Crystalline Diradical Dianions of Pyrene‐Fused Azaacenes

Although diradicals and azaacenes have been greatly attractive in fundamental chemistry and functional materials, the isolable diradical dianions of azaacenes are still unknown. Herein, we describe the first isolation of pyrene‐fused azaacene diradical dianion salts [(18‐c‐6)K(THF)₂]⁺[(18‐c‐6)K]⁺? 1 ^2?.. and [(18‐c‐6)K(THF)]²⁺? 2 ^2?.. by reduction of the neutral pyrene‐fused azaacene derivatives 1 and 2 with excess potassium graphite in THF in the presence of 18‐crown‐6. Their electronic structures were investigated by various experiments, in conjunction with theoretical calculations. It was found that both dianions are open‐shell singlets in the ground state and their triplet states are thermally readily accessible owing to the small singlet–triplet energy gap. This work provides the first examples of crystalline diradical dianions of azaacenes with considerable diradical character.     

Syntheses and Structures of 5-Membered Heterocycles Featuring 1,2-Diphospha-1,3-Butadiene and Its Radical Anion

LGa(P₂OC)cAAC 2 features a 1,2-diphospha-1,3-butadiene unit with a delocalized π-type HOMO and a π*-type LUMO according to DFT calculations. [LGa(P₂OC)cAAC][K(DB-18-c-6)] 3 [K(DB-18-c-6] containing the 1,2-diphospha-1,3-butadiene radical anion 3 ⋅ ⁻ was isolated from the reaction of 2 with KC₈ and dibenzo-18-crown-6. 3 reacted with [Fc][B(C₆F₅)₄] (Fc=ferrocenium) to 2 and with TEMPO to [L^−HGa(P₂OC)cAAC][K(DB-18-c-6)] 4 [K(DB-18-c-6] containing the 1,2-diphospha-1,3-butadiene anion 4⁻ . The solid state structures of 2 , 3 K(DB-18-c-6], and 4 [K(DB-18-c-6] were determined by single crystal X-ray diffraction (sc-XRD).     

Reduction of Digallane [(dpp‐bian)Ga?Ga(dpp‐bian)] with Group 1 and 2 Metals

The reduction of digallane [(dpp‐bian)Ga? Ga(dpp‐bian)] ( 1 ) (dpp‐bian=1,2‐bis[(2,6‐diisopropylphenyl)imino]acenaphthene) with lithium and sodium in diethyl ether, or with potassium in THF affords compounds featuring the direct alkali metal–gallium bonds, [(dpp‐bian)Ga? Li(Et₂O)₃] ( 2 ), [(dpp‐bian)Ga? Na(Et₂O)₃] ( 3 ), and [(dpp‐bian)Ga? K(thf)₅] ( 7 ), respectively. Crystallization of 3 from DME produces compound [(dpp‐bian)Ga? Na(dme)₂] ( 4 ). Dissolution of 3 in THF and subsequent crystallization from diethyl ether gives [(dpp‐bian)Ga? Na(thf)₃(Et₂O)] ( 5 ). Ionic [(dpp‐bian)Ga]^?[Na([18]crown‐6)(thf)₂]⁺ ( 6 a ) and [(dpp‐bian)Ga]^?[Na(Ph₃PO)₃(thf)]⁺ ( 6 b ) were obtained from THF after treatment of 3 with [18]crown‐6 and Ph₃PO, respectively. The reduction of 1 with Group 2 metals in THF affords [(dpp‐bian)Ga]₂M(thf)_n (M=Mg ( 8 ), n=3; M=Ca ( 9 ), Sr ( 10 ), n=4; M=Ba ( 11 ), n=5). The molecular structures of 4 – 7 and 11 have been determined by X‐ray crystallography. The Ga? Na bond lengths in 3 – 5 vary notably depending on the coordination environment of the sodium atom.     

Quinoidal Azaacenes: 99 % Diradical Character

Quinoidal azaacenes with almost pure diradical character (y=0.95 to y=0.99) were synthesized. All compounds exhibit paramagnetic behavior investigated by EPR and NMR spectroscopy, and SQUID measurements, revealing thermally populated triplet states with an extremely low-energy gap ΔE_ST′ of 0.58 to 1.0 kcal mol⁻¹. The species are persistent in solution (half-life≈14–21 h) and in the solid state they are stable for weeks.     

Stepwise Reduction of Azapentabenzocorannulene

Mono‐ and dianions of 2‐tert‐butyl‐3a²‐azapentabenzo[bc,ef,hi,kl,no]corannulene ( 1 a ) were synthesized by chemical reduction with sodium and cesium metals, and crystallized as the corresponding salts in the presence of 18‐crown‐6 ether. X‐ray diffraction analysis of the sodium salt, [{Na⁺(18‐crown‐6)(THF)₂}₃{Na⁺(18‐crown‐6)(THF)}( 1 a ^2?)₂], revealed the presence of a naked dianion. In contrast, controlled reaction of 1 a with Cs allowed the isolation of singly and doubly reduced forms of 1 a , both forming π‐complexes with cesium ions in the solid state. In [{Cs⁺(18‐crown‐6)}( 1 a ^?)]?THF, asymmetric binding of the Cs⁺ ion to the concave surface of 1 a ^? is observed, whereas in [{Cs⁺(18‐crown‐6)}₂( 1 a ^2?)], two Cs⁺ ions bind to both the concave and convex surfaces of the dianion. The present study provides the first successful isolation and characterization of the reduced products of heteroatom‐containing buckybowl molecules.     

Di‐Benzo‐18‐Crown‐6 and its Derivatives as Ligands in the Search for Ion Channels

Based on the previously reported one‐dimensional channel system [(H₂O)?(DB18C6)(μ₂‐H₂O)_2/2][(H₃O)?(DB18C6)(μ₂‐H₂O)_2/2]I₃ ( 2 ), which is realized by stacking of crown ether molecules (DB18C6 = dibenzo‐18‐crown‐6), other synthetic approaches towards ionic channels and their results are presented in this paper. The “cutting out” approach using DB18C6 as scissor, applied on NaI, yields the compound [Na?(DB18C6)I(THF)][Na?(DB18C6)(H₂O)₂]I(THF)₂(CHI₃) ( 1 ), in high yield. It is based on a neutral and a cationic complex of sodium by DB18C6 linked via H‐bonding to give short chain fragments. The anion exchange approach, trying to replace I₃^? by Br₃^? leads to the intercalation of a cation into a DB18C6 chain in [(Me₃NPh)(DB18C6)]Br₃ ( 3 ). A similar reaction as for the synthesis of 2 , but replacing iodide with bromine, yields finally a brominated DB18C6 ligand. In the presence of iron, the compound [(H₅O₂)?(Br₄‐DB18C6)₂][FeBr₄], 4 , is observed, in which a H₅O₂⁺‐cation is encapsuled by two brominated crown ether molecules. The absence of Fe and an excess of Br₂ leads to the complexation of H₃O⁺, and co‐crystallisation of bromine in [(H₃O)?(Br₄‐DB18C6)]Br₃Br₂ ( 5 ).     

Potassium Carboxylates by Direct Carbonylation of Potassium Alkoxides

Reaction of the K⁺ alkoxide of linalool ( 1 ) in benzene with CO at 425–440 bar and 120–130° for 12–30 h gave the K⁺ salt of 2,6-dimethyl-2-vinyl-5-heptenoic acid ( 4a ) in a ca. 25% yield based on ca. 65% converted alkoxide. Reaction of the [K⁺ ? 18-crown-6] alkoxide of 1 with CO at 50–55 bar and 40° for 90–140 h gave a mixture containing mainly the [K⁺ ? 18-c-6] salts of 4a (ca. 62%) and of the homogeranic acids 3a and 6a (together ca. 27% of the mixture) in a ca. 35% combined yield based on 50–60% converted alkoxide. The uncomplexed or complexed K⁺ alkoxide of (S)? 1 gave, with ca. 85% net retention, the K⁺ salt of (S)- 4a . Reaction of the [K⁺ ? 18-c-6] alkoxide of geraniol ( 2 ) with CO at 50 bar and 40° for 65–70 h gave myrcene ( 10 ) and geranyl formate ( 11 ) in a ca. 40–50% yield each based on ca. 85% converted alkoxide. Reaction of the [K⁺ ? 18-c-6] alkoxide of 3-pentyl-1,4-pentadien-3-ol ( 14 ) at 50 bar and r.t. for 70 h gave a mixture of the [K⁺ ? 18-c-6] salts of 2-pentyl-2-vinyl-3-butenoic acid ( 15a ) (67%) and the 4-pentyl-2,4-hexadienoic acids 18a and 19a (together 23% of the mixture) in a ca. 90% combined yield based on ca. 65% converted alkoxide.     

n‐Type Azaacenes Containing B←N Units

We disclose a novel strategy to design n‐type acenes through the introduction of boron–nitrogen coordination bonds (B←N). We synthesized two azaacenes composed of two B←N units and six/eight linearly annelated rings. The B←N unit significantly perturbed the electronic structures of the azaacenes: Unique LUMOs delocalized over the entire acene skeletons and decreased aromaticity of the B←N‐adjacent rings. Most importantly, these B←N‐containing azaacenes exhibited low‐lying LUMO energy levels and high electron affinities, thus leading to n‐type character. The solution‐processed organic field‐effect transistor based on one such azaacene exhibited unipolar n‐type characteristics with an electron mobility of 0.21 cm² V^?1 s^?1.     

Synthesis of 6-Styrylheptalenes

4-Methylazulenes 3 , 15 , and 23 were transformed into 4-[(methylthio)methyl]azulene 4 , and azulene-4-carbaldehyde dimethyl dithioacetals 16 and 24 , respectively. Vilsmeier formylation of 4 and 16 , and subsequent reduction led to the 1-methyl derivatives 6 and 18 , respectively. The thermal reaction of azulenes 6 , 18 , and 24 with dimethyl acetylenedicarboxylate (ADM) in toluene afforded heptalenes with a (methylthio)methyl group or a [bis(methylthio)]methyl group at C(6). Chlorination of [(methylthio)methyl]heptalene 7 , followed by treatment with HgO and BF₃⋅OEt₂ in aqueous tetrahydrofuran (THF), led to 6-formylheptalene-dicarboxylate 12 in excellent yield. Similarly, hydrolysis of 18 and 24 by HgO and BF₃⋅OEt₂ in aqueous THF afforded the 6-formyl derivatives 21 and 27 , respectively. Wittig reaction of the 6-formyl-substituted heptalenes and phosphonium salts 13a – e in the two-phase system CH₂Cl₂/2n aqueous NaOH resulted in the formation of 6-styryl-substituted heptalenes.     

Preparation and crystal structure of bis(dibenzo-18-crown-6)-(tetrachlorocuprato(II)-Cl,Cl′, Cl″, Cl‴)dipotassium diaqua(dibenzo-18-crown-6)potassium dichlorocuprate(I)-dibenzo-18-crown-6

New mixed complex compound bis(dibenzo-18-crown-6)(tetrachlorocuprato(II)-Cl, Cl′, Cl″, Cl?) dipotassium diaqua(dibenzo-18-crown-6)potassium dichlorocuprate(I)dibenzo-18-crown-6 [(CuCl₄)[K(Db18C6)]₂]·[K(Db18C6)(H₂O)₂]⁺·[CuCl₂]^?·Db18C6 was prepared and its structure was studied by the X-ray structural analysis. The structure was found to be disordered. The asymmetric part of its unit cell contains 1/4 of each of its four components. For a given [CuCl₄]^2? anion its Cu²⁺ cation is disordered over two equally probable positions and its independent Cl atom is disordered over three positions differing by occupancy. In this structure two [K(Db18C6)]⁺ fragment of the complex molecule and the complex cation [K(Db18C6)(H₂O)₂]⁺ are of guest-host type with K⁺ cation as the guest. In this structure the statistically disordered alternating cations and Db18C6 molecules form infinite chains. The statistically disordered [CuCl₂]^? anions also form infinite chains.     

Salts of Anionic Metal Carbonyl Clusters with Cryptand[2.2.2](Na+), DB‐18‐crown‐6(Na+), and Paramagnetic Cp*2Cr+ Cations Obtained by Reduction

Reduction of neutral metal clusters (Co₄(CO)₁₂, Ru₃(CO)₁₂, Fe₃(CO)₁₂, Ir₄(CO)₁₂, Rh₆(CO)₁₆, {CpMo(CO)₃}₂, {Mn(CO)₅}₂) by decamethylchromocene (Cp*₂Cr) or sodium fluorenone ketyl in the presence of cryptand[2.2.2] and DB‐18‐crown‐6 was studied. Nine new salts with paramagnetic Cp*₂Cr⁺, cryptand[2.2.2](Na⁺), and DB‐18‐crown‐6(Na⁺) cations and [Co₆(CO)₁₅]^2– ( 1 , 2 ), [Ru₆(CO)₁₈]^2– ( 3 – 4 ) dianions, [Rh₁₁(CO)₂₃]^3– ( 6 ) trianions, and new [Ir₈(CO)₁₈]^2– ( 5 ) dianions were obtained and structurally characterized. The increase of nuclearity of clusters under reduction was shown. Fe₃(CO)₁₂ preserves the Fe₃ core under reduction forming the [Fe₃(CO)₁₁]^2– dianions in 7 . The [CpMo(CO)₃]₂ and [Mn(CO)₅]₂ dimers dissociate under reduction forming mononuclear [CpMo(CO)₃]^– ( 8 ) and [Mn(CO)₅]^– ( 9 ) anions. In all anions the increase of negative charge on metal atoms shifts the bands attributed to carbonyl C–O stretching vibrations to smaller wavenumbers in agreement with the elongation of the C–O bonds in 1 – 9 . In contrast, the M–C(CO) bonds are noticeably shortened at the reduction. Magnetic susceptibility of the salts with Cp*₂Cr⁺ is defined by high spin Cp*₂Cr⁺ (S = 3/2) species, whereas all obtained anionic metal clusters and mononuclear anions are diamagnetic. Rather weak magnetic coupling between S = 3/2 spins is observed with Weiss temperature from –1 to –11 K. That is explained by rather long distances between Cp*₂Cr⁺ and the absence of effective π–π interaction between them except compound 7 showing the largest Weiss temperature of –11 K. The {DB‐18‐crown‐6(Na⁺)}₂[Co₆(CO)₁₅]^2– units in 2 are organized in infinite 1D chains through the coordination of carbonyl groups of the Co₆ clusters to the Na⁺ ions and π–π stacking between benzo groups of the DB‐18‐crown‐6(Na⁺) cations.     

Quinoidal Azaacenes: 99 % Diradical Character

Quinoidal azaacenes with almost pure diradical character (y=0.95 to y=0.99) were synthesized. All compounds exhibit paramagnetic behavior investigated by EPR and NMR spectroscopy, and SQUID measurements, revealing thermally populated triplet states with an extremely low‐energy gap ΔE_ST′ of 0.58 to 1.0 kcal mol^?1. The species are persistent in solution (half‐life≈14–21 h) and in the solid state they are stable for weeks.     

Zur Reaktion von Makrozyklen mit Lanthanoiden. II. Die Strukturen von [K(thf)3]2[(C22H28N4)2Sm2] · 4THF und [(C22H22N4)Co] · DME

On the Reaction of Macrocycles with Lanthanoids. II. The Crystal Structures of [K(thf)₃]₂[(C₂₂H₂₈N₄)₂Sm₂] · 4 THF and [(C₂₂H₂₂N₄)Co] · DME In a complicated redox reaction [(TMTAA)K₂] and [SmI₂(thf)₂] form the polynuclear metal complex [K(thf)₃]₂[(TMTAT)₂Sm₂]. This complex crystallizes with four molecules THF per formula unit and its structure was determined by single crystal X-ray investigation (spacegroup P2₁/c (No. 14), z = 4, a = 998.0(2) pm, = b = 2618.3(6) pm, c = 1619.4(3) pm, β = 96.52(2)°). In the dimeric unit [(TMTAT)₂Sm₂]^2? the Sm³⁺ ions are bonded to the four N atoms of the macrocyclic ligand and one C₆H₄ ring of the second ligand is attached η⁶ like to one metal ion. Additionally two [K(thf)₃]⁺ fragments are bonded to this central unit, and therefor coordination number seven results for the K⁺ ion. [TMTAA]^2? is not reduced by [Cp₂Co] in a similar reaction. The monomeric paramagnetic complex [(TMTAA)Co] (μ_eff = 2,76 μ_B) is formed instead. The structure reveils a square planar coordination of the Co atom by the four N atoms of the TMTAA ligand (spacegroup C2/c (No. 15), z = 4, a = 1945.1(4) pm, b = 1165.6(2) pm, c = 1144.7(2) pm, β = 116.38(1)°).     

Indeno[2,1-a]fluorene-11,12-dione Radical Anions: Synthesis,Characterization, and Properties

The one-electron reduction of indeno[2,1-a]fluorene-11,12-dione ( IF ) with various alkali metals prepare the radical anion salts. The data about different structures, properties, and characterization was obtained by single-crystal X-ray diffraction, electron paramagnetic resonance (EPR) spectroscopy, superconducting quantum interference device (SQUID) measurements, and physical property measurement system (PPMS). Compound IF ^.−K⁺(18-c-6) is regarded as a one-dimensional magnetic chain through C−H⋅⋅⋅C interaction. Theoretical calculations and magnetic results showed that [ IF ^.−K⁺(15-c-5)]₂ is a dimer with an open-shell ground state. Compounds IF ^.−Na⁺(15-c-5) and IF ^.−K⁺(cryptand) are monoradical anion salts: IF ₂^.−Li⁺ possesses unique π-stack structure with an interplanar separation less than 3.46 Å, making it a semiconductor (δ_RT=1.9×10⁻⁴ S ⋅ cm⁻¹). This work gives insights into multifunctional radical anions, and describes the design and development of different functional radicals.     

A thermodynamic study of complex formation between dicyclohexyl-18-crown-6 (DCH18C6) and La3+, UO 22+ , Ag+, and NH 4+ cations in acetonitrile-tetrahydrofuran binary media using conductometric method

The complex formation between La³⁺, UO₂²⁺ Ag⁺, and NH₄⁺ cations and macrocyclic ligand, dicyclohexyl-18-crown-6 (DCH18C6), was studied in acetonitrile-tetrahydrofuran (AN-THF) binary mixtures at different temperatures using the conductometric method. The results show that with the exception of complexation of the NH₄⁺ cation with DCH18C6 in pure acetonitrile, the stoichiometry of all the complexes is being 1: 1 (M: L). The stability constants of the complexes were determined using a GENPLOT computer program. The nonlinear behavior which was observed for changes of log K _f of the complexes versus the composition of the mixed solvent was discussed in terms of solvent-solvent interaction in their binary solution, which results in changing the chemical and physical properties of the constituent solvents when they mix with one another and, therefore, changing the solvation capacities of the metal cations, crown ether molecules, and even the resulting complexes with changing the mixed solvent composition. The results show that the selectivity of DCH18C6 for the studied cations changes with the composition of the AN-THF binary system. The sequence of stabilities of complexes in an AN-THF binary solution (mol. % AN = 75.0) at 25°C is [(DCH18C6)La)]³⁺ > [(DCH18C6)UO₂]²⁺ > [(DCH18C6)Ag]⁺ ∼ [(DCH18C6)NH₄]⁺, but in the case of other binary systems of AN/THF (mol. % AN = 25.0 and 50.0) is [(DCH18C6)La]⁺ > [(DCH18C6)NH₄]⁺ ∼ [DCH18C6)UO₂]²⁺ > [(DCH18C6)Ag]⁺. The text was submitted by the authors in English.     

Stable Oxindolyl‐Based Analogues of Chichibabin's and Müller's Hydrocarbons

Chichibabin's and Müller's hydrocarbons are classical open‐shell singlet diradicaloids but they are highly reactive. Herein we report the successful synthesis of their respective stable analogues, OxR‐2 and OxR‐3 , based on the newly developed oxindolyl radical. X‐ray crystallographic analysis on OxR‐2 reveals a planar quinoidal backbone similar to Chichibabin's hydrocarbon, in accordance with its small diradical character (y₀=11.1 %) and large singlet–triplet gap (ΔE_S‐T=−10.8 kcal mol⁻¹). Variable‐temperature NMR studies on OxR‐2 disclose a slow cis/trans isomerization process in solution through a diradical transition state, with a moderate energy barrier (ΔG^≠_298K=15–16 kcal mol⁻¹). OxR‐3 exhibits a much larger diradical character (y₀=80.6 %) and a smaller singlet–triplet gap (ΔE_S‐T=−3.5 kcal mol⁻¹), and thus can be easily populated to paramagnetic triplet diradical. Our studies provide a new type of stable carbon‐centered monoradical and diradicaloid.     

The Preparation of Luminescent,Mechanochromic Molecular Containers from Non-Emissive Components: The Box Cations, [Au6(Triphos)4Br]5+ and [Au6(Triphos)4Br2]4+

Two new molecular boxes, the mono-bromo box [Au₆(Triphos)₄Br](SbF₆)₅⋅6(CH₂Cl₂), 4 mB , and the dibromo box, [Au₆(Triphos)₄Br₂⋅H₂O](SbF₆)₄⋅4(CH₂Cl₂), 5 dB , have been prepared in crystalline form. Although constructed from non-luminescent components, both are strongly luminescent. Like its chloro counterpart, the mono-bromo box [Au₆(Triphos)₄Br](SbF₆)₅⋅6(CH₂Cl₂), 4 mB , is mechanochromic. Under grinding, it loses its luminescence. The bromo-bridged helicate, [(μ-Br){Au₃(Triphos)₂}₂](CF₃SO₃)₅⋅2(CH₂Cl₂), 3μ-H , with a cation that is isomeric with the box [Au₆(Triphos)₄Br]⁵⁺, has also been prepared and crystallographically characterized. Unlike its chloro analogue, [(μ-Br){Au₃(Triphos)₂}₂](CF₃SO₃)₅⋅2(CH₂Cl₂) is not luminescent. Thus, the cation produced upon grinding may be the cation present in the bromo-bridged helicate, [(μ-Br){Au₃(Triphos)₂}₂](CF₃SO₃)₅⋅2(CH₂Cl₂), 3μ-H . The dibromo box, [Au₆(Triphos)₄Br₂⋅H₂O](SbF₆)₄⋅4(CH₂Cl₂), 5 dB , is not significantly mechanochromic.     

A high-spin diradical dianion and its bridged chemically switchable single-molecule magnet

Triplet diradicals have attracted tremendous attention due to their promising application in organic spintronics, organic magnets and spin filters. However, very few examples of triplet diradicals with singlet–triplet energy gaps (ΔE_ST) over 0.59 kcal mol⁻¹ (298 K) have been reported to date. In this work, we first proved that the dianion of 2,7-di-tert-butyl-pyrene-4,5,9,10-tetraone (2,7-tBu₂-PTO) was a triplet ground state diradical in the magnesium complex 1 with a singlet–triplet energy gap ΔE_ST = 0.94 kcal mol⁻¹ (473 K). This is a rare example of stable diradicals with singlet–triplet energy gaps exceeding the thermal energy at room temperature (298 K). Moreover, the iron analog 2 containing the 2,7-tBu₂-PTO diradical dianion was isolated, which was the first single-molecule magnet bridged by a diradical dianion. When 2 was doubly reduced to the dianion salt 2K2, single-molecule magnetism was switched off, highlighting the importance of diradicals in single-molecule magnetism.

We report a triplet diradical dianion in magnesium complex with ΔE_ST = 0.94 kcal mol⁻¹ (473 K). Its iron analog is the first single-molecule magnet bridged by a diradical dianion, and the SMM property is switched off through two-electron reduction.     

Isopiestic measurement and solubility evaluation of the ternary system (CaCl2 + SrCl2 + H2O) at T = 298.15 K

Water activities in the ternary system (CaCl₂ + SrCl₂ + H₂O) and its sub-binary system (CaCl₂ + H₂O) at T = 298.15 K have been elaborately measured by an isopiestic method. The data of the measured water activity were used to justify the reliability of solubility isotherms reported in the literature by correlating them with a thermodynamic Pitzer–Simonson–Clegg (PSC) model. The model parameters for representing the thermodynamic properties of the (CaCl₂ + H₂O) system from (0 to 11) mol ⋅ kg⁻¹ at T = 298.15 K were determined, and the experimental water activity data in the ternary system were compared with those predicted by the parameters determined in the binary systems. Their agreement indicates that the PSC model parameters can reliably represent the properties of the ternary system. Under the assumption that the equilibrium solid phases are the pure solid phases (SrCl₂ ⋅ 6H₂O and CaCl₂ ⋅ 6H₂O)_(s) or the ideal solid solution consisting of CaCl₂ ⋅ 6H₂O_(s) and SrCl₂ ⋅ 6H₂O_(s), the solubility isotherms were predicted and compared with experimental data from the literature. It was found that the predicted solubility isotherm agrees with experimental data over the entire concentration range at T = 298.15 K under the second assumption described above; however, it does not under the first assumption. The modeling results reveal that the solid phase in equilibrium with the aqueous solution in the ternary system is an ideal solid solution consisting of SrCl₂ ⋅ 6H₂O_(s) and CaCl₂ ⋅ 6H₂O_(s). Based on the theoretical calculation, the possibility of the co-saturated points between SrCl₂ ⋅ 6H₂O_(s) and the solid solution (CaCl₂ ⋅ 6H₂O + SrCl₂ ⋅ 6H₂O)_(s) and between CaCl₂ ⋅ 6H₂O_(s) and the solid solution (CaCl₂ ⋅ 6H₂O + SrCl₂ ⋅ 6H₂O)_(s), which were reported by experimental researchers, has been discussed, and the Lippann diagram of this system has been presented.     

Geometry optimization of the ring-opened oxirane diradical: mechanism of the addition reaction of the triplet oxygen atom to olefins

Geometry optimizations of several low-lying diradical states of the ring-opened oxirane (·CH₂CH₂O·) were performed by using the energy gradients of the UHF MINDO/3, STO-3G and 4-31G solutions. Both the STO-3G and 4-3 IG methods predict that the most stable form is the triplet state of the non-twisted σπ conformation in which the unpaired spins localized on the terminal carbon and oxygen atoms are oriented perpendicularly to each other. The singlet σσ diradical state in which both the radical-site p orbitals are coplanar with the molecular framework is only 2.3 (STO-3G) and 1.2 (4-31G) kcal/mol less stable than the triplet σπ diradical state. It is found that the geometry of the singlet σσ diradical is unique in that the C-C-O angle is noticeably small as compared with various other diradical states. Implications of these results to the mechanism of the oxirane-forming O(³P) + C₂H₄ reaction are discussed.