Lead mixed-valent clusters

Remarkably few isolable complexes exhibit silver-silver covalency. The ionization potential [144] and bond length (2.5310(10) A) [145] of singly bonded Ag-Ag have been determined by spectroscopic studies on supersonic beams. Small clusters Ag ( = 2-5) have been synthesized and studied in an argon matrix [146], and the gas-phase synthesis and reaction chemistry of mixed-valent silver(0/I) clusters have been studied by mass spectrometry [147]. Pulse radiolysis of Ag+ solutions or glasses in water and ethanol has allowed the study of unstable clusters as intermediates in metal colloid formation thus, the absorption and EPR spectra of [Ag2], [Ag4], and [Ag4] have been recorded [148]. These are fully delocalized Ag(0,I) ions in which partial occupation of silver 5s-orbital combinations leads to net metal-metal bonding. 

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