Probing the Electronic Structure and Aromaticity of Pentapnictogen Cluster Anions Pn5- (Pn = P, As, Sb, and Bi) Using Photoelectron Spectroscopy and ab Initio Calculations
17 May 2002-Journal of Physical Chemistry A (American Chemical Society)-Vol. 106, Iss: 23, pp 5600-5606
TL;DR: In this article, the electronic structure and chemical bonding of the pentapnictogen cluster anions, Pn5- (Pn = P, As, Sb, and Bi), were investigated using both photoelectron spectroscopy and ab initio calculations.
Abstract: The electronic structure and chemical bonding of the pentapnictogen cluster anions, Pn5- (Pn = P, As, Sb, and Bi), were investigated using both photoelectron spectroscopy and ab initio calculations. Well-resolved photoelectron spectra were obtained for the anions at several photon energies and were analyzed according to the theoretical calculations. The ground state of all the Pn5- species was found to be the aromatic cyclic D5h structure with a C2v low-lying isomer. We found that the C2v isomer gains stability from P5- to Sb5-, consistent with the experimental observation of the coexistence of both isomers in the spectra of Sb5-. The valence molecular orbitals (MOs) of the D5h Pn5- were analyzed and compared to those of the aromatic C5H5- hydrocarbon. The same set of π-MOs is shown to be occupied in the D5h Pn5- and C5H5- species, except that the MO ordering is slightly different. Whereas the three π-MOs in C5H5- all lie above the σ-MOs, the third π orbital (1a2‘ ‘ in Pn5-) lies below the σ-MOs. The stab...
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TL;DR: These new developments have shown that aromaticity and antiaromaticity in metal systems have frequently multiple nature, being o-aromatic/antiaromatic and n-Aromatic/Antiaromatic, which is not found in organic aromatic/antaromatic molecules.
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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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Cites background from "Probing the Electronic Structure an..."
...Among these series, P5 - is the only inorganic cluster that has been studied previously both experimentally and with theoretical methodologies [21,125–128]....
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TL;DR: The stability, reactivity, and aromaticity of the Be32- dianion and its bimetallic species are investigated, and the recently discovered direct Zn-Zn bond is stabilized through the complexation with Be32-, and a new compound is reported.
Abstract: The stability, reactivity, and aromaticity of the Be32- dianion and its bimetallic species are investigated. The aromaticity of these systems is analyzed in the light of the DFT-based reactivity descriptors, namely, hardness (eta) and polarizability (alpha), molecular orbital (MO) analysis, and the nucleus-independent chemical shift (NICS). The recently discovered direct Zn-Zn bond is stabilized through the complexation with Be32-, and a new compound [(Be3)2Zn2]2- is reported. The chemical nature and selectivity of the Be32- unit in its bimetallic form are analyzed using the atomic charge (Qk) and nucleophilicity excess (Deltaomega++g) descriptors to examine its applicability in the field of molecular electronics.
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01 Jan 2008
TL;DR: In this paper, it is shown that even small effects can have a large impact on the chemistry of these compounds and the analysis of subtle changes in aromaticity can be of importance in the future.
Abstract: Phosphorus an element with an electronegativity somewhat less than that of carbon and is an excellent and versatile building block of aromatic systems. Thus, in many systems carbon can be replaced efficiently by phosphorus. The versatility is a consequence of the many different bonding modes available for the pnicogen element. The extent of the aromaticity is different with the different bonding modes, and can also be fine tuned by utilizing various substituents that have inductive or steric effects. It is noteworthy that even small effects can have a large impact on the chemistry of these compounds. Thus, the analysis of subtle changes in aromaticity can be of importance in the future.
54 citations
References
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TL;DR: A way is found to visualize and understand the nonlocality of exchange and correlation, its origins, and its physical effects as well as significant interconfigurational and interterm errors remain.
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