Closed-shell Electronic Configuration Research Articles

High‐Spin and Reactive Fe13 Cluster with Exposed Metal Sites

AbstractAtomically defined large metal clusters have applications in new reaction development and preparation of materials with tailored properties. Expanding the synthetic toolbox for reactive high nuclearity metal complexes, we report a new class of Fe clusters, Tp*4W4Fe13S12, displaying a Fe13 core with M−M bonds that has precedent only in main group and late metal chemistry. M13 clusters with closed shell electron configurations can show significant stability and have been classified as superatoms. In contrast, Tp*4W4Fe13S12 displays a large spin ground state of S=13. This compound performs small molecule activations involving the transfer of up to 12 electrons resulting in significant cluster rearrangements.

High-Spin and Reactive Fe13 Cluster with Exposed Metal Sites.

Atomically defined large metal clusters have applications in new reaction development and preparation of materials with tailored properties. Expanding the synthetic toolbox for reactive high nuclearity metal complexes, we report a new class of Fe clusters, Tp*4 W4 Fe13 S12 , displaying a Fe13 core with M-M bonds that has precedent only in main group and late metal chemistry. M13 clusters with closed shell electron configurations can show significant stability and have been classified as superatoms. In contrast, Tp*4 W4 Fe13 S12 displays a large spin ground state of S=13. This compound performs small molecule activations involving the transfer of up to 12 electrons resulting in significant cluster rearrangements.

Probing the structural evolution, electronic and vibrational properties of anionic sodium-doped magnesium clusters

Bimetallic clusters aroused a great deal of attention in materials science because of their novel properties, depending sensitively on their size, structure, and composition. Herein, we report a theoretical study of the geometry, stability, electronic and vibrational properties of bimetallic NaMgn– (n = 2–11) clusters through CALYPSO code within DFT calculations. The most stable NaMgn– clusters were found to be planar structure at n = 2, triangular pyramid-based structure at n = 3–5, pentagonal pyramid-based structure at n = 6–7 and the triangular prism-based structure at n = 8–11. Most of them are structurally consistent with anionic magnesium clusters, in which the Na atom tends to localize on the convex site. Stability studies conform to the NaMg3– and NaMg9–clusters to being the magic number structure with prominent stability, which benefits from short interatomic bonds and closed-shell 1S21P6 and 1S21P61D102S2 electronic configurations. Bonding nature analysis not only reflects the delocalized bonding properties in the NaMg3– and NaMg9– clusters, but also reveals that the Mg-Mg bond is stronger than the Na-Mg bond. For the NaMgn– clusters, calculated PES, IR, and Raman spectra could be used as essential evidence for identifying cluster structures experimentally in the future.

Probing the effects of lithium doping on structures, properties, and stabilities of magnesium cluster anions

Bimetallic clusters have aroused tremendous interest because the property changes like structure, size, and composition have occurred. Herein, a structural search of the global minimum for anionic (n = 2–11) clusters is performed using an efficient crystal structure analysis by particle swarm optimization (CALYPSO) structural searching program with subsequent density functional theory (DFT) calculations. A great variety of low energetic isomers are converged, and the most stable ones are confirmed by comparing their total energy of each size. It is found that the clusters are structurally consistent with corresponding Mg clusters anions except for and . In all the doped clusters, the Li atom prefers to occupy the convex position. Simulated photoelectron spectra (PES), Infrared (IR), and Raman spectra of could be used as an essential evidence for identifying cluster structures experimentally in the future. Stability study reveals that a tower-like structure of has prominent stability and can be identified as a magic number cluster. The reason might be that there are both closed-shell 1S21P61D102S2 electronic configurations and stronger Li–Mg bonds caused by sp hybridization in the cluster.

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.

Pressure-induced dynamically stable HeK2S under moderate conditions

It is accepted that helium as one of inert gases is hard to combine due to its stable closed shell electron configuration. With the maturity of first principles calculations, helides are not rare under high pressures, which fuels the enthusiasm for finding helium-based compounds at moderate conditions. Here, we performed a first principle exploration on the crystal structures and the corresponding electronic properties of HeK2S at 0–100 GPa. Two phases with Fm-3m and Cmma space groups are predicted, dynamically stable at ambient pressure and high pressure. As concerns the structures, K2S acts as a precompressor to stabilize the helium sublattice. Our work reveals that no chemical bond is formed when He atom insertion, which is stabilized by long-range Coulomb interaction force.

Electrical conductivity through π-π stacking in a two-dimensional porous gallium catecholate metal-organic framework.

Metal-organic frameworks (MOFs) are hybrid materials known for their nanoscale pores, which give them high surface areas but generally lead to poor electrical conductivity. Recently, MOFs with high electrical conductivity were established as promising materials for a variety of applications in energy storage and catalysis. Many recent reports investigating the fundamentals of charge transport in these materials focus on the role of the organic ligands. Less consideration, however, is given to the metal ion forming the MOF, which is almost exclusively a late first-row transition metal. Here, we report a moderately conductive porous MOF based on trivalent gallium and 2,3,6,7,10,11-hexahydroxytriphenylene. Gallium, a metal that has not been featured in electrically conductive MOFs so far, has a closed-shell electronic configuration and is present in its trivalent state-in contrast to most conductive MOFs, which are formed by open-shell, divalent transition metals. Our material, made without using any harmful solvents, displays conductivities on the level of 3 mS/cm and a surface area of 196 m2 /g, comparable to transition metal analogs.

B8C10: A C2v planar polycyclic structure bridged by the central strong C[sbnd]C bond and strengthened by the aromaticity

Global-searching for B8C10− anion and B8C10 neutral is executed based on CALYPSO genetic algorithm with DFT calculations, and their structural and bonding properties are investigated by quantum chemical calculations. B8C10− anion has a cross-bridged three-ringed structure, while B8C10 neutral adopts a C2v symmetric planar polycyclic structure cross-bridged by the central CC bond. B8C10− can be regarded as a superhalogen anion because of the large VDE of 3.56 eV. B8C10 neutral has a closed-shell electronic configuration with HOMO-LUMO gap of 2.44 eV and σ plus π double delocalized bonding characters. More interestingly, B8C10 neutral exhibits some aromaticity.

Hydrogen-Bonded Complexes of Neutral Nitroxide Radicals with 2-Propanol Studied by Multifrequency EPR/ENDOR

The hydrogen bond plays a key role in weak directional intermolecular interactions. It is operative in determining molecular conformation and aggregation, and controls the function of many chemical systems, ranging from inorganic, organic to biological molecules. Although an enormous amount of spectroscopic information has been collected about hydrogen-bond formation between molecules with closed-shell electronic configuration, the details of such interactions between open-shell radicals and closed-shell molecules are still rare. Here we report on an investigation of hydrogen-bonded complexes between pyrroline-type as well as piperidine-type neutral nitroxide radicals and an alcohol, i.e., 2-propanol. These nitroxide radicals are commonly used as EPR spin labels and probes. To obtain information on the geometry of the complexes and their electronic structure, multi-resonance EPR techniques at various microwave frequencies (X-, Q-, W-band, 244 GHz) have been employed in conjunction with DFT calculations. The planar five-membered ring system of the pyrroline-type nitroxide radical was found to form exclusively well-defined in-plane σ-type hydrogen-bonded complexes with one 2-propanol molecule in the first solvation shell in frozen solution. The measured hyperfine parameters of the hydrogen-bridge proton and the internal magnetic parameters describing the electron Zeeman and the electron-nuclear hyperfine and nuclear quadrupole interactions are in good agreement with values predicted by state-of-the-art DFT calculations. In contrast, multi-resonance EPR on the non-planar six-membered ring system of the piperidine-type nitroxide radical (TEMPOL) reveals a more complex situation, i.e., a mixture of a σ-type with, presumably, an out-of-plane π-type complex, both present in comparable fraction in frozen solution. For TEMPOL, the DFT calculations failed to predict magnetic interaction parameters that are in good agreement with experiment, apparently due to the considerable flexibility of the nitroxide and hydrogen-bonded complex. The detailed information about nitroxide/solvent complexes is of particular importance for Dynamic Nuclear Polarization (DNP) and site-directed spin-labeling EPR studies that employ nitroxides as polarizing agents or spin labels, respectively.

Three-State Switching of an Anthracene Extended Bis-thiaxanthylidene with a Highly Stable Diradical State.

A multistable molecular switching system based on an anthracene-extended bis-thiaxanthylidene with three individually addressable states that can be interconverted by electrochemical, thermal, and photochemical reactions is reported. Besides reversible switching between an open-shell diradical- and a closed-shell electronic configuration, our findings include a third dicationic state and control by multiple actuators. This dicationic state with an orthogonal conformation can be switched electrochemically with the neutral open-shell triplet state with orthogonal conformation, which was characterized by EPR. The remarkably stable diradical shows kinetic stability as a result of a significant activation barrier for isomerization to a more stable neutral closed-shell folded geometry. We ascribe this activation barrier of ΔG⧧(293 K) = 25.7 kcal mol–1 to steric hindrance in the fjord region of the overcrowded alkene structure. The folded closed-shell state can be converted back to the diradical state by irradiation with 385 nm. The folded state can also be oxidized to the dicationic state. These types of molecules with multiple switchable states and in particular stable diradicals show great potential in the design of new functional materials such as memory devices, logic gates, and OFETs.

Mechanistic Insights into the P450 TleB-Catalyzed Unusual Intramolecular C-N Bond Formation Involved in the Biosynthesis of Indolactam V.

Indolactam V, a known biosynthetic precursor of indolactam alkaloids, is the main pharmacophore of this family and exhibits potential protein kinase C activation. A key step in the biosynthesis of indolactam V is the formation of an indole-fused nine-membered lactam core by intramolecular C-N bond formation. In this work, we report a computational study of the unique cytochrome P450 TleB enzyme-catalyzed direct and selective C-H bond amination reaction that can generate indolactam V from the dipeptide N-methylvalyl-tryptophanol. By performing molecular dynamics simulations and quantum-mechanical/molecular-mechanical calculations, we revealed that the C-H bond amination involves one step of proton transfer from N1-H of the indole ring to the FeIV═O unit, one step of hydrogen abstraction of N13-H in the side chain of the substrate by the FeIV-OH unit, and diradical coupling, in which two conformational changes of the side chain of the substrate are necessary. In the enzyme-substrate complex of TleB, the N-H bond of the indole ring of the substrate forms a strong hydrogen bond with the FeIV═O unit in compound I, and the porphyrin radical cation accepts an electron from the substrate to form the closed-shell electronic configuration. Thus, compound I in the enzyme-substrate complex cannot be described as FeIV═O coupled to a porphyrin radical cation, which is different from those of other P450 enzymes. Besides, two stages of conformational changes of the side chains of the substrate may increase the relative energies of reaction intermediates by 10-12 kcal/mol. From the structure point of view, it is the rotatable long side chain of the substrate and the large flexible active pocket of TleB that make the intramolecular diradical coupling feasible. Our findings may provide useful information to further understand the Tleb-catalyzed intramolecular C-H bond amination and the other bio-catalyzed intramolecular diradical coupling.

Double σ-Aromaticity in a Planar Zinc-Doped Gold Cluster: Au9Zn.

The strong relativistic effects result in many interesting chemical and physical properties for gold and gold compounds. One of the most surprising findings has been that small gold clusters prefer planar structures. Dopants can be used to tune the electronic and structural properties of gold nanoclusters. Here we report an experimental and theoretical investigation of a Zn-doped gold cluster, Au9Zn-. Photoelectron spectroscopy reveals that Au9Zn- is a highly stable electronic system with an electron binding energy of 4.27 eV. Quantum chemical studies show that the global minimum of Au9Zn- has a D3h structure with a closed-shell electron configuration (1A1'), which can be viewed as replacing the central Au atom by Zn in the open-shell parent Au10- cluster. The high electronic stability of Au9Zn- is corroborated by its extremely large HOMO-LUMO gap of 3.3 eV. Chemical bonding analyses revealed that the D3h Au9Zn- are bonded by two sets of delocalized σ bonds, giving rise to double σ aromaticity and its remarkable stability. Two planar low-lying isomers are also observed, corresponding to a similar triangular structure with the Zn atom on the edge and another one with one of the corner Au atoms moved to the edge of the triangle.

BN adamantane isomers: an optical absorption spectrum study

In this work, we have systematically investigated the structural, electronic, and optical absorption properties of the boron nitride (BN) adamantane isomers (B $$_x$$ N $$_{10-x}$$ , with x= 4, 5 or 6), using both DFT and TD-DFT methods. These isomers were built by replacing carbon atoms of the adamantane molecule by boron and nitrogen atoms and keeping all isomers in closed-shell electronic configuration. Optimized nanostructures indicate that these BN adamantane exhibit good stability. In addition, the current study indicates that the new BN-isomers have an excellent absorption in the UV-C region, and a moderate absorption in the UV-B and UV-A regions. These characteristics enable this new BN adamantane as potential candidates to be used in the development of new nano-optoelectronic devices.

Infrared photodissociation spectroscopy of heteronuclear group 15 metal-iron carbonyl cluster anions AmFe(CO)n- (A = Sb, Bi; m, n = 2, 3).

Heteronuclear group 15 metal-iron carbonyl cluster complexes of AmFe(CO)n- (A = Sb, Bi; m, n = 2-3) were generated in the gas phase and studied by infrared photodissociation spectroscopy in the carbonyl stretching region. Their structures were determined by comparing the experimental spectra with predicted spectra derived from DFT calculations at the B3LYP and BP86 levels. All of the AmFe(CO)n- cluster anions were determined to have Fe(CO)n- fragments with all of the CO ligands terminally bonded to the iron center, and they can be regarded as being formed via the interactions of the neutral group 15 metal clusters with the Fe(CO)n- fragments. Bonding analyses indicated that each A2Fe(CO)n- (n = 2, 3) cluster anion contained two A-Fe single bonds and one A-A double bond. Each A3Fe(CO)n- (n = 2, 3) cluster anion involved three A-Fe single bonds and three A-A single bonds. There is an isolobal relationship between the Fe(CO)3- group and the group 15 atoms. The substitution of an Fe(CO)3- group in place of one A atom in the tetrahedral A4 molecule resulted in an A3Fe(CO)3- cluster anion with the closed-shell electronic configuration for all the group 15 metals and iron atoms.

Anion photoelectron spectroscopy and quantum chemistry calculations of TaSi16−/0 clusters: global minimum fullerene-like cage structure, bonding and superatom properties

TaSi16− has a fullerene-like cage structure, σ + π double delocalized bonding patterns, a superatom closed-shell electron configuration, and aromaticity.

Donor-Acceptor Conjugated Macrocycles with Polyradical Character and Global Aromaticity.

SummaryPolyradical character and global aromaticity are fundamental concepts that govern the rational design of cyclic conjugated macromolecules for optoelectronic applications. Here, we report donor-acceptor (D−A) conjugated macromolecules with and without π-spacer derivatives to tune the antiferromagnetic couplings between the unpaired electrons. The macromolecules without π-spacer have a closed-shell electronic configuration and show global nonaromatic character in the singlet and lowest triplet states. However, the derivatives with π-spacer develop a nearly pure open-shell diradical and a very high polyradical character, not reported for D−A type macromolecules. Furthermore, the π-spacer derivatives display global nonaromaticity in the singlet ground state, but global aromaticity in the lowest triplet state, according to Baird's rule. The absorption spectra of the open-shell macromolecules calculated with time-dependent density functional theory indicate intensive light absorption in the near-infrared region and broadening to 2,500 nm, making these materials suitable for numerous optoelectronic applications.

Exploring the structural stability order and electronic properties of transition metal M@Ge12 (M = Co, Pd, Tc, and Zr) doped germanium cage clusters–A density functional simulation

In the present report, the structural stability order and electronic properties of the transition metal M@Ge12 (M = Co, Pd, Tc, and Zr) doped germanium cage has been carried out at B3LYP/LANL2DZ ECP level by using spin polarized density functional theory. Initially, we selected five lowest energy structure of neutral TM doped Ge12 cluster with high symmetry point like D6h-symmetric hexagonal prism (HP), the D6d-symmetric hexagonal anti-prism (HAP), D2d-symmetric bi-capped pentagonal prism (BPP), perfect icosahedrons (Ih) and Fullerene type structures. Further, we discussed the electronic origin of stability as well as electronic properties by calculating binding energy, HOMO-LUMO gap, charge transfer mechanism and density of states. We indentified that the Pd, Tc, and Zr encapsulated Ge12 cage with hexagonal prism [HP] structures are minimum energy structures while Co@Ge12 cage prefer HAP structure. The magnitudes of binding energy of the clusters indicate that the doping of 4d transition metal gives most stable structure rather than 3d transition metal Co atom. The large HOMO-LUMO gap and natural bond orbital analysis explain the stability of these clusters using closed shell electronic configuration and the contribution of π and σ bond. Charge transfer mechanism shows that the Tc, Pd and Zr atoms play role as an electron donor in the system whereas Co inclined to accept the electrons. The importances of “d” orbital in localized electrons near the Fermi level are also explained through partial density of states.

Synthesis, characterization and metal ions sensing applications of meta-benziporphodimethene-embedded polyacrylamide/carboxymethyl guargum polymeric hydrogels in water

ABSTRACT We have developed a robust procedure for the visual on-site detection of zinc, cadmium and mercury metal ions in an aqueous medium using a polymeric hydrogel matrix-based colorimetric sensor. Zn2+, Cd2+and Hg2+, owing to their biological significant value and environmental harm, have attracted more attention. The selective detection of Zn2+, Cd2+and Hg2+ metal ions has always been challenging due to their closed-shell d10 electronic configuration which makes them spectroscopically silent. A polyacrylamide/carboxymethyl guargum polymeric hydrogel-based metal ion sensor was synthesized by in situ embedding 11, 16-bis (phenyl)-6, 6, 21, 21-tetramethyl-m-benzi-6,21-porphodimethene (meta-BPDM) in a host hydrogel. The meta-BPDM-embedded hydrogel shows high stability, sensitivity and selectivity when it is dipped into the aqueous solutions of Zn2+, Cd2+and Hg2+ metal ions. During detection, the binding of these metal ions in hydrogel causes hydrogel to change from red to bluish-green which was visually detected and confirmed by UV–visible spectroscopy. The meta-BPDM-embedded polymeric hydrogel was characterized by using solid-state UV–visible spectroscopy, scanning electron microscopy, X-ray diffraction, thermogravimetric analysis, Fourier-transform infrared spectroscopy, energy-dispersive X-ray analysis and its sensing properties were studied. The meta-BPDM-embedded polymeric hydrogel was found to be an excellent colorimetric sensor for Zn2+, Cd2+ and Hg2+ in aqueous medium without leaching of meta-BPDM from the hydrogel. The selectivity to sense these ions is mainly dependent on the binding constant of these metal ions with the meta-BPDM embedded in the hydrogel. The sensitivity of the hydrogel was 0.5, 1, and 2 mg/L with Hg2+, Zn2+ and Cd2+, respectively.

Designing Donor-Acceptor Conjugated Macrocycles with Polyradical Character and Global (Anti)Aromaticity

Polyradical character and global (anti)aromaticity are fundamental concepts that govern rational design of cyclic conjugated macromolecules for optoelectronic applications. Here, we have designed donor-acceptor (D-A) macromolecules with ring topology along with their pi-spacer derivatives, and analyzed their unique electronic properties with density functional theory (DFT). The macromolecules with n = 8 and 16 repeat D-A units display similar singlet-triplet energy gap and have closed-shell electronic configuration with no diradical character (y0 = 0). These macromolecules also display global nonaromatic character, which is supported by NICS(0), AICD, and 2D-ICSS analysis. However, the derivatives with pi-spacer (n = 8-pi) develop near pure open-shell character (y0=1) with increased singlet-triplet gap. Furthermore, these derivatives display global antiaromaticity in the singlet ground-state according to Huckel's rule, and global aromaticity in the lowest triplet state following Baird's rule, and have a very high polyradical character, which is not reported for D-A type macromolecules. The calculated absorption spectra with time-dependent DFT (TDDFT) indicates intensive light absorption in the near-infrared (NIR) region broadening to 2500 nm. These macrocycles also display a size-dependent absorption maxima when the number of repeat units increased from n = 8 to 16. Furthermore, due to the development of open-shell character in the pi-spacer derivatives, a significant red-shift in the absorbance wavelength is observed.

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.