J. Phys. Chem. A, 115, 13724, 2011

DOI:10.1021/jp2094164

J. E. Del Bene, I. Alkorta, G. Sánchez-Sanz and J. Elguero

Structures, Energies, Bonding, and NMR Properties of Pnicogen Complexes H2XP:NXH2 (X= H, CH3 , NH2 , OH, F, Cl)

Ab initio calculations have been carried out in a systematic investigation of P···N pnicogen complexes H2XP:NXH2 for X ═ H, CH3, NH2, OH, F, and Cl, as well as selected complexes with different substituents X bonded to P and N. Binding energies for complexes H2XP:NXH2 range from 8 to 27 kJ mol–1 and increase to 39 kJ mol–1 for H2FP:N(CH3)H2. Equilibrium structures have a nearly linear A–P–N arrangement, with A being the atom directly bonded to P. Binding energies correlate with intermolecular N–P distances as well as with bonding parameters obtained from AIM and SAPT analyses. Complexation increases 31P chemical shieldings in complexes with binding energies greater than 19 kJ mol–1. One-bond spin–spin coupling constants 1pJ(N–P) across the pnicogen interaction exhibit a quadratic dependence on the N–P distance for complexes H2XP:NXH2, similar to the dependence of 2hJ(X–Y) on the X–Y distance for complexes with X–H···Y hydrogen bonds. However, when the mixed complexes H2XP:NX′H2 are included, the curvature of the trendline changes and the good correlation between 1pJ(N–P) and the N–P distance is lost.

Mol. Phys., 109, 2543, 2011

DOI:10.1080/00268976.2011.621458

G. Sánchez-Sanz, I. Alkorta, and J. Elguero.

Theoretical study of the HXYH dimers (X,Y=O,S,Se). Hydrogen bonding and chalcogen-chalcogen interactions. 

A theoretical study of the HXYH (X, Y = O, S and Se) monomers and dimers has been carried out by means of MP2 computational methods. For the monomers, isomerization (H2X=Y//HXYH) and rotational transition state barriers have been calculated. Additionally, the molecular electrostatic potential of the isolated monomers has also been analysed. Due to the chiral nature of these compounds, homo and heterochiral dimers have been explored. The number of minima found for the dimers range between 13 and 22. The electron density of the complexes has been characterized with the Atoms in Molecules (AIM) methodology finding a large variety of interactions. The DFT-SAPT method has been used to analyse the components of the interaction energies. Concerning chalcogen–chalcogen interactions, although the most stable minima are formed through hydrogen bonds (especially if OH groups are present in the molecules) as the size of the atoms involved in the interaction increase, the chalcogen–chalcogen contacts become more important.

Chem. Phys. Lett., 512, 184, 2011

DOI:10.1016/j.cplett.2011.07.043

J. E. Del Bene, I. Alkorta, G. Sánchez-Sanz and J. Elguero.

31P-31P Spin-spin Coupling Constans for Pnicogen Homodimers.

Ab initio calculations have been carried out in a systematic investigation of pnicogen homodimers (PH2X)2, for X = F, OH, NC, NH2, CCH, CN, CH3, H, and BH2. Complex binding energies range from 7 to 34 kJ mol−1, which is within the range observed for neutral hydrogen-bonded complexes. One-bond spin–spin coupling constants across the pnicogen interaction 1pJ(P–P) exhibit a quadratic dependence on the P–P distance, similar to the dependence of 2hJ(X–Y) on the X–Y distance for complexes with X–H⋯Y hydrogen bonds. Thus, computed values of 1pJ(P–P) could be used to extract P–P distances from experimentally measured coupling constants.

Comput. Theor. Chem., 947, 37, 2011

DOI:10.1016/j.comptc.2011.07.009

G. Sánchez-Sanz, I. Alkorta, and J. Elguero

A theoretical study of the conformation of 2,2-bifuran,2,2-bithiophene, 2,2-bitellurophene and mixed derivates: chalcogen-chalcogen interactions or dipole-dipole effects. 

Using as models 2,2′-biheterocycles (furan, thiophene, selenophene, tellurophene) the possibility of stabilizing effects due to the proximity of two chalcogen atoms (O, S, Se, Te) was explored. The geometries of the ground states were compared satisfactorily with the available experimental results. The torsional barriers through planar and orthogonal transition states were calculated and discussed in function of the nature of the chalcogen atoms. Special attention was devoted to dipole moments that were calculated by a vector summation with good results.

Tetrahedron, 67, 7316, 2011

DOI:10.1016/j.tet.2011.07.042

G. Sánchez-Sanz, I. Alkorta, and J. Elguero

Isomerization barriers in bis(4H-thiopyran) and in bithioxanthenes. 

The inversion and rotation mechanisms for the isomerization of Feringa’s bithioxanthenes existing in two conformations, up/up and up/down, have been calculated at the B3LYP/6-31G(d) and B3LYP/6-311++G(d,p) levels. The inversion mechanism that maintains the double bond nature of the central bond is a classical one but the rotation mechanisms that break the double bond to form a biradical needs to explore the singlet and triplet states. To do this we have removed the four fused phenyl rings of bithioxanthene and calculated at the CASSCF and CASPT2 levels bis(4H-thiopyran) proving that B3LYP calculations yield reasonable results for the rotation barriers.

J. Phys. Chem. A, 115, 12124, 2011

DOI:10.1021/jp205300c

C. Trujillo, G. Sánchez-Sanz , I. Alkorta and J. Elguero.

Simultaneous Interactions of Anions and Cations with Cyclohexane and Adamantane: Aliphatic Cyclic Hydrocarbons as Charge Insulators.

With ab initio MP2 computational methods, a theoretical study has been carried out to characterize the interaction between aliphatic cyclic hydrocarbons, as models of molecular hydrocarbon monolayers, with cations (Li+, Na+, and K+), anions (F, Cl, and Br), and both simultaneously in opposite faces of the hydrocarbons. In addition, the energetic barrier for the cation crossing through the hydrocarbon ring has been calculated. The hydrocarbons chosen for this study are cyclohexane (C6H12) and adamantane (C10H16). The energies obtained for the M+:hydrocarbon:X complexes indicate positive cooperativity in the cases where the hydrocarbon is cyclohexane while diminutive effects are found in the adamantane complexes. The density functional theory–symmetry adapted perturbation theory analysis of the interaction energies shows that the most important term in the complexes with cations is the induction, while in the complexes with anion and with cations and anions simultaneously the most important term is the repulsion-exchange one. The electron density of the complexes has been analyzed using the atoms in molecules methodology and provides some insight to the electron transfer within the complexes.

Int. J. Mass Spect., 299, 20, 2011

DOI:10.1016/j.ijms.2010.09.005

G. Sánchez-Sanz, S. Díaz-Tendero, M. Alcamí and F. Martín.

Theoretical study of the stability of small triply charged carbon clusters Cn3+ (n=3-12).

Using density functional theory, coupled cluster and multireference methods, dissociation energies and 3rd ionization potentials for, respectively, triply charged and neutral carbon clusters have been evaluated. The results show that the smaller Cn3+ clusters are metastable, i.e., they present a fragmentation channel with negative dissociation energy. The lowest dissociation channel always corresponds to evaporation of a singly charged carbon atom. Good agreement with available experimental data is found for most two-fragment channels. The third ionization potential of the corresponding neutral species decreases with cluster size.

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