Long-distance electronic interaction in a molecular wire consisting of a ferrocenyl–ethynyl unit bridging two [(η5-C5H5)(dppe)M] metal centers

Several multinuclear ferrocenyl–ethynyl complexes of formula [(η⁵-C₅H₅)(dppe)M^II?CC–(fc)_n–CC–M^II(dppe)(η⁵-C₅H₅)] (fc = ferrocenyl; dppe = Ph₂PCH₂CH₂PPh₂; 1: M^II = Ru²⁺, n = 1; 2: M^II = Ru²⁺, n = 2; 3: M^II = Ru²⁺, n = 3; 4: M^II = Fe²⁺, n = 2; 5: M^II = Fe²⁺, n = 3) were studied. Structural determinations of 2 and 4 confirm the ferrocenyl group directly linked to the ethynyl linkage which is linked to the pseudo-octahedral [(η⁵-C₅H₅)(dppe)M] metal center. Complexes of 1–5 undergo sequential reversible oxidation events from 0.0 V to 1.0 V referred to the Ag/AgCl electrode in anhydrous CH₂Cl₂ solution and the low-potential waves have been assigned to the end-capped metallic centers. The solid-state and solution-state electronic configurations in the resulting oxidation products of [1]⁺ and [2]²⁺ were characterized by IR, X-band EPR spectroscopy, and UV–Vis at room temperature and 77 K. In [1]⁺ and [2]²⁺, broad intervalence transition band near 1600 nm is assigned to the intervalence transition involving photo-induced electron transfer between the Ru³⁺ and Fe²⁺ metal centers, indicating the existence of strong metal-to-metal interaction. Application of Hush’s theoretical analysis of intervalence transition band to determine the nature and magnitude of the electronic coupling between the metal sites in complexes [1]⁺ and [2]²⁺ is also reported. Computational calculations reveal that the ferrocenyl–ethynyl-based orbitals do mix significantly with the (η⁵-C₅H₅)(dppe)Ru metallic orbitals. It clearly appears from this work that the ferrocenyl–ethynyl spacers strongly contribute in propagating electron delocalization.     

Synthesis and evaluation of two novel rhodamine-based fluorescence probes for specific recognition of Fec+ ion

Two low cytotoxic fluorescence probes Rb1 and Rb2 detecting Fe³⁺ were synthesized and evaluated. Rb1 and Rb2 exhibited an excellent selectivity to Fe³⁺, which was not disturbed by Ag⁺, Li⁺, K⁺, Na⁺, NH₄⁺, Fe²⁺, Pb²⁺, Ba²⁺, Cd²⁺, Ni²⁺, Co²⁺, Mn²⁺, Zn²⁺, Mg²⁺, Hg²⁺, Ca²⁺, Cu²⁺, Ce³⁺, AcO^?, Br^?, Cl^?, HPO₄^2?, HSO₃^?, I^?, NO₃^?, S₂O₃^2?, SO₃^2? and SO₄^2? ions. The detection limits were 1.87 × 10^?7 M for Rb1 and 5.60 × 10^?7 M for Rb2, respectively. 1:1 stoichiometry and 1:2 stoichiometry were the most likely recognition mode of Rb1 or Rb2 towards Fe³⁺, and the corresponding OFF–ON fluorescence mechanisms of Rb1 and Rb2 were proposed.     

Non-chromatographic speciation analysis of mercury by flow injection on-line preconcentration in combination with chemical vapor generation atomic fluorescence spectrometry

A novel non-chromatographic approach for direct speciation of mercury, based on the selective retention inorganic mercury and methylmercury on the inner wall of a knotted reactor by using ammonium diethyl dithiophosphate and dithizone as complexing agents respectively, was developed for flow injection on-line sorption preconcentration coupled with chemical vapor generation non-dispersive atomic fluorescence spectrometry. With the sample pH kept at 2.0, the preconcentration of inorganic mercury on the inner walls of the knotted reactor was carried out based on the exclusive retention of Hg–DDP complex in the presence of methylmercury via on-line merging the sample solution with ammonium diethyl dithiophosphate solution, and selective preconcentration methylmercury was achieved with dithizone instead of ammonium diethyl dithiophosphate. A 15% (v/v) HCl was introduced to elute the retained mercury species and merge with KBH₄ solution for atomic fluorescence spectrometry detection. Under the optimal experimental conditions, the sample throughputs of inorganic mercury and methylmercury were 30 and 20 h^− 1 with the enhancement factors of 13 and 24. The detection limits were found to be 3.6 ng l^− 1 for Hg²⁺ and 2.0 ng l^− 1 for CH₃Hg⁺. The precisions (RSD) for the 11 replicate measurements of each 0.2 μg l^− 1 of Hg²⁺ and CH₃Hg⁺ were 2.2% and 2.8%, respectively. The developed method was validated by the analysis of certified reference materials (simulated natural water, rice flour and pork) and by recovery measurements on spiked samples, and was applied to the determination of inorganic mercury and methylmercury in biological and environmental water samples.     

A new colorimetric and fluorescent ratiometric sensor for Hg2+ based on 4-pyren-1-yl-pyrimidine

A novel fluorescent ratiometric chemosensor based on 4-pyren-1-yl-pyrimidine (PPM) has been designed and prepared for the detection of Hg²⁺ in the presence of other competing metal ions in acetonitrile. The photo exhibits fluorescence color change of PPM from blue to green without and with Hg²⁺, which red shift of wavelength about 105 nm in fluorescence emission spectra. It can serve as a highly selective chemodosimeter for Hg²⁺ with ratiometric and naked-eye detection. The photophysical properties of PPM confirmed a 2:1 (PPM–Hg²⁺) binding model and the spectral response toward Hg²⁺ was proved to be reversible.     

Determination of inorganic and total mercury by vapor generation atomic absorption spectrometry using different temperatures of the measurement cell

A simple and inexpensive laboratory-built flow injection vapor generation system coupled to atomic absorption spectrometry (FI-VG AAS) for inorganic and total mercury determination has been developed. It is based on the vapor generation of total mercury and a selective detection of Hg^2 + or total mercury by varying the temperature of the measurement cell. Only the inorganic mercury is measured when the quartz cell is at room temperature, and when the cell is heated to 650 °C or higher the total Hg concentration is measured. The organic Hg concentration in the sample is calculated from the difference between the total Hg and Hg^2 + concentrations. Parameters such as the type of acid (HCl or HNO₃) and its concentration, reductant (NaBH₄) concentration, carrier solution (HCl) flow rate, carrier gas flow rate, sample volume and quartz cell temperature, which influence FI-VG AAS system performance, were systematically investigated. The optimized conditions for Hg^2 + and total Hg determinations were: 1.0 mol l^− 1 HCl as carrier solution, carrier flow rate of 3.5 ml min^− 1, 0.1% (m/v) NaBH₄, reductant flow rate of 1.0 ml min^− 1 and carrier gas flow rate of 200 ml min^− 1. The relative standard deviation (RSD) is lower than 5.0% for a 1.0 μg l^− 1 Hg solution and the limit of quantification (LOQ, 10 s) is 55 ng g^− 1. Certified samples of dogfish muscle (DORM-1 and DORM-2) and non-certified fish samples were analyzed, using a 6.0 mol l^− 1 HCl solution for analyte extraction. The Hg^2 + and CH₃Hg⁺ concentrations found were in agreement with certified ones.     

A Schiff base fluorescence probe for highly selective turn-on recognition of Zn2+

A simple Schiff base CTS, synthesized between 2-hydroxy-1-naphthaldehyde and 2-benzylthio-ethanamine, was found to be a good turn-on fluorescence probe for the detection of Zn²⁺, due to the restriction of the rotation of the bond between CN and naphthalene ring and/or the blocking of the photo-induced electron transfer (PET) mechanism of the nitrogen atom to naphthalene ring. Excellent selectivity for Zn²⁺ was evidenced, over many other competing ions, including Fe³⁺, Cr³⁺, Ni²⁺, Co²⁺, Fe²⁺,Mn²⁺, Ca²⁺, Hg²⁺, Pb²⁺, Cu²⁺, Mg²⁺, Ba²⁺, Cd²⁺, Ag⁺, Li⁺, K⁺, and Na⁺, in EtOH/HEPES buffer (95:5, v/v, pH = 7.4). It was noteworthy that Cd²⁺ had no interference with Zn²⁺. The stoichiometric complex of CTS-Zn²⁺ was determined to be 2:1 for CTS and Zn²⁺ in molar, based on the Job plot and single crystal X-ray diffraction data. The binding constant of the complex was 85.7 M^?2 with a detection limit of 5.03 × 10^?7 M. The fluorescence bio-imaging capability of CTS to detect Zn²⁺ in live cells was also studied. These results indicated that CTS could serve as a favorable probe for Zn²⁺.     

Effect of intraligand π-delocalization on the photophysical properties of two new Ru(II) complexes

Two new Ru(II) complexes, [Ru(bpy)₂(1-COO-iqu)]⁺ (2; bpy = 2,2′-bipyridine, 1-COO-iqu^? = isoquinoline-1-carboxylate) and [Ru(bpy)₂(3-COO-iqu)]⁺ (3; 3-COO-iqu^? = isoquinoline-3-carboxylate), were prepared and their crystal structures solved. The ground and excited state properties of 2 and 3 were characterized and compared to those of [Ru(bpy)₃]²⁺ (1). The presence of the oxygen atom in the Ru(II) coordination sphere makes 2 and 3 easier to oxidize than 1. The Ru → bpy MLCT absorption and emission of 2 and 3 are red-shifted relative to that of 1 in CH₂Cl₂, and the E₀₀ energies were estimated to be 1.89 eV and 1.95 eV from the low temperature emission of 2 and 3, resulting in excited state oxidation potentials of ?1.03 V and ?1.10 V vs SCE, respectively. In addition to the short-lived emissive ³MLCT state, a long-lived species is observed in the transient absorption of 3 in DMSO (τ = 49 μs) and pyridine (τ = 44 μs), assigned to a solvent-coordinated complex. This intermediate is not observed for 3 in non-polar solvents or for 2. The absence of the solvent coordinated intermediate in 2 is explained by the stronger Ru–O bond afforded by the lower conjugation in that extends onto the carboxylic acid in the 1-COO-iquo^?ligand, compared to that in the 3-COO-iqu^?ligand in 3. Transient absorption experiments also show that the ³MLCT excited state of 3 is able to reduce methyl viologen.     

Zeptomolar detection of Hg2 + based on label-free electrochemical aptasensor: One step closer to the dream of single atom detection

An ultra-sensitive and highly selective electrochemical label-free aptasensor is proposed for the quantitation of Hg^2 + based on the hybridization/dehybridization of double-stranded DNA (dsDNA) on a gold electrode. Thiol-substituted single-stranded DNA (ssDNA) is self-assembled on the gold electrode surface through the SAu interaction. The hybridization of ssDNA with complementary DNA (cDNA) and the consequences of dehybridization in the presence of mercury ions are followed through differential pulse voltammetry (DPV) responses using a [Fe(CN)₆]^{3 −/4 −} redox probe. The formation of a thymine–Hg^2 +–thymine (T–Hg^2 +–T) complex is the key to producing a highly selective and sensitive aptasensor for Hg^2 + determination. Specifically, the present electrochemical aptasensor is able to quantify Hg^2 + ions in concentrations from 5 zeptomolar (zM) to 55 picomolar (pM) with a limit of detection of 0.6 zM, close to the dream of single atom detection, without requiring a complicated procedure or expensive materials.     

A benzothizole-based fluorescent probe for Hg2+ recognition utilizing ESIPT coupled AIE characteristics

A new benzothizole-based fluorescent probe 1 for Hg²⁺ recognition utilizing “ESIPT+AIE” strategy has been developed. In THF/H₂O (1:1, v/v, PBS 20 mM, pH = 8.5) mixed solution, probe 1 displays rapid fluorescence responses to Hg²⁺ ions with high selectivity and sensitivity through Hg²⁺-triggered releasing of a compound possessing “ESIPT+AIE” characteristics. Cell imaging investigations indicate that probe 1 is cell permeable with low toxicity to MCF-7 cells, and applicable to detect Hg²⁺ ions in living MCF-7 cells.     

A highly sensitive and selective resonance Rayleigh scattering method for Hg2+ based on the nanocatalytic amplification

In 0.2 mol/L HCl–0.22 mol/L HNO₃ medium, trace Hg²⁺ catalyzed NaH₂PO₂ reduction of HAuCl₄ to form gold nanoparticles (AuNPs), which exhibited a strong resonance Rayleigh scattering (RRS) effect at 370 nm. With increasing of [Hg²⁺], the RRS effect enhanced due to more AuNP generated from the catalytic reaction. Under the chosen conditions, the enhanced RRS intensity at 370 nm is linear to Hg²⁺ concentration in the range of 5.0–450 × 10⁻⁹ mol/L, with a detection limit of 0.1 nmol/L. This RRS method was applied for the determination of Hg in water samples, with high sensitivity and good selectivity, and its results were agreement with that of atomic fluorescence spectrometry.     

Intramolecularly donor-stabilized silenes: Part 6. The synthesis of 1-[2,6-bis(dimethylaminomethyl)phenyl]silenes and their reaction with aromatic aldehydes

The intramolecularly donor-stabilized silenes ArR¹SiC(SiMe₃)₂ (3a–d) (3a: R¹ = Me; 3b: R¹ = t-Bu; 3c: R¹ = Ph; 3d: R¹ = SiMe₃; Ar = 2,6-(Me₂NCH₂)₂C₆H₃) were prepared by treatment of the (dichloromethyl)oligosilanes (Me₃Si)₂R¹Si–CHCl₂ (1a–d), with 2,6-bis(dimethylaminomethyl)phenyllithium (molar ratio 1:2). For 3c and 3d, X-ray structural analyses were performed indicating that only one dimethylamino group of the tridentate ligand is coordinated to the electrophilic silene silicon atoms, i.e., the central silicon atoms are tetracoordinated. The N → Si donation leads to pyramidalization at the silene silicon atoms; the configuration at the silene carbon atoms is planar. For a chemical characterization 3a and 3c were treated with water to give the silanols ArR¹Si(OH)–CH(SiMe₃)₂ (5a,c). Studies of the reactions of 3a and 3c with benzaldehyde, 4-chlorobenzaldehyde or 4-methoxybenzaldehyde, respectively, revealed an unexpected reaction path leading to the substituted 2-oxa-1-sila-1,2,3,4-tetrahydronaphthalenes 12a, 12c, 13 and 14. Both 12a and 12c were structurally characterized by X-ray analyses. The formation of these six-membered cyclic compounds, which is discussed in detail, gives support to a dipolar mechanism for the general reaction of silenes with carbonyl derivatives.     

High-throughput investigation and characterization of strontium-phosphonatoethanesulfonates

Using the polyfunctional ligand 2-phosphonethanesulfonic acid (H₃L) a high-throughput (HT) study was started for the systematic investigation of the system SrCl₂/H₃L/NaOH/H₂O. The HT experiment comprising 48 individual reactions were performed to systematically investigate the influence of pH of the starting mixture as well as the molar ratio Sr²⁺:H₃L. Two new compounds SrH(O₃P–C₂H₄–SO₃) (1) and Sr₃(O₃P–C₂H₄–SO₃)₂(H₂O)₂ (2) were obtained and structurally characterized by single-crystal X-ray diffraction. The reaction products synthesized under hydrothermal conditions always contain traces of SrSO₄, which are due to the decomposition of small amounts of the ligand. While compound 2 could only be obtained under hydrothermal conditions, the synthesis of 1 could be accomplished under milder reaction conditions and a reaction scale-up could be performed. Compound 1 crystallizes in a monoclinic system with space group C2/c (no. 15), a = 534.73(11) pm, b = 1648.7(3) pm, c = 825.43(17) pm, β = 105.34(3)°, V = 701.8(2)–10⁶ pm³, Z = 4, R1 = 0.0268, and wR₂ = 0.0642 for I > 2σ(I). Compound 2 crystallizes in a triclinic system with space group P-1 (no. 2), a = 700.97(14) pm, b = 1008.5(2) pm, c = 1274.8(3) pm, α = 97.63(3)°, β = 92.03(3)°, γ = 92.03(3)°, V = 843.7(3)–10⁶ pm³, Z = 2, R1 = 0.0360, and wR₂ = 0.0896 for I > 2σ(I). In the structure of compound 1 the phosphorous and sulfur atoms cannot be distinguished due to identical crystallographic positions. Thus, an averaged structure was obtained which is built up by edge-sharing SrO₈ polyhedra that form infinite M–O–M chains. Compound 2 contains corner-, edge-, and face-sharing SrO₈ polyhedra which form inorganic M–O–M layers. These M–O–M chains (1) and layers (2) are connected to a three-dimensional network by the –CH₂CH₂– group of the ligand, respectively. Additional characterization by thermogravimetric analysis and IR-spectroscopy for compound 1 is also presented.     

Molecular spin ladders self-assembly from [Ni(dmit)2]− building blocks: Syntheses,structures and magnetic properties

Two ion-pair compounds, consisting of 1-(4′-R-benzyl)pyridinium ([RBzPy]⁺, R = NO₂ (1) and Br (2)) and [Ni(dmit)₂]⁻ (dmit²⁻ = 2-thioxo-1,3-dithion-4,5-dithiolato), have been synthesized and structurally characterized. The anions of [Ni(dmit)₂]⁻ stack into dimers, which further construct into two-leg ladder through terminal S⋯S interactions in 1, lateral S⋯S interactions in 2. The weak H-bonding interactions of C–H⋯S were observed in 2, while only weak van de Waals interactions between anion and cations in 1. The magnetic susceptibilities measured in 2–300 K indicate AFM exchange interaction domination both two compounds. A peculiar magnetic transition at ∼100 K was observed in 1. An AFM ordering below ∼11 K was found in 2, and the best fit to magnetic susceptibility above 45 K in this compound, using a dimer model with s = 1/2, give rise to Δ/k_B = 36.1 K, zJ = −0.91 K, C = 3.2 × 10⁻³ emu K mol⁻¹ and χ₀ = −4.0 × 10⁻⁶ emu mol⁻¹ with g of 2.0 fixed.     

Hemilability of 2-(1H-imidazol-2-yl)pyridine and 2-(oxazol-2-yl)pyridine ligands: Imidazole and oxazole ring Lewis basicity,Ni(II)/Pd(II) complex structures and spectra

Fourteen new organic molecules A1–A4, B1–B5, C1–C4 and D and a series of transition metal(II) complexes (Ni1–Ni9 and Pd1–Pd2b) were synthesized and studied in order to characterize the hemilability of 2-(1H-imidazol-2-yl)pyridine and 2-(oxazol-2-yl)pyridine ligands (A1–A4 = 2-R²-6-(4,5-diphenyl-1R¹-imidazol-2-yl)pyridines, R¹ = H or CH₃, R² = H or CH₃; B1–B5 = 1-R²-2-(pyridin-2-yl)-1R¹-phenanthro[9,10-d]imidazoles/oxazoles, R¹ = H or CH₃, R² = H or CH₃; C1–C4 = 2-(6-R²-pyridin-2-yl)-1H-imidazo/oxazo[4,5-f][1,10]phenanthrolines, R² = H or CH₃; D = 2-mesityl-1H-imidazo[4,5-f][1,10]phenanthroline). They were also used to study the substituent effects on the donor strengths as well as the coordination chemistries of the imidazole/oxazole fragments of the hemilabile ligands.All the observed protonation–deprotonation processes found within pH 1–14 media pertain to the imidazole or oxazole rings rather than the pyridyl Lewis bases. The donor characteristics of the imidazole/oxazole ring can be estimated by spectroscopic methods regardless of the presence of other strong N donor fragments. The oxazoles possessed notably lower donor strengths than the imidazoles. The electron-withdrawing influence and capacity to hinder the azole base donor strength of 4,5-azole substituents were found to be in the order phenanthrenyl (B series) > 4,5-diphenyl (A series) > phenanthrolinyl (C series). An X-ray structure of Ni5b gave evidence for solvent induced ligand reconstitution while the structure of Pd2b provided evidence for solvent induced metal–ligand bond disconnection.Interestingly, alkylation of 1H-imidazoles did not necessarily produce the anticipated push of electron density to the donor nitrogen. Furthermore, substituents on the 4,5-carbons of the azole ring were more important for tuning donor strength of the azole base. DFT calculations were employed to investigate the observed trends. It is believed that the information provided on substituent effects and trends in this family of ligands will be useful in the rational design and synthesis of desired azole-containing chelate ligands, tuning of donor properties and application of this family of ligands in inorganic architectural designs, template-directed coordination polymer preparations, mixed-ligand inorganic self-assemblies, etc.     

Copper and cadmium phosphonates based on 2-quinolinephosphonate

Hydrothermal reactions of 2-quinolinephosphonic acid (1) and CuSO₄ or CdSO₄ result in two new compounds with formula Cu(2-C₉H₆NPO₃) (2) and Cd(2-C₉H₆NPO₃)(H₂O) (3). Compound 2 has a layer structure in which dimers of edge-sharing {CuO₄N} square-pyramids are linked by {CPO₃} tetrahedra through corner sharing. Compound 3 shows a new type of layer structure where chains of corner sharing {CdO₅N} octahedra are connected by {CPO₃} tetrahedra into an inorganic layer. The quinoline groups fill in the inter-layer spaces in both cases. Crystal data for 1: monoclinic, space group P2₁/c, a = 10.270(2) Å, b = 13.566(3) Å, c = 6.9818(16) Å, β = 101.916(4)°, V = 951.8(4) Å³, Z = 4. For 2: monoclinic, space group P2₁/c, a = 13.976(3) Å, b = 7.9398(18) Å, c = 7.8687(18) Å, β = 101.150(5)°, V = 856.7(3) Å³, Z = 4. For 3: monoclinic, space group P2₁/c, a = 17.164(4) Å, b = 5.4870(12) Å, c = 10.850(2) Å, β = 101.557(4)°, V = 1001.1(4) Å³, Z = 4. The magnetic measurement on 2 reveals a dominant antiferromagnetic exchange coupling between the Cu(II) centers. A quasi-reversible electrochemical reaction is observed for complex 2 immobilized on the surface of GC electrode, corresponding to the redox couple Cu²⁺/Cu⁺. The fluorescent properties of 1–3 are also investigated.     

A N,N′-diacetate benzodioxotetraazamacrocycle and its transition metal complexes

Reaction of 2,9-dioxo-1,4,7,10-tetraazabicyclo[1.10.1]hexadeca-1(11),13,15-triene-4,7-diacetic acid (H₂L1) with CuCl₂ · 2H₂O in ethanol at pH 6 led to the monomeric benzodioxochlorocomplex [Cu(L′1)Cl] (1) (HL′1 = monoethylesther of H₂L1). X-ray structural analysis has shown that in complex 1 the Cu is five-coordinated by two nitrogen and two oxygen atoms of the macrocycle and by a chloride, displaying a square pyramidal coordination geometry. One of the acetate arms does not coordinate to the Cu and has suffered an in situ ethanolic esterification reaction. The protonation constants of H₂L1 and the stability constants of its complexes with Cu²⁺, Ni²⁺, Zn²⁺, Cd²⁺ and Pb²⁺ were determined by potentiometric methods and in some cases by ¹H NMR spectroscopy. The stability constants of the complexes follow the trend [Ni(H₋₁L1)]⁻ > [Cu(H₋₁L1)]⁻ ≫ [Pb(H₋₁L1)]⁻ > [Zn(H₋₁L1)]⁻ > [Cd(H₋₁L1)]⁻, probably due to steric requirements. Spectroscopic measurements (absorption and EPR) at different pH values have shown the effect of the pH on the coordination sphere of the Cu complexes.     

Iridium aminyl radical complexes as catalysts for the catalytic dehydrogenation of primary hydroxyl functions in natural products

The cationic tetra-coordinated 16 electron complex [Ir(trop₂dach)]⁺OTf⁻ (1) where (OTf⁻ = CF₃SO₃⁻) and the neutral amine amido complex [Ir(trop₂dach-1H)] (2) were isolated and structurally characterized. The NH function in 1 is easily deprotonated (pK_a^DMSO = 10.5) to yield the amino amido complex [Ir(trop₂dach-1H)] (2), which is deprotonated at pK_a^DMSO = 19.6 to the anionic di(amido) iridate [Ir(trop₂dach-2H)]⁻ (3); [(R,R)-top₂dach stands for the tetrachelating diamino diolefin ligand (R,R)-N,N′-bis(5H-dibenzo[a,d]cyclohepten-5-yl)-1,2-diaminocyclohexane; (R,R)-top₂dach-1H and (R,R)-top₂dach-2H indicate the mono and double deprotonated form]. Complex 3 is easily oxidized by 1,4-benzoquinone (BQ) to the neutral iridium aminyl radical complex [Ir(trop₂dach-2H)] (4). In combination with BQ as hydrogen acceptor and catalytic amounts of base, 4 serves as catalyst in the highly efficient dehydrogenation of functionalized primary alcohols to the corresponding aldehydes, RCH₂OH + BQ → RCHO + H₂BQ (H₂BQ = catechol). Alcohols like geraniol and retinol are rapidly converted to geranial and retinal, while the conversion of sterically hindered alcohols like lavandulol is slower and the primary product, lavandulal, isomerizes to isolavandulal in a classical base-catalyzed reaction.     

Mono- and di-nuclear complexes of thiosemicarbazones with copper(I): Synthesis,spectroscopy and structures

Reactions of copper(I) halides with a series of thiosemicarbazones, namely, benzaldehyde thiosemicarbazone (R¹R²CN–NH–C(S)–NH₂, R¹ = Ph, R² = H; Hbtsc), 2-benzoylpyridine thiosemicarbazone (R¹ = Ph, R² = py; Hbpytsc), and acetone thiosemicarbazone (R¹ = R² = Me; Hactsc), in the presence of PPh₃ has formed dimeric complexes, viz. sulfur bridged [Cu₂(μ-S-Hbtsc)₂Br₂(PPh₃)₂]·2H₂O (1), iodo-bridged [Cu₂(μ-I)₂(η¹-S-Hbtsc)₂(PPh₃)₂] (2), and heterobridged [Cu₂(μ₃-S,N³-Hactsc)(η¹-Br)(μ-Br)(PPh₃)₂] (3), as well as mononuclear complexes [CuX(η¹-S-Hbpytsc)(PPh₃)₂]·CH₃CN (X = Br, 4; Cl, 5). Complexes 1, 2, 4 and 5 involve thiosemicarbazone ligands in η¹-S bonding mode while in compound 3, ligand acts in N³, S-chelation-cum-S-bridging mode (μ₃-S,N³ mode). The intermolecular interactions such as, N²H?X, HN¹H?X (X = S, Br, Cl), CH?π interactions lead to 2D networks. All the complexes have been characterized with the help of elemental analyses, IR, ¹H, and ³¹P NMR spectroscopy, and single crystal X-ray crystallography. The role of a solvent in alteration of nuclearity and bonding modes of complexes has been highlighted.     

Two novel Keggin tungstocobaltates grafted by cobaltII complex group(s): K[Co(phen)2(H2O)]2[HCoW12O40]·2H2O and [Co(2,2′-bipy)3]1.5{[Co(2,2′-bipy)2(H2O)][HCoW12O40]}·0.5H2O

Two novel inorganic–organic hybrid compounds composed of Keggin tungstocobaltate framework and cobalt(II)–N coordination complexes, K[Co(phen)₂(H₂O)]₂[HCoW₁₂O₄₀]·2H₂O (1) (phen = 1,10-phenanthroline) and [Co(2,2′-bipy)₃]_1.5{[Co(2,2′-bipy)₂(H₂O)][HCoW₁₂O₄₀]·0.5H₂O (2) (bipy = bipyridine), have been synthesized under hydrothermal conditions by directly using Keggin POMs as starting materials, which were characterized by elemental analyses, IR, TG analyses and X-ray single crystal diffraction. Crystal data for compound 1: C₄₈H₄₁Co₃KN₈O₄₄W_12, triclinic, space group P-1, a = 10.918(5) Å, b = 13.401(5) Å, c = 13.693(5) Å, α = 69.291(5)°, β = 71.568(5)°, γ = 78.421(5)°, V = 1768.9(12) Å³, Z = 1; for compound 2: C₁₃₀H₁₀₄Co₇N₂₆O₈₃W_24, orthorhombic, space group, C2/c, a = 46.839(9) Å, b = 14.347(3) Å, c = 26.147(5) Å, α = β = γ = 90°, V = 17,570(6) Å³, Z = 4. Compound 1 exhibits a pseudo-1D chainlike structure, in which potassium ions act as linkages of Keggin unit doubly grafted by [Co(phen)₂(H₂O)] complex. Compound 2 represents a [Co(2,2′-bipy)₂(H₂O)]²⁺ mono-grafted Keggin tungstocobaltate derivative with 1.5[Co(2,2′-bipy)₃]²⁺ countercations. The cyclic voltammetric behavior of 1-CPE is similar to the parent 3-CPE, but the cyclic voltammetric behavior of Co^II shows a little difference. Variable-temperature magnetic susceptibility measurement of compound 1 demonstrates the presence of antiferromagnetic interactions.     

Electronic and vibrational spectra of tourmaline – The impact of electron beam irradiation and heat treatment

Irradiation and heat treatment were performed on tourmalines of various colors from Antandrokomby, Madagascar. The samples were irradiated with 10 MeV electrons to fluencies of 2 ×10¹⁷ cm⁻² for 1 h and were heated at 550 °C for 3 h in air. Their electronic and vibrational spectra were investigated by UV–vis, mid-infrared, and WD-XRF spectroscopy for comparison to pristine samples. Changes in the Mn³⁺ ions after irradiation resulted in darker pink tourmalines, which had absorption peaks at 390 and 520 nm. These samples became colorless after subsequent heat treatment. After irradiation, colorless, light blue and yellow tourmalines displayed a new absorption band at 365 nm. Alteration of the stretching absorption bands and wavenumber after irradiation could be explained by the following reactions:OH⁻ + e⁻ beam irradiation → O⁻ + H°,Mn²⁺ + e⁻ beam irradiation → Mn³⁺ + e⁻ andFe²⁺ + e⁻ beam irradiation → Fe³⁺ + e⁻.Stretching vibration of the BO₃ structure occurred at 1330 cm⁻¹, while the SiO vibration absorption bands were assigned to around 1100 cm⁻¹. Colorless, green, and yellow tourmalines showed high-intensity peaks around 3608 and 3505 cm⁻¹ after irradiation. Pink and dark green tourmalines showed low-intensity peaks at 3605 and 3585 cm⁻¹, respectively. The combination modes of stretching and bending in the range of 4600–4300 cm⁻¹ were split after irradiation and heat treatment, and different color changes occurred after irradiation.