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Syntheses of Mixed-Ligand Tetranuclear Gold(I)−Nitrogen Clusters by Ligand Exchange Reactions with the Dinuclear Gold(I) Formamidinate Complex Au2(2,6-Me2Ph-form)2

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posted on 08.01.2007, 00:00 by Hanan E. Abdou, Ahmed A. Mohamed, John P. Fackler
The reaction of the sterically crowded dinuclear gold(I) amidinate complex Au2(2,6-Me2Ph-form)2, 1, with the less bulky bidentate nitrogen ligands results in the formation of tetranuclear gold(I) complexes. When the less bulky amidinate, K(4-MePh-form), A, was reacted with 1 in a 1:1 stoichiometric ratio, crystals containing equal amounts of the tetranuclear and dinuclear gold(I) aryl formamidinates, Au4(4-MePh-form)4 and Au2(2,6-Me2Ph-form)2, where 2,6-Me2Ph-form = B, were found in the same unit cell, 2·2THF:  space group P1̄, a = 10.794(11) Å, b = 14.392(15) Å, c = 25.75(3) Å, α = 82.564(17)°, β = 85.443(18)°, γ = 82.614(19)°. The reaction of K(4-MePh-form), A, and 1 in a 1:2 ratio (excess) produced the tetranuclear complex only, 3. The potassium salt of the exchanged bulky ligand, K(2,6-Me2Ph-form), formed as a byproduct. The reaction of the dinuclear gold(I) complex Au2(2,6-Me2Ph-form)2 with the 3,5-diphenylpyrazolate salt, K(3,5-Ph2pz), resulted in the formation of two tetranuclear mixed-ligand complexes, Au4(3,5-Ph2pz)2(2,6-Me2Ph-form)2·2THF, 4·2THF (space group P21/c, a = 11.5747(19) Å, b = 25.497(4) Å, c = 21.221(3) Å, β = 96.979(3)°) and Au4(3,5-Ph2pz)3(2,6-Me2Ph-form)·THF, 5·THF (space group P21/c, a = 23.058(5) Å, b = 14.314(3) Å, c = 18.528(4) Å, β = 90.94(3)°. The block crystals from the tetranuclear complex, 4·2THF, contain mixed ligands with each pyrazolate ring facing an amidinate ring. The tetranuclear mixed ligand complex, 5·THF, was isolated as needles with ligands alternating above and below the Au4 plane. The two tetranuclear mixed-ligand complexes emit at 490 and 530 nm, respectively, under UV excitation.

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