Inorganics, Volume 7, Issue 2 (February 2019) – 13 articles

Scorpionate ligands with three soft sulfur donor sites have become very important in coordination chemistry. Despite its ability to form highly electrophilic species, electron-deficient thiopyridazines have rarely been used, whereas the chemistry of electron-rich thioheterocycles has been explored rather intensively. Here, the unusual chemical behavior of a thiopyridazine (6-tert-butylpyridazine-3-thione, H^tBuPn) based scorpionate ligand towards zinc is reported. Thus, the reaction of zinc halides with tris(6-tert-butyl-3-thiopyridazinyl)borate Na[Tn^tBu] leads to the formation of discrete torus-shaped hexameric zinc complexes [Tn^tBuZnX]₆ (X = Br, I) with uncommonly long zinc halide bonds. In contrast, reaction of the sterically more demanding ligand K[Tn^Me,tBu] leads to decomposition, forming Zn(HPn^Me,tBu)₂X₂ (X = Br, I). The latter can be prepared independently by reaction of the respective zinc halides and two equiv of HPn^Me,tBu. The bromide compound was used as precursor which further reacts with K[Tn^Me,tBu] forming the mononuclear complex [Tn^Me,tBu]ZnBr(HPn^Me,tBu). The molecular structures of all compounds were elucidated by single-crystal X-ray diffraction analysis. Characterization in solution was performed by means of ¹H, ¹³C and DOSY NMR spectroscopy which revealed the hexameric constitution of [Tn^tBuZnBr]₆ to be predominant. In contrast, [Tn^Me,tBu]ZnBr(HPn^Me,tBu) was found to be dynamic in solution. Full article

Achieving control over the phase-selective synthesis of mixed metal oxide materials remains a challenge to the synthetic chemist due to diffusion-driven growth, which necessitates the search for new compounds with pre-existent chemical bonds between the phase-forming elements. We report here a simple solvothermal process to fabricate LiCrO₂ and Li₂CrO₄ nanoparticles from bimetallic single-source precursors, demonstrating the distinctive influence of molecular design and calcination conditions on the resulting nanomaterials. The chemical identity of [Li₂Cr(O^tBu)₄Cl(THF)₂] (1) and [LiCr(O^tBu)₂(PyCH=COCF₃)₂(THF)₂] (2) was unambiguously established in the solid state by single-crystal X-ray diffraction, revealing the formation of a coordination polymeric chain in compound 1, whereas electron paramagnetic resonance spectroscopy (EPR) studies revealed a monomeric structure in solution. TEM analysis of synthesized LiCrO₂ nanoparticles showed nearly uniform particles size of approximately 20 nm. The sensitivity of the LiCrO₂ phase towards oxidation was investigated by X-ray diffraction, revealing the formation of the stable Li₂CrO₄ after calcination in air. Full article

The thermolysis of arachno-1 [(Cp*Ru)₂(B₃H₈)(CS₂H)] in the presence of tellurium powder yielded a series of ruthenium trithia-borinane complexes: [(Cp*Ru)₂(η¹-S)(η¹-CS){(CH₂)₂S₃BH}] 2, [(Cp*Ru)₂(η¹-S)(η¹-CS){(CH₂)₂S₃B(SMe)}] 3, and [(Cp*Ru)₂(η¹-S)(η¹-CS){(CH₂)₂S₃BH}] 4. Compounds 2–4 were considered as ruthenium trithia-borinane complexes, where the central six-membered ring {C₂BS₃} adopted a boat conformation. Compounds 2–4 were similar to our recently reported ruthenium diborinane complex [(Cp*Ru){(η²-SCHS)CH₂S₂(BH₂)₂}]. Unlike diborinane, where the central six-membered ring {CB₂S₃} adopted a chair conformation, compounds 2–4 adopted a boat conformation. In an attempt to convert arachno-1 into a closo or nido cluster, we pyrolyzed it in toluene. Interestingly, the reaction led to the isolation of a capped butterfly cluster, [(Cp*Ru)₂(B₃H₅)(CS₂H₂)] 5. All the compounds were characterized by ¹H, ¹¹B{¹H}, and ¹³C{¹H} NMR spectroscopy and mass spectrometry. The molecular structures of complexes 2, 3, and 5 were also determined by single-crystal X-ray diffraction analysis. Full article

The oxygen-evolution reaction (OER) in the near-neutral pH-regime is of high interest, e.g., for coupling of OER and CO₂-reduction in the production of non-fossil fuels. A simple model is proposed that assumes equal proton activities in the catalyst film and the near-surface electrolyte. Equations are derived that describe the limitations relating to proton transport mediated by fluxes of molecular “buffer bases” in the electrolyte. The model explains (1) the need for buffer bases in near-neutral OER and (2) the pH dependence of the catalytic current at high overpotentials. The latter is determined by the concentration of unprotonated buffer bases times an effective diffusion constant, which can be estimated for simple cell geometries from tabulated diffusion coefficients. The model predicts (3) a macroscopic region of increased pH close to the OER electrode and at intermediate overpotentials, (4) a Tafel slope that depends on the reciprocal buffer capacity; both predictions are awaiting experimental verification. The suggested first-order model captures and predicts major trends of OER in the near-neutral pH, without accounting for proton-transport limitations at the catalyst–electrolyte interface and within the catalyst material, but the full quantitative agreement may require refinements. The suggested model also may be applicable to further electrocatalytic processes. Full article

Halogen bonds are prevalent in many areas of chemistry, physics, and biology. We present a statistical model for the interaction energies of halogen-bonded systems at equilibrium based on high-accuracy ab initio benchmark calculations for a range of complexes. Remarkably, the resulting model requires only two fitted parameters, X and B—one for each molecule—and optionally the equilibrium separation, $R_{\mathrm{e}}$ , between them, taking the simple form $E=XB/R_{\mathrm{e}}^n$ . For $n=4$ , it gives negligible root-mean-squared deviations of 0.14 and 0.28 kcal mol ${}^{-1}$ over separate fitting and validation data sets of 60 and 74 systems, respectively. The simple model is shown to outperform some of the best density functionals for non-covalent interactions, once parameters are available, at essentially zero computational cost. Additionally, we demonstrate how it can be transferred to completely new, much larger complexes and still achieve accuracy within 0.5 kcal mol ${}^{-1}$ . Using a principal component analysis and symmetry-adapted perturbation theory, we further show how the model can be used to predict the physical nature of a halogen bond, providing an efficient way to gain insight into the behavior of halogen-bonded systems. This means that the model can be used to highlight cases where induction or dispersion significantly affect the underlying nature of the interaction. Full article

Many elegant inorganic designs have been developed to aid medical imaging. We know better now how to improve imaging due to the enormous efforts made by scientists in probe design and other fundamental sciences, including inorganic chemistry, physiochemistry, analytical chemistry, and biomedical engineering. However, despite several years being invested in the development of diagnostic probes, only a few examples have shown applicability in MRI in vivo. In this short review, we aim to show the reader the latest advances in the application of inorganic agents in preclinical MRI. Full article

Reaction of the o-[(o-hydroxyphenyl)methylideneamino]benzenesulfonic acid (H₂L) (1) with CuCl₂·2H₂O in the presence of pyridine (py) leads to [Cu(L)(py)(EtOH)] (2) which, upon further reaction with 2,2’-bipyridine (bipy), pyrazine (pyr), or piperazine (pip), forms [Cu(L)(bipy)]·MeOH (3), [Cu₂(L)₂(μ-pyr)(MeOH)₂] (4), or [Cu₂(L)₂(μ-pip)(MeOH)₂] (5), respectively. The Schiff base (1) and the metal complexes (2–5) are stabilized by a number of non-covalent interactions to form interesting H-bonded multidimensional polymeric networks (except 3), such as zigzag 1D chain (in 1), linear 1D chain (in 2), hacksaw double chain 1D (in 4) and 2D motifs (in 5). These copper(II) complexes (2–5) catalyze the peroxidative oxidation of cyclic hydrocarbons (cyclooctane, cyclohexane, and cyclohexene) to the corresponding products (alcohol and ketone from alkane; alcohols, ketone, and epoxide from alkene), under mild conditions. For the oxidation of cyclooctane with hydrogen peroxide as oxidant, used as a model reaction, the best yields were generally achieved for complex 3 in the absence of any promoter (20%) or in the presence of py or HNO₃ (26% or 30%, respectively), whereas 2 displayed the highest catalytic activity in the presence of HNO₃ (35%). While the catalytic reactions were significantly faster with py, the best product yields were achieved with the acidic additive. Full article

Suramin (SUR) is a known drug for treating parasitic infections though research studies and some clinical trials have shown its applicability for a plethora of other diseases. Herein we report on a novel SUR nanocarrier for the drug delivery to cells. We synthesized periodic mesoporous organosilica nanoparticles with spherical morphology, having mean diameter of 240 nm and high surface area (778 m²/g). The material’s surface is modified with an amine-containing organic moiety N-[3-(Trimethoxysilyl)propyl]ethylenediamine (DA), followed by surface attachment with the drug. The rate of SUR release in physiological condition was low, though in vitro experiments on MRC-5 cell line demonstrate effective delivery of the drug to the cells and low toxicity of the materials without the adsorbed drug. These results are promising for opening new treatment strategies with SUR-bearing nanocarriers, with high efficiency and low adverse effects on healthy tissues. Full article

We present the synthesis and structural characterization of the manganese-containing polyoxotungstate, [(Mn(H₂O)₃)₂(H₂W₁₂O₄₂)]⁶⁻ (1), obtained by reaction of MnCl₂ with six equivalents of Na₂WO₄ in the presence of Zn(CH₃COO)₂ in acetate medium (pH 4.7). This has been assessed by various techniques (FTIR, TGA, UV-Visible, XPS, elemental analysis, single crystal X-ray and electrochemistry). Single-crystal X-ray analyses showed that, in the solid state, 1 forms a 2-D network in which [H₂W₁₂O₄₂]¹⁰⁻ fragments are linked in pairs via Mn²⁺ ions, leading to linear chains of the form [(Mn(H₂O)₃)₂(H₂W₁₂O₄₂)]_n⁶ⁿ⁻. The connection between chains occurs also via Mn²⁺ ions which bind [H₂W₁₂O₄₂]¹⁰⁻ fragments belonging to two adjacent chains, forming an infinite 2-D network. A complete electrochemical study was done in aqueous solution where 1 is stable in the pH range 1 to 6. This complex undergoes multiple electron-transfer processes that lead to the electro-generation of manganese high oxidation state species that catalyse water electro-oxidation. 1 is also effective in the electro-catalytic reduction of nitrite and dioxygen. Full article

Photosystem II (PSII) uses water as the terminal electron donor, producing oxygen in the Mn₄CaO₅ oxygen evolving complex (OEC), while cytochrome c oxidase (CcO) reduces O₂ to water in its heme–Cu binuclear center (BNC). Each protein is oriented in the membrane to add to the proton gradient. The OEC, which releases protons, is located near the P-side (positive, at low-pH) of the membrane. In contrast, the BNC is in the middle of CcO, so the protons needed for O₂ reduction must be transferred from the N-side (negative, at high pH). In addition, CcO pumps protons from N- to P-side, coupled to the O₂ reduction chemistry, to store additional energy. Thus, proton transfers are directly coupled to the OEC and BNC redox chemistry, as well as needed for CcO proton pumping. The simulations that study the changes in proton affinity of the redox active sites and the surrounding protein at different states of the reaction cycle, as well as the changes in hydration that modulate proton transfer paths, are described. Full article

A new phosphine ligand bearing a thiophene moiety, C₄H₃SNHCOCH₂CH₂PPh₂ (L), has been prepared by reaction of the aminophosphine Ph₂PCH₂CH₂NH₂ with thiophenecarbonylchloride in the presence of triethylamine. The coordination behavior towards gold(I), gold(III) and silver(I) species has been studied and several metal compounds of different stoichiometry have been achieved, such as [AuL₂]OTf, [AuXL] (X = Cl, C₆F₅), [Au(C₆F₅)₃L], [AgL₂]OTf or [Ag(OTf)L]. Additionally, the reactivity of the chloride gold(I) species with biologically relevant thiolates was explored, thus obtaining the neutral thiolate compounds [AuL(SR)] (SR = 2-thiocitosine, 2-thiolpyridine, 2-thiouracil, 2-thionicotinic acid, 2,3,4,6-tetra-6-acetyl-1-thiol-β-d-glucopyranosato or thiopurine). The antitumor activity of the compounds was measured by the MTT method in several cancer cells and the complexes exhibit excellent cytotoxic activity. Full article

A new oxindolimine ligand derived from isatin (1H-indole-2,3-dione) and 2-aminomethylbenzimidazole was synthesized, leading to two novel complexes after metalation with copper(II) perchlorate or zinc(II) chloride, [Cu(isambz)₂](ClO₄)₂ (complex 1) and [Zn(isambz)Cl₂] (complex 2). This new ligand was designed as a more lipophilic compound, in a series of oxindolimine–metal complexes with antitumor properties, having DNA, mitochondria, and some proteins, such as CDK1 kinase and topoisomerase IB, as key targets. The new complexes had their reactivity to human serum albumin (HSA) and DNA, and their cytotoxicity toward tumor cells investigated. The binding to CT-DNA was monitored by circular dichroism (CD) spectroscopy and fluorescence measurements using ethidium bromide in a competitive assay. Consequent DNA cleavage was verified by gel electrophoresis with complex 1, in nmolar concentrations, with formation of linear DNA (form III) after 60 min incubation at 37 °C, in the presence of hydrogen peroxide, which acts as a reducing agent. Formation of reactive oxygen species (ROS) was observed, monitored by spin trapping EPR. Interaction with HSA lead to α-helix structure disturbance, and formation of a stable radical species (HSA–Tyr·) and carbonyl groups in the protein. Despite showing oxidative ability to damage vital biomolecules such as HSA and DNA, these new complexes showed moderate cytotoxicity against hepatocellular carcinoma (HepG₂) and neuroblastoma (SHSY5Y) cells, similarly to previous compounds in this series. These results confirm DNA as an important target for these compounds, and additionally indicate that oxidative damage is not the leading mechanism responsible for their cytotoxicity. Additionally, this work emphasizes the importance of ligand characteristics and of speciation in activity of metal complexes. Full article