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Downloaded on 02/05/2013 21:36:10.Published on 06 September 2011 on http://pubs.rsc.org | doi:10.1039/C1SC00487Ecomplexes, [XAuCN] (X ¼ F, Cl, Br, I). Density functionaland ab initio wavefunction calculations are carried out on thefour [XAuCN] species to help spectral interpretation andchemical bonding analyses.Experimental methodThe experiment was carried out using a magnetic-bottle type PESapparatus equipped with an electrospray ionization (ESI) sourceand an ion trap time-of-flight mass spectrometer. Details of theapparatus have been described elsewhere 17 and only a briefdescription is given here. All the [XAuCN] anions (X ¼ Cl, Br,I) were produced by ESI from 0.1 mM solutions of KAu(CN) 2mixed with the corresponding potassium halides (KX) ina methanol/water (90/10) solvent. The anions of interest wereselected by a mass gate and decelerated before being interceptedby a probe laser beam. The photodetached electrons wereanalyzed by a 2.5-meter long magnetic-bottle time-of-flight tube,modified from the original design. 17 As shown below, theshortened flight tube does not affect the electron energy resolutionsignificantly. Similar experiments using KF did not producethe [FAuCN] anion and no experimental data was obtained forthis species. In general, it appears that Au(I) does not formcomplexes with F ligands. For example, we were not able toobserve AuF 2 complexes previously while AuX 2 complexeswith heavier halides were readily observed. 14,15Two laser systems were used for photodetachment in thecurrent investigation. An F 2 excimer laser (157 nm: 7.866 eV) wasused to obtain spectra at high electron binding energies. A dyelaser equipped with a frequency-doubling unit provides tunablelaser wavelengths from 600 to 206 nm. Because the resolution ofthe magnetic-bottle type PES analyzer depends on the photoelectronkinetic energies, the dye laser wavelengths are usuallychosen to enhance the resolution for low binding energy features.Because of the relatively high electron binding energies of the[XAuCN] species, a wavelength of 206.19 nm (6.013 eV) wasused in the current experiment to obtain higher resolutionspectra, which yielded more accurate adiabatic electron bindingenergies. Time-of-flight photoelectron spectra were collected andconverted to kinetic energy spectra calibrated with the knownspectra of Au and I . The electron binding energy spectrareported were obtained by subtracting the kinetic energy spectrafrom the respective detachment photon energies. The kineticenergy resolution (DE/E) of the magnetic-bottle electron analyzerwas 3%, i.e., 30 meV for 1 eV electrons.Computational methodsThe theoretical studies were performed using both densityfunctional theory (DFT) and ab initio wavefunction theory(WFT) methods. DFT calculations were done on [XAuCN](X ¼ F, Cl, Br, I) and their neutrals using the generalizedgradient approximation (GGA) with the PBE exchange–correlationfunctional 18 implemented in the Amsterdam DensityFunctional (ADF 2009.01) program. 19 The Slater basis setswith the quality of triple-z plus two polarization functions(TZ2P) were used, with the frozen core approximation appliedto inner shells [1s 2 -4f 14 ] for Au, [1s 2 ] for C, N, and F, [1s 2 -2p 6 ]for Cl, [1s 2 -3d 10 ] for Br, and [1s 2 -4d 10 ] for I. The scalarrelativistic (SR) and spin–orbit (SO) coupling effects were takeninto account by the zero-order-regular approximation(ZORA). 20 Geometries were fully optimized at the SR-ZORAlevel and single-point energy calculations were performed withthe inclusion of the SO effects. Vibrational frequency calculationswere carried out at the SR-ZORA level to verify that theanion species were minima on the potential energy surface. TheB3LYP hybrid functional 21 was also used to optimize[XAuCN] with the Gaussian 03 program 22 to compare withthe PBE results that used the pure GGA results. Thecomparison of GGA and hybrid functionals tends to providea useful evaluation of the accuracy of DFT results.We further performed high-level ab initio WFT calculationsfor [XAuCN] (X ¼ F, Cl, Br, I) using more sophisticatedelectron correlation methods implemented in the MOLPRO2008 program. 23 In these calculations, we used both the CCSD(T) (coupled-cluster with single and double and perturbativetriple excitations) 24 and CASSCF (complete-active-space selfconsistentfield) methods. 25 The geometries of [XAuCN] wereoptimized at the level of CCSD(T) with scalar relativistic effectsincluded; single-point CCSD(T) energies of the ground andexcited states of the neutrals were calculated at the geometriesof the anions, which accurately generate the state-specific scalarrelativistic energies of all the states. The electron bindingenergies corresponding to one-electron transitions from theclosed-shell ground states of [XAuCN] to the ground andexcited states of the XAuCN neutrals were obtained using theCASSCF/CCSD(T)/SO approach that we used previously forAu(CN) 2 and AuI 2 . 9,15 In this approach, the SO splittingswere treated as a perturbation to the scalar relativistic stateenergies and were calculated on the basis of CASSCF wavefunctions with the diagonal matrix elements replaced by theindividual CCSD(T) state energies. The SO coupling effect wasincluded by using a state-interacting method 26 with SO pseudopotentials.27 The theoretical PES spectra were simulatedusing Gaussian functions with a line width of 0.035 eV. Thesimulated PES intensities were simply scaled according to theexperimental observation. In the MOLPRO and Gaussian 03calculations, we used the Stuttgart energy-consistent relativisticpseudopotentials ECP60MDF (Au) and ECP28MDF (I) andthe corresponding valence triple-z basis sets cc-pVTZ-PP forAu 28 and I. 29 The all-electron basis sets cc-pVTZ were used forC, N, F, 30 Cl, 31 and Br. 32 The cc-pVTZ-PP and cc-pVTZ basissets are abbreviated as VTZPP and VTZ hereafter.Experimental resultsView Article OnlineThe photoelectron spectra of [XAuCN] (X ¼ Cl, Br, I) areshown in Fig. 1 and 2 at 157 and 206.19 nm, respectively. Thespectra for the three species are similar and their binding energiesdecrease systematically from X ¼ Cl to I. The vertical detachmentenergies (VDEs) of all the observed features are given inTable 1, where they are compared with theoretical calculations(vide infra). Five major electron detachment bands are observedfor [ClAuCN] (Fig. 1), where the bands X and A are overlappingand are partially resolved in the 206 nm spectrum(Fig. 2). Because of the overlap, the VDE of the X band can onlybe estimated to be 5.5 eV. From the detachment threshold inthe 206 nm spectrum, an adiabatic detachment energy (ADE) for2102 | Chem. Sci., 2011, 2, 2101–2108 This journal is ª The Royal Society of Chemistry 2011