Inorganic Chemistry Frontiers Blog

In recent years, derivatives of carbazole have been studied intensively with focus on their optical properties to scry for applicability as materials in OLEDs and OFETs. Fine tuning of the electronic properties of the materials was achieved by a large variety of substitution patterns both on the central nitrogen atom and the carbon periphery.

Recently, the group of Dr. Hinz (Karlsruhe Institute of Technology, Germany) has investigated a series of alkali metal carbazolides with bulky arenes in positions 1 and 8 of the carbazole scaffold (see Figure 1). The alkali metal complexes of the type [(Cbz)M] show visible fluorescence with emissions maxima in the range of 520 and 460 nm in dependence of the metal ion. Quantum yields of up to 29% in the solid state were measured for the rubidium derivative.

The electronic transitions were rationalised with the aid of TD-DFT calculations. Upon HOMO→LUMO+1 excitation, density shifts from the carbazole scaffold to the arenes in positions 1 and 8 and thus are intraligand transitions. The geometry of the complexes only change slightly upon excitation which enables the highly efficient fluorescence.

Coordination of additional toluene molecules to the alkali metal shifts the emission maximum to lower energy and enables a second emission band arising from an interligand excitation from the carbazole to a toluene molecule. The quantum yields for the complexes in toluene solution are even higher than in the solid state and reach 100% for the lithium complex.

Corresponding author:

Alexander Hinz studied chemistry in Rostock, Germany, and is currently a junior group leader at the Karlsruhe Institute of Technology. The work of the Hinz group is focused on molecular main group chemistry and devoted to the investigation of low-coordinated, but highly reactive compounds.

E-mail: alexander.hinz@kit.edu

Single-molecule magnets (SMMs) are molecules that retain the slow relaxation of their magnetization upon removal of an applied magnetic field, acting as magnets below a characteristic temperature known as the blocking temperature. Research in this field has recently focused on the use of radicals as ligands to enhance the performance of SMMs through the exchange coupling of the radical- and metal-based spins. The strong interaction between the spin of the radical with the unpaired electrons of a metal ion effectively suppresses the quantum tunneling of the magnetization (QTM) and fast spin relaxation pathways involving spin excited states, thus promoting a thermal relaxation pathway for magnetization reversal. The latter is particularly important when designing lanthanide (Ln) based SMMs as the core-like nature of the 4f orbitals makes magnetic coupling challenging and thus they tend to suffer from through-barrier relaxation of the magnetization (i.e., QTM, Raman and direct mechanisms).

To this day several attempts towards this direction have been made leading to the isolation of strongly coupled Ln SMMs with the N₂^•3--based family exhibiting very good magnetic performance. However, the rational incorporation of the N₂ species into complexes is a synthetic challenge and it does not offer any room for structural modification. For this reason, other radicals, such as tetrazines have been explored by the group of Prof. Muralee Murugesu of the University of Ottawa. In the past the researchers had successfully incorporated the 1,2,4,5-tetrazine radical anion (tz^•−) into tetranuclear “Ln₄” metallocenes which led to strong magnetic coupling and significant magnetic hysteresis (H_c = 3 T).

Recently, the researchers aimed to isolate a dinuclear building block so that the role of the bridging ligand in the overall magnetic coupling in Ln systems can be better understood. In further detail, they have utilized the high performing {Cp^*₂Ln^III}⁺ moieties and bridge them by employing the tz^•−_, leading to the isolation of a new family of radical-bridged Ln metallocenes: [(Cp^*₂Ln^III)₂(tz^•−)(THF)₂](BPh₄), (Ln = Gd (1), Tb (2), Dy (3); THF = tetrahydrofuran).

They showed that a strong magnetic coupling between the Ln^III ions and the tz^•− was achieved, revealing a J_Gd-rad = -7.2 cm^-1 for 1 which is even comparable to some N₂^•3- bridged SMMs. Due to this, both 2 and 3 displayed zero-field SMM behavior with slow relaxation of the magnetization and magnetic hysteresis.

Ab initio calculations verified the strong antiferromagnetic Ln-rad coupling and showed that the magnetic state of 2 and 3 can be interpreted as a “giant-spin” where the relaxation of the magnetization is related to changes in the magnetic state of the overall exchange-coupled system. The slow relaxation of these SMMs is mediated via thermally activated processes through the first excited KDs which correspond to an Ising-type ferrimagnetic spin configuration where the magnetic moments of the Ln^III ions are co-aligned while the magnetic moment of the radical points to the opposite direction.

The researchers believe that the results presented in this work will be helpful for future strategies on designing new lanthanide metal complexes employing radical ligands in the pursuit of new strongly-coupled zero field SMMs.

Corresponding author:

Prof. Muralee Murugesu received his PhD from the University of Karlsruhe in 2002 under the supervision of Prof. A. K. Powell. He undertook postdoctoral stays at the University of Florida (2003–2005) with Prof. G. Christou, and jointly at the University of California, Berkeley and the University of California, San Francisco under the supervision of Prof. J. R. Long and the Nobel Laureate Prof. S. Pruissner (2005–2006). In 2006, he joined the University of Ottawa as an assistant professor and since 2015 he is a full professor. Prof. Murugesu’s research focuses on the design and development of Single-Molecule Magnets, Metal-Organic Frameworks and High-Energy materials.

Cancer is a major health issue worldwide, and the development of innovative and effective drugs is an ultimate demand for research. Iron compounds have aroused a great interest in the search for new metal based chemotherapics, on account of their relatively low toxicity and their redox chemistry, exportable to physiological media.

Some ferrocene derivatives have shown a promising anticancer potential, with a strong activity mostly associated with Fe^II to Fe^III oxidation, leading to alteration of the cellular redox balance and subsequent production of toxic substances (reactive oxygen species, ROS). However, they provide a limited variability of the metal coordination set, and they need to be carefully formulated for in vivo applications due to a generally insufficient water solubility.

Since 2019, a series of cationic [Fe^IFe^I] complexes based on the [Fe₂Cp₂(CO)₂] core and comprising a vinyliminium bridging ligand have emerged as a novel class of potential chemotherapeutic agents. Thanks to the unique features of the bimetallic core, these complexes are easily prepared up to gram scale from a commercial precursor in a few synthetic steps. Remarkably, they are amphiphilic and appreciably water-soluble, and exhibit an antiproliferative activity against cancer cell lines which depends on the ligand substituents. The choice of the latter is virtually limitless, thanks to the generality of the synthetic procedure, and this feature allows to optimise physico-chemical properties for biological purposes. Different mechanisms, mainly ROS production but also protein interaction and weak DNA binding, may contribute to the mode of action of these dinuclear structures.

Recently, the group of Fabio Marchetti and co-workers have reported, for the first time, the conjugation of a ferrocenyl moiety with a diiron framework, as a strategy to obtain robust mixed-valence triiron compounds featured by a potent cytotoxicity and excellent selectivity towards cancer cell lines (i.e., IC₅₀ values in the low micromolar/nanomolar range on the cancer cell lines, and up to 35 times higher values on the nontumoral cells).

A combination of stability studies, electrochemical experiments, iron cellular uptake and targeted biological studies indicate that the cationic triiron complexes synergistically combine the redox behaviour of the ferrocenyl moiety with the amphiphilicity and the versatility of the diiron vinyliminium structure, and that their powerful activity arises from the ability to disrupt the redox homeostasis of tumour cells, through the overproduction of intracellular ROS and the alteration of the thioredoxin reductase, assessed on a synthetic dodecapeptide as a simplified model of the enzyme.

Corresponding Author:

Fabio Marchetti received his Degree in Industrial Chemistry from the University of Bologna in 1999 (summa cum laude), and the PhD in Chemistry from the same University in 2003. In 2006 he obtained a researcher position at the University of Pisa, and since October 2018 he has been Full Professor in the same University. FM has co-authored over 200 scientific publications on international journals, 2 book chapters and 2 international patents. His research interests regard the synthesis, the characterization and the properties of new transition metal compounds, and the metal-mediated activation of small organic molecules.

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

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

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.

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. 

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

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.

 

 

 

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