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Brønsted acids, such as phosphoric acids derived from chiral 1,1′‐bi‐2‐naphthol (BINOL), are important catalysts in the formation of carbon–carbon and carbon–heteroatom bonds, for example. The catalytic activity of these Brønsted acids is strongly linked to their acidity, and as such, the evaluation of compounds to determine pKa values provides insight into their catalytic activity. Herein, a 19F{1H} NMR methodology is detailed to determine the pKa of a fluorinated binaphthyl‐derived phosphinic acid, rac‐1, in acetonitrile and in the presence of a fluorinated sulfonamide reference compound (2–4). The approach was tested initially using 2 and 3, with the ΔpKa (0.08) in strong agreement with previously reported values (6.6 for 2 and 6.68/6.73 for 3). Sigmoidal curves of normalised chemical shift change (Δδ) against equivalents of the base phosphazene P1‐tBu added overlapped for 2 and 3, but in the case of rac‐1 and either 2, 3 or 4, there was significant separation. A variety of different approaches for determining the ΔpKa were compared. Values of pKa determined when the normalised Δδ was 90% were optimal for 2 and 3, whereas a normalised Δδ of 75% was optimal for 4, resulting in the pKa of rac‐1 being determined to be 8.47–8.71. [ABSTRACT FROM AUTHOR]

A series of 4d–4f {Ru III2 Dy III2 } and {Ru III2 Gd III2 } 'butterfly' (rhombohedral) complexes have been synthesized and characterized and their magnetic properties investigated. Earlier, we have reported the first 4d/4f SMM – [Ru III2 Dy III2 (OMe)2(O2CPh)4(mdea)2(NO3)2] (1Dy) with a Ueff value of 10.7 cm−1. As the structural distortion around the DyIII centres and the RuIII⋯DyIII exchange interactions are key to enhancing the anisotropy, in this work we have synthesised three more {Ru2Dy2} butterfly complexes where structural alteration around the DyIII centres and alterations to the bridging groups are performed with an aim to improve the magnetic properties. The new complexes reported here are [Ru2Dy2(OMe)2(O2C(4-Me-Ph)4(mdea)2(MeOH)4], 2Dy, [Ru2Dy2(OMe)2(O2C(2-Cl,4,5-F-Ph)4(mdea)2(NO3)2], 3Dy, and an acac derivative [Ru2Dy2(OMe)2(acac)4(NO3)2(edea)2], 4Dy, where acac− = acetylacetonate, edea2− = N-ethyldiethanolamine dianion. Complex 2Dy describes alteration in the DyIII centers, while complexes 3Dy and 4Dy are aimed to alter the RuIII⋯DyIII exchange pathways. To ascertain the 4d–4f exchange, the Gd-analogues of 1Dy and 4Dy were synthesised [Ru2Gd2(OMe)2(O2CPh)4(mdea)2(NO3)2], 1Gd, [Ru2Gd2(OMe)2(acac)4(NO3)2(edea)2], 4Gd. Both ac and dc susceptibility studies were performed on all these complexes, and out-of-phase signals were observed for 3Dy in zero-field while 2Dy and 4Dy show out-of-phase signals in the presence of an applied field. Complex 3Dy reveals a barrier height Ueff of 45 K. To understand the difference in the magnetic dynamic behavior compared to our earlier reported {Ru III2 Dy III2 } analogue, detailed theoretical calculations based on ab initio CASSCF/RASSI-SO calculations have been performed. Calculations reveal that the JRu⋯Dy value varies from −1.8 cm−1 (4Dy) to −2.4 cm−1 (3Dy). These values are also affirmed by DFT calculations performed on the corresponding GdIII analogues. The origin of the largest barrier and observation of slow magnetic relaxation in 3Dy is routed back to the stronger single-ion anisotropy and stronger JRu⋯Dy exchange which quenches the QTM effects more efficiently. This study thus paves the way forward to tune local structure around the LnIII center and the exchange pathway to enhance the SMM characteristics in other {3d–4f}/{4d–4f} SMMs. [ABSTRACT FROM AUTHOR]

We present the syntheses, structures, magnetic data and theoretical analyses for two families of heptanuclear clusters, wherein two staggered dysprosium(III) triangles are linked by various M(III) d‐/p‐block ions. The families differ in the counter‐anion and are of formulae [DyIII6MIII(OH)8(o‐tol)12(MeOH)5(NO3)] ⋅ 4MeOH and [DyIII6MIII(OH)8(o‐tol)12(MeOH)6]Cl ⋅ 6MeOH (M=Cr, Mn, Fe, Co, Al; o‐tol=o‐toluate). We find that variation of the central metal ion M is crucial in tuning the toroidal moments on the triangular units, with diamagnetic M linking ions enhancing the ferrotoroidic coupling. By detailed simulation and analysis of various magnetic measurements, including sub‐kelvin microSquid hysteresis loops, we identified the specific signature of the M linking ions' modulation of toroidal properties, including the mechanism whereby anisotropic, paramagnetic M ions lead to hysteresis profiles with larger remnant magnetisations and broader coercive fields. [ABSTRACT FROM AUTHOR]

The Evans method is routinely utilised to collect paramagnetic susceptibility data via the employment of relevant Nuclear Magnetic Resonance (NMR) methods. As the sample is normally spun, the lack of such a function on benchtop NMR instrumentation required a “static” approach to be employed. We have utilised the static Evans method approach to measure the magnetic susceptibilities, and subsequently the effective magnetic moment, of a series of synthesised transition metal acetylacetonate complexes in order to appraise the d-electron configuration. The obtained values were compared to those obtained using a Guoy balance and theoretical calculations. The collection of T1 relaxation data further exemplifies the effect of the paramagnetic centre in terms of aiding relaxation, and therefore links to Magnetic Resonance Imaging (MRI) contrast agents, thus providing students with real-world perspective of the experiment conducted. [ABSTRACT FROM AUTHOR]

We report four new complexes based on a {LnIII6} wheel structure, three of which possess a net toroidal magnetic moment. The four examples consist of {TbIII6} and {HoIII6} wheels, which are rare examples of non DyIII based complexes possessing a toroidal magnetic ground state, and a {DyIII6} complex which improves its toroidal structure upon lowering the crystallographic symmetry from trigonal (R3‾) to triclinic (P1‾). Notably the toroidal moment is lost for the trigonal {ErIII6} analogue. This suggests the possibility of utilizing the popular concept of oblate and prolate electron density of the ground state MJ levels of lanthanide ions to engineer toroidal moments. High symmetry and dipolar coupling are key criteria for engineering toroidal moments in ring/wheel species, the oblate nature of the electron density of the LnIII ion also play a significant role while lowering of the crystallographic symmetry helps to improve the toroidal properties. [ABSTRACT FROM AUTHOR]

Abstract: The synthesis, magnetic properties, and theoretical studies of three heterometallic {CrIIILnIII6} (Ln=Tb, Ho, Er) complexes, each containing a metal topology consisting of two Ln3 triangles connected via a CrIII linker, are reported. The {CrTb6} and {CrEr6} analogues display slow relaxation of magnetization in a 3000 Oe static magnetic field. Single‐crystal measurements reveal opening up of the hysteresis loop for {CrTb6} and {CrHo6} molecules at low temperatures. Ab initio calculations predict toroidal magnetic moments in the two Ln3 triangles, which are found to couple, stabilizing a con‐rotating ferrotoroidal ground state in Tb and Ho examples and extend the possibility of observing toroidal behaviour in non DyIII complexes for the first time. [ABSTRACT FROM AUTHOR]

A cyclam (1,4,8,11-tetraazacyclotetradecane)-based macrocycle bearing two benzyl and two 2-hydroxy-3,5-di-tert-butylbenzyl pendent arms was synthesized and characterized using spectroscopic techniques and single crystal X-ray diffraction. The macrocycle crystallizes in the triclinic space group P-1, with the asymmetric unit containing one-half of the molecule. The structure is stabilized by hydrogen-bonding which exists between the phenolic protons and the nitrogen atoms of the macrocyclic ring. The presence of this hydrogen bonding is observed in the 1H-NMR due to the deshielded nature of the phenolic OH peak (δ 9.99). Cyclic voltammetry of the ligand revealed a single quasi-reversible peak at -0.58 V (Epc = -0.48 V and Epa = -0.68 V), which is due to the electrochemical oxidation of the phenol to the phenoxyl radical. [ABSTRACT FROM AUTHOR]

Toroidal quantum states are most promising for building quantum computing and information storage devices, as they are insensitive to homogeneous magnetic fields, but interact with charge and spin currents, allowing this moment to be manipulated purely by electrical means. Coupling molecular toroids into larger toroidal moments via ferrotoroidic interactions can be pivotal not only to enhance ground state toroidicity, but also to develop materials displaying ferrotoroidic ordered phases, which sustain linear magneto-electric coupling and multiferroic behavior. However, engineering ferrotoroidic coupling is known to be a challenging task. Here we have isolated a {CrIIIDyIII6} complex that exhibits the much sought-after ferrotoroidic ground state with an enhanced toroidal moment, solely arising from intramolecular dipolar interactions. Moreover, a theoretical analysis of the observed sub-Kelvin zero-field hysteretic spin dynamics of {CrIIIDyIII6} reveals the pivotal role played by ferrotoroidic states in slowing down the magnetic relaxation, in spite of large calculated single-ion quantum tunneling rates. [ABSTRACT FROM AUTHOR]

The syntheses, structures, magnetic and thermodynamic properties of three related triethanolamine-based GdIII complexes are described. The smallest, a dimer ([Gd2]), can be viewed as the subunit from which the two larger complexes, a linear tetramer ([Gd2]2) and a cyclic hexamer ([Gd2]3), are composed by further deprotonation of the triethanolamine ligand. In all cases, nearest neighbour magnetic ions are weakly correlated by antiferromagnetic isotropic exchange, whose strength does not change significantly from one complex to another; J ranging from −0.10 to −0.13 cm−1. Therefore, rather than the strength of the coupling, it is the spin topology that is the dominant factor in determining the differences between the physical properties – specifically, the nuclearity and the transition from open (dimer and tetramer) to cyclic (hexamer) boundary conditions. Indeed the hexanuclear wheel reaches the continuum limit of classical Heisenberg spin chains. In terms of the magnetocaloric properties, the smaller the nuclearity, the larger the magnetic entropy and adiabatic temperature changes. [ABSTRACT FROM AUTHOR]