Author Archive

Best Inorganic Chemistry Frontiers Covers of 2021

We are delighted to announce the Best Inorganic Chemistry Frontiers Covers of 2021!

Read below the scientific papers.

A red-light-chargeable near infrared MgGeO3:Mn2+,Yb3+ persistent phosphor for bioimaging and optical information storage applications

Inorg. Chem. Front., 2021,8, 5149-5157
https://doi.org/10.1039/D1QI01158H

Issue 24 Volume 8 Outside Front Cover

Binuclear metal complexes with a novel hexadentate imidazole derivative for the cleavage of phosphate diesters and biomolecules: distinguishable mechanisms

Inorg. Chem. Front., 2021,8, 2684-2696
https://doi.org/10.1039/D1QI00108F

Issue 11 Volume 8 Inside Front Cover

Designing lanthanide coordination nanoframeworks as X-ray responsive radiosensitizers for efficient cancer therapy

Inorg. Chem. Front., 2021,8, 3433-3439
https://doi.org/10.1039/D1QI00442E

Issue 14 Volume 8 Inside Front Cover

Congratulations to the winners of Best Inorganic Chemistry Frontiers Covers of 2021!

We expressed our sincere appreciation for all the support and contributions from our authors, reviewers, and readers in the past 2021.

Looking forward to receiving your high-quality work in 2022.

Happy Chinese New Year!

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A highly active and E-selective Co catalyst for transfer-semihydrogenation of alkynes

The efficient semihydrogenation of internal alkynes to selectively produce either E– or Z-alkenes is one of the main challenges in homogeneous catalysis. Numerous systems were reported in the past, however, such reactions typically require either the use of gaseous hydrogen at high pressure, noble metal catalysts, or rather high catalyst loading at long reaction times, the latter resulting in alkene isomerisation or overreduction to produce alkanes. Amine boranes such as ammonia borane (H3B·NH3) are known to be well-suited for transfer hydrogenation reactions, providing stoichiometric amounts of H2 either by dehydrogenation (i.e. H2 production), followed by hydrogenation, or by stepwise hydride and proton transfer to an organic substrate. Homogeneous precatalysts based on the Co(II) oxidation state have been reported in the past, however, mechanistic insights into such systems were rather limited to date.

Recently, the groups of Jiao and Beweries at LIKAT Rostock have demonstrated that PNN(H) Co(II) complexes serve as very efficient precatalysts for the selective formation of E-alkenes at very mild conditions, suing MeOH and H3B·NH3 as the hydrogen source. This reaction is suggested to take place exclusively via the Co(II) oxidation state, which was corroborated though a combination of control experiments, EPR spectroscopy, and DFT analysis. Key feature for the high activity of this Co system is the proton responsive PNN(H) ligand, possessing a pyrazole fragment that undergoes deprotonation during catalyst activation. The results presented herein could be relevant for the design of other proton responsive ligands for non-noble metal free transfer hydrogenation reactions.

Corresponding author:

PD Dr. Torsten Beweries (Leibniz Institute for Catalysis, Rostock)

Torsten Beweries is head of the department Coordination Chemistry and Catalysis at the Leibniz Institute for Catalysis in Rostock (Germany). He received his PhD in Chemistry at LIKAT in 2008, working on the coordination chemistry of hafnocenes. He then moved to the University of York (UK) for a postdoctoral stay with Prof. Robin N. Perutz in 2009, working on late transition metal complexes for halogen bonding. He returned to LIKAT in 2010, where he established an independent research group. The research field of PD Dr. Torsten Beweries is organometallic chemistry and homogeneous catalysis with focus on new pincer ligands and complexes, main group polymers, and unusual metalacyclic systems. He is the author of 91 articles indexed by SCI and cited more than 1600 times with an index H = 23.

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Unprecedented Organometallic Rare Earth Complexes Containing a Large, Flexible Salophen Ligand

Organometallic chemistry of the rare earth and actinide elements has been a driving force for the development of novel functional materials and catalysts for decades, giving rise to impressive advances in the fields of single-molecule magnetism, luminescence, and polymer sciences. Excitingly, organometallic approaches have always been on the forefront of fundamental chemistry and allowed breakthroughs in the field, not only with the lighter metals but also some of the heaviest actinide candidates. The inherent reactivity of organometallic compounds owing to the apparent labile and reactive metal-carbon bonds renders the isolation and characterization of such molecules exceptionally challenging, especially when aiming at polymetallic rare earth complexes, and is therefore underdeveloped to this date. Consequently, the exploration of suitable synthetic routes to access bridged organometallic metallocene complexes is of great interest for the rare earth and more general inorganic chemistry community.  

Recently, the group of Selvan Demir at Michigan State University has demonstrated that two rare earth metallocene fragments are able to capture the tetradentate salophen ligand, giving rise to the first series of dinuclear salophen-bridged rare earth metallocene complexes with the metals yttrium, gadolinium and dysprosium, Figure 1. These molecules also constitute the first metallocene salophen complexes for any metal ion. Remarkably, the flexibility of the salophen bridge allows the binding pockets to face outwards upon complexation to the metal ions which is a rare, yet intriguing, coordination mode. Consequently, a substantial separation of the metal centers (7.858 – 7.895 Å) occurs leading to weak electronic or magnetic communication between the rare earths. Since the magnitude of magnetic exchange coupling between paramagnetic metal centers and/or organic radical is crucial for the generation of better-performing multinuclear single-molecule magnets,  the magnetic communication in these salophen complexes was explored. 

Figure 1. (A) Schematic view of the salophen-bridged rare earth metallocene complexes. (B) Structure of the rare earth molecules as obtained through single-crystal X-ray diffraction. (C) Arial view of the calculated highest occupied molecular orbital.

The dynamic magnetic properties of the paramagnetic dysprosium complex revealed characteristics of single-molecule magnet behavior, while the static magnetic susceptibility data collected for the paramagnetic gadolinium complex allowed quantification of the magnetic exchange, Figure 2. The determined coupling is of similar magnitude to other polynuclear rare earth complexes containing diamagnetic bridging ligands. DFT calculations on the diamagnetic yttrium conger revealed negligible orbital overlap between the metal center and the salophen ligand in the highest occupied molecular orbital, Figure 1, which may account for the weak magnetic coupling in the paramagnetic variants.

Notably, the lowest unoccupied molecular orbital might be able to be populated with an unpaired electron. Radicals, innate to unpaired electrons, promote strong exchange coupling when placed between rare earth magnetic moments and are, thus, extremely sought-after in the fields of single-molecule magnetism and spintronics. Excitingly, cyclic voltammetry measurements of the salophen

Figure 2. (A) Electron uptake of the dysprosium molecule via electrochemistry. (B) Single-molecule magnet features of the dysprosium complex.

complexes revealed a quasi-reversible feature attributed to the reduction and oxidation of the salophen bridge on the timescale of the electrochemical experiment, Figure 2. This paves the way for chemical reductions of these molecules to generate coveted metal-radical compounds in the future. Noteworthy, chemical functionalization of the salophen backbone may readily be attained which serves as an additional path to augment magnetic coupling and as such highlights the enormous potential of the salophen ligand in organometallic chemistry.

Selvan Demir is an Assistant Professor of Chemistry at Michigan State University. She earned her Dr. rer. Nat. at the University of Cologne researching on scandium solid state chemistry with Prof. Gerd Meyer and scandium organometallic chemistry with Prof. William J. Evans at the University of California, Irvine. Subsequently, she focused on lanthanide-based single-molecule magnets and porous aromatic frameworks with Prof. Jeffrey R. Long at the University of California, Berkeley, and worked on transuranics with Dr. David K. Shuh at the Lawrence Berkeley National Laboratory. Afterwards, she took up a junior professorship of inorganic chemistry at the University of Göttingen. Since 2019, she researches with her group at Michigan State University, on various areas surrounding the chemistry of the rare earth elements and actinides. The research group focuses mainly on organometallic chemistry, small molecule activation, single-molecule magnetism, and lanthanide/actinide separations. A particular emphasis is also on heavy p-block element and uranium chemistry.

 

 

 

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Enantioselective chiral sorption of 1-phenylethanol by homochiral 1D coordination polymers

Amongst the myriad uses of metal-organic frameworks (MOFs) and coordination polymers, separation of complex mixtures, either gaseous or in solution, is one of the most promising applications due to the regular array of well-defined pores. Integration of specific points of interaction that are complementary to the targeted guest species can provide highly selective materials. In particular, precise control of the 3D space within pores may provide a mechanism for enantioselective discrimination for which the exact spatial arrangement of multiple sites of interaction is paramount.

The vast majority of research in this area is driven by 3D metal-organic frameworks, often those possessing permanent porosity. However, for solution-based applications this need not be a prerequisite and materials comprising lower dimensionality coordination polymers may be just as effective is they contain solvent-filled pores.

Recently the group of David Turner at Monash University has shown that a 1D coordination polymer, with pores formed by alignment of loops within the 1D chain, is capable of sorbing 1-phenylethanol with a good degree of enantioselectivity (Figure 1). A closely related material shows no such selectivity, and a reduced uptake capacity, highlighting the importance of structural match between the host framework and the analyte. Ground samples showed higher uptake than unground crystals for the active material, suggesting an influence of surface area or ease of permeation into the solid. Both static (soaking) and dynamic (“micro-LC”) methods showed enhanced uptake of one enantiomer from a racemic solution of 1-phenylethanol, albeit not perfect separation. The group was also able to crystallographically determine the binding site of the preferred enantiomer (Figure 2), showing an array of hydrogen bonding interactions that lie behind the enhanced uptake of one enantiomer over the other.

These results highlight the potential of non-3D coordination polymers in chemical separations and demonstrate the array of host-guest interactions that are required for separations of very similar compounds.

Figure 1. The chiral material contains guest-filled pores resulting from the alignment of loops within the 1D coordination polymer.

Figure 2. The preferred enantiomer of the guest is found crystallographically within the binding pocket, highlighting the array of interactions that hold it in place and provide the enantioselectivity.

Corresponding Author:

David Turner is a Senior Lecturer in the School of Chemistry at Monash University, Australia. After receiving his PhD in 2004 from King’s College, London, he held a number of fellowships at Monash University prior to joining as a Faculty member. Research in the Turner group revolves around metallosupramolecular assemblies, exploring both coordination polymers/MOFs and coordination cages with a particular emphasis on chirality. Dr Turner has published over 130 papers, in addition to two books, attracting almost 5000 citations and an h-index of 32.

https://research.monash.edu/en/persons/david-turner

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A New 2D Layered Aluminophosphate |Hada|6[Al6(PO4)8](H2O)11 Supported Highly Uniform Ag Nanoparticles for 4-Nitrophenol Reduction

Since Wilson and Flanigen found the first microporous aluminophosphate (AlPO) in 1982, the synthesis of AlPO materials with novel frameworks and study their potential properties, such as adsorption, catalysis, and separation, has attracted intense interest of researchers. As the main family of AlPO based materials, 2D layered materials show a rich variety of structures and compositions depending on the diverse coordination and connection modes of Al and P atoms. In recent years, 2D materials, possessing highly exposed surfaces and diverse structures, have become a dramatic category of supports. However, 2D molecular sieves are serving as catalyst supports are very few.

Recently, Prof. Jiuxing Jiang at Sun Yat-sen University and Dr. Jiang-Zhen Qiu of Zhongkai University of Agriculture and Engineering synthesized a new 2D layered aluminophosphate compound by adopting rigid and bulky template of 3,5,N,N-tetramethyladamantane-1-amine (ada) through hydrothermal conditions, which is named the Zhongkai University of Agriculture and Engineering NO.1 (ZHKU-1), with the composition |Hada|6[Al6(PO4)8](H2O)11. The structure of ZHKU-1 was constructed from the alternate connection of AlO4 and triply bridged PO4 tetrahedra ([O=PO3]3-) to form a 4, 6, 12-net (Figure 1). The inorganic sheets are linked and separated by protonated amine and H2O molecules by extensive H-bonds, giving a new 2D structure with an interlayer space of 19.6 Å.

Figure 1 Crystal structure figures of ZHKU-1

ZHKU-1, as a 2D material with a more exposed surface, could be adapted for encapsulating metal nanoparticles (NPs). Ag species are immobilized on the supports of ZHKU-1 by UV reduction and deposition, forming the catalyst of Ag@ZHKU-1 with high loading of 4.9 wt%. The HRTEM images reveal the highly uniform Ag clusters with visually observed sizes of 1.9 nm (Figure 2).

Figure 2 The characterizations of Ag@ZHKU-1 for HRTEM and corresponding mapping images

Since 4-nitrophenol (4-NP) is a notorious industrial pollutant, Ag@ZHKU-1 is applied to the model reaction for 4-NP reduction. The catalytic results show that the reduction reaction of 4-NP into 4-aminophenol could be completely performed within 75 s in NaBH4 solution (Figure 3). Moreover, the catalytic activity was almost the same, with almost 99% conversion after eight cycles. The remarkable catalytic activity and recyclability of Ag@ZHKU-1can be attributed to the high dispensability of Ag nanoclusters confined to the 2D support, which provides more accessible Ag active sites to 4-NP.

Figure 3 Catalytic activity and recycling tests for 4-nitrophenol reduction are over Ag@ZHKU-1 catalyst

This work reports a new 2D layered aluminophosphate compound, which expends the aluminophosphates family. Furthermore, the confinement of metal Ag on this new layer structure through photodeposition gives rise to a small size (~1.9 nm) of AgNPs with homogeneous dispersion. The catalyst of Ag@ZHKU-1 shows excellent catalytic activity and high conversion for 4-nitrophenol reduction. This work is significant for designing 2D aluminophosphate materials to confine small metal nanoparticles for catalytic application.

Prof: Jiuxing Jiang (ORCID: 0000-0001-9664-3235). I received Ph.D degree from Jilin University in 2010. Afterward, I spent 5 years for a Post Doc. stay in Instituto Technologia Quimica (UPV-CSIC) in Valencia Spain supervised by Prof: Avelino Corma. After independent work in Sun Yat-sen University (2015-now), I keep my interesting on the topologically new zeolite synthesis (four three letter code, IRR, -IRY, -IFU, -SYT were granted by Structure Committee of Internation Zeolite Association), and zeolite based heterogeneous catalysis, such as: acid-base catalysis, catalytic ammonium synthesis, NH3-SCR for deNOx reaction, porous materials for energy storage, etc. I have published more than 20 high-impact journal articles, such as Science, Angew. Chem. Int, Ed, Chem.Sci, Chem. Mater. etc. Among them, the work on the synthesis and structure of zeolite ITQ-43 was published in Science, 2011, 333, 1131-1134 and was selected as annually breakthrough of 2011 by Science. Currently serve as a member of Zeolite Committee of Chinese Chemical Society and youth editorial member of Journal of Chemical Research in Chinese University.

Jiang-Zhen Qiu: She received her Ph.D. degree in 2019 from Sun Yat-sen University with M.S. Supervisor Prof. Ming-Liang Tong and Ph.D. Supervisor Prof. Jiuxing Jiang. In 2020, she was introduced to Chemical Engineering of Zhongkai University of Agriculture and Engineering as an “Excellent Doctor”. Her interested research fields include synthesizing new topological structures of zeolite and exploring multifunctional materials with novel functionalities such as light, conductivity, magnetism, or catalysis. Currently, she and her collaborators published 10 papers in related fields, such as Chem. Mater., Chem. Sci., Inorg. Chem. Front., Chem. Commun., Chem. Eur. J.

 

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Optimizing the relaxivity at high fields: systematic variation of the rotational dynamics in polynuclear Gd-complexes based on the AAZTA ligand

Magnetic Resonance Imaging (MRI) is one of the most important and prominent techniques in in clinical diagnostic medicine, in preclinical studies and in biomedical research. As well as many other imaging modalities, MRI also makes extensive use of contrast agents (CAs) that allow achieving remarkable improvements in medical diagnosis in terms of higher specificity, better tissue characterization and functional information. For the vast majority, the clinically used CAs are coordination complexes in which a GdIII ion is encapsulated within octadentate chelators based on polyaminocarboxylate anions and has a directly bound water molecule. Their use is widespread and is estimated to correspond to approximately 40 million administrations per year of GdIII chelates worldwide.

Their effectiveness (relaxivity; the increase in the relaxation rate R1 of the water protons normalized to a 1 mM concentration of the paramagnetic ion) at the magnetic fields of clinical interest is dominated and limited by the fast rotational dynamics and tends to decrease with the increased magnetic field. However, the current trend in MRI development is towards higher magnetic field strengths and most scanners operate at 1.5 or 3 T, while there is increasing use of those at 7 T. Therefore, a different approach for the relaxivity enhancement of Gd-based CAs becomes necessary for the modern high-field systems.

Recently, the group of Mauro Botta and colleagues from the University of Eastern Piedmont in Alessandria (Italy) investigated the optimization of the efficacy of Gd-based CAs, between 1 and 7 T, by systematically modulating the rotational dynamics through the synthesis of polynuclear systems containing between two and eight GdIII chelates (Figure 1).

Figure 1. [Gd(AAZTA)(H2O)2] and polynuclear Gd2-6L2-L6 complexes 

The [Gd(AAZTA)(H2O)2] chelate was used as a building block due to its remarkable properties: a) ease and high-yield synthesis, presence of two inner sphere water molecules in fast exchange with the bulk; b) high thermodynamic stability; c) kinetic inertness in the presence of physiological concentrations of CuII and ZnII higher than that of the clinical agent [Gd(DTPA)]2-; d) negligible tendency to formation of ternary complexes with endogenous anions. The study demonstrates that the strategy for relaxation enhancement varies with the strength of the magnetic field used.

Up to 3 T, efficacy is limited by molecular rotation and therefore increases proportionally with the increase in molecular size. Between 3 and 7 T, the issue of local flexibility or anisotropic rotation, evaluated with NMR techniques and computational models, becomes more and more relevant and medium-sized rigid systems (tri- or tetranuclear) provide the best results. At ultra-high fields (> 7 T), small and compact mono- or binuclear complexes are most effective (Figure 2).

 

Figure 2. Upper: T1-weighted phantom MR-images at 3 and 7 T on selected polynuclear complexes highlighting the effective signal enhancement of the new MRI probes at clinically relevant magnetic field strengths in comparison to the commercial MRI agent ProHance®. Lower: Signal enhancement (298 K) of Gd3L3, Gd4L4 and Gd6L6 compared to Prohance at 1, 3 and 7 T.

The results of this study allow identifying the most effective strategy for optimizing the CAs, each suited to a well-defined range of applied magnetic field strength.

 

Mauro Botta is full professor of Inorganic Chemistry in the Department of Sciences and Technological Innovation at the University of Eastern Piedmont (Italy). He received the “Laurea” cum laude in Chemistry at the University of Turin in 1985. His scientific interests have focused on the use of NMR techniques for the characterization of inorganic systems, starting from organometallic clusters and then moving on the complexes of the f-elements. Recipient of the “Raffaello Nasini” gold medal award for Inorganic Chemistry of the Italian Chemical Society and of the “GIDRM gold medal for magnetic resonance”. He has published over 280 papers (index H = 63; citation: 12800) and several book chapters on these topics and filed 5 patents.

 

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Tailoring MOFs and COFs for artificial photosynthesis

Over a couple of decades, solar-to-chemical energy conversion—so called “artificial photosynthesis”—has been regarded as a holy grail that enables a carbon-neutral production and use of fuels and chemicals. In principle, various kinds of chemicals can be produced using semiconducting materials or photosensitizers with a proper bandgap and band-edge positions for target redox reactions. Despite conceptual simplicity and elegance, the realization of artificial photosynthesis is a highly challenging task. Its realization requires not only the development of various functional components such as light-harvesting, charge separation/ transporting, and catalytically active materials, but also their rational and precise assembly into an integrated device. Conventional solar-to-chemical conversion devices are mainly composed of inorganic materials and suffer from low efficiency and poor stability issues. These issues originate from the intrinsic problems of conventional inorganic materials, such as low absorption coefficient, high recombination of charge carriers, low electrical conductivity, poor catalytic activity. Furthermore, they have limited flexibility in engineering their physicochemical properties compared to organic materials.

Figure 1. Solar-to-chemical energy conversion by (a) powder-type photocatalysts and (b) photoelectrochemical (PEC) cells.

On the other hand, porous reticular materials such as metal organic frameworks (MOFs) and covalent organic frameworks (COFs) are recently drawing huge attention from researchers as promising functional materials. The structure and properties of MOFs and COFs can be tailored by employing various metal nodes and/or organic linkers, introducing additional functional groups, and employing different symmetry combinations, even with similar building blocks. These have led to the boom of studies about their design and synthesis for various applications such as catalysis, separation, sensing, etc.

Figure 2. Schematic illustration of the structure and properties of MOFs and COFs.

Recently, Prof. Jungki Ryu, Hyunwoo Kim, and Nayeong Kim at Ulsan National Institute of Science and Technology (UNIST) reported a comprehensive review paper especially about the application of MOFs and COFs in solar-to-chemical energy conversion. Porous structure and readily tunable physicochemical properties of MOFs and COFs can be highly beneficial to improve light absorption, charge separation, and access to reactants. As a result, they have been employed as diverse functional components for various target photo-reactions, such as hydrogen evolution reaction, oxygen evolution reaction, and CO2 reduction reaction. To help readers readily understand recent progress and challenges in the application of MOFs and COFs for solar-to-chemical energy conversion, they have organized more than 200 recent studies on the basis of their function and target reaction in chronological order. In addition, they reviewed the application of MOFs and COFs parallelly to provide insights for researchers. For example, one can find similar strategies employed for their application and also expect future research directions for relatively new COFs based on the research progress for MOFs. Lastly, they pointed out that further studies are required especially for the growth of MOF and COF thin films to make more significant research progress in the application of MOFs and COFs for artificial photosynthesis.

Jungki Ryu is an associate professor in the UNIST School of Energy and Chemical Engineering. He received his bachelor’s and PhD degrees in Materials Science and Engineering from Yonsei University in 2006 and Korea Advanced Institute of Science and Technology (KAIST) in 2011, respectively. Before joining UNIST in 2014, he had worked as a postdoctoral associate at the Massachusetts Institute of Technology for 3 years. He is currently interested in designing innovative electrochemical and photoelectrochemical devices inspired by nature for a sustainable future. Currently, he is the author of more than 50 articles indexed by SCI(E) and cited over 3,000 times with an H-index of 28.

Homepage: https://www.bioinspired-materials.com/

Twitter account: @bfml_unist, @jungki1981

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