• Wang, Q.
• Rabe, A.
• Sundholm, Dage Matts Börje

Abstract

Nuclear magnetic resonance (NMR) chemical shifts and the magnetically induced current density (MICD) susceptibility of four osmium containing molecules have been calculated at the density functional theory (DFT) level using three relativistic levels of theory. The calculations were performed at the quasi-relativistic level using an effective core potential (ECP) for Os, at the all-electron scalar exact two-component (X2C) relativistic level, and at the relativistic X2C level including spin-orbit coupling (SO-X2C). In earlier studies, the osmapentalene (1) and the osmapentalynes (2 and 3) were considered Craig-type M &amp; ouml;bius aromatic and it was suggested that the analogous osmium compound (4) is Craig-type M &amp; ouml;bius antiaromatic. Here, the ring-current strengths were obtained with the gauge including magnetically induced currents (GIMIC) method by integrating the MICD susceptibility passing through planes that intersect chemical bonds and by line integration of the induced magnetic field using Amp &amp; egrave;re-Maxwell's law. The ring-current calculations suggest that 1, 2 and 3 are weakly aromatic and that 4 is nonaromatic. The accuracy of the MICD susceptibility was assessed by comparing calculated NMR chemical shifts to available experimental data. Visualization of the MICD susceptibility shows that the ring current does not pass from one side of the molecular plane to the other, which means that the MICD susceptibility of the studied molecules does not exhibit any M &amp; ouml;bius topology as one would expect for Craig-type M &amp; ouml;bius aromatic and for Craig-type M &amp; ouml;bius antiaromatic molecules. Thus, molecules 1-3 are not Craig-type M &amp; ouml;bius aromatic and molecule 4 is not Craig-type M &amp; ouml;bius antiaromatic as previously suggested. Calculations of the 1H NMR and 13C NMR chemical shifts of atoms near the Os atom show the importance of including spin-orbit effects. Overall, our study revisits the understanding of the aromaticity of organometallic molecules containing transition metals.<br/><br/>Current-density calculations on osmapentalene and osmapentalyne suggest that the Craig-type M &amp; ouml;bius aromaticity/antiaromaticity concept should be abandoned.

Topics

• density
• impedance spectroscopy
• compound
• theory
• strength
• positron annihilation lifetime spectroscopy
• Photoacoustic spectroscopy
• density functional theory
• current density
• susceptibility
• Nuclear Magnetic Resonance spectroscopy
• organometallic
• Osmium