Current density maps, magnetizability, and nuclear magnetic shielding tensors of bis-heteropentalenes. III. Thieno-thiophene isomers

• Published in: Molecular physics Vol. 103; no. 6-8; pp. 789 - 801
• Main Authors: Cuesta, I. García, Jartín, R. Soriano, de Merás, A. Sánchez, Lazzeretti, P.
• Format: Journal Article
• Language: English
• Published: Taylor & Francis Group 20.03.2005
• ISSN: 0026-8976; 1362-3028
• DOI: 10.1080/00268970512331340574

Near Hartree-Fock values of the magnetic susceptibility and nuclear magnetic shielding of bis-heteropentalenes consisting of two thiophene units ([2,3-b], [3,2-b], [3,4-b], and [3,4-c] isomers) have been estimated via computational schemes relying on continuous transformation of the origin of the current density within the coupled Hartree-Fock approximation and extended gaugeless Gaussian basis sets. The results are compared with those obtained via London gauge-including orbitals. Maps of streamlines and the modulus of the ring current density induced by a magnetic field normal to the molecular plane are reported for the three isomers of higher symmetry, showing that the intense diamagnetic flow of the π electrons causes strong magnetic anisotropy and a down-field chemical shift of the out-of-plane component of the proton shielding tensor in thieno-thiophenes. 'Diatropicity matrices' for the series of bis-heteropentalenes formed by two fused five-membered heterocyclic systems with different heteroatoms can be constructed by choosing the out-of-plane component of either the magnetic susceptibility or the proton magnetic shielding as indicator. Alternative measures of relative aromaticity are obtained by the modulus of the induced π current densities.