Photoluminescence of Tetranuclear Mercury(i1) Complexes

In recent years we have observed photoluminescence from tetrameric Cu(1) [1], Ag(I) [2], and Au(I) [ 31 clusters in solution or low-temperature glasses. In addition, emission from dimeric Au(I) complexes was reported by other groups [ 4,5 1. We assigned the luminescence of the tetramers to metalcentered s-d transitions which are modified by metal-metal interaction in these d’O clusters [ l-31. Other important d’O metal ions are those of the IIb group (Zn *’ Cd*+, Hg’+). While semiconductors , such as ZnS, CdS [ ($71, and HgI, [ 8101 are well known to show photoluminescence, any emission from the M2+ ions or their molecular complexes #’ has not been reported to our knowledge. It was even stated that a characteristic emission from Hg(I1) is unlikely [ 121. However, inanalogy to Cu(I), Ag(I), and Au(I) we anticipated that Hg(I1) clusters might be luminescent, too. This expectation was based on the fact that the energy separation between the nd” and nd’(n+ 1 )s’ configuration of Hg2+ (a43000 cm-‘) is very similar to that of Ag+ ( = 39000 cm-‘) [ 13 1. For the present study we chose the complexes [ Hg( pyph )Cl ] 4 [ 14 ] with pyph = 2-pyridylphenyl and [Hg,(SPh)6(PPh3)4]2f [ 151 with Ph=phenyl as suitable Hg( II) clusters.