An overview of recent studies, which show the important role played by computational chemistry in explaining and predicting the behavior of a great variety of systems is presented. The first example illustrates the useful interplay experiment-theory which allowed to unambiguously characterize the X2(CH3)7 + (X = Si, Ge, Sn, Pb) cations as paradigmatic examples of molecular systems involving pentacovalently bound carbon atoms. Also, the possibility of deeply analyzing the bonding in molecular systems, led to a rationalization of the quite different behavior of acetylene and iminoborane derivatives, in spite of being isoelectronic species. Similarly, the analysis of the bonding perturbations usually associated with ion-molecule interactions in the gas phase, or with protonation and deprotonation processes, has made possible the characterization of non-conventional complexes as the key structures in the interactions of unsaturated and aromatic Si and Ge containing compounds with transition metal ions or to explain the dramatic enhanced acidity of alkylboranes and α,β- unsaturated borane derivatives.
Keywords: Molecular orbital theory, density functional theory, bonding, gas-phase ion chemistry, non-conventional structures, intrinsic reactivity, Computational Chemistry, Gas-phase basicity or acidity scales, Uracil, Density functional theory (DFT), MP2 or DFT calculations, Atoms in molecules (AIM), The electron localization function (ELF) theory, Natural bond orbital (NBO) method, Bond critical points (BCP), Becke and Edgecombe electron localization function, Pentacovalent Carbon Atoms, Methylborane, Dysinaptic V(C,C) basinHole effect
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