Abstract:We study the dependence of the aurophilic attraction (Au'-Au') in perpendicular model systems of the type [(CIAuPH,),] on the a b initio method, basis sct and different pseudopotentials used, and on relativity. The effects of varying the "halogen" (X = F, H, CI, Me, Br, -C=CH, I), the "phosphine" (L = PH,, PMe,, -N=CH) and the metal (M = Cu, Ag, ALI) on the M-M' interaction of the [(XML),] dimer are also studied. The depth of the interaction potential increases with the softness of the group X. It decreases by 27% for M = Au, X = C1 and L = PH, if relativistic effects are omitted at fixed geometry.Keywords a b initio calculations -bond theoryclosed-shell attraction * gold -relativistic effects
We study the dependence of the intramolecular M I -M I interaction on electron correlation effects in eight-membered and [Au 2 Te 4 ] 2at the quasirelativistic pseudopotential ab initio MP2 and Hartree-Fock levels. The intramolecular M I -M I distances, R, at the MP2 level fall in the same range as the experimental ones. The R values are reduced from HF to MP2 level. All the calculations suggest that correlation effects are essential. The reduction of R depends on the particular M-L combination (L ) ligand). In the rings, short Cu I -Cu I distances are recovered for the first time. The explicit inclusion of the counterions is unimportant for M I and essential for M II , as shown by a study of the oxidative addition of Cl 2 to the model [Au 2 (CH 2 PH 2 CH 2 ) 2 ]. The Au(I) is then oxidized to Au(II), and the Au-Au distance is shortened to 261 pm, corresponding to a σ bond. This value is in agreement with experiment.
We have prepared self-assembled monolayers (SAMs) of 4-aminothiophenol (4-ATP) and 1-(4-mercaptophenyl)-2,6-diphenyl-4-(4-pyridyl)pyridinium tetrafluoroborate (MDPP) functionalized with iron phthalocyanine (FePc) and copper phthalocyanine (CuPc) adsorbed on gold (111) electrodes. The catalytic activity of these SAMs/MPc was examined for the reduction of O 2 in aqueous solutions and compared to that of bare gold and with gold coated directly with preadsorbed MPc molecules. Scanning tunneling microscopy (STM) studies confirm the functionalization of the 4-ATP by MPc. STM images reveal that iron phthalocyanine molecules are chemically anchored to 4-aminothiophenol organic monolayers, probably having an "umbrella" type orientation with regards to the surface. The electrocatalytic studies carried out with Au/4-ATP/FePc and Au/ MDPP/FePc electrodes show that the O 2 reduction takes place by the transfer of 4-electron to give water in contrast to a 2-electron transfer process observed for the bare gold. The modified electrode obtained by simple adsorption of FePc directly to the Au(111) surface still promotes the 4-electron reduction process, but it shows a lower activity than the electrodes involving SAMs with FePc molecules positioned at the outmost portion of the selfassembled monolayers. The activity of the electrodes increases as follow: Au < Au/FePc < Au/4-ATP/FePc < Au/MDPP/FePc with the highest activity when FePc molecules are more separated from the Au surface. In contrast, the less active CuPc shows almost the same activity in all three configurations. Theoretical calculations suggest the importance of the back-bonding into the adduct formation, showing the relevance of the supporting gold surface on the electron-transfer process mediated by anchoring ligands.
The linear-chain polymer [Tl[Au(C(6)Cl(5))(2)]](n), 1, reacts in the solid state and in solution with different volatile organic compounds such as tetrahydrofuran, acetone, tetrahydrothiophene, 2-fluoropyridine, acetonitrile, acetylacetone, and pyridine. Solid-state exposure of 1 to vapors of the above VOCs produces a selective and reversible change in its color that is perceptible to the human eye and even deeper under UV irradiation, allowing 1 to function as a sensor for these VOCs. Heating the samples exposed to the VOCs for a few minutes at 100 degrees C regenerates the original material without degradation, even after several exposure/heating cycles. The reversibility is further confirmed by X-ray powder diffraction measurements of complex 1 before and after exposure to vapors and again after heating the samples. The products obtained by reactions of complex 1 with the above VOCs as ligands in solution contain extended linear chains of alternating gold and thallium centers with two molecules of the organic ligands attached to each thallium atom. The stoichiometry of these materials has been confirmed by single-crystal X-ray diffraction as [Tl(THF)(2)[Au(C(6)Cl(5))(2)]](n), 3, and [Tl(acacH)(2)[Au(C(6)Cl(5))(2)]](n), 5. Comparison of FT-IR, UV-vis, and luminescence spectra at room temperature and at 77 K of the solid samples of complexes 2-9 with the spectra of complex 1 after its exposure to VOCs suggests interaction occurs between the organic VOCs and thallium in each case. Thermogravimetric analyses data indicate that all the thallium centers in these derivatives of complex 1 are neither fully nor equally coordinatively saturated. The materials formed appear to be intermediates between complex 1 with no VOCs attached and complexes 3-9 which contain two organic ligands coordinated to each thallium. A crystal structure analyses of one of these intermediates, [Tl(THF)(0.5)[Au(C(6)Cl(5))(2)]](n), 1.0.5THF, confirms this. Density functional calculations are in accord with the observed experimental results. Analysis reveals a substantial participation of the metal atoms in transitions that give rise to the observed emissions. Crystallographic data are as follows. For 1.0.5THF: triclinic, P1, a = 8.9296(1) A, b = 11.2457(1) A, c = 21.2465(3) A, alpha = 96.7187(7) degrees, beta = 92.5886(6) degrees, gamma = 98.5911(8) degrees, V = 2090.87(4) A(3), and Z = 2. For 3: monoclinic, P2(1)/c, a = 26.4163(6) A, b = 12.1619(2) A, c = 28.0813(6) A, alpha = 90 degrees, beta = 161.9823(6) degrees, gamma = 90 degrees, V = 2790.51(10) A(3), and Z = 4. For 5: monoclinic, P2(1)/c, a = 9.8654(2) A, b = 29.8570(5) A, c = 11.6067(2) A, alpha = 90 degrees, beta = 114.5931(6) degrees, gamma = 90 degrees, V = 3108.64(10) A(3), and Z = 4.
Abstract:We study the nature of the aurophilic attraction (Au'-Au') at its long-range limit for the model systems [(X-Au-L),] (n = 2, 3; X = C1, I, L = PH,, PMe,; X = H, L = -N-CH) at the ab initio M P 2 and Hartree-Fock levels. The nature of the interactions and nonadditive effects at various orientations are related to simple electrostatic induction and dispersion expressions involving the individual properties of each monomer.Keywords a b initio calculations * closed-shell attraction -gold * long-range interactions * relativistic effects
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