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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Inorganic Chemistry Frontiers 2020 Best Paper Prizes

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Inorganic Chemistry Frontiers 2020 Best Paper Prizes

From this year onwards, we would like to introduce the Inorganic Chemistry Frontiers Best Paper prizes which recognize the most outstanding papers published in the journal. After a selection process involving the Associate Editors, Editorial and Advisory Board members, we have chosen to award not only a best paper but also a runner-up and a best review.

Best Paper 

High performance single-molecule magnets, Orbach or Raman relaxation suppression?

Alejandro Castro-Alvarez, Yolimar Gil, Leonel Llanos and Daniel Aravena

Inorg. Chem. Front., 2020,7, 2478-2486
https://doi.org/10.1039/D0QI00487A

 

Corresponding author:

Daniel Aravena is Associate Professor at University of Santiago of Chile. He was born in 1985 in Linares, Chile and received his undergraduate degree in Chemistry at University of Chile in 2009. He obtained his M. Sc. (2011) and Ph. D. (2013) from University of Barcelona (Spain) under the direction of Prof. Eliseo Ruiz. After a postdoctoral stage at Max-Planck Institute for Chemical Energy Conversion (Mülheim an der Ruhr, Germany) with Prof. Frank Neese and Prof. Mihail Atanasov, he joined University of Santiago de Chile in 2015. D.A. research focus in the calculation of spectroscopic and magnetic properties of diverse inorganic systems, such as Single Molecule Magnets, guest responsive Metal-Organic Frameworks, molecular devices, photomagnetic and spin-crossover compounds.

Currently, he is involved in the development of new models to simulate magnetic relaxation and the ab initio description of spin-orbit effects for excited state dynamics of inorganic complexes.

ORCID: https://orcid.org/0000-0003-3140-4852

 

Best Paper Runner-up

High-efficiency photocatalytic water splitting by a N-doped porous g-C3N4 nanosheet polymer photocatalyst derived from urea and N,N-dimethylformamide

Feng Guo, Lijing Wang, Haoran Sun, Mingyang Li and Weilong Shi

Inorg. Chem. Front., 2020,7, 1770-1779
https://doi.org/10.1039/D0QI00117A

 

Corresponding author:

Weilong Shi got his PhD from Huazhong University of Science and Technology in China, did his Postdoctoral at Zhengzhou University and is a Lecturer at Jiangsu University of Science and Technology, a Member of Jiangsu Composites Society. His research interests include design, construction and modification of carbon-based (carbon dots, carbon nitride) nano-semiconductor composite photocatalytic materials, as well as photocatalytic degradation of organic pollutants in aquatic environment and water splitting into hydrogen under visible light. So far, a total of 42 papers were published by SCI first author or correspondence author, 13 ESI highly cited papers, 6 ESI hot papers, 1 Running Up Best Paper in Inorganic Chemistry Frontiers of 2020, H-index 29. He is now in charge of the National Natural Science Foundation of China, Jiangsu Province “mass entrepreneurship and innovation doctor” talent project, Henan Province postdoctoral research project and so on.

ORCID: https://orcid.org/0000-0002-3555-4543

 

Best Review

Recent advances in MOF-based photocatalysis: environmental remediation under visible light

Qi Wang, Qiaoyuan Gao, Abdullah M. Al-Enizi, Ayman Nafady and Shengqian Ma

Inorg. Chem. Front., 2020,7, 300-339
https://doi.org/10.1039/C9QI01120J

 

Corresponding authors:

Qi Wang obtained her Ph.D. degree in 2009 under the supervision of Prof. Jincai Zhao from the Institute of Chemistry, Chinese Academy of Science. She is currently a professor in the School of Environmental Science and Engineering at Zhejiang Gongshang University. She worked as a visiting scholar in the University of South Florida in 2019. Her research interests focus on photocatalysis, photoelectrocatalysis and environmental catalysis.

ORCID: https://orcid.org/0000-0002-1941-5287

Shengqian Ma obtained his B.S. degree from Jilin University, China in 2003, and graduated from Miami University (Ohio) with a Ph.D. degree in 2008. After finishing two-year Director’s Postdoctoral Fellowship at Argonne National Laboratory, he joined the Department of Chemistry at the University of South Florida (USF) as an Assistant Professor in August 2010. He was promoted to an Associate Professor with early tenure in 2015 and to a Full Professor in 2018. His current research interest focuses on the development of functional porous materials including metal–organic frameworks (MOFs), covalent organic frameworks (COFs), and porous organic polymers (POPs) for energy, biology, and environment-related applications.

ORCID: https://orcid.org/0000-0002-1897-7069

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Copper catalysts for photo- and electro-catalytic hydrogen production

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The development of carbon neutral, or better still carbon zero (H2) future fuels with production driven by green energy (renewables, such as solar, wind or wave generated energy) is an urgent necessity. To be cost competitive, green production of hydrogen requires long lived, high activity catalysts made from inexpensive, earth abundant metal ions.

 

Over the last few decades, various earth-abundant molecular cobalt, iron and nickel catalysts have exhibited activity for HER under photo- and electro-catalytic conditions. Prior to this study only 15 molecular copper complexes had been tested as catalysts for the H2 evolving reaction (HER) under either photo or electro-catalytic conditions.

 

Recently, Abdullah Abudayyeh in the group of Sally Brooker at the University of Otago and collaborators Garry Hanan and Olivier Scott at the University of Montreal reported the results of testing three copper(II) complexes – with a range of geometries, from square planar 1 to square pyramidal 2 and trigonal bipyramidal 3 (Figure 1) – as catalysts for HER under both photo- and electro-catalytic conditions.

Figure 1.  Right: Square planar 1 (pink), square pyramidal 2 (red) and trigonal bipyramidal 3 (green) copper(II) complexes. Left: HER electrocatalysis data shows that only square planar([CuIILEt]BF4 is, or forms, a good electrocatalyst for HER, and that it is still active after 6 hours. Black line = control.

The research team showed that under photocatalytic conditions the 3 copper complexes have modest turnover numbers (TON=460-620), but the control, using Cu(BF4)2, had a higher TON (740), and the blank (no copper) also had significant activity (TONequiv=290). So this is a cautionary tale: whilst these complexes initially appeared to be promising catalysts for photocatalytic HER, running the control and blank – studies often not reported – shows otherwise.

 

Hence the team changed focus and tested all three copper complexes as HER electrocatalysts in MeCN/acetic acid solution (Figure 1). The macrocyclic square planar complex, [CuIILEt]BF4 (1) (Figure 1, pink), is shown to be, or to form, an effective and stable electrocatalyst for HER in MeCN with acetic acid as the proton source (TON = 12.5 over six hours at -1.6 V vs 0.01 M AgNO3/Ag; at 100 mVs-1, Ecat/2=-1.64 V so overpotential necessary for catalysis=0.23 V), whilst the other two complexes, 2 and 3, had activities similar that of the control.

 

Preliminary ‘rinse and repeat’ and ‘drop of Hg’ tests – for the formation of catalytically active heterogeneous deposit on the glassy carbon working electrode or nanoparticles, respectively – are consistent with homogeneous catalysis by 1. But the authors note that it is distinctly possible that these initial test results are ‘false negatives’ (they recommend reading the excellent review by J. Dempsey on this topic), as the CVs show a stripping process consistent with the deposition of metallic copper on the electrode, so it remains possible that a heterogeneous catalytically active species forms, but is not seen as it is unstable in air or falls off the electrode during the rinse step.

 

Future studies on 1 aim to determine whether the catalytically active species is homogeneous or heterogeneous, but regardless of the outcome, the observed HER performance is promising and long lived.

 

Left to right: Abdullah, Olivier, Humphrey, Garry and Sally

 

 

Abdullah M. Abudayyeh completed his BSc in Chemistry in Mu’tah University, Jordan. He received his MSc in organic chemistry from the University of Jordan, working on Schiff base amidine systems. On successful completion of his MSc he worked as a chemistry teacher at the United Nations secondary school in Jordan for five years and then in a couple of other schools in Jordan, before moving to the University of Bradford, UK, in 2015. There he pursued his second MSc degree, developing thin films of Zr-based metal-organic frameworks (MOFs) on a conductive FTO substrate, which he completed with distinction. He then moved to Dunedin, New Zealand, to take up a University of Otago PhD scholarship in Professor Sally Brooker’s research group, working on coordination complexes as catalysts for the hydrogen evolution reaction (HER).

 

Olivier Schott graduated with the Bachelor of Chemistry and two Masters: Supramolecular and Molecular Chemistry and Chemical Physics and Materials at Université de Strasbourg (France). His first steps in research with Professor Julve and Professor Kurmoo were related to the synthesis of supramolecular inorganic architectures for the study of magnetic exchange interactions between transition metals. During an international student exchange, he joined the Green Energy Group of Université de Montreal (Canada) under the direction of Professor Garry S. Hanan and became a PhD candidate. In the domain of molecular artificial photosynthesis, he is investigating various poly-metallic N-rich supramolecular systems for the photocatalysis of solar fuels. In 2019, he got a PhD fellowship: Fonds Québécois de la Recherche sur la Nature et les Technologies (FRQNT) and received three times the J. Armand Bombardier Excellence Award.

 

 

Humphrey L. C. Feltham obtained his MSc and PhD (both with distinction) in Chemistry from the University of Otago under the supervision of Professor Sally Brooker, working on tetrametallic 3d-4f macrocyclic Single Molecule Magnets. From 2012-2018 he was a research associate in Professor Brooker’s team, working on projects ranging from the tuning of spin crossover complexes to the covalent immobilisation of magnetically and catalytically interesting complexes onto Au nanoparticles and PEDOT films. In 2019, he joined the chemistry team at Ligar Limited Partnership (www.ligar.nz), developing novel polymers for the removal or recovery of valuable or unwanted molecules from a variety of solutions. eg. removing smoke taints from wine, recovering bioactive molecules from plant extracts, remediating toxins from drinking water, and modifying flavour of beverages.

 

Professor Garry S. Hanan received his Ph. D. degree from l’Université Louis Pasteur in Strasbourg, France, in 1995.  After working in at the Max-Plank Institut fuer Kohlenforschung (1996-1997) and l’Università di Messina (1997-1998) as a post-doctoral Fellow, he started his academic career at the University of Waterloo in 1998 (Assistant Professor). In 2002 he moved to the Université de Montréal (as Associate Professor) where he is currently a Full Professor.  He was recently awarded an Accelerator Grant and is currently the leader of a Strategic Project, both funded by the Natural Sciences and Engineering Research Council of Canada (NSERC).  His current research interests include metal-assembled complexes, inorganic photochemistry, and photocatalytic hydrogen production.

 

Professor Sally Brooker (MNZM, FRSNZ, FNZIC, FRSC) studied at the University of Canterbury, New Zealand [BSc(Hons) first class; PhD with Professor Vickie McKee]. After postdoctoral research at Georg-August-Universität Göttingen, Germany, with Professor George M. Sheldrick, she took up a Lectureship at the University of Otago where she is now a full Professor and Sesquicentennial Distinguished Chair. She has been the recipient of numerous awards, most recently including a 2017 Queens Birthday Honour for services to science (MNZM), the 2017 Hector Medal (RSNZ) and 2017 Burrows Award (RACI). Her research interests concern the design, synthesis and full characterisation of, primarily paramagnetic, di- and poly-metallic complexes of transition metal and lanthanide ions with polydentate acyclic and macrocyclic ligands, as these have interesting redox, magnetic, catalytic and photophysical properties (otago.ac.nz/brooker).

 

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Investigation on Nanostructured Cu Based Electrocatalysts for Improvising Water Splitting: A Review

By .

The effective use of earth abundant electrocatalyst copper in splitting of water as nanostructures with different combinations is central in replacing the noble metals for the industrialization of hydrogen generation. Being the carbonaceous fuels as front line suppliers of energy, they adversely lead to affect the environment with the greenhouse gases emission. Considering the electrocatalytic way of splitting water, it is one of the finest ways of producing pure hydrogen with fast rate and assisted with no other undesired by-products and hence researchers across the world focus maximum attention to make it commercially applicable.

To replace the noble metals, transition metals based catalysts are promising and the importance of Cu based nanostructures as effective electrocatalysts for both oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) needs greater attention. Moreover, various synthetic approaches with Cu nanostructures like mono, bi and tri metallic catalysts as oxides hydroxides, sulfides, selenides, tellurides and phosphides were studied for OER and HER in different pH conditions will give a vast analysis on Cu based catalysts towards real scale water splitting electrocatalytically.

Hence, to precise, a brief understanding on Cu-based nanostructures in electrocatalytic water splitting is highly needed to be applied with other advancements in catalysts development for the viable hydrogen generation with electrocatalytic water splitting.

Recently, Karthick. K and Subrata Kundu and co-authors have highlighted the nanostructures of Cu based oxides, hydroxides, sulfides, selenides, tellurides and phosphides as catalysts for water splitting application and the merits of which have been explored in detail as a review. The possibilities of enhancing the activity and durability with Cu based catalysts were studied and among which enhancing the activity with the formation of nanostructures, growing over 3D conducting supports, enhancing the electrical conductivity with graphene, increasing the metallic active sites by different methods like electrodeposition, adding other transition metals and also by varying the stoichiometric ratios had resulted in ensuring astonishing activity and stability.

Figure 1. Cu nanostructures as catalysts for enabling high scale OER and HER activities by studying them as oxides, LDHs, chalcogenides and phosphides.

 

Authors:

K. Karthick

CSIR – Central Electrochemical Research Institute

K. Karthick had received his B.Sc degree from Government Arts and Science College, Udumalapet, India and M.Sc degree from The American College – Madurai, India in general chemistry. He qualified UGC-JRF in December-2014 and joined under Dr. Subrata Kundu’s research Group since August-2015. He is currently working towards his Ph.D thesis mainly focused on Electrocatalytic Water splitting applications.

https://scholar.google.co.in/citations?user=RU1m2ScAAAAJ&hl=en

Dr. Subrata Kundu

CSIR – Central Electrochemical Research Institute

Dr. Subrata Kundu received his Ph.D from the Indian Institute of Technology (IIT), Kharagpur, India in early 2005. Then he moved to University of Nebraska, Lincoln, USA and later to Texas A&M University, College station, Texas, USA as a post-doc fellow (from 2005 to 2010). He is currently working as a Senior Scientist at CSIR-CECRI, Karaikudi, India. Dr. Kundu is serving as an editorial board member of several international journals including prestigious ‘Scientific Reports’ from Nature publishers since 2015. Dr. Kundu and his co-workers are working in the forefront area of Material Sciences with emphasizes on energy, environment, catalysis and electrocatalysis.

https://scholar.google.co.in/citations?user=4siGGnQAAAAJ&hl=en

https://www.cecri.res.in/Profile?empcode=40257

https://anantharaj1402.wixsite.com/dr-sk-group

 

Article information:

Investigation on Nanostructured Cu Based Electrocatalysts for Improvising Water Splitting: A Review
Karthick Kannimuthu, K. Sangeetha, S. Sam Sankar, Arun Karmakar, Ragunath Madhu and Subrata Kundu
Inorg. Chem. Front., 2020, Accepted Manuscript
https://doi.org/10.1039/D0QI01060J

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Palladium bis-pincer complexes with controlled rigidity and inter-metal distance

By .

Arylamines are an important molecular unity that is widely used in the design and creation of organic functional materials for applications such as solar cells, light emitting diodes, and electrochromic devices. Due to their electron-rich nature, these molecules can be readily oxidized into radical cations, whose persistence is essential for the performance of organic electronic devices.

The properties of arylamines and their oxidized radical cation states can be modulated by coordination with transition metals at the nitrogen site, because of the inductive effect from the metal, and the interactions between the p-orbital on the nitrogen atom and the d orbitals of the metal center.

In the past few years, the Ozerov group and collaborators at Texas A&M University demonstrated synthesis and redox properties of several bimetallic pincer complexes with arylamine backbones, where two pincer-type metal cores were connected by non-conjugated linkers or ynediyl linkers via metal-ligand bonds. Recently, in collaboration with the Fang group at Texas A&M, they reported the synthesis of bimetallic complexes where two redox sites are connected with via organic ligand-to-ligand linkers that modulate the degree of separation between redox sites (Figure 1).

Figure 1. Bimetallic bis(pincer) complexes synthesized in this work.

Cyclic voltammograms of all these complexes revealed two quasireversible oxidation waves. For 1-3, the separation of the two oxidation waves increased as the proximity between two redox sites increased. The comproportionation constants were calculated, which revealed that compounds 2, 3, and 4 belong to the Robin-Day Class III mixed valence systems, whereas compound 1 falls into the range of Class II. The largest comproportionation constant of 3.1×1011 was found in compound 3, suggesting the high stability of this radical cationic intermediate. UV-vis-NIR spectra of the radical cations of 2, 3, and 4 showed intensive absorption peaks in the NIR region, revealing the highly delocalized nature of these radical species. The Hush electron coupling integrals of these mixed valence molecules fall into the range of Class III systems, which is in a good agreement of the cyclic voltammetry analysis.

Figure 2. Cyclic voltammograms of complexes 14 (ca. 0.001 M in CH2Cl2) with [nBu4N]PF6 electrolyte (0.1 M), scan rate 100 mV/s, potentials referenced to Fc+/Fc at 0 V.

Single-crystal diffraction was performed to establish solid-state structures of compounds 3, as well as its oxidized states, to shed the light on the mechanism of its oxidation process. The geometric differences among these structures lie mainly in the changes in the bond distances associated with the central p-diaminobenzene unit, which revealed the transformation from a benzenoidal structure to a quinoidal structure (Figure 3).

Figure 3. Dominant resonance forms of compound 3 at different oxidation states.

In conclusion, the square-planar palladium center imposes a more rigid geometry on the organic ligand that leads to different degrees of the pi delocalization over the extended system. A stronger electronic communication between two redox sites was found at a closer proximity between them. Such a presence of palladium centers is important in stabilizing the mono- and bis-oxidized forms of these molecules. These bis(pincer) complexes are potential building blocks for more complicated conjugated molecules and polymers that can find applications in organic electronic devices.

Authors:

Oleg V. Ozerov

Oleg Ozerov is Emile and Marta Schweikert Professor in the Department of Chemistry at Texas A&M University.  He received his Diploma (1998) from the Higher Chemical College of the Russian Academy of Sciences and his PhD degree (2000) from the University of Kentucky where he worked with Prof. Folami T. Ladipo.  Following a postdoctoral appointment with Prof. Kenneth G. Caulton in Indiana University (2000-02), Dr. Ozerov started his independent academic career at Brandeis University, before moving to Texas A&M in 2009.  He is a recipient of the ACS Award in Pure Chemistry (2012) and of the Norman Hackerman Award in Chemical Research from the Welch Foundation (2012), and has served as an associate editor of Inorganic Chemistry Frontiers since 2013.  The Ozerov group pursues studies in molecular transition metal and main group chemistry.

https://www.chem.tamu.edu/rgroup/ozerov/index.html

 

Lei Fang

Lei Fang is an associate professor in the Department of Chemistry at Texas A&M University. He received his BS (2003) and MS (2006) degrees from Wuhan University. His PhD study was started at University of California Los Angeles in 2006, and completed at Northwestern University in 2010, under the mentorship of Sir Fraser Stoddart. Subsequently, he spent two and a half years at Stanford University as a postdoctoral scholar working with Professor Zhenan Bao. In 2013, he joined the faculty of Texas A&M University, where he currently leads a multidisciplinary research team focusing on functional organic materials.

https://www.chem.tamu.edu/rgroup/fang/

Article information:

Palladium bis-pincer complexes with controlled rigidity and inter-metal distance
Cheng-Han Yu, Congzhi Zhu, Xiaozhou Ji, Wei Hu, Haomiao Xie, Nattamai Bhuvanesh, Lei Fang and Oleg V. Ozerov
Inorg. Chem. Front., 2020, Advance Article
https://doi.org/10.1039/D0QI01111H

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Unsymmetrical Siloxanes and Hydrosiloxanes via Main-Group Catalysis

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In a period of increasing society’s awareness in terms of sustainable science developments, scientists shall endeavor to resign from the use of highly expensive TM-catalysts. From this point of view, the utilization of abundant main-group catalysts begins to play a very important role in the synthesis of the wide range of chemicals.

Organosilicon derivatives, and in particular siloxane-based ones are used in the myriad aspects of daily lives. Their structural uniqueness has consequently led researchers to expand new synthetic solutions that rely on a modification of silicon-oxygen backbones (both short- and long-chained ones), which hence results in the preparation of new interesting materials.

Recently, Krzysztof Kuciński et al. have demonstrated that unsymmetrical disiloxanes, as well as trisiloxanes and hydrosiloxanes, can be efficiently obtained in the presence of main-group (pre)catalysts via practical and atom-economical dehydrogenative coupling of silanols with hydrosilanes (Figure 1).

Figure 1. A Silylation of Silanols with Hydrosilanes via Main-Group Catalysis

The salient features of their findings include (i) the use of commercially available and inexpensive (pre)catalyst, (ii) mild reaction conditions (rt-60oC) and operational simplicity, (iii) the applicability of primary, secondary and most challenging tertiary hydrosilanes, (iv) high chemoselectivity, and (v) some mechanistic insights into this transformation.

 

Figure 2. Illustrations of Si-H band disappearance recorded using real time FT-IR spectroscopy during the silylation of methylphenylsilane 4a with tert-butyldimethylsilanol 2a.

It is furthermore noteworthy that this strategy set the stage for the synthesis of highly important hydrosiloxanes, which can be used in further processes such as hydrosilylation. Lastly, this study also provides a blueprint for the development of a broad range of other coupling reactions.

Authors:

Krzysztof Kuciński

Adam Mickiewicz University in Poznań

Krzysztof Kuciński has been an Assistant Professor in the Department of Chemistry and Technology of Silicon Compounds at Adam Mickiewicz University in Poznan (Poland) since March 2019. He studied chemistry at AMU Poznan, and did his Ph.D. with Prof. G. Hreczycho at the same institution (2018). His research interests include organoboron and organosilicon chemistry with a strong emphasis on the sustainability of the processes. He is the co-author of 28 articles indexed by SCI.

https://publons.com/researcher/1856219/krzysztof-kucinski

 

Grzegorz Hreczycho

Adam Mickiewicz University in Poznań

Grzegorz Hreczycho received his Ph.D. (2007, supervisor: Prof. Dr. Bogdan Marciniec) and Habilitation (2015) in chemistry from Adam Mickiewicz University in Poznan (Poland). His research interests cover novel applications of silicon, boron, and germanium compounds and in addition coupling reactions catalyzed by transition metal complexes and Lewis acid catalysts. More than 60 research publications and patents document his activity in the fields of organometallic chemistry, homogeneous catalysis, and organic synthesis.

Article information:

Silylation of Silanols with Hydrosilanes via Main-Group Catalysis: The Synthesis of Unsymmetrical Siloxanes and Hydrosiloxanes
Krzysztof Kuciński, Hanna Stachowiak and Grzegorz Hreczycho
Inorg. Chem. Front., 2020, Accepted Manuscript
https://doi.org/10.1039/D0QI00904K

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Shifting directional control from H-bonds to I∙∙∙I interactions

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Since the early study at the beginning of the XX century of the first macrocycles ever analysed, among them the azacycloalkane 1,4,8,11-tetraazacyclotetradecana -more commonly known as cyclam-, such cyclic structures have shown compelling and encouraging properties. Indeed, beyond their broad use in nature –including roles both as signalling molecules and metabolites employed in modulating immune-system responses-, synthetic macrocycles have been used, for instance, to facilitate ion transport across hydrophobic membranes, drug delivery and the development of molecular machines.

Among these compounds, aza-macrocycles –and particularly those that include a pyridine ring in their structure, such as those showed in Figure 1- generally allow for strong coordination of metal cations which anyhow leaves free positions in the cations’ coordination sphere; this is an engaging feature to take advantage of. Thus, in last decades, a set of design strategies have been developed for exploiting these features in catalysis, recognition, enzyme mimicking and inhibition, interactions with macromolecules, and so forth. Among them we recall the main, perhaps first-generation, approach, of converting the macrocycle into the head of a scorpiand-type ligand featuring a functional tail with either further donor atoms, binding sites for supramolecular guests, adequate groups for grafting on surfaces, etc.

Recently, the groups of Antonio Bianchi (University of Florence) and Enrique García-España (University of Valencia) have focused on the effect of small structural changes (methylation) in the ability of aza-macrocycle-based Cu(II) complexes of stabilizing polyiodide networks, as a controlled manner to simultaneously boost electronic properties and robustness of these materials.

Figure 1. A) Structure of the three analogous polyazacyclophanes studied by the groups of professors Bianchi and García-España. B) Representation of a polyiodide network stabilized by the Cu(II) complexes of the azamacrocyclic ligands playing a counterion role.

The groups have demonstrated how the three analogous polyazacyclophanes shown in Figure 1 form the same CuL2+ complex as prevalent species in solution, so that a level playing field exist where only N‑methylation distinguishes them. Then they used them as countercation for polyiodide growth.

XRD analysis on the resulting crystals clearly show that methylation is a valuable tool to gradually shift directional control of subtending pairing preferences from H-bond to I···I interactions: this affects global packing and actively incorporates metal centres into polyiodide chains, setting the scene for further developments.

This contribution is based upon work from COST Action CA18202, NECTAR – Network for Equilibria and Chemical Thermodynamics Advanced Research, supported by COST (European Cooperation in Science and Technology).

Authors:

Matteo Savastano

University of Florence

Matteo Savastano is a research fellow at Dept. of Chemistry “Ugo Schiff”, University of Florence (Italy). He received his Ph.D. in Chemical Science from the same University in early 2018 under Prof. Antonio Bianchi. Matteo Savastano has been a visiting student at ICMol, University of Valencia (Spain) and at University of Jaén (Spain), enjoying fruitful collaborations to this day. His main interests are anion and cation coordination chemistry, supramolecular interactions, solution equilibria and polyiodide chemistry. In 2015 he was awarded with the Fernando Pulidori Prize (awarded to a young researcher in the area of thermodynamics). He has authored 30 papers in indexed journals

Álvaro Martínez-Camarena

University of Valencia

Álvaro Martínez-Camarena is postdoc researcher in the Institute of Molecular Science at the University of Valencia (Spain). He received his PhD in Nanoscience and Nanotechnology at the Faculty of Chemistry in 2019 under the supervision of Prof. Enrique García-España. In 2017 and 2018 he carried out research stays at the University of Vienna and Florence. The research field of Álvaro deals with the supramolecular chemistry and the development of mimetic agents of superoxide and catalase enzymes based on aza-macrocyclic complexes. In 2019 he was awarded with the Fernando Pulidori Prize (awarded to a young researcher in the area of thermodynamics). He is the author of 15 papers indexed by SCI.

 

Article information:

Stabilization of polyiodide networks with Cu(II)-complexes of small methylated polyazacyclophanes: shifting directional control from H-bonds to I∙∙∙I interactions
Álvaro Martínez-Camarena, Matteo Savastano, Jose Miguel Llinares, Begoña Verdejo, Antonio Bianchi, Enrique García-España and Carla Bazzicalupi
Inorg. Chem. Front., 2020, Accepted Manuscript
https://doi.org/10.1039/D0QI00912A

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Controllable Synthesis of Fluorinated Poly(styrene-butadiene)

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Synthetic rubbers have played an irreplaceable role in our morden society since we are living in the world “on wheel“. On the other hand these materials are difficult to be reused and recycled and nearly impossible to be bio-degradated, which are the main source of “black pollution“. For the sustainable development of the tyres and rubber industries, to fabricate “green tyres“ has been the challenging project in the past three decades. Styrene-butadiene rubber (SBR) is the most widely applied synthetic rubber in the passenger cars, which mixing with functionalized fillers, has been employed to fabricate “green tyres“. One of the strategies is synthesizing functional SBR to improve their compatibility with polar fillers, anticipated to endow the tyres excellent wear-resistance (prolonged use time) and low-rolling resistance whilst not sacrifice the wet-skid resistance.

Radical and ionic (co)polymerizations of polar monomers were usually adopted to produce functional poly(styrene-butadiene), while the obtained polymers were provided with poor regularity. By contrast, coordination polymerization was powerful in controlling microstructure of polymer chains, however, functional groups were usually poisonous to the applied catalysts.

Recently, the group of Dongmei Cui have demonstrated that syndio- and cis-1,4 dually selective copolymerization of para-fluorostyrene (pFS) and butadiene (BD) using rare-earth metal catalysts and di- and multi-block P(pFS-BD) copolymers were successfully synthesized by switching the monomers’ loading modes.

The authors firstly copolymerized of pFS and BD using pyridyl-methylene-fluorenyl supported complexes[(Py-CH2-Flu)Ln(CH2SiMe3)2(THF)n (Ln = Sc (1a), n = 0; Ln = Lu (1b), n = 1)]. The polymerization catalyzed by 1a gave a crosslinked copolymer because the scandium active species initiated the polymerization of the dangling C=C bonds of the 1,2-regulated PBD segments. Catalyst 1b showed low activity and poor controllability. Interestingly, by using pyridyl-cyclopentadienyl supported complexes[(Py-Cp)Ln(η3-C3H5)2 (Ln = Sc (2a), Lu (2b))] , which provided the active rare-earth metal center with an open coordination sphere to avoid low cis-1,4 selectivity and cross-linking process, the authors obtained syndio- and cis-1,4 dually regulated poly(fluorostyrene-butadiene). By merit of the livingness characteristics of copolymerizing pFS and BD, a multi-block copolymer was isolated via pulse loading of butadiene.

Figure 1. 13C NMR spectra of multi-block and diblock poly(pFS-BD).

The microstructures of resultant copolymers were confirmed by 1H and 13C NMR  measurements(Figure 1) and different phase morphologies of the di- and multi-block polymers were displayed through atomic force microscopy (AFM) (Figure 2). Strikingly, the multi-block copolymers of a novel type of fluoro styrene-butadiene rubber showd high thermal stability (Td = 368 oC) (Figure 3).

Figure 2. AFM micrographs of a spin-coated thin film of diblock poly(pFS-BD)(left) and multi-block poly(pFS-BD)(right).

Figure 3. TG and DTG curves of multi-block poly(pFS-BD).

This work designed rare-earth metal catalyts through regulating the electronic and steric effects of ligands to copolymerize para-fluorostyrene and butadiene, which paved a new avenue to access functional styrene-butadiene copolymer with controllable regio- and stereo- regularities as well as sequence distribution.

Corresponding Author

Prof. Dongmei Cui

Changchun Institute of Applied Chemistry, CAS

Dongmei Cui is a professor in State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry, CAS. She received her PhD at Changchun Institute of Applied Chemistry in 2001. The research fields of Professor Dongmei Cui are designing organo-lanthanide catalysts and precisely controlled coordination polymerizations. She has reported more than 180 articles indexed by SCI and has been invited to give several presentations internationally.

Article information:

Syndio- and cis-1,4 Dually Selective Copolymerization of Polar Fluorostyrene and Butadiene using Rare-earth Metal Catalysts
Yuanhao Zhong, Chunji Wu and Dongmei Cui
Inorg. Chem. Front., 2020,
https://doi.org/10.1039/D0QI00719F

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