K<Subscript>3</Subscript>VO<Subscript>2</Subscript>(SO<Subscript>4</Subscript>)<Subscript>2</Subscript>: Formation conditions,crystal structure,and physicochemical properties

Potassium oxosulfatovanadate(V) K₃VO₂(SO₄)₂ has been obtained by solid-phase synthesis from K₂SO₄, K₂S₂O₇, and V₂O₅ (2: 1: 1), and its formation conditions, crystal structure, and physiochemical properties have been studied. The conversions of K₃VO₂(SO₄)₂ in contact with potassium vanadates and other potassium oxosulfatovanadates(V) are considered in terms of phase relations in the K₂O-V₂O₅-SO₃ system, which models the active component of vanadium catalysts for sulfur dioxide oxidation into sulfur trioxide. The X-ray diffraction pattern of K₃VO₂(SO₄)₂ is indexed in the monoclinic system (space group P2₁) with unit cell parameters of a = 10.0408(1) Å, b = 7.2312(1) Å, c = 7.3821(1) Å, β = 104.457(1)°, Z = 2, and V = 519.02 ų. The crystal structure of K₃VO₂(SO₄)₂ is built from [VO₂(SO₄)₂]^3? complex anions, in which the vanadium atom is in an octahedral oxygen environment formed by two terminal oxygen atoms (V-O(6) = 1.605(7) Å, V-O(10) = 1.619(7) Å and four oxygen atoms of the two chelating sulfate anions. The vibrational spectra of K₃VO₂(SO₄)₂ are analyzed using these structural data.     

Raman spectroscopy evidence of 1:1:1 complex formation during dissolution of WO3 in a melt of K2S2O7:K2SO4

Highly inert yellow solid WO₃ was found to be soluble in considerable amounts in molten K₂S₂O₇ at elevated temperatures (∼650 °C), if only similar molar amounts of sulfates were also present. The dissolution reaction of WO₃ into a melt consisting of a 1:1 molar mixture of K₂S₂O₇ and K₂SO₄ was studied in detail, and Raman spectroscopy was used to characterize the products. In combination with single crystal X-ray crystal structure determination, it was shown that a new dimeric compound, K₈[{W^VIO₂(SO₄)₂}₂(μ-SO₄)₂], was formed and its assigned Raman spectrum at room temperature is given. The WO₂²⁺ cores of the dimeric complex have their symmetrical and antisymmetrical stretching modes ν₁(WO₂²⁺) and ν₃(WO₂²⁺) at around 1054 (strong) and 1042 (weak), and the bending mode ν₂(WO₂²⁺) at around 292 (medium intensity), respectively (positions given in cm⁻¹).     

Phase equilibria in the V2O5-NaVO3-Ca(VO3)2-Mn2V2O7 system and interactions of phases with H2SO4 and NaOH solutions

Phase composition of the V₂O₅-NaVO₃-Ca(VO₃)₂-Mn₂V₂O₇ system was studied, and a subsolidus phase diagram constructed. The tetrahedration of the diagram is determined by the fact that the end-member of Ca_1–x Mn _x (VO₃)₂ solid solution is in equilibrium with all compounds of the system (V₂O₅, NaVO₃, Ca(VO₃)₂), vanadium β-bronzes Na _x V₂O₅ (0.22 ≤ x ≤ 0.40) and κ-bronzes (0.25 ≤ x ≤ 0.45, 0 ≤ y ≤ 0.16), Mn₂V₂O₇, and Na₂Mn₃(V₂O₇)₂ and with the end-members of reciprocal solid solutions based on calcium and sodium metavanadates. At 20°C, the degree of vanadium dissolution α for Na₂Ca(VO₃)₄ is 100% for 0.5 ≤ pH ≤ 10; for the other phases of the system, vanadium dissolution ranges from 100 to 10% for pH below 3.5; in the alkaline pH range, ≤ 10%. Sodium for calcium substitution in Ca(VO₃)₂ increases α in aqueous NaOH to 20%. For Na₂Mn₃(V₂O₇)₂, α decreases from 92 to 80% as pH changes from 0.5 to 2.5; at pH above 4, α = 30%.     

Reaction with SO3 in Ionic Liquids: The Example of K2(S2O7)­(H2SO4)

The ionic liquid 1‐butyl‐3‐methylimidazolium hydrogensulfate, [bmim]HSO₄, turned out to be resistant even to strong oxidizers like SO₃. Thus, it should be a suitable solvent for the preparation of polysulfates at low temperatures. As a proof of principle we here present the synthesis and crystal structure of K₂(S₂O₇)(H₂SO₄), which has been obtained from the reaction of K₂SO₄ and SO₃ in [bmim]HSO₄. In the crystal structure of K₂(S₂O₇)(H₂SO₄) (orthorhombic, Pbca, Z = 8, a = 810.64(2) pm, b = 1047.90(2) pm, c = 2328.86(6) pm, V = 1978.30(8) ų) two crystallographically unique potassium cations are coordinated by a different number of monodentate and bidentate‐chelating disulfate anions as well as by sulfuric acid molecules. The crystal structure consists of alternating layers of [K₂(S₂O₇)] slabs and H₂SO₄ molecules. Hydrogen bonds between hydrogen atoms of sulfuric acid molecules and oxygen atoms of the neighboring disulfate anions are observed.     

Darstellung,Ramanspektren und Kristallstrukturen von V2O3(SO4)2, K[VO(SO4)2] und NH4[VO(SO4)2]

Preparation, Raman Spectra, and Crystal Structures of V₂O₃(SO₄)₂, K[VO(SO₄)₂], and NH₄[VO(SO₄)₂] The oxo-sulfato-vanadates(V) V₂O₃(SO₄)₂, K[VO(SO₄)₂], and NH₄[VO(SO₄)₂] have been prepared as crystals suitable for X-ray structure determination. In all structures sulfate acts as an unidentate ligand only toward a single vanadium atom. The structure of V₂O₃(SO₄)₂ consists of a threedimensional network of pairs of cornershared VO₆ octahedra with one terminal oxygen atom each, and SO₄ tetrahedra. All oxygen atoms of the sulfate ions are coordinated. NH₄[VO(SO₄)₂] and K[VO(SO₄)₂] are isostructural. VO₆ octahedra with one terminal oxygen atom and pairs of sulfate tetrahedra form infinite chains by corner sharing. The chains are weakly interlinked to layers. The sulfate ions are distorted towards planar SO₃ molecules and single oxygen atoms attached to vanadium. This structural detail gives an explanation for the mechanism of the reversible reaction K[VO(SO₄)₂] ? K[VO₂(SO₄)] + SO₃ at 400°C. Raman spectra of the compounds have been recorded and interpreted with respect to their structures. Crystal data: V₂O₃(SO₄)₂, monoclinic, space group P2₁/a, a = 947.2(4), b = 891.3(3), c? 989.1(4) pm, β = 104.56(3)°, Z = 4, 878 unique data, R(R_w) = 0.039(0,033); K[VO(SO₄)₂], orthorhombic, space group P2₁2₁2₁, a = 495.3(2), b = 869.6(9), c = 1 627(1)pm, Z = 4, 642 unique data, R(R_w) = 0,11(0,10); NH₄[VO(SO₄)₂], orthorhombic, space group P2₁2₁2₁, a = 495.3(1), b = 870.0(2), c = 1 676.7(4)pm, Z = 4, 768 unique data, R(R_w) = 0.088(0.083).     

Sulfinylimine: Wichtige neue Bausteine zur Entwicklung der Chemie der Polysulfanmono- und -disulfonsäuren

Sulfinylimines: Important Building Blocks for Developing the Polysulfanemonoand -disulfonic Acid Chemistry Besides hydrolysis of perfluoroorganosulfanesulfinylimines in closed systems, reactions of R_fS_xCl with K₂S₂O₅ or M₂S₂O₃ are also productive methods for the preparation of perfluoroorganosulfanemonosulfonates. The free acid CF₃SSSO₃H is made by treating the potassium salt with a strong acidic cation resin. It is unstable and shows a pK_s-value of approx. –0,5 providing an acidity comparable with polyphosphoric acids. Metathetical reactions of the potassium salts with [(C₆H₅)₄M]Cl (M = P, As) or [R₄N][ClO₄] (R = n-C₃H₇, n-C₄H₉) respectively lead to well crystallized salts. Single crystals are used for x-ray structure analysis. These prove the polysulfanesulfon-moiety to be present in these molecules. Sulfur-sulfur-bonds can also be evidenced by chlorolysis reactions. Not only with Cl₂ but also with SCl₂ R_fS_xCl or R_fS_x+1Cl and ClSO₂OM are formed respectively. In this way CF₃SSSCl is prepared for the first time. The reaction of CF₃SeBr and K₂S₂O₅ provides K[CF₃SeSO₃] which is unstable and decomposes to CF₃SeSeCF₃, K₂S₂O₆, SO₂ and KBr. When S₂Cl₂ is reacted with (CH₃)₃SiNSO besides the main product S₂(NSO)₂ also minor amounts of S_x(NSO)₂ (x = 3, 4, 5) are formed. While hydrolysis of S₂(NSO)₂ leads quantitively to (NH₄)₂S₄O₆, a mixture of ammoniumpolysulfanedisulfonates are obtained from S_x(NSO)₂ which could not be separated. It is demonstrated that chemical reactivity is dominated by disproportionation of S₂(NSO)₂ into S(NSO)₂ and sulfur. Additonal sulfinylimines are obtained by metathesis of XNSO (X = Cl, Br) and AgSCN or AgSeCN respectively. The structures of S₂(NSO)₂ and OSNSCN are established by x-ray methods. By spectroscopical evidence it is shown that OSNSeCN is isostructured with OSNSCN.     

Hydrothermal synthesis and characterization of (Na,K)Ti2(PO4)3 solid solutions

Na_1?x K_xTi₂(PO₄)₃ (0 ≤ x ≤ 1) solid solutions are synthesized through ion exchange under hydrothermal conditions and a sol-gel process. The unit cell parameters are calculated for (Na,K) titanium phosphates. Cation-exchange reactions in the NaTi₂(PO₄)₃-KTi₂(PO₄)₃-NaCl-KCl-H₂O system are studied at T = 973 K and p = 200 MPa. The solid phase with compositions in the range 0 ≤ x ≤ 0.7 is enriched with sodium; in the range 0.7 ≤ x ≤ 1.0, it is enriched with potassium. The excess functions of mixing for the solid solutions are described in terms of the Margules model. Titanium phosphates Na_1?x K_xTi₂(PO₄)₃ show greater nonideality than zirconium phosphates Na_1?x K_xZr₂(PO₄)₃ and lower thermodynamic stability in decay into pure components at high pressures and temperatures.     

Synthesis and X-ray and Spectral Study of the Compounds [Q4N]2[Fe2(S2O3)2(NO)4] (Q = Me,Et, n-Pr,n-Bu)

Iron nitrosyl complexes with general formula [Q₄N]₂[Fe₂(S₂O₃)₂(NO)₄] (Q = Me, Et, n-Pr, n-Bu) were synthesized by the exchange reaction of K₂[Fe₂(S₂O₃)₂(NO)₄] with tetraalkylammonium bromides. The molecular and crystal structure of [(CH₃)₄N]₂[Fe₂(S₂O₃)₂(NO)₄] were studied by X-ray diffraction analysis. The iron atom in the four-membered cycle of the [2Fe–2S] anion is bound to another Fe atom and to two sulfur atoms and is coordinated by two nonequivalent NO groups, each bridging sulfur atom being bound to the SO₃group. The structurally equivalent iron atoms are in the state Fe^1–(S= 1/2). The Mössbauer spectroscopy method shows that the complexes are diamagnetic due to the strong Fe–Fe bond. It is found that the SO₃group provides higher stability of the thiosulfate anion than the anion in Roussin's red salt [Fe₂S₂(NO)₄]^2–.     

Studies on the compounds in BaFeS system. III. Phase relation of Ba1+xFe2S4 with infinitely adaptive structure

Samples of the infinitely adaptive phase Ba_1+xFe₂S₄ (or Ba_p(Fe₂S₄)_q; p, q: integer) were carefully prepared by changing the nominal composition and annealing temperature T_a. The single-phase materials, defined in this paper as a member of the infinitely adaptive series Ba_p(Fe₂S₄)_q, were obtained by the addition of excess sulfur in the nominal composition range 0.05 ≤ x ≤ 0.20 at T_a ranging from 650 to 880°C. X-Ray powder diffraction showed the existence of many members of the Ba_p(Fe₂S₄)_q series. The supercell periodicity was markedly dependent on T_a. The composition of reaction products estimated from X-ray diffraction, the method proposed by Grey based on crystallographic considerations, deviated in practice from the nominal composition. This fact suggests random distribution of Ba and Fe vacancies.     

Synthesis and structure of alkali metal zirconium vanadate phosphates

Mixed vanadate phosphates in the systems MZr₂(VO₄) _x (PO₄)_{3 ? x} , where M is an alkali metal, were synthesized and studied by X-ray diffraction, electron probe microanalysis, and IR spectroscopy. Substitutional solid solutions with the structure of the mineral kosnarite (NZP) are formed at the compositions 0 ≤ x ≤ 0.2 for M = Li; 0 ≤ x ≤ 0.4 for M = Na; 0 ≤ x ≤ 0.5 for M = K; 0 ≤ x ≤ 0.3 for M = Rb; and 0 ≤ x ≤ 0.2 for M = Cs. Apart from the high-temperature NZP modification, lithium vanadate phosphates LiZr₂(VO₄) _x (PO₄)_{3 ? x} with 0 ≤ x ≤ 0.8 synthesized at temperatures not exceeding 840°C crystallize in the scandium tungstate type structure. The crystal structures of LiZr₂(VO₄)_0.8(PO₄)_2.2 (space group P2₁/n, a = 8.8447(6) Å, b = 8.9876(7) Å, c = 12.3976(7) Å, β = 90.821(4)○, V = 985.4(1) ų, Z = 4) and NaZr₂(VO₄)_0.4(PO₄)_2.6 (space group $R\bar 3c$ = 8.8182(3) Å, c = 22.7814(6) Å, V = 1534.14(1) ų, Z = 6) were refined by the Rietvield method. The framework of the vanadate phosphate structure is composed of tetrahedra (that are statistically occupied by vanadium and phosphorus atoms) and ZrO₆ octahedra. The alkali metal atoms occupy extra-framework sites.     

Structural and vibrational studies of Li[Kx(NH4)1−x]SO4 and Li2KNH4(SO4)2 mixed crystals

Mixed crystals of Li[K_x(NH₄)_1−x]SO₄ have been obtained by evaporation from aqueous solution at 313 K using different molar ratios of mixtures of LiKSO₄ and LiNH₄SO₄. The crystals were characterized by Raman scattering and single-crystal and powder X-ray diffraction. Two types of compound were obtained: Li[K_x(NH₄)_1−x]SO₄ with x?0.94 and Li₂KNH₄(SO₄)₂. Different phases of Li[K_x(NH₄)_1−x]SO₄ were yielded according to the molar ratio used in the preparation. The first phase is isostructural to the room-temperature phase of LiKSO₄. The second phase is the enantiomorph of the first, which is not observed in pure LiKSO₄, and the last is a disordered phase, which was also observed in LiKSO₄, and can be assumed as a mixture of domains of two preceding phases. In the second type of compound with formula Li₂KNH₄(SO₄)₂, the room-temperature phase is hexagonal, symmetry space group P6₃ with cell-volume nine times that of LiKSO₄. In this phase, some cavities are occupied by K⁺ ions only, and others are occupied by either K⁺ or NH₄⁺ at random. Thermal analyses of both types of compounds were performed by DSC, ATD, TG and powder X-ray diffraction. The phase transition temperatures for Li[K_x(NH₄)_1−x]SO₄x?0.94 were affected by the random presence of the ammonium ion in this disordered system. The high-temperature phase of Li₂KNH₄(SO₄)₂ is also hexagonal, space group P6₃/mmc with the cell a-parameter double that of LiKSO₄. The phase transition is at 471.9 K.     

Hydrothermal Syntheses, Structures, and Properties of Two New Potassium Vanadium Phosphates: K3(VO) (V2O3) (PO4)2(HPO4) and K3 (VO) (HV2O3) (PO4)2(HPO4)

Two new potassium vanadium phosphates have been prepared and their structures have been determined from analysis of single crystal X-ray data. The two compounds, K₃(VO)(V₂O₃) (PO₄)₂(HPO₄) and K₃(VO)(HV₂O₃)(PO₄)₂(HPO₄), are isostructural, except for the incorporation of an extra hydrogen atom into the nearly identical frameworks. The structures consist of a three-dimensional network of [VO]_n chains connected through phosphate groups to a [V₂O₃] moiety. Magnetic susceptibility experiments indicate that in the case of the di-hydrogen compound, there are no significant magnetic interactions between the three independent vanadium (IV) centers. Crystal data: for K₃(VO)(V₂O₃)(PO₄)₂ (HPO₄), M_r = 620.02, orthorhombic space group Pnma (No. 62), a = 7.023(4) Å, b = 13.309(7) Å, c = 14.294(7) Å, V = 1336(2) ų, Z = 4, R = 5.02%, and R_w = 5.24% for 1238 observed reflections [I > 3σ(I)]; for K₃(VO)(HV₂O₃)(PO₄)₂(HPO₄), M_r = 621.04, orthorhombic space group Pnma (No. 62), a = 6.975(3) Å, b = 13.559(7) Å, c = 14.130(7) Å, V = 1336(1) ų, Z = 4, R = 6.02%, and R_w = 6.34% for 1465 observed reflections [I > 3σ(I)].     

Phase formation in the Ag2MoO4-CoMoO4-Al2(MoO4)3 system

The subsolidus region of the Ag₂MoO₄-CoMoO₄-Al₂(MoO₄)₃ ternary salt system was studied by X-ray powder diffraction analysis. New compounds Ag_1?x Co_1?x Al_{1 + x} (MoO₄)₃ (0 ≤ x ≤ 0.4) and AgCo₃Al(MoO₄)₅ were detected to form. The variable-composition phase Ag_1?x Co_1?x Al_{1 + x} (MoO₄)₃ is of the NASICON structure type (space group \(R\bar 3c\) ). AgCo₃Al(MoO₄)₅ crystallizes in the triclinic symmetry (space group \(P\bar 1\) Z = 2) with the unit cell parameters a = 6.9101(6), b = 17.519(1), c = 6.8241(6) Å, α = 87.356(7)°, β = 101.078(7)°, and γ = 91.985(9)°. The compounds are thermally stable until 770–780 and 760°C, respectively.     

Ionic conductivity and crystal chemistry of ramsdellite type compounds,Li2+x(LixMg1−xSn3)O8, 0 ≤ x ≤ 0.5 and Li2Mg1−xFe2xSn3−xO8, 0 ≤ x ≤ 1

Solid solution phases Li_2+x(Li_xMg_1−xSn₃)O₈: 0 ≤ x ≤ 0.5 and Li₂Mg_1−xFe_2xSn_3−xO₈: 0 ≤ x ≤ 1, both with ramsdellite type structure, have been synthesized by solid state reaction at 1773 and 1523 K, respectively. The relationship of the ramsdellite structure to the recently illustrated, tetragonal-packed structure is given. The Li_2+x(Li_xMg_1−xSn₃)O₈ solid solutions exhibit conductivities 4 × 10⁻⁶–5 × 10⁻⁴ (Ω cm)⁻¹ at 573 K and corresponding activation energies, 0.93−0.74 eV. The highest conductivity was observed for Li_2.3(Li_0.3Mg_0.7Sn₃)O₈, x = 0.3. In the solid solution series Li₂Mg_1−xFe_2xSn_3−xO₈, the highest conductivity was exhibited by Li₂Fe₂Sn₂O₈, 2 × 10⁻⁵ (Ω cm)⁻¹ at 573 K.     

Coordination Chemistry of [Nb2(S2)2]4+ Clusters: Preparation and Crystal Structures of K4[Nb2(S2)2(C2O4)4] · 6 H2O and (NH4)6[Nb2(S2)2(C2O4)4](C2O4)

Bis(disulfido)bridged Nb^IV cluster oxalate complexes [Nb₂(S₂)₂(C₂O₄)₄]^4– were prepared by ligand substitution reaction from the aqua ion [Nb₂(μ‐S₂)₂(H₂O)₈]⁴⁺ and isolated as K₄[Nb₂(S₂)₂(C₂O₄)₄] · 6 H₂O ( 1 ), (NH₄)₆[Nb₂(S₂)₂(C₂O₄)₄](C₂O₄) ( 2 ) and Cs₄[Nb₂(S₂)₂(C₂O₄)₄] · 4 H₂O ( 3 ). The crystal structures of 1 and 2 were determined. The crystals of 1 belong to the space group P1, a = 720.94(7) pm, b = 983.64(10) pm, c = 1071.45(10) pm, α = 109.812(1)°, β = 91.586(2)°, γ = 105.257(2)°. The crystals of 2 are monoclinic, space group C2/c, a = 1567.9(2) pm, b = 1906.6(3) pm, c = 3000.9(4) pm, β = 95.502(2)°. The packing in 2 shows alternating layers of cluster anions and of ammonium/uncoordinated oxalates perpendicular to the [1 0 1] direction. Vibration spectra, electrochemistry and thermogravimetric properties of the complexes are also discussed.     

Systems Li<Subscript>2</Subscript>O(Na<Subscript>2</Subscript>O)-CdO-V<Subscript>2</Subscript>O<Subscript>5</Subscript>: Phase composition and phase diagrams

The subsolidus phase composition of the M₂O-CdO-V₂O₅ systems with M = Li or Na is studied. Double orthovanadates MCdVO₄ and MCd₄(VO₄)₃ form solid solutions of composition Li_{1 ? 2x/3}Cd _x/3CdVO₄ (0 ≤ x ≤ 1, orthorhombic space group Cmcm, modulation at x = 0.6) and Na_{3 ? 2x} Cd_{3 + x} (VO₄)₃ (0 ≤ x ≤ 0.10 and 0.30 ≤ x ≤ 1, orthorhombic space group Cmcm and Pn2₁ a or Pnma, respectively). In the range 0.10 < x < 0.30, the end-members of the solid solutions coexist. Isothermal sections of the systems are mapped.     

The phase relationship among compounds Ba1+xFe2S4

The dependence of composition of the phases Ba_1+xFe₂S₄ on sulfur vapor pressure and starting composition was investigated at 650, 747, and 800°C. The infinitely adaptive series Ba_1+xFe₂S₄ spans the compositions 0.072 ≤ x ≤ 0.142. The value of x decreases as the sulfur vapor pressure increases at a given temperature. Varying the ratio of $\text{Ba}\text{Fe}$ in the starting mixture has no effect on the Ba_1+xFe₂S₄-sulfur fugacity relationship. The phase BaFe₂S₄ is not part of the infinitely adaptive series.     

Phase ratios in the M<Subscript>2</Subscript>O-V<Subscript>2</Subscript>O<Subscript>5</Subscript>-SO<Subscript>3</Subscript> (M = Rb,Cs) systems and the properties of the compounds formed in these systems

Powder X-ray diffraction and microscopy have been used to study phase ratios of the M₂O-V₂O₅-SO₃ (M = Rb, Cs) systems, which model the active component of rubidium-vanadium and cesium-vanadium catalysts for sulfuric acid production at high sulfur dioxide conversions. We have stated that each system forms four compounds: M₃VO₂(SO₄)₂, MVO₂SO₄, M₄V₂O₃(SO₄)₄, and MVO(SO₄)₂. The thermal properties of these compounds and their interaction with water vapor saturated at room temperature have been studied. The unit cell parameters have been determined for the compounds MVO₂SO₄ (M = K, Rb), MVO(SO₄)₂, and M[VO₂(SO₄)(H₂O)₂] · H₂O (M = Rb, Tl). The reciprocal transformations of the components and phases of the M₂O-V₂O₅-SO₃ systems match the Lux-Flood ideas of the acid-base properties of oxide compounds.     

Polycations Stabilised by Borosulfates: [Au3Cl4][B(S2O7)2] and the One-Dimensional Metal [Au2Cl4][B(S2O7)2](SO3)

(SO₄)-rich silicate analogue borosulfates are able to stabilise cationic cluster-like and chain-like aggregates. Single crystals of [Au₃Cl₄][B(S₂O₇)₂] and [Au₂Cl₄][B(S₂O₇)₂](SO₃) were obtained by solvothermal reaction with SO₃, and the electronic properties were investigated by means of density functional theory–based calculations. [Au₃Cl₄][B(S₂O₇)₂] exhibits a cluster-like cation, and the cationic gold-chloride strands in [Au₂Cl₄][B(S₂O₇)₂](SO₃) are found to resemble one-dimensional metallic wires. This is confirmed by polarisation microscopy.     

Molten potassium pyrosulfate: The reactions of seven metal oxalates

The reactions of Li₂C₂O₄, Na₂C₂O₄, K₂C₂·H₂O, CaC₂·H₂O, ZnC₂O₄, La₂(C₂O₄)₃ and K₂TiO(C₂O₄)₂· 2H₂O with K₂S₂O₇ were investigated using thermal methods of analysis. Reaction products were analysed by various techniques. It was found that anhydrous oxalates reacted with K₂S₂O₇, evolving a mixture of CO₂ and CO with the formation of K₂SO₄ and the corresponding metal sulfates, which, in the reactions of ZnC₂O₄ and K₂TiO(C₂O₄)₂ 2H₂O, probably existed as K₂[Zn(SO₄)₂] and K₄[Ti(SO₄)₄], respectively. Water was found to be an additional product in the hydrated metal oxalate reactions. The stoichiometries of these reactions have been established from the thermogravimetric and acidimetric results.