Inorganic Chemistry Frontiers Blog

Molecular magnetism is a diverse field within chemistry with strong links to other disciplines across physical sciences. Current research focuses on magnetic memory and quantum information processing but also extends to medical diagnostics and catalysis. Here we highlight some of the exciting research on this topic that was recently published in Inorganic Chemistry Frontiers. Hope you find them enjoyable to read.

	Low-coordinate bis(imidazolin-2-iminato) dysprosium(III) single-molecule magnets Rong Sun, Chen Wang, Bing-Wu Wang, Zhe-Ming Wang, Yao-Feng Chen, Matthias Tamm and Song Gao Inorg. Chem. Front., 2023,10, 485-492 https://doi.org/10.1039/D2QI02180C
	Single-ion magnetism behaviors in lanthanide(III) based coordination frameworks Qingyun Wan, Masanori Wakizaka and Masahiro Yamashita Inorg. Chem. Front., 2023,10, 5212-5224 https://doi.org/10.1039/D3QI00925D
	Actinide-based single-molecule magnets: alone or in a group? Ming Liu, Xiao-Han Peng, Fu-Sheng Guo and Ming-Liang Tong Inorg. Chem. Front., 2023,10, 3742-3755 https://doi.org/10.1039/D3QI00523B
	The importance of second sphere interactions on single molecule magnet performance Brodie E. Matheson, Tyson N. Dais, Marryllyn E. Donaldson, Gareth J. Rowlands and Paul G. Plieger Inorg. Chem. Front., 2023,10, 6427-6439 https://doi.org/10.1039/D3QI01634J
	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

We welcome you to submit your next paper to Inorganic Chemistry Frontiers and contribute to the advancement of this fascinating field.

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
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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

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.

Figure 1. A: Schematic view of the bisimidazole-bridged rare earth metallocene complexes. B: Structure of the complexes as determined through single-crystal X-ray diffraction analysis. C: Plot of the bisimidazole-centered highest occupied molecular orbital of the yttrium complex.

Figure 2. A: Absorption spectra of the rare earth complexes in the ultraviolet/visible region of the electromagnetic spectrum. B: Dynamic magnetic measurement revealed slow magnetic relaxation and single-molecule magnet behavior for the dysprosium complex.

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.

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.

Figure 1 Preparation of the rubidium carbazolide complex, its molecular structure, luminescence behaviour and the orbitals involved in the excitation and emission process.

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).

Figure 1. A) Synthesis of the radical-bridged dinuclear compounds (1-3). (B) Molecular structure of 3. Partial labelling and omission of the BPh4- moiety and H-atoms have been employed for clarity. The solid teal lines represent the orientation of the principal magnetic axes of the ground Kramers doublet. C) Variable temperature dc susceptibility of 1 (teal circles), 2 (blue circles) and 3 (magenta circles) under an applied field of 1000 Oe. The solid red line represents the fit as determined from the application of the -2J formalism. Insert: Simplified illustration of the two J-model which was used to fit the data highlighting the antiparallel spin alignment of the LnIII ions with respect to the tz•- ligand.

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.

Figure 2 Left: Frequency-dependence of the out-of-phase magnetic susceptibility (χ’’) at zero-field for 2 (A) and 3 (D) at the respective temperature regions. Solid lines represent fits to the generalized Debye model. Middle: Cole-Cole plots for 2 (B) and 3 (E) at the respective temperature regions (Hdc = 0 Oe). Solid lines represent fits to the generalized Debye model. Right: Temperature-dependence of the relaxation times (τ) for 2 (C) and 3 (F) with the respective estimated standard deviations (gray bars). The estimated standard deviations of the τ were calculated from the α-parameters of the generalized Debye fits and the log-normal distribution. The solid red lines represent the best-fit while the dashed orange and purple lines in (C) represent the individual components of the magnetic relaxation for QTM and Orbach processes, respectively.

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
University of Ottawa

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.