Carbene Character in a Series of Neutral PCcarbeneP Cobalt(I) Complexes – Radical Carbenes Versus Nucleophilic Carbenes

Cobalt(I) complexes supported by a series of PCcarbeneP pincer ligands of varying donicity, differing in the aryl group linking the phosphine arms with the anchoring carbon donor, are described. Addition of the proligands to cobalt bromide results in the formation of a series of cobalt(II) tetrahedral complexes, Ln-1, which serve as excellent precur-sors to the corresponding PCalkylP and PCcarbeneP complexes. Square planar cobalt PCcarbeneP complexes, L2R-3-X (X = Cl, Br), are readily synthesized by addition of a bulky aryloxide radical to the corresponding PCalkylP complex, L1-2-Br or via addition of L2R to ClCo(PPh3)3 in the presence of trityl radical or by addition of NaHBEt3 and trityl radical to iso-lated L2R-1. For the L2NMe2 PCcarbeneP complexes, salt metathesis reactions with either CsOH·H2O, LiCH2TMS, or LiNH2 result in the corresponding hydroxo, alkyl, and amine complexes, L2NMe2-3-R (R = OH, CH2TMS, NH2). Reaction of L2NMe2-3-OH with benzoic acid affords the 2-O2CPh derivative The nature of the carbene bond in either ligand plat-form as well as the effects of the X-type capping ligand on the Co=C bond are explored computationally and show that triplet structures are relatively more stable in for the less electron donating ligand L1 while singlet Co(I) carbenes dominate for the more electron rich L2 derivatives. For L2NMe2 complexes, the effect of the trans ligand X was also probed. Pi donors imbue the carbene with singlet character while the strongly  donating alkyl derivative exhibits significant triplet character.

Characterization and Structural Insights of the Reaction Products by Direct Leaching of the Noble Metals Au, Pd and Cu with N,N′-Dimethyl-piperazine-2,3-dithione/I2 Mixtures

In the context of new efficient and safe leaching agents for noble metals, this paper describes the capability of the Me2pipdt/I2 mixture (where Me2pipdt = N,N′-dimethyl-piperazine-2,3-dithione) in organic solutions to quantitatively dissolve Au, Pd, and Cu metal powders in mild conditions (room temperature and pressure) and short times (within 1 h in the reported conditions). A focus on the structural insights of the obtained coordination compounds is shown, namely [AuI2(Me2pipdt)]I3 (1), [Pd(Me2pipdt)2]I2 (2a) and [Cu(Me2pipdt)2]I3 (3), where the metals are found, respectively, in 3+, 2+ and 1+ oxidation states, and of [Cu(Me2pipdt)2]BF4 (4) and [Cu(Me2dazdt)2]I3 (5) (Me2dazdt = N,N′-dimethyl-perhydrodizepine-2,3-dithione) compared with 3. Au(III) and Pd(II) (d8 configuration) form square–planar complexes, whereas Cu(I) (d10) forms tetrahedral complexes. Density functional theory calculations performed on the cationic species of 1–5 help to highlight the nature of the bonding in the different complexes. Finally, the valorization of the noble metals-rich leachates is assessed. Specifically, gold metal is quantitatively recovered from the solution besides the ligands, showing the potential of these systems to promote metal recycling processes.

Asymmetric construction of tetrahedral chiral zinc with high configurational stability and catalytic activity

Chiral metal complexes show promise as asymmetric catalysts and optical materials. Chiral-at-metal complexes composed of achiral ligands have expanded the versatility and applicability of chiral metal complexes, especially for octahedral and half-sandwich complexes. However, Werner-type tetrahedral complexes with a stereogenic metal centre are rarely used as chiral-at-metal complexes because they are too labile to ensure the absolute configuration of the metal centre. Here we report the asymmetric construction of a tetrahedral chiral-at-zinc complex with high configurational stability, using an unsymmetric tridentate ligand. Coordination/substitution of a chiral auxiliary ligand on zinc followed by crystallisation yields an enantiopure chiral-only-at-zinc complex (> 99% ee). The enantiomer excess remains very high at 99% ee even after heating at 70 °C in benzene for one week. With this configurationally stable zinc complex of the tridentate ligand, the remaining one labile site on the zinc can be used for a highly selective asymmetric oxa-Diels-Alder reaction (98% yield, 87% ee) without substantial racemisation.

Thallium mobility in mining wastes at the Crven Dol locality, Allchar deposit, North Macedonia

<p>In order to better understand the environmental behaviour of thallium, we have chosen the abandoned As–Sb–Tl–Au Allchar deposit (North Macedonia) with unique mineral composition and high thallium grades of the ore. We used pore water analyses, selective extractions, single-crystal and powder X-ray diffraction (PXRD), SEM-EDS, electron microprobe analysis (EMPA), and Raman spectroscopy to determine the distribution and speciation of thallium in waste dump material at the Tl-rich Crven Dol locality in the northern part of the Allchar deposit.</p><p>PXRD studies showed that the various solid waste samples are comprised mostly of carbonates (dolomite and calcite), gypsum, quartz, muscovite, kaolinite-group minerals followed by orpiment, realgar, pyrite, marcasite, lorandite, and various iron and calcium arsenates and iron (hydro)oxides, both amorphous and crystalline. Raman spectra, SEM-EDS and EMPA also showed the presence of Ca-Fe-, Ca-Mn-, and Ca-Mg-arsenates.</p><p>The main primary source of Tl in the waste is lorandite (TlAsS<sub>2</sub>), which occurs as prismatic crystals and anhedral grains up to 1 mm and is frequently intergrown with realgar. Other Tl sources, included in either realgar or orpiment, are minor Tl sulphosalts such as fangite (Tl<sub>3</sub>AsS<sub>4</sub>), raguinite (TlFeS<sub>2</sub>), picotpaulite (TlFe<sub>2</sub>S<sub>3</sub>) and jankovićite (Tl<sub>5</sub>Sb<sub>9</sub>(As,Sb)<sub>4</sub>S<sub>22</sub>). The Tl dissolved during weathering is precipitated as micaceous subparallel crystals of poorly crystalline to amorphous thallium arsenates (representing previously unknown mineral species), forming porous aggregates up to 100 µm. These Tl arsenates are intergrown with dolomite and Ca-Fe-arsenates and appear as two chemically different phases. The first, more common phase shows a variable Tl:As ratio ranging from ca. 2.1 to 4.1 and a variable Ca content (2.2 to 4.1 at.%). In the second, Tl-richer phase, the Tl:As ratio varies from ca. 5.1 to 8.4. Raman spectra of the Tl arsenates display broad bands and may be divided in the fingerprint region into two relevant ranges, 350–600 and 700–900 cm<sup>−1</sup>, both attributed to arsenate tetrahedral complexes showing As–O(<em>X</em>) symmetric stretching with <em>X</em> = H<sup>+</sup> or H<sub>2</sub>O.</p><p>Another relatively common Tl precipitate is dorallcharite [TlFe<sup>3+</sup><sub>3</sub>(SO<sub>4</sub>)<sub>2</sub>(OH)<sub>6</sub>], crystallizing in the form of tiny, well-formed platelets that are grouped into aggregates up to 400 µm in size. Tl is also accumulated in (probably cryptomelane-type) Mn oxides (up to 3.6 at.%), pharmacosiderite (up to 0.9 at.%), and jarosite (up to 0.9 at.%).</p><p>The pore water contained high aqueous concentrations of Tl (up to 660 μg·L<sup>−1</sup>) and As (up to 196 mg·L<sup>−1</sup>). Although these concentrations are low with respect to their total concentrations in the solid phase (Tl: 0.07-1.44 wt. %; As: 0.72-8.67 wt. %), mild extractions (ammonium nitrate and phosphate) mobilized up to 44% of the total Tl and 23% of the total As, indicating that a large amount of these toxic elements is bound weakly (sorption) to solids and can be easily mobilized into the pore water.</p><p>Financial support of the Austrian Science Fund (FWF) [P 30900-N28] is gratefully acknowledged.</p>

New 3- hydrazonoindolin-2-one Cd(II) complexes with amino pyridine ligands, Synthesis, Characterization and biological activity evaluation

This research includes synthesis and characterization of some of Cd(II) complexes with (3-hydrazonoindolin-2-one)(HZI) ligand and amino pyridine ligands. Treatment equialmolar of CdCl2.2.5H2O and (HZI) ligand with two moles of n-aminopyridine (n-amp) (n:2,3,4) ligands afford a tetrahedral complexes of the type [Cd(HZI)(n-amp)2]Cl2, where (HZI) ligand behaves as a bidentate chelating fashion through the N atom of azomethine group and O atom of carbonyl group. Whereas the (n-amp)(n: 2,3,4) was bonded monodentate mode through the N atom of heterocyclic ring. The prepared complexes have been characterized by molar conductivity, elemental analysis, infrared spectra and 1H-NMR and 13C-NMR spectra. Also the evaluation of biological activity of the prepared complexes against two types of gram positive bacteria (Staphylococcus Epidermidis and Staphylococcus aureus) and (Citrobacer Freundii) and gram negative, all prepared complexes showed activity against Staphylococcus aureus more than amikacin, while the [Cd(HZI)(3-amp)2]Cl2 complex showed high activity against Staphylococcus Epidermidis and Citrobacter freundii more than another prepared complexes http://dx.doi.org/10.25130/tjps.25.2020.028

Tetrahedral photoluminescent manganese(ii) halide complexes with 1,3-dimethyl-2-phenyl-1,3-diazaphospholidine-2-oxide as a ligand

Photoluminescent Mn(ii) tetrahedral complexes characterized by intense emission in the green region were isolated from the reaction of MnX2 (X = Cl, Br, I) and the ligand 1,3-dimethyl-2-phenyl-1,3-diazaphospholidine-2-oxide.

Light harvesting indolyl-substituted phosphoramide ligand for the enhancement of Mn(ii) luminescence

Excitation of the coordinated ligands in tetrahedral complexes having the general formula [MnX2L2] (X = Cl, Br, I; L = N,N′,N′-tetramethyl-P-indol-1-ylphosphonic diamide) causes bright green luminescence from the Mn(ii) centre.

Influence of Zn+2 Doping on Ni-Based Nanoferrites; (Ni1−x ZnxFe2O4)

Nickel zinc nanoferrites (Ni1−xZnxFe2O4) were synthesized via a chemical co-precipitation method having stoichiometric proportion (x) altering from 0.00 to 1.00 in steps of 0.25. The synthesized nanoparticles were sintered at 800 °C for 12 h. X-ray diffraction patterns illustrate that the nanocrystalline cubic spinel ferrites have been obtained after sintering. The Scherrer formula is used to evaluate the particle size using the extreme intense peak (311). The experimental results demonstrate that precipitated particles’ size was in the range of 20–60 nm. Scanning electron microscopy (SEM) is used to investigate the elemental configuration and morphological characterizations of all the prepared samples. FTIR spectroscopy data for respective sites were examined in the range of 300–1000 cm−1. The higher frequency band ν1 were assigned due to tetrahedral complexes while lower frequency band ν2 were allocated due to octahedral complexes. Our experimental results demonstrate that the lattice constant a0 increases while lattice strain decreases with increasing zinc substitution in nickel zinc nanoferrites.

Influence of ligand positional isomerism on the molecular and supramolecular structures of cobalt(II)-phenylimidazole complexes

In a study to evaluate the impact of flexible positional isomeric ligands on the coordination geometry and self-assembly process of 3d metal complexes, the synthesis of eight new cobalt(II) complexes with the 2-phenylimidazole (LH) and 5-phenylimidazole (L′H) ligands has been carried out. A variety of parameters/conditions have been probed using the general CoII/X −/LH or L′H (X − = Cl−, Br−, I−, NO3 −, NCS−, ClO4 −, SO4 2−) reaction system. Interestingly, X-ray analyses reveal two distinct groups of complexes: reactions with LH only lead to tetrahedral or quasi-tetrahedral complexes {i.e. [CoCl2(LH)2] (1), [CoI2(LH)2] (2), [Co(NO3)2(LH)2] (3), [Co(NCS)2(LH)2] (4)}, whereas L′H favours octahedral coordination {i.e. [Co(L′H)4(MeCN)(H2O)]I2 (5), [Co(L′H)4(MeCN)(H2O)](NO3)2 (6) and [Co(NCS)2(L′H)4)]·2MeOH (7·2MeOH)}. A tetrahedral [Co(NCS)2(L′H)2)] (8) complex was also concurrently isolated with complex 7. The effects of the positional isomeric ligands LH and L′H and of the coordinated inorganic anions on the stoichiometry and packing arrangements of the complexes are thoroughly discussed. The supramolecular assembly is firmly directed, in all types of complexes, by robust N—H...X (X = Cl, I, O or S) motifs, leading to varying dimensionalities (1D, 2D or 3D) and packing arrangements. The formation of these motifs has been activated by choosing appropriate anions X, acting as terminal ligands or counterions. At a second level of organization, additional subordinate C—H...X (X = Cl, I, O or S), C—H...π and π...π intermolecular interactions complement the rigidity of the complexes' packing towards compact 3D assemblies. Hirshfeld surface analyses provided insight into the intermolecular interactions, allowed quantification of the individual contact types and comparison between the complexes.