Synthesis, structure, and optical properties of new cadmium chalcogenide clusters of the type [Cd₁₀E₄(E'Ph)₁₂(PR₃) ₄], (E, E' = Te, Se, S)

New cadmium chalcogenide cluster molecules [Cd₁₀E₄(E'Ph)₁₂(PⁿPr ₃)₄], E = Te, E' = Te (1) and [Cd₁₀E₄(E'Ph)₁₂-(PⁿPr ₂Ph)₄] E = Te, E' = Se (2); E = Te E' = S (3); E = Se, E' = S (4) have been synthesized and structurally characterized by single crystal X-ray structure analysis. The influence of the variation of the chalcogen atom is investigated by structural means and by optical spectroscopy. All cluster-molecules have a broad emission in the blue-visible range at low temperature as indicated by photoluminescence (PL) measurements. A clear classification of the emission peak position can be made based on the E' species suggesting that the emission is assigned to transitions associated with the cluster surface ligands. Photoluminescence excitation and absorption measurements display a systematic shift of the band gap to the higher energies with the variation of E and E' from Te to Se to S, as also occurs in the respective series of the bulk semiconductors.