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Inorganics, Volume 8, Issue 2 (February 2020) – 9 articles

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Cover Story (view full-size image) Magnetic contrast agents are widely used in magnetic resonance imaging in order to change signals [...] Read more.
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Open AccessArticle
Controlling the Lifetime of the Triplet MLCT State in Fe(II) Polypyridyl Complexes through Ligand Modification
Inorganics 2020, 8(2), 16; https://doi.org/10.3390/inorganics8020016 - 20 Feb 2020
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Abstract
A computational study is presented in which two strategies of ligand modifications have been explored to invert the relative energy of the metal-to-ligand charge transfer (MLCT) and metal-centered (MC) state in Fe(II)-polypyridyl complexes. Replacing the bipyridines by stronger σ donors increases the ligand-field [...] Read more.
A computational study is presented in which two strategies of ligand modifications have been explored to invert the relative energy of the metal-to-ligand charge transfer (MLCT) and metal-centered (MC) state in Fe(II)-polypyridyl complexes. Replacing the bipyridines by stronger σ donors increases the ligand-field strength and pushes the MC state to higher energy, while the use of ligands with a larger π conjugation leads to lower MLCT energies. Full article
(This article belongs to the Special Issue Novel Ligand Design in Coordination Compounds)
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Open AccessCommunication
On the Possible Coordination on a 3MC State Itself? Mechanistic Investigation Using DFT-Based Methods
Inorganics 2020, 8(2), 15; https://doi.org/10.3390/inorganics8020015 - 19 Feb 2020
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Abstract
Understanding light-induced ligand exchange processes is key to the design of efficient light-releasing prodrugs or photochemically driven functional molecules. Previous mechanistic investigations had highlighted the pivotal role of metal-centered (MC) excited states in the initial ligand loss step. The question remains whether they [...] Read more.
Understanding light-induced ligand exchange processes is key to the design of efficient light-releasing prodrugs or photochemically driven functional molecules. Previous mechanistic investigations had highlighted the pivotal role of metal-centered (MC) excited states in the initial ligand loss step. The question remains whether they are equally important in the subsequent ligand capture step. This article reports the mechanistic study of direct acetonitrile coordination onto a 3MC state of [Ru(bpy)3]2+, leading to [Ru(bpy)21-bpy)(NCMe)]2+ in a 3MLCT (metal-to-ligand charge transfer) state. Coordination of MeCN is indeed accompanied by the decoordination of one pyridine ring of a bpy ligand. As estimated from Nudged Elastic Band calculations, the energy barrier along the minimum energy path is 20 kcal/mol. Interestingly, the orbital analysis conducted along the reaction path has shown that creation of the metallic vacancy can be achieved by reverting the energetic ordering of key dσ* and bpy-based π* orbitals, resulting in the change of electronic configuration from 3MC to 3MLCT. The approach of the NCMe lone pair contributes to destabilizing the dσ* orbital by electrostatic repulsion. Full article
(This article belongs to the Special Issue Photochemistry & Photophysics of Transition Metal Complexes)
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Open AccessArticle
Excited-State Relaxation in Luminescent Molybdenum(0) Complexes with Isocyanide Chelate Ligands
Inorganics 2020, 8(2), 14; https://doi.org/10.3390/inorganics8020014 - 17 Feb 2020
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Abstract
Diisocyanide ligands with a m-terphenyl backbone provide access to Mo0 complexes exhibiting the same type of metal-to-ligand charge transfer (MLCT) luminescence as the well-known class of isoelectronic RuII polypyridines. The luminescence quantum yields and lifetimes of the homoleptic tris(diisocyanide) Mo [...] Read more.
Diisocyanide ligands with a m-terphenyl backbone provide access to Mo0 complexes exhibiting the same type of metal-to-ligand charge transfer (MLCT) luminescence as the well-known class of isoelectronic RuII polypyridines. The luminescence quantum yields and lifetimes of the homoleptic tris(diisocyanide) Mo0 complexes depend strongly on whether methyl- or tert-butyl substituents are placed in α-position to the isocyanide groups. The bulkier tert-butyl substituents lead to a molecular structure in which the three individual diisocyanides ligated to one Mo0 center are interlocked more strongly into one another than the ligands with the sterically less demanding methyl substituents. This rigidification limits the distortion of the complex in the emissive excited-state, causing a decrease of the nonradiative relaxation rate by one order of magnitude. Compared to RuII polypyridines, the molecular distortions in the luminescent 3MLCT state relative to the electronic ground state seem to be smaller in the Mo0 complexes, presumably due to delocalization of the MLCT-excited electron over greater portions of the ligands. Temperature-dependent studies indicate that thermally activated nonradiative relaxation via metal-centered excited states is more significant in these homoleptic Mo0 tris(diisocyanide) complexes than in [Ru(2,2′-bipyridine)3]2+. Full article
(This article belongs to the Special Issue Photochemistry & Photophysics of Transition Metal Complexes)
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Open AccessArticle
Structural Damage of Two-Dimensional Organic–Inorganic Halide Perovskites
Inorganics 2020, 8(2), 13; https://doi.org/10.3390/inorganics8020013 - 06 Feb 2020
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Abstract
Organic–inorganic halide perovskites are promising photovoltaic materials with excellent optoelectronic properties. However, the extreme structural instability hinders their wide application as well as the microstructure characterization using high energy beams such as transmission electron microscopy (TEM). Here, taking BA2FAPb2I [...] Read more.
Organic–inorganic halide perovskites are promising photovoltaic materials with excellent optoelectronic properties. However, the extreme structural instability hinders their wide application as well as the microstructure characterization using high energy beams such as transmission electron microscopy (TEM). Here, taking BA2FAPb2I7 and BA2MAPb2I7 as examples, we investigate their structural evolution resulting from high energy electron irradiation, moist air, and low temperature, respectively. The results show that the long organic chains are the first to be damaged under electron beam, which is mainly arising from their instability and weak bonding with the framework of [PbI6]4− octahedrons. Then the short organic cations and the framework of [PbI6]4− octahedrons collapses gradually. The final products are clusters of detached PbI2 particles, which can also be observed in the sample degraded in moist air. In addition, the structures of BA2FAPb2I7 and BA2MAPb2I7 are discovered to undergo a phase transformation at liquid nitrogen temperature, which calls attention to the community that cryo-TEM methods should be used cautiously for organic–inorganic halide perovskite materials. Full article
(This article belongs to the Special Issue Inorganic Materials for Solar Energy Conversion)
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Investigation of Hydrogen Storage Characteristics of MgH2 Based Materials with Addition of Ni and Activated Carbon
Inorganics 2020, 8(2), 12; https://doi.org/10.3390/inorganics8020012 - 02 Feb 2020
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Abstract
Magnesium-based materials are promising as hydrogen storage media due to their high theoretical hydrogen absorption capacity, abundance and low price. The subject of this study are the hydrogen sorption characteristics of the composites 80 wt % MgH2-15 wt % Ni-5 wt [...] Read more.
Magnesium-based materials are promising as hydrogen storage media due to their high theoretical hydrogen absorption capacity, abundance and low price. The subject of this study are the hydrogen sorption characteristics of the composites 80 wt % MgH2-15 wt % Ni-5 wt % activated carbon (synthesized from polyolefin wax, a waste product of polyethylene production at low pressure which will be denoted further in the text as POW) and 90 wt % MgH2-5 wt % Ni-5 wt % POW, prepared by ball milling under argon atmosphere. Structure, phase and surface composition of the samples before and after hydrogenation are determined by XRD and TEM. The maximum absorption capacity value of the composites at a temperature 573 K and after 60 min. of hydrogenation are 5.3 wt % H2 for the material with higher Ni content and 5.5 wt % H2 for the other sample. The presence of both additives—nickel and activated carbon derived from POW—has a positive impact on hydrogenation kinetics and the capacity achieved. The results from TEM characterization, e.g., the polycrystalline SAED (selected area electron diffraction) show the presence of graphite, Mg and monoclinic Mg2NiH4. Full article
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Open AccessCommunication
Magnetic Composite Submicron Carriers with Structure-Dependent MRI Contrast
Inorganics 2020, 8(2), 11; https://doi.org/10.3390/inorganics8020011 - 30 Jan 2020
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Abstract
Magnetic contrast agents are widely used in magnetic resonance imaging in order to significantly change the signals from the regions of interest in comparison with the surrounding tissue. Despite a high variety of single-mode T1 or T2 contrast agents, there is [...] Read more.
Magnetic contrast agents are widely used in magnetic resonance imaging in order to significantly change the signals from the regions of interest in comparison with the surrounding tissue. Despite a high variety of single-mode T1 or T2 contrast agents, there is a need for dual-mode contrast from the one agent. Here, we report on the synthesis of magnetic submicron carriers, containing Fe3O4 nanoparticles in their structure. We show the ability to control magnetic resonance contrast by changing not only the number of magnetite nanoparticles in one carrier or the concentration of magnetite in the suspension but also the structure of the core–shell itself. The obtained data open up the prospects for dual-mode T1/T2 magnetic contrast formation, as well as provides the basis for future investigations in this direction. Full article
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Open AccessArticle
Adsorption Properties of Ce5(BDC)7.5(DMF)4 MOF
Inorganics 2020, 8(2), 9; https://doi.org/10.3390/inorganics8020009 - 26 Jan 2020
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Abstract
In this article we report on the spectroscopic and adsorptive studies done on Ce(III)-based MOF possessing, upon desolvation, open metal sites, and a discrete surface area. The Ce-based MOF was synthesized from terephthalic acid linker (H2BDC) and Ce3+ cations by [...] Read more.
In this article we report on the spectroscopic and adsorptive studies done on Ce(III)-based MOF possessing, upon desolvation, open metal sites, and a discrete surface area. The Ce-based MOF was synthesized from terephthalic acid linker (H2BDC) and Ce3+ cations by the classical solvothermal method. Preliminary powder X-ray diffraction analysis showed that the obtained materials corresponded to the ones reported by other authors. Spectroscopic techniques, such as XAS and in situ FTIR with probe molecules were used. In situ FTIR spectroscopy confirmed the successful removal of DMF molecules within the pore system at temperatures above 250 °C. Moreover, the use of CO as a probe molecule evidenced the presence of a Ce3+ open metal sites. Detailed volumetric and calorimetric CO2 adsorption studies are also reported. Full article
(This article belongs to the Special Issue Functional Coordination Polymers and Metal–Organic Frameworks)
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Open AccessReview
Evaluating Ligand Modifications of the Titanocene and Auranofin Moieties for the Development of More Potent Anticancer Drugs
Inorganics 2020, 8(2), 10; https://doi.org/10.3390/inorganics8020010 - 26 Jan 2020
Viewed by 377
Abstract
Over time platinum-based anticancer drugs have dominated the market, but their side effects significantly impact the quality of life of patients. Alternative treatments are being developed all over the world. The titanocene and auranofin families of compounds, discovered through an empirical search for [...] Read more.
Over time platinum-based anticancer drugs have dominated the market, but their side effects significantly impact the quality of life of patients. Alternative treatments are being developed all over the world. The titanocene and auranofin families of compounds, discovered through an empirical search for other metal-based therapeutics, hold tremendous promise to improve the outcomes of cancer treatment. Herein we present a historical perspective of these compounds and review current efforts focused on the evolution of their ligands to improve their physiological solution stability, cancer selectivity, and antiproliferative performance, guided by a clear understanding of the coordination chemistry and aqueous speciation of the metal ions, of the cytotoxic mechanism of action of the compounds, and the external factors that limit their therapeutic potential. Newer members of these families of compounds and their combination in novel bimetallic complexes are the result of years of scientific research. We believe that this review can have a positive impact in the development and understanding of the metal-based drugs of gold, titanium, and beyond. Full article
(This article belongs to the Special Issue Novel Ligand Design in Coordination Compounds)
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Open AccessArticle
Bi2O3-Modified Ceramics Based on BaTiO3 Powder Synthesized in Water Vapor
Inorganics 2020, 8(2), 8; https://doi.org/10.3390/inorganics8020008 - 23 Jan 2020
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Abstract
Bi2O3 was investigated in the role of a modifier for BaTiO3 powder synthesized in a water vapor atmosphere at 200 °C and 1.55 MPa. Modification was aimed at increasing the sinterability of the powder as well as improving the [...] Read more.
Bi2O3 was investigated in the role of a modifier for BaTiO3 powder synthesized in a water vapor atmosphere at 200 °C and 1.55 MPa. Modification was aimed at increasing the sinterability of the powder as well as improving the structural and dielectric properties of the obtained ceramics. The morphology and phase contents of the synthesized BaTiO3 powder were controlled by the methods of SEM and XRD. Properties of pure and Bi-doped BaTiO3 ceramics were comprehensively studied by XRD, SEM, dielectric spectroscopy, and standard approaches for density and mechanical strength determination. Doping with Bi2O3 favored BaTiO3 ceramic densification and strengthening. The room-temperature dielectric constant and the loss tangent of Bi-doped BaTiO3 were shown to stabilize within the frequency range of 20 Hz to 2 MHz compared to non-doped material. The drop of dielectric constant between room temperature and Curie point was significantly reduced after Bi2O3 addition to BaTiO3. Bi2O3 appeared to be an effective modifier for BaTiO3 ceramics produced from non-stoichiometric powder synthesized in water vapor. Full article
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