Magnetochemistry, Volume 2, Issue 3 (September 2016) – 9 articles

The physical implementation of quantum information processing (QIP) is an emerging field that requires finding a suitable candidate as a quantum bit (qubit), the basic unit for quantum information, which can be organised in a scalable manner to implement quantum gates (QGs) capable of performing computational tasks. Supramolecular chemistry offers a wide range of chemical tools to bring together, with great control, different molecular building blocks in order to grow supramolecular assemblies that have the potential to achieve the current milestones in the field. In this review, we are particularly interested in the latest research developments on the supramolecular chemistry approach to QIP using {Cr₇Ni} wheels as qubits for the physical implementation of QGs. Special emphasis will be given to the unique high degree of chemical tunability of this unique class of heterobimetallic octanuclear rings, which results in an attractive playground to generate aesthetically pleasing supramolecular assemblies of increasing structural complexity and interesting physical properties for quantum computing. Full article

A class of two dinuclear dysprosium based complexes 1 and 2 were synthesized by employing salicyloylhydrazone derived pentadentate ligand (L). Structural analysis reveals that in complex 1, two Dy^III centers are in muffin (C_s) coordination geometry while in 2, one Dy^III center is in bicapped square antiprism (D_4d) and other one is in triangular dodecahedron (D_2d) coordination geometry. AC magnetic susceptibility measurements disclose that complexes 1 and 2 exhibit single-molecule magnet (SMM) behavior, with effective energy barrier of 36.4 and 9.7 K, respectively. The overall studies reveal that small differences in the coordination environment around the Dy^III centers played a significant role in the difference in relaxation dynamics of the complexes. In order to elucidate the role of intermolecular interactions between nearby Dy^III centers in the magnetic relaxation behavior, a diamagnetic isostructural Y^III analog (3) was synthesized and magnetic behavior was examined. Full article

We report on magnetic studies of inhomogeneous commercial and synthesized amorphous carbon (a-C) and a-C doped with sulfur (a-CS) powders which exhibit (i) peculiar magnetic behavior and (ii) traces of two superconducting (SC) phases T_C ~ 33 and at 65 K. (i) The temperature dependence of zero-field-cooled (ZFC) curves measured up to room temperature show well distinguished elusive peaks at around 50–80 K, and their origin is not yet known. These peaks are totally washed-out in the second ZFC sweeps and in the FC branches as well. As a result, in the vicinity of the peaks, the FC curves lie below the ZFC peaks (FC < ZFC), a phenomenon which is rarely observed. These magnetic anomalies are intrinsic properties of a-C and a-CS materials (ii) SC was observed in three different a-C sources: (a) The commercial a-C powder contains 0.21% of sulfur and it is suggested that two different a-CS phases (at 33 and 65 K) are the origin of the two SC states observed. The compositions of these two phases are not yet unknown. The small SC volume fractions of the 33 K phase can be enhanced by a solid reaction with additional sulfur at 250 °C; (b) the synthesized (a-C) powder (obtained from decomposition of sucrose) is not SC. However, when mixed with sulfur and heated at 400 °C under a protective atmosphere, the a-CS powder obtained also show traces of a SC phase at T_C = 42 K; (c) The same occurs in a-C thin films. The as-grown films are not SC but a SC phase at T_C = 34 K emerges after the films were reacted with sulfur at elevated temperatures. It is concluded, therefore, that all SC phases observed are due to different unknown a-CS phases. Since the a-C and a-CS powders possess SC and magnetic states, we believe that these powders resemble the high T_C curates and Fe-As based systems in which the SC and the magnetic states are closely related to each other. Full article

The present paper discusses the use of two information-theoretical quantities—namely, the classical and quantum Fisher information—in the context of molecular magnetism. These functions quantify the suitability of a given observable to the estimation of a physical parameter and provide the highest precision allowed by quantum mechanics in such an estimation process. The quantum Fisher information also quantifies the degree of macroscopicity of a quantum state. As illustrative examples of such applications, we compute the classical and quantum Fisher information of the Fe ${}_4$ molecular nanomagnet, used as a probe of an applied magnetic field or as a platform for generating Schrödinger cat states. Full article

The first complexes with lanthanoid ions and the nitroanilato ligand have been synthesized (nitroanilate dianion = [C₆O₄(NO₂)₂]²⁻ = dianion of the 3,6-dinitro-2,5-dihydroxo-1,4-dibenzoquinone ligand). This family of dimers can be formulated as [Ln₂(C₆O₄(NO₂)₂)₃(H₂O)₁₀]·6H₂O with Ln(III) = Sm (1), Gd (2), Tb (3), Dy (4), Ho (5), and Er (6). The X-ray structure of this family of isostructural complexes shows that they all present a dimeric structure where the Ln³⁺ ions are connected by a bis-bidentate nitroanilato ligand. Each metal completes its nonacoordination environment with a terminal bidentate nitroanilato ligand and five water molecules in a slightly distorted tri-capped trigonal prismatic geometry. The magnetic properties of this family show the expected contributions of the lanthanoid ions without any noticeable magnetic interaction through the nitroanilato ligand. The compounds present luminesce of the nitroanilato ligand superimposed with a weaker emission from the lanthanide ion in compound 5 (Ho). Full article

This work addresses the question of the identification of the excited states that are mainly responsible for the magnitude and nature of the magnetic anisotropy in high-spin mononuclear transition metal complexes. Only few states are actually responsible for the single ion magnetic anisotropy, and these states can be anticipated from rather simple rules. We show that in high-spin complexes atomic selection rules still prevail and that molecular selection rules from the symmetry point group are more selective than those of the double group. The predictive power of these rules is exemplified on a penta-coordinate Co(II) complex investigated with correlated ab initio calculations, including relativistic contributions. The electronic structure of excited states coupled to the ground state through spin-orbit coupling informs us about the nature (either axial or planar) of their contribution to the anisotropy. From this information, it is possible to anticipate the nature and strength of the ligand field and predict the magnetic anisotropy, which may guide the synthesis of improved anisotropic complexes. Such results can also be used to improve the quality of ab initio calculations of the spin Hamiltonian parameters and to reduce the computational cost. Full article

The combined use of di-2-pyridyl ketone, (py)₂CO, and acetates (MeCO₂⁻) in nickel(II) chemistry in H₂O-MeCN under basic conditions (Et₃N) afforded the coordination cluster [Ni₁₁(OH)₆(O₂CMe)₁₂{(py)₂C(OH)(O)}₄(H₂O)₂] (1) in 80% yield, where (py)₂C(OH)(O)⁻ is the monoanion of the gem-diol form of (py)₂CO. The complex contains a novel core topology. The core of 1 comprises a central non-linear {Ni₃(μ₂-OH)₄}²⁺ subunit which is connected to two cubane {Ni₄(OH)(μ₃-OR)₂(μ₃-OR′)}⁴⁺ subunits [RO⁻ = (py)₂C(OH)(O)⁻ and R′O⁻ = MeCO₂⁻] via the OH⁻ groups of the former which become μ₃. The linkage of the Ni₃ subunit to each Ni₄ subunit is completed by two η¹:η¹:μ₂ and one η¹:η³:μ₄ MeCO₂⁻ groups. Peripheral ligation is provided by two terminal monodentate MeCO₂⁻ and two terminal aqua ligands. The (py)₂C(OH)(O)⁻ ligands adopt the η¹:η¹:η³:μ₃ coordination mode. From the twelve MeCO₂⁻ ligands, two are η¹, two η¹:η³:μ₄ and eight adopt the syn, syn η¹:η¹:μ₂ coordination mode; four of the latter bridge Ni^II centers at opposite faces of the cubane subunits. Complex 1 is the largest nickel(II)/(py)₂CO-based ligand coordination cluster discovered to date and has an extremely rare nuclearity (Ni₁₁) in the cluster chemistry of nickel(II). Variable-temperature, solid state dc susceptibility, and variable-field magnetization studies at low temperatures were carried out on complex 1. The study of the data reveals an S = 3 ground state, which has been well rationalized in terms of known magnetostructural correlations and the structural features of 1. An attempt has also been made to interpret the magnetic properties of the undecanuclear cluster in a quantitative manner using four exchange interaction parameters and the obtained J values are discussed. The role of H₂O in the solvent medium that led to 1, and the high nickel(II) and acetate to di-2-pyridyl ketone reaction ratio employed for its preparation, on the nuclearity and identity of the cluster are critically analyzed. Full article

Two novel 1D coordination chains containing the curcuminoid (CCMoid) ligand 9Accm have been characterized: [Co^II(9Accm)₂(4,4´-bpy)]_n (1) and [Ni^II(9Accm)₂(4,4´-bpy)]_n (2). The two compounds were synthesized by solvothermal and microwave (MW) assisted techniques, respectively, and crystals of both systems were directly obtained from the mother solutions. Crystal structures of 1 and 2 prove that both systems are isostructural, with the ligands in a trans configuration. The two chains have been magnetically characterized in solution by paramagnetic ¹H NMR, where 1 displayed typical features from Co^II systems, with spread out signals; meanwhile, 2 showed diamagnetic behaviour. The dissociation of the latest in solution and the stability of the “[Ni(9Accm)₂]” unit were proved by further experiments in C₅D₅N. Additional UV-Vis absorption and fluorescence studies in solution were performed using exclusively 1. In the solid state χ_MT vs. T and M/Nµ_B vs. H/T data were collected and fitted for 1 and 2; both systems display Ising plane anisotropy, with significant D values. System 1 presented slow relaxation of the magnetization, displaying frequency dependence in the in-phase/out-phase ac magnetic susceptibility data, when an external dc field of 0.2 T was applied. Finally, 1 was deposited on a HOPG (highly oriented pyrolytic graphite) substrate by spin-coating and analysed by AFM. Full article

This special issue, entitled “Spin Crossover (SCO) Research”, illustrates the current relevance of a focused topic, which is inturn highly versatile. Indeed, the collection of papers presented constitutes a sampler that shows the topical importance of this area by attracting the interest of many top researchers and how it is approached under a multidisciplinary perspective.[...] Full article