Implications of molecular orbital symmetries and energies for the electron delocalization of inorganic clusters
Isostructural clusters exhibit contrasting magnetic properties when the no. of electrons differs. Surprisingly, the same is true even for isoelectronic cages (e.g. Oh B6H62- is diatropic, whereas Oh Si62- is paratropic) or for those with different substituents (e.g. Td B4H4 is paratropic, whereas Td B4F4 is diatropic). Indeed, the total nucleus-independent chem. shift (NICS) values, based on shieldings computed at cluster centers, may range considerably in magnitude and even change from diatropic (upfield shifted) to paratropic (downfield shifted). Similarly, individual dissected canonical MO contributions to the total NICS values computed at the "gauge-including AOs" level vary greatly. This contrasting behavior arises from MO energy differences, from the extent of orbital overlap and from symmetry-based selection rules derived from group theory. Differences in magnetic properties may originate from the symmetry of the orbitals; specifically from the forbidden nature of the HOMO->LUMO electronic excitation weighted by the occupied-unoccupied orbital energy difference. Thus, HOMO-NICS values are generally highly paratropic if the HOMO->LUMO rotational transition is allowed by symmetry selection rules. [on SciFinder (R)]
Keywords: NMR (chem. shift; implications of MO symmetries and energies for electron delocalization of inorg. clusters); Clusters; Electron delocalization; Electronic excitation; HOMO; LUMO; Molecular orbital; Rotational transition (implications of MO symmetries and energies for electron delocalization of inorg. clusters) ; MO symmetry energy electron delocalization inorg cluster; nucleus independent chem shift electronic excitation HOMO LUMO cluster
General Physical Chemistry
Department of Chemistry and Center for Computational Chemistry,University of Georgia,Athens,GA,USA.
written in English.
71-43-2 (Benzene); 1120-53-2 (1,3-Cyclobutadiene); 12356-13-7; 12429-97-9; 17156-85-3; 27174-99-8 (Tetraborane(4); 49567-49-9; 99685-96-8 (Fullerene-C60); 145633-27-8; 149271-56-7; 531508-90-4; 643760-80-9; 878757-05-2; 947598-89-2; 947603-08-9 Role: PRP (Properties) (implications of MO symmetries and energies for electron delocalization of inorg. clusters)
Record created on 2007-10-22, modified on 2016-08-08