Pb(m)-Phenyl (m = 1-5) complexes: an anion photoelectron spectroscopy and density functional study

The phenyl-lead metal complexes ([Pb(m)C6H5]-) produced from the reactions between benzene and lead clusters formed by laser ablation on a lead solid sample are studied by photoelectron spectroscopy (PES) and density functional theory (DFT). The adiabatic electron affinities (EAs) of [Pb(m)C6H5]- are obtained from PES at 308 nm, and the differences between the PES of [Pb(m)C6H5]- and the PES of Pbm- are discussed in detail. The results reveal that the phenyl group binds perpendicularly on lead clusters through the Pb-C sigma bond and the complexes have a closed shell structure. Calculations with DFT are carried out on the structural and electronic properties of [Pb(m)C6H5]-, and the adiabatic detachment energy for the optimized structures of anion are in agreement with the experimental PES results. The density of states (DOS) calculated is compared with experimental PES and is discussed. The most possible structures for each species are concluded, and the bonding between Pb and phenyl is analyzed, which also proves that the phenyl group binds perpendicularly on lead clusters through the Pb-C sigma bond.     

Photoelectron spectroscopic and theoretical study of aromatics-Pb(m) anionic complexes (aromatics = C6H5, C5H4N, C4H3O, and C4H4N; m = 1-4): a comparative study

The reactions between lead vapored by laser ablation and different aromatic molecules (C6H6, C5H5N, C4H4O, or C4H5N) seeded in argon carrier gas were studied by a reflectron time-of-flight mass spectrometer (RTOF-MS) with a photoelectron spectrometer. The adiabatic electron affinities (EAs) of the dominant anionic products PbmC6H5(-), Pb(m)C5H4N(-) (m = 1-4) and Pb(m)C4H3 (-), Pb(m)C4H4N(-) (m = 1-3) dehydrogenated complexes are obtained from the photoelectron spectra with 308 and 193 nm photon, respectively. It is found that the EAs of Pb(m)C4H4N are higher than those of Pb(m)C6H5, Pb(m)C5H4N, and Pb(m)C4H3O with the same metal number m. The possible structures for Pb(m)C4H4N(-) complexes were calculated with density functional theory (DFT) and the most stable structure was confirmed. The adiabatic detachment energies for the most stable structure were in agreement with the experimental PES results. The calculated density of state (DOS) agrees with the experimental PES spectrum well. It was confirmed by the theoretical calculations that the C4H4N group bonds on lead clusters through the Pb-N sigma bond.     

Theoretical study on the structure and formation mechanism of [C6H5Mm]- (M=Ag, Au; m=1-3)

The structures and formation mechanisms of the important intermediate phenyl-coinage metal complexes [C(6)H(5)M(m)](-) (M==Ag, Au, m = 1-3) are investigated at B3LYP//6-311G(d, p)/Lanl2dz level using Gaussian 03 program. The adiabatic electron affinity and vertical dissociation energy of [M(m)](-) and [C(6)H(5)M(m)](-) are calculated, which are excellently coincident with the experimental determination. The C(6)H(5) group bonds on metal clusters through M--C sigma bond in the complex [C(6)H(5)M(m)](-). The complexes [C(6)H(5)M(m)](-) (M==Ag, Au; m = 2-3) are generated through a stepwise reaction. The first step is a direct insertion reaction between [M(m)](-) (M==Ag, Au, m = 1-3) and C(6)H(6,) which leads to the generation of intermediate [C(6)H(5)M(m)H](-) (m = 1-3) with the activation and cleavage of C--H bond. The second step is the neutral metal atom abstracting the H atom to yield the product [C(6)H(5)M(m)](-).     

Experimental and theoretical study on the structure and formation mechanism of [C6H5Cu(m)]- (m = 1-3)

The important intermediate phenyl-copper metal complexes [C(6)H(5)Cu(m)]- (m = 1-3), which are produced from the reactions between copper metal clusters formed by laser ablation and the benzene molecules seeded in argon carrier gas, are studied by photoelectron spectroscopy(PES) and density functional theory (DFT). Their structures and bonding patterns are investigated, which results in the conclusion that C(6)H(5) groups bond perpendicularly on copper clusters through Cu-C sigma bond. The formation mechanism of these complexes has been studied at B3LYP//6-311G(d, p)/Lanl2dz level. Direct insertion reaction between [Cu(m)]- and C(6)H(6) yields intermediate complex [C(6)H(5)Cu(m)H]-, and then eliminates the H atom, or releases the H atom to other neutral Cu atoms or anionic Cu ions via H abstraction reaction. The first step is the rate-limiting step with C-H activation and cleavage, and H abstraction by neutral Cu atom is the most energetically favorable pathway for the final step. Moreover, the complex [C(6)H(5)Cu(2)]- is ascertained to be easier to be generated than [C(6)H(5)Cu(3)]- and [C(6)H(5)Cu]-, which are in excellent agreement with the experimental results.     

过渡金属团簇M20和M20(PMe3)4(M=Cu,Ag,Au)的量子化学理论研究

采用从头计算MP2和DFT理论方法,对过渡金属团簇M20和M20( PMe3)4(M=Cu,Ag,Au)的几何结构、电子结构以及团簇各组成部分之间的结合能进行了研究.所研究的体系具有较大的前线轨道能隙,与C60接近,显示出特别的稳定性.考虑电子相关效应的MP2方法能够对团簇的结构给予可靠的描述.离域泛函GGA对Cu和A...     

Photoelectron imaging and theoretical calculations of gold-silver hydrides: comparing the characteristics of Au, Ag and H in small clusters

Structures and electronic properties of the mixed metal hydride anions AuAgH(-), Au(2)AgH(-), AuAg(2)H(-) and their neutrals are studied using anionic photoelectron imaging and theoretical calculations. The three isomers of AuAgH(-) are determined to be linear and those of AuAgH are determined to have C(s) symmetry. The structures of Au(2)AgH(-), AuAg(2)H(-) and their corresponding neutrals are determined to be planar with C(s) or C(2v) symmetries. The vertical detachment energies (VDEs) and adiabatic detachment energies (ADEs) of these anions are reported. Similar to the homonuclear Au(m)(-) and Ag(n)(-) clusters, the metal hydride anions with an even number of valence electrons have higher VDEs than those with an odd number. Variation of the VDEs of these metal hydride anions with interchange of Au, Ag and H (for example Au(m)Ag(n)(-)→ Au(m-1)Ag(n+ 1)(-), or Au(m-1)Ag(n)H(-)) will be shown to be characterized by the electronegativities of Au, Ag and H. The results presented in this study provide important insights into the similar and different characteristics of these three elements in small clusters.     

Metal effect on the supramolecular structure, photophysics, and acid-base character of trinuclear pyrazolato coinage metal complexes

Varying the coinage metal in cyclic trinuclear pyrazolate complexes is found to significantly affect the solid-state packing, photophysics, and acid-base properties. The three isoleptic compounds used in this study are [[3,5-(CF3)2Pz]M]3 with M = Cu, Ag, and Au (i.e., Cu3, Ag3, and Au3, respectively). They form isomorphous crystals and exist as trimers featuring nine-membered M3N6 rings with linear two-coordinate metal sites. On the basis of the M-N distances, the covalent radii of two-coordinate Cu(I), Ag(I), and Au(I) were estimated as 1.11, 1.34, and 1.25 angstroms, respectively. The cyclic [[3,5-(CF3)2Pz]M]3 complexes pack as infinite chains of trimers with a greater number of pairwise intertrimer M...M interactions upon proceeding to heavier coinage metals. However, the intertrimer distances are conspicuously short in Ag3 (3.204 angstroms) versus Au3 (3.885 angstroms) or Cu3 (3.813 angstroms) despite the significantly larger covalent radius of Ag(I). Remarkable luminescence properties are found for the three M3 complexes, as manifested by the appearance of multiple unstructured phosphorescence bands whose colors and lifetimes change qualitatively upon varying the coinage metal and temperature. The multiple emissions are assigned to different phosphorescent excimeric states that exhibit enhanced M...M bonding relative to the ground state. The startling luminescence thermochromic changes in crystals of each compound are related to relaxation between the different phosphorescent excimers. The trend in the lowest energy phosphorescence band follows the relative triplet energy of the three M(I) atomic ions. DFT calculations indicate that [[3,5-(R)2Pz]M]3 trimers with R = H or Me are bases with the relative basicity order Ag < Cu < Au while fluorination (R = CF3) renders even the Au trimer acidic. These predictions were substantiated experimentally by the isolation of the first acid-base adduct, [[Au3]2:toluene]infinity, in which a trinuclear Au(I) complex acts as an acid.     

Unique CO chemisorption properties of gold hexamer: Au6(CO)n- (n = 0-3)

Elucidating the chemisorption properties of CO on gold clusters is essential to understanding the catalytic mechanisms of gold nanoparticles. Gold hexamer Au(6) is a highly stable cluster, known to possess a D(3)(h) triangular ground state structure with an extremely large HOMO-LUMO gap. Here we report a photoelectron spectroscopy (PES) and quasi-relativistic density functional theory (DFT) study of Au(6)-CO complexes, Au(6)(CO)(n)(-) and Au(6)(CO)(n) (n = 0-3). CO chemisorption on Au(6) is observed to be highly unusual. While the electron donor capability of CO is known to decrease the electron binding energies of Au(m)(CO)(n)(-) complexes, CO chemisorption on Au(6) is observed to have very little effect on the electron binding energies of the first PES band of Au(6)(CO)(n)(-) (n = 1-3). Extensive DFT calculations show that the first three CO successively chemisorb to the three apex sites of the D(3)(h) Au(6). It is shown that the LUMO of the Au(6)-CO complexes is located in the inner triangle. Thus CO chemisorption on the apex sites (outer triangle) has little effect on this orbital, resulting in the roughly constant electron binding energies for the first PES band in Au(6)(CO)(n)(-) (n = 0-3). Detailed molecular orbital analyses lead to decisive information about chemisorption interactions between CO and a model Au cluster.     

Complexes of cationic coinage metal clusters Mn (M=Cu, Ag, Au; n=1–4) and H2S: a theoretical study

Geometries and vibrational frequencies of complexes of cationic coinage metal clusters M_n⁺ (M=Cu, Ag, Au; n=1–4) and H₂S are computed using density functional theory. Thermochemical values for M_n⁺H₂S decomposition channels involving loss of an H atom, H₂ molecule, M atom, or M₂ molecule are also computed. Significantly different results are obtained for closed-shell (n odd) and open-shell (n even) complexes.     

Complexes of gold(I), silver(I), and copper(I) with pentaaryl[60]fullerides

Gold(I), silver(I), and copper(I) phosphine complexes of 6,9,12,15,18-pentaaryl[60]fullerides 1a and 1b, namely, [(4-MeC(6)H(4))(5)C(60)]Au(PPh(3)) (2a), [(4-t-BuC(6)H(4))(5)C(60)]Au(PPh(3)) (2b), [(4-MeC(6)H(4))(5)C(60)]Ag(PCy(3)) (3a), [(4-t-BuC(6)H(4))(5)C(60)]Ag(PPh(3)) (3b), [(4-t-BuC(6)H(4))(5)C(60)]Ag(PCy(3)) (3c), [(4-MeC(6)H(4))(5)C(60)]Cu(PPh(3)) (4a), and [(4-t-BuC(6)H(4))(5)C(60)]Cu(PPh(3)) (4b), have been synthesized and characterized spectroscopically. All complexes except for 3c were also characterized by single-crystal X-ray diffraction. Several coordination modes between the cyclopentadienyl ring embedded in the fullerene and the metal centers are observed, ranging from η(1) with a slight distortion toward η(3) in the case of gold(I), to η(2)/η(3) for silver(I), and η(5) for copper(I). Silver complexes 3a and 3b are rare examples of crystallographically characterized Ag(I) cyclopentadienyls whose preparation was possible thanks to the steric shielding provided by fullerides 1a and 1b, which stabilizes these complexes. Silver complexes 3a and 3b both display unexpected coordination of the cyclopentadienyl portion of the fulleride anion with Ag(I). DFT calculations on the model systems (H(5)C(60))M(PH(3)) and CpMPH(3) (M = Au, Ag, or Cu) were carried out to probe the geometries and electronic structures of these metal complexes.     

Octahedral and tetrahedral coinage metal clusters: is three-dimensional d-orbital aromaticity viable?

The first quantitative evidence for the viability of three-dimensional aromatic clusters involving d-orbitals in pseudo-octahedral coinage metal cages M(6)Li(2) (M = Cu, Ag, Au) as well as in tetrahedral coinage metal cages M'(4)Li(4) (M' = Cu, Ag) was obtained computationally. These cages exhibit many features similar to those of their square planar M(4)Li(2) analogues. The large negative nucleus-independent chemical shifts (NICS) at the cage centers indicate three-dimensional delocalization. This diatropic character arises mostly from d-orbital delocalization combined with substantial contributions from the lowest-valence orbitals. The bonding molecular orbitals of the pseudo-octahedral clusters M(6)Li(2) (M = Cu, Ag, Au) are analogous to those in similar octahedral clusters involving p-orbital delocalization (e.g., B(6)H(6)(2-)). The M'(4)Li(4) clusters exhibit two isomeric forms: metal tetrahedral cages tetracapped by lithium cations on the outside [(M'(4)).4Li] and lithium tetrahedra on the inside capped by coinage metal atoms on each of the four faces [(Li(4)).4M]. Whereas the (M'(4)).4Li type structure is preferred for copper, gold and silver favor the (Li(4)).4M arrangement. NBO-NICS analysis shows that the large diatropic character in (M'(4)).4Li structures is due to the favorable contribution from both s- and d-orbitals, whereas the small NICS values in the center of (Li(4)).4M are due only to the diatropic contributions from the s-orbitals.     

Enhanced stability by three-dimensional aromaticity of endohedrally doped clusters X(10)M(0/-) with X = Ge, Sn, Pb and M = Cu, Ag, Au

The group 14 clusters encapsulated by coinage metals in neutral and anionic states X(10)M(0/-) (X = Ge, Sn, Pb and M = Cu, Ag, Au) are investigated using quantum chemical calculations with the DFT/B3LYP functional and coupled-cluster CCSD(T) theory. Addition of transition metals into the empty cages forms high symmetry endohedral structures, except for Ge(10)Ag(0/-). In agreement with experiments available for X(10)Cu, the D(4d) global minima of the anions are calculated to be magic clusters with large frontier orbital gaps, high vertical and adiabatic detachment energies, and large embedding energies and binding energies as compared to those of the empty cages X(10)(2-). The enhanced stability of these magic clusters can be rationalized by the three-dimensional aromaticity.     

On‐Surface Reactive Planarization of Pt(II) Complexes

A series of Pt(II) complexes with tetradentate luminophores has been designed, synthesized, and deposited on coinage metal surfaces with the aim to produce highly planar self‐assembled monolayers. Low‐temperature scanning tunneling microscopy (STM) and density functional theory (DFT) calculations reveal a significant initial nonplanarity for all complexes. A subsequent metal‐catalyzed separation of the nonplanar moiety at the bridging unit via the scission of a C?N bond is observed, leaving behind a largely planar core complex. The activation barrier of this bond scission process is found to depend strongly on the chemical nature of both bridging group and coordination plane, and to increase from Cu(111) through Ag(111) to Au(111).     

Infrared spectra of CH3-MF and several fragments prepared by methyl fluoride reactions with laser-ablated Cu, Ag, and Au atoms

Reactions of laser-ablated, excited group 11 metal atoms with CH(3)F isotopomers have been carried out, leading to the generation of CH(3)-MF and CH(2)F-M complexes for Cu, Ag, and Au in addition to smaller complexes for gold. The products in the infrared spectra identified on the basis of their frequencies, isotopic shifts, and correlation with DFT calculated frequencies reveal that M-F insertion by the coinage metals and H atom release readily occur. The relatively low dissociation energies of CH(3)-AuF to give several smaller Au complexes are consistent with the observation of these fragments. The C-Au bonds of CF-AuH and CH(2)-AuF exhibit considerable π character, and the methylidene CH(2)-AuF contains a true double bond. In contrast, the bond orders of CH(2)-Au and CH(2)-AuH are lower, indicating that F bonded to Au contracts the gold 5d orbitals for better overlap with the carbon 2p orbital for π bonding.     

Formation and emission of gold and silver carbide cluster ions in a single C60- surface impact at keV energies: experiment and calculations

Impact of fullerene ions (C(60)(-)) on a metallic surface at keV kinetic energies and under single collision conditions is used as an efficient way for generating gas phase carbide cluster ions of gold and silver, which were rarely explored before. Positively and negatively charged cluster ions, Au(n)C(m)(+) (n = 1-5, 1 ≤ m ≤ 12), Ag(n)C(m)(+) (n = 1-7, 1 ≤ m ≤ 7), Au(n)C(m)(-) (n = 1-5, 1 ≤ m ≤ 10), and Ag(n)C(m)(-) (n = 1-3, 1 ≤ m ≤ 6), were observed. The Au(3)C(2)(+) and Ag(3)C(2)(+) clusters are the most abundant cations in the corresponding mass spectra. Pronounced odd/even intensity alternations were observed for nearly all Au(n)C(m)(+/-) and Ag(n)C(m)(+/-) series. The time dependence of signal intensity for selected positive ions was measured over a broad range of C(60)(-) impact energies and fluxes. A few orders of magnitude immediate signal jump instantaneous with the C(60)(-) ion beam opening was observed, followed by a nearly constant plateau. It is concluded that the overall process of the fullerene collision and formation∕ejection of the carbidic species can be described as a single impact event where the shattering of the incoming C(60)(-) ion into small C(m) fragments occurs nearly instantaneously with the (multiple) pickup of metal atoms and resulting emission of the carbide clusters. Density functional theory calculations showed that the most stable configuration of the Au(n)C(m)(+) (n = 1, 2) clusters is a linear carbon chain with one or two terminal gold atoms correspondingly (except for a bent configuration of Au(2)C(+)). The calculated AuC(m) adiabatic ionization energies showed parity alternations in agreement with the measured intensity alternations of the corresponding ions. The Au(3)C(2)(+) ion possesses a basic Au(2)C(2) acetylide structure with a π-coordinated third gold atom, forming a π-complex structure of the type [Au(π-Au(2)C(2))](+). The calculation shows meaningful contributions of direct gold-gold bonding to the overall stability of the Au(3)C(2)(+) complex.     

Infrared spectra and structures of the coinage metal dihydroxide molecules

Laser-ablated Cu, Ag, and Au atoms react with H2O2 and with H2 + O2 molecules during condensation in excess argon to give four new IR absorptions in each system (O-H stretch, M-O-H bend, O-M-O stretch, and M-O-H deformation modes) that are due to the coinage metal M(OH)2 dihydroxide molecules. Isotopic substitution (D2O2, 18O2, 16O18O, D2, and HD) and comparison with frequencies computed by DFT verify these assignments. The calculations converge to 2B(g) ground electronic state structures with C2h symmetry, 111-117 degrees M-O-H bond angles, and substantial covalent character for these new metal dihydroxide molecules, particularly for Au(OH)2. This is probably due to the high electron affinity of gold owing to the effect of relativity.     

Unusual hydrogen bonding behavior in binary complexes of coinage metal anions with water

We have studied the interaction of atomic coinage metal anions with water molecules by infrared photodissociation spectroscopy of M-.H2O.Ar(n) clusters (M=Cu, Ag, Au; n=1, 2). We compare our observations with calculations on density-functional and coupled cluster levels of theory. The gold anion is bound to the water molecule by a single ionic hydrogen bond, similar to the halide-water complexes. In contrast, zero-point motion in the silver and copper complexes leads to a deviation from this motif.     

Interaction of coinage metal clusters with chalcogen dihydrides

The interaction of chalcogen dihydrides (H 2E; E = O, S, and Se) with small coinage metal clusters (M n ; M = Cu, Ag, and Au, n = 3 and 4) is studied based on density functional theory, with a focus on the nature of chalcogen-metal bonds. A newly developed pseudopotential-based correlation-consistent basis set is used for metal clusters together with the 6-311++G** basis set for the remaining atoms. Geometrical data identified that no significant deviation has been observed for molecules before and after complexation. For these three metals, binding energy calculations indicate that gold has the highest and silver has the lowest affinities for interaction with H 2E. In comparison with gold and copper, complexation between silver and chalcogen dihydrides is significantly weaker. It is found that interaction of H 2E molecules with the coinage metals have the order of H 2Se > H 2S > H 2O. Therefore, in agreement with experimental works, our calculations confirm that the gold-selenium bond is the most stable. The nature of M-E bonds is also interpreted by means of the quantum theory of atoms in molecules (QTAIM) and natural bond orbital (NBO) analyses. According to the QTAIM results, the bonds are found to be partially ionic and partially covalent. Natural resonance theory (NRT) is used to calculate natural bond order and bond polarity. The NRT result indicates that the percentage of polarity of M-E bonds is affected by coinage metals.     

Reactions of mixed silver-gold cluster cations AgmAun + (m+n=4,5,6) with CO: radiative association kinetics and density functional theory computations

Near thermal energy reactive collisions of small mixed metal cluster cations Ag(m)Au(n) (+) (m+n=4, 5, and 6) with carbon monoxide have been studied in the room temperature Penning trap of a Fourier transform ion-cyclotron-resonance mass spectrometer as a function of cluster size and composition. The tetrameric species AgAu(3) (+) and Ag(2)Au(2) (+) are found to react dissociatively by way of Au or Ag atom loss, respectively, to form the cluster carbonyl AgAu(2)CO(+). In contrast, measurements on a selection of pentamers and hexamers show that CO is added with absolute rate constants that decrease with increasing silver content. Experimentally determined absolute rate constants for CO adsorption were analyzed using the radiative association kinetics model to obtain cluster cation-CO binding energies ranging from 0.77 to 1.09 eV. High-level ab initio density functional theory (DFT) computations identifying the lowest-energy cluster isomers and the respective CO adsorption energies are in good agreement with the experimental findings clearly showing that CO binds in a "head-on" fashion to a gold atom in the mixed clusters. DFT exploration of reaction pathways in the case of Ag(2)Au(2) (+) suggests that exoergicities are high enough to access the minimum energy products for all reactive clusters probed.     

Photoelectron imaging of Ag(-)(H2O)x and AgOH(-)(H2O)y (x=1,2, y=0-4)

The photoelectron images of Ag(-)(H(2)O)(x) (x=1,2) and AgOH(-)(H(2)O)(y) (y=0-4) are reported. The Ag(-)(H(2)O)(1,2) anionic complexes have similar characteristics to the other two coinage metal-water complexes that can be characterized as metal atomic anion solvated by water molecules with the electron mainly localized on the metal. The vibrationally well-resolved photoelectron spectrum allows the adiabatic detachment energy (ADE) and vertical detachment energy (VDE) of AgOH(-) to be determined as 1.18(2) and 1.24(2) eV, respectively. The AgOH(-) anion interacts more strongly with water molecules than the Ag(-) anion. The photoelectron spectra of Ag(-)(H(2)O)(x) and AgOH(-)(H(2)O)(y) show a gradual increase in ADE and VDE with increasing x and y due to the solvent stabilization.