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1.
Phys Chem Chem Phys ; 2020 Sep 10.
Artigo em Inglês | MEDLINE | ID: mdl-32909020

RESUMO

DFT calculations were carried out on bare Au32 and Au33 nanoclusters with various charges, in order to analyze their stability with respect to different cluster electron numbers. Results indicate that in addition to the neutral Au32 hollow species, significant HOMO-LUMO gaps are computed for [Au32]8+ (hollow) and [Au32]4+ (two-shell structure). Species with smaller HOMO-LUMO gaps can reach stability upon "passivation" by a ligand shell, as experimentally exemplified. Icosahedral frameworks of Ih or lower symmetry are favored for the cationic nanoclusters whereas different structures are computed for the anionic ones.

2.
Chem Commun (Camb) ; 2020 Aug 13.
Artigo em Inglês | MEDLINE | ID: mdl-32789413

RESUMO

Cluster anions [Cp*RuPb11]3- (1) and [Cu@Cp*RuPb11]2- (2) represent the first vertex-substituted zintl icosahedra and 1 is the first non-centered zintl icosahedron isolated in the condensed phase. Complexes 1 and 2 are both 12-vertex, 26-electron closo-clusters with C5v point symmetry and are static on the 207Pb NMR time scale in solution.

3.
Phys Chem Chem Phys ; 22(34): 19213-19222, 2020 Sep 14.
Artigo em Inglês | MEDLINE | ID: mdl-32812576

RESUMO

The physical nature of host-guest (HG) interactions occurring between molecular triangles and linear anions was explored using density functional theory (DFT) calculations combined with energy decomposition analyses (EDA), nuclear independent chemical shift (NICS), and non-covalent interaction index (NCI). We demonstrate that: (i) in addition to the host being significantly rigid, the strain energies are not negligible, especially for host 2; (ii) halogen anions interact mainly by electrostatic forces (ΔEelst > ΔE > ΔEdisp), meanwhile; (iii) trihalogen anions interact mostly by dispersion forces (ΔEdisp > ΔEelst≈ΔE). The NICS and NCI calculations corroborate the idea that HG interactions are considerably mediated through dispersion terms, and also indicate an antiaromatic character inside the host walls.

4.
Acta Crystallogr B Struct Sci Cryst Eng Mater ; 76(Pt 2): 166-176, 2020 Apr 01.
Artigo em Inglês | MEDLINE | ID: mdl-32831220

RESUMO

Dinuclear CuII complexes with 3,5-dinitrobenzoates and 2,2'-bipyridine (2) or 1,10-phenanthroline (3) were synthesized and characterized. A complete energy framework analysis using the HF/3-21G energy model was performed which found that dispersion forces and C-H...O interactions are responsible for the crystal structure features. The magnetic properties of the complexes show a weak magnetic exchange between spins, resulting in low exchange constants of -2.72 (1) cm-1 and -1.10 (1) cm-1 for complexes (2) and (3), respectively. This results from the low overlap between magnetic orbitals induced by 3,5-dinitrobenzoate bridges and the arrangement of the magnetic orbitals. Consequently, the dinuclear complexes (2) and (3) behave as spin-isolated multinuclear CuII species in contrast to the trinuclear complex with similar ligands.

5.
Artigo em Inglês | MEDLINE | ID: mdl-32608037

RESUMO

In this work, the largest heterometallic supertetrahedral clusters, [Zn6 Ge16 ]4- and [Cd6 Ge16 ]4- , were directly self-assembled through highly-charged [Ge4 ]4- units and transition metal cations, in which 3-center-2-electron σ bonding in Ge2 Zn or Ge2 Cd triangles plays a vital role in the stabilization of the whole structure. The cluster structures have an open framework with a large central cavity of diameter 4.6 Šfor Zn and 5.0 Šfor Cd, respectively. Time-dependent HRESI-MS spectra show that the larger clusters grow from smaller components with a single [Ge4 ]4- and ZnMes2 units. Calculations performed at the DFT level indicate a very large HOMO-LUMO energy gap in [M6 Ge16 ]4- (2.22 eV), suggesting high kinetic stability that may offer opportunities in materials science. These observations offer a new strategy for the assembly of heterometallic clusters with high symmetry.

6.
Phys Chem Chem Phys ; 22(25): 14268-14275, 2020 Jul 01.
Artigo em Inglês | MEDLINE | ID: mdl-32555845

RESUMO

Endohedral metallofullerenes are key species for expanding the range of viable fullerenes, their versatility, and applications. Here we report our computational evaluation on the formation of spherical aromatic counterparts of the C60 fullerene from relativistic DFT calculations, based on the inclusion of Cr, Mo and W endohedral atoms. The resulting M@C60 endohedral fullerenes are 66-π electron neutral species exhibiting bonding properties and electronic structure mimicking the aromaticity and diamagnetic insulator behavior of alkali-C606- phases. The resulting structures are interesting candidates for further experimental realization as novel neutral building blocks for more flexible nanostructured organic materials, highlighting truly spherical aromatic neutral species retaining the truncated icosahedral structure of the seminal Buckminster fullerene.

7.
Chemphyschem ; 2020 Jun 23.
Artigo em Inglês | MEDLINE | ID: mdl-32573902

RESUMO

Molecular recognition is the key driver in the formation of supramolecular complexes, enabling the selective encapsulation of specific guests. Here, we explore the delicate balance between different energetic terms in the formation of an efficient host for fluoride anions based on a cylindrophane structure, which can be achieved by the incorporation of ligand sites into a cyanuric acid based cyclophane framework, resulting a close proximity between the ammonium hydrogens and the anion. This study describes the character and contribution of different energetic and repulsive terms that favor the efficient inclusion of fluoride. Our findings are useful for further rational design and synthesis of efficient and highly selective fluoride hosts, which have been generally less well described than complexing agents for other halides.

8.
Chem Commun (Camb) ; 56(48): 6583-6586, 2020 Jun 16.
Artigo em Inglês | MEDLINE | ID: mdl-32400811

RESUMO

In this work, we report a dimeric cluster anion, {[CuGe9Mes]2}4-, which was isolated as the [K(2,2,2-crypt)]+ salt and characterized by using single-crystal X-ray diffraction and ESI mass spectroscopy. The title cluster represents the first locally σ-antiaromatic compound in the solid state, as well as the first heteroatomic antiaromatic compound.

9.
Chemphyschem ; 2020 May 15.
Artigo em Inglês | MEDLINE | ID: mdl-32413178

RESUMO

The shielding cone concept is one of the most characteristic aspects of planar aromatic species. Herein, we explored how two neighbor aromatic moieties behave as dual planar-planar, planar-spherical, and spherical-spherical species given by biphenyl, [PhCB11 H11 ]- , and [CB11 H11 ]2 2- , respectively. Our results show two separate aromatic regimes given by Clar's sextet and spherical aromatic states, with independent shielding cones sharing shielding regions of moderate strength, which can be extended for networks involving multiple independent aromatic states.

10.
Phys Chem Chem Phys ; 2020 Apr 20.
Artigo em Inglês | MEDLINE | ID: mdl-32307509

RESUMO

The induced magnetic field of C2N (N = 3-14) carbon rings was dissected to contributions from out-of-plane and in-plane π orbitals revealing two concurrent long range shielding or deshielding cones as a manifestation of the dual aromatic and antiaromatic character of C4n+2 and of C4n rings respectively. Aromaticity based on the magnetic criterion was evaluated with regard to the bonding pattern and geometrical characteristics that elucidate the influence of bond length and bond angle alteration on out-of-plane and in-plane magnetic responses. Ground state polyynic geometries of C4n+2 rings exhibit comparable shielding cones to annulenes, decreasing the magnetic response with regard to the ring size and similar πout and πin diatropicity. Transition state cumulenic rings display increased aromaticity expressed by a very strong constant magnetic response and augmented πout diatropicity with regard to πin. The variations of the induced magnetic field are explained on the basis of frontier orbital interactions through rotational excitations, which enable further rationalization of the aromatic/antiaromatic behavior.

11.
Chemistry ; 2020 Feb 13.
Artigo em Inglês | MEDLINE | ID: mdl-32056301

RESUMO

The icosahedral [M@Pb12 ]3- (M=Co(1), Rh(2), Ir(3)) cluster ions were prepared from K4 Pb9 and Co(dppe)Cl2 (dppe=1,2-bis(diphenylphosphino)ethane)/[Rh(PPh3 )3 Cl]/[Ir(cod)Cl]2 (cod=1,5-cyclooctadiene), respectively, in the presence of 18-crown-6/ 2,2,2-cryptand in ethylenediamine/toluene solvent mixtures. The [K(2,2,2-cryptand)]+ salt of 1 and the [K(18-crown-6)]+ salt of 3 were characterized via X-ray crystallography; the ions 1 and 3 are isostructural and isoelectronic to the [Rh@Pb12 ]3- (2) ion as well as to the group 10 clusters [M'@Pb12 ]2- (M'=Ni, Pd, Pt). The ions are all 26-electron clusters with near perfect icosahedral Ih point symmetry. Clusters 1-3 show record downfield 207 Pb NMR chemical shifts due to σ-aromaticity of the cluster framework. Calculated and observed 207 Pb NMR chemical shifts and 207 Pb-x M J-couplings (x M=59 Co, 103 Rh, 193 Ir) are in excellent agreement and DFT analysis shows that the variations of 207 Pb NMR chemical shifts for the [M@Pb12 ]2, 3- ions (M=Co, Rh, Ir, Ni, Pd, Pt) are mainly governed by the perpendicularly oriented σ11 component of the chemical shift anisotropy tensor. The laser desorption ionization time-of-flight (LDI-TOF) mass spectra contain the molecular ions as well as several new gas phase clusters derived from the parents. The DFT-minimized structures of these ions are described.

12.
Chemistry ; 26(1): 326-330, 2020 Jan 02.
Artigo em Inglês | MEDLINE | ID: mdl-31680347

RESUMO

Helicenes consist of several fused rings twisted around an axis, forming a cylindrical helix, with π-delocalized electrons in the non-planar rings. Induced magnetic fields dissecting the orbital contributions of [6]-, [7]-, and [14]helicene are discussed. Computations show a deshielding cone produced by the π-electrons along the helical axis. Unexpectedly, the response of the core electrons produces a shielding cone, which is cumulative and sensitive to the curvature of the systems owing to the overlap of the other ring responses. A warning is provided regarding the evaluation of the delocalization in curved systems in which the x- and y-components of the induced magnetic field become relevant.

13.
Chemistry ; 26(9): 2073-2079, 2020 Feb 11.
Artigo em Inglês | MEDLINE | ID: mdl-31851761

RESUMO

The chemical bonding of Zintl clusters is still an evolving and hot topic in modern chemistry. In this paper we synthesized a novel [K([2.2.2]crypt)]4 [In8 Bi13 ] complex in a condensed phase. The quantum chemical calculations and X-ray data revealed that the compound consists of the 1:1 mixture of [Bi@In8 Bi12 ]3- and [Bi@In8 Bi12 ]5- clusters. To the date, those clusters are the largest binary clusters composed of In and Bi elements. Herein, we introduce a spherical aromatic description of chemical bonding for such clusters. We show through AdNDP, ELF, and induced magnetic field and quantitative NICS analyzes that both clusters are spherically aromatic which explains their high symmetry, stability, and peculiar magnetic properties. We believe that this work will help researchers in the further development and understanding of chemical bonding in Zintl clusters.

14.
Inorg Chem ; 59(4): 2188-2199, 2020 Feb 17.
Artigo em Inglês | MEDLINE | ID: mdl-31851494

RESUMO

Organic azide complexes of copper(I) and silver(I), [(SIPr)CuN(1-Ad)NN][SbF6], [(SIPr)CuN(2-Ad)NN][SbF6], [(SIPr)CuN(Cy)NN][SbF6], and [(SIPr)AgN(1-Ad)NN][SbF6] have been synthesized by using Ag[SbF6] and the corresponding organic azides with (SIPr)CuBr and (SIPr)AgCl (SIPr = 1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene). The copper and silver organic azide complexes were characterized by various spectroscopic techniques and X-ray crystallography. Group trends of isoleptic Cu(I), Ag(I), and Au(I) organic azide complexes are presented on the basis of experimental data and a detailed computational study. The νasym(N3) values of the metal-bound 1-AdNNN in [(SIPr)MN(1-Ad)NN]+ follow the order Ag < Cu < Au. DFT calculations show that gold(I) forms the strongest bond with 1-AdNNN in this series, while silver has the weakest interaction. Furthermore, auxiliary ligand free coinage metal N-heterocyclic carbene complexes, [(SIPr)M][SbF6], have been synthesized via metathesis reactions of (SIPr)MCl (M = Cu, Ag, Au) with Ag[SbF6]. X-ray crystal structures of dinuclear [(SIPr)Ag]2[SbF6]2 and [(SIPr)Au]2[SbF6]2 are also reported. They show close metallophilic contacts. [(SIPr)Au]2[SbF6]2 reacts with OEt2, SMe2, and CNtBu to afford [(SIPr)Au(OEt2)][SbF6], [(SIPr)Au(SMe2)][SbF6], and [(SIPr)Au(CNtBu)][SbF6] adducts, respectively.

15.
Phys Chem Chem Phys ; 22(3): 1422-1426, 2020 Jan 21.
Artigo em Inglês | MEDLINE | ID: mdl-31859297

RESUMO

δ-Bonds have been intimately related to metal-metal bonds of d-elements since the archetypal d4-d4 [Re2Cl8]2- ion with a σ2π4δ2 bond. Currently, the notion of multiple superatom arrangements as initial steps toward molecular materials within the building-up approach is dominated by P-shell characteristics, as given in the well-described Au25(SR)18 ligand protected cluster. In this work we rationalize the Au22(dppo)6 cluster as a triple-bonded 22-valence electron (ve) supermolecule, featuring a bonding scheme based on 1D + 1D shell combinations, which largely contrasts with the 14-ve Au38(SR)24 with mainly 1P + 1P patterns mimicking a F2 molecule. The resulting Π4Δ2-bonding pattern shows an unprecedented superatomic counterpart of a d-shell based bond inherently related to transition-metal dimers, adding useful key aspects to the understanding of species based on cluster-assembly.

16.
Chemistry ; 2019 Dec 22.
Artigo em Inglês | MEDLINE | ID: mdl-31867789

RESUMO

Structural characterization of the discrete [Sn@Cu12 @Sn20 ]12- cluster exposed a fascinating architecture composed of three concentric structural layers in which an endohedral Sn atom is enclosed in a Cu12 icosahedron, which in turn is embedded in an Sn20 dodecahedron. Herein, the possibility of sustaining aromatic behavior for this prototypical multilayered species was evaluated, in order to extend this concept to more complex clusters on the basis of magnetic response and bonding analysis by the AdNDP approach. This revealed characteristic features of spherical aromatics, given by the ability to sustain the shielding cone property, similar to archetypal aromatics. The favorable bonding pattern in the [Sn@Cu12 @Sn20 ]12- cluster fulfills the 2(N+1)2 Hirsch rule for aromaticity; thus, the cluster could be regarded as a first member of aromatic multilayered structures. The set of four 13c-2e aromatic bonds that was identified in the internal SnCu12 structure results in spherical aromatic character of this multilayered cluster. This insight builds a bridge between the traditional concept of Hückel's aromaticity and the aromaticity of complex and stable 3D systems that may be explored on the basis of magnetic response and bonding analysis. It also may open a way to novel findings in bottled clusters displaying aromatic behavior in multilayer structures, which are of great interest for inorganic nano- and material sciences due to their unprecedented stability.

17.
Phys Chem Chem Phys ; 21(45): 25215-25219, 2019 Dec 07.
Artigo em Inglês | MEDLINE | ID: mdl-31696890

RESUMO

The most characteristic feature of planar π-aromatics is the ability to sustain a long-range shielding cone under a magnetic field oriented in a specific direction. In this article, we showed that similar magnetic responses can be found in σ-aromatic and spherical aromatic systems. For [Au13]5+, long-range characteristics of the induced magnetic field in the bare icosahedral core are revealed, which are also found in the ligand protected [Au25(SH)18]- model, proving its spherical aromatic properties, also supported by the AdNDP analysis. Such properties are given by the 8-ve of the structural core satisfying the Hirsch 2(N + 1)2 rule, which is also found in the isoelectronic [M@Au12]4+ core, a part of the [MAu24(SR)18]2- (M = Pd, Pt) cluster. This contrasts with the [M@Au12]6+ core in [MAu24(SR)18]0 (M = Pd, Pt), representing 6-ve superatoms, which exhibit characteristics of planar σ-aromatics. Our results support the spherical aromatic character of stable superatoms, whereas the 6-ve intermediate electron counts satisfy the 4N + 2 rule (applicable for both π- and σ-aromatics), showing the reversable and controlled interplay between 3D spherical and 2D σ-aromatic clusters.

18.
J Mol Model ; 25(11): 322, 2019 Oct 25.
Artigo em Inglês | MEDLINE | ID: mdl-31654139

RESUMO

The textbook concept of shielding cone is one of the characteristic properties for planar aromatic species, which explains the nuclear shielding of neighbor molecules located above and below the molecular plane. Here, we explore its resemblance in spherical aromatic fullerenes, where particularly for C606-, it explains the record for the highest shielding observed via 3He-NMR for the endohedral 3He@C606- species. Our results compare the behavior for He@C60 and He@C606- denoting relevant changes in their magnetic response behavior, where an induced shielding cone was observed for the latter with its long-range shielding character. In contrast to planar aromatics which give rise to a shielding cone property only for a perpendicularly oriented field, it was found that the shielding cone in spherical aromatic fullerenes occurs to any orientation. Thus, the orientation dependence behavior of the shielding cone is accounted, unraveling a characteristic shielding cone pattern in He@C606- which further rationalizes its record on the most shielded He nucleus, upon rotation or tumbling from the aromatic ring about the applied field. For the C70 case, the opposite situation has been characterized via 3He-NMR experiments, which is explained in terms of the deshielding/shielding region inside the C70 cage. Graphical abstract.

19.
Phys Chem Chem Phys ; 21(36): 20232-20238, 2019 Sep 18.
Artigo em Inglês | MEDLINE | ID: mdl-31490515

RESUMO

The induced magnetic field of B40 was dissected into contributions from π, σ and core electrons revealing the origins for the formation of the strong long range shielding response characterizing the spherical aromatic nature of the cavernous D2d structure. Our analysis showed the complementary role of π and σ orbitals for the formation of the global shielding cone, with weak π contributions at a long range and strong σ contributions inside the cage, supporting the molecule as double aromatic with weak π and strong σ delocalization. Similar local variations of both π and σ magnetic responses were identified portraying peripheral diatropic and local paratropic currents. The weak π aromaticity is explained on the basis of symmetry rules pertaining to its electronic structure which forbid small gap paratropic rotational excitations.

20.
Phys Chem Chem Phys ; 21(32): 17779-17785, 2019 Aug 15.
Artigo em Inglês | MEDLINE | ID: mdl-31372619

RESUMO

The energetically preferred structures of the gold clusters Au9+, Au113+, and Au124+ with eight skeletal electrons have been studied by density functional theory for comparison with the 8-electron Au102+ cluster shown previously to have a highly favored Td tetracapped octahedral structure. The low-energy structures for the Au9+ and Au113+ clusters are found to be similar relatively spherical polyhedra. Such systems can be considered to exhibit spherical aromaticity in accord with their filled 1S21P6 shells, their diatropic NICS(0) values ranging from -21.4 to -44.3 ppm, and their shielding cone surfaces. However, the preferred spherical polyhedra for Au9+ and Au113+ are not the same as the closo deltahedra found in the BnHn2- borane dianions. Instead they have smaller internal cavities formed by capping faces of smaller deltahedra or by formation of internal Au-Au bonds. The lowest energy Au124+ structures are not similar nearly spherical polyhedral structures. Instead they are derived from planar gold subclusters by adding more gold atoms to form tetrahedral Au4 bubbles. The planar origin of the low-energy Au124+ structures relates to the energetic preference for neutral Au<14 clusters for planar structures or nearly planar structures containing small polyhedral bubbles. The presence of σ-holes has been identified on the surfaces of the complete series of the Aun(n-8)+ (n = 9 to 12) clusters. The strength of their electrostatic interactions is predicted to increase upon increasing cluster size.

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