Theoretical Study of The Luminescence Effects in Trinuclear Silver Organometallic Compounds
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THEORETICAL STUDY OF THE LUMINESCENCE EFFECTS IN TRINUCLEAR SILVER ORGANOMETALLIC COMPOUNDS Roberto Salcedo, L.Enrique Sansores & Ana Martínez, Instituto de Investigaciones en Materiales, UNAM, PO Box 70-360, Circuito Exterior, Ciudad Universitaria, Coyoacán, 04510 México, D.F. México. ABSTRACT The luminescence and related phenomena of a trinuclear silver organometallic complex has been studied from a theoretical viewpoint (B3LYP/6-31G* level). The study takes into account the relation between this compound and the [Au(CH3N=COCH3)3] that has been characterised and studied on the base of its solvoluminescence behaviour. INTRODUCTION The solvoluminescence behavior of some gold complexes has been established and studied recently [1]. The particular case of [Au(CH3N=COCH3)3] 1 has generated interesting experimental [2] and theoretical [3] works. The main interest comes from the reports of Balch [2] who found a very interesting feature about this compound, it developes strong luminescence when it is first UV light irradiated and after put in contact with a solvent (chloroform). This phenomenon was studied by Sansores et al [3] from a theoretical point of view and it was proposed that the luminescence arises from an excitonic state in solid state corresponding to a triplet that has an energy value of 2.36 eV, a value very near to the yellow emission obseved by Balch. It has been observed that closed shell d10 atoms such as gold(I) and others have a marked tendency to form dimers, oligomers or in general polymers. This feature has been a matter of interesting theoretical and experimental works [4]. Particularly the linear chain complexes in many cases show intense emissions in the solid state. On this basis it has been suggested [1] that the arrangement in solid state is fundamental for creating sites where electrons and holes can be trapped accounting for the needed energy storage to produce the solvoluminescence effect. However, the theoretical analysis from Sansores et al [3] shows that there is a transition from an α-HOMO to a β-LUMO of a triplet state of the discrete molecule which corresponds to an excitonic state in such a way that the destruction of this excitonic state can account for the solvoluminescence effect. Therefore, both the oligomer and the discrete molecule can cooperate for the effect. It should be noted that the effect has only been experimentaly observed in the case of gold complexes [1,2]. However there are some other analogues containing other types of metal centres that are susceptible to present similar characteristics. In particular silver compounds are very attractive to be studied following the same line since this last metal is more accessible than gold. A silver analogue of the compound studied by Balch and coworkers has been synthesized [5] 2 and it seems it has similar characteristics to the gold compound. In this case the strong relativistic effects found in gold compounds are not present [6] and this feature can be important in searching the source of the solvoluminescence effect. Theref
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