Density Functional Methodology Research Articles

DFT Struggles to Predict the Energy Landscape for Iron Pyridine Diimine-Catalyzed [2 + 2] Cycloaddition of Alkenes: Insights into the Problem and Alternative Solutions.

In recent years, noninnocent pyridine diimine (PDI) complexes featuring first-row transition metals have emerged as prominent catalysts, demonstrating efficacy in a diverse range of vital organometallic transformations. However, the inherent complexity of the fundamental reactivity paradigm in these systems arises from the presence of a noninnocent ligand and the multispin feasibility of 3d metals. While density functional theory (DFT) has been widely used to unravel mechanistic insights, its limitations as a single-reference method can potentially misrepresent spin-state energetics, compromising our understanding of these intricate systems. In this study, we employ extensive high-level ab initio state averaged-complete active space self-consistent field/N-electron valence state perturbation theory (SA-CASSCF/NEVPT2) calculations in combination with DFT to investigate an iron-PDI-catalyzed [2 + 2] cycloaddition reaction of alkenes. The transformation proceeds through two major steps: oxidative cyclization and reductive elimination. Contrary to the predictions of DFT calculations, which suggest two-state reactivity in the reaction and identify reductive elimination as the turnover-limiting step, SA-CASSCF/NEVPT2-corrected results unequivocally establish a single-state reactivity scenario with oxidative cyclization as the turnover-limiting step. SA-CASSCF/NEVPT2-based insights into electronic ground states and electron distribution elucidate the intriguing interactions between the PDI ligand and the iron center, revealing the highly multiconfigurational nature of these species and providing a precise depiction of metal-ligand cooperativity throughout the transformation. A comparative assessment of several widely recognized DFT functionals against SA-CASSCF/NEVPT2-corrected data indicates that single-point energy calculations using the modern density functional MN15 on TPSSh geometries offer the most reliable density functional methodology, in scenarios where SA-CASSCF/NEVPT2 computational cost is a consideration.

Predicted High-Energy Density MN8 Containing Anionic 18-Crown-6 Ring-Based Polynitrogen Monolayers Acting as Cryptand.

In this study, we investigate the potential of the 18-crown-6-like two-dimensional (2D)-N8 structure to accommodate electrons from metals without compromising its covalent nitrogen network. Employing the crystal structure prediction enhanced by evolutionary algorithm and density functional theory methodology, we successfully predicted the existence of 16 layered M@2D-N8 complexes from a total of 39 MN8 systems investigated at 100 GPa (M = s-block Na-Cs, Be-Ba and d-block Ag, Au, Cd, Hg, Hf, W, and Y). Among those, there are 13 quenchable M@2D-N8 compounds that are dynamically stable at 1 atm. Orbital interactions and bonding analysis show that 2D-N8 presents a flat localized π* band that can accommodate one or two electrons without breaking the 2D covalent nitrogen network. Depending on the metal-to-polynitrogen charge transfer (formally, 1-4 electrons), these N-rich phases are semiconducting or metallic under ambient conditions. Ab initio molecular dynamics simulations show that K(I)@2D-N8 and Ca(II)@2D-N8 are thermally stable up to 600 K, while the Hf(IV)@2D-N8 compound is thermally not viable at 400 K because of the weakening of the N═N bonds due to a strong four-electron reduction. These metal 18-crown-6 ring-based polynitrogen compounds, as expected due to their high nitrogen content (eight nitrogen atoms per metal), could potentially serve as new high-energy density materials.

The Effect of 8,5'-Cyclo 2'-deoxyadenosine on the Activity of 10-23 DNAzyme: Experimental and Theoretical Study.

The in vivo effectiveness of DNAzymes 10-23 (Dz10-23) is limited due to the low concentration of divalent cations. Modifications of the catalytic loop are being sought to increase the activity of Dz10-23 in physiological conditions. We investigated the effect of 5'S or 5'R 5',8-cyclo-2'deoxyadenosine (cdA) on the activity of Dz10-23. The activity of Dz10-23 was measured in a cleavage assay using radiolabeled RNA. The Density Functional Tight Binding methodology with the self-consistent redistribution of Mulliken charge modification was used to explain different activities of DNAzymes. The substitution of 2'-deoxyadenosine with cdA in the catalytic loop decreased the activity of DNAzymes. Inhibition was dependent on the position of cdA and its absolute configuration. The order of activity of DNAzymes was as follows: wt-Dz > ScdA5-Dz ≈ RcdA15-Dz ≈ ScdA15-Dz > RcdA5-Dz. Theoretical studies revealed that the distance between phosphate groups at position 5 in RcdA5-Dz was significantly increased compared to wt-Dz, while the distance between O4 of dT4 and nonbonding oxygen of PO2 attached to 3'O of dG2 was much shorter. The strong inhibitory effect of RcdA5 may result from hampering the flexibility of the catalytic loop (increased rigidity), which is required for the proper positioning of Me2+ and optimal activity.

On the influence of solvent on the stereoselectivity of glycosylation reactions

Methodology development in carbohydrate chemistry entails the stereoselective formation of C–O bonds as a key step in the synthesis of oligo- and polysaccharides. The anomeric selectivity of a glycosylation reaction is affected by a multitude of parameters, such as the nature of the donor and acceptor, activator/promotor system, temperature and solvent. The influence of different solvents on the stereoselective outcome of glycosylation reactions employing thioglucopyranosides as glycosyl donors with a non-participating protecting group at position 2 has been studied. A large change in selectivity as a function of solvent was observed and a correlation between selectivity and the Kamlet-Taft solvent parameter π* was found. Furthermore, molecular modeling using density functional theory methodology was conducted to decipher the role of the solvent and possible reaction pathways were investigated.

Theoretical study of the interaction between the antibiotic linezolid and the active site of the 50S ribosomal subunit of the bacterium Haloarcula marismortui.

First antibiotic in the oxazolidinone class, linezolid fights gram-positive multiresistant bacteria by inhibiting protein synthesis through its interaction with the 50S subunit of the functional bacterial ribosome. For its antimicrobial action, it is necessary that its chiral carbon located in the oxazolidinone ring is in the S-conformation. Computational calculation at time-dependent density functional theory methodology, ultraviolet-visible (UV-Vis), and electronic circular dichroism spectra was obtained for noncomplexed and complexed forms of linezolid to verify the possible chirality of nitrogen atom in the acetamide group of the molecule. The molecular system has two chiral centers. So, there are now four possible configurations: RR, RS, SR, and SS. For a better understanding of the system, the electronic spectra at the PBE0/6-311++G(3df,2p) level of theory were obtained. The complexed form was obtained from the crystallographic data of the ribosome, containing the S-linezolid molecular system. The computational results obtained for the electronic properties are in good agreement with the experimental crystallographic data and available theoretical results.

Structural Analysis and Reactivity Insights of (E)-Bromo-4-((4-((1-(4-chlorophenyl)ethylidene)amino)-5-phenyl-4H-1,2,4-triazol-3-yl)thio)-5-((2-isopropylcyclohexyl)oxy) Furan-2(5H)-one: A Combined Approach Using Single-Crystal X-ray Diffraction, Hirshfeld Surface Analysis, and Conceptual Density Functional Theory

This study presents a comprehensive exploration of the structure–reactivity relationship of (E)-3-bromo-4-((4-((1-(4-chlorophenyl)ethylidene)amino)-5-phenyl-4H-1,2,4-triazol-3-yl)thio)-5-((2-isopropylcyclohexyl)oxy)furan-2(5H)-one. The study embarked on an in-depth investigation into the solid-state crystal structure of this organic compound, employing computational Density Functional Theory (DFT) and related methodologies, which have not extensively been used in the examination of such compounds. A single-crystal X-ray diffraction (SCXRD) analysis was initially performed, supplemented by a Hirshfeld surfaces analysis. This latter approach was instrumental in visualizing and quantifying intermolecular interactions within the crystal structures, offering a detailed representation of the molecule’s shape and properties within its crystalline environment. The concept of energy framework calculations was utilized to understand the varied types of energies contributing to the supramolecular architecture of the molecules within the crystal. The Conceptual DFT (CDFT) was applied to predict global reactivity descriptors and local nucleophilic/electrophilic Parr functions, providing a deeper understanding of the compound’s chemical reactivity properties. The aromatic character and π–π stacking ability were also evaluated with the help of LOLIPOP and ring aromaticity measures. This comprehensive approach not only provides a detailed description of the structure and properties of the investigated compound but also offers valuable insights into the design and development of new materials involving 1,2,4-triazole systems.

DFT Study of the Adsorption and SERS of Pyridine on M10N10 (M, N = Cu, Ag) Tetrahedral Clusters.

This work presents a theoretical detailed analysis of the surface-enhanced Raman spectroscopy (SERS) of the pyridine-M10N10 (M, N = Ag, Cu) tetrahedral (Td) clusters considering two binding positions: vertex (V) and surface (S). In addition to the well-known monometallic Td structure, we added two different bimetallic Ag-Cu compositions, named Td1 and Td2 geometries. Density functional methodology with the use of BP86 and CAM-B3LYP exchange-correlation functionals (XCs) and LANL2DZ pseudopotential has been employed for analyzing the electronic structure and geometries, the chemical static (CHEM), and resonant Raman mechanisms (RR): charge transfer RR-CT and intracluster excitation RR-CR. The static CHEM mechanism shows an increase in the enhancement factors (EFs) of Py-V concerning Py-S positions, which can also be distinguished by the averaged adsorption energies and bond polarizabilities. The static SERS response for Cu-Py-V junction is from 5 to 10 times greater than Ag-Py-V EFs and up to 28 times greater than Py-S complexes. For the static Raman, we found that the analyses of ν8a and ν1 normal modes are related to the EF changes and allow us to distinguish V from S complexes. The TDDFT calculations show striking differences between BP86 and CAM-B3LYP XCs analyzed spectra, and CAM-B3LYP granted a clear distinction between V and S for the location of CT-type transitions. In addition, important differences were obtained from the analysis of the charge transfer excitations between both XCs. Resonant Raman calculations evidenced significant enhancements for RR-CT and RR-CR as compared to the static enhancements, and RR-CT can be distinguished from the RR-CR mechanism, while specific normal modes help to differentiate the vertex from the surface Py-junction. Bimetallic Ag-Cu nanostructures represent promising choices for SERS substrates, showing EFs higher than those of monometallic Ag.

Structural, Electronic, and Mechanical Properties of Zr2SeB and Zr2SeN from First-Principle Investigations.

MAX phases have exhibited diverse physical properties, inspiring their promising applications in several important research fields. The introduction of a chalcogen atom into a phase of MAX has further facilitated the modulation of their physical properties and the extension of MAX family diversity. The physical characteristics of the novel chalcogen-containing MAX 211 phase Zr2SeB and Zr2SeN have been systematically investigated. The present investigation is conducted from a multi-faceted perspective that encompasses the stability, electronic structure, and mechanical properties of the system, via the employment of the first-principles density functional theory methodology. By replacing C with B/N in the chalcogen-containing MAX phase, it has been shown that their corresponding mechanical properties are appropriately tuned, which may offer a way to design novel MAX phase materials with enriched properties. In order to assess the dynamical and mechanical stability of the systems under investigation, a thorough evaluation has been carried out based on the analysis of phonon dispersions and elastic constants conditions. The predicted results reveal a strong interaction between zirconium and boron or nitrogen within the structures of Zr2SeB and Zr2SeN. The calculated band structures and electronic density of states for Zr2SeB and Zr2SeN demonstrate their metallic nature and anisotropic conductivity. The theoretically estimated Pugh and Poisson ratios imply that these phases are characterized by brittleness.

DFT based comparative analysis of the physical properties of some binary transition metal carbides XC (X = Nb, Ta, Ti)

Binary metallic carbides belong to technologically prominent class of compounds. Present work theoretically explores the structural, mechanical, optoelectronic, and some thermal properties of XC (X = Nb, Ta, Ti) compounds using the density functional methodology. A number of the results obtained are novel. The computed elastic constants and moduli disclose that the compounds possess moderate elastic anisotropy and reasonably good machinability (machinability index above 1.45 for all the compounds), mixed bonding characteristics, high Vickers hardness (in the range 19–25 GPa) with very high Debye temperatures (in the range 800–925 K) and brittle characteristics. The elastic/structural stability conditions are fulfilled for all the carbides under study. The Young's modulus and bulk modulus of TiC are lower than those of NbC and TaC. All the XC (X = Nb, Ta, Ti) compounds are hard and suitable for heavy duty structural applications. The electronic band structures show finite density of states at the Fermi level revealing metallic character of the XC (X = Nb, Ta, Ti) compounds. Mixed bonding features are evident from the charge density distribution maps of the XC (X = Nb, Ta, Ti) compounds. The lattice dynamical properties, such as the phonon dispersion curves and phonon density of states for XC (X = Nb, Ta, Ti) are investigated. Absence of negative phonon modes in the Brillouin zone indicates that the carbides under study are dynamically stable. The energy dependent optical constants are nearly isotropic. The optical absorption, reflectivity spectra, and the high value of the low energy index of refraction of XC (X = Nb, Ta, Ti) compounds reveal that they hold promise to be utilized in optoelectronics. The computed melting temperature, lattice thermal conductivity, Debye temperature, and minimum phonon thermal conductivity of the XC (X = Nb, Ta, Ti) compounds exhibit conformity with the computed elastic and bonding characteristics. Extremely high melting point (4399 K) of the compound TaC suggests that it is a very good candidate for applications at high-temperatures.

First-principles insights into sulfur oxides (SO2 and SO3) adsorption and dissociation on layered iron sulfide (FeS) catalyst

The adsorption of sulfur oxides (SOx) represents the fundamental step towards their conversion to lower-risk sulfur-containing species. Herein, we investigate the adsorption and dissociation mechanism of sulfur dioxide (SO2) and sulfur trioxide (SO3) on layered iron sulfide (FeS) nanocatalyst (001), (011), and (111) surfaces using density functional theory methodology. Both SO2 and SO3 exhibit strong reactivity towards the (011) and (111) surfaces, with the most stable geometry for SO2 and SO3 on the (011) surface predicted to be a tridentate η23(S,O,O) and a bidentate η22(O,O) configuration, respectively, whereas on the (111) surface, they are predicted to be coordinated in a monodentate η21(S) and η21(O) geometry, respectively. Significant charge donation from the FeS surface to the SOx species is observed, which resulted in elongation of S−O bond lengths, confirmed by vibrational frequency analyses. Favourable reaction energy and activation barrier is predicted for SO2 dissociation at the (111) surface.

Theoretical exploration of inherent electronic, structural, mechanical, thermoelectric, and thermophysical response of KRu4Z12 (Z = As12, Sb12) filled skutterudite materials.

Using the density functional theory methodology, we have thoroughly examined KRu4As12 and KRu4Sb12 skutterudites, including their structural, electronic, mechanical, transport, and thermodynamic properties. First and foremost, using the Birch-Murnaghan equation of state, the structural stability has been calculated in terms of their total ground state and cohesive energies. With the use of the approximation approaches GGA and GGA + mBJ, the electrical structure and density of the states reveal their metallic nature. This demonstration predicts the dominant ferromagnetic spin configuration of materials by considering their electronic behavior and magnetic interactions. The ductile behavior of these alloys is also addressed by their mechanical qualities, which indicate how they might be used in engineering and industrial settings. Moreover, the semi-classical Boltzmann transport theory has been employed to examine the Seebeck coefficient as well as the electric and thermal conductivities. The general tendency of these compounds demonstrates their various potential uses as electrode materials. The quasi-harmonic Debye approximation is a method used to analyze the stability of a system under high pressures and accounts for the temperature dependency of thermodynamics. It combines the quasi-harmonic approximation, which considers the anharmonicity of vibrations, with the Debye model, which describes the vibrational modes of a solid. This approach allows for a more accurate representation of the system's behavior at different temperatures and pressures. By implementing this approximation, researchers can gain insights into the stability and thermodynamic properties of materials under extreme conditions.

Local Structure in α-BIMEVOXes (ME = Ge, Sn).

The BIMEVOXes are among the best oxide ion conductors at low and intermediate temperatures. Their high conductivity is associated with local defect structure. In this work, the local structures of two BIMEVOX compositions, Bi2V0.9Ge0.1O5.45 and Bi2V0.95Sn0.05O5.475, are examined using total neutron and X-ray scattering methods, with both compositions exhibiting the ordered α-phase at 25 °C and the disordered γ-phase at 700 °C. While the diffraction data for the α-phase do not allow for the polar (C2) and nonpolar (C2/m) structures to be readily distinguished, measurements of dielectric permittivity suggest the α-phase is weakly ferroelectric in character, consistent with calculations of spontaneous polarization based on a combination of density functional calculations and machine learning methodology. Reverse Monte Carlo (RMC) analysis of total scattering data reveals Ge preferentially adopts tetrahedral geometry at both temperatures, while Sn is found to predominantly adopt octahedral coordination in the α-phase and tetrahedral coordination in the γ-phase. In all cases, V polyhedra are found to consist of tetrahedral, pentacoordinate, and octahedral geometries, as also predicted by the crystallographic analysis and confirmed by 51V solid state NMR spectroscopy. Although similar long-range structures are observed at room temperature, the oxide ion vacancy distributions were found to be quite different between the two studied compositions, with a nonrandom deficiency in vacancy pairs in the second-nearest shell along the ⟨100⟩ tetragonal direction for BIGEVOX10, compared with a long-distance (>8.0 Å) ordering of equatorial vacancies for BISNVOX05. This is attributed to the differences in the preferred coordination geometries of the substituent cations in the two systems. Impedance spectroscopy measurements reveal both compositions show high conductivity in the order of 10-1 S cm-1 at 600 °C.

Synthesis of Quinoline‐Pyrene Derivatives and Theoretical Investigation of Their Fluorescence and Electronic Properties

AbstractSynthesis of novel fluorescent quinoline‐pyrene conjugates is described. The key intermediates 2‐substituted 8‐propynyloxy quinoline and azidomethyl pyrene were connected with triazole bridge by 1,3‐dipolar alkyne‐azide cycloaddition reaction. Density functional theory methodology with B3LYP/6‐311++G(d,p) basis set was applied computationally to gather information about the structural and electronic properties of the quinoline‐pyrene compounds. In addition, the metal coordination properties of the triazole bridged molecules were investigated through interactions with several cations. The effect of metal coordination on the stability of the complexes have also been discussed through computations on chelatoaromaticity.

Evaluation of Crocin as green corrosion inhibitor for aluminum in NaCl solution

The role of Crocin, which is a natural organic substance from the Greek plant Crocus sativus, is investigated as a green corrosion inhibitor for the AA 1050 commercial aluminum alloy in 0.01 M sodium chloride solution. Its action was assessed by Linear and Tafel Polarization, as well as by mass loss measurements and confirmed by observation and analysis of the surface morphology of the specimens by Scanning Electron Microscopy. Corrosion inhibition efficiency of Crocin improves with concentration and at 1.25 mM was estimated in the range of 90-95%, which indicates the formation of an adsorbed layer that isolates and protects the surface. Experimental results showed that Crocin acts as a mixed-type inhibitor with predominantly anodic effectiveness, also retarding pitting corrosion process. The inhibitive action of Crocin was explained by theoretical calculations employing density functional theory, semiempirical PM6 and molecular mechanics methodologies, showing good agreement with experimental results. The reactivity of Crocin is attributed to chemisorption on the Al2O3 surface through its vicinal hydroxyls of the sugar moiety. This process is assisted by the π-conjugated system of the polyene chain together with the extended electron delocalization over the oxygen atoms of the esterified carboxyl groups, as well as by the intense electrostatic potential regions located on the sugar moiety of the Crocin molecule.

A DFT study of the adsorption and surface enhanced Raman spectroscopy of pyridine on Au20, Ag20, and bimetallic Ag8Au12 clusters

This work presents a theoretical detailed analysis of the surface-enhanced Raman spectroscopy (SERS) of the pyridine – Au20, pyridine – Ag20, and pyridine – Ag8Au12 model systems considering different symmetries of the clusters. In addition to the well-known Td geometry of this twenty atoms metal cluster, low energy structures have been analyzed (Cs and Cb). Density functional methodology with the use of PBE, PBE0, and scalar – relativistic pseudopotentials have been employed for the electronic structure calculations of these molecule–metal complexes. The projected state density analysis has shown a different behavior that distinguishes vertex (V) pyridine position from surface (S) adsorption site on both Td and Cs geometries. Adsorption of pyridine on the V position is always energetically favored as compared to S substitution. The chemical mechanism of enhancement has been analyzed through charge-transfer in the adsorption of pyridine to the metal cluster and charge-transfer excitations between both moieties. There is a close relationship between the amount of charge transfer from the pyridine molecule to the cluster and the SERS enhancements. The highest enhancement factors were obtained precisely for the Au20 cubic structure, where 102 order enhancements were calculated. A back – donation of charge triggers the highest enhancements obtained for this case. The bimetallic case also shows an improvement in the enhancements as compared to Td and Cs geometries. In addition, a direct relationship between resonant charge – transfer excitations in the 500–530 nm range and SERS enhancement have been obtained. Cs and cubic clusters show higher chemical enhancements than Td structures, thus representing a promise as SERS substrates.

Unique O═N...O Pnicogen Interactions in Nitromethane Dimers: Evidence Using Matrix Isolation Infrared Spectroscopy and Computational Methodology.

Geometries of nitromethane homodimers have been revisited using ab initio and density functional methodologies, following their formation within cryogenic matrices, confirmed using infrared spectroscopy. In contrast to the claim that the intermolecular interactions are due to dispersion forces or very weak hydrogen bonds, in the present work, concrete evidence for the prevalence of O═N...O pnicogen bonding has been presented. The pnicogen bonds have been found to be primarily responsible for the characteristic geometry of a homodimer. The formation of a nitromethane dimer with pnicogen bonding stabilization is evidenced using matrix isolation infrared spectroscopy with Ne and Ar matrices and computations. The interactions within homodimers have been characterized using quantum theory of atoms in molecules, natural bond orbital, energy decomposition, electrostatic potential mapping, and noncovalent interaction analyses. The larger intermolecular separations in liquid nitromethane indicated by previous molecular dynamics-based studies alongside the supposed invariance of infrared spectra in the gas phase and liquid phase could have led to the assumption of a lack of intermolecular interactions. However, the prevalence of hydrogen and pnicogen bonds across these larger than usual separations is affirmed by the geometries presented here.

Selective detection of manganese(II) ions based on the fluorescence turn-on response via histidine functionalized carbon quantum dots

Herein, water-soluble emissive carbon quantum dots (His-CQDs) were synthesized from pyrolysis of sodium citrate in the presence of histidine under hydrothermal conditions. The as-synthesized His-CQDs were characterized using Fourier transform infrared (FT–IR), fluorescence spectroscopy, dynamic light scattering (DLS), and transmission electron microscopy (TEM) techniques. The obtained His-CQDs display a strong emission peak at 534 nm when excited at 476 nm with a high quantum yield (61.8 %). The as-synthesized His-CQDs were applied as a new platform for highly selective determination of Mn(II) based on the fluorescence “turn-on” response with a limit of detection of 1.85 µg L−1 (at 3σ) and a linear range of 3.50–35.5 µg L−1 in aqueous solution. The sensing mechanism of the His-CQDs probe for the detection of Mn(II) was studied via density functional theory (DFT), FT-IR, and EDTA complexation methodology. In addition, His-CQDs were successfully applied to determine the accurate amounts of Mn(II) in whole blood control material. More importantly, the integrating such an efficient sensor with point-of-care technology can enable portable, easy-to-use, and rapid sensing systems for better biological and clinical applications.

Room temperature plasticity of zirconia-yttria-titania ceramics: Experimental indications and structural modelling

Yttria-stabilized tetragonal zirconia (Y-TZP) ceramics have excellent mechanical properties. However, such materials cannot undergo plastic deformation at room temperature due to their high hardness and brittleness values, hindering machinability. To overcome these limitations, we propose a zirconia-yttria-titania ceramics, based on zirconia containing 3mol% yttria and up to 15mol% titania. The zirconia-yttria-titania powders were synthesized by co-precipitation method, uniaxially pressed and sintered at 1400?C/5 h. Sample characterizations were carried out by X-ray diffraction, scanning electron microscopy and mechanical properties through Vickers hardness and toughness measurements. Compared to the Y-TZP ceramics, the yttria stabilised tetragonal zirconia ceramics co-doped with 10mol%Ti showed noticeable increase of tetragonality parameter, higher toughness and lower hardness values, indicating plasticity at room temperature. Furthermore, the atomistic simulation by Density Functional Theory methodology suggests the occurrence of spatial arrangement of the atoms, explaining the proposed plasticity.

A nonsymmetric Dy2 single-molecule magnet with two relaxation processes triggered by an external magnetic field: a theoretical and integrated EPR study of the role of magnetic-site dilution.

The 1 : 2 reaction between Dy(O2CMe)3·4H2O and 1-acetyl-2-napthol (LH) in MeOH has provided access to the complex [Dy2L6(MeOH)]·MeOH (1·MeOH) in a good yield. The structures of the isomorphous complex 1·MeOH and its doped diamagnetic yttrium analogue [Dy0.14Y1.86L6(MeOH)]·MeOH (Dy@Y2) have been determined by single-crystal X-ray crystallography and characterized based on elemental analyses, IR spectra, and powder X-ray patterns. Combined dc and ac magnetic susceptibility and the magnetization data for 1 suggest that this complex shows slow magnetic relaxation. Under a 0 Oe dc field, a single relaxation mechanism is seen while two magnetization relaxation processes are evident under a 1500 G external magnetic field. The fit to the Arrhenius law has been performed using the 1.8-10 K ac data, affording an effective barrier for the magnetization reversal of 13 K and 7 K under the external dc field. Theoretical studies have been performed using ab initio and density functional methodologies to understand the electronic structure and the magnetic relaxation dynamics resulting from the single DyIII ion as well as from the dinuclear exchange-coupled states. Rich powder EPR spectra at the X-band and Q-band were obtained from Dy@Y2, as well as from the 1·MeOH dimer, while simulation studies revealed the ferromagnetic nature of the interaction between the DyIII ions in accordance with theoretical studies.

Structural and Energetic Properties of Amino Acids and Peptides Benchmarked by Accurate Theoretical and Experimental Data.

Structural, energetic, and spectroscopic data derived in this work aim at the setup of an "experimentally validated" database for amino acids and polypeptides conformers. First, the "cheap" composite scheme (ChS, CCSD(T)/(CBS+CV)MP2) is tested for evaluation of conformational energies of all eight stable conformers of glycine, by comparing to the more accurate CCSD(T)/CBS+CV computations (Phys. Chem. Chem. Phys. 2013, 15, 10094-10111 and J Mol. Model. 2020, 26, 129). The recently proposed jun-ChS (J. Chem. Theory and Comput. 2020, 16, 988-1006), employing the jun-cc-pVnZ basis set family for CCSD(T) computations and CBS extrapolation, yields conformational energies accurate to 0.2 kJ·mol-1, at reduced computational cost with respect to aug-ChS employing aug-cc-pVnZ basis sets. The jun-ChS composite scheme is further applied to derive conformational energies for three dipeptide analogues Ac-Gly-NH2, Ac-Ala-NH2, and Gly-Gly. Finally, dipeptide conformational energies and semiexperimental equilibrium rotational constants along with the CCSD(T)/(CBS+CV)MP2 structural parameters (J. Phys. Chem. Lett. 2014, 5, 534-540) stand as the reference for benchmarking of selected density functional methodologies. The double-hybrid functionals B2-PLYP-D3(BJ) and DSD-PBEP86, perform best for structural and energetic characterization of all dipeptide analogues. From hybrid functionals CAM-B3LYP-D3(BJ) and ωB97X-D3(BJ) represent promising methods applicable for larger peptide-based systems for which computations with double-hybrid functionals are not feasible.