Toward rational construction of gold, gold-silver, and gold-mercury string complexes: syntheses, structures, and properties of [Au(Tab)2]2L2 (L = I and PF6), {[(Tab)2M][Au(CN)2]}2 (M = Au and Ag), and {[Hg(Tab)2][Au(CN)2]2} [Tab = 4-(trimethylammonio)benzenethiolate

The reaction of AuI with 2 equiv of TabHPF6 [TabH = 4-(trimethylammonio)benzenethiol] in the presence of excess Et3N in dimethylformamide (DMF)/MeOH afforded a binuclear gold(I) complex [Au(Tab)2]2I2.2H2O (1). Anion exchange of 1 with NH4PF6 in DMF gave rise to the more soluble complex [Au(Tab)2]2(PF6)2 (2). Treatment of 2 with K[Au(CN)2] produced a tetranuclear gold(I) complex {[(Tab)2Au][Au(CN)2]}2 (3). Analogous reactions of two known mononuclear complexes [Ag(Tab)2](PF6) (4) and [Hg(Tab)2](PF6)2 (5) with 1 or 2 equiv of K[Au(CN)2] generated one Ag2Au2 complex {[(Tab)2Ag][Au(CN)2]}2 (6) and one Au/Hg complex {[Hg(Tab)2][Au(CN)2]2} (7), respectively. Compounds 1-3, 6, and 7 were fully characterized by elemental analysis, IR spectra, UV-vis spectra, 1H NMR, and single-crystal X-ray crystallography. 1 and 2 have a similar [Au(Tab)2]2(2+) dimeric structure in which the two [Au(Tab)2]+ cations are connected via one Au-Au aurophilic interaction. In the structure of 3 or 6, each of the two pairs of [M(Tab)2]+ cation and [Au(CN)2]- anion is held together via ionic interactions to form a {[(Tab)2M][Au(CN)2]} species (M = Au, 3; Ag, 6). Two such species are further connected by one Au-Au aurophilic bonding interaction to form an uncommon Au(4) or Ag2Au2 linear string structure with three ligand-unsupported metal-metal bonds. For 7, the [Hg(Tab)2]2+ dication and the [Au(CN)2]2(2-) dianion are interconnected by the secondary Hg...N(CN) interactions to form a 1D chain structure. The thermal and luminescent properties of 1-3, 6, and 7 in solid state were also investigated.     

Genesis of gold clusters from mononuclear gold complexes on TiO2: reduction and aggregation of gold characterized by time-resolved X-ray absorption spectroscopy

Mononuclear gold complexes bonded to TiO(2) were synthesized from Au(CH(3))(2)(C(5)H(7)O(2)), and their decomposition and conversion into gold nanoclusters on the TiO(2) surface were characterized by time-resolved X-ray absorption and infrared spectroscopies as the temperature of the sample in flowing helium was ramped up. Mass spectra of the evolved gases were also measured during this process. The results show (a) the onset of formation of CH(4) as a decomposition product, (b) the reduction of Au(III) to Au(0), and (c) the formation of Au-Au bonds, all occurring in approximately the same temperature range (about 335-353 K), indicating that the reduction and aggregation of the supported gold are simultaneous processes facilitated by the removal of methyl ligands initially bonded to the gold. IR spectra recorded during the treatment indicate that water on the TiO(2) surface may be involved in the process by reacting with methyl groups bonded to Au(III) to give CH(4).     

Synthesis and structural characterization of luminescent trinuclear gold(I) complexes with dithiocarbamates

We have synthesized a series of trinuclear gold(I) complexes, namely, [Au3(mu-dpmp)(S2CNR2)nCl3-n] (n = 0-3; R = Me, CH2Ph), [Au3(mu-dpmp)(mu-S2CNR2)Cl](CF3SO3) (R = Me, CH2Ph), and [Au3(mu-dpmp)(mu-S2CNMe2)(C6F5)]X (X = Cl, CF3SO3), containing the triphosphine dpmp [bis(diphenylphosphinomethyl)phenylphosphine] and varying amounts of dithiocarbamate. NMR experiments show fluxional behavior in solution for most of these derivatives because several arrangements of the ligands are possible. The crystal structure of [(mu-dpmp)(AuCl)3] has been determined by X-ray diffraction studies; the molecule displays mirror symmetry and involves an angular arrangement of the gold atoms [Au-Au-Au 119.603(14) degrees, Au-Au 3.3709(4) A]. We have studied the optical properties of these derivatives in the solid state, finding a red shift as a function of the dithiocarbamate number and, for some derivatives, wavelength-dependent emission spectra at low temperature.     

Synthesis, structure, and reactions of binuclear gold(I) complexes containing two different bridging ligands

The binuclear cycloaurated compounds [Au(2)(mu-C(6)H(3)-2-PPh(2)-n-Me)(2)] (n = 5, 1a; n = 6, 1b) react with the digold(I) complexes [Au(2)(mu-S(2)CN(n)()Bu(2))(2)] and [Au(2)(mu-dppm)(2)](PF(6))(2) to give heterobridged dinuclear complexes [Au(2)(mu-C(6)H(3)-2-PPh(2)-n-Me)(mu-S(2)CN(n)Bu(2))] (n = 5, 5a; n = 6, 5b) and [Au(2)(mu-C(6)H(3)-2-PPh(2)-n-Me)(mu-dppm)]PF(6), (n = 5, 9a; n = 6, 9b), respectively. Complex 5a exists in the solid state as an infinite zigzag chain of dimeric units with intramolecular Au-Au separations of 2.8331(3) and 2.8243(3) A for independent molecules and intermolecular Au-Au separations of 3.0653(3) and 3.1304(3) A. Both 5a and 5b undergo oxidative addition with halogens to give the heterovalent, gold(I)-gold(III) compounds [XAu(I)(mu-2-Ph(2)PC(6)H(3)-n-Me)Au(III)X(eta(2)-S(2)CN(n)Bu(2))] [n = 5, X = Cl (6a), I (8a); n = 6, X = Cl (6b), Br (7b), I (8b)]. Compound 8a has been shown by X-ray crystallography to contain a gold(III) atom coordinated in a planar array by bidentate, chelating di-n-butyldithiocarbamate, iodide, and the sigma-aryl carbon atom, together with a gold(I) atom that is linearly coordinated by the phosphorus atom of the arylphosphine and by iodide. The intramolecular gold-gold distance of 3.2201(3) A indicates little or no interaction between the metal atoms. In contrast to the behavior of the homobridged complexes 1a and 1b, the heterobridged dithiocarbamate complexes 5a and 5b give structurally similar products on reaction with halogens, irrespective of the position of the ring methyl substituent. Crystal data for [Au(2)(mu-C(6)H(3)-2-PPh(2)-5-Me)(mu-S(2)CN(n)Bu(2))] (5a): triclinic, space group P1 (No. 2), with a = 11.3398(1), b = 15.9750(2), c = 16.4400(3) A, alpha = 91.0735(9), beta = 109.3130(7), gamma = 90.7666(8) degrees, V = 2809.47(6) A(3), and Z = 4. Crystal data for [IAu(I)(mu-2-Ph(2)PC(6)H(3)-5-Me)Au(III)I(eta(2)- S(2)CN(n)Bu(2))] (8a): triclinic, space group P1 (No. 2), with a = 8.6136(2), b = 9.3273, c = 21.1518(4) A, alpha = 84.008(1), beta = 84.945(1), gamma = 75.181(1) degrees, V = 1630.54(6) A(3), and Z = 2.     

Unraveling the mechanisms of O2 activation by size-selected gold clusters: transition from superoxo to peroxo chemisorption

The activation of dioxygen is a key step in CO oxidation catalyzed by gold nanoparticles. It is known that small gold cluster anions with even-numbered atoms can molecularly chemisorb O(2) via one-electron transfer from Au(n)(-) to O(2), whereas clusters with odd-numbered atoms are inert toward O(2). Here we report spectroscopic evidence of two modes of O(2) activation by the small even-sized Au(n)(-) clusters: superoxo and peroxo chemisorption. Photoelectron spectroscopy of O(2)Au(8)(-) revealed two distinct isomers, which can be converted from one to the other depending on the reaction time. Ab initio calculations show that there are two close-lying molecular O(2)-chemisorbed isomers for O(2)Au(8)(-): the lower energy isomer involves a peroxo-type binding of O(2) onto Au(8)(-), while the superoxo chemisorption is a slightly higher energy isomer. The computed detachment transitions of the superoxo and peroxo species are in good agreement with the experimental observation. The current work shows that there is a superoxo to peroxo chemisorption transition of O(2) on gold clusters at Au(8)(-): O(2)Au(n)(-) (n = 2, 4, 6) involves superoxo binding and n = 10, 12, 14, 18 involves peroxo binding, whereas the superoxo binding re-emerges at n = 20 due to the high symmetry tetrahedral structure of Au(20), which has a very low electron affinity. Hence, the two-dimensional (2D) Au(8)(-) is the smallest anionic gold nanoparticle that prefers peroxo binding with O(2). At Au(12)(-), although both 2D and 3D isomers coexist in the cluster beam, the 3D isomer prefers the peroxo binding with O(2).     

Gold(I)-dithioether supramolecular polymers: synthesis, characterization, and luminescence

A series of discrete compounds and supramolecular polymers were synthesized by self-assembly of dithioether building blocks and HAuCl4.3H2O. In complexes 1 {[AuL(1-Me)Cl], where L(1-Me) is bis(methylthio)methane} and 2 {[Au2L(2-Ph)Cl2], where L(2-Ph) is 1,2-bis(phenylthio)ethane}, adjacent units are connected via aurophilic interactions. Complex 1, a one-dimensional (1D) supramolecular polymer, and complex 2, a two-dimensional supramolecular network, both feature nearly linear [Au-Au-](infinity) chains. Complexes 4a, 4b, and 4c, all of which contain 1,3-bis(phenylthio)propane (L(3-Ph)), are polymorphs having the composition [Au2L(3-Ph)Cl2]. Complex 3 {[Au2L(1-Ph)Cl2], where L(1-Ph) is bis(phenylthio)methane}and complexes 4a and 4b consist of nearly identical 1D supramolecular polymers formed through Au-Au interactions. The third polymorph, 4c, is a molecular complex, as it does not have metal-metal interactions. Complex 5 {[Au2L(4-Ph)Cl2], where L(4-Ph) is 1,4-bis(phenylthio)butane} is also molecular. UV-vis spectra showed that the absorption bands of these complexes are allowed ligand-centered transitions between 230 and 260 nm. Complexes 1, 2, and 6 {[AuL(3-Me)Cl], where L(3-Me) is 1,3-bis(methylthio)propane} exhibited solid-state luminescence at 5 K with vibronic progressions and band maxima at approximately 570 nm. It is suggested that complex 6 contains [Au-Au-](infinity) chains.     

The elusive structures of pentakis[(triphenylphosphine)gold]ammonium(2+) bi

[Pentakis[(triphenylphosphine)gold(I)]ammonium(2+)] bis[(tetrafluoroborate)(1-)] was prepared from [tetrakis[(triphenylphosphine)gold(I)]-ammonium(1+)] [tetrafluoroborate(1-)] and [(triphenylphosphine)gold(I)] tetrafluoroborate in hexamethyl phosphoric triamide and tetrahydrofuran at 20 degrees C in 53% yield and crystallized from dichloromethane as the new solvate [[(Ph3P)Au]5N]3 [BF4]6 [CH2Cl2]4. The crystal structure of this product has been determined by single-crystal X-ray methods [monoclinic, P2(1/n), a = 34.200(3), b = 15.285(1), c = 53.127(3) A, beta = 107.262(2) degrees, V = 26521(3) A3, Z = 12, at 153 K]. The lattice contains three independent trinuclear dications that have no crystallographically imposed symmetry and are mutually similar in their molecular structure. The geometry of the [Au5N] core with pentacoordinate nitrogen atoms is intermediate between trigonal-bipyramidal and square pyramidal with severe distortions to minimize the Au-Au distances along some of the edges of the polyhedra. The three structures are thus different from that found previously in the tetrahydrofuran solvate [[(Ph3P)-Au]5N](BF4)2(C4H8O)2, where the geometry of the same trinuclear dication is closer to the trigonal-bipyramidal reference model. The new results are discussed in the light of the structures of tetra(gold)ammonium cations in salts of the type [[(Ph3P)Au]4N]+X- and of related tetra-, penta-, and hexacoordinate poly(gold)phosphonium, -arsonium, -sulfonium, and -selenonium cations.     

On the chemical bonding of gold in auro-boron oxide clusters AunBO- (n = 1-3)

During experiment on Au-B alloy clusters, an auro-boron oxide cluster Au2BO- was observed to be an intense peak dominating the Au-B mass spectra, along with weaker signals for AuBO- and Au3BO-. Well-resolved photoelectron spectra have been obtained for the three new oxide clusters, which exhibit an odd-even effect in electron affinities. Au2BO- is shown to be a closed shell molecule with a very high electron detachment energy, whereas AuBO and Au3BO neutrals are shown to be closed shell species with large HOMO-LUMO gaps, resulting in relatively low electron affinities. Density functional calculations were performed for both AunBO- (n = 1-3) and the corresponding HnBO- species to evaluate the analogy between bonding of gold and hydrogen in these clusters. The combination of experiment and theory allowed us to establish the structures and chemical bonding of these tertiary clusters. We find that the first gold atom does mimic hydrogen and interacts with the BO unit to produce a linear AuBO structure. This unit preserves its identity when interacting with additional gold atoms: a linear Au-[AuBO] complex is formed when adding one extra Au atom and two isomeric Au2-[AuBO] complexes are formed when adding two extra Au atoms. Since BO- is isoelectronic to CO, the AunBO- species can be alternatively viewed as Aun interacting with a BO- unit. The structures and chemical bonding in AunBO- are compared to those in the corresponding AunCO complexes.     

Gold apes hydrogen. The structure and bonding in the planar B7Au2- and B7Au2 clusters

We produced the B7Au2- mixed cluster and studied its electronic structure and chemical bonding using photoelectron spectroscopy and ab initio calculations. The photoelectron spectra of B7Au2- were observed to be relatively simple with vibrational resolution, in contrast to the complicated spectra observed for pure B7-, which had contributions from three isomers (Alexandrova et al. J. Phys. Chem. A 2004, 108, 3509). Theoretical calculations show that B7Au2- possesses an extremely stable planar structure, identical to that of B7H2-, demonstrating that Au mimics H in its bonding to boron, analogous to the Au-Si bonding. The ground-state structure of B7Au2- (B7H2-) can be viewed as adding two Au (H) atoms to the terminal B atoms of a higher-lying planar isomer of B7-. The bonding and stability in the planar B7Au2- (B7H2-) clusters are elucidated on the basis of the strong covalent B-Au (H) bonding and the concepts of aromaticity/antiaromaticity in these systems.     

Aurophilicity-based one-dimensional arrays of gold(I) phenylene-1,3- and -1,4-dithiolates

Phenylene-1,3-dithiol is converted into a trinuclear gold complex by treatment with 1 equiv of [[(Ph(3)P)Au](3)O](+)BF(4)(-). In the product, the phenylene unit bears one gold thiolate and one di(gold)sulfonium function. These components aggregate into one-dimensional arrays through head-to-tail aurophilic contacts between the two functions. In the association process, the Au[bond]S[bond]Au angle of the sulfonium group is opened up to accommodate the incoming gold atom between its metal centers. A similar mode of aggregation is found for the triply aurated biphenylene-4,4'-dithiol obtained using the tri(gold)oxonium salt with tri(p-tolyl)phosphine ligands. Probably for steric reasons, in this oligomerization process, the gold(I) thiolate unit is attached side-on to the digold sulfonium unit with retention of the small Au[bond]S[bond]Au angle. Under similar reaction conditions, and with the same molar ratio of the components, phenylene-1,4-dithiol is converted into the bis-sulfonium salt: 1,4-[[(p-Tol)(3)PAu](2)S](2)C(6)H(4)(BF(4))(2), the dications of which also associate into chains. Along the chains, the phenylene spacers alternate with tetranuclear gold clusters which arise from intimate aggregation of pairs of gold atoms. Together with previous findings, the present results show that gold thiolate (-SAuL) and digold sulfonium functions [-S(AuL)(2)(+)] in proper orientation at an arene unit (alpha-omega) can be considered as "soldering" points which can be used for joining up the molecular units into one-dimensional arrays solely through metal-metal contacts, which appear to be operative even against Coulomb repulsion between cations. The reaction of biphenylene-4,4'-dithiol with 2 equiv of sodium methoxide and [tri(c-hexyl)phosphine]gold chloride gives only neutral digold dithiolate complex 4 which is not associated owing to the steric bulk of the tri(c-hexyl)phosphine ligands.     

Mono-, di-, and trinuclear luminescent silver(I) and gold(I) N-heterocyclic carbene complexes derived from the picolyl-substituted methylimidazolium salt: 1-methyl-3-(2-pyridinylmethyl)-1H-imidazolium tetrafluoroborate

The N-heterocyclic carbene (NHC) precursor, 1-methyl-3-(2-pyridinylmethyl)-1H-imidazolium tetrafluoroborate, [HCH3im(CH2py)]BF4, reacted with AgBF4 in the presence of aqueous NaOH to produce the silver complex [Ag(CH3im(CH2py))2]BF4 (1) which was then reacted with Au(tht)Cl to form the corresponding gold(I) complex, [Au(CH3im(CH2py))2]BF4 (2). Complex 2 reacted with 1 equiv of AgBF4 to produce the mixed-metal species [AuAg(CH3im(CH2py))2](BF4)2 (3). The reaction of 2 with 1 equiv of Au(tht)Cl followed by metathesis with NaBF4 produces the dimetallic gold complex [Au2(CH3im(CH2py))2](BF4)2 (4). The reaction of [Ag(CH3im(CH2py))2]BF4 (1) with 1 equiv of AgBF4 produces the trinuclear [Ag3(CH3im(CH2py))3(NCCH3)2](BF4)3 (5) complex, which appears to dissociate into a dimetallic complex in solution. Complexes 1-5 were characterized by 1H NMR, 13C NMR, UV-vis, luminescence spectroscopy, elemental analysis, mass spectrometry, and X-ray crystallography. The CH3im(CH2py) ligands in 3 are arranged in a head-to-head fashion spanning a Au-Ag separation of 3.0318(5) A with the carbene portion of the ligand remaining coordinated to the Au(I) center. In 4, the ligands are arranged in a head-to-tail fashion with an Au-Au separation of 3.1730(5) A. In 5, the ligands bridge the nearly symmetrical Ag3 triangular core with short Ag-Ag separations of 2.7765(8), 2.7832(8), and 2.7598(8) A. All of these complexes, including the ligand precursor, are intensely luminescent in solution and the solid state.     

Reactions of a gold(I) thiolate complex [Au(Tab)(2)](2)(PF(6))(2) (Tab = 4-(trimethylammonio)benzenethiolate) with diphosphine ligands

Reactions of a gold(i) thiolate complex [Au(Tab)(2)](2)(PF(6))(2) (Tab = 4-(trimethylammonio)benzenethiolate) with equimolar 1,2-bis(diphenylphosphine)ethane (dppe), 1,3-bis-(diphenylphosphine)propane (dppp) or 1,4-bis-(diphenylphosphine)butane (dppb) in MeOH-DMF-CH(2)Cl(2) gave rise to three polymeric complexes [Au(2)(Tab)(2)(dppe)](2)(PF(6))(4)·2MeOH (1·2MeOH), [Au(2)(Tab)(2)(dppp)]Cl(2)·0.5MeOH·4H(2)O (2·0.5MeOH·4H(2)O), and [Au(4)(μ-Tab)(2)(Tab)(2)(dppb)](PF(6))(4)·4DMF (3·4DMF), respectively. Analogous reaction of 1 with dppb in DMF/C(2)H(4)Cl(2) produced one tetranuclear complex [Au(2)(μ-Tab)(Tab)(2)](2)Cl(4)·2DMF·4H(2)O (4·2DMF·4H(2)O). Complexes 1-4 were characterized by elemental analysis, IR spectra, UV-vis spectra, (1)H and (31)P{(1)H} NMR and single crystal X-ray analysis. Compounds 1 and 2 consist of [Au(Tab)](2) dimeric fragments that are bridged by dppe or dppp ligands to form a 1D linear chain extending along the a axis. For 3, each [Au(4)(Tab)(2)(μ-Tab)(2)] fragment is linked by a pair of dppb ligands to afford another 1D chain extending along the c axis. For 4, the four [Au(Tab)](+) fragments are linked by two Au-Au bonds and two doubly bridging Tab ligands to form a {[Au(Tab)](4)(μ-Tab)(2)} chair-like cyclohexane structure. Hydrogen-bonding interactions in 2 and 4 lead to the formation of interesting 2D hydrogen-bonded networks. The luminescent properties of 1-4 in solid state were also investigated.     

A photoelectron spectroscopic and computational study of sodium auride clusters, NanAun- (n = 1-3)

Negatively charged sodium auride clusters, NanAun- (n = 1-3), have been investigated experimentally using photoelectron spectroscopy and ab initio calculations. Well-resolved electronic transitions were observed in the photoelectron spectra of NanAun- (n = 1-3) at several photon energies. Very large band gaps were observed in the photoelectron spectra of the anion clusters, indicating that the corresponding neutral clusters are stable closed-shell species. Calculations show that the global minimum of Na2Au2- is a quasi-linear species with Cs symmetry. A planar isomer of D2h symmetry is found to be 0.137 eV higher in energy. The two lowest energy isomers of Na3Au3- consist of three-dimensional structures of Cs symmetry. The global minimum of Na3Au3- has a bent-flake structure lying 0.077 eV below a more compact structure. The global minima of the sodium auride clusters are confirmed by the good agreement between the calculated electron detachment energies of the anions and the measured photoelectron spectra. The global minima of neutral Na2Au2 and Na3Au3 are found to possess higher symmetries with a planar four-membered ring (D2h) and a six-membered ring (D3h) structure, respectively. The chemical bonding in the sodium auride clusters is found to be highly ionic with Au acting as the electron acceptor.     

Structural studies of lanthanide ion complexes of pure gold, pure silver and mixed metal (gold-silver) dicyanides

Crystal structures of four lanthanide complexes of La[Au(CN)2](3).3H2O, La[Ag(CN)2](3).3H2O, La[Ag(0.83)Au(0.17)(CN)2](3).3H2O, and La[Ag(0.39)Au(0.61)(CN)2](3).3H2O are reported. Studies reveal that all the structures reported are isostructural. All systems were found to be in the hexagonal crystal system, space group P6(3)/mcm. The metal-metal distance for the pure gold system is 3.332 (1) A versus 3.359(1) A for the pure silver system. The mixed-metal systems have shown no distinct differences in the location of the metal atoms, with the La[Ag(0.83)Au(0.17)(CN)2](3).3H2O complex having a metal-metal Ag-Au separation of 3.346(1) A, and 3.344(1) A for the La[Ag(0.39)Au(0.61)(CN)2](3).3H2O complex. The crystal structures of the pure and mixed La complexes have been solved to provide evidence of Ag-Au heterometallic interactions and as a basis for understanding the interesting optical properties of the systems.     

Aurophilic self-assembly of a Mo4Au2 phosphinidene complex with an unprecedented H-shaped planar metal core

The isomers [Mo2Cp2(mu-kappa(1):kappa(1),eta(6)-PR*)(CO)2] (1) and [Mo2Cp(mu-kappa(1):kappa(1),eta(5)-PC5H4)(CO)2(eta(6)-HR*)] (2) (Cp = eta(5)-C5H5; R* = 2,4,6-C6H2(t)Bu3) react with [AuCl(THT)] and with the cation [Au(THT)2](+) (THT = tetrahydrothiophene) to give phosphinidene-bridged Mo2Au complexes resulting from the addition of an AuCl or Au(THT)(+) electrophile to their multiple P-Mo bonds. Removal of the Cl(-) or THT ligand from these derivatives causes a dimerization of the trinuclear structures to give the cationic derivative [{AuMo2Cp(mu3-kappa(1):kappa(1):kappa(1),eta(5)-PC5H4)(CO)2(eta(6)-HR*)}2](2+), which displays a novel H-shaped metal core held by strong Mo-Au dative bonds [2.768(1) A] and an aurophilic interaction [Au-Au = 3.022(1) A].     

Electronic structures and absorption spectra of linkage isomers of trithiocyanato (4,4',4' '-tricarboxy-2,2':6,2' '-terpyridine) ruthenium(II) complexes: a DFT study

Black dye (BD), isomer 1 ([Ru(II)(H3-tctpy)(NCS)3](-1), where H3-tctpy = 4,4',4' '-tricarboxy-2,2':6,2' '-terpyridine) is known to be an excellent sensitizer for dye-sensitized solar cells and exhibits a very good near-IR photo response, compared to other ruthenium dyes. Because isothiocyanate is a linear ambidentate ligand, BD has three other linkage isomers, [Ru(H3-tctpy)(NCS)2(SCN)](-1), isomer 2 and 2', and [Ru(H3-tctpy))(SCN)3](-1), isomer 3. In this study, we have calculated the geometry of BD and its isomers by DFT. Further, we have analyzed the bonding in these isomers using NBO methods. TDDFT calculations combined with scalar relativistic zero-order regular approximations (SR-ZORA) have been carried out to simulate the absorption spectra. Calculations have been performed for the isomers both in vacuo and in solvent (ethanol). The inclusion of the solvent is found to be important to obtain spectra in good agreement with the experiment. The first absorption bands are dominated by the metal-to-ligand charge transfer (MLCT) and ligand-to-ligand charge transfer (LLCT).     

Gold as hydrogen. An experimental and theoretical study of the structures and bonding in disilicon gold clusters Si2Au(n)- and Si2Au(n) (n = 2 and 4) and comparisons to Si2H2 and Si2H4

In a previous communication, we showed that a single Au atom behaves like H in its bonding to Si in a series of Si-Au clusters, SiAu(n) (n = 2-4) (Kiran et al. Angew. Chem., Int. Ed. 2004, 43, 2125). In this article, we show that the H analogy of Au is more general. We find that the chemical bonding and potential energy surfaces of two disilicon Au clusters, Si(2)Au(2) and Si(2)Au(4), are analogous to Si(2)H(2) and Si(2)H(4), respectively. Photoelectron spectroscopy and ab initio calculations are used to investigate the geometrical and electronic structures of Si(2)Au(2)(-), Si(2)Au(4)(-), and their neutral species. The most stable structures for both Si(2)Au(2) and Si(2)Au(2)(-) are found to be C(2)(v), in which each Au bridges the two Si atoms. For Si(2)Au(4)(-), two nearly degenerate dibridged structures in a cis (C(2)(h)) and a trans (C(2)(v)) configuration are found to be the most stable isomers. However, in the neural potential energy surface of Si(2)Au(4), a monobridged isomer is the global minimum. The ground-state structures of Si(2)Au(2)(-) and Si(2)Au(4)(-) are confirmed by comparing the computed vertical detachment energies with the experimental data. The various stable isomers found for Si(2)Au(2) and Si(2)Au(4) are similar to those known for Si(2)H(2) and Si(2)H(4), respectively. Geometrical and electronic structure comparisons with the corresponding silicon hydrides are made to further establish the isolobal analogy between a gold atom and a hydrogen atom.     

Cationic gold carbonyl complex on a phosphine support

A cationic gold carbonyl complex has been synthesized and characterized using several techniques including X-ray crystallography. [(Mes(3)P)Au(CO)][SbF(6)] (Mes = 2,4,6-Me(3)C(6)H(2)) has a linear, two-coordinate gold atom. This compound displays the CO stretching frequency at 2185 cm(-1). The (13)C NMR signal of the gold-bound (13)CO appears as a doublet centered at δ 182.6 ((2)J(C,P) = 115 Hz). A computational study shows that the Au-CO bond consists of electrostatic attraction, Au ← CO donation, and significant Au → CO π-back-bonding components. Polarization of the CO bond caused by the electrostatic effect of the cationic gold center is mainly responsible for the large blue shift in the CO stretching frequency.     

Structure evolution of gold cluster anions between the planar and cage structures by isoelectronic substitution: Au(n)- (n = 13-15) and MAu(n)- (n = 12-14; M = Ag, Cu)

The structural and electronic effects of isoelectronic substitution by Ag and Cu atoms on gold cluster anions in the size range between 13 and 15 atoms are studied using a combination of photoelectron spectroscopy and first-principles density functional calculations. The most stable structures of the doped clusters are compared with those of the undoped Au clusters in the same size range. The joint experimental and theoretical study reveals a new C(3v) symmetric isomer for Au(13)(-), which is present in the experiment, but has hitherto not been recognized. The global minima of Au(14)(-) and Au(15)(-) are resolved on the basis of comparison between experiment and newly computed photoelectron spectra that include spin-orbit effects. The coexistence of two isomers for Au(15)(-) is firmly established with convincing experimental evidence and theoretical calculations. The overall effect of the isoelectronic substitution is minor on the structures relative to those of the undoped clusters, except that the dopant atoms tend to lower the symmetries of the doped clusters.     

Synthesis, structure, luminescence, and theoretical studies of tetranuclear gold clusters with phosphinocarborane ligands

Treatment of the tetranuclear gold cluster [Au4((PPh2)2C2B9H10)2(AsPh3)2] (1), which contains the nido-carborane-diphosphine [7,8-(PPh2)2C2B9H10]-, with various tertiary phosphines leads to derivatives [Au4((PPh2)2C2B9H10)2-(PR3)2] (PR3 = PPh3 (2), P(4-MeC6H4)3 (3), P(4-OMeC6H4)3 (4)). The X-ray crystal structure of complex 4 shows a tetrahedral framework of gold atoms, two of which are chelated by the diphosphine, and two are coordinated to one monophosphine ligand each. These compounds are very stable and are obtained in high yield. MP2 calculations suggest that the two types of chemically nonequivalent gold atoms can be formally assigned as Au(I) (those attached to the arsines or phosphines) and Au(0) (those bonded to the anionic diphosphine) and emphasize the role of correlation in the gold-gold interactions. The compounds are luminescent. The emission is assigned to a gold-centered spin-forbidden transition; the assignment of the oxidation state of the gold centers on this basis leads to results coincident with those obtained by theoretical calculations.