Synthesis of Isomeric Tb3+-Phthalocyanine Double-Decker Complexes Depending on the Difference in the Direction of Coordination Plane and Their Magnetic Properties

A C_4h symmetrically substituted phthalocyanine, 1,8,15,22-tertrakis(2,4-dimethylpent-3-oxy)phthalocyanine (H₂TdMPPc), was used to synthesize Tb³⁺-phthalocyanine double-decker complexes ([Tb(TdMPPc)₂]s). Because H₂TdMPPc has C_4h symmetry, S,S, R,R, and meso isomers of [Tb(TdMPPc)₂] were obtained depending on the difference in the direction of the coordination plane of two C_4h-type phthalocyanines with respect to a central Tb³⁺ ion. We investigated the physical properties of these [Tb(TdMPPc)₂] isomers, including their single-ion magnetic properties, and found that the spin-reversal energy barrier (U_eff) of the meso isomer was apparently higher than that of the enantiomers. Detailed crystal structural analyses indicated that the meso isomer has a more symmetrical structure than do the enantiomers, thereby suggesting that the higher U_eff of the meso isomer originated from the more highly symmetrical structure.     

Fine Structure and the Huge Zero-Field Splitting in Ni2+ Complexes

We perform a thorough study of the ground state magnetic properties of nickel-based 3d8 complexes. This includes an in-depth analysis of the contribution of the crystal field, spin exchange and spin–orbit interactions to the ground state magnetic properties. Of particular interest to the current investigation are the presence and occurrence of non-trivial zero-field splitting. The study focuses on the cases of Ni2+ ideal octahedral, trigonal bipyramidal, square planar and tetrahedral geometries. We provide results for the complete energy spectrum, the fine structure related to the ground state and the second set of excited states, low-field magnetic susceptibility and magnetization. In addition, we examine the zero-field fine structure in square pyramidal, trigonal pyramidal and trigonal planar complexes. The obtained results unequivocally show that a moderate or highly coordinated 3d8 complex can neither exhibit spin–orbit-driven large and giant magnetic anisotropy nor a huge zero-field splitting. Moreover, in the trigonal bipyramidal coordination, a fine structure associated to the ground state cannot result from the spin-orbit coupling alone.     

SIMPRE1.2: Considering the hyperfine and quadrupolar couplings and the nuclear spin bath decoherence

SIMPRE is a fortran77 code which uses an effective electrostatic model of point charges to predict the magnetic behavior of rare‐earth‐based mononuclear complexes. In this article, we present SIMPRE1.2, which now takes into account two further phenomena. First, SIMPRE now considers the hyperfine and quadrupolar interactions within the rare‐earth ion, resulting in a more complete and realistic set of energy levels and wave functions. Second, and to widen SIMPRE's predictive capabilities regarding potential molecular spin qubits, it now includes a routine that calculates an upper‐bound estimate of the decoherence time considering only the dipolar coupling between the electron spin and the surrounding nuclear spin bath. Additionally, SIMPRE now allows the user to introduce the crystal field parameters manually. Thus, we are able to demonstrate the new features using as examples (i) a Gd‐based mononuclear complex known for its properties both as a single ion magnet and as a coherent qubit and (ii) an Er‐based mononuclear complex. © 2016 Wiley Periodicals, Inc.     

An updated version of the computational package SIMPRE that uses the standard conventions for Stevens crystal field parameters

The crystal field approach used by SIMPRE is analyzed, verifying the exactness of the results concerning energy levels and magnetic properties calculated by the package. To coincide with the prevailing conventions, we reformulate the presentation of the crystal field parameters, so that the results are now, also from a formal point of view, strictly correct. New calculations are presented to test the influence of neglecting the excited J states, a common but critical approximation employed by SIMPRE. For that, we examine the case of Er(trensal) complex (H₃trensal = 2,2′,2″‐tris(salicylideneimino)triethylamine) where the influence of this approximation is found to be minimal. A patched version of the code, SIMPRE 1.1, and an updated version of the user manual are now available. Finally, we comment on “Software package SIMPRE – revisited,” which apparently revisits a software package without inspecting or using the code. © 2014 Wiley Periodicals, Inc.     

Influence of Ag+ on the Magnetic Response of [2.2.2]Paracyclophane: NMR Properties of a Prototypical Organic Host for Cation Binding Based on DFT Calculations

The complexation of metal cations into a host–guest situation is particularly well exemplified by [2.2.2]paracyclophane and Ag^I, which leads to a strong cation–π interaction with a specific face of the host molecule. Through this study we sought a deeper understanding of the effects the metal center has on the NMR spectroscopic properties of the prototypical organic host, generating theoretical reasons for the observed experimental results with an aim to determine the role of the cation–π interaction in a host–guest scenario. From an analysis of certain components of the induced magnetic field and the ¹³C NMR shielding tensor under its own principal axis system (PAS), the local and overall magnetic behavior can be clearly described. Interestingly, the magnetic response of such a complex exhibits a large axis-dependent behavior, which leads to an overall shielding effect for the coordinating carbon atoms and a deshielding effect for the respective uncoordinated counterparts, evidence that complements previous experimental results. This proposed approach can be useful to gain further insight into the local and overall variation of NMR shifts for host–guest pairs involving both inorganic and organic hosts.     

Association Complexes of Calix[6]arenes with Amino Acids Explained by Energy-Partitioning Methods

Intermolecular complexes with calixarenes are intriguing because of multiple possibilities of noncovalent binding for both polar and nonpolar molecules, including docking in the calixarene cavity. In this contribution calix[6]arenes interacting with amino acids are studied with an additional aim to show that tools such as symmetry-adapted perturbation theory (SAPT), functional-group SAPT (F-SAPT), and systematic molecular fragmentation (SMF) methods may provide explanations for different numbers of noncovalent bonds and of their varying strength for various calixarene conformers and guest molecules. The partitioning of the interaction energy provides an easy way to identify hydrogen bonds, including those with unconventional hydrogen acceptors, as well as other noncovalent bonds, and to find repulsive destabilizing interactions between functional groups. Various other features can be explained by energy partitioning, such as the red shift of an IR stretching frequency for some hydroxy groups, which arises from their attraction to the phenyl ring of calixarene. Pairs of hydrogen bonds and other noncovalent bonds of similar magnitude found by F-SAPT explain an increase in the stability of both inclusion and outer complexes.     

An Outline of the Latest Crystallographic Studies on Inhibitor-Enzyme Complexes for the Design and Development of New Therapeutics against Tuberculosis

The elucidation of the structure of enzymes and their complexes with ligands continues to provide invaluable insights for the development of drugs against many diseases, including bacterial infections. After nearly three decades since the World Health Organization’s (WHO) declaration of tuberculosis (TB) as a global health emergency, Mycobacterium tuberculosis (Mtb) continues to claim millions of lives, remaining among the leading causes of death worldwide. In the last years, several efforts have been devoted to shortening and improving treatment outcomes, and to overcoming the increasing resistance phenomenon. The structural elucidation of enzyme-ligand complexes is fundamental to identify hot-spots, define possible interaction sites, and elaborate strategies to develop optimized molecules with high affinity. This review offers a critical and comprehensive overview of the most recent structural information on traditional and emerging mycobacterial enzymatic targets. A selection of more than twenty enzymes is here discussed, with a special emphasis on the analysis of their binding sites, the definition of the structure–activity relationships (SARs) of their inhibitors, and the study of their main intermolecular interactions. This work corroborates the potential of structural studies, substantiating their relevance in future anti-mycobacterial drug discovery and development efforts.     

Magnetic Solid-Phase Extraction Based on Magnetic Sulfonated Reduced Graphene Oxide for HPLC–MS/MS Analysis of Illegal Basic Dyes in Foods

In this study, a magnetic solid-phase extraction (MSPE) method coupled with High-Performance Liquid Chromatography Mass Spectrometry (HPLC–MS/MS) for the determination of illegal basic dyes in food samples was developed and validated. This method was based on Magnetic sulfonated reduced graphene oxide (M-S-RGO), which was sensitive and selective to analytes with structure of multiaromatic rings and negatively charged ions. Several factors affecting MSPE efficiency such as pH and adsorption time were optimized. Under the optimum conditions, the calibration curves exhibited good linearity, ranging from 5 to 60 µg/g with correlation coefficients >0.9950. The limits of detection of 16 basic dyes were in the range of 0.01–0.2 µg/L. The recoveries ranged from 70% to 110% with RSD% < 10%. The results indicate that M-S-RGO is an efficient and selective adsorbent for the extraction and cleanup of basic dyes. Due to the MSPE procedures, matrix effect and interference were eliminated in the analysis of HPLC–MS/MS without the matrix-matched standards. Thus, validation data showed that the proposed MSPE–HPLC–MS/MS method was rapid, efficient, selective, and sensitive for the determination of illegal basic dyes in foods.     

Software package SIMPRE—Revisited

This article elucidates the pitfalls identified in the software package SIMPRE recently developed by Baldoví et al. (J. Comput. Chem. 2013, 34, 1961) for modeling the spectroscopic and magnetic properties of single ion magnets as well as single‐molecule magnets. Analysis of the methodology used therein reveals that the crystal field parameters (CFPs), expressed nominally in the Stevens formalism, exhibit features characteristic for the CFPs expressed in the Wybourne notation. The resemblance of the two types of CFPs introduces a serious confusion that may lead to wrong comparisons of the CFPs taken from various sources. To clarify this confusion, the properties of the CFPs ( , ) associated with the Stevens operators ( X = S , J , or L ), which belong to the class of the tesseral‐tensor operators, are contrasted with those of the CFPs B_kq associated with the Wybourne operators , which belong to the class of the spherical‐tensor operators. Importantly, the confused properties of Stevens and Wybourne operators may bear on reliability of SIMPRE calculations. To consider this question independent calculations are carried out using the complete approach and compared with those of the restricted approach utilized earlier. It appears that the numerical results of the package SIMPRE are formally acceptable, however, the meaning of the CFPs must be properly reformulated. Several other conceptual problems arising from misinterpretations of the crucial notions and the CFP notations identified therein are also discussed and clarified. © 2014 Wiley Periodicals, Inc.     

SIMPRE: A software package to calculate crystal field parameters,energy levels,and magnetic properties on mononuclear lanthanoid complexes based on charge distributions

This work presents a fortran77 code based on an effective electrostatic model of point charges around a rare earth ion. The program calculates the full set of crystal field parameters, energy levels spectrum, and wave functions, as well as the magnetic properties such as the magnetization, the temperature dependence of the magnetic susceptibility, and the Schottky contribution to the specific heat. It is designed for real systems that need not bear ideal symmetry and it is able to determine the easy axis of magnetization. Its systematic application to different coordination environments allows magneto‐structural studies. The package has already been successfully applied to several mononuclear systems with single‐molecule magnetic behavior. The determination of effective point charge parameters in these studies facilitates its application to new systems. In this article, we illustrate its usage with two example studies: (a) an ideal cubic structure coordinating a lanthanoid ion and (b) a system with slow relaxation of the magnetization, LiHo_xY_(1‐x)F₄. © 2013 Wiley Periodicals, Inc.     

轴向卤离子配位调控金属冠醚铽(III)配合物的慢磁弛豫行为

以金属冠醚[15-MC_Ni（II）-5]和卤素离子分别作为Tb（III）在赤道平面和轴向上的配体,成功地组装了三例混合过渡金属-稀土配合物{TbNi₅X₂}（X=F,Cl,Br）,其中TbNi₅F₂为首例双氟端基配位的稀土配合物.X射线单晶衍射分析结果表明,配合物中Tb（III）离子采用具有高轴次对称性的五角双锥（D_5h）配位方式,表明利用金属冠醚策略可以定向构筑含五角双锥稀土基元的混合过渡金属-稀土配合物.交流磁化率的测试结果表明,Tb（III）轴向的电荷分布对配合物的慢磁弛豫行为有着重要的影响.依次削弱轴向配体X^-的电负性,在1 kOe外场下{TbNi₅F₂}和{TbNi₅Cl₂}分别表现出场诱导的单分子磁体和弱的慢磁弛豫行为,而{TbNi₅Br₂}则由于快速的磁量子隧穿而不表现出慢的磁弛豫行为.     

Switching of Single‐Molecule Magnetic Properties of TbIII–Porphyrin Double‐Decker Complexes and Observation of Their Supramolecular Structures on a Carbon Surface

Double‐decker complexes based on single‐molecule magnets (SMMs) are a class of highly promising molecules for applications in molecular spintronics, wherein control of both the ligand oxidative states and the 2D supramolecular structure on carbon materials is of great importance. This study focuses on the synthesis and study of 2,3,7,8,12,13,17,18‐octaethylporphyrin (OEP)–Tb^III double‐decker complexes with different electronic structures comprising protonated, anionic, and radical forms. Magnetic susceptibility measurements revealed that only the anionic and radical forms of the OEP–Tb^III double‐decker complexes exhibited SMM properties. The barrier heights for magnetic moment reversal were estimated to be 207 and 215 cm^?1 for the anionic and radical forms, respectively. Scanning tunneling microscopy (STM) investigations revealed that these OEP–Tb^III complexes form well‐ordered monolayers upon simple dropcasting from dilute dichloromethane solutions. All three complexes form an isomorphic pseudo‐hexagonal 2D pattern, regardless of the differences in the electronic structures of their porphyrin–Tb cores. This finding is of interest for SMM technology as ultrathin films of these materials undergoing chemical transformations will not require any detrimental reorganization. Finally, we demonstrate self‐assembly of the protonated 5,15‐bisdodecylporphyrin (BDP)–Tb^III double‐decker complex as an example of successful supramolecular design to achieve controlled alignment of SMM‐active sites.     

A Statistically Supported Antioxidant Activity DFT Benchmark—The Effects of Hartree–Fock Exchange and Basis Set Selection on Accuracy and Resources Uptake

Polyphenolic compounds are now widely studied using computational chemistry approaches, the most popular of which is Density Functional Theory. To ease this process, it is critical to identify the optimal level of theory in terms of both accuracy and resource usage—a challenge we tackle in this study. Eleven DFT functionals with varied Hartree–Fock exchange values, both global and range-separated hybrids, were combined with 14 differently augmented basis sets to calculate the reactivity indices of caffeic acid, a phenolic acid representative, and compare them to experimental data or a high-level of theory outcome. Aside from the main course, a validation of the widely used Janak’s theorem in the establishment of vertical ionization potential and vertical electron affinity was evaluated. To investigate what influences the values of the properties under consideration, linear regression models were developed and thoroughly discussed. The results were utilized to compute the scores, which let us determine the best and worst combinations and make broad suggestions on the final option. The study demonstrates that M06–2X/6–311G(d,p) is the best fit for such research, and, curiously, it is not necessarily essential to include a diffuse function to produce satisfactory results.     

Weak Coordinating Character of Organosulfonates in Oriented Silica Films: An Efficient Approach for Immobilizing Cationic Metal-Transition Complexes

Iron (II) tris(2,2′-bipyridine) complexes, [Fe(bpy)₃]²⁺, have been synthesized and immobilized in organosulfonate-functionalized nanostructured silica thin films taking advantage of the stabilization of [Fe(H₂O)₆]²⁺ species by hydrogen bonds to the anionic sulfonate moieties grafted to the silica nanopores. In a first step, thiol-based silica films have been electrochemically generated on indium tin oxide (ITO) substrates by co-condensation of 3-mercaptopropyltrimethoxysilane (MPTMS) and tetraethoxysilane (TEOS). Secondly, the thiol function has been modified to sulfonate by chemical oxidation using hydrogen peroxide in acidic medium as an oxidizing agent. The immobilization of [Fe(bpy)₃]²⁺ complexes has been performed in situ in two consecutive steps: (i) impregnation of the sulfonate functionalized silica films in an aqueous solution of iron (II) sulfate heptahydrate; (ii) dipping of the iron-containing mesostructures in a solution of bipyridine ligands in acetonitrile. The in situ formation of the [Fe(bpy)₃]²⁺ complex is evidenced by its characteristic optical absorption spectrum, and elemental composition analysis using X-ray photoelectron spectroscopy. The measured optical and electrochemical properties of immobilized [Fe(bpy)₃]²⁺ complexes are not altered by confinement in the nanostructured silica thin film.     

Perturbing the O–H…O Hydrogen Bond in 1-oxo-3-hydroxy-2-propene

Ab initio MP2/aug’-cc-pVTZ calculations have been carried out to identify and characterize equilibrium structures and transition structures on the 1-oxo-3-hydroxy-2-propene: Lewis acid potential energy surfaces, with the acids LiH, LiF, BeH₂, and BeF₂. Two equilibrium structures, one with the acid interacting with the C=O group and the other with the interaction occurring at the O–H group, exist on all surfaces. These structures are separated by transition structures that present the barriers to the interconversion of the two equilibrium structures. The structures with the acid interacting at the C=O group have the greater binding energies. Since the barriers to convert the structures with interaction occurring at the O–H group are small, only the isomers with interaction occurring at the C=O group could be experimentally observed, even at low temperatures. Charge-transfer energies were computed for equilibrium structures, and EOM-CCSD spin–spin coupling constants ^2hJ(O–O), ^1hJ(H–O), and ¹J(O–H) were computed for equilibrium and transition structures. These coupling constants exhibit a second-order dependence on the corresponding distances, with very high correlation coefficients.     

The Activating Effect of Strong Acid for Pd-Catalyzed Directed C–H Activation by Concerted Metalation-Deprotonation Mechanism

A computational study on the origin of the activating effect for Pd-catalyzed directed C–H activation by the concerted metalation-deprotonation (CMD) mechanism is conducted. DFT calculations indicate that strong acids can make Pd catalysts coordinate with directing groups (DGs) of the substrates more strongly and lower the C–H activation energy barrier. For the CMD mechanism, the electrophilicity of the Pd center and the basicity of the corresponding acid ligand for deprotonating the C–H bond are vital to the overall C–H activation energy barrier. Furthermore, this rule might disclose the role of some additives for C–H activation.     

Granulation of Nickel–Aluminum–Zirconium Complex Hydroxide Using Colloidal Silica for Adsorption of Chromium(VI) Ions from the Liquid Phase

We combined a nickel–aluminum–zirconium complex hydroxide (NAZ) with colloidal silica as a binder to prepare a granulated agent for adsorbing heavy metals from aqueous media. Three samples with different particle diameters were prepared to evaluate the effects on the properties: small (NAZ-S), medium (NAZ-M), and large (NAZ-L). We confirmed the granulation of the prepared samples at a binder content of 25%. NAZ-S had the largest specific surface area and number of hydroxyl groups, followed by NAZ-M and then NAZ-L. Regarding the adsorption capacity, NAZ-S adsorbed the most chromium(VI) ions followed by NAZ-M and then NAZ-L. The binding energy of Cr(2p) at 575–577 eV was detected after adsorption, and the effects of the temperature, contact time, and pH on the adsorption of chromium(VI) ions were evaluated. We identified the following adsorption mechanism: ion exchange with sulfate ions in the interlayer region of the NAZ samples. Finally, the chromium(VI) ions adsorbed by the NAZ samples were easily desorbed using a desorption solution. The results showed that NAZ offers great potential for the removal of chromium(VI) ions from aqueous solutions.     

Modelling the Magnetic Behaviour of Square‐Pyramidal CoII5 Aggregates: Tuning SMM Behaviour through Variations in the Ligand Shell

Three new μ₄‐bridged Co^II₅ clusters with similar core motifs have been synthesised with the use of N‐tert‐butyldiethanolamine (tbdeaH₂) and pivalic acid (piv): [Co^II₅(μ₄‐N₃)(tbdea)₂(μ‐piv)₄(piv)(CH₃CN)₂]?CH₃CN ( 1 ), [Co^II₅(μ₄‐Cl)(Cl)(tbdea)₂(μ‐piv)₄(pivH)₂] ( 2 ) and [Co^II₅(μ₄‐N₃)(Cl)(tbdea)₂(μ‐piv)₄(pivH)₂] ( 3 ). Magnetic measurements were performed for all three compounds. It was found that while the chloride‐bridged cluster 2 does not show an out‐of‐phase signal, which excludes single‐molecule magnet (SMM) behaviour, the azide‐bridged compounds 1 and 3 show out‐of‐phase signals as well as frequency dependence of the ac susceptibility, as expected for SMMs. We confirmed that 1 is a SMM with zero‐field quantum tunnelling of the magnetisation at 1.8 K. Compound 3 is likely a SMM with a blocking temperature well below 1.8 K. We established a physical model to fit the χT versus T and M versus B curves of the three compounds to reproduce the observed SMM trend. The analysis showed that small changes in the ligand shell modify not only the magnitude of exchange constants, but also affect the J and g matrices in a non‐trivial way.