ISSN:
0018-019X
Keywords:
Chemistry
;
Organic Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
The electronic structures of the 4-4 SBU, the β-cage, and the β-cage with two 4-4 SBU's attached to it have been studied by means of EH-MO calculations. No indication of the formation of a band structure has been found. The HOMO region consists of many closely spaced, localized states, 98.6% of them concentrated on the O-atoms. Reversible color changes of Cu+1 and Ag+1 zeolites observed upon hydration-dehydration experiments can be understood as charge-transfer transitions from the HOMO concentrated on the zeolite O-atoms to the metal cations. As soon as the Cu+1 or Ag+1 are partially hydrated, the ns* and np* states are shifted to higher energies. The luminescence observed with dehydrated Cu+1-zeolites X is caused by a 4p*←HOMO absorption, followed by spontaneous 4s*←4p* emission. After a detailed study of a Cu+1 in the 6-6 SBU, we discuss the electronic structure of a β-cage filled with 1,2,4,8, and 9 Cu+1. In each case, the β-cage is found to be too small to allow the formation of a band structure. The levels caused by the added copper are distinctly quantized. Calculations on [Ag3(H2O)3]3+ in a β-cage are reported. The direct interaction between the Ag-atoms is significant. As a consequence, the states formed by Ag 5s and 5p atomic orbitals are delocalized over the three Ag-centers. In both the Cu+1 and the Ag+1 zeolites, the ligand-field picture is found to be insufficient to explain the electronic structure, when the metal is coordinated to the zeolite oxygen framework.
Additional Material:
12 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/hlca.19870700227
