\bar 4\)2(1)/c,a = b = 10.641(1) Å, c = 18.942(1) Å, V = 2144.6(2) ų, ρ_calcd = 1.627 g/cm³, Z = 4. In the structure of II, 2D cationic layers of fused square rings exist; the rings consist of four Ag⁺ cations linked by four bridging ligands of diethylpyrazine Et₂Pyz. The coordination polyhedron of the Ag⁺ ion is an irregular four-vertex polyhedron.     

Uranyl cyanoacetate [UO<Subscript>2</Subscript>(H<Subscript>2</Subscript>O)<Subscript>2</Subscript>(NCCH<Subscript>2</Subscript>COO)<Subscript>2</Subscript>]: Synthesis,crystal structure,and absorption spectra

The U(VI) complex with cyanoacetic acid, [UO₂(H₂O)₂(NCCH₂COO)₂] (I), was synthesized from an aqueous solution, and its X-ray diffraction analysis was carried out. The crystals are orthorhombic: space group Pca2 ₁, a = 25.9605(7) Å, b = 6.7634(2) Å, c = 6.3398(2) Å, V = 1113.15(6) ų at 100 K, and Z = 4. The coordination polyhedron of the uranium atom is a distorted pentagonal bipyramid. The cations UO ₂ ²⁺ are bound into infinite zigzag chains by the bridging carboxyl groups of one of the anions of cyanoacetic acid. The carboxyl oxygen atom of the second anion, which is not involved in coordination, and the nitrogen atoms of the cyano groups form hydrogen bonds with the coordination water molecules. The layer structure of the compound is formed through the hydrogen bonds. The absorption spectra in the visible and infrared ranges of the crystalline compound are measured and analyzed.     

Structure and characterization of a 1d double chain copper(II) complex {[Cu(BIX)<Subscript>2</Subscript>(H<Subscript>2</Subscript>O)<Subscript>2</Subscript>](PhCOO)<Subscript>2</Subscript>}<Subscript><Emphasis Type="Italic">n</Emphasis></Subscript>

A novel copper(II) complex {[Cu(BIX)₂(H₂O)₂](PhCOO)₂} _n (1) (BIX = 1,4-bis(imidazole-1-methyl))-benzene) is synthesized and characterized by elemental analysis, IR, TG, and single crystal X-ray diffraction. Complex 1 crystallizes in the triclinic crystal system with the P-1 space group, Z = 1, a = 9.465(2) Å, b = 9.703(2) Å, c = 12.060(2) Å, α = 77.26(3)°, β = 70.37(3)°, γ = 67.14(3)°, and V = 956.1(3) ų. The crystal structural analysis of complex 1 shows that the copper center is six-coordinated in an elongated octahedral geometry by four N atoms from four different BIX and two O atoms from two water molecules; two neighboring Cu(II) cations are bridged by two BIX extending into an infinite 1D double chain structure.     

Structure and some properties of [UO<Subscript>2</Subscript>(SeO<Subscript>4</Subscript>)(C<Subscript>5</Subscript>H<Subscript>12</Subscript>N<Subscript>2</Subscript>O)<Subscript>2</Subscript>(H<Subscript>2</Subscript>O)]

The complex [UO₂(SeO₄)(C₅H₁₂N₂O)₂(H₂O)] (I) was synthesized and studied by thermal analysis, IR spectroscopy, and X-ray crystallography. The crystals are orthorhombic: a = 13.1661(3) Å, b = 16.4420(5) Å, c = 17.4548(6) Å, Pbca, Z = 8, R = 0.0423. The structural units of crystal I are chains with the composition coinciding with that of the compounds of the AB₂M ₃ ¹ crystal chemical group of the uranyl complexes (A = UO ₂ ²⁺ , B² = SeO ₄ ^2? , M¹ = C₅H₁₂N₂O and H₂O).     

Synthesis,characterization and very strong luminescence of a new 3 D europium sulfate Eu<Subscript>2</Subscript>(H<Subscript>2</Subscript>O)<Subscript>4</Subscript>(SO<Subscript>4</Subscript>)<Subscript>3</Subscript>

A new 3 D europium sulfate Eu₂(H₂O)₄(SO₄)₃ 1 is synthesized solvothermally and characterized by single crystal X-ray diffraction, IR spectrum, TG, powder XRD, and ultraviolet excitation and emission spectrum. This compound crystallizes in the triclinic system with the space group P-1, a = 6.7520(9) Å, b = 9.1077(12) Å, c = 10.5910(14) Å, α = 94.432(2)°, β = 107.1170(10)°, γ = 99.160(2)°, V = 609.17(14) ų, Z = 2. The open framework of the title compound is an eight-membered ring channel along the crystallographic a-axis, which is built up by EuO₈ polyhedra and SO₄ tetrahedra.     

Crystal structures of [Zn(SALIMP)(CH<Subscript>3</Subscript>CO<Subscript>2</Subscript>)]<Subscript>2</Subscript> and [Cu(SALIMP)Cl] with 2-[[(2-pyridinylmethyl) imino]methyl]phenol (HSALIMP) as a ligand

Two complexes [Zn(SALIMP)(CH₃CO₂)]₂ (1) and [Cu(SALIMP)Cl] (2) are obtained by the reactions of zinc(II) and copper(II) salts with a tridentate Schiff base ligand 2-[[(2-pyridinylmethyl) imino]methyl]phenol (HSALIMP). Their structure is determined by single crystal X-ray diffraction. Data for complex 1: C₃₀H₂₈N₄O₆Zn₂, CCDC number: 668213, M _r = 671.3, monoclinic, C2/c, with a = 34.670(5) Å, b = 15.266(2) Å, c = 23.464(4) Å, β = 114.045(2)°, V = 11341(3) ų, Z = 16, F(000) = 5504, GOOF(F ²) = 0.894, the final R = 0.0520 and wR = 0.1272 for 10515 observed reflections with I > 2σ(I); complex 2: C₁₃H₁₂N₂OClCu, CCDC number: 668211, M _r = 311.24, triclinic, P-1, with a = 7.4050(8) Å, b = 10.2369(11) Å, c = 16.2873(17) Å, α = 87.728(2)°, β = 87.818(2)°, γ = 78.279(2)°, V = 1207.4(2) ų, Z = 4, F(000) = 632, GOOF(F ²) = 1.077, the final R = 0.0326 and wR = 0.0381 for 4209 observed reflections with I > 2σ(I).     

Synthesis,structure, and properties of M<Subscript>3</Subscript>VO<Subscript>2</Subscript>(SO<Subscript>4</Subscript>)<Subscript>2</Subscript> (M = Rb,Cs)

Vanadium(V) complexes of general composition M₃VO₂(SO₄)₂ (M = Rb, Cs) were synthesized by a solid-state route. The individuality of the synthesized compounds was proved by X-ray and neutron diffraction, vibrational spectroscopy, and microscopic analysis. The X-ray diffraction patterns of M₃VO₂(SO₄)₂ were indexed to fit the monoclinic system (space group P2/c, Z = 4) with the following unit cell parameters: a = 11.6487(2) Å, b = 8.4469(2) Å, c = 12.1110(2) Å, β = 109.483(1)°, V = 1123.43 ų (Rb); a = 12.0546(3) Å b = 8.7706(2) Å, c = 12.6496(3) Å, β = 109.843(2)°, V = 1257.99 ų (Cs). In the crystal structure of M₃VO₂(SO₄)₂, [VO₂(SO₄)₂]^3? complex anions can be discerned in which the vanadium atom is surrounded by five oxygen atoms: two oxygen atoms form short terminal V–O bonds, and three oxygen atoms are from the two sulfato groups, one of which acts as a monodentate ligand and the other acts as a bidentate chelating ligand.     

High-temperature heat capacity and thermodynamic properties of pyrovanadate Pb<Subscript>2</Subscript>V<Subscript>2</Subscript>O<Subscript>7</Subscript> and orthovanadate Pb<Subscript>3</Subscript>(VO<Subscript>4</Subscript>)<Subscript>2</Subscript>

The heat capacities of Pb₂V₂O₇ and Pb₃(VO₄)₂ as a function of temperature in the range 350–965 K have been studied by the differential scanning calorimetry method. The C_P = f(T) curve for Pb₂V₂O₇ is described by the equation C_p = (230.76 ± 0.51) + (73.60 ± 0.50)×10^-3T ? (18.38 ± 0.54)×10⁵T^-2 in the entire temperature range. For Pb₃(VO₄)₂, there is a well-pronounced extreme point in the C_P = f(T) curve at T = 371.5 K, which is caused by the existence of a structural phase transition. The thermodynamic properties of the oxide compounds have been calculated.