Category Archives: European Journal of Inorganic Chemistry

Surprising Impact of Donor Charge on the Water Exchange Rates of Gd(III) AAZTA Derivatives

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Surprising Impact of Donor Charge on the Water Exchange Rates of Gd(III) AAZTA Derivatives

Coordinated water molecules in Bis-hydrated Gd(III)-AAZTA derivatives have unexpectedly fast exchange rates, which do not follow the trend with complex charge observed previously for contrast agents used in magnetic resonance imaging (MRI).


Abstract

We report the synthesis of three new heptadentate ligands derived from H4AAZTA (6-amino-6-methylperhydro-1,4-diazepinetetraacetic acid) that contain a dimethyl-amide group (AAZTA-MA)3−, two dimethyl-amide groups (AAZTA-BMA)2− or two acetylglycine groups (AAZTA(Gly)2)4−. The corresponding Gd(III) complexes were investigated using 1H NMR relaxometry and 17O NMR chemical shifts and transverse relaxation rates. A computational DFT study was also performed to aid the analysis of the NMR data. The Gd(III) complexes contain two water molecules coordinated to the metal ion. In contrast to the prevailing trend, the amide derivatives discussed in this context exhibit comparatively rapid water exchange rates that do not align with the changes in the overall electric charge of the complexes: k ex 298=14.4×106 s−1, 14.5×106 s−1 and 9.56×106 s−1 for [Gd(AAZTA-MA)(H2O)2], [Gd(AAZTA-BMA)(H2O)2]+ and [Gd(AAZTA(Gly)2(H2O)2]−, respectively. The analysis of the data and the computational work suggest that the relatively fast water exchange rates could be linked to the occurrence of associatively activated mechanisms, which is somewhat unexpected for nine-coordinated complexes.

Citric acid as multidentate flexible ligand for multinuclear late‐3 d‐metal complexes and single‐molecule magnets

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Citric acid as multidentate flexible ligand for multinuclear late-3 d-metal complexes and single-molecule magnets

Citrate which is a unique bio-derived ligand has great potential to serve as a bridge between spin quantum magnetism and green chemistry. This review focuses on the structures and magnetism of discrete citrate complexes of late-3d-metals, as well as their single-molecule magnet properties.


Abstract

Citric acid (citH4) is a ubiquitous product in nature with an interesting chemistry owing to its three carboxy and one hydroxy groups, which can be deprotonated in a stepwise manner into six kinds of citrate anions involving two protonation isomers. Deprotonated citrates easily coordinate to late-3d-metal ions (Mn, Fe, Co, Ni, Cu, and Zn), affording complexes including mono-, di-, tri-, tetra-, hexa-, hepta-, octa-, nona-, and 21-nuclear complexes with a variety of structures. Magnetic interactions between metal centers are mainly generated via superexchange through hydroxylate or carboxylate bridging, whereas weaker magnetic dipole interactions appear in the absence of superexchange interactions. In citrate complexes, both ferromagnetic and antiferromagnetic interactions have been found. Citrate has a great potential to serve as a bridge between spin quantum magnetism and green chemistry. In this review, the structures and magnetism of discrete citrate complexes of late-3d-metals, as well as their single-molecule magnet properties are discussed.

Probing the effects of gold doping on structural, electronic and nonlinear optical properties of caged X20H20 (X=Si, Ge, Sn, Pb) clusters

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Probing the effects of gold doping on structural, electronic and nonlinear optical properties of caged X20H20 (X=Si, Ge, Sn, Pb) clusters

Using first-principles methods, we explored the doping of gold atom into carbon family clusters (Si20, Ge20, Sn20, Pb20), and the Au atom and charged states can effectively modulate the electronic properties of clusters, while the neutral Au@X20H20 (X=Si, Sn) clusters possess the large nonlinear optical responses, especially for Au@Sn20H20, served as novel optoelectronic materials.


Abstract

Carbon family elements (Si, Ge, Sn, Pb) have attracted a lot of attention because of their unique structural features and potential applications in microelectronics industry. Here, the structure, chemical stability, electronic properties, and nonlinear optical properties of neutral and charged Au@X20H20 (X=Si, Ge, Sn, Pb) clusters have been systematically studied using density-functional theory calculations. Structurally, the neutral/anionic Au@X20H20 (X=Si, Ge, Sn) as well as cationic Au@Pb20H20 possess Au-endohedral (XH)20 unit, forming fullerene-like framework, whereas other species are Au-doped structures with hydrogen-bridged bond. Analysis of binding energy and HOMO-LUMO energy gaps reveals that the charged clusters possess high chemical stabilities due to closed-shell structures. The charge transfers from X20 cage to Au atom, and the Au atom acts as electron acceptor. The Au atom and charged states play an important role in the structural stability, and can effectively modulate the electronic properties of clusters. Interestingly, the neutral Au@X20H20 (X=Si, Sn) clusters possess large first hyperpolarizabilities, especially for Au@Sn20H20, which has remarkably giant value (~5.65×108 a. u.), and the enhanced NLO behaviors can be further explained by the TDDFT calculation. The work may provide a theoretical reference for further applications considered as novel cluster-assembled nanomaterials.

Mechanistic Insights into Ru‐catalyzed Alkene Epoxidation with Nitrous Oxide as a Terminal Oxidant

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Mechanistic Insights into Ru-catalyzed Alkene Epoxidation with Nitrous Oxide as a Terminal Oxidant

Simple kinetic studies provided insights to inform future catalyst designs able to employ N2O as an oxidant under mild conditions. Results suggest the use of low alkene concentrations, possible saturation behavior at high N2O pressures and a potential catalyst turnover involving disproportionation of RuIV(O) and RuIV(O)(N2O).


Abstract

Nitrous oxide (N2O) is a greenhouse gas produced in the manufacture of 6,6-nylon and nitric acid. While an attractive oxidant that releases only N2 as a by-product, the kinetic stability of N2O typically requires high temperatures and pressures for activation. This work describes initial kinetics of oxygen transfer in the epoxidation of cholesteryl acetate with N2O catalysed by D4 -Ru(VI)(por)(O)2 complexes in efforts to provide a better mechanistic understanding of this chemistry. Insights include a need for low concentrations of the alkene to avoid competitive binding to the metal, possible saturation behavior at high N2O pressures, transfer of only one oxygen of RuVI(O)2 to substrate and a possible catalyst turnover involving disproportionation of RuIV(O) and RuIV(O)(N2O) to active RuVI(O)2, RuIV(O) and N2. These insights will be used in future designs of improved catalysts and reaction protocols that may operate efficiently at low pressures of N2O and ambident temperature.

Uranium Cyanides from Reactions in Liquid Ammonia Solution

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Uranium Cyanides from Reactions in Liquid Ammonia Solution

So far there are only very few uranium cyanides. Three novel uranium cyanides have been obtained from reactions of uranium halides with cyanides in liquid ammonia as a solvent.


Abstract

Reactions of uranium tri- and tetrahalides, UBr3, UI3, UCl4, and UI4, with different cyanides MCN (M=K, Ag) in liquid anhydrous ammonia led to three novel uranium(IV) cyanide compounds. The reaction of UCl4 in the presence of KCN resulted in the compound [U(CN)(NH3)8]Cl3 ⋅ 3NH3, while UBr3 and UI3 were oxidized in the presence of AgCN to form the compounds (μ-CN){(H3N)5U(μ-NH2)3U(NH3)5}]Br4 ⋅ 2NH3, and (μ-CN){(H3N)5U(μ-NH2)3U(NH3)5}]I4 ⋅ 2NH3. The reaction of UI4 with KCN in aNH3 also yielded the compound (μ-CN){(H3N)5U(μ-NH2)3U(NH3)5}]I4 ⋅ 2NH3. The compounds (μ-CN){(H3N)5U(μ-NH2)3U(NH3)5}]X 4 ⋅ 2NH3 (X=Br, I) crystallize in different space groups, Pmn21 (no. 31) and Imm2 (no. 44), respectively. In both cases, the (μ-CN){(H3N)5U(μ-NH2)3U(NH3)5}]4+ cation forms infinite strands. We conducted quantum-chemical calculations and Intrinsic Bond Orbital analyses on the observed [U(CN)(NH3)8]3+ cation and the [(μ-CN)2{(H3N)5U(μ-NH2)3U(NH3)5}]3+ model cation to gain insight into the bonding situation.

Controllably Modulating Oxygen Vacancies on Nonstoichiometric Nd−Ce−O Binary Oxides for Low‐temperature Oxidative Coupling of Methane

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Controllably Modulating Oxygen Vacancies on Nonstoichiometric Nd−Ce−O Binary Oxides for Low-temperature Oxidative Coupling of Methane

As the amount of Nd3+ increases, the oxygen vacancies in Nd−Ce−O composite oxides gradually increase, leading to an amount increasing in the C2-selective O2 − species generated by the oxygen vacancies, and the number of surface moderate basic sites, hence improving the OCM reaction performance.


Abstract

Herein, we synthesised a series of nonstoichiometric Nd−Ce−O composite oxides with a fluorite or rare-earth C-type phase structure using the glycine combustion method for the oxidative coupling of methane (OCM) reaction. As the amount of Nd3+ increases, the oxygen vacancies in this series of composite oxides gradually increase, leading to an amount increasing in the C2-selective oxygen species O2 − generated by the oxygen vacancies. In addition, with the increase in Nd3+, the number of moderate basic sites on the catalyst surface also improves, another significant factor affecting the OCM reaction performance of the composite oxides. Nd0.9Ce0.1O1.55 possesses optimal low-temperature OCM reaction performance, achieving 8.0 % C2 yield at 450 °C and 14.1 % C2 yield at 700 °C. This can be attributed to the nonstoichiometric rare-earth C-type crystalline phase structure of Nd0.9Ce0.1O1.55, which exhibits the highest abundance of oxygen vacancies, selective oxygen species O2 −, and moderate basic sites.

Lanthanide Amide Complexes Supported by the Bis‐tris(pyrazolyl)borate Ligand Environment

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Lanthanide Amide Complexes Supported by the Bis-tris(pyrazolyl)borate Ligand Environment

The specific synthetic conditions to successfully access primary lanthanide amides in the bis-hydrotris(1-pyrazolyl)borate ligand environment [Ln(Tp)2(NHArCF3)] 3-Ln (Ln=Y, Dy; ArCF3=C6H3(CF3)2-3,5) are reported by either metathesis of [Ln(Tp)2(OTf)] 1-Ln (OTf=CF3SO3) with K(NHArCF3) or protonolysis of [Ln(Tp)2(N′′)] 2-Ln (N′′=N(SiMe3)2) with H2NArCF3 in toluene.


Abstract

Synthesis of primary lanthanide amides in the bis-hydrotris(1-pyrazolyl)borate ligand environment has been achieved. Salt metathesis of [Dy(Tp)2(OTf)] 1-Dy (OTf=CF3SO3) with K(N′′) (N′′=N(SiMe3)2) in toluene yielded the [bis(silyl)]amide [Dy(Tp)2(N′′)] 2-Dy. Complexes 1-Ln and 2-Ln were both used to access primary lanthanide amides, where either metathesis of 1-Ln with K(NHArCF3) (ArCF3=C6H3(CF3)2-3,5) or protonolysis of 2-Ln with H2NArCF3 in toluene yielded [Ln(Tp)2(NHArCF3)] 3-Ln (Ln=Y, Dy). The synthesis of parent amides was also attempted, but the metathesis of 1-Y with NaNH2 yielded complicated reaction mixtures, but from which the dimeric parent amide [{Y(Tp)2(μ-NH2)}2] 4-Y and an ‘ate’-salt [{Y(Tp)2(μ 2-OTf)(μ 3-OTf)Na(THF)2}2] 5-Y were isolated. Full characterisation data are presented for all complexes, including the structure determination.

Mechanistic Insights of the Ir‐bipyridonate Catalyzed Aqueous Methanol Dehydrogenation and Transfer Dehydrogenation to Acetophenone: Experimental and DFT Study

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Mechanistic Insights of the Ir-bipyridonate Catalyzed Aqueous Methanol Dehydrogenation and Transfer Dehydrogenation to Acetophenone: Experimental and DFT Study

The mechanism of aqueous methanol dehydrogenation to yield carbon dioxide, either producing H2 in the absence of acceptor or transferring hydrogen to acetophenone to yield 1-phenylethanol, has been elucidated by a combination of DFT calculations, which includes solvating MeOH molecules, and NMR/kinetics experimental investigations.


Abstract

The mechanisms of the Cp*IrIII(bpyOO)-catalyzed (bpyOO=bidentate (NN) doubly deprotonated 2,2′-bipyridine-6,6′-diol) acceptorless methanol dehydrogenation and acetophenone transfer hydrogenation by methanol under basic conditions have been explored by the combination of 1H NMR, kinetics, and DFT computational studies. During dehydrogenation of methanol and of its dehydrogenated derivatives, the presence of two iridium hydride species (anionic [Cp*Ir(bpyOO)H]−, C* and neutral [Cp*Ir(bpyOOH)H], D*), which interconvert depending on pH, was detected. The DFT studies on a Cp model system highlighted three interrelated catalytic cycles of methanol, formaldehyde and formic acid dehydrogenation, all leading to the same hydride intermediates C and D. The dehydrogenation of methanol prefers a direct β-hydride transfer pathway from the methoxide ion to Ir, rather than the classical β-hydride elimination pathway from a coordinated methoxide ligand, but an alternative bifunctional H+/H− transfer with involvement of a ligand O atom may become competitive at lower pH. The transfer hydrogenation of acetophenone using methanol as hydrogen source features species C* as resting state, with the acetophenone reduction being rate-determining and following the reverse pathway of methanol oxidation, with a first-order acetophenone decay and a kinetic isotope effect of 2.36±0.09.

Synthesis, Structural and Redox Properties of Vanadyl β‐Cyanoporphyrin and its Utilization as Efficient Catalyst for Epoxidation of Olefins and Oxidative Bromination of Phenols

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Synthesis, Structural and Redox Properties of Vanadyl β-Cyanoporphyrin and its Utilization as Efficient Catalyst for Epoxidation of Olefins and Oxidative Bromination of Phenols

The elegant synthesis of free base 2-cyano-meso-tetraphenylporphyrin (H2TPPCN) is reported. Its vanadyl complex, [VIVOTPPCN], has been utilized as efficient and green catalyst for the bromination of various phenols in water at room temperature and epoxidation of olefins. The catalyst is recyclable and reusable.


Abstract

2-Cyano-5,10,15,20-tetraphenylporphyrin [H2TPPCN] (1) having cyano group at one of β-pyrrolic positions using nucleophilic substitution reaction of tetrabutylammonium cyanide (TBACN) on free-base 2-nitro-5,10,15,20-tetraphenylporphyrin, and its oxidovanadium(IV) complex [VIVOTPPCN] (2) were synthesized in good yields. Both the porphyrins 1 and 2 have been characterized by UV-Vis spectroscopy, mass spectrometry, and cyclic voltammetric techniques. Single crystal X-Ray crystallography revealed quasi-planar geometry for 1. Compounds 1 and 2 exhibited a red shift (λmax=7–9 nm) in the Soret band relative to [MTPP], where M=2H, VIVO owing to the electron-withdrawing effect of the cyano group at the β-position. The first oxidation (ΔE1/2=110–140 mV) and reduction potentials (ΔE1/2=220–260 mV) of 1 and 2 are anodically shifted relative to [MTPP] where M=2H, VIVO. Porphyrin 2 has been utilized as a catalyst for two reactions: epoxidation of olefins and bromination of phenols. The bromination of phenol using KBr/H2O2/HClO4 in water resulted in 100 % conversion with a TOF value as high as 19.6 s−1 in 0.5 h. Using H2O2/NaHCO3 in a CH3CN/H2O solvent mixture at 60 °C, epoxidation was carried out, and the highest conversion rate with a turnover frequency of 1.9 s−1 was achieved in the case of cyclohexene. Catalyst 2 was recovered successfully at the end of the reaction up to 5 cycles and had good thermal stability, indicating its industrial viability and applicability. Moreover, these cyano-functionalized porphyrins could be further utilized for the generation of molecular self-assemblies, post-functionalization of porphyrin core and various applications. The current findings in this work present insights for a facile approach for the synthesis of β-cyano functionalized porphyrin 1 and further shed light on the utility of its vanadyl complex 2 as an efficient catalyst for olefin epoxidation and phenol bromination reactions.

Comprehensive Photophysical and Nonlinear Spectroscopic Study of Thioanisolyl‐Picolinate Triazacyclononane Lanthanide Complexes

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Comprehensive Photophysical and Nonlinear Spectroscopic Study of Thioanisolyl-Picolinate Triazacyclononane Lanthanide Complexes

Three thioanisolyl-picolinates were incorporated with tacn in a joint macrocyclic ligand sensitising visible Eu(III) emission with 44 % quantum yield, near-infrared Yb(III) and Nd(III), and dual vis-NIR Sm(III) luminescence. Eu(III) and Sm(III) emission was achieved via one- (1 P, at 330 nm) and two-photon (2 P, at 640–710 nm) excitation.


Abstract

Detailed photophysical studies of luminescent lanthanide complexes are presented and elaborated using a newly developed thioanisolyl-picolinate antenna and the related tacn macrocyclic ligand. The new ligand proved to sensitise Nd(III), Sm(III), Eu(III) and Yb(III) emission. Eu(III) complex showed complete energy transfer, yielding high quantum yield (44 %) and brightness, while the Tb(III) analogue underwent a thermally activated back-energy transfer, resulting in a strong oxygen quenching of the triplet excited state. Transient absorption spectroscopy measurements of Gd(III), Tb(III) and Eu(III) compounds confirmed the sensitization processes upon the charge-transfer antenna excitation. The triplet excited state lifetime of the Tb(III) complex was 5-times longer than that of the Gd(III) analogue. In contrast, the triplet state was totally quenched by the energy transfer to the 4f-metal ion in the Eu(III) species. Nonlinear two-photon absorption highlighted efficient biphotonic sensitization in Eu(III) and Sm(III) complexes. In case of the Nd(III) compound, one-photon absorption in 4f–4f transitions was predominant, despite the excitation at the antenna two-photon band. This phenomenon was due to the Nd(III) 4f–4f transitions overlapping with the wavelength-doubled absorption of the complex.