New halide-centered discrete Agl8 cubic clusters containing diselenophosphate ligands, {Ag8(X)[Se2P(OR)2]6}(PF6) (X = Cl, Br; R = Et, Pr, Or):: Syntheses, structures, and DFT calculations

Six clusters Ag-8(mu(8)-X)[Se2P(OR)(2)](6)(PF6) (R = Et, X = Cl, 1a, X = Br, 1b; R = Pr, X = Cl, 2a, X = Br, 2b; R = Pr-i, X = Cl, 3a, X = Br, 3b) were isolated from the reaction of [Ag(CH3CN)(4)](PF6), NH4[Se2P(OR)(2)], and Bu4NX in a molar ratio of 4:3:1 in CH2X2. Positive FAB mass spectra show m/z peaks at 2573.2 for 1a, 2617.3 for 1b, 2740.9 for 2a, 2786.9 for 2b, 2742.3 for 3a, and 2787.0 for 3b due to respective molecular cation, (M - PF6)(+), P-31 NMR spectra of 1a-3b display a singlet at delta 82.3, 81.5, 82.9, 81.7, 76.3, and 75.8 ppm with a set of satellites (J(PSe) = 661, 664, 652, 652, 656, and 656 Hz, respectively). The X-ray structure (1a-2b) consists of a discrete cationic cluster in which eight silver ions are linked by six diselenophosphate ligands and a central mu(8)-Cl or mu(8)-Br ion with a noncoordinating PF6- anion. The shape of the molecule is a halide-centered distorted Ag-8 cubic cluster. The dsep ligand exhibits a tetrametallic tetraconnective (mu(2), mu(2)) coordination pattern, and each caps on a square face of the cube. Each silver atom of the cube is coordinated by three selenium atoms and the central chloride or bromide ion. Additionally, molecular orbital calculations at the B3LYP level of the density functional theory have been carried out to study the Ag-mu(8)-X (X = Cl, Br) interactions for cluster cations [Ag-8(mu(8)-X){Se2P(OR)(2)}(6)](+). Calculations show very weak bonding interactions exist between mu(8)-X and Ag atoms of the cube.