Breaking Symmetry Relaxes Structural and Magnetic Restraints, Suppressing QTM in Enantiopure Butterfly Fe Dy SMMs*.

The {Fe Dy } 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 [Fe Dy (μ -OH) (Me-teaH) (O CPh) ] compound, where the [N,N-bis-(2-hydroxyethyl)-amino]-2-propanol (Me-teaH ) 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 [Fe Dy (μ -OH) (Me-teaH) (O CPh) ] since the R enantiomer underwent significant racemisation. To investigate this further, we prepared the [Fe Dy (μ -OH) (Me-teaH) (O CPh) (NO ) ] version, which could be obtained as the RS-, R- and S-compounds.

Magnetization Blocking in Fe Dy Molecular Magnets: Ab Initio Calculations and EPR Spectroscopy.

The magnetism and magnetization blocking of a series of [Fe Dy (OH) (teaH) (RC H COO) ] complexes was investigated, in which teaH =triethanolamine and R=meta-CN (1), para-CN (2), meta-CH  (3), para-NO  (4) and para-CH  (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.

Direct surface visualization of biofilms with high spin coordination clusters using Magnetic Resonance Imaging.

Unlabelled: 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.

Effect of Ligand Field Tuning on the SMM Behavior for Three Related Alkoxide-Bridged Dysprosium Dimers.

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.

Ligand field variations: tuning the toroidal moment of Dy6 rings.

Two new examples of Dy6 cyclic coordination clusters have been synthesised in order to discover how the toroidal moment in such a motif can be tuned and optimised.

Characterisation and application of ultra-high spin clusters as magnetic resonance relaxation agents.

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.

Nuclear magnetic resonance relaxivities: investigations of ultrahigh-spin lanthanide clusters from 10 MHz to 1.4 GHz.

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.

Para versus meta ligand substituents as a means of directing magnetic anisotropy in Fe2Dy2 coordination clusters.

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.

Magnetic anisotropy and exchange coupling in a family of isostructural Fe(III)2Ln(III)2 complexes.

The reaction of [Fe3O(O2CPh)6(H2O)3](O2CPh) with lanthanide/rare earth nitrate salts in the presence of triethanolamine (H3tea) in acetonitrile/methanol solution yields a series of compounds with isostructural tetranuclear core motifs [Fe(III)2Ln(III)2(μ3-OH)2(teaH)2(O2CCPh)6]·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" Fe2Ln2 motif. Compounds 1-13 were investigated using a combination of experimental techniques and theoretical studies.

Effect of ligand substitution on the interaction between anisotropic Dy(III) ions and 57Fe nuclei in Fe2Dy2 coordination clusters.

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.

Heterometallic 20-membered {Fe16Ln4} (Ln = Sm, Eu, Gd, Tb, Dy, Ho) metallo-ring aggregates.

The reaction of triethanolamine (teaH(3)) with [Fe(III)(3)O(O(2)CCH(3))(6)(H(2)O)(3)]Cl·6H(2)O and Ln(NO(3))(3)·6H(2)O in acetonitrile yields [Fe(16)Ln(4)(tea)(8)(teaH)(12)(μ-O(2)CCH(3))(8)](NO(3))(4)·16H(2)O·xMeCN (Ln = Sm (1), Eu (2), Gd (3), Tb (4), Dy (5), Ho (6); x = 10 or 11). These 20-membered metallo-ring complexes are the largest such single-stranded oxygen-bridged rings so far reported. The structure is stabilised by two of the acetate ligands, which form anti,anti-bridges across the centre of the ring, pinching the ring and giving it rigidity.