Inorganic Chemistry Frontiers Blog

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

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 1–4 (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

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-60^oC) 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

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

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 (T_d = 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

We are delighted to announce that Professor Svetlana Mintova (CNRS, France) has joined Inorganic Chemistry Frontiers as Associate Editor.

Biography Svetlana Mintova is Director of Research, 1st Class in Centre national de la recherche scientifique (CNRS), Laboratoire Catalyse et Spectrochimie (LCS), School of Engineering and Normandy University – Caen, France, and Invited Professor in China University of Petroleum, Qingdao, China. She received her PhD from the Technological University of Sofia, Bulgaria, in 1992. Following academic appointments at the Bulgarian Academy of Science and University of Munich (LMU), Germany, she was appointed as a senior researcher at the CNRS, France, in 2006. She is the recipient of the Baron Axel Cronstedt award from the Federation of European Zeolite Associations (FEZA, 2014), the Donald Breck award from the International Zeolite Association (IZA, 2016), the Qingdao award in recognition for social and research contributions (2019), and the Shandong International Science and Technology Cooperation Award (2019). She is a council member of the IZA, the FEZA, and the Chair of the “Synthesis Commission” of the IZA. ORCID: 0000-0002-0738-5244

Research Highlights

Her scientific interests include preparation of porous materials, zeolites, porous films, coatings, composites and related applications including catalysis, sorption, host-guest chemistry, sensors, membranes, and nanosized porous materials for biomedical applications and optical devices.

Check some of her publications at Royal Society of Chemistry:

Incorporation of trivalent cations in NaX zeolite nanocrystals for the adsorption of O₂ in the presence of CO₂
Sarah Komaty, Ayoub Daouli, Michael Badawi, Clément Anfray, Moussa Zaarour, Samuel Valable and Svetlana Mintova
Phys. Chem. Chem. Phys., 2020,22, 9934-9942
https://doi.org/10.1039/D0CP00111B

Defect-engineered zeolite porosity and accessibility
Zhengxing Qin, Leila Hafiz, Yanfeng Shen, Stijn Van Daele, Philippe Boullay, Valerie Ruaux, Svetlana Mintova, Jean-Pierre Gilson and Valentin Valtchev
J. Mater. Chem. A, 2020,8, 3621-3631
https://doi.org/10.1039/C9TA11465C

Micro- and macroscopic observations of the nucleation process and crystal growth of nanosized Cs-pollucite in an organotemplate-free hydrosol
Eng-Poh Ng, Aleid Ghadah Mohammad S, Severinne Rigolet, T. Jean Daou, Svetlana Mintova and Tau Chuan Ling
New J. Chem., 2019,43, 17433-17440
https://doi.org/10.1039/C9NJ03151K