Jonas Braun

In this study, we investigated whether copper(II)‐bispidine complexes can be heterogenized on epoxy‐functionalized agarose beads to provide reusable heterogeneous catalysts. The ligands employed are rigid N ‐donor systems based on the 3,7‐diazabicyclo[3.3.1]nonane scaffold, and the corresponding copper complexes are known to catalyze the aziridination of styrene. To enable covalent attachment to the epoxy groups of the beads, hydroxy‐functionalized linkers were introduced into the ligand framework. However, immobilization was found to be dominated by noncovalent interactions. Nevertheless, only minimal copper leaching was observed, and the resulting immobilisates were reused over six consecutive reaction cycles. At high catalyst loadings, comparable yields of 17%–21% were obtained for the different complexes, indicating restricted active‐site accessibility within the support. Lowering the catalyst loading markedly improved catalytic performance, resulting in average yields of approximately 40% over six cycles. Under these conditions, immobilization could even enhance the performance of otherwise slowly reacting complexes compared with homogeneous catalysis under air, possibly by restricting oxygen access to the active Cu ^I species and alleviating mass‐transport limitations associated with high catalyst loadings in heterogeneous systems. Overall, the results demonstrate that catalyst loading, active‐site accessibility, and transport within the agarose matrix are key factors governing the performance of immobilized copper(II)‐bispidine catalysts.

The synthesis of lanthanide complexes with low coordination numbers is challenging because the large ionic radii of lanthanide ions generally promote the formation of highly coordinated species. Achieving lower coordination geometries requires introducing significant steric hindrance. We report two low coordinated, almost perfectly octahedral lanthanide complexes [LnIII(Ph3PO)4(HBS)2](OTf) (Ln = DyIII (1), YbIII (2) and NdIII (3), Ph3PO = triphenylphosphine oxide; HBS = 4-hydroxybenzenesulfonate). Their magnetic and temperature-dependent luminescent properties have been systematically investigated showing field induced Single Molecule Magnet behavior and f-f optical transitions. To rationalize these properties with Complete Active Space Spin Orbit Configuration Interaction calculations, we have extended our program to compute magnetic dipole oscillator strengths. We showed that the octahedral ligand field acts as the magnetic main axes, that small geometric distortions induce significant anisotropy and simulated luminescent and magnetic data in very good agreement with experiment.

A series of [Ni ₈ Ln ₄ (CO ₃ ) ₄ (L) ₈ (NO ₃ ) ₂ (H ₂ O) ₈ (MeOH) ₄ ](NO ₃ ) ₂ (Ln = Dy ( 1 ), Gd ( 2 ), Y ( 3 )) cyclic coordination clusters containing four carbonate bridges were isolated and studied using SQUID and microSQUID experiments and quantum mechanical calculations. The dodecanuclear Ni ₈ Dy ₄ complex exhibits slow relaxation of the magnetization confirmed by the presence of temperature‐ and field‐dependent magnetic hysteresis loops. The competing interactions and the anisotropic nature within the cluster were analyzed using DFT and ab initio calculations and revealed that the spin structure of the Dy ^III ions is steered by the interactions mediated through the Ni ^II ions.

Single-molecule toroics host closed magnetic vortices carrying toroidal moments τ , whose electric-dipole symmetry enables magnetoelectric spin control. Yet opposite toroidal chiralities are degenerate in conventional magnetic fields, making direct detection of τ challenging. Current approaches probe toroidal dynamics only indirectly through weak residual magnetism, while finite-temperature toroidal polarisation and realistic preparation/readout conditions remain unestablished. Here we show that the Fe ₁₀ Dy ₁₀ molecule hosts a 62-billion-dimensional low-energy manifold pervaded by toroidal character, rendered tractable by an ab initio-informed transfer-matrix framework that reproduces experimental data. The model reveals a large toroidal response robust to thermal fluctuations, quantified by a finite-temperature toroidal susceptibility ξ . We then propose a preparation-and-readout protocol in which a train of temporally asymmetric near-infrared pulses accumulates toroidal polarisation, converted through magnetoelectric response into a measurable electric-field-induced magnetic signal. These results establish Fe ₁₀ Dy ₁₀ as a molecular system where τ can be prepared, accumulated and read out under realistic conditions.

Magnetic relaxation, mediated through molecular and lattice vibrations, is recognised as the next hurdle to overcome in terms of high‐performaning Single Molecule Magnets (SMMs). One strategy is to confine molecular and lattice vibrations through intra‐ and intermolecular interactions to modulate the phonon spectrum. Here, we report the use of halogen bonding to engineer the crystal lattice of a Dy ₂ dimer [Dy ₂ Cl ₄ (Hopch‐Br) ₂ ]·CCl ₄ involving disordered lattice solvent. The strength of the resulting network has been estimated using quantum chemical calculations. The magnetic data were investigated with SQUID magnetometry, revealing antiferromagnetic interactions between the two Dy ^III ions as well as slow relaxation of magnetisation, with the results being in excellent agreement with ab‐initio calculations.

Gd(III)-Gd(III) exchange interactions are central to a number of applications, such as the magnetocaloric effect or single molecule magnetism. Broken-symmetry density functional theory is the most widely used computational technique for these calculations, yet no comprehensive benchmark has been established. Here, we present the computational analysis of 27 binuclear Gd(III) compounds in comparison to experimental data and propose a best-practice workflow. We encourage the explicit treatment of scalar relativistic effects and the use of a combination of hybrid functionals with different amounts of exact exchange. Furthermore, we investigated this testbed for structure-property relationships and demonstrated the use of the recommended methodology on two tetranuclear Gd(III) clusters.

The determination of the orientations of the individual Dy ^III anisotropy axes in polynuclear complexes is challenging but crucial for the understanding of systems showing Single Molecule Magnet or Single Molecule Toroic behavior. In particular, the experimental proof of a toroidal ground state from magnetization data often remains ambiguous. Here, we report the coordination cluster [Co ^III ₃ Dy ^III ₃ (µ ₃ -OH) ₄ (O ₂ C-C ₆ H ₄ -p-Me) ₆ (pmide) ₃ (H ₂ O) ₃ ]Cl ₂ · 10MeCN (1) (H ₂ pmide = N-2-pyridylmethyldiethanolamine) which crystallizes with threefold symmetry and contains an equilateral Dy ^III ₃ triangle surrounded by a triangle of diamagnetic Co ^III ions. We also report a multi-technique investigation of its toroidal magnetic spin structure, including ¹⁶¹ Dy Synchrotron Mössbauer Spectroscopy which shows an abrupt transition from a non-magnetic to a magnetic state. The experimental orientations of the individual Dy ^III magnetic axes were assessed using torque magnetometry and micro-SQUID measurements and both experiments converged on a spin structure that is in very good agreement with ab initio calculations. Such a multi-technique approach, including ¹⁶¹ Dy Synchrotron Mössbauer Spectroscopy, provides a roadmap for the unambiguous identification of such toroidal states.

We present three air-stable radical-containing compounds, [M^III₂(phsq)₄(NO₃)₂(MeOH)₂]·2MeOH (M = Dy (1), Y (2), Gd (3); Hphsq = 9,10-phenanthrenesemiquinone), in which strong intramolecular inter-radical interactions force two lanthanide ions into close proximity and isolate them from the lattice. Magnetic measurements on (1) showed it to be an SMM with maxima in the ac susceptibility up to 18 K (1000 Hz). Modeling the magnetic data using three different analytical approaches reveals the absence of zero-field quantum tunneling of magnetization (ZFQTM) as a relaxation pathway. This is a result of significant internal magnetic fields identified by ab initio calculations that appear to quench the ZFQTM. This can be verified from measurements performed on an Y-doped sample (1a), which show that strong ZFQTM is present in the DyY analogue.

We report the synthesis of two new biquinoxen-σ^H-adducts (3,3′-diisopropoxy-4,4′-dimethyl-3,3′,4,4′-tetrahydro-2,2′-biquinoxaline (Mbqn-(OⁱPr)₂) (1) and 3,3′-bis(isopropylthio)-4,4′-dimethyl-3,3′,4,4′-tetrahydro-2,2′-biquinoxaline (Mbqn-(SⁱPr)₂) (2)) with the same molecular structure other than the exchange of two oxygen atoms with sulphur atoms. This enables us to directly compare the optical properties and stability of the compounds as a result of this substitution. For freshly prepared solutions of 1, a fluorescence quantum yield of 97% is observed, whereas for 2, the value is much lower at 7%. We furthermore note a decrease in quantum yields for solutions investigated after certain storage times, indicating a reactive channel. We note that this decomposition is much faster for solutions of 2 compared with compound 1. For 1, the decomposition likely proceeds to the biquinoxen dipseudobase via an equilibrium, whereas for 2 the decomposition product remains unidentified. The decomposition of 1 in particular was followed using ultrafast transient absorption spectroscopy, investigating the dynamics of the biquinoxen system after photoexcitation. Given the redox activity of biquinoxens, additionally the oxidation of the compounds was investigated using (spectro)electrochemistry.