Synthesis, characterization, luminescence, and electrochemistry of new tetranuclear Gold(I) amidinate clusters:: Au4[PhNC(Ph)NPh]4, Au4[PhNC(CH3)NPh]4, and Au4[ArNC(H)NAr]4

The syntheses and the X-ray structures of the tetranuclear gold(I) benzamidinate, Au-4[PhNC(Ph)NPh](4), and the tetranuclear gold(I) acetamidinate, Au-4[PhNC(CH3)NPh](4), clusters are reported. The clusters are produced by the reaction of the sodium salt of an amidine ligand with the gold precursor Au(THT)Cl in a (1:1) stoichiometry. The average Au...Au distance between adjacent Au(I) atoms is similar to 2.9 angstrom, typical of compounds having an aurophilic interaction. The four gold atoms are arranged in a square (Au...Au...Au... = 88-91 degrees) in the acetamidinate and in a distorted square (Au...Au...Au... = 82-97 degrees) in the benzamidinate derivative. Electrochemical oxidation of the tetranuclear complex Au-4[PhNC(Ph)NPh](4) show three reversible waves at 0.87, 1.19, 1.42 V vs. Ag/AgCl at a scan rate of 100 mV/s in CH2Cl2 similar to the three reversible waves seen before from the tetranuclear complexes Au-4[ArNC(H)NAr](4), Ar = C6H4-4-OMe, Ar = C6H4-4-Me, and Ar = C6H3-3,5-Cl. A summary of the chemistry of the tetranuclear Au(I) amidinate complexes Au-4[ArNC(H)NAr](4), Ar = C6H4-4-OMe, C6H3-3,5-Cl, C6H4-4-Me, C6H4-3-CF3, C6F5, C10H7 also is presented. The tetranuclear clusters Au-4[ArNC(H)NAr](4), Ar = C6H4-4-OMe, Ar = C6H4-3-CF3, Ar = C6H4-4-Me and Ar = C6H4-3,5-Cl are the first tetranuclear gold(I) cluster species from group 11 elements to show fluorescence at room temperature. The lifetimes of the naphthyl and trifluoromethylphenyl complexes are in the millisecond range indicating phosphorescent processes. Recently it has been shown that Au-4[ArNC(H)NAr](4) are very effective catalysts upon calcination for room temperature CO oxidation.