Ligand Substitution in Cubic Clusters: Surprising Isolation of the Cocrystallization Products of Cu88-Se)[S-P(OEt) 2]6 and Cu6[S2P(OEt) 2]6

C. W. Liu, Chiu Mine Hung, Bidyut Kumar Santra, Ju Chun Wang, Hsien Ming Kao, Zhenyang Lin

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Abstract

The cluster {Cu88-Se)[S2P(OEt) 2]6}0.54{Cu6[S 2P(OEt)2]6}0.46 (2) was prepared in 78% yield from the reaction of Cu8(Se)[Se2P(OPr) 2]6 (1) and NH4S2P(OEt)2 in toluene. The central selenide ion in 2 was characterized by 77Se NMR at δ -976 ppm. The simulated solid-state 31P NMR spectrum shows two components with an intensity ratio close to 55:45. The peak centered at 100.7 ppm is assigned to the 31P nuclei in the hexanuclear copper cluster, and that at 101.1 ppm is due to the octanuclear copper cluster. The single-crystal X-ray diffraction analysis confirms the cocrystallization structures of Cu8(Se)[S2P(OEt)2]6 (54%) and Cu6[S2P(OEt)2]6 (46%) (2: trigonal, space group R3, a = 21.0139(13) Å, c = 11.404(3) Å γ = 120°, Z = 3). While the octanuclear copper cluster possesses a 3-fold crystallographic axis which pass through the Cu(2), Se, and Cu(2A) atoms, the six copper atoms having the S6 point group symmetry in Cu 6[S2P(OEt)2]6 form a compressed octahedron. The Cu8(μ8-Se) cubic core in Cu8-(μ 8-Se)[S2P(OEt)2]6 is larger in size than the metal core in Cu8(μ8-Se)[Se2P(OPr)2] 6 (1) although the bite distance of the Se-containing bridging ligand is larger than that of the S ligand. To understand the nature of the structure contraction of the metal core and metal-μ8-Se interaction, molecular orbital calculations have been carried out at the B3LYP level of density functional theory. MO calculations suggest that Cu-μ8-Se interactions are not very strong and a half bond can be formally assigned to each Cuμ8-Se bond. Moderate Cu⋯Cu repulsion exists, and it is the bridging ligands that are responsible for the observed Cu⋯Cu contacts. Hence, the S-ligating copper clusters have greater Cu⋯Cu separations because each Cu carries more positive charge in the presence of the more electronegative S-containing ligands.

Original languageEnglish
Pages (from-to)8551-8556
Number of pages6
JournalInorganic Chemistry
Volume42
Issue number25
DOIs
StatePublished - 15 Dec 2003

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