Emission quenching of binuclear pyrophosphito platinum(II) complexes in aqueous solution by sulphur dioxide. Spectroscopic measurements on sulphur dioxide addition and chromous ion reduction

The emission intensity at 517 nm from Pt₂(pop)₄⁴⁻ (pop = P₂O₅H₂²⁻) is quenched by the addition of sulphur dioxide. The sulphur dioxide coordinates at the axial platinum(II) sites by a η¹-SO₂ bond. This coordination is supported by ³¹p NMR and Raman spectroscopy of aqueous solutions. The electronic spectrum of a sulphur dioxide saturated solution of Pt₂(pop)₄⁴⁻ shows an absorption at 428.5nm ( = 4.1 × 10⁴). From the decrease in the chromophore for uncomplexed Pt₂(pop)₄⁴⁻ the equilibrium constant for SO₂ binding is estimated to be 1.74 M₂l⁻². The effect of adding different quenchers to aqueous solutions of Pt_2(pop)4⁴⁻ is discussed. The compound Pt₂(pop)₄⁴⁻ will undergo 2-electron reduction with chromous ion.     

Persulphate quenching of the excited state of ruthenium(II) tris-bipyridyl dication: thermal reactions

The rate constant for the reaction between the sulphate radical (SO₄^√−) and the ruthenium (II) tris-bipyridyl dication (Ru(bipy)₃²⁺) is (3.3±0.2)×10⁹ mol⁻¹ dm³ s⁻¹ in 1 mol dm⁻³ H₂SO₄ and (4.9±0.5)×10⁹ mol⁻¹ dm³ s⁻¹ in 0.1 mol dm⁻³, pH 4.7 acetate buffer. The SO₄^√−radical produced by the electron transfer quenching of Ru(bipy)₃^2+* by S₂O₈²⁻ reacts rapidly with both acetate buffer and chloride ions. These side reactions result in a reduction in the overall quantum yield of Ru(bipy)₃³⁺ production and reduced reaction selectivity when Ru(bipy)₃^2+* is quenched by persulphate.     

On the origin of the splittings of the ν3(SO4) modes in the specular reflectance IR spectra of gypsum

The IR polarized spectra of gypsum CaSO₄·2H₂O were recorded at incidence angles of approximately 10 and 16 degrees. Band singlet or doublet was observed for the higher frequency ν₃(SO₄²⁻) mode of B_u symmetry type, depending on polarization (n or p). A doublet was observed for the lower frequency ν₃(SO₄²⁻) mode of B_u symmetry type too, irrespectively of the type of polarization. In order to give an explanation for the doublets origin, a model permittivity function was constructed. Quite good agreement exists between the reflectance based on the model permittivity function and the experimentally measured one for the high-frequency doublet. The origin of the lower frequency doublet could not be explained in this way, but may be speculated to result from an Evans type interaction between a combination of a water libration and ν₂(SO₄²⁻), with the lower frequency ν₃(SO₄²⁻) mode.     

A spectroscopic study on the reaction-controlled phase transfer catalyst in the epoxidation of cyclohexene

The epoxidation of cyclohexene with hydrogen peroxide in a biphase medium (H₂O/CHCl₃) was carried out with the reaction-controlled phase transfer catalyst composed of quaternary ammonium heteropolyoxotungstates [π-C₅H₅N(CH₂)₁₅CH₃]₃[PW₄O₁₆]. A conversion of about 90% and a selectivity of over 90% were obtained for epoxidation of cyclohexene on the catalyst. The fresh catalyst, the catalyst under reaction conditions and the used catalysts were characterized by FT-IR, Raman and ³¹P NMR spectroscopy. It appears that the insoluble catalyst could degrade into smaller species, [(PO₄){WO(O₂)₂}₄]³⁻, [(PO₄){WO(O₂)₂}₂{WO(O₂)₂(H₂O)}]³⁻, and [(PO₃(OH)){WO(O₂)₂}₂]²⁻ after the reaction with hydrogen peroxide and becomes soluble in the CHCl₃ solvent. The active oxygen in the [W₂O₂(O₂)₄] structure unit of these soluble species reacts with olefins to form the epoxides and consequently the corresponding W---Ob---W (corner-sharing) and W---Oc---W (edge-sharing) bonds are formed. The peroxo group [W₂O₂(O₂)₄] can be regenerated when the W---Ob---W and W---Oc---W bonds react with hydrogen peroxide again. These soluble species lose active oxygen and then polymerize into larger compounds with the W---Ob---W and W---Oc---W bonds and then precipitate from the reaction solution after the hydrogen peroxide is consumed up. Part of the used catalyst seems to form more stable compounds with Keggin structure under the reaction conditions.     

The chemistry of peroxovanadium species in aqueous solutions. Structure and reactivity of a neutral diperoxovanadium complex as provided by V-NMR data, ab initio calculations and kinetic results

The addition of hydrogen peroxide to vanadium (V) precursors in aqueous acidic solutions leads to the formation of a cationic monoperoxospecies [VO(O₂)]⁺ and an anionic diperoxocomplex [VO(O₂)₂]⁻, depending on the pH and on the excess of H₂O₂. The latter may undergo protonation to form the neutral complex [HVO(O₂)₂]. ⁵¹V-NMR data and ab initio calculations suggest that the neutral complex is formed via protonation of a peroxide oxygen and that in such a species, as well as in the other two peroxovanadium derivatives, the usual η² arrangement of the peroxo groups is maintained. The comparison of reactivity data of the three complexes in the self-decomposition reaction and in the oxidation of uracil, indicates that the neutral diperoxocomplex exhibits an oxidizing power considerably larger than that of the other two peroxovanadium species.     

Synthesis, structural and spectroscopic characterisation of three di-μ-fluoro-bis[dioxouranyl] complexes

Three novel uranyl complexes with organic phosphine oxide ligands and bridging fluorides have been synthesised and structurally characterised. In [ UO₂(μ-F)(TPPO)_{3 2}][BF₄]₂ · ⁿC₆H₁₄, 1, and [ UO₂(-μF)(TBPO)_{3 2}][BF₄]₂ 2, (where TPPO and TBPO are triphenylphosphine oxide and tri-n-butylphosphine oxide, respectively) two UO₂ ²⁺ moieties are bridged by two fluorides with three additional terminal PO donor ligands coordinated to each uranium centre. The dicationic complexes are both charge balanced by two uncoordinated tetrafluoroborate anions. In the related structure, [UO₂(μ-F)(F)(DPPMO₂)]₂ · 2MeOH (3), terminal fluoride is also coordinated to both uranyl centres (where DPPMO₂ = bis(diphenylphosphine oxide)methane). All three complexes were prepared during attempted syntheses of complexes with tetrafluoroborate directly coordinated to uranium. It is clear from these results that the fluorophilicity of UO₂ ²⁺ causes the abstraction of fluoride from [BF₄]⁻, with the weakly coordinating anion only present as a counter cation in 1 and 2, and absent completely in 3.     

The first tetranuclear vanadium(V) peroxo complex: Preparation, vibrational spectra and X-ray crystal structure of K6[V4O4(O2)8(PO4)]·9H2O

The vanadium(V) peroxo phosphato complex K₇[V₄O₄(O₂)₈(PO₄)]·9H₂O has been obtained from the KVO₃---KH₂PO₄---KOH---H₂O₂---H₂O---C₂H₅OH system. The X-ray structural analysis revealed a tetranuclear anionic structure in which two dinuclear [V₂O₂(O)₂)₂(μ-η¹ : η²-O₂)₂] units are connected by the μ₄-PO₄ group.     

Three new polynuclear tetracarboxylato-bridged copper(II) complexes: Syntheses, X-ray structure and magnetic properties

The synthesis, crystal structure and magnetic measurements of three new polynuclear tetracarboxylato-bridged copper(II) complexes, i.e. {[Cu₄(phen)₂(μ-O₂CC₂H₅)₈] · (H₂O)}_n (1), [Cu₂(μ-O₂CC₆H₄OH)₄(C₇H₇NO)₂] · 6H₂O (2) and [Cu₂(μ-O₂CCH₃)₄(C₇H₇NO)₂] (3) (phen = 1,10-phenanthroline, O₂CC₆H₄OH = 3-hydroxy benzoate, C₇H₇NO = 4-acetylpyridine) are reported. All compounds consist of dinuclear units, in which two Cu(II) ions are bridged by four syn,syn-η¹:η¹:μ carboxylates, showing a paddle-wheel cage type with a square-pyramidal geometry, arranged in different ways. The structure of compound 1 consists of an one-dimensional structure generated by an alternating classical dinuclear paddle-wheel unit and an unusual dinuclear Cu₂(μ-OCOC₂H₅)₂(μ-O₂CC₂H₅)₂(phen)₂unit, which are connected to each other via a syn,anti-triatomic propionato bridge in an axial-equatorial configuration. The adjacent chains are connected to generate a 2D structure through the face-to-face π–π interaction between phen rings. Structures of compounds 2 and 3 both consist of a symmetric dinuclear Cu(II) carboxylate paddle-wheel core and pyridyl nitrogen atoms of 4-acetylpyridine ligand at the apical position, and just differ in the substituents of the equatorial ligands.

The magnetic properties have been measured and correlated with the molecular structures. It is found that in the two classical paddle-wheel compounds the Cu(II) ions are strongly antiferromagnetically coupled with J = −278.5 and −287.0 cm⁻¹ for complexes 2 and 3, respectively. In compound 1 the magnetic susceptibility could be fitted with two different, independent Cu(II) units, one strongly coupled and one weakly coupled; the paddle-wheel dinuclear unit has the strongest antiferromagetic coupling with a value for J of −299.5 cm⁻¹, whereas the Cu(II) ions in the propionato-bridged dinuclear unit of 1 display a very weak antiferromagnetic coupling with a value for J = −0.75 cm⁻¹, due to the orthogonality of the magnetic orbitals. Also the exchange within the chain is therefore very weak. The magneto-structural correlations for complexes 1, 2, and 3 are discussed on the basis of the structural parameters and magnetic data for the complexes.     

The reactions of a dinuclear ferric complex (oxo) di-iron(III) triethylenetetraamminehexaacetate, Fe2O(ttha), with oxidizing and reducing free radicals. A pulse radiolysis study

The rate constants at which oxidizing and reducing radicals react with the dinuclear iron(III) complex Fe₂O(ttha)²⁻ were measured in neutral aqueous solution. The rate constants for reduction of the complex by ·CO₂^.− CH₃^.CHOH and O₂^.− were found to be comparable with rate constants previously measured in mononuclear iron(III) polyaminocarboxylate systems. Fe₂O(ttha)²⁻ reacts slowly with O₂^.− (k₈ = (1.2 ± 0.2) × 10⁴ dm³ mol⁻¹ s⁻¹) and, hence, is a relatively poor catalyst for the dismutation of superoxide radical. The hydrated electron reduces the complex at a diffusion-controlled rate in a process which consumes one proton: e_aq⁻ + Fe₂O(ttha)²⁻ → Fe₂^III,IIO(ttha)³⁻ The reduction by carbon-centered radicals produces a (III,II) mixed-valence complex with an absorption spectrum different from that of the Fe₂(II,III) species produced from reduction by the hydrated electron. The oxidizing radicals ^.OH and ·CO₃⁻ appear to act as reductants of the complex via ligand oxidation rather than by oxidation of the Fe₂^IIIO core to Fe₂^III,IVO. In the former case ligand attack appears to occur mainly at the methylene carbon of a glycinate group. The decarboxylation product, CO₂, was detected by its aquation reaction in the presence of a pH sensitive dye, bromthymol blue.     

Metallorganische lewissäuren : XX. Reaktionen von (π-C5H5)(CO)2LM-X (L = CO, PR3; M = Mo, W; X = BF4, PF6, AsF6, SbF6) mit Schwefel-haltigen liganden

The compounds (π-C₅H₅)(CO)₂LM-X (L = CO, PR₃; M = Mo, W; X = BF₄, PF₆, AsF₆, SbF₆) react with H₂S, p-MeC₆H₄SH, Ph₂S and Ph₂SO(L′) to give ionic complexes [(π-C₅H₅)(CO)₂LML′]⁺ X⁻. Also sulfur-bridged complexes, [(π-C₅H₅)(CO)₃W---SH---W(CO)₃(π-C₅H₅)]⁺ AsF₆⁻ and [(π-C₅H₅)(CO)₃M-μ-S₂C=NCH₂Ph-M(CO)₃(π-C₅H₅)], have been obtained. Reactions with SO₂ and CS₂ have been examined.     

Matrix isolation infrared spectroscopic and theoretical study of noble gas coordinated dipalladium–dioxygen complexes

The reaction products of palladium atoms with molecular oxygen in solid argon have been investigated using matrix isolation infrared absorption spectroscopy and quantum chemical calculations. In addition to the previously reported mononuclear palladium–dioxygen complexes: Pd(η²–O₂) and Pd(η²–O₂)₂, dinuclear palladium–dioxygen complexes: Pd₂(η²–O₂) and Pd₂(η²–O₂)₂ were formed under visible light irradiation and were identified on the basis of isotopic substitution and theoretical calculations. In addition, experiments doped with xenon in argon coupled with theoretical calculations suggest that the Pd(η²–O₂), Pd₂(η²–O₂) and Pd₂(η²–O₂)₂ complexes are coordinated by two argon or xenon atoms in solid argon matrix, and therefore, should be regarded as the Pd(η²–O₂)(Ng)₂, Pd₂(η²–O₂)(Ng)₂ and Pd₂(η²–O₂)₂(Ng)₂ (NgAr or Xe) complexes isolated in solid argon.     

Photophysics of ruthenium(II) complexes with 2-(2′-pyridyl) pyrimidine and 2,2′-bipyridine ligands in fluid solution

The photophysics of three complexes of the form Ru(bpy)₃₋(pypm)²⁺ (where bpy2,2′-bipyridine, pypm 2-(2′-pyridyl)pyrimidine and P=1, 2 or 3) was examined in H₂O, propylene carbonate, CH₃CN and 4:1 (v/v) C₂H₅OH---CH₃OH; comparison was made with the well-known photophysical behavior of Ru(bpy)₃²⁺. The lifetimes of the luminescent metal-to-ligand charge transfer (MLCT) excited states were determined as a function of temperature (between −103 and 90 °C, depending on the solvent), from which were extracted the rate constants for radiative and non-radiative decay and ΔE, the energy gap between the MLCT and metal-centered (MC) excited states. The results indicate that ^*Ru(bpy)₂(pypm)²⁺ decays via a higher lying MLCT state, whereas ^*Ru(pypm)₃²⁺ and ^*Ru(pypm)₂(bpy)²⁺ decay predominantly via the MC state.     

Copper thioether chemistry: Synthesis and X-ray crystal structures of binuclear copper(I) complexes [Cu2(L)] {L = [24]aneS8, [28]aneS8} incorporating octathia macrocycles

Reaction of L {L = [24]aneS₈, [28]aneS₈} with two molar equivalents of [Cu(NCMe)₄]X (X⁻ = ClO₄⁻, BF₄⁻, PF₆⁻) in MeCN affords the white binuclear copper(I) complexes [Cu₂(L)]²⁺. A single crystal X-ray structure determination of [CU₂([24]aneS₈)](BF₄)₂ shows two tetrahedral copper(I) centres, each of which is coordinated to four thioether sulphur-donors, Cu---S(1) = 2.263(3), Cu---S(4) = 2.363(3), Cu---S(7) = 2.349(3), Cu---S(10) = 2.261(3) Å. The Cu … Cu distance is 5.172(3) Å. A single crystal X-ray structure determination Of [CU₂([28]aneS₈)](ClO₄)₂ shows that this complex also contain two tetrahedral copper(I) centres, each coordinated to four thioether sulphur-donors, Cu---S(1) = 2.278(5), Cu---S(4) = 2.333(5), Cu---S(8) = 2.328(5), CU---S(11) = 2.268(5) Å. The Cu … Cu distance of 6.454(3) Å is greater than in [CU₂([24]aneS₈)]²⁺ , reflecting the greater cavity size in [CU₂([28]aneS₈)]²⁺. Cyclic voltammetry of [CU₂([24]aneS₈)]²⁺ and [CU₂([28]aneS₈)]²⁺ at platinum electrodes in MeCN (0.1 M ⁿBU₄NPF₆) shows irreversible oxidations at E_pa, = +0.88 V, +0.92 V vs Fc/Fc⁺, respectively, at a scan rate of 200 mV s⁻¹. Coulometric measurements in MeCN confirm these oxidations to be two-electron (one electron per copper) processes to give binuclear copper(II) species. Oxidation of the binuclear copper(I) precursors with H₂SO₄ or HNO₃ affords ESR-active copper(II) species which presumably incorporate SO₄²⁻ and NO₃⁻ bridges.     

Syntheses and X-ray crystal structures of [Co(η-CO3)(NH3)4](NO3)·0.5H2O and [(NH3)3Co(μ-OH)2(μ-CO3)Co(NH3)3][NO3]2·H2O

[Co(η²-CO₃)(NH₃)₄](NO₃)·0.5H₂O and [(NH₃)₃Co(μ-OH)₂(μ-CO₃)Co(NH₃)₃][NO₃]₂·H₂O were prepared by prolonged aerial oxidation of a solution of Co(NO₃)₂·6H₂O and ammonium carbonate in aqueous ammonia. The formation of these side products highlights the richness of the chemistry of these systems and the possibility of by products if methods are not strictly adhered to. The X-ray crystal structures of [Co(η²-CO₃)(NH₃)₄][NO₃]·0.5H₂O and [(NH₃)₃Co(μ-OH)₂(μ-CO₃)Co(NH₃)₃][NO₃]₂·H₂O reveal a monomeric octahedral cobalt center with η²-bound CO₃²⁻ in the former, while the latter consists of a dimeric array where the two cobalt centers are bridged by two OH⁻ and one μ₂-CO₃²⁻ groups with three terminal NH₃ ligands for each Co center. In both complexes extensive hydrogen bonding interactions are evident.     

Are excimers formed along with hydrated electrons in the UV excitation of cyanocuprate(I) ions in aqueous solution?

The three cyanocuprate(I) complexes, Cu(CN)₂⁻, Cu(CN)₃²⁻, and Cu(CN)₄³⁻, photoeject electrons with high efficiency when excited in aqueous solution by 266 nm laser pulses of 7 ns duration with quantum yields of 0.37±0.06, 0.224±0.021, and 0.240±0.005, for Cu(CN)₂⁻ (at 2 M ionic strength), Cu(CN)₃²⁻, and Cu(CN)₄³⁻ (both measured at 1 M ionic strength). Along with hydrated electrons, two transient intermediates, absorbing at 460 and 340 nm, respectively, form consecutively after excitation through bimolecular reactions with ground-state Cu(I) in solutions of Cu(CN)₂⁻, and Cu(CN)₃²⁻, but not in Cu(CN)₄³⁻. All photoprocesses are essentially monophotonic. A mechanism is proposed that suggests the formation of a dinuclear excited-state complex such as an excimer.     

Fraction of excited-state oxygen formed as b Σg in solution-phase-photosensitized reactions II. Effects of sensitizer substituent

The fraction F_Σ of excited-state oxygen formed as b ¹Σ_g⁺ was determined for a series of triplet-state photosensitizers in CCl₄ solutions. F_Σ was determined by monitoring the intensities of (a) O₂(b ¹Σ_g⁺) fluorescence at 1926 nm (O₂(b ¹Σ_g⁺)→O₂(a ¹Δ_g) and (b) O₂(a ¹ Δ_g) phosphorescence at 1270 nm (O₂(a ¹Δ_g) → O₂(X³Σ_g⁻)). Oxygen excited states were formed by energy transfer from substituted benzophenones and acetophenones. The data indicate that F_Σ depends on several variables including the orbital configuration of the lowest triplet state and the triplet-state energy. The available data indicate that the sensitizer-oxygen charge transfer (CT) state is not likely to influence F_Σ strongly by CT-mediated mixing of various sensitizer-oxygen states.     

Das Reaktionsverhalten von Cp2NbCl2 gegenüber WF6—Struktur von [Cp2NbCl2]4[WF6]2[WCl6]

The oxidation of Cp₂NbCl₂ with pure WF₆ in SO₂ solution yielded the cationic metallocene species [Cp₂NbCl₂]⁺[WF₆]⁻ essentially in quantitative yield. The same reaction carried out in the presence of either equimolar amounts or a two-fold excess of HCN led to the preparation of the new niobocenium salt [Cp₂NbCl₂]₄⁺[WF₆]²⁻ which was studied by single crystal X-ray diffraction. This compound represents the first example of a structurally characterized metallocene-WF₆⁻ complex, and crystallizes in the tetragonal system: space group, P4₁2₁2(No. 92), a = 11.083(8) Å, c = 48.285 (9) Å; Z = 8; R = 0.0759, R_W = 0.0841. ab]Die Oxidation von Cp₂NbCl₂ mit reinem WF₆ führt in SO₂-Lösung zur Synthese von [Cp₂NbCl₂ ]⁺[WF₆]⁻ in nahezu quantitativer Ausbeute. Die analoge Reaktion führt unter Anwesenheit der äquimolaren Menge oder eines zweifachen Überschusses an HCN zur Ausbildung des Niobocenium-Komplexsalzes [Cp₂NbCl₂]₄⁺ [WF₆]₂⁻[WCl₆]²⁻, von dem eine Röntgenstrukturanalyse angefertigt wurde. Diese Verbindung repräsentiert den ersten structurell charakterisierten Vertreter eines Metallocen-WF₆⁻-Komplexes und kristallisiert im tetragonalen System: Raumgruppe P4₁2₁2 (Nr. 92), a = 11.083(8) Å, c = 48.285(9) Å; Z = 8; R = 0.0759, R_W = 0.0841. kw]Niobium; X-ray diffraction; Oxidation; Metallocenes     

O and N NMR studies of the Co(II), Cu(II) and Mn(II) complexes of glycine in aqueous solution

The ¹⁷O and ¹⁴N paramagnetic relaxation rates and chemical shifts of glycine as well as of water, in aqueous solutions of Co(II), Cu(II), and Mn(II) were measured as a function of pH, temperature and metal ion concentration; the relaxation results were fitted to a theoretical equation linking the Swift-Connick equation to the stability constants of all major complexes in equilibrium. As a result, the stability constants of all major complexes were determined, and from the temperature-dependent measurements the thermodynamic parameters for some of these complexes were also calculated. In addition to the bidentate complexes ML⁺, ML₂ and ML₃⁻, monodentate complexes of the type MHL²⁺ and M(HL)₂²⁺, mixed complexes of the type MHL₂⁺ and MHL₃ were also considered. In the case of the Cu(II)-glycine system at pH> 12 two additional species were considered, namely ML₂(OH)⁻ and ML₂(OH)₂²⁻, suggested by the drastic reduction of the paramagnetic broadening in that pH range.     

Reactions of the cationic diruthenium carbonyl complex [Ru2(μ-dppm)2(CO)4(μ,η-O2CMe)] with bidentate ligands; intramolecularly assisted stereospecific synthesis via the second-sphere face-to-face π–π stacking interactions

The reactions of the diruthenium carbonyl complexes [Ru₂(μ-dppm)₂(CO)₄(μ,η²-O₂CMe)]X (X=BF₄⁻ (1a) or PF₆⁻ (1b)) with neutral or anionic bidentate ligands (L,L) afford a series of the diruthenium bridging carbonyl complexes [Ru₂(μ-dppm)₂(μ-CO)₂(η²-(L,L))₂]X_n ((L,L)=acetate (O₂CMe), 2,2′-bipyridine (bpy), acetylacetonate (acac), 8-quinolinolate (quin); n=0, 1, 2). Apparently with coordination of the bidentate ligands, the bound acetate ligand of [Ru₂(μ-dppm)₂(CO)₄(μ,η²-O₂CMe)]⁺ either migrates within the same complex or into a different one, or is simply replaced. The reaction of [Ru₂(μ-dppm)₂(CO)₄(μ,η²-O₂CMe)]⁺ (1) with 2,2′-bipyridine produces [Ru₂(μ-dppm)₂(μ-CO)₂(η²-O₂CMe)₂] (2), [Ru₂(μ-dppm)₂(μ-CO)₂(η²-O₂CMe)(η²-bpy)]⁺ (3), and [Ru₂(μ-dppm)₂(μ-CO)₂(η²-bpy)₂]²⁺ (4). Alternatively compound 2 can be prepared from the reaction of 1a with MeCO₂H–Et₃N, while compound 4 can be obtained from the reaction of 3 with bpy. The reaction of 1b with acetylacetone–Et₃N produces [Ru₂(μ-dppm)₂(μ-CO)₂(η²-O₂CMe)(η²-acac)] (5) and [Ru₂(μ-dppm)₂(μ-CO)₂(η²-acac)₂] (6). Compound 2 can also react with acetylacetone–Et₃N to produce 6. Surprisingly [Ru₂(μ-dppm)₂(μ-CO)₂(η²-quin)₂] (7) was obtained stereospecifically as the only one product from the reaction of 1b with 8-quinolinol–Et₃N. The structure of 7 has been established by X-ray crystallography and found to adopt a cis geometry. Further, the stereospecific reaction is probably caused by the second-sphere π–π face-to-face stacking interactions between the phenyl rings of dppm and the electron-deficient six-membered ring moiety of the bound quinolinate (i.e. the N-included six-membered ring) in 7. The presence of such interactions is indeed supported by an observed charge-transfer band in a UV–vis spectrum.     

Simultaneous derivative spectrophotometric determination of thorium and uranium in a micellar medium

Derivative photometric methods for trace analysis of Th(IV) and UO₂(II), and their simultaneous determination in mixtures using 5,8-dihydroxy-1,4-naphthoquinone in a micellar medium are reported. Molar absorptivity and Sandell's sensitivity of 1:2 Th(IV) and 1:1 UO₂(II) complexes at their λ_max, 614.5 nm and 637.0 nm are, 1.19 × 10⁴ 1/mol/cm and 1.12 × 10⁴ 1/mol/cm and 1.95 × 10⁻² μg/cm² and 2.13 × 10⁻² μg/cm² μg/cm², respectively. Calibration graph is linear over the range 9.28 × 10⁻²−18.56 μg/ml of Th(IV) and 9.52 × 10⁻²−19.04 μg/ml of UO₂(II). Though presence of Th(IV) and UO₂(II) causes interference in each others determination, 9.28 × 10⁻¹−9.28 μg/ml Th(IV) and 9.52 × 10⁻¹−9.52 μg/ml UO₂(II) when present together, can be simultaneously determined using derivative spectra.