Inorganic Chemistry Frontiers Blog

We are delighted to announce the establishment of our inaugural Early Career Advisory Board at Inorganic Chemistry Frontiers. This initiative aims to provide a direct channel for engaging with early-career researchers, supporting their professional development, and infusing our journal with fresh innovative perspectives from the younger generation.

We warmly invite you to nominate emerging investigators to the board or encourage your colleagues to self-nominate before 25 February 2024.  

Role of the Early Career Advisory Board

At Inorganic Chemistry Frontiers, we value the voices of early-career researchers. Joining the board, you will be part of a dynamic group of emerging investigators, helping shape the future of a leading inorganic chemistry journal and benefiting from networking opportunities with the journal’s Editorial and Advisory Board members.

Your insights will be invaluable as you provide feedback on the journal’s scientific standards, suggest emerging topics and researchers worth featuring, and contribute to promotional and visibility initiatives within your community.

Terms of Service

Normally, members of the Early Career Advisory Board will serve a term of two years, with an option for reappointment for a maximum of two consecutive terms.

Eligibility

• Nominations are open to researchers of any nationality from academia or industry.
• Candidates should typically be no more than 6 years from starting an independent research position (Assistant Professor or industry equivalent); appropriate consideration will be given to those who have taken a career break, followed a different career path or work in systems where their time period to independence may vary.
• Candidates should demonstrate a commitment to advancing inorganic chemistry through developing high-quality journals.

How to Nominate

Please email the following information to InorgChemFrontiersED@rsc.org for your nominations.

Self-nominations are very welcome. If you are interested in joining our Early Career Advisory Board, please provide:

• An up-to-date CV which highlights your engagements in academic activities (conferences participation etc.) and services to the wider community (journals, societies, etc.)
• Any supplementary materials, such as a brief supporting statement from an active Principal Investigator or contact information of references.

To nominate someone else, please provide:

• Candidate’s name, position, affiliation, website URL and contact details, along with a brief description of the candidate’s research contribution and community engagement
• Nominator’s name, position, affiliation and contact details
• Any supporting materials, such as an up-to-date CV of the candidate

Selection Criteria

Editorial Board of the journal will consider the following aspects of all nominations as appropriate:

• Profile within institute and/or community
• Involvement in community and advocacy activities
• Area and quality of research
• Motivation to join Early Career Advisory Board

We look forward to receiving your nominations!

Kind Regards,

Prof Song Gao 
Editor-in-Chief, Inorganic Chemistry Frontiers
Sun Yat-sen University and Peking University

Dr Wenjun Liu
Executive Editor, Inorganic Chemistry Frontiers
Royal Society of Chemistry

From unprecedented 2,2′-bisimidazole-bridged rare earth organometallics to magnetic hysteresis in the dysprosium congener

Florian Benner and Selvan Demir

Inorg. Chem. Front., 2023, 10, 4981-4992

https://doi.org/10.1039/D3QI00546A

Single-molecule magnets (SMMs) are molecules that show slow magnetic relaxation, originating from a bistable magnetic ground state with a thermal barrier to spin relaxation (U_eff). Remarkably, SMM can exhibit open magnetic hysteresis loops which correspond to retaining magnetic memory just like tiny bar magnets can. This property renders SMMs exciting for potential applications in high-density information storage, magnetic refrigeration, quantum computing and spintronics. Over the last years, the SMM field exploited mononuclear dysprosium metallocenium cations as spin carriers, where the well-defined coordination sphere imposed by cyclopentadienyl ligands strongly amplifies the easy axis of the dysprosium(III) ion. To date, synthetically accessible single-ion magnets operate at best slightly above the boiling temperature of liquid nitrogen (77 K).   Consequently, it was realized that lanthanide ions must be strongly coupled to one another to increase operating temperatures, ideally towards room temperature. To this end, the nature of the bridging ligand is vital and the exploration of new organic bridging ligands along with their utility in coupling lanthanide metallocene fragments is crucial. That knowledge will aid to devise design principles of SMMs with amplified magnetic coupling between lanthanide metallocene moieties.

Recently, the group of Selvan Demir at Michigan State University implemented the bridging ligand 2,2′-bisimidazole for the first time into rare earth and magnetochemistry, where this tetranitrogen ligand connects two metallocenium units (Figure 1). The synthesized series consists of three compounds comprising the diamagnetic yttrium, the paramagnetic gadolinium (isotropic) and paramagnetic dysprosium (anisotropic) ions. Excitingly, the dinuclear dysprosium complex features SMM behavior and on the timescale of magnetic hysteresis measurements, open hysteresis loops of up to 5 K. The half-filled f-electron valence shell for trivalent gadolinium ions allows quantification of the magnetic exchange coupling since the orbital singlet affords magnetic behavior that is free of complications arising from spin-orbit coupling. Thus, dc magnetic susceptibility measurements on the respective gadolinium complex revealed weak antiferromagnetic interaction between the metal ions. Due to its comparable ionic size, the yttrium analog served as a diamagnetic surrogate to the lanthanides, enabling the in-depth investigation of the electronic structure of these complexes via spectroscopic methods and density functional theory (DFT) calculations. In this way, absorption spectra were related to the underlying electronic structure of these complexes, revealing prevalent excitations from the predominantly ligand-based frontier orbitals into metal-based higher-lying orbitals. This provided also profound insight into the redox (in)activity of the bisimidazole bridge, which, in contrast to its annulated 2,2′-bisbenzimidazole analog, showed no reactivity towards reductants or oxidants. This was primarily ascribed to the title compounds lacking accessible ligand-based low-lying π* orbitals, unlike the opposite observation for the respective bisbenzimidazole counterparts. In sum, the fact that the bisimidazole ligand retains and enhances the single-ion anisotropy of the dysprosium ions while providing a wealth of substitution sites for future chemical modification renders this ligand system highly promising for the construction of higher nuclearity systems.

 

Corresponding Author:

Selvan Demir is an Assistant Professor of Chemistry at Michigan State University. She received a Dr. rer. nat. in Chemistry from 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 was a Postdoctoral Scholar, where she conducted research on lanthanide-based single-molecule magnets and porous aromatic frameworks with Prof. Jeffrey R. Long at the University of California, Berkeley. Simultaneously, she explored the 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. Her research program has a strong emphasis on organometallic chemistry, small molecule activation, organic radicals, single-molecule magnets, qubits, bismuth chemistry, dibenzocyclooctatetraene chemistry, and lanthanide/actinide separations.

Advances in the coordination chemistry of multinuclear compounds have been exploited to drive the self-assembly of many new discrete metallo-supramolecular motifs. Due to the nature of the metal-ligand interactions, many of these systems have a dynamic character with reversible association and dissociation able to generate complex mixtures. Unveil such dynamic behaviours, it is a priority to fully understand, control and design their functional properties. Among metallo-supramolecular systems, lanthanide (Ln) based architectures attracts much attention due to their remarkable optical and magnetic properties. However, design and control of the final supramolecule is very challenging due to the inner nature of the 4f orbitals and consequent small ligand-field effects. There is, however, a steady variation of the effective ionic radius (EIR) across the series, the so called “lanthanide contraction”. Although the radii difference (ΔEIR) is quite small (ca. 0.20 Å between La³⁺ and Lu³⁺ and ca. 0.02 Å between two consecutive lanthanides), it can have important chemical consequences on the nature and features of supramolecular complexes.

Recently, a group headed by Marzio Rancan of ICMATE-CNR (Italy) and collaborators from the University of Padova (Italy) and Dortmund University (Germany) have demonstrated that ΔEIR strongly affects the kinetics of Ln ions exchange between preassembled quadruple-stranded [Ln₂L₄]^2– cages (Figure 1).

The process has been qualitatively and quantitatively characterized by time-dependent electrospray ionization mass spectrometry (ESI-MS). Mixing a series of two homonuclear [Ln^A₂L₄]²⁻ and [Ln^B₂L₄]²⁻ with increasing Ln³⁺ ΔEIR always leads to the formation of a statistical mixture of homo- and heteronuclear helicates due to the Ln exchange. All the studied systems have an equilibrium constant close to K = 4. The Ln³⁺ ΔEIR, hence, does not affect the thermodynamics of the process that is mainly governed by statistical factors and entropy-driven. On the other hand, they demonstrate that the rate of the dynamic ion exchange is Ln radius-dependent (Figure 1b). The kinetic constants of the forward and backward reactions revealed an exponential trend depending on the Ln³⁺ ΔEIR of the two homonuclear pre-assembled cages (Figure 1c): from the minimum to the maximum value of ΔEIR, the kinetic constants increase by three orders of magnitude. This fundamental study hints new tools and guidelines to study dynamic processes in metallo-supramolecular ensembles, and for the precise preparation and control of lanthanide-based mixed coordination-driven systems.

Corresponding author:

Marzio Rancan is a Research Fellow at ICMATE-CNR (Italy). He received his PhD in Molecular Sciences at the University of Padova in 2009. He did post-doctoral studies at CNR, University of Padova and spent one year in the Molecular Magnetism Group at The University of Manchester (UK).  His current research is focused on the synthesis and characterization of coordination-driven molecular and supramolecular architectures with functional properties. He is the author of about 60 articles.

WEBSITE: http://wwwdisc.chimica.unipd.it/FMNLab/index.html

ORCID: https://orcid.org/0000-0001-9967-5283

RESEARCHGATE: https://www.researchgate.net/profile/Marzio-Rancan

Zirconium-89 complexation chemistry is an important area of research in the context of developing radiolabelled proteins for applications in diagnostic positron emission tomography (PET) imaging. For this imaging technology, the metalloradionuclide ⁸⁹Zr⁴⁺ ion needs to be sequestered by a ligand to form a coordination complex that is thermodynamically, kinetically, and metabolically stable in biological systems. In this regard, desferrioxamine B (DFO), a natural bacterial siderophore, is one of the outstanding hexadentate linear chelator for zirconium-89, used in clinical trials with ⁸⁹ZrDFO-radiolabeled antibodies (mAbs). Nevertheless, preclinical studies have demonstrated that ⁸⁹ZrDFO-mAbs can suffer from dissociation and metal ion release in vivo resulting in partial bone uptake in mice which could be partially due to the incomplete coordination sphere around the metallic cation. Driven by the goal of increasing the stability of the ⁸⁹Zr⁴⁺ coordination complex toward demetallation in vivo, several groups around the world have explored the synthesis and coordination chemistry of novel multidentate chelates with coordination numbers from 6 to 8 but the development of heptadentate remained unexplored.

Recently, a collaborative work between the group of Prof. Dr Jason P. Holland (University of Zurich, Switzerland) and a team from the Institut Plurisdisciplinaire Hubert Curien (IPHC, CNRS, University of Strasbourg, France) have demonstrated that photoactivatable heptadentate chelates could be a new alternative for the ultra-fast, light-induced production of stable ⁸⁹Zr-mAbs in vivo (Figure 1). The researchers synthesise new chelates, used density functional theory to predict the thermodynamic stability, and studied the in vitro stability of the radiolabelled complexes to find the most promising candidate for in vivo application.

The researchers also selected the most stable complex (Zr-2) and produced ⁸⁹Zr-radiolabelled onartuzumab (the monoclonal antibody component of MetMAb^TM which binds to the human hepatocyte growth-factor receptor c-MET) using photoradiochemical methods. Finally, the pharmacokinetic profile and c-MET targeting was evaluated in vivo and ex vivo by using PET imaging and biodistribution studies in female athymic nude mice bearing subcutaneous MKN-45 human gastric cancer xenografts (Figure 2).

 

Overall, the researchers proved that [⁸⁹Zr]Zr-2-onartuzumab provides specific tumour targeting and high tumour-to-organ contrast on the PET pictures and from the biodisitribution analysis. The results obtained in the study confirm that heptadentate complexes of ⁸⁹Zr display improved stability in vivo compared with hexadentate analogs and are promising candidates for future ⁸⁹Zr-radiotracer design.

About the corresponding author

Jason P. Holland is from Yorkshire in the UK and is currently an SNSF Professor for Medicinal Radiochemistry at the University of Zurich. Research activities in the Holland group focus on advancing radiolabelling methods through novel bioconjugation approaches for labelling bioactive molecules with various radionuclides (¹⁸F, ⁶⁴Cu, ^67/68Ga, ^86/90Y, ^99mTc, ¹¹¹In, ¹⁷⁷Lu, ¹⁸⁸Re, etc).

E-mail: jason.holland@chem.uzh; Twitter: @HollandLab_