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 Fe10Dy10 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 Fe10Dy10 as a molecular system where τ can be prepared, accumulated and read out under realistic conditions.

The {Fe2Dy2} butterfly systems can show single molecule magnet (SMM) behaviour, the nature of which depends on details of the electronic structure, as previously demonstrated for the [Fe2Dy2(mu(3)-OH)(2)(Me-teaH)(2)(O2CPh)(6)] compound, where the [N,N-bis-(2-hydroxyethyl)-amino]-2-propanol (Me-teaH(3)) ligand is usually used in its racemic form. Here, we describe the consequences for the SMM properties by using enantiopure versions of this ligand and present the first homochiral 3d/4 f SMM, which could only be obtained for the S enantiomer of the ligand for [Fe2Dy2(mu(3)-OH)(2)(Me-teaH)(2)(O2CPh)(6)] since the R enantiomer underwent significant racemisation. To investigate this further, we prepared the [Fe2Dy2(mu(3)-OH)(2)(Me-teaH)(2)(O2CPh)(4)(NO3)(2)] version, which could be obtained as the RS-, R- and S-compounds. Remarkably, the enantiopure versions show enhanced slow relaxation of magnetisation. The use of the enantiomerically pure ligand suppresses QTM, leading to the conclusion that use of enantiopure ligands is a "gamechanger" by breaking the cluster symmetry and altering the intimate details of the coordination cluster's molecular structure.

Cyclic coordination clusters (CCCs) are proving to provide an extra dimension in terms of exotic magnetic behavior as a result of their finite but cyclized chain structures. The Fe18Dy6 CCC is a Single Molecule Magnet with the highest nuclearity among Ln containing clusters. The three isostructural compounds [Fe18Ln6(μ-OH)6(ampd)12(Hampd)12(PhCO2)24](NO3)6·38MeCN for Ln = DyIII (1), LuIII (2), or YIII (3), where H2ampd = 2-amino-2-methyl-1,3-propanediol, are reported. These can be described in terms of the cyclization of six {Fe3Ln(μOH)(ampd)2(Hampd)2(PhCO2)4}+ units with six nitrate counterions to give the neutral cluster. The overall structure consists of two giant Dy3 triangles sandwiching a strongly antiferromagnetically coupled Fe18 ring, leading to a toroidal arrangement of the anisotropy axis of the Dy ions, making this the biggest toroidal arrangement on a molecular level known so far.

161 Dy time-domain synchrotron Mössbauer spectroscopy (SMS), just recently presented as a novel tool to investigate Dy(III)-based single-molecule magnets (SMMs), has now been applied on two polynuclear Dy 6 -based wheel compounds possessing special features of single-molecule toroics (SMTs). The magnitude of the magnetic hyperfine field revealed for the Dy 6 ring system [Dy 6 (teaH) 6 (NO 3 ) 6 ]·8MeOH is with B 0 = 574.3(5) T characteristic for Dy(III) with a 6 H 15/2 ground state. The ligand substituted compound [Dy 6 (Me-teaH) 6 (NO 3 ) 6 ]·6MeCN possesses within the experimental errors the same magnetic hyperfine characteristics ( B 0 = 574.9(5) T). Consequently, the herein studied organic ligand variation has no perceptible influence on the magnetic hyperfine field sensed by the 161 Dy(III) nuclei in these particular homometallic Dy(III) 6 -wheels.

The magnetism and magnetization blocking of a series of [Fe2Dy2(OH)(2)(teaH)(2)(RC6H4COO)(6)] complexes was investigated, in which teaH(3)=triethanolamine and R=meta-CN (1), para-CN (2), meta-CH3 (3), para-NO2 (4) and para-CH3 (5), by combining ab initio calculations and EPR measurements. The results of broken-symmetry DFT calculations show that in all compounds the Fe-Fe exchange interaction is antiferromagnetic and stronger by far than the Fe-Dy and Dy-Dy interactions. As a result, the lowest two exchange doublets probed by EPR spectroscopy mostly originate from the Ising interaction of the dysprosium ions in all compounds. A correct quantitative description of the splitting of these two doublets requires, however, an explicit account of the Fe-Dy and Fe-Fe interactions. Due to the inversion symmetry of the complexes, the doublets under consideration are described by a collinear Ising exchange interaction. This picture is also supported by the EPR spectra, which could be simulated with parameters close to those extracted from the calculations. The magneto-structural analysis shows an increase of the antiferromagnetic Fe-Fe exchange interaction with increasing Fe-O-Fe angle and Fe-Fe distance. For the Dy-Fe interaction, the opposite tendency is observed, that is, a decrease of antiferromagnetic exchange coupling with increasing Dy-O-Fe angle and Dy-Fe distance. The transversal g factors extracted from the ab initio calculations have values in the range of 0.01-0.2, testifying to the lack of high axiality of the ground state of the dysprosium ions. This explains the lack/poor single-molecule magnetic behavior of this series of compounds at the investigated temperatures of a few Kelvin. Due to a very small gap (fractions of a wavenumber) between the ground and first-excited exchange doublet, relaxation takes place by magnetic moment reversal at individual dysprosium sites in the considered temperature domain.

The cyclisation of a short chain into a ring provides fascinating scenarios in terms of transforming a finite array of spins into a quasi-infinite structure. If frustration is present, theory predicts interesting quantum critical points, where the ground state and thus low-temperature properties of a material change drastically upon even a small variation of appropriate external parameters. This can be visualised as achieving a very high and pointed summit where the way down has an infinity of possibilities, which by any parameter change will be rapidly chosen, in order to reach the final ground state. Here we report a mixed 3d/4f cyclic coordination cluster that turns out to be very near or even at such a quantum critical point. It has a ground state spin of S = 60, the largest ever observed for a molecule (120 times that of a single electron). [Fe 10 Gd 10 (Me-tea) 10 (Me-teaH) 10 (NO 3 ) 10 ]·20MeCN forms a nano-torus with alternating gadolinium and iron ions with a nearest neighbour Fe–Gd coupling and a frustrating next-nearest neighbour Fe–Fe coupling. Such a spin arrangement corresponds to a cyclic delta or saw-tooth chain, which can exhibit unusual frustration effects. In the present case, the quantum critical point bears a ‘flatland’ of tens of thousands of energetically degenerate states between which transitions are possible at no energy costs with profound caloric consequences. Entropy-wise the energy flatland translates into the pointed summit overlooking the entropy landscape. Going downhill several target states can be reached depending on the applied physical procedure which offers new prospects for addressability.

The DyIII ions in the dimer [Dy2(H2tea)2(O2CPh)4]·2H2O (1) (H3tea = triethanolamine) have the 9-coordinate monocapped square-antiprismatic ligand field environment. Compound 1 shows slow relaxation of magnetization which is observable only with applied magnetic fields. This is consistent with the idea that low-symmetry ligand fields allow for the quantum tunneling of magnetization. This is reflected by the fact that there are no observable maxima in the out-of-phase ac susceptibility above 1.8 K. The {g}-tensor of the DyIII ions {g x = 11, g y = 8.2, g z = 1} further underlying the reduced uniaxiality in this system was determined in electron paramagnetic resonance (X- and Q-band) studies of 1 at temperatures down to 4 K.

The first use of the cyanoacetate ligand in 3d/4f-metal chemistry leads to {Fe2IIIM4III} (M = Dy, Gd, Y) coordination clusters with a squashed octahedral core structure; the DyIII compound exhibits slow relaxation of the magnetisation.

Magnetic Resonance Imaging is a powerful tool for the investigation of a biofilms' physical structure determining mass transport behavior which is of major importance in biofilm research. The entire biofilm is imaged in situ non-invasively and non-destructively on a meso-scale. In this study, different contrast agents were applied to study the biofilm's properties with the focus on mass transport, which is achieved by varying the contrast agents with respect to their NMR and interaction properties. The spatio-temporal tracking of these cluster, molecular and particulate contrast agents in biofilms was achieved by T1-, T2-weighted and proton density images during short (20h) and long (14 d) term exposures. The best biofilm surface visualization was observed when applying a new high spin coordination cluster (Fe10Gd10) showing a high affinity to the biofilm's surface and a fast immobilization within minutes. Contrarily, the small molecular contrast agents show no immobilization and fully penetrated into the biofilm. A concentration equilibrium was observed which was confirmed in back diffusion experiments. Interactions between larger nanoparticulate contrast agents and the biofilm required hours to achieve immobilization. Thus, the penetration depth into the biofilm is predominantly size-dependent. Here, it is shown that biofilm surface interactions can be observed in situ and spatio-temporarily resolved. The reported methodology demonstrates a new means to explore mass transfer of various substances in biofilms. STATEMENT OF SIGNIFICANCE:In biofilm research, the investigation of the biofilms' physical structure is of high relevance for the understanding of mass transport processes. However, commonly used imaging techniques for biofilm imaging such as CLSM or electron microscopy rarely visualize the real biofilm due to their invasiveness and destructiveness. Magnetic Resonance Imaging (MRI) represents the ideal tool to image the biofilm in situ, non-invasively and non-destructively with a spatial resolution of several 10μm. To gain specific structural and functional information, a variety of MRI contrast agents (molecular and particulate) was applied with different properties for the first time. Results elucidate the interactions between the biofilms' surface and the contrast agents and open a new field for biotechnological applications by functional contrast enhancement.

Two new examples of Dy-6 cyclic coordination clusters have been synthesised in order to discover how the toroidal moment in such a motif can be tuned and optimised.

The synthesis and characterization of three Dy2 compounds, [Dy2(HL1)2(NO3)4] (1), [Dy2(L2)2(NO3)4] (2), and [Dy2(HL3)2(NO3)4] (3), formed using related tripodal ligands with a central tertiary amine bearing picolyl and alkoxy arms, 2-[(2-hydroxy-ethyl)-pyridin-2-ylmethylamino]-ethanol (H2L1), 2-(bis-pyridin-2-ylmethylamino)-ethanol (HL2), and 2-(bis-pyridin-2-ylmethylamino)-propane-1,3-diol (H2L3), are reported. The compounds are rare examples of alkoxide-bridged {Dy2} complexes and display capped square antiprism coordination geometry around each Dy(III) ion. Changes in the ligand field environment around the Dy(III) ions brought about through variations in the ligand donors can be gauged from the magnetic properties, with compounds 1 and 2 showing antiparallel coupling between the Dy(III) ions and 3 showing parallel coupling. Furthermore, slow relaxation of the magnetization typical of SMM behavior could be observed for compounds 2 and 3, suggesting that small variations in the ligand field can have a significant influence on the slow relaxation processes responsible for SMM behavior of Dy(III)-based systems.

In Magnetic Resonance Tomography (MRT) image contrast can be improved by adding paramagnetic relaxation agents such as lanthanide ions. Here we report on the use of highly paramagnetic isostructural Fe(III)/4f coordination clusters with a [Fe10Ln10] core to enhance relaxation. Measurements were performed over the range of (1)H Larmor frequencies of 10 MHz to 1.4 GHz in order to determine the relevant parameters for longitudinal and transverse relaxivities. Variation of the lanthanide ion allows differentiation of relaxation contributions from electronic states and molecular dynamics. We find that the transverse relaxivities increase with field, whereas the longitudinal relaxivities depend on the nature of the lanthanide. In addition, the Gd(III) analogue was selected in particular to test the interaction with tissue observed using MRT. Studies on biofilms used in waste water treatment reveal that the behaviour of the high-spin clusters is different from what is observed for common relaxation agents with respect to the penetration into the biofilms. The Fe10Gd10 cluster adheres to the surface of the biofilm better than the commercial agent Gadovist.

We investigated the electronic properties of the molecular magnetic nanotoruses [Fe III 10 Ln III 10 (Me‐tea) 10 (Me‐teaH) 10 (NO 3 ) 10 ], examining the dependence on the lanthanide (Ln) of both the intra and intermolecular electronic channels. Using femtosecond absorption spectroscopy we show that the intramolecular electronic channels follow a three‐step process, which involves vibrational cooling and crossing to shallow states, followed by recombination. A comparison with the energy gaps showed a relationship between trap efficiency and gaps, indicating that lanthanide ions create trap states to form excitons after photo‐excitation. Using high‐resistance transport measurements and scaling techniques, we investigated the intermolecular transport, demonstrating the dominant role of surface‐limited transport channels and the presence of different types of charge traps. The intermolecular transport properties can be rationalized in terms of a hopping model, and a connection is provided to the far‐IR spectroscopic properties. Comparison between intra and intermolecular processes highlights the role of the excited electronic states and the recombination processes, showing the influence of Kramers parity on the overall mobility.

Paramagnetic relaxation enhancement is often explored in magnetic resonance imaging in terms of contrast agents and in biomolecular nuclear magnetic resonance (NMR) spectroscopy for structure determination. New ultrahigh-spin clusters are investigated with respect to their NMR relaxation properties. As their molecular size and therefore motional correlation times as well as their electronic properties differ significantly from those of conventional contrast agents, questions about a comprehensive characterization arise. The relaxivity was studied by field-dependent longitudinal and transverse NMR relaxometry of aqueous solutions containing Fe(III)(10)Dy(III)(10) ultrahigh-spin clusters (spin ground state 100/2). The high-field limit was extended to 32.9 T by using a 24 MW resistive magnet and an ultrahigh-frequency NMR setup. Interesting relaxation dispersions were observed; the relaxivities increase up to the highest available fields, which indicates a complex interplay of electronic and molecular correlation times.

On page 6280, A. K. Powell, A.-N. Unterreiner, K. Goß, and co-workers report an investigation of both intra- and intermolecular electron transfer processes in a family of nanotoroidal Fe(III)10Ln(III)10 cyclic coordination clusters. Photo-induced intramolecular electron transport proceeds via exciton formation on the oxygen bridges. Intermolecular tranport is rationalized using a hopping model. In both cases, the Kramers parity of the lanthanide ion is important.

The reaction of [Fe3O(O2CPh)(6)(H2O)(3)](O2CPh) with lanthanide/rare earth nitrate salts in the presence of triethanolamine (H(3)tea) in acetonitrile/methanol solution yields a series of compounds with isostructural tetranuclear core motifs [Fe(2)(III)Ln(2)(III)(mu(3)-OH)(2)(teaH)(2)(O2CCPh)(6)]center dot 3MeCN (Ln = Ce (1), Pr (2), Nd (3), Sm (4), Eu (5), Gd (6), Tb (7), Dy (8), Ho (9), Er (10), Tm (11), Yb (12), Y (13)). In all cases the core topology is a defect-dicubane planar or "butterfly" Fe(2)Ln(2) motif. Compounds 1-13 were investigated using a combination of experimental techniques and theoretical studies. Magnetic susceptibility measurements were carried out on all compounds. The magnetic coupling between the two Fe-III centres is antiferromagnetic, with J(FeFe) ca. -6.71(4) cm(-1), while the Fe-Ln couplings are much weaker, e.g. J(FeGd) = 0.18(1) cm(-1). Compounds 6, 7, 8 and 13 were selected for Mossbauer studies in order to investigate the influence of isotropic (Gd-III), highly anisotropic non-Kramers and Kramers (Tb-III and Dy-III) and diamagnetic (Y-III) rare earth ions on the local environment of the Fe-III centres. Compounds 3, 6, 8 and 13 were also studied using X-Band EPR spectroscopy. For 13, with the diamagnetic Y-III ion, this made it possible to obtain the D, E, J(FeFe) and g parameters for the iron centres. It is shown that the low-temperature spectra of compounds 3, 6 and 8 are determined by magnetic properties of rare-earth ions and the dipole-dipole interactions between the Ln(III) ions. The Fe-Ln interactions were confirmed as very weak and dipolar in nature by the temperature dependence of EPR spectra at T > 20 K.

The modulation of the magnetic anisotropy using the electronic features of the ligands was monitored by performing magnetic, spectroscopic and theoretical studies on a series of {Fe2Dy2} coordination clusters.

Five [FeIII mYbIII n] Cyclic Coordination Clusters (CCCs) which show completely different arrangements of their cyclic cores have been synthesised and characterised. These represent five out of seven compounds which were obtained by fine-tuning the reaction conditions (Fe-III-source, Ln(III)-salt, chiral/nonchiral aminoalcohol ligands) used previously to synthesise the non-cyclic [Fe2Yb2(OH)(2)(teaH)(2)(O2CPh) 6] compound 1. Thus the five new CCCs [Fe5Yb3(m(3)-OH)(teaH) 7(O2CPh) 8](CF(3)SO3)$ 10MeCN (m 5; n 2, 2), [Fe4Yb2(m-OH)(m-OMe)(2)(Me-teaH)(4)(O2CPh) 7].3CH3CN (m = 4; n = 2, 3), [Fe3Yb2(m-OH)(Me-teaH) 4(O2CPh) 6].MeCN (m 3; n 2, 4), [Fe4Yb2(Me-tea) 4(Me-teaH) 2(OTs) 2].MeCN$ 3MeOH (m 4; n 2, 5) and [Fe10Yb10(Me-tea) 10(Me-teaH) 10(NO3) 10].21MeCN (m 10; n 10, 6) as well as the binuclear complex [Yb2(tipH(2))(2)(O2CPh)(4)] (7) are reported. The formation of compounds 2, 3 and 4, which were obtained using [Fe3O(O2CCPh) 6(H2O)(3)](+) as the source of FeIII, can be rationalised in terms of cleaving the triangular {(Fe3O)-O-III} starting material into mononuclear and dinuclear FeIII/benzoate species. Furthermore, it was found that for compounds 3-6, the interplay of ligand chirality, hydrogen-bonding interactions and the nature of anionic species present are decisive directional influences on the resulting nature of the cyclic compounds.

A series of [Fe(2)Dy(2)(OH)(2)(teaH)(2)(RC(6)H(4)COO)(6)] compounds has been synthesized and studied using Mössbauer spectroscopy. It is suggested that the local crystal field of the Dy(III) centers and the external magnetic field can control their shape anisotropy and thus the interactions between the dysprosium and iron centers.