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Magnetic characterization of the geometry and chemistry of small metal clusters
Author(s) -
Mile Brynmor,
Sillman Philip D.
Publication year - 1995
Publication title -
magnetic resonance in chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.483
H-Index - 72
eISSN - 1097-458X
pISSN - 0749-1581
DOI - 10.1002/mrc.1260331308
Subject(s) - homonuclear molecule , chemistry , heteronuclear molecule , electron paramagnetic resonance , pentagonal bipyramidal molecular geometry , unpaired electron , crystallography , paramagnetism , cluster (spacecraft) , molecule , nuclear magnetic resonance spectroscopy , nuclear magnetic resonance , stereochemistry , crystal structure , physics , organic chemistry , computer science , programming language , quantum mechanics
The application of electron paramagnetic resonance (EPR) spectroscopy in determining the geometric and electronic structures of small naked clusters, M n , of the alkali and coinage metals ( n < 9) is assessed. The EPR spectra and the paramagnetic parameters derived therefrom provide stringent tests of quantitative molecular orbital calculations. Perturbations of the cluster shape by interaction with substrate molecules are readily detected and have a bearing on the dynamic nature of the active sites of heterogeneous catalysts. Previous studies of the metal trimers in hydrocarbon matrices are extended to the preparation of an unusual acute Na 3 cluster associated with water and the heteronuclear clusters Na 2 Li and Au 2 Ag. Both adopt static obtuse 2 B 2 geometries and show no fluxionality, in contrast to the homonuclear pseudo‐rotating Jahn—Teller clusters Li 3 and Na 3 . There is a reversal in paramagnetic parameters in the series Cu 3 , Ag 3 , Au 3 which is due in part to the emergence of relativistic effects because of the high charge on the gold nucleus. The first ENDOR spectrum is reported of a metal cluster Li 3 , the parameters fitting exactly those determined from the more complex EPR spectrum of Li 3 . A new heteronuclear septameric species, Na 2 K 5 , has been examined which has the pentagonal bipyramidal structure seen for homonuclear septamer clusters. There is an unpaired spin density of 0.41 on the apical sodium nuclei with only 0.004 at the basal potassium nuclei.