The Effect of Guest Metal Ions on the Reduction Potentials of Uranium(VI) Complexes: Experimental and Theoretical Investigations

Two mononuclear uranyl complexes, [UO₂L¹] ( 1 ) and [UO₂L²] ⋅ 0.5 CH₃CN ⋅ 0.25 CH₃OH ( 2 ), have been synthesized from two multidentate N₃O₄ donor ligands, N,N′-bis(5-methoxysalicylidene)diethylenetriamine (H₂L¹) and N,N′-bis(3-methoxysalicylidene)diethylenetriamine (H₂L²), respectively, and have been structurally characterized. Both complexes 1 and 2 showed a reversible U^VI/U^V couple at −1.571 and −1.519 V, respectively, in cyclic voltammetry. The reduction potential of the U^VI/U^V couple shifted towards more positive potential on addition of Li⁺, Na⁺, K⁺, and Ag⁺ metal ions to acetonitrile solutions of complex 2 , and the resulting potential was correlated with the Lewis acidity of the metal ions and was also justified by theoretical DFT calculations. No such shift in reduction potential was observed for complex 1 . All four bimetallic products, [UO₂L²Li_0.5](ClO₄)_0.5 ( 3 ), [UO₂L²Na(ClO₄)]₂ ( 4 ), [UO₂L²Ag(NO₃)(H₂O)] ( 5 ), and [(UO₂L²)₂K(H₂O)₂]PF₆ ( 6 ), formed on addition of the Li⁺, Na⁺, Ag⁺, and K⁺ metal ions, respectively, to acetonitrile solutions of complex 2 , were isolated in the solid state and structurally characterized by single-crystal X-ray diffraction. In all the species, the inner N₃O₂ donor set of the ligand encompasses the equatorial plane of the uranyl ion and the outer open compartment with O₂O′₂ donor sites hosts the second metal ion.     

Radical Anions,Radical-Anion Salts,and Anionic Complexes of 2,1,3-Benzochalcogenadiazoles

By means of cyclic voltammetry (CV) and DFT calculations, it was found that the electron-acceptor ability of 2,1,3-benzochalcogenadiazoles 1 – 3 (chalcogen: S, Se, and Te, respectively) increases with increasing atomic number of the chalcogen. This trend is nontrivial, since it contradicts the electronegativity and atomic electron affinity of the chalcogens. In contrast to radical anions (RAs) [ 1 ]^.− and [ 2 ]^.−, RA [ 3 ]^.− was not detected by EPR spectroscopy under CV conditions. Chemical reduction of 1 – 3 was performed and new thermally stable RA salts [K(THF)]⁺[ 2 ]^.− ( 8 ) and [K(18-crown-6)]⁺[ 2 ]^.− ( 9 ) were isolated in addition to known salt [K(THF)]⁺[ 1 ]^.− ( 7 ). On contact with air, RAs [ 1 ]^.− and [ 2 ]^.− underwent fast decomposition in solution with the formation of anions [ECN]⁻, which were isolated in the form of salts [K(18-crown-6)]⁺[ECN]⁻ ( 10 , E=S; 11 , E=Se). In the case of 3 , RA [ 3 ]^.− was detected by EPR spectroscopy as the first representative of tellurium–nitrogen π-heterocyclic RAs but not isolated. Instead, salt [K(18-crown-6)]⁺₂[ 3 -Te₂]²⁻ ( 12 ) featuring a new anionic complex with coordinate Te−Te bond was obtained. On contact with air, salt 12 transformed into salt [K(18-crown-6)]⁺₂[ 3 -Te₄- 3 ]²⁻ ( 13 ) containing an anionic complex with two coordinate Te−Te bonds. The structures of 8 – 13 were confirmed by XRD, and the nature of the Te−Te coordinate bond in [ 3 -Te₂]²⁻ and [ 3 -Te₄- 3 ]²⁻ was studied by DFT calculations and QTAIM analysis.     

Formation and hydrolysis of gas‐phase [UO2(R)]+: R═CH3, CH2CH3, CH═CH2, and C6H5

The goals of the present study were (a) to create positively charged organo‐uranyl complexes with general formula [UO₂(R)]⁺ (eg, R═CH₃ and CH₂CH₃) by decarboxylation of [UO₂(O₂C─R)]⁺ precursors and (b) to identify the pathways by which the complexes, if formed, dissociate by collisional activation or otherwise react when exposed to gas‐phase H₂O. Collision‐induced dissociation (CID) of both [UO₂(O₂C─CH₃)]⁺ and [UO₂(O₂C─CH₂CH₃)]⁺ causes H⁺ transfer and elimination of a ketene to leave [UO₂(OH)]⁺. However, CID of the alkoxides [UO₂(OCH₂CH₃)]⁺ and [UO₂(OCH₂CH₂CH₃)]⁺ produced [UO₂(CH₃)]⁺ and [UO₂(CH₂CH₃)]⁺, respectively. Isolation of [UO₂(CH₃)]⁺ and [UO₂(CH₂CH₃)]⁺ for reaction with H₂O caused formation of [UO₂(H₂O)]⁺ by elimination of ·CH₃ and ·CH₂CH₃: Hydrolysis was not observed. CID of the acrylate and benzoate versions of the complexes, [UO₂(O₂C─CH═CH₂)]⁺ and [UO₂(O₂C─C₆H₅)]⁺, caused decarboxylation to leave [UO₂(CH═CH₂)]⁺ and [UO₂(C₆H₅)]⁺, respectively. These organometallic species do react with H₂O to produce [UO₂(OH)]⁺, and loss of the respective radicals to leave [UO₂(H₂O)]⁺ was not detected. Density functional theory calculations suggest that formation of [UO₂(OH)]⁺, rather than the hydrated U^VO₂⁺, cation is energetically favored regardless of the precursor ion. However, for the [UO₂(CH₃)]⁺ and [UO₂(CH₂CH₃)]⁺ precursors, the transition state energy for proton transfer to generate [UO₂(OH)]⁺ and the associated neutral alkanes is higher than the path involving direct elimination of the organic neutral to form [UO₂(H₂O)]⁺. The situation is reversed for the [UO₂(CH═CH₂)]⁺ and [UO₂(C₆H₅)]⁺ precursors: The transition state for proton transfer is lower than the energy required for creation of [UO₂(H₂O)]⁺ by elimination of CH═CH₂ or C₆H₅ radical.     

Insertion of trivalent uranium in macrocyclic crown-ethers: EXAFS and X-ray structural analyses

The structure of the first U(III) macrocyclic coordinated complex, [U(III)(BH₄)₂ dicyclohexyl-(18-crown-6)]₂U(IV)C1₅(BH₄) (complex I), has been determined from three dimensional X-ray diffraction data. The metal atom in trivalent state is inserted in the crown cavity as a monovalent cation [U(BH₄)₂]⁺. This compound resulted from a partial oxidation in a dichloromethane solution of U₃(III)(BH₄)₉[dicyclohexyl-(18-crown-6)]₂ (complex ^II).EXAFS analysis performed on powdered sample of the homologue of complex II, U₃(BH₄)₉[18-crown-6]₂ (complex III) has shown the presence of carbon atoms in the vicinity of the uranium atom and hence has proved that all the oxygen atoms of the crown-ether are directly coordinated to the metal.In parallel, an EXAFS study on the uranyl complex UO₂(18-crown-6)(C1O₄)2 (complex IV) has verified the insertion of the uranyl ion in the solid state, and given evidence for its partial de-insertion in an acetonitrile solution.     

Crystal structures of the dicyclohexyl-(18-crown-6) uranyl perchlorate complex and of its hydrolysis product

The structures of dicyclohexyl-(18-crown-6) uranyl perchlorate, [(C₂₀H₃₆O₆)UO₂] (ClO₄)₂ (complex I) and of dicyclohexyl-(18-crown-6) uranyl hydroxyperchlorate [C₂₀H₃₆O₆]₃ [(UO₂)₂(H₂O)₆] · (ClO₄)₂, CH₃CN, (complex II) have been determined from three dimension X-ray diffraction data.The uranyl group is directly coordinated to the oxygen atoms of the polyether ring in complex I; its hydrolysis (complex II) leads to a dimerization of the uranyl ions by sharing two OH groups with an U-U distance of only 3.827(8) Å. The polyether molecules are connected by hydrogen bonds with the dimeric ion [(UO₂)₂ (OH)₂ (H₂O)₆]²⁺.     

Synthesis, spectroscopy, electrochemistry and thermal study of uranyl N3O2 Schiff base complexes

The new [UO₂L(CH₃OH)] [where L?=?bis(salicylaldehyde)2,6-diiminopyridine (L¹), bis(5-methoxysalicylaldehyde)2,6-diiminopyridine (L²), bis(5-bromosalicylaldehyde)2,6-diiminopyridine (L³), bis(5-nitrosalicylaldehyde)2,6-diiminopyridine (L⁴)] complexes were synthesized and characterized by IR, UV?Cvis and elemental analysis. Methanol solvent is coordinated to uranyl complexes. The electrochemical properties of the uranyl complexes were investigated by cyclic voltammetry in DMF solvent. Thermogravimetry and differential thermoanalysis of the uranyl complexes were carried out in the range of 20?C700?°C. The UO₂L⁴ complex was decomposed in two and the others were decomposed in three stages. Up to 85?°C, the coordinated solvent was released then the Schiff base ligands were decomposed in one or two steps. Decomposition of synthesized complexes is related to the Schiff base characteristics. The thermal decomposition reaction is first order for the studied complexes.     

Synthesis and crystal structure of bis[(18-crown-6)oxonium]tetrabromomanganese(II)

A new complex compound, bis[(18-crown-6)oxonium]tetrabromomanganese(II), 2[(H₃O)⁺(18-crown-6)]·[MnBr₄]^2–, was prepared and studied by X-ray diffraction to reveal its unusual cubic crystal structure, space group Fd $ \bar 3 A new complex compound, bis[(18-crown-6)oxonium]tetrabromomanganese(II), 2[(H₃O)⁺(18-crown-6)]·[MnBr₄]^2–, was prepared and studied by X-ray diffraction to reveal its unusual cubic crystal structure, space group Fd, a 20.424 ?, and Z 8. In this crystal structure, the complex cation [(H₃O)⁺(18-crown-6)] the point symmetry position and the anion [MnBr₄]²⁻ with the point symmetry 23. The complex cation [(H₃O)⁺(18-crown-6)] has a guest-host structure, and, unlike metal complexes by hydrogen bonds between H₃O⁺ hydrogens and 18-crown-6 oxygens, rather than by coordination bonds. The pyramidal cation H₃O⁺ in this crystal structure is statistically disordered, and the tetrahedral anion [MnBr₄]²⁻ is reorientationally disordered. Original Russian Text ? A.N. Chekhlov, 2008, published in Zhurnal Obshchei Khimii, 2008, vol. 78, No. 10, pp. 1622–1626.     

Two Uranyl Complexes with Pyromellitic Acid. A Heterometallic Complex with U=O–CuII Interaction

Two uranyl complexes based on pyromellitic acid were hydrothermally synthesized, and their X‐ray single‐crystal diffraction structures were determined. Complex [UO₂(Hbtec)]^–(Himd)⁺ · H₂O ( 1 ) (H₄btec = pyromellitic acid, imd = imidazole), is an ionic complex, which shows a typical (4, 4) topological structure in the space. A heterometallic complex, UO₂Cu(btec)(phen) ( 2 ) (phen = 1,10‐phenanthroline) results from the reaction of uranyl nitrate and copper(II) bromide with pyromellitic acid. The structure of complex 2 revealed that the chains of UO₇ and CuO₃N₂ units were connected to each other through the carboxyl groups and U=O–Cu interactions to create a two‐dimensional framework.     

Stability constants of cesium complexes with 18-crown-6 in ionic liquids

The stability constants of the complex[Cs(18C6)]⁺ (18C6 is 18-crown-6 (L)) in N-butylpyridinium methyl sulfate (I) and of the complex [Cs(18C6)₂]⁺ in 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide (II) were measured by using ¹³³Cs NMR spectroscopy at 23°C. It was found that logK(Cs + L) in solvent I is 1.20±0.13 and logK(CsL + L) in solvent IIis 1.18±0.05. For the complex [Cs(18C6)₂]⁺, the dependence of its stability constant on the temperature in the 23–50°C range was obtained and the enthalpy change in the complexation was determined: ΔH(CsL + L)= ?47 kJ/mol. It was demonstrated that the enthalpy change is favorable for the formation of [Cs(18C6)₂]⁺, while the entropy change hinders the complexation.     

Synthesis,characterization, and photochemistry of the supramolecules formed from chromium(III) thiocyanato anion associated with crown ethers

A series of anionic chromium(III) thiocyanato complexes with metal crown ether cations have been prepared and characterized. These complexes have the form [Crown-M]₂⁺[Cr(NCS)₅(H₂O)]²⁻ and [Crown-M]₃⁺[Cr(NCS)₆]³⁻, where M=Na⁺, K⁺, or NH₄⁺ and crown represents the crown ether. The crown ethers are 15-crown-5, B-15-crown-5, 18-crown-6, DB-18-crown-6, and DB-24-crown-8, where B- and DB- stand for benzo- and dibenzo-, respectively. The complexes are stable for at least 20 h in the dark in dimethylformamide(DMF) or in acetonitrile, and they release thiocyanate slowly, k=(0.71–2.67)×10⁻⁹ mol/(L s) in acetonitrile in the dark. Photoanation of thiocyanate was observed for the complexes in DMF and in acetonitrile. The quantum yields of thiocyanate release in DMF and in acetonitrile are reported. The quantum yields were in the range 0.05 to 0.52 mol einstein⁻¹ and were solvent and wavelength dependent. In general, larger quantum yields were observed in DMF than in acetonitrile. The photoreaction mechanism is discussed.     

Etude des complexes sulfosalicylate de cuivre(III), nickel(II), cobalt(II) et uranyle(II) a l'aide d'une resine echangeuse de cations: Study of the sulphosalicylate complexes ofcopper(II), nickel(II), cobalt(II) and uranyl(II) by means of cation-exchange resins.

Study of the sulphosalicylate complexes of copper(II), nickel(II), cobalt(II) and uranyl(II) by means of cation-exchange resins.The conditional stability constants of the 1:1 complexes of the sulphosalicylate ions (L^3-) with copper(II), nickel(II), cobalt(II) and uranyl ions have been determined in a sodium perchlorate solution (0.1 M) and at various pH values by a cation-exchange method based on Schubert's procedure. The limits of application of the method are discussed. The variation with pH of the conditional stability constants can be explained by the existence of the complexes: CuH₂L, CuHL, CuL^-; NiH₂L⁺, NiHL, NiL^-; CoHL, CoL^-; UO₂H₂L⁺, UO₂HL, UO₂L^-, UO₂LOH^2-. The stability constants of these complexes are reported. Distribution diagrams of the various complexes of each element with pH and total concentration of sulphosalicylate parameters are given.     

Synthesis and crystal structure of hexakis(isothiocyanato)erbium(III) thiocyanate bis(18-crown-6)dipotassium bis[(18-crown-6)ethanolpotassium]

A new complex compound, [K₂(18-crown-6)₂[K(18-crown-6)(EtOH)]₂[Er(NCS)₆](SCN) (I), was synthesized and its crystal structure was studied by X-ray diffraction. In this work, the synthes and X-ray difraction stady of the crystals of a new complex, hexakis (isothiocyanato) erbiu(III) thiocyanate bis(18-crown-6) dipotassium bis(18-crown-6) ethanolpotassium], [K₂(18-crown-6)₂][K(18-crown-6)(ETON)]₂[Er(NCS)₆(SCN)(I)] are described. In crystal I, the alternating [Er(NCS)₆]^3? anions and binuclear complex cation [K(18-crown-6)₂]²⁺ from infinite chains via the F-S bonds, while two complex cations [K(18-crown-6)(ETON)]⁺ and the statistically disordered SCN^? anion between them are linked by the hydragen bonds O-H…S and O-H…N. Complex I contains the host-guest complex cations [K₂(18-crown-6)₂)]²⁺ and [K(18-crown-6)(ETON)]⁺ [1]. The alternating octabedral [Er(NCS)₆]^3? anions and binuclear complex cations [K₂(18-crown-6)₂]²⁺of crystal I form infinite chains via the K-S bonds, while two complex cations [K(18-crown-6)(EtOH)]⁺ and the statistically disordered SCN^? anion lying between them are linked by interionic hydrogen bonds O-H…S and O-H…N. Complex I contains the host-guest complex cations [K₂(18-crown-6)₂]²⁺ and [K(18-crown-6)(EtOH)]⁺ [1].     

The Influence of Nucleophilic and Redox Pincer Character as well as Alkali Metals on the Capture of Oxygen Substrates: The Case of Chromium(II)

Dimeric [CrL]₂, where L is the conjugate base of bis-pyrazolyl pyridine, is evaluated for its ability to undergo inner sphere and outer sphere redox chemistry. It reacts with Cp₂Fe⁺ to give [Cr₄(HL)₄(μ₄-O)]²⁺, still containing divalent Cr. Reduction (KC₈) of [CrL]₂ by two electrons gives [K₂(THF)₃Cr₃L₃(μ₃-O)], and by four electrons gives [K₄(THF)₁₀Cr₂L₂(μ-O)], each of which has scavenged (hydr)oxide from glass surface because of the electrophilicity of the underligated Cr. [K₄(THF)₁₀Cr₂L₂(μ-O)], is shown by comprehensive DFT calculations and analysis of intra-ligand bond lengths to contain a pyridyl radical L³⁻ and Cr^II, illustrating that this pincer is proton-responsive, redox active, and a versatile donor to associated K⁺ ions here. The K⁺ electrophiles interact with electron-rich oxo, but do not significantly (>5 kcal mol⁻¹) alter spin state energies. Inner sphere oxidation of [CrL]₂ with a quinone gives [Cr₂L₂(semiquinone)₂], while pre-reduced [CrL]₂²⁻ reacts with quinone to give [K₃(THF)₃Cr₂L₂(catecholate)₂(μ-OH)], a product of capture of two undercoordinated LCr(catecholate)¹⁻ by hydroxide.     

Heterometallic Trinuclear Complexes of Macrocyclic Oxamide: Synthesis,Crystal Structures,and Magnetic Properties

Two heterometallic trinuclear complexes of macrocyclic oxamide [Co(Ni L¹ )₂ L² (H₂O)] · 3H₂O ( 1 ) and [Mn(Ni L¹ )₂ L² (H₂O)] · 0.5CH₃OH · 1.5H₂O ( 2 ) (H₂ L¹ = 2,3‐dioxo‐5,6,14,15‐dibenzo‐1,4,8,12‐tetraazacyclopentadeca‐7,13‐diene, H₂ L² = 5‐sulfosalicylic acid) were synthesized and structurally characterized by elemental analysis, IR spectroscopy, and X‐ray diffraction. Single‐crystal X‐ray analyses reveal that both the complexes contain discrete neutral trinuclear [(Ni L¹ )₂M L² (H₂O)] (for 1 and 2 , M = Co, Mn, respectively) moieties. The structures of 1 and 2 have oxamido‐bridged trinuclear [M^IINi^II₂] units and consist of one‐dimensional chains formed by strong intermolecular hydrogen bonds. Furthermore, the magnetic properties of complex 1 were investigated and discussed in detail.     

Synthesis, characterisation and chemical reactivity of some new dioxouranium(VI) complexes of 2-aminobenzoylhydrazone of butane-2,3-dione

A new series of dioxouranium(VI) complexes of a potential ONNO tetradentate donor 2-aminobenzoylhydrazone of butane-2,3-dione (L₁H₂) have been synthesized. At pH 2·5–4·0, the donor (L₁H₂) reacts in the keto form and complexes of the type [UO₂(L₁H₂)(X)₂] (X⁻=Cl⁻, Br⁻, NO ₃ ⁻ , NCS⁻, ClO ₄ ⁻ , CH₃COO⁻, 1/2SO ₄ ²⁻ ) are obtained. At higher pH (6·5–7), the complex of the enol form having the formula [UO₂(L₁)(H₂O)] has been isolated. On reaction with a monodentate lewis base (B), both types of complexes yield adducts of the type [UO₂(L₁)(B)]. All these complexes have been characterised adequately by elemental analyses and other standard physicochemical techniques. Location of the bonding sites of the donor molecule around the uranyl ion, status of the uranium-oxygen bond and the probable structure of the complexes have also been discussed.     

Structural Diversity of Sheets in Rubidium Uranyl Oxoselenates: Synthesis and Crystal Structures of Rb2[(UO2)(SeO4)2(H2O)](H2O), Rb2[(UO2)2(SeO4)3(H2O)2](H2O)4, and Rb4[(UO2)3(SeO4)5(H2O)]

Single crystals of three rubidium uranyl selenates, Rb₂[(UO₂)(SeO₄)₂(H₂O)](H₂O) ( 1 ), Rb₂[(UO₂)₂(SeO₄)₃(H₂O)₂](H₂O)₄ ( 2 ), and Rb₄[(UO₂)₃(SeO₄)₅(H₂O)] ( 3 ), have been prepared by evaporation from aqueous solutions made out of mixtures of uranyl nitrate, selenic acid and Rb₂CO₃. The structures of all compounds have been solved by direct methods on the basis of X‐ray diffraction data sets. The crystallographic data are as follows: ( 1 ): orthorhombic, Pna2₁, a = 13.677(2), b = 11.8707(13), c = 7.6397(9) Å, V = 1240.4(3) ų, R₁ = 0.045 for 2396 independent observed reflections; ( 2 ): triclinic, P1¯, a = 8.4261(12), b = 11.8636(15), c = 13.3279(18) Å, α = 102.612(10), β = 107.250(10), γ = 102.510(10)°, V = 1183.7(3) ų, R₁ = 0.067 for 4762 independent observed reflections; ( 3 ): orthorhombic, Pbnm, a = 11.3761(14), b = 15.069(2), c = 19.2089(17) Å, V = 3292.9(7) ų, R₁ = 0.075 for 3808 independent observed reflections. The structures of the phases 1 , 2 , and 3 are based upon uranyl selenate hydrate sheets composed from corner‐sharing pentagonal [UO₇]^8— bipyramids and [SeO₄]^2— tetrahedra. In the crystal structure of 1 , the sheets have composition [(UO₂)(SeO₄)₂(H₂O)]^2— and run parallel to (001). The interlayer contains Rb⁺ cations and additional H₂O molecules. In structure of 2 , the [(UO₂)₂(SeO₄)₃(H₂O)₂]^2— sheets are oriented parallel to (101). Highly disordered Rb⁺ cations and H₂O molecules are located between the sheets. The structure of 3 is based upon [(UO₂)₃(SeO₄)₅(H₂O)]^4— sheets stacked parallel to (010) and contains Rb⁺ cations in the interlayers. The topologies of the uranyl oxoselenate sheets observed in the structures of 1 , 2 , and 3 are related to the same simple and highly‐symmetric graph consisting of 3‐connected white and 6‐connected black vertices.     

Synthesis of N'-[4'-Benzo(15-Crown-5)]-4-Tolylaminoglyoxime and N'-[4'-Benzo(15-Crown-5)]-4-Chlorophenylaminoglyoxime and Their Complexes with Copper (II), Nickel (II) and Cobalt (II)

N'-[4'-benzo(15-crown-5)]-4-tolylaminoglyoxime (H₂L¹),the sodium chloride salt of H₂L¹ (H₂L¹...NaCl),N'-[4'-benzo(15-crown-5)]-4-chlorophenylaminoglyoxime(H₂L²) and the sodium chloride salt of H₂L² (H₂L²...NaCl)have been prepared from p-chlorophenylchloroglyoxime,p-tolylchloroglyoxime, 4'-aminobenzo[15-crown-5] and sodiumbicarbonate or sodium bicarbonate and sodium chloride. Nickel (II),cobalt (II) and copper (II) complexes of H₂L and H₂L...NaClhave a metal-ligand ratio of 1 : 2 and the ligand coordinatesthrough the two N atoms, as do most of the vic-dioximes. Their IR spectra and elemental analyses are given, together with¹H NMR spectra of the ligands.     

Thermodynamics of cesium complexes formation with 18-crown-6 in ionic liquids

Thermodynamic data for cesium complexes formation with 18-crown-6 (18C6, L) [Cs(18C6)]⁺ in N-butyl-4-methyl-pyridinium tetrafluoroborate ([BMPy][BF₄], I), in 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF₄], II) and in 1-butyl-3-methylimidazolium dicyanamide ([BMIM][N(CN)₂], III) were measured with NMR ¹³³Cs technique at 23–50 °C. The stability of cesium complex in RTILs is estimated to be in the range between water and DMFA. Stability constants for [Cs(18C6)]⁺ are found to decrease as temperature is increasing. The following values for lgK(Cs+L) and ΔH(Cs+L) at 23 °C are determined: 2.6 (0.3), ?47(1) kJ/mol (RTIL I); 2.8(0.3), ?80(3) kJ/mol (RTIL II) and 3.03 (0.08), ?47(2) kJ/mol (RTIL III). It is demonstrated that enthalpy change promotes complex formation while the corresponding change of entropy is negative and provides decomposition of [Cs(18C6)]⁺.     

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).     

Gallium “Shears” for C=N and C=O Bonds of Isocyanates

Digallane [L¹Ga−GaL¹] ( 1 , L¹=dpp-bian=1,2-[(2,6-iPr₂C₆H₃)NC]₂C₁₂H₆) reacts with RN=C=O (R=Ph or Tos) by [2+4] cycloaddition of the isocyanate C=N bonds across both of its C=C−N−Ga fragments to afford [L¹(O=C−NR)Ga−Ga(RN−C=O)L¹] (R=Ph, 3 ; R=Tos, 4 ). The reactions with both isocyanates result in new C−C and N−Ga single bonds. In the case of allyl isocyanate, the [2+4] cycloaddition across one C=C−N−Ga fragment of 1 is accompanied by insertion of a second allyl isocyanate molecule into the Ga−N bond of the same fragment to afford compound [L¹Ga−Ga(AllN− C=O)₂L¹] ( 5 ) (All=allyl). In the presence of Na metal, the related digallane [L²Ga−GaL²] ( 2 ; L²=dpp-dad=[(2,6-iPr₂C₆H₃)NC(CH₃)]₂) is converted into the gallium(I) carbene analogue [L²Ga:]⁻ ( 2 A ), which undergoes a variety of reactions with isocyanate substrates. These include the cycloaddition of ethyl isocyanate to 2 A affording [Na₂(THF)₅]{L²Ga[EtN−C(O)]₂GaL²} ( 6 ), cleavage of the N=C bond with release of 1 equiv. of CO to give [Na(THF)₂]₂[L²Ga(p-MeC₆H₄)(N−C(O))₂−N(p-MeC₆H₄)]₂ ( 7 ), cleavage of the C=O bond to yield the di-O-bridged digallium compound [Na(THF)₃]₂[L²Ga-(μ-O)₂-GaL²] ( 8 ), and generation of the further addition product [Na₂(THF)₅][L²Ga(CyNCO₂)]₂ ( 9 ). Complexes 3 – 9 have been characterized by NMR (¹H, ¹³C), IR spectroscopy, elemental analysis, and X-ray diffraction analysis. Their electronic structures have been examined by DFT calculations.