DFT study of “all-metal” aromatic compounds

Tsipis, Constantinos A.

doi:10.1016/j.ccr.2005.01.031

Cited by 170 publications

(121 citation statements)

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“…Recently discovered [11], all-metal and semimetal aromatic clusters represent one of the new boundaries of material science (three recent reviews on this kind of clusters can be found in Refs. [12][13][14]). The unusual stability of all these clusters comes from their aromatic character.…”

Section: Introductionmentioning

confidence: 99%

“…Indeed, the aromaticity is a key property of these compounds since it explains their molecular and electronic structure, stability, and reactivity. At variance with the classical aromatic organic molecules that possess only π-electron delocalization, these compounds present σ-, π-, and δ-(involving d orbitals) [15][16][17] or even φ-(involving f orbitals) [18] electron delocalization, exhibiting characteristics of what has been called multifold aromaticity [12][13][14][19][20][21][22]]. …”

Section: Introductionmentioning

confidence: 99%

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A Critical Assessment of the Performance of Magnetic and Electronic Indices of Aromaticity

et al. 2010

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Abstract:The lack of reference aromatic systems in the realm of inorganic aromatic compounds makes the evaluation of aromaticity in all-metal and semimetal clusters a difficult task. To date, calculation of nucleus-independent chemical shifts (NICS) has been the most widely used method to discuss aromaticity in these systems. In the first part of this work, we briefly review our previous studies, showing some pitfalls of the NICS indicator of aromaticity in organic molecules. Then, we refer to our study on the performance of some aromaticity indices in a series of 15 aromaticity tests, which can be used to analyze the advantages and drawbacks of aromaticity descriptors. It is shown that indices based on the study of electron delocalization are the most accurate among those analyzed in the series of proposed tests, while NICS(1) zz and NICS(0) πzz present the best behavior among NICS indices. In the second part, we discuss the use of NICS and electronic multicenter indices (MCI) in inorganic clusters. In particular, we evaluate the aromaticity of two series of all-metal and semimetal clusters with predictable aromaticity trends by means of NICS and MCI. Results show that the expected trends are generally better reproduced by MCI than NICS. It is concluded that NICS(0) π and NICS(0) πzz are the kind of NICS that perform the best among the different NICS indices analyzed for the studied series of inorganic compounds.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

A Critical Assessment of the Performance of Magnetic and Electronic Indices of Aromaticity

et al. 2010

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“…1,2 the concept of aromaticity was extended from its usual organic realm to the field of all-metal inorganic clusters. Compared to the aromaticity encountered in organic molecules, primarily being of the traditional π-type, all-metal systems can exhibit a multifold aromaticity [3][4][5] and conflicting aromaticity, 2,3,[6][7][8][9] arising from their σ-, π-, δ-10,11 and even φ-12 electron delocalization. Until recently, there was no report on the existence of a ring current, there is no direct way to extract and thus beyond doubt prove the existence of an underlying ring current.…”

Section: Introductionmentioning

confidence: 99%

“…1,2 the concept of aromaticity was extended from its usual organic realm to the field of all-metal inorganic clusters. Compared to the aromaticity encountered in organic molecules, primarily being of the traditional π-type, all-metal systems can exhibit a multifold aromaticity [3][4][5] and conflicting aromaticity, 2,3,[6][7][8][9] arising from their σ-, π-, δ- The problem with claims that a certain species is aromatic is that this conclusion may depend rather significantly on the property used to characterize aromaticity. As an example: a ring that exhibits bond length equalization as in benzene but does not sustain a ring current could be classified by some as aromatic but by others as not aromatic depending on the relative importance they attach to the property of bond lengths equalization or ring currents respectively.…”

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confidence: 99%

Ring Currents in Polycyclic Sodium Clusters

Radenković

Bultinck

2011

J. Phys. Chem. A

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In the recent work by Khatua et al. [Khatua, S.; Roy, D. R.; Bultinck, P.; Bhattacharjee, M.; Chattaraj, P. K. Phys. Chem. Chem. Phys. 2008, 10, 2461-2474 the synthesis and structure of a fac-trioxo molybdenum metalloligand and its sodium complex containing 1D hexagonal chains of sodium ions was reported. In the same paper, the aromaticity of hexagonal Na-clusters was quantified by means of the nucleus-independent chemical shift and electronic multicentre indices. It was shown that the aromaticity of hexagonal Na-clusters is of the same order as the aromaticity of analogous benzenoid hydrocarbons. In the present study current density maps are used to rationalize the aromaticity of polycyclic Na-clusters. It is shown that although polycyclic Na-systems sustain a diatropic ring current, the induced current density is several times weaker than in analogous benzenoid hydrocarbons. A detailed analysis indicates that the current density in hexagonal Na-systems is almost completely determined by four HOMO σ-electrons. 1,2 the concept of aromaticity was extended from its usual organic realm to the field of all-metal inorganic clusters. Compared to the aromaticity encountered in organic molecules, primarily being of the traditional π-type, all-metal systems can exhibit a multifold aromaticity [3][4][5] and conflicting aromaticity, 2,3,[6][7][8][9] arising from their σ-, π-, δ- The problem with claims that a certain species is aromatic is that this conclusion may depend rather significantly on the property used to characterize aromaticity. As an example: a ring that exhibits bond length equalization as in benzene but does not sustain a ring current could be classified by some as aromatic but by others as not aromatic depending on the relative importance they attach to the property of bond lengths equalization or ring currents respectively. The same is true for e.g., electron delocalization and ring currents. Although one of us has previously shown that electron delocalization and ring currents in carbohydrates go hand in hand, 20-23 the more general and subtle interrelationship is that a delocalized system is a necessary but not sufficient requirement for a ring current. In previous work on Na 6 systems, electron delocalization was gauged by the multicentre index and information on a ring current was obtained indirectly from NICS values. The problem with NICS, however, is that although usually a negative (or aromatic) NICS value reflects the 3 existence of a ring current, there is no direct way to extract and thus beyond doubt prove the existence of an underlying ring current. INTRODUCTION COMPUTATIONAL METHODSThe structures of the Na 4n+2 (n = 1-5) entities (Figure1) were taken from the experimental structural data given by Khatua et al. 13,14 The molecular structures of the linear polyacenes C 4n+2 H 2n+4 (n = 1-5) were optimized at the B3LYP/6-311+G* level.Computed Hessian matrices showed the optimized structures to correspond to minima on the potential energy surface.The current density maps presented in this pap...

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“…[3] It has been shown that main-group clusters may exhibit multiple aromaticity (s and p), multiple antiaromaticity (s and p), and conflicting aromaticity (s aromaticity and p antiaromaticity or s antiaromaticity and p aromaticity). [4][5][6] Here, we report experimental and theoretical evidence of d aromaticity, which is only possible in transition-metal systems. It is discovered in the [Ta 3 O 3 ]…”

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confidence: 95%

δ Aromaticity in [Ta₃O₃]⁻

Zhai

Аверкиев²,

Zubarev³

et al. 2007

Angew Chem Int Ed

135

119

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The concept of aromaticity was introduced into organic chemistry to describe delocalized p bonding in planar, cyclic, and conjugate molecules possessing (4n+2) p electrons.[1] In recent years, this concept has been advanced into main-group molecules including organometallic compounds with cyclic cores of metal atoms [2] and, in particular, all-metal clusters.[3]It has been shown that main-group clusters may exhibit multiple aromaticity (s and p), multiple antiaromaticity (s and p), and conflicting aromaticity (s aromaticity and p antiaromaticity or s antiaromaticity and p aromaticity). [4][5][6] Here, we report experimental and theoretical evidence of d aromaticity, which is only possible in transition-metal systems. [7] in which they showed the presence of a new type of chemical bond-a d bond between the two Re atoms. Since then, a branch of inorganic chemistry has been developed that involves multiple metal-metal bonding [8] with bond orders higher than three, the maximum allowed for main-group systems. Power and co-workers recently reported the synthesis of a Cr 2 compound with a quintuple bond (s 2 p 4 d 4 ) between the two Cr atoms. [9] This work, along with recent quantum chemical studies of multiple bonds in U 2 and [Re 2 Cl 8 ] 2À , [10] has generated renewed interest in multiple metal-metal bonding. [11][12][13] The presence of d bonds between two transition-metal atoms suggests that multicenter transition-metal species with a completely delocalized cyclic d bond may exist, thus raising the possibility of d aromaticity analogous to p or s aromaticity in main-group systems. We have been interested in understanding the electronic structure and chemical bonding of early transition-metal oxide clusters as a function of size and composition, and in using them as potential molecular models for oxide catalysts. [14][15][16] During our investigation of tantalum oxide clusters, we found the presence of d aromaticity in the [ Ta 3 O 3 ] À cluster, in which each Ta atom is in a low oxidation state of Ta II and still possesses three electrons for Ta-Ta bonding.The experiment was conducted by using a magneticbottle-type photoelectron spectroscopy apparatus equipped with a laser vaporization cluster source.[17] [Ta m O n ] À clusters with various compositions were produced by laser vaporization of a pure tantalum disk target in the presence of a helium carrier gas seeded with O 2 , and were size-separated by time-of-flight mass spectrometry. The [Ta 3 O 3 ] À species was mass-selected and decelerated before photodetachment by a pulsed laser beam. Photoelectron spectra were obtained at two relatively high photon energies, 193 nm (6.424 eV) and 157 nm (7.866 eV), to guarantee access to all valence electronic transitions (Figure 1). Three well-resolved bands (X, A, and B) were observed at the lower-binding-energy side. The X band is much more intense and shows a discernible splitting at 193 nm (Figure 1 a). Surprisingly, no well-defined electronic transitions were observed beyond 3.7 eV, where continuous signals were...

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DFT study of “all-metal” aromatic compounds

Cited by 170 publications

References 186 publications

A Critical Assessment of the Performance of Magnetic and Electronic Indices of Aromaticity

A Critical Assessment of the Performance of Magnetic and Electronic Indices of Aromaticity

Ring Currents in Polycyclic Sodium Clusters

δ Aromaticity in [Ta₃O₃]⁻

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DFT study of “all-metal” aromatic compounds

Cited by 170 publications

References 186 publications

A Critical Assessment of the Performance of Magnetic and Electronic Indices of Aromaticity

A Critical Assessment of the Performance of Magnetic and Electronic Indices of Aromaticity

Ring Currents in Polycyclic Sodium Clusters

δ Aromaticity in [Ta3O3]−

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δ Aromaticity in [Ta₃O₃]⁻