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Introduction to Single-Molecule Toroics
No full textThis book deals with molecular systems which host toroidal magnetic states, referred in the literature as single-molecule toroics (SMTs). The study of such molecules finds its origin in the broader context of molecular magnetism (MM) whose birth and rich history are detailed in Magneto-Structural Correlation in Exchange Coupled Systems, a book written by Willet, Gatteschi and Kahn in 1985. For further developments in MM, please refer to Kahn’s Molecular Magnetism first published in 1993; for recent developments, to the book Molecular Nanomagnets by Villain, Sessoli and Gatteschi published in 2006; and Introduction to Molecular Magnetism: From Transition Metals to Lanthanides by Benelli and Gatteschi from 2015. In recent decades, molecular-based magnetic materials have attracted a great deal of attention due to their potential applications in magnetic storage devices, molecular spintronics and quantum information technologies based on molecular qubits [1–3]. These magnetic materials are composed of molecules which, like traditional bulk magnets, are able to retain their magnetisation even after the removal of a magnetic field. Early dilution studies of this effect, however, readily demonstrated that molecular magnetism is resultant from the intrinsic magnetic anisotropy of the individual molecules and that, in fact, intermolecular interactions between constituent molecules are not necessary to observe the phenomenon. Considerable growth in molecular magnetism has led to the discovery of single-molecule magnets (SMMs), single-chain magnets (SCMs) and spin crossover (SCO) molecules [1–3]. So too has the SMT subdiscipline grown out of MM, in this case from the study of polynuclear molecular rings comprised of strongly, magnetically anisotropic molecules whose magnetic axes adopt a characteristic, non-collinear vortex configuration [4–7]
High and low spin mononuclear and dinuclear iron(II) complexes of 4-amino and 4-pyrrolyl-3,5-di(2-pyridyl)-4H-1,2,4-triazoles
No full textThe first dinuclear iron(II) complexes of any 4-substituted 3,5-di(2-pyridyl)-4H-1,2,4-triazole ligands, [Fe(II)2(adpt)2(H2O)1.5(CH3CN)2.5](BF4)4 and [Fe(II)2(pldpt)2(H2O)2(CH3CN)2](BF4)4, are presented [where adpt is 4-amino-3,5-di(2-pyridyl)-4H-1,2,4-triazole and pldpt is 4-pyrrolyl-3,5-di(2-pyridyl)-4H-1,2,4-triazole]. Both dinuclear complexes feature doubly triazole bridged iron(II) centers that are found to be [high spin-high spin] at all temperatures, 4-300 K, and to exhibit weak antiferromagnetic coupling. In the analogous monometallic complexes, [Fe(II)(Rdpt)2(X)2](n+), the spin state of the iron(II) center was controlled by appropriate selection of the axial ligands X. Specifically, both of the chloride complexes, [Fe(II)(adpt)2(Cl)2] x 2 MeOH and [Fe(II)(pldpt)2(Cl)2] x 2 MeOH x H2O, were found to be high spin whereas the pyridine adduct [Fe(II)(adpt)2(py)2](BF4)2 was low spin. Attempts to prepare [Fe(II)(pldpt)2(py)2](BF4)2 and the dinuclear analogues [Fe(II)2(Rdpt)2(py)4](BF4)4 failed, illustrating the significant challenges faced in attempts to develop control over the nature of the product obtained from reactions of iron(II) and these bis-bidentate ligands
The role of acid in the formation of hydrogen-bonded networks featuring 4,4'-dicarboxy-2,2'-bipyridine (H2dcbp): Synthesis, structural and magnetic characterisation of {[Cu(H2dcbp)Cl2].H2O}2 and [Cu(H2dcbp)(NO3)2(H2O)]
Full text linkReported herein are the synthesis, structural and magnetic characterisation of two hydrogen-bonded networks featuring the 4,4?-dicarboxy-2,2?-bipyridine (H2dcbp) ligand: {[Cu(H2dcbp)(Cl)2]·H2O}2 1 and [Cu(H2dcbp)(NO3)2(H2O)] 2. Compounds 1 and 2 result from the reaction of CuCl2 and Cu(NO3)2, respectively, with H2dcbp under hydrothermal conditions in the presence of either HCl or HNO3. The acid ensures that H2dcbp remains protonated and provides the anions required for charge balance irrespective of Cu(II) precursor. Within 1 and 2 the H2dcbp ligand performs a dual role of Cu(II) coordination, via the 2,2?-bipyridine moiety, and propagates the formation of chains through hydrogen-bonding involving the peripheral 4,4?-dicarboxylic acid functionalities. Additional hydrogen bonding between the 4,4?-dicarboxylic acid groups, metal bound chloride and nitrate anions, in 1 and 2 respectively, and water molecules generate 3D networks. Variable temperature magnetic susceptibility measurements reveal very weak antiferromagnetic coupling between the Cu(II) centres across the chloride bridges in 1 (J = ?3.02 cm?1)
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Mixed d-f Block Single-Molecule Toroics
No full textSingle Molecule Toroics pp 15–66Cite as
Mixed d-f Block Single-Molecule Toroics
Keith S. Murray, Stuart K. Langley, Kuduva R. Vignesh, Gopalan Rajaraman, Kieran Hymas & Alessandro Soncini
Chapter
First Online: 24 November 2022
3 Accesses
Abstract
In this chapter, we focus on the single-molecule toroidal (SMT) behaviour of a family of “double dysprosium triangle” heptanuclear species which contain a bridging d-block M(III) or a p-block M(III) ion. They are of general formula [MIIIDyIII 6(OH)8(o-tol)12(NO3)(MeOH)5]∙3MeOH, labelled MDy 6, where o-tol = o-toluate. The parent compound has M = Cr, with subsequent family members having M = Mn, Fe, Co and Al, the latter two having diamagnetic M(III) centres. This heptanuclear family could also be made using chloride as counter-anion rather than nitrate, the molecular structures being similar to the nitrates though the unit cells are different. The LnIII ion could also be varied to include Tb, Ho and Er and, thus, allow exploration of SMT behaviour in non-Dy analogues. The syntheses, structures and magnetic and EPR properties are described, starting with the parent CrDy 6. Theoretical calculations are described in detail, with MOLCAS methods employed to determine anisotropy directions, blocking barriers and relaxation effects and a newly developed model used to calculate magnetically coupled toroidal states and the role of these states in spin dynamics. The direct simulation of the micro-Squid magnetic hysteresis loops of all family members is described as well as that of the original Dy 3 material. Toroido-structural correlations are presented with strategies developed to optimize the important ferrotoroidic coupling between Dy3 triangles in these heptanuclear toroidal species. Finally, we give a brief summary of SMT behaviour in ring-shaped 3d-4f toroidal species
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
The ligand, the metal and the 'Holey'-host: Synthesis, structural and magnetic characterisation of Co(ii), Ni(ii) and Mn(ii) metal-organic frameworks incorporating 4,4'-dicarboxy-2,2'-bipyridine
No full textWe report herein the single crystal structures of four metal–organic framework complexes incorporating the 4,4?-dicarboxy-2,2?-bipyridine ligand, H2dcbp: ?-[Co(dcbp)(H2O)2], 1; ?-[Co(dcbp)(H2O)2], 2, [Ni(dcbp)(H2O)2], 3 and {[Mn(dcbp)]·½DEF}, 4 (DEF = diethylformamide). In each complex the ligand is deprotonated giving neutral species with 1 ? 1 stoichiometry that form three-dimensional coordination polymers. Supramolecular isomerism (polymorphism) in 1 and 2 arises from the different ligand connectivity around the octahedral Co(II) centres. The two coordinated water molecules in 1 occupy cis positions, which are trans to the chelating bipyridine nitrogen atoms, leaving the carboxylate oxygen atoms in axial trans positions. In 2 all like donors occupy cis positions. Different modes of carboxylate coordination in 1 and 2 give dissimilar network topologies. A rare example of two interpenetrating 6482-b (quartz-like) chiral networks in 1 results from both dcbp carboxylate groups coordinating in a monodentate fashion to adjacent Co(II) centres, whereas in 2 only one carboxylate group bridges between adjacent Co(II) centres giving rise to a single chiral (10,3)-a net. In 1 and 2 the coordinated water molecules hydrogen bond to the non-coordinated carboxylate oxygen atoms. These interactions give rise to water–carboxylate double helices in 1, and support the coordination network in 2. Strikingly for a pair of dimorphs the crystal densities of 1 and 2 differ by ca. 0.3 g cm?3 (1.654 vs. 1.940 g cm?3, respectively). Compound 3 is isomorphous with 1 and likewise features two chiral interpenetrating nets of quartz topology. In 4, chelating bipyridine nitrogen atoms and four carboxylate oxygen atoms from a total of five adjacent dcbp ligands provide distorted octahedral geometry around Mn(II). The carboxylate groups bridge adjacent Mn(II) centres to produce bis-carboxylato chains which cross-link and generate a 3D network that is perforated with channels. The channels are occupied with disordered DEF molecules. The network topology in 4 is quite different to 1–3 and has a (4.62)(42.6)(43.66.86) Schläfli notation. Magnetic susceptibility studies performed on 1, 2, {[Mn(dcbp)]·½DMF} 5 (DMF = dimethylformamide) and {[Mn(dcbp)]·2H2O} 6 reveal very weak antiferromagnetic coupling between the metal centres in each case
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