Synthesis and x-ray crystal structure of [PPN]+2[RuIr4(CO)9(μ2-CO)6]2-

The dianion [RuIr₄(CO)₁₅]^2- has been obtained by reductive carbonylation of mixtures of Ir₄(CO)₁₂ and RuCl₃ · χ H²O, and the bis(triphenylphosphine)-iminium salt has been characterized by single-crystal X-ray diffraction techniques. Crystal data: [((C₆H₅)₃P)₂N]₂[RuIr₄(CO)₁₅], space group P$\text{1}$ (Z  2), a  11.425(3), b  14.141(2), c  25.979(5) Å, α  84.55(1), β  83.53(2), γ  80.71(2)°. The mixed-metal cluster has a structure with an elongated trigonal bipyramidal array of metal atoms in which Ru occupies an apical position. The anion is unstable in vacuum or in an N₂ atmosphere yielding predominantly another mixed-metal species which is not as yet fully characterized. Upon reexposure to CO, this latter species is converted back to [RuIr₄(CO)₁₅]^2-, plus additional products.     

[Rh12Sb(CO)27]3-. an example of encapsulation of antimony by a transition metal carbonyl cluster

The reaction of Rh(CO)₂acac with triphenylantimony in the presence of cesium benzoate in tetraethylene glycol/dimethyl ether solution resulted in the selective formation of [Rh₁₂Sb(CO)₂₇]^3- (66% yield) after 3 h of contact time under ≈400 atm of carbon monixide and hydrogen (CO/H₂  1) at 140–160°C. The cluster has been isolated as the [Cs(18-Crown-6)₂]⁺, [(CH₃)₄]⁺, [(C₂H₅)₄N]⁺, (Ph₃P)₂N]⁺ and [PhCH₂N(C₂H₅)₃]⁺ salts. The [(C₂H₅)₄N]₃ [Rh₁₂Sb(CO)₂₇] complex has been characterized via a complete three-dimensional X-ray diffraction study. The complex crystallizes in the space group R$\text{3}$c with a  23.258(13) Å, c  22.811(4) Å, V  10 686 ų and p(calcd.)  2.334 g cm^-3 for mol.wt. 2503.66 and Z  6. Diffraction data were collected with an Enraf-Nonius CAD 4 automated diffractometer using graphite-monochromatized Mo-Kα radiation. The structure was solved by direct methods and refined by difference-Fourier and least-squares techniques. All non-hydrogen atoms have been located and refined: final discrepancy indices are R_f  3.5% and R_wf  4.6% for 3011 reflections. The anion's structure consists of twelve rhodium atoms situated at the corners of a distorted icosahedron with contacts of 2.807(1), 2.861(1), 2.874(1), 2.999(1), 3.017(1) and 3.334(1) Å and rhodium—antimony contacts of 2.712(0) Å. Rhodium—rhodium bond distances of 2.807 and 3.017 Å are in the range usually found for these complexes although a distance of 3.334 Å may be longer than expected from bonding interactions. The sum of the covalent radii of antimony and rhodium, 2.80 Å, is intermediate between the two observed RhSb contacts. The anion cluster structure is that of distorted icosahedron. This polyhedron has previously been found in [B₁₂H₁₂]^2- but not with transition metal clusters. A comparison between the structures of rhodium carbonyl clusters and boranes shows the occurrence of similar structural features. Applications of bonding theories based on the boranes, such as Wade's rules, to rhodium carbonyl clusters shows the extent in which these rules are obeyed.     

The reaction of trihydrobistriphenylphosphine iridium IrH3(PPh3)2 with diazonium salts

The reaction of IrH₃(PPh₃)₂ with p-substituted aryldiazonium salts gives the compounds [IrH₂(NHNC₆H₄R)(PPh₃)₂]⁺BF₄^- at low temperature (-10°C) and the o-metalated complexes [I$\text{rH(NHN}$C₆H₃R)(PPh₃)₂]⁺BF₄^- (R  F, OCH₃) at 40–50°C. The reactions of the o-metalated complexes with CO, PPh₃, NaI and HCl have been studied.     

Synthesis and structure of FeRu3(CO)13(μ-PPh2)2; A “64-electron” cluster complex with a planar triangulated rhomboidal array of metal atoms

The species FeRu₃(CO)₁₃(μ-PPH₂)₂, synthesized from Ru₃(CO)₁₂ and Fe(CO)₄(Ph₂PPPh₂),has been characterized both spectroscopically and via a single-crystal X-ray structural analysis. This complex crystallizes in the centrosymmetric triclinic space group P$\text{1}$ [No. 2, C_i¹] with a  10.066(3), b  12.899(3), c  17.003(4) Å, α  111.89(2), β  91.02(2), γ  102.00(2)°, V  1992.7(9) ų, Z  2, ?(obsd)  1.79(2) g cm^-3 and ?(calcd)  1.82 cm^-3. Diffraction data were collected with a Syntex P2₁ automated four-circle diffractometer and the structure was refined to R_F  6.0% and R_WF  3.6% for all 5213 reflections (R_F  3.8%, R_WF  3.6% for those 4140 reflections with |F_o|> 3σ(|F_o|).The metal atoms define a planar triangulated rhombus, with atoms Ru(1) and Ru(2) at the bridgehead, and Fe(1) and Ru(3) at the acute apices. Fe(1) is linked to four terminal carbonyl ligands and is associated with the heteronuclear bonds Fe(1)Ru(1)  2.861(1) Å and Fe(1)Ru(2)  2.868(1) Å. The ruthenium atoms are each bonded to three terminal carbonyl groups. The retheniumruthenium distances are Ru(1)Ru(2)  3.098(1), Ru(1)Ru(3)  3.147(1), and Ru(2)Ru(3)  3.171(1) Å. The structure is completed by Ph₂P bridges across the Ru(1)Ru(3) and Ru(2)(ru(3) vectors (<Ru(1)P(1)Ru(3)  84.89(5)° and <Ru(2)P(2)Ru(3)  85.56(6)°).     

X-ray study of Hg2Cl2Br2 and HgCl2HgBr2 reactions in solid state

The reactions (I) Hg₂Cl₂(s) + Br₂(g) and (II) HgCl₂(s) + HgBr₂(s) have been investigated by an X-ray method. Both the reactions yield two forms of the mixed halide HgClBr, designated as α-HgClBr and β-HgClBr. The cell parameters of the two are as follows:α-HgClBr: $\text{a = 6.196}\text{A}\text{?}$, $\text{b = 13.12}\text{A}\text{?}$, $\text{c = 4.37}\text{A}\text{?}$, z = 4, ? = 5.91 g/cm³. The powder pattern and cell parameters are similar to that of HgCl₂. Therefore it is probable that the chlorine atoms, in the linear halogenHghalogen molecules of HgCl₂ structure have been replaced by bromines, and since the radius of the bromine atom is larger than that of chlorine, the lattice is larger in this case.β-HgClBr: $\text{a = 6.78}\text{A}\text{?}$, $\text{b = 13.175}\text{A}\text{?}$, $\text{c = 4.17}\text{A}\text{?}$, z = 4, ? = 5.40. These parameters are the same as those reported in the literature for β-Hg(ClBr)₂, and its X-ray powder pattern is similar to HgCl₂. Therefore this phase also has linear halogenHghalogen molecules but the distribution of Cl and Br atoms is perhaps random.Heating the products (I) and (II) up to the melting point increases the amount of α phase and decreases the β phase, whereas crystallization increases the β phase. DTA study has supported the X-ray findings.     

Valence state of the Fe ions in Sr1−yLayFeO3

The Sr²⁺_1?yLa³⁺_yFeO₃ system with 0.1 ≦ y ≦ 0.6 has been studied mainly by the Mössbauer effect. The results are discussed referring to the Ca_1?xSr_xFeO₃ system. The following four kinds of electronic phases have been observed: the paramagnetic and the antiferromagnetic average valence phases and the corresponding mixed valence phases. Two kinds of Fe ions coexist, in general, in the mixed valence phases. In the antiferromagnetic mixed valence phase, typically at 4 K, the magnetic hyperfine field and the center shift each takes a wide range of value depending on the composition, while a beautiful correlation is kept between them. The extreme values are close to those expected for Fe³⁺ and Fe⁵⁺. The appropriate chemical formulas are, therefore, Ca_1?xSr_xFe^(3+Δ)+_0.5Fe^(5?Δ)+_0.5O₃ and $\text{Sr}{}_{\mathrm{1?y}}\text{La}{}_{\mathrm{y}}\text{Fe}{}^{\mathrm{(3+\delta )+}}{}_{\mathrm{<mtext>(1+y)</mtext><mtext>2</mtext>}}\text{Fe}{}^{\mathrm{(5?\delta )+}}{}_{\mathrm{<mtext>(1?y)</mtext><mtext>2</mtext>}}\text{O}{}_3$.     

Fulvene—platinum complexes: x-ray crystal structure of [Pt(η2-C5H4CPh2)(PPh3)2]

Bis(cycloocta-1,5-diene)platinum reacts with 2,3,4,5-tetraphenylfulvene to afford the complex [Pt(η²-CH₂C₅Ph₄)(cod)] (cod  C₈H₁₂) in which the metal atom is coordinated to the exo-cyclic double bond of the fulvene. Related compounds [Pt(η²-CH₂C₅Ph₄L₂] (L  PPh₃, PMePh₂, PMe₂Ph, AsPh₃ or CNBu^t have also been prepared and characterised. Reaction of the complexes [Pt(C₂H₄)₂(L)] (L  P(cyclo-C₆H₁₁)₃, PPh₃ or AsPh₃) with 2,3,4,5-tetraphenylfulvene yields the compounds [Pt(C₂H₄)(η²-CH₂C₅PH₄)(L)]. NMR data for the new species are reported and discussed. 6,6-Diphenylfulvene reacts with [Pt(cod)₂] and PPh₃ ($\text{1}\text{2}$ mol ratio) to give the complex [Pt(η²-C₅H₄CPh₂)-(PPh₃)₂] in which the metal atom is bonded to carbon atoms C(2) and C(3) of the fulvene ring. This was established by an X-ray diffraction study. Crystals are monoclinic, space group P2₁/n, with Z  4 in a unit cell of dimensions a  13.761(4), b  21.653(13), c  17.395(6) Å, β,  104.46(2)°. The structure has been solved and refined to R  0.064 (R′  0.064) for 3139 independent diffracted intensifies measured at room temperature. The platinum atom is in a trigonal environment formed by the two ligated phosphorus atoms and the CC bond of the fulvene which is elongated to 1.52(3) Å. The c₅ fulvene ring is planar, and makes an angle of 108° with the coordination plane around the platinum. In this plane the metal atom is slightly asymmetrically bonded with PtC 2.15(2) and 2.24(2) Å, and PtP 2.280(6) and 2.301(6) Å.     

Nd3+, Eu3+, and Gd3+ ions as local probes in the NaxSr3−2xLnx(PO4)2 and KCaLn(PO4)2 rare earth phosphates

Use of Nd³⁺, Eu³⁺, and Gd³⁺ as local structural probes allows the determination of the rare earth positions in the Na_xSr_3?2xLn_x(PO₄)₂ (Ln = La to Tb) and KCaLn(PO₄)₂ phases (Ln = rare earth). Moreover, a common feature of both series is a particularly high splitting of the excitation ${}^6\text{P}{}_{\mathrm{<mtext>7</mtext><mtext>2</mtext>}}$ and ${}^6\text{P}{}_{\mathrm{<mtext>5</mtext><mtext>2</mtext>}}$ levels of the Gd³⁺ ions.     

The formation of a new mixed cobalt rhodium carbonyl from Co2(CO)8 and Rh4(CO)12: Infrared spectroscopic characterization under carbon monoxide pressure

The formation of a new compound, the most characteristic IR absorption bands of which appear at 2007 cm^-1 and 1956 cm^-1, has been in the reaction between Co₂(CO)₈ and Rh₄(CO)₁₂ under carbon monoxide pressure in a hydrocarbon medium. The same compound is also formed either by the reaction of Co₂(CO)₈ with [Rh(CO)₂Cl]₂ or by the reaction of Co₃Rh(CO)₁₂ with carbon monoxide. The new complex has not been isolated in a pure state, but the formula CoRh(CO)₇ is proposed on the basis of the stoichiometry of its formation and its physico-chemical properties. Equilibrium constants and thermo-dynamic parameters for the reaction 2 Co₂(CO)₈ + Rh₄(CO)₁₂  4 CoRh(CO)₇ have been estimated. Possible structures for the new complex are discussed on the basis of its IR spectrum.     

Surface supported metal cluster carbonyls. Chemisorption decomposition and reactivity of Rh4(CO)12 supported on silica and alumina

Chemisorption of Rh₄(CO)₁₂ on to a highly divided silica (Aerosil “0” from Degussa), Leads to the transformation: 3 Rh₄(CO)₁₂ → 2 Rh₆(CO)₁₆ + 4 CO. Such an easy rearrangement of the cluster cage implies mobility of zerovalent rhodium carbonyl fragments on the surface. Carbon monoxide is a very efficient inhibitor of this reaction, and Rh₄(CO)₁₂ is stable as such on silica under a CO atmosphere. Both Rh₄(CO)₁₂ and Rh₆(CO)₁₆ are easily decomposed to small metal particles of higher nuclearity under a water atmosphere and to rhodium(I) dicarbonyl species under oxygen. From the Rh^I(CO)₂ species it is possible to regenate first Rh₄(CO)₁₂ and then Rh₆(CO)₁₆ by treatment with CO (P_co ? 200 mm Hg) and H₂O (P_H2O ? 18 mm Hg). The reduction of Rh^I(CO)₂ surface species by water requires a nucleophilic attack to produce an hypothetical [Rh(CO)_n]_m species which can polymerize to small Rh₄ or Rh₆ clusters in the presence of CO but which in the absence of CO lead to metal particles of higher nuclearity. Similar results are obtained on alumina.     

Catalytic hydrogenation of 1,3-trans-pentadiene over Rh4(CO)12 supported on γ-Al2O3

Rh₄(CO)₁₂ anchored on γ-Al₂O₃ (Rh₄(CO)₁₂/Al₂O₃) has been studied as a catalyst for the hydrogenation of 1,3-trans-pentadiene. Under mild conditions (1 atm H₂ and temperatures between 60°C and 80°C) hydrogenation occurs at only one of the double bonds of the diene, and analysis of the products shows that the terminal double bond is preferentially hydrogenated. Hydrogenation of the second double bond of the conjugated diene occurring only after all the 1,3-trans-pentadiene has been consumed. In this respect Rh₄(CO)₁₂/Al₂O₃ behaves like toluene solutions of Rh₄(CO)₁₂. Anchoring of Rh₄(CO)₁₂ on the solid support gives a catalyst which is less active but more stable than toluene solutions of Rh₄(CO)₁₂. The effects of CO and of triphenylphosphine on catalytic activity and on specificity of Rh₄(CO)₁₂/Al₂O₃ have also been investigated and both shown to cause a reduction of the rate of hydrogenation of 1,3-trans-pentadiene.     

Synthesis and characterisation of HRuRh3(CO)12. Crystal structures of HRuRh3(CO)12, HRuRh3(CO)10(PPh3)2 and HRuCo3(CO)10(PPh3)2

A new ruthenium-rhodium mixed-metal cluster HRuRh₃(CO)₁₂ and its derivatives HRuRh₃(CO)₁₀(PPh₃)₂ and HRuCo₃(CO)₁₀(PPh₃)₂ have been synthesized and characterized. The following crystal and molecular structures are reported: HRuRh₃(CO)₁₂: monoclinic, space group P2₁/c, a 9.230(4), b 11.790(5), c 17.124(9) Å, β 91.29(4)°, Z = 4; HRuRh₃(CO)₁₀(PPh₃)₂·C₆H₁₄: triclinic, space group P$\text{1}$, a 11.777(2), b 14.079(2), c 17.010(2) Å, α 86.99(1), β 76.91(1), γ 72.49(1)°, Z = 2; HRuCo₃(CO)₁₀(PPh₃)₂·CH₂Cl₂: triclinic, space group P$\text{1}$, a 11.577(7), b 13.729(7), c 16.777(10) Å, α 81.39(4), β 77.84(5), γ 65.56°, Z = 2. The reaction between Rh(CO)₄^? and (Ru(CO)₃Cl₂)₂ tetrahydrofuran followed by acid treatment yields HRuRh₃(CO)₁₂ in high yield. Its structural analysis was complicated by a 80–20% packing disorder. More detailed structural data were obtained from the fully ordered structure of HRuRh₃(CO)₁₀(PPh₃)₂, which is closely related to HRuCo₃(CO)₁₀(PPh₃)₂ and HFeCo₃(CO)₁₀(PPh₃)₂. The phosphines are axially coordinated.     

Partial substitution of rhodium for cobalt in the misfit [Pb0.7Co0.4Sr1.9O3][CoO2]1.8 oxide

The partial substitution of Co by Rh in the [Pb_0⋅7Co_0.4Sr_1.9O₃]^RS[CoO₂]_1.8 family has been investigated. By transmission electron microscopy and X-ray powder diffraction, it is shown that the substitution of Rh for Co takes place at the two cobalt sites of the structure but for the low enough Rh contents, this substitution is made preferentially at the level of the CdI₂-like layer. Thus, a generic formula [Pb_0.7(Co_0.4−zRh_z)Sr_1.9O₃]^RS[Co_1−yRh_yO₂]_b1/b2 (0?y?0.5 and 0?z?0.3) can be proposed for this new family of misfit phase. As observed for the pure misfit cobaltite, the thermoelectric power is also very large, close to +140 μV/K at room temperature. The Rh cation can adopt a mixed valency Rh³⁺/Rh⁴⁺ (4d⁶/4d⁵) with low spin states t_2g⁶/t_2g⁵ equivalent to the ones of low spin Co³⁺/Co⁴⁺ (3d⁶/3d⁵). The large thermopower observed in the Rh substituted compounds is therefore a direct proof that the coexistence of low spin states t_2g⁶/t_2g⁵ contributes to the thermoelectric power enhancement in these oxides.     

The enthalpies of formation of CH3Mn(CO)5 and of CH3Re(CO)5, and the strengths of the CH3Mn and CH3Re bonds

From measurements of the heats of iodination of CH₃Mn(CO)₅ and CH₃Re(CO)₅ at elevated temperatures using the ‘drop’ microcalorimeter method, values were determined for the standard enthalpies of formation at 25° of the crystalline compounds: ΔH^o_f[CH₃Mn(CO)₅, c] = ?189.0 ± 2 kcal mol^?1 (?790.8 ± 8 kJ mol^?1), ΔH^o_f[Ch₃Re(CO)₅,c] = ?198.0 ± kcal mol^?1 (?828.4 ± 8 kJ mo^?1). In conjunction with available enthalpies of sublimation, and with literature values for the dissociation energies of MnMn and ReRe bonds in Mn₂(CO)₁₀ and Re₂(CO)₁₀, values are derived for the dissociation energies: D(CH₃Mn(CO)₅) = 27.9 ± 2.3 or 30.9 ± 2.3 kcal mol^?1 and D(CH₃Re(CO)₅) = 53.2 ± 2.5 kcal mol^?1. In general, irrespective of the value accepted for D(MM) in M₂(CO)₁₀, the present results require that, D(CH₃Mn) = $\text{1}\text{2}$D(MnMn) + 18.5 kcal mol^?1 and D(CH₃Re) = $\text{1}\text{2}$D(ReRe) + 30.8 kcal mol^?1.     

Study of Pr1−xMn1+xO3 perovskites

The structural and magnetic properties of the Pr_1?xMn_1+xO₃ perovskites were studied. The increase of x (i.e., $\text{Pr}\text{Mn}\text{< 1}$) leads to the decrease of the orthorhombic deformation and of the Néel temperature and, simultaneously, to an increase of the ferromagnetic contribution. The latter effect is explained from the suggested distribution of the cations (Pr³⁺_1?xMn²⁺_x)_A(Mn³⁺_1?xMn⁴⁺_x)O^2?₃ by the double exchange of Mn³⁺Mn⁴⁺ pairs at the B—sublattice.     

Excess molar enthalpies of {(1 − x2 − x3)Al + x2Bi + x3Ga}(I) alloys

The excess molar enthalpies H_m^E{(1 ? x₂ ? x₃)Al + x₂Bi + x₃Ga}(I) have been measured between 725 and 1170 K along the sections $\text{(1 ? x}{}_2\text{? x}{}_3\text{)}\text{x}{}_3\text{=}\text{1}\text{3}$, 1, and 3, and $\text{x}{}_2\text{x}{}_3\text{=}\text{1}\text{3}$, 1, and 3, with a high-temperature Calvet calorimeter using both the direct- and indirect-drop methods of mixing; experimental uncertainty is quoted respectively at 6.7 per cent and 9.9 per cent. The equilibrium temperatures confirmed phase boundaries previously determined by potentiometry, d.t.a., and calculation. Extrapolation of the experimental excess molar enthalpies to the limiting binary alloys {(1 ? x₂)Al + x₂Bi} allows new values for the excess molar enthalpies of these alloys to be proposed. The excess molar enthalpies of the ternary liquid mixtures can be represented correctly using these new values and Bonnier's equation.     

Imidazolate bridged polynuclear rhodium(I) complexes. X-ray structure of [Rh(2-Meimidazolate)(CO)2]4

The synthesis and properties of polynuclear complexes of general formulae [M(RIm)(diolefin)_x, [M(RIm)(CO)₂]_x and [M(RIm)(CO)L]_x (M  Rh, Ir; RIm  imidazolate, 2-methylimidazolate, 2-benzylbenzimidazolate; L  PPh₃ or P(OPh)₃) are reported. The crystal structure of the novel complex [Rh(2-MeIm)-(CO)₂]₄ (2-MeIm  2-methylimidazolate) has been determined by X-ray methods. The crystals are orthorhombic, space group P2₁2₁2₁, with Z  4 in a unit cell of dimensions a 19.427(12), b 13.419(8), c 12.346(9) Å. The structure has been solved by combined Patterson and direct methods and refined by full-matrix least-squares to R  0.043 for 937 independent observed reflections. It consists of discrete tetrameric complexes in which each Rh atom is in a nearly cis square planar arrangement, bonded to two carbon atoms of carbonyl groups and to two nitrogen atoms of two 2-methylimidazolate ligands, each of which, acting as an exo-bidentate ligand, bridging two metal atoms, so that the four bridging 2-MeIm ligands and the four Rh atoms form a multiatomic ring.     

Cation ordering in Ca2La8(SiO4)6O2

The distribution of La³⁺ and Ca²⁺ over the cation sites in Ca₂La₈(SiO₄)₆O₂ was determined by single-crystal X-ray diffraction. Ca₂La₈(SiO₄)₆O₂ has the apatite structure, and all available evidence indicates that the space group is $\text{P6}{}_3\text{m}$, thus precluding a completely ordered structure. The 6h lattice sites are occupied by La³⁺. In contrast, the 4f sites are occupied equally by La³⁺ and Ca²⁺ ions. Consideration of the properties of the La³⁺ and Ca²⁺ ions suggests that this distribution is thermodynamically favored for this composition. A simple Ising model suggests ordered columns. These would not be precluded by space group $\text{P6}{}_3\text{m}$, if the correlation between adjacent columns were random.     

The chemical oxidation and electronic spectra of the complexes trans-[M(CNR)2(Ph2PCH2CH2PPh2)2] (M = Mo or W)

Oxidation of the complexes $\text{trans}$-[M(CNR)₂(dppe)₂] (A) (M = Mo or W; R = Me, Bu^t or CH₃C₆H₄-$\text{4}$; dppe = Ph₂PCH₂CH₂PPh₂) with diiodine or silver (I) salts gives the paramagnetic cations $\text{trans}$-[M(CNR)₂(dppe)₂]⁺, (M = Mo, R = CH₃C₆H₄-$\text{4}$; M = W, R = Bu^t) and $\text{trans}$-[M(CNR)₂(dppe)₂]²⁺ (M = Mo, R = Me or CH₃C₆H₄-$\text{4}$; M = W, R = Me or Bu^t). Mixtures of products are generally produced when dichlorine or dibromine are the oxidising agents, however pure salts, the seven-coordinate complex cations [MX(CNC₆H₄CH₃-$\text{4}$)₂(dppe)₂]⁺ (B, X = Cl or Br) have been isolated. A simple molecular orbital scheme is proposed for complexes (A) and used to discuss their electronic spectra and their oxidation.     

Isothermal decomposition of ternary oxide AxByOz on an isobar—Stability of perovskite ABO3 (A = La,Sm, Dy; B = Mn,Fe) in a reducing atmosphere

The isothermal decomposition of any ternary oxide A_xB_yO_z on liberation of n moles of oxygen at a constant pressure is found to be driven by the mixing entropy ΔS_m = ?nRln P_O2 of the total entropy change ΔS = ΔS° + ΔS_m. The stability of A_xB_yO_z towards isothermal decomposition into a biphasic solid mixture is derived from the equilibrium condition $\text{ΔG1 = 0}$ as functions of standard changes ΔH° and ΔS°. Assuming ΔS° = 44n and calculating ΔH° in terms of lattice energies U(ABO₃) and U(A₂O₃), the stability of perovskites is given as a function of the ionic radius of the A³⁺ ion. The calculated stability agrees well with that observed. The effect of electronic entropy change ΔS_e on ΔS° is demonstrated for AFeO₃ (A = La, Sm, Dy).