Open-shell Electronic Configurations Research Articles

Expanding the Landscape of Phosphorous-Based Open Shell Species: Stable Mono-, Di-, and Trianionic Radicals Based on a Contorted Triphosphaalkene.

The stepwise reduction of the highly contorted truxene-based triphosphaalkene 1 using KC8 led to the isolation of mono-, di-and tri-anionic species. The solid-state molecular structures of mono- and diradical anionic species were elucidated by single crystal X-ray diffractions, revealing elongated P-C bonds and a pronounced "indene" aromatization compared to the parent system. All three radical species displayed distinct Electron Paramagnetic Resonance (EPR) spectra, providing compelling evidence for the open-shell electronic configuration of both the diradical and triradical species-an observation unprecedented in any previously reported phosphorous-based anionic polyradicals. Mulliken spin density calculations revealed a dominant localization of radical spin on a single phosphorous atom in the monoanion. In the dianion, spin localization is observed on two phosphorous atoms (~34% each), with a minor contribution from the third phosphorous (0.13%), while the trianion demonstrates a uniform distribution of spin density (~30%) across each phosphorous atom.

Electronic Structures and Spectra of Donor-Acceptor Conjugated Oligomers.

Narrow band gap donor-acceptor conjugated polymers present excellent paradigms in photonics and optoelectronics due to their chemical tunability, correlated electronic structures, and tunable open-shell electronic configurations. However, rational design for enhancing the properties of these molecular systems remains challenging. In this study, we employed density functional theory (DFT) calculations to investigate prototypical narrow band gap donor-acceptor conjugated oligomers, consisting of alternating cyclopentadithiophene (CPDT) donors paired with benzothiadiazole (BT), benzoselenadiazole (BSe), benzobisthiadiazole (BBT), and thiadiazoloquinoxaline (TQ) acceptors. Analyses of structures, singlet-triplet gaps, and absorption spectra of oligomers with up to ten repeat units have shown that when incorporating the BT, BSe, and TQ acceptors, the backbone curvature resulted in spiral structures that were energetically favored over their linear counterparts, causing differences in the calculated circular dichroism spectra. Oligomers with BBT-based acceptors preferred, however, a linear geometry, consistent with an open-shell electronic structure. Calculated singlet-triplet splittings demonstrated the importance of long chains and specific structures for consistency with the experiment, while effects of the solvent were also quantified. Based on the predicted low-energy conformations, one-photon absorption spectra for the considered oligomers have shown that using the Tamm-Dancoff approximation within time-dependent DFT for the large systems offers good agreement with the first absorption maxima in measured experimental spectra, thus validating the method for large donor-acceptor oligomers. Natural transition orbital analyses provided insights into the excited-state characteristics. Two-photon absorption maxima were accurately predicted, but the cross-sections were overestimated or underestimated, as dependent on the level of theory employed, to be addressed in future work.

Exploring New Carbon Allotropes and Nanographenes on Surfaces

The quest for planar sp2-hybridized carbon allotropes other than graphene has stimulated substantial research efforts because of their predicted unique mechanical, electronic, and transport properties. However, the syntheses of these nonbenzenoid networks remain challenging due to the lack of reliable protocols for generating nonhexagonal rings. We have developed various on-surface synthesis strategies by which straight polymer chains are linked to form the nonbenzenoid carbon networks. In this way, we synthesized biphenylene network, a new carbon allotrope with 4-6-8-membered rings, which is metallic already at very small dimensions. Similarly, we generated phagraphene nanoribbons, which are based on 5-6-7-membered rings.Acenes are another interesting class of carbon materials that have fascinated chemists and physicists due to their potential for use in organic electronic applications. We show the synthesis of tridecacene (13ac) and pentadecacene (15ac), the longest acenes known to date, via multistep single-molecule manipulation of suitable precursor molecules on Au(111). We find antiferromagnetic open-shell ground state electron configurations for both acenes. 15ac shows a low-bias spin-excitation feature, indicating a singlet-triplet gap of around 124 meV. Investigation of 15ac complexes with up to 6 gold atoms suggest considerable multiradical contributions to the electronic ground state of 15ac.Altering the electronic and magnetic properties of carbon-based nanomaterials can also be achieved by doping with heteroatoms. We present an access to a variety of nitrogen-containing 0D and 1D carbon nanostructures including planar and curved cycloarenes with different cavities as well as N-doped graphene nanoribbons.

Dual-quartet phosphorescent emission in the open-shell M1Ag13 (M = Pt, Pd) nanoclusters

Dual emission (DE) in nanoclusters (NCs) is considerably significant in the research and application of ratiometric sensing, bioimaging, and novel optoelectronic devices. Exploring the DE mechanism in open-shell NCs with doublet or quartet emissions remains challenging because synthesizing open-shell NCs is difficult due to their inherent instability. Here, we synthesize two dual-emissive M1Ag13(PFBT)6(TPP)7 (M = Pt, Pd; PFBT = pentafluorobenzenethiol; TPP = triphenylphosphine) NCs with a 7-electron open-shell configuration to reveal the DE mechanism. Both NCs comprise a crown-like M1Ag11 kernel with Pt or Pd in the center surrounded by five PPh3 ligands and two Ag(SR)3(PPh3) motifs. The combined experimental and theoretical studies revealed the origin of DE in Pt1Ag13 and Pd1Ag13. Specifically, the high-energy visible emission and the low-energy near-infrared emission arise from two distinct quartet excited states: the core-shell charge transfer and core-based states, respectively. Moreover, PFBT ligands are found to play an important role in the existence of DE, as its low-lying π* levels result in energetically accessible core-shell transitions. This novel report on the dual-quartet phosphorescent emission in NCs with an open-shell electronic configuration advances insights into the origin of dual-emissive NCs and promotes their potential application in magnetoluminescence and novel optoelectronic devices.

Synthesis of Tridecacene by Multistep Single-Molecule Manipulation.

Acenes represent a unique class of polycyclic aromatic hydrocarbons that have fascinated chemists and physicists due to their exceptional potential for use in organic electronics. While recent advances in on-surface synthesis have resulted in higher acenes up to dodecacene, a comprehensive understanding of their fundamental properties necessitates their expansion toward even longer homologues. Here, we demonstrate the on-surface synthesis of tridecacene via atom-manipulation-induced conformational preparation and dissociation of a trietheno-bridged precursor on a Au(111) surface. The generated tridecacene has been investigated by scanning tunneling microscopy and spectroscopy (STM/STS), combined with first-principles calculations. We observe that the STS transport gap (1.09 eV) shrinks again following the gap reopening of dodecacene (1.4 eV). Spin-polarized density functional theory calculations confirm an antiferromagnetic open-shell ground-state electronic configuration for tridecacene in the gas phase. Interestingly, tridecacene's open-shell character is significantly reduced upon interaction with the Au(111) surface despite being only physisorbed. The interaction with the surface leads to a lowering of the magnetization of tridecacene, a reduced gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO), compared to the gas phase, and a reduced relative energy to the nonmagnetic state, making it nearly isoenergetic. These observations show qualitatively that the influence of the Au(111) substrate on the properties of long acenes is significant, which is important for interpreting the measured STS transport gaps. Our work contributes to a fundamental understanding of the electronic properties of long acenes, confirming a nonmonotonous length-dependent HOMO-LUMO gap, and to the development of multistep tip-assisted synthesis of elusive compounds.

Molecular adsorption on coinage metal subnanoclusters: A DFT+D3 investigation.

Gold and silver subnanoclusters with few atoms are prominent candidates for catalysis-related applications, primarily because of the large fraction of lower-coordinated atoms exposed and ready to interact with external chemical species. However, an in-depth energetic analysis is necessary to characterize the relevant terms within the molecular adsorption process that can frame the interactions within the Sabatier principle. Herein, we investigate the interaction between Agn and Aun subnanoclusters (clu, n=2-7) and N2 , NO, CO, and O2 molecules, using scalar-relativistic density functional theory calculations within van der Waals D3 corrections. The onefold top site is preferred for all chemisorption cases, with a predominance of linear (≈180°) and bent (≈120°) molecular geometries. A larger magnitude of adsorption energy is correlated with smaller distances between molecules and clusters and with the weakening of the adsorbates bond strength represented by the increase of the equilibrium distances and decrease of molecular stretching frequencies. From the energetic decomposition, the interaction energy term was established as an excellent descriptor to classify subnanoclusters in the adsorption/desorption process concomitant with the Sabatier principle. The limiting cases: (i) weak molecular adsorption on the subnanoclusters, which may compromise the reaction activation, where an interaction energy magnitude close to 0eV is observed (e.g., physisorption in N2 /Ag6 ); and (ii) strong molecular interactions with the subnanoclusters, given the interaction energy magnitude is larger than at least one of the individual fragment binding energies (e.g., strong chemisorption in CO/Au4 and NO/Au4 ), conferring a decrease in the desorption rate and an increase in the possible poisoning rate. However, the intermediate cases are promising by involving interaction energy magnitudes between zero and fragment binding energies. Following the molecular closed-shell (open-shell) electronic configuration, we find a predominant electrostatic (covalent) nature of the physical interactions for N2 ⋯clu and CO ⋯clu (O2 ⋯clu and NO⋯clu), except in the physisorption case (N2 /Ag6 ) where dispersive interaction is dominant. Our results clarify questions about the molecular adsorption on subnanoclusters as a relevant mechanistic step present in nanocatalytic reactions.

Capturing the Long-Sought Dy@C2v(5)-C80 via Benzyl Radical Stabilization.

Endohedral metallofullerenes (EMFs) are one type of intriguing metal/carbon hybrid molecule with the molecule configuration of sphere cavity-encapsulating metal ions/metal clusters due to their unique physicochemical properties and corresponding application in the fields of biological materials, single molecule magnet materials and energy conversion materials. Although the EMF family is growing, and versatile EMFs have been successfully synthesized and confirmed using crystal structures, some expected EMF members have not been observed using the conventional fullerene separation and purify strategy. These missing EMFs raise an interesting scientific issue as to whether this is due to the difficulty in separating them from the in situ formed carbon soot. Herein, we successfully captured a long-sought dysprosium-based EMF bearing a C2v(5)-C80 cage (Dy@C2v(5)-C80) in the form of Dy@C2v(5)-C80(CH2Ph)(Ph = −C6H5) from carbon soot containing versatile EMFs using simple benzyl radical functionalization and unambiguously confirmed the molecule structure using single crystal X-ray diffraction characterization. Meanwhile, the crystal structure of Dy@C2v(5)-C80(CH2Ph) showed that a single benzyl group was grafted onto the (5,6,6)-carbon, suggesting the open-shell electronic configuration of Dy@C2v(5)-C80. The theoretical calculations unveiled that the benzyl radical addition enables the modulation of the electronic configuration of Dy@C2v(5)-C80 and the corresponding stabilization of Dy@C2v(5)-C80 in conventional organic solvents. This facile stabilization strategy via benzyl radical addition exhibits the considerable capability to capture these missing EMFs, with the benefit of enriching the endohedral fullerene family.

Electronic and Spin-State Effects on Dinitrogen Splitting to Nitrides in a Rhenium Pincer System.

Bimetallic nitrogen (N2) splitting to form metal nitrides is an attractive method for N2 fixation. Although a growing number of pincer-supported systems can bind and split N2, the precise relationship between the ligand properties and N2 binding/splitting remains elusive. Here we report the first example of an N2-bridged rhenium(III) complex, [(trans-P2tBuPyrr)ReCl2]2(μ-η1:η1-N2) (P2tBuPyrr = [2,5-(CH2PtBu2)2C4H2N]-). In this case, N2 binding occurs at a higher oxidation level than that in other reported pincer analogues. Analysis of the electronic structure through computational studies shows that the weakly π-donor pincer ligand stabilizes an open-shell electronic configuration that leads to enhanced binding of N2 in the bridged complex. Utilizing SQUID magnetometry, we demonstrate a singlet ground state for this Re-N-N-Re complex, and we offer tentative explanations for antiferromagnetic coupling of the two local S = 1 sites. Reduction and subsequent heating of the rhenium(III)-dinitrogen complex leads to chloride loss and cleavage of the N-N bond with isolation of the terminal rhenium(V) nitride complex (P2tBuPyrr)ReNCl.

Stabilizing a three-center single-electron metal-metal bond in a fullerene cage.

Trimetallic carbide clusterfullerenes (TCCFs) encapsulating a quinary M3C2 cluster represent a special family of endohedral fullerenes with an open-shell electronic configuration. Herein, a novel TCCF based on a medium-sized rare earth metal, dysprosium (Dy), is synthesized for the first time. The molecular structure of Dy3C2@Ih(7)-C80 determined by single crystal X-ray diffraction shows that the encapsulated Dy3C2 cluster adopts a bat ray configuration, in which the acetylide unit C2 is elevated above the Dy3 plane by ∼1.66 Å, while Dy–Dy distances are ∼3.4 Å. DFT computational analysis of the electronic structure reveals that the endohedral cluster has an unusual formal charge distribution of (Dy3)8+(C2)2−@C806− and features an unprecedented three-center single-electron Dy–Dy–Dy bond, which has never been reported for lanthanide compounds. Moreover, this electronic structure is different from that of the analogous Sc3C2@Ih(7)-C80 with a (Sc3)9+(C2)3−@C806− charge distribution and no metal–metal bonding.

Interaction of 1,1-Diamino-2,2-Dinitroethylene with Aluminum and Gallium Admixture - DFT Treatment

Interaction of 1,1-diamino-2,2-dinitroethylene with nAl+mGa (n,m:1,2) admixture has been investigated within the constraints of density functional theory at the level of UB3LYP/6-311++G(d,p). Various multiplicity states arise for the composites due to the open-shell ground state electronic configurations of Al and Ga atoms. The composites are electronically stable, thermodynamically exothermic and have favorable Gibbs’ free energy of formation values. Various quantum chemical properties have been obtained and discussed. The calculated UV-VIS spectra indicate that some of the composites are infrared absorbing systems beyond 700 nm.

Combining EXAFS and Computer Simulations to Refine the Structural Description of Actinyls in Water.

EXAFS spectroscopy is one of the most used techniques to solve the structure of actinoid solutions. In this work a systematic analysis of the EXAFS spectra of four actinyl cations, [UO2]2+, [NpO2]2+, [NpO2]+ and [PuO2]2+ has been carried out by comparing experimental results with theoretical spectra. These were obtained by averaging individual contributions from snapshots taken from classical Molecular Dynamics simulations which employed a recently developed [AnO2]2+/+ –H2O force field based on the hydrated ion model using a quantum-mechanical (B3LYP) potential energy surface. Analysis of the complex EXAFS signal shows that both An-O and An-O single scattering paths as well as multiple scattering ones involving [AnO2]+/2+ molecular cation and first-shell water molecules are mixed up all together to produce a very complex signal. Simulated EXAFS from the B3LYP force field are in reasonable agreement for some of the cases studied, although the k= 6–8 Å region is hard to be reproduced theoretically. Except uranyl, all studied actinyls are open-shell electron configurations, therefore it has been investigated how simulated EXAFS spectra are affected by minute changes of An-O bond distances produced by the inclusion of static and dynamic electron correlation in the quantum mechanical calculations. A [NpO2]+−H2O force field based on a NEVPT2 potential energy surface has been developed. The small structural changes incorporated by the electron correlation on the actinyl aqua ion geometry, typically smaller than 0.07 Å, leads to improve the simulated spectrum with respect to that obtained from the B3LYP force field. For the other open-shell actinyls, [NpO2]2+ and [PuO2]2+, a simplified strategy has been adopted to improve the simulated EXAFS spectrum. It is computed taking as reference structure the NEVPT2 optimized geometry and including the DW factors of their corresponding MD simulations employing the B3LYP force field. A better agreement between the experimental and the simulated EXAFS spectra is found, confirming the a priori guess that the inclusion of dynamic and static correlation refine the structural description of the open-shell actinyl aqua ions.

Ab Initio Intermolecular Potential Energy Surfaces and Cross Second Virial Coefficients for the Dimer N2-NO.

Ab initio intermolecular potential energy surfaces (PES) of N2-NO have been constructed at the level of theory CCSD(T) with the augmented correlation-consistent basis sets aug-cc-pVmZ (with m = 2, 3, 4). The nitrogen in the closed-shell electronic configuration X1Σ+ and nitric oxide in the open-shell electronic configuration A2Σ+ were employed to calculate ab initio intermolecular interaction energies. The two new ab initio 5-site intermolecular pair potentials at the theoretical level CCSD(T)/aug-cc-pVmZ (with m = 4, 24) were developed appropriately and are suitable for N2-NO dimer by using the nonlinear least-squares fitting method combining MIO and Levenberg–Marquardt algorithms. The correlation quality of these two potentials was found to be very good with R2 values in the range of 0.98372 to 0.99775. The cross second virial coefficients B12(T) of the N2-NO dimer were calculated in the temperature range of 100 to 470 K using the two ab initio 5-site potentials. The discrepancies between the calculated results and the experimental data can be acceptable.

Interaction of 1,1-Diamino-2,2-Dinitroethylene and Gallium - DFT Treatment

1,1-diamino-2,2-dinitroethylene, commonly known as FOX-7, is an insensitive pull-push type explosive of nitramine class. Aluminized FOX-7, depending on its Al content and multiplicity was found to be susceptible to decomposition. Gallium atom, a third group element below Al, also has an open shell electronic configuration. The present study considers FOX-7+nGa composites (n:1-3) and within the constraints of density functional theory at the level of UB3LYP/6-311++G(d,p) it has been found that gallium atom does not initiate any bond rupture. However, certain distortions in bond lengths and angles occur which might have some effect on the ballistic properties of FOX-7. Certain geometrical, quantum chemical and energy values of the composites as well as some spectral properties are presented.

Spin-orbit coupling from a two-component self-consistent approach. I. Generalized Hartree-Fock theory.

Formal and computational aspects are discussed for a self-consistent treatment of spin-orbit coupling within the two-component generalization of the Hartree-Fock theory. A molecular implementation into the CRYSTAL program is illustrated, where the standard one-component code (typical of Hartree-Fock and Kohn-Sham spin-unrestricted methodologies) is extended to work in terms of two-component spinors. When passing from a one- to a two-component description, the Fock and density matrices become complex. Furthermore, apart from the αα and ββ diagonal spin blocks, one has also to deal with the αβ and βα off-diagonal spin blocks. These latter blocks require special care as, for open-shell electronic configurations, certain constraints of the one-component code have to be relaxed. This formalism intrinsically allows us to treat local magnetic torque as well as noncollinear magnetization and orbital current-density. An original scheme to impose a specified noncollinear magnetization on each atomic center as a starting guess to the self-consistent procedure is presented. This approach turns out to be essential to surpass local minima in the rugged energy landscape and allows possible convergence to the ground-state solution in all of the discussed test cases.

Exploring the conformational space of cobalt(III)–salen catalyst for CO2/epoxide copolymerization: Effect of quaternary ammonium salts on preference of alternative isomers

Model catalysts for CO2 /epoxide copolymerization based on Co(III) complexes were studied, with focus on the preference of their alternative isomers, cisβ vs. trans. The systems range from model structures without the co-catalyst, as derived from crystallographic data, to complex models with two (CH2 )4 N+ R3 co-catalyst chains (R = Me, Bu) grafted onto a Co(III)-salcy core. To explore the conformational space of the latter complexes, a computational protocol was developed, combining a systematic model-building approach with static and molecular dynamics calculations, and multilevel energy assessment (PM7 and DFT). Results demonstrate an influence of the co-catalyst on the relative stability of the isomers. The cisβ isomer is preferred for complexes without N+ -chains and the cisβ ↔ trans isomerization is feasible. Five-coordinate species and open-shell electronic configurations are energetically disfavored. The cisβ preference decreases with the introduction and enlargement of (CH2 )4 N+ R3 : both isomers can be populated for R = Me, while the trans isomer is visibly preferred for R = Bu. © 2018 Wiley Periodicals, Inc.

Hyper Open-Shell Excited Spin States of Transition-Metal Compounds: FeF2, FeF2···Ethane, and FeF2···Ethylene.

Spin-state energetics are important for understanding properties that involve more than one spin state, for example, catalysis occurring on two or more potential energy surfaces corresponding to different electronic spins. Very often, multiple-spin processes involve transition-metal compounds, and therefore, it is important to understand the electronic structure and energetics of such compounds in different spin states. In this work, we benchmark relative spin-state energies of FeF2 with respect to the quintet ground spin state using both single-configurational and multiconfigurational methods, and we examine how they are affected by the binding of ethane and ethylene to the iron center. We also benchmark the binding energies of the complexes. The single-configurational methods used in this work are the Hartree-Fock method, 32 exchange-correlation functionals, and the CCSD(T) coupled-cluster method in both restricted and unrestricted formalisms. The multiconfigurational methods that have been used are CASSCF, CASPT2, CASPT3, MRCI, MRCI+Q, and MR-ACPF. The spin-state splitting energies depend on the functional chosen, and of the 32 exchange-correlation functionals investigated here, we find that for the septet and spin-projected triplet states of FeF2 the M06 functional is the best when compared to our best estimates from multireference calculations. If all nine excitation energies are considered, where there are three excited spin states (singlet, triplet, and septet) for each of the three systems (FeF2, FeF2···ethane, and FeF2···ethylene), the three best-performing functionals are HLE16, SOGGA11-X, and M06-2X. We find that the binding of ethane perturbs the relative spin-state energy of FeF2 by only a small amount, but the stronger binding of ethylene has a larger effect. For the spin-state splitting energies of FeF2 using single-reference CCSD(T), we find that the predicted results depend very strongly on precisely how the calculations are done, in particular, on the spin-restricted or spin-unrestricted character of the SCF reference state, which can differ even by around 50 kcal/mol for the SCF reference state and the subsequent CCSD(T) calculations. Upon analyzing the wave functions of both the spin-restricted or spin-unrestricted formalisms, we find that the lowest-energy singlet and triplet states of the complexes, just like FeF2 in isolation, can have more unpaired electrons than they are usually assumed to have, i.e., they can be hyper open-shell electronic configurations, and this can significantly lower the energy.

Hyper Open-Shell States: The Lowest Excited Spin States of O Atom, Fe2+ Ion, and FeF2.

Excited spin states are important for reactivity, catalysis, and magnetic applications. This work examines the relative energies of the spin states of O atom, Fe2+ ion, and FeF2 and characterizes their excited spin states. Both single-configuration and multireference methods are used to establish the character of the lowest singlet excited state of all three systems and the lowest triplet excited state of Fe2+ and FeF2. We find that the conventional representation of the orbital occupancies is incorrect in that the states have more unpaired electrons than the minimum number required by their total electron spin quantum number. In particular, we find that, for a given spin state, an electronic configuration with more than 2S unpaired electrons is more stable than the configuration with 2S unpaired electrons (where S is the spin of the system). For instance, triplet FeF2 with four unpaired electrons is lower in energy than triplet FeF2 with two unpaired electrons. Such highly open-shell configurations are labeled as hyper open-shell electronic configurations in this work and are compared to ordinary open-shell or closed-shell electronic configurations. The hyper open-shell states considered in this work are especially interesting because, unlike typical biradicals and polyradicals, the unpaired electrons are all on the same center. This work shows that the conventional perspective on spin-state energetics that usually assumes ordinary open shells for single-centered radicals needs modification to take into account, whenever possible, hyper open-shell configurations as well.

The role of nonmagnetic d0 vs. d10B-type cations on the magnetic exchange interactions in osmium double perovskites

Polycrystalline samples of double perovskites Ba2BOsO6 (B=Sc, Y, In) were synthesized by solid state reactions. They adopt the cubic double perovskite structures (space group, Fm-3m) with ordered B and Os arrangements. Ba2BOsO6 (B=Sc, Y, In) show antiferromagnetic transitions at 93K, 69K, and 28K, respectively. The Weiss-temperatures are −590K for Ba2ScOsO6, −571K for Ba2YOsO6, and −155K for Ba2InOsO6. Sc3+ and Y3+ have the open-shell d0 electronic configuration, while In3+ has the closed-shell d10. This indicates that a d0 B-type cation induces stronger overall magnetic exchange interactions in comparison to a d10. Comparison of Ba2BOsO6 (B=Sc, Y, In) to their Sr and Ca analogues shows that the structural distortions weaken the overall magnetic exchange interactions.

Active role of nonmagnetic cations in magnetic interactions for double-perovskiteSr2BOsO6(B=Y,In,Sc)

Using first-principles density functional theory, we have investigated the electronic and magnetic properties of recently synthesized and characterized 5d double-perovskites Sr2BOsO6 (B=Y, In, Sc). The electronic structure calculations show that in all compounds, the Os5+ (5d3) site is the only magnetically active one, while Y3+, In3+ and Sc3+ remain in nonmagnetic states, with Sc/Y and In featuring d0 and d10 electronic configurations, respectively. Our studies reveal the important role of closed-shell (d10) versus open-shell (d0) electronic configurations of the nonmagnetic sites in determining the overall magnetic exchange interactions. Although the magnetic Os5+ (5d3) site is the same in all compounds, the magnetic super-exchange interactions mediated by non-magnetic Y/In/Sc species are strongest for Sr2ScOsO6, weakest for Sr2InOsO6, and intermediate in case of the Y (d0), due to different energy overlaps between Os-5d and Y/In/Sc-d states. This explains the experimentally observed substantial differences in the magnetic transition temperatures of these materials, despite of an identical magnetic site and underlying magnetic ground state. Furthermore, short range Os-Os exchange-interactions are more prominent than long range Os-Os interactions in these compounds, which contrasts with the behavior of other 3d-5d double-perovskites.

All-Electron Scalar Relativistic Calculations on the Adsorption of Small Gold Clusters Toward Methanol Molecule.

Under the framework of DFT, an all-electron scalar relativistic calculation on the adsorption of Aun (n = 1-13) clusters toward methanol molecule has been performed with the generalized gradient approximation at PW91 level. Our calculation results reveal that the small gold cluster would like to bond with oxygen of methanol molecule at the edge of gold cluster plane. After adsorption, the chemical activities of hydroxyl group and methyl group are enhanced to some extent. The even-numbered AunCH3OH cluster with closed-shell electronic configuration is relatively more stable than the neighboring odd-numbered AunCH3OH cluster with open-shell electronic configuration. All the AunCH3OH clusters prefer low spin multiplicity (M = 1 for even-numbered AuNCH3OH clusters, M = 2 for odd-numbered AunCH3OH clusters) and the magnetic moments are mainly contributed by gold atoms. The odd-even alterations of magnetic moments and electronic configurations can be observed clearly and may be simply understood in terms of the electron pairing effect.