Intermolecular interactions between gold clusters and selected amino acids cysteine and glycine: a DFT study

The intermolecular interactions between Au_n (n = 3–4) clusters and selected amino acids cysteine and glycine have been investigated by means of density functional theory (DFT). Present calculations show that the complexes possessing Au-NH₂ anchoring bond are found to be energetically favored. The results of NBO and frontier molecular orbitals analysis indicate that for the complex with anchoring bonds, lone pair electrons of sulfur, oxygen, and nitrogen atoms are transferred to the antibonding orbitals of gold, while for the complex with the nonconventional hydrogen bonds (Au···H–O), the lone pair electrons of gold are transferred to the antibonding orbitals of O-H bonds during the interaction. Furthermore, the interaction energy calculations show that the complexes with Au-NH₂ anchoring bond have relatively high intermolecular interaction energy, which is consistent with previous computational studies.     

Catalytic mechanisms of Au<Subscript>11</Subscript> and Au<Subscript>11-n</Subscript>Pt<Subscript>n</Subscript> (<Emphasis Type="Italic">n</Emphasis>=1–2) clusters: a DFT investigation on the oxidation of CO by O<Subscript>2</Subscript>

The oxidation of CO catalyzed by clusters of Au₁₁, Au₁₀Pt and Au₉Pt₂ was investigated using the M06 functional suite of the density functional theory. Au and Pt atoms were described with the double-ζ valence basis set Los Alamos National Laboratory 2-double-z (LanL2DZ), whereas the standard 6-311++G(d,p) basis set was employed for the C and O atoms. Our theoretical model showed that (1) after coordination to Au and Au-Pt cluster, O₂ and CO are apparently activated, and Mulliken charges show that the gold atoms in the active sites of Au11 are negatively charged; (2) Au-Pt clusters with 11 atoms can effectively catalyze the oxidation of CO by O₂; (3) Au₁₁ exhibits good catalytic performance for the oxidation of CO; (4) oxidation of CO occurs preferably on the Au–Pt active sites in Pt-doped clusters, and the single-center mechanisms are more favorable energetically than the two-center mechanisms; (5) after adsorption, an O₂ molecule oxidates two CO molecules via stepwise mechanisms; and (6) the catalytic processes are highly exothermic.     

Phosphane-stabilized gold clusters: investigation of the stability of [Au13(PMe2Ph)10Cl2]3+

The phosphane-stabilized gold cluster [Au₁₃(PMe₂Ph)₁₀Cl₂]³⁺ was studied using density functional theory. The extraordinary stability of the cluster has been attributed to the stability of the gold core and the protection conferred by ligands. Here, five stability factors of the gold core were explained and verified by investigating the Au₁₃⁵⁺ core in detail. Interactions between the gold core and several PR₃ ligands (R = Me, H, I, Br, Cl, F) were investigated according to the different electron donor abilities of each ligand; bonding energy between the ligand and the gold core was found to increase with the electronegativity of the R substituent. Furthermore, two other aspects of the ligands were clarified: how the ligand stabilizes the Au₁₃⁵⁺ core, and which kind of ligand provides the best stabilization for the cluster.     

Catalysis of the acetylene hydrochlorination reaction by Si-doped Au clusters: a DFT study

The mechanisms for the acetylene hydrochlorination reaction on pristine Au₇ and Au₈ clusters and on the Si-doped Au clusters Au₆Si and Au₇Si were systematically investigated via density functional theory using the PBE functional. The band gap (?E_g) of the Au₇Si cluster was found to smaller than that of its undoped equivalent (Au₈), thus enhancing its catalytic activity, and Au₇Si presented a significantly reduced activation barrier (16.69 kcal mol^?1) for the acetylene hydrochlorination reaction compared with the pristine Au₈ cluster (21.83 kcal mol^?1). On the other hand, the activation barrier for the acetylene hydrochlorination reaction was not lower for the Au₆Si cluster than for the pristine Au₇ cluster because the band gap (?E_g) of Au₆Si was found to be larger than that of Au₇. Hence, the current work shows that the catalytic activities of gold clusters can be systematically modified by doping them. Our findings also suggest how to enhance the acetylene hydrochlorination reaction by doping foreign atoms into Au clusters.

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Graphical abstract The Si-doped Au₇Si cluster showed stronger catalytic activity for the acetylene hydrochlorination reaction compared with the pristine Au₈ cluster.

     

Structural change from doping the gold cluster

Doping gold clusters with a transition metal (M@Au_n) causes structural change. To determine the mechanism by which these changes occur, the central gold atom of Au₅ was doped with its same row transition metals Pt, Ir, Os, Re, and W. Based on theoretical calculations, a similar trend was found in other gold clusters.     

Metal cluster topology. 1. Osmium carbonyl clusters

Important theoretical approaches to metal cluster bonding including the Wade-Mingos skeletal electron pair method, the Teo topological electron count, the King-Rouvray graph theory derived method, and Lauher's extended Hückel calculations are shown to agree in their apparent skeletal electron counts for the most prevalent metal cluster polyhedra including the tetrahedron, the trigonal bipyramid (both ordinary and elongated), square pyramid, octahedron, bicapped tetrahedron, pentagonal bipyramid, and capped octahedron. The graph theory derived method is used to treat osmium carbonyl clusters containing from five to eleven osmium atoms. In this connection most osmium carbonyl clusters can be classified into the following types: (1) Clusters exhibiting edge- localized bonding containing multiple tetrahedral chambers (e.g., Os₅(CO)₁₆, Os₆(CO)₁₈, H₂Os₇(CO)₂₀ and HOs₈(CO)₂₂⁻); (2) Capped octahedral clusters derived from osmium carbonyl fragments of the type Os_6+p(CO)_19+2p (p = 0, 1, 2, and 4) (e.g., Os₆- (CO)₁₈²⁻, Os₇(CO)₂₁, Os₈(CO)₂₂²⁻, and H₄Os₁₀- (CO)₂₄²⁻). Other more unusual osmium carbonyl clusters such as the planar Os₆(CO)₁₇ [P(OCH₃)₃]₄, the Os₉ cluster [Os₉(CO)₂₁C₃H₂R]⁻, and the Os₁₁ cluster Os₁₁C(CO)₂₇²⁻ can also be treated satisfactorily by these methods. The importance of the number of ligands around isoelectronic Os_n systems in determining the cluster polyhedron is illustrated by the different cluster polyhedra found for each member of the following isoelectronic pairs: HOs₆- (CO)₁₈⁻/H₂Os₆(CO)₁₈. Os₇(CO)₂₁/H₂Os₇(CO)₂₀, Os₈(CO)₂₂²⁻/HOs₈(CO)₂₂⁻. The tendency for osmium carbonyl clusters frequently to form polyhedra exhibiting edge-localized rather than globally delocalized bonding relates to the facility for osmium carbonyl vertices to contribute more than three internal orbitals to the cluster bonding. In this way Wade's well-known analogy between boron hydride clusters and metal clusters, which assumes exactly three internal orbitals for each vertex atom, is frequently no longer followed in the case of osmium carbonyl clusters.     

Why are cyclodisilazane rings more stable than cyclodisiloxanes? A qualitative molecular orbital approach to the bonding in cyclodisilazanes and cyclodisiloxanes

The approximate molecular orbitals of cyclic Si₂E₂ (E=nitrogen or oxygen) rings are discussed. It is shown that, due to high silicon 3p_z orbital contribution to the siloxane HOMO, the 3d orbitals can not strenghten the silicon-oxygen bond. In contrast, in the silazane ring considerable Si(3d_π)N(2pπ) bonding may occur. These additional π bonds are responsible for the relative stability of cyclodisilazane rings as compared with the isoelectronic cyclodisiloxane rings.     

Probing the structural, electronic and magnetic properties of multicenter Fe2S2 0/−, Fe3S4 0/− and Fe4S4 0/− clusters

The structural, electronic and magnetic properties of neutral and anion Fe₂S₂, Fe₃S₄ and Fe₄S₄ have been investigated with the aid of previous photoelectron spectroscopy and density functional theory calculations. Theoretical electron detachment energies (both vertical and adiabatic) of anion clusters for the lowest energy structure were computed and compared with the experimental results to verify the ground states. The optimized structures show that the ground state structures of Fe₂S₂ ^0/?, Fe₃S₄ ^0/? and Fe₄S₄ ^0/? favor high spin state and are similar to their structures in proteins. The electron delocalization pattern for all the clusters and the nature of bonding between Fe and S atoms were studied by analyzing molecular orbitals. Natural population analysis demonstrates that Fe atoms act as an electron donor in all clusters, and the electron density difference map clearly shows the direction of the electron flow over the whole complex. Furthermore, the investigated magnetism shows that the Fe atoms carried most of the magnetic moments, which is due mainly to the 3d state, while only very small magnetic moments are found on S atoms.     

Discovery of pyrrolo[2,3-d]pyrimidin-4-ones as corticotropin-releasing factor 1 receptor antagonists with a carbonyl-based hydrogen bonding acceptor

A new class of pyrrolo[2,3-d]pyrimidin-4-one corticotropin-releasing factor 1 (CRF₁) receptor antagonists has been designed and synthesized. In general, reported CRF₁ receptor antagonists possess a sp²-nitrogen atom as hydrogen bonding acceptor (HBA) on their core scaffolds. We proposed to use a carbonyl group of pyrrolo[2,3-d]pyrimidin-4-one derivatives as a replacement for the sp²-nitrogen atom as HBA in classical CRF₁ receptor antagonists. As a result, several pyrrolo[2,3-d]pyrimidin-4-one derivatives showed CRF₁ receptor binding affinity with IC₅₀ values in the submicromolar range. Ex vivo ¹²⁵I-sauvagine binding studies showed that 2-(dipropylamino)-3,7-dimethyl-5-(2,4,6-trimethylphenyl)-3,7-dihydro-4H-pyrrolo[2,3-d]pyrimidin-4-one (16b) (30 mg/kg, po) was able to penetrate into the brain and inhibit radioligand binding to CRF₁ receptors (frontal cortex, olfactory bulb, and pituitary) in mice. We identified pyrrolo[2,3-d]pyrimidin-4-one derivatives as the first CRF₁ antagonists with a carbonyl-based HBA.     

Theoretical studies of the magnetic couplings and the chemical indices of the biomimetic models of oxyhemocyanin and oxytyrosinase

Magnetic interactions and the nature of the chemical bonds of the biomimetic Cu₂(μ-η²:η²-O₂) complexes of oxyhemocyanin and oxytyrosinase have been investigated with hybrid density functional theory. The Cu₂(μ-η²:η²-O₂) species has drawn attention in type III copper proteins because this structure is suggested as an important motif in biological systems. Many synthetic modeling approaches have been performed and greatly developed our understanding of the character of the Cu₂(μ-η²:η²-O₂) species. Natural orbital analysis clearly shows that the superexchange interaction of the d_xy orbitals of the Cu ions through the π^∗ orbitals of μ-η²:η² peroxide is responsible for the antiferromagnetic couplings of these Cu₂O₂ system and that the distortion of the Cu₂O₂ core from a planar structure to a butterfly structure and elongation of the Cu-O bonds cause the reduction of orbital interactions between the d_xy ± d_xy orbitals of the dicopper site and the σ^∗ and π^∗ orbitals of peroxide, weakening the magnetic coupling between the Cu sites via μ-η²:η²-peroxide.     

Theoretical investigation of ZnO and its doping clusters

Four clusters of ZnO, O–Zn–SR (–SR = ligand) and doping ZnO structures (with Cr, Cu, Al atoms) were investigated using density functional theory at theB3LYP/Lanl2dz level. The characteristics of Zn₃O₃ and Zn₄O₄ structures, which are the units of experimental wurtzite and zinc blende structures, were found to be similar to those of experimental ZnO nanocrystals. Moreover, the calculated Raman and IR spectra of ZnO clusters were almost consistent with experimental results. Raman spectra were observed to shift to higher frequencies with decreasing numbers of atoms. Both ligands and solvent make the wavelength of absorption peaks shift to blue. All transitions of absorption peaks for these pure clusters were from d to p orbitals. Finally, doping clusters and experimental doping nanocrystals were similar in character. The doping of metal changed the orbital of ZnO nanocrystals. The transitions in doping clusters (Cr–ZnO, Cu–ZnO) are from d to d orbitals, while Al–ZnO clusters have s–p transitions.     

Biosynthesis of gold nanoparticles by Azospirillum brasilense

Plant-associated nitrogen-fixing soil bacteria Azospirillum brasilense were shown to reduce the gold of chloroauric acid to elemental gold, resulting in formation of gold nanoparticles. Extracellular phenoloxidizing enzymes (laccases and Mn peroxidases) were shown to participate in reduction of Au⁺³ (HAuCl₄) to Au⁰. Transmission electron microscopy revealed accumulation of colloidal gold nanoparticles of diverse shape in the culture liquid of A. brasilense strains Sp245 and Sp7. The size of the electron-dense nanospheres was 5 to 50 nm, and the size of nanoprisms varied from 5 to 300 nm. The tentative mechanism responsible for formation of gold nanoparticles is discussed.     

A systematic search for the structures,stabilities, and electronic properties of bimetallic Ca<Subscript>2</Subscript>-doped gold clusters: comparison with pure gold clusters

The local meta-GGA exchange correlation density functional (TPSS) with a relativistic effective core potential was employed to systematically investigate the geometric structures, stabilities, and electronic properties of bimetallic Ca₂Au _n (n = 1–9) and pure gold Au _n (n ≤ 11) clusters. The optimized geometries show that the most stable isomers for Ca₂Au _n clusters have 3D structure when n > 2, and that one Au atom capping the Ca₂Au _n−1 structure for different-sized Ca₂Au _n (n = 1–9) clusters is the dominant growth pattern. The average atomic binding energies and second-order difference in energies show that the Ca₂Au₄ isomer is the most stable among the Ca₂Au _n clusters. The same pronounced even–odd alternations are found in the HOMO–LUMO gaps, VIPs, and hardnesses. The polarizabilities of the Ca₂Au _n clusters show an obvious local minimum at n = 4. Moreover, the inverse corrections to the polarizabilities versus the ionization potential and hardness were found for the gold clusters.     

Metal-sulfur dπ-pπ buffering of the oxidations of metal-thiolate complexes: Photoelectron spectroscopy of (η-C5H5)Fe(CO)2SR (SR = SCH3, SBu) and (η-C5H5)Re(NO)(PR3)SCH3 (PR3 = PPr3, PPh3)

The metal-sulfur bonding present in the transition metal-thiolate complexes CpFe(CO)₂SCH₃, CpFe(CO)₂S^tBu, CpRe(NO)(PⁱPr₃)SCH₃, and CpRe(NO)(PPh₃)SCH₃ (Cp = η⁵-C₅H₅) is investigated via gas-phase valence photoelectron spectroscopy. For all four complexes a strong dπ-pπ interaction exists between a filled predominantly metal d orbital of the [CpML₂]⁺ fragment and the purely sulfur 3pπ lone pair of the thiolate. This interaction results in the highest occupied molecular orbital having substantial M-S π^∗ antibonding character. In the case of CpFe(CO)₂SCH₃, the first (lowest energy) ionization is from the Fe-S π^∗ orbital, the next two ionizations are from predominantly metal d orbitals, and the fourth ionization is from the Fe-S π orbital. The pure sulfur pπ lone pair of the thiolate fragment is less stable than the filled metal d orbitals of the [CpFe(CO)₂]⁺ fragment, resulting in a Fe-S π^∗ combination that is higher in sulfur character than the Fe-S π combination. Interestingly, substitution of a tert-butyl group for the methyl group on the thiolate causes little shift in the first ionization, in contrast to the shift observed for related thiols. This is a consequence of the delocalization and electronic buffering provided by the Fe-S dπ-pπ interaction. For CpRe(NO)(PⁱPr₃)SCH₃ and CpRe(NO)(PPh₃)SCH₃, the strong acceptor ability of the nitrosyl ligand rotates the metal orbitals for optimum backbonding to the nitrosyl, and the thiolate rotates along with these orbitals to a different preferred orientation from that of the Fe complexes. The initial ionization is again the M-S π^∗ combination with mostly sulfur character, but now has considerable mixing among several of the valence orbitals. Because of the high sulfur character in the HOMO, ligand substitution on the metal also has a small effect on the ionization energy in comparison to the shifts observed for similar substitutions in other molecules. These experiments show that, contrary to the traditional interpretation of oxidation of metal complexes, removal of an electron from these metal-thiolate complexes is not well represented by an increase in the formal oxidation state of the metal, nor by simple oxidation of the sulfur, but instead is a variable mix of metal and sulfur content in the highest occupied orbital.     

A DFT study on equilibrium geometries, stabilities, and electronic properties of small bimetallic Na-doped Au(n) (n = 1-9) clusters: comparison with pure gold clusters

A systematic study on the geometric structures, relative stabilities, and electronic properties of small bimetallic Au _n Na (n = 1-9) clusters has been performed by means of first-principle density functional theory calculations at the PW91PW91 level. The results show that the optimized ground-state isomers adopt planar structures up to n = 5, and the Na-capped geometries are dominant growth patterns for n = 6-9. Dramatic odd-even alternative behaviors are obtained in the second-order difference of energies, fragmentation energies, highest occupied-lowest unoccupied molecular orbital energy gaps, and chemical hardness for both Au _n Na and Au _n+1 clusters. It is found that Au₅Na and Au₆ have the most enhanced stability. Here, the size evolutions of the theoretical ionization potentials are in agreement with available experimental data, suggesting a good prediction of the lowest energy structures in the present study. In addition, the charge transfer has been analyzed on the basis of natural population analysis.     

Ruthenium(II) thiacrown complexes: Synthetic, spectroscopic, electrochemical, DFT, and single crystal X-ray structural studies of [Ru([15]aneS5)Cl](PF6)

We wish to report the synthesis of the Ru(II) crown thioether complex, (1,4,7,10,13-pentathiacyclopentadecane)chlororuthenium(II) hexafluorophosphate, [Ru([15]aneS₅)Cl](PF₆), and a study of its properties utilizing single crystal X-ray diffraction, electronic spectroscopy, NMR spectroscopy, density functional theory calculations and cyclic voltammetry. The crystal structure shows a single [15]aneS₅ macrocycle and a chloro ligand coordinated in a distorted octahedral fashion around the ruthenium(II) center. A significant shortening (0.15 Å) of the trans Ru-S bond length occurs in this complex compared to the related PPh₃ complex (2.4458(10) to 2.283(1) Å) due to the differences in the trans influence of the two ligands. ¹³C NMR spectroscopy demonstrates that the structure of [Ru([15]aneS₅)Cl]⁺ is retained in solution. As expected for a Ru(II) complex, the electronic absorption spectrum shows two d-d transitions at 402 and 331 nm. These are red-shifted compared to hexakis(thioether)ruthenium(II) complexes and consistent with the weaker ligand field effect of the chloro ligand. The electrochemical behavior of the complex in acetonitrile shows a single one-electron reversible oxidation-reduction at +0.722 V versus Fc/Fc⁺ which is assigned as the Ru(II)/Ru(III) couple. DFT calculations for [Ru([15]aneS₅)Cl]⁺ show a HOMO with orbital contributions from a t_2g type orbital of the Ru ion, a π component from a p orbital of the axial S atom of [15]aneS₅, and a p orbital of the chloro ligand while the LUMO consists of orbital contributions of d_x²-y² orbital of the Ru center and p orbitals of the four equatorial S donors.     

Reexamination of structures,stabilities, and electronic properties of holmium-doped silicon clusters HoSi<Subscript><Emphasis Type="Italic">n</Emphasis></Subscript> (<Emphasis Type="Italic">n</Emphasis> = 12–20)

The total energies, growth patterns, equilibrium geometries, relative stabilities, hardnesses, intramolecular charge transfer, and magnetic moments of HoSi _n (n?=?12–20) clusters have been reexamined theoretically using two different density functional schemes in combination with relativistic small-core Stuttgart effective core potentials (ECP28MWB) for the Ho atoms. The results show that when n?=?12–15, the most stable structures are predicted to be exohedral frameworks with a quartet ground state, but when n?=?16–20, they are predicted to be endohedral frameworks with a sextuplet ground state. These trend in stability across the clusters (gauged from their dissociation energies) was found to be approximately the same regardless of the DFT scheme used in the calculations, with HoSi₁₃, HoSi₁₆, HoSi₁₈, and HoSi₂₀ calculated to be more stable than the other clusters. The results obtained for cluster hardness indicated that doping the Ho atom into Si₁₃ and Si₁₆ leads to the most stable HoSi _n clusters, while doping Ho into the other Si _n clusters increases the photochemical sensitivity of the cluster. Analyses of intracluster charge transfer and magnetic moments revealed that charge always shifts from the Ho atom to the Si _n cluster during the creation of exohedral HoSi _n (n?=?12–15) structures. However, the direction of charge transfer is reversed during the creation of endohedral HoSi _n (n?=?16–20) structures, which implies that Ho acts as an electron acceptor when it is encapsulated in the Si _n cage. Furthermore, when the most stable exohedral HoSi _n (n?=?12–15) structures are generated, the 4f electrons of Ho are virtually unchanged and barely participate in intracluster bonding. However, in the most stable endohedral HoSi _n (n?=?16–20) frameworks, a 4f electron does participate in bonding. It does this by transferring to the 5d orbital, which hybridizes with the 6s and 6p orbitals and then interacts with Si valence sp orbitals. Meanwhile, the total magnetic moments of the HoSi _n (n?=?16–20) clusters are considerably higher than those of HoSi _n (n?=?12–15). Interestingly, the endohedral HoSi₁₆ and HoSi₂₀ clusters can be viewed as the most suitable building blocks for novel high-density magnetic storage nanomaterials and for novel optical and optoelectronic photosensitive nanomaterials, respectively.     

Stability and electronic properties of praseodymium-doped silicon clusters PrSin (<Emphasis Type="Italic">n</Emphasis> = 12–21)

The neutral PrSi _n (n = 12–21) species considering various spin configurations were systematically studied using PBE0 and B3LYP schemes in combination with relativistic small-core potentials (ECP28MWB) for Pr atoms and cc-pVTZ basis set for Si atoms. The total energy, growth-pattern, equilibrium geometry, relative stability, hardness, charge transfer, and magnetic moments are calculated and discussed. The results reveal that when n < 20, the ground-state structure of PrSi _n evaluated to be prolate clusters. Starting from n = 20, the ground-state structures of PrSi _n are evaluated to be endohedral cagelike clusters. Although the relative stabilities based on various binding energies and different functional is different from each other, the consensus is that the PrSi₁₃, PrSi₁₆, PrSi₁₈, and PrSi₂₀ are more stable than the others, especially the PrSi₂₀. Analyses of hardness show that introducing Pr into Si _n (n = 12–21) elevates the photochemical sensitivity, especially for PrSi₂₀. Calculated result of magnetic moment and charge transfer shows that the 4f electrons of Pr in the clusters are changed, especially in endohedral structures such as PrSi₂₀, in which one electron transfers from 4f to 5d orbital. That is, the 4f electron of Pr in the clusters participates in bonding. The way to participate in bonding is that a 4f electron transfers to 5d orbital. Although the 4f electron of Pr atom participates in bonding, the total magnetic moment of PrSi _n is equal to that of isolated Pr atom. The charge always transfers from Pr atom to Si _n cluster for the ground state structures of PrSi_n (n = 12–19), but charge transfer is reverse for n ≥ 20. The largest charge transfer for endohedral structure reveals that the bonding between Pr and Si _n is ionic in nature and very strong. The fullerenelike structure of PrSi₂₀ is the most stable among all of these clusters and can act as the building blocks for novel functional nanotubes.     

Stabilization of gold nanowires inside nanoaggregates of cyclo[8]thiophene, cyclo[8]selenophene, and cyclo[8]tellurophene: a theoretical study

The stabilities and electronic properties of gold clusters containing up to six atoms trapped inside cyclo[8]thiophene (CS8), cyclo[8]selenophene (CSe8), and cyclo[8]tellurophene (CTe8) nanoaggregates have been studied using the M06 functional. The 6-31G(d) basis set was used for all atoms except Au and Te, for which the LANL2DZ(d,p) pseudopotential basis set was applied. Single-point energy calculations were performed with the 6-311G(d,p) basis set for all atoms except for Au and Te, for which the cc-TZVP-pp pseudopotential basis set was used. Among the three studied macrocycles, only CS8 and CSe8 were found to be capable of nanoaggregate formation. In the lowest-energy conformer of CTe8, the tellurophene fragments adopt an anti orientation, thus impeding a tubular arrangement of the macrocycles. The formation of gold clusters inside the CS8 and CSe8 nanoaggregates is a thermodynamically favorable process, and could represent a potentially useful method of stabilizing metal nanowires. The binding energy between the nanoaggregate and the gold cluster is always higher for selenium-containing complexes than for sulfur-containing ones because Se has a higher affinity than S for Au in such complexes. Interactions of the gold cluster with the nanoaggregate walls can change the geometry of the most stable isomer for the cluster. The relative energies of different isomers are rather similar, suggesting that they coexist. For nanoaggregates containing Au₆ clusters, the cluster geometry when it is inside a nanoaggregate is different from the geometry of the cluster when it is not inside the nanoaggregate, due to the geometric restrictions imposed by the nanoaggregate cavity. The reorganization energy needed to change the geometry leads to lower binding energies for these complexes compared to those of some smaller systems, although the formation of a complex between Au₆ and a nanoaggregate with six CS8 or CSe8 macrocycles is still thermodynamically viable.     

Insight into coordination of dilead unit by molecules of 4-thiazolidinone-2-thione: Structural and computational studies

The reaction of Pb²⁺ ions with 4-thiazolidinone-2-thione (Hrd) yields to coordination of the uncommon dilead unit (Pb₂²⁺) by the N-deprotonated molecule of the ligand. The powder structure determination of the complex reveals an almost planar dimeric structure with the {N,S} coordination mode. The intermolecular distance of the Pb-Pb moiety (3.51(4) Å) is lower than the van der Waals parameter suggesting the formation of a bond. The structure in the solid state and DFT calculations of molecular orbitals and the presence of a bond critical point between the lead atoms clearly demonstrate the existence of a single bond within the Pb-Pb unit formed by the 6p orbital electrons. The lone pairs of the 6s orbitals do not participate in bonding with the ligand atoms and are likely bisdirected. FT-IR and FT-Raman spectra confirm the molecular structure since all the modes of the NH group disappear in the spectra of the complex, while the stretching mode of the CS bond shifts to lower values, as would be expected for this coordination fashion.