Inorganic Chemistry Frontiers Blog

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.

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

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.

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).

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.

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.

 

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 Gd^III 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 Gd^III 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 Gd^III chelates (Figure 1).

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 Cu^II and Zn^II 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).

 

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.

 

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.

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.

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

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([Cu^IIL^Et]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 (TON_equiv=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, [Cu^IIL^Et]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, E_cat/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).

 

The latest InorgChemFront issue is published online.

The front cover story, Two metal–organic zeolites for highly sensitive and selective sensing of Tb³⁺  is contributed by Meiling Li, Guojian Ren, Fuxiang Wang, Zhimeng Li, Weiting Yang, Dongxu Gu, Yinghui Wang, Guangshan Zhu and Qinhe Pan.

The inside cover features a story on Base induced C–CN bond cleavage at room temperature: a convenient method for the activation of acetonitrile by Xiaofeng Zhang, Zilong Zhang, Shiqun Xiang, Yingzu Zhu, Changneng Chen and Deguang Huang.

Following review article is included in current issue:

Recent insights into near-infrared light-responsive carbon dots for bioimaging and cancer phototherapy
Bo Zhou, Zhengxi Guo, Zhaoxing Lin, Lizheng Zhang, Bang-Ping Jiang and Xing-Can Shen
Inorg. Chem. Front., 2019,6, 1116-1128
https://doi.org/10.1039/C9QI00201D

Inorganic Chemistry Frontiers is delighted to share with you the HOT articles of January 2019!

You can access these publications for free till 31 March 2019 by logging into your free Royal Society of Chemistry publishing personal account (http://pubs.rsc.org).

Metal chelate induced in situ wrapping of Ni3S2 nanoparticles into N, S-codoped carbon networks for highly efficient sodium storage
Jiabao Li, Jinliang Li, Taiqiang Chen, Ting Lu, Wenjie Mai and Likun Pan
Inorg. Chem. Front., 2019, Advance Article
http://dx.doi.org/10.1039/C8QI01326H