Supramolecular assembly of gold(I) complexes of diphosphines and N,N'-bis-4-methylpyridyl oxalamide

We report herein the supramolecular assembly and spectroscopic and luminescent properties of gold(I) complexes of diphosphines (dppm [bis(diphenylphosphino)methane], dppp [1,3-bis(diphenylphosphino)propane], and dpppn [1,5-bis(diphenylphosphino)pentane]) and N,N'-bis-4-methylpyridyl oxalamide (L). The dppm and dppp cases form the rectangular structures, [dppm(Au(2))L](2)(ClO(4))(4) and [dppp(Au(2))L](2)(ClO(4))(4), with four gold(I) ions at the corners, as well as two L and two dppm or dppp ligands as edges, featuring 38- and 42-membered rings for the former and the latter, respectively. Remarkably, the packing of the dppp complexes shows interesting one-dimensional rectangular channels in the solid state, most likely due to intermolecular pi...pi interactions. The dpppn complex has been structurally characterized as a one-dimensional coordination polymer, {[(dpppn)(3.5)(Au(7))L(3.5)](PF(6))(7)}. The absorptions and emissions of the compounds are in general due to intraligand transitions, but aurophilic or pi...pi interactions could also make partial contributions. The dipyridyl amide system with the amides incorporated into the bridging ligands as well as the one-dimensional rectangular channels in the solid state for the dppp-based rectangle make this a promising family of metal-containing cyclic peptides in crystal engineering and molecular-recognition studies.     

Synthesis of New Thiourea-Metal Complexes with Promising Anticancer Properties

In this work, two thiourea ligands bearing a phosphine group in one arm and in the other a phenyl group (T2) or 3,5-di-CF₃ substituted phenyl ring (T1) have been prepared and their coordination to Au and Ag has been studied. A different behavior is observed for gold complexes, a linear geometry with coordination only to the phosphorus atom or an equilibrium between the linear and three-coordinated species is present, whereas for silver complexes the coordination of the ligand as P^S chelate is found. The thiourea ligands and their complexes were explored against different cancer cell lines (HeLa, A549, and Jurkat). The thiourea ligands do not exhibit relevant cytotoxicity in the tested cell lines and the coordination of a metal triggers excellent cytotoxic values in all cases. In general, data showed that gold complexes are more cytotoxic than the silver compounds with T1, in particular the complexes [AuT1(PPh₃)]OTf, the bis(thiourea) [Au(T1)₂]OTf and the gold-thiolate species [Au(SR)T1]. In contrast, with T2 better results are obtained with silver species [AgT1(PPh₃)]OTf and the [Ag(T1)₂]OTf. The role played by the ancillary ligand bound to the metal is important since it strongly affects the cytotoxic activity, being the bis(thiourea) complex the most active species. This study demonstrates that metal complexes derived from thiourea can be biologically active and these compounds are promising leads for further development as potential anticancer agents.     

Coordination Behavior of Sterically Protected Phosphaalkenes on the AuCl Moiety Leading to Catalytic 1,6‐Enyne Cycloisomerization

Mes*‐substituted 2,3‐dimethyl‐1,4‐diphosphabuta‐1,3‐diene, 1,2‐diphenyl‐3,4‐diphosphinidenecyclobutene, 2,2‐bis(methylsulfanyl)‐1‐phosphaethene, and 3,3‐diphenyl‐1,3‐diphosphapropenes (Mes*=2,4,6‐tri‐tert‐butylphenyl) were employed as P ligands of gold(I) complexes. The (E,E)‐2,3‐dimethyl‐1,4‐diphosphabuta‐1,3‐diene functioned as a P2 ligand for digold(I) complex formation with or without intramolecular Au–Au contact, which depends on the conformation of the 1,3‐diphosphabuta‐1,3‐diene. The 1,2‐diphenyl‐3,4‐diphosphinidenecyclobutene, which has a rigid s‐cis P?C? C?P skeleton, afforded the corresponding digold(I) complexes with a slight distortion of the planar diphosphinidenecyclobutene framework and intramolecular Au–Au contact. In the case of the 2,2‐bis(methylsulfanyl)‐1‐phosphaethene, only the phosphorus atom coordinated to gold, and the sulfur atom showed almost no intra‐ or intermolecular coordination to gold. On the other hand, the 1,3‐diphosphapropenes behaved as nonequivalent P2 ligands to afford the corresponding mono‐ and digold(I) complexes. Some phosphaalkene–gold(I) complexes showed catalytic activity for 1,6‐enyne cycloisomerization without cocatalysts such as silver hexafluoroantimonate.     

Gold(I) catalysts with bifunctional P, N ligands

A series of phosphanes with imidazolyl substituents were prepared as hemilabile PN ligands. The corresponding gold(I) complexes were tested as bifunctional catalysts in the Markovnikov hydration of 1-octyne, as well as in the synthesis of propargylamines by the three component coupling reaction of piperidine, benzaldehyde, and phenylacetylene. While the activity in the hydration of 1-octyne was low, the complexes are potent catalysts for the three component coupling reaction. In homogeneous solution the conversions to the respective propargylamine were considerably higher than under aqueous biphasic conditions. The connectivity of the imidazolyl substituents to the phosphorus atom, their substitution pattern, as well as the number of heteroaromatic substituents have pronounced effects on the catalytic activity of the corresponding gold(I) complexes. Furthermore, formation of polymetallic species with Au(2), Au(3), and Au(4) units has been observed and the solid-state structures of the compounds [(5)(2)Au(3)Cl(2)]Cl and [(3c)(2)Au(4)Cl(2)]Cl(2) (3c = tris(2-isopropylimidazol-4(5)-yl phosphane, 5 = 2-tert-butylimidazol-4(5)-yldiphenyl phosphane) were determined. The gold(I) complexes of imidazol-2-yl phosphane ligands proved to be a novel source for bis(NHC)gold(I) complexes (NHC = N-heterocyclic carbene).     

Neutral gold complexes with tridentate SNS thiosemicarbazide ligands

Na[AuCl(4)]·2H(2)O reacts with tridentate thiosemicarbazide ligands, H(2)L1, derived from N-[N',N'-dialkylamino(thiocarbonyl)]benzimidoyl chloride and thiosemicarbazides under formation of air-stable, green [AuCl(L1)] complexes. The organic ligands coordinate in a planar SNS coordination mode. Small amounts of gold(I) complexes of the composition [AuCl(L3)] are formed as side-products, where L3 is an S-bonded 5-diethylamino-3-phenyl-1-thiocarbamoyl-1,2,4-triazole. The formation of the triazole L3 can be explained by the oxidation of H(2)L1 to an intermediate thiatriazine L2 by Au(3+), followed by a desulfurization reaction with ring contraction. The chloro ligands in the [AuCl(L1)] complexes can readily be replaced by other monoanionic ligands such as SCN(-) or CN(-) giving [Au(SCN)(L1)] or [Au(CN)(L1)] complexes. The complexes described in this paper represent the first examples of fully characterized neutral Gold(III) thiosemicarbazone complexes. All the [AuCl(L1)] compounds present a remarkable cell growth inhibition against human MCF-7 breast cancer cells. However, systematic variation of the alkyl groups in the N(4)-position of the thiosemicarbazone building blocks as well as the replacement of the chloride by thiocyanate ligands do not considerably influence the biological activity. On the other hand, the reduction of Au(III) to Au(I) leads to a considerable decrease of the cytotoxicity.     

Molecular Gold Wire from Mixed‐Valent AuI/III Complexes

Crystals of mixed‐valent Au complexes have been grown from solutions of cyclohexanecarbonitrile and a stoichiometric amount of gold(I) and gold(III) chloride. The purely obtained compound was characterized as bis(cyclohexanecarbonitrile)gold(I) tetrachloridoaurate(III). The crystal packing of the mixed valent Au(I/III) compound demonstrates a columnar arrangement of the gold(I) and gold(III) atoms. The new structure displays the shortest unsupported gold(I)–gold(III) interactions with the sub‐van der Waals distance of 324–325 pm, which is assumed as an aurophilic bonding interaction.     

Theoretical and photoluminescence studies on the d10-s2 AuI-TlI interaction in extended unsupported chains

The reactions of solutions of TlPF(6) and OPPh(3) in tetrahydrofuran or acetone with NBu(4)[AuR(2)] (R=C(6)Cl(5), C(6)F(5)) gave the new complexes [Au(C(6)Cl(5))(2)](2)[Tl(OPPh(3))][Tl(OPPh(3))(L)] (L=THF (1), acetone (2)) and the previously reported [Tl(OPPh(3))(2)][Au(C(6)F(5))(2)] (3). The crystal structures of complexes 1 and 2 display extended unsupported chains with short intermolecular interactions between alternating gold(I) and thallium(I) centres. Moreover, the Tl(I) centres show two different types of geometrical environments, such as pseudotetrahedral and distorted trigonal-bipyramidal, due to the presence of solvent molecules that act as ligands in the solid-state structure. Quasirelativistic and nonrelativistic ab initio calculations were performed to study the nature of the intermetallic Au(I)-Tl(I) interactions and are consistent with the presence of a high ionic contribution (80 %) and dispersion-type (van der Waals) interaction with a charge-transfer contribution (20 %) when relativistic effects are taken into account. All complexes are luminescent in the solid state at room temperature and at 77 K. Complexes 1 and 2 show site-selective excitation, probably due to the different environments around the Tl(I) centres. The DFT and time-dependent (TD)-DFT calculations are in agreement with the experimental excitation spectra for all complexes and confirm the site-selective excitation behaviour as a function of the Tl(I) geometrical environment.     

Selenolate gold complexes with aurophilic Au(I)-Au(I) and Au(I)-Au(III) interactions

The gold(I) selenolate compound [Au(2)(SePh)(2)(mu-dppf)] (dppf = 1,1'-bis(diphenylphosphino)ferrocene) has been prepared by reaction of [Au(2)Cl(2)(mu-dppf)] with PhSeSiMe(3) in a molar ratio 1:2. This complex reacts with gold(I) or gold(III) derivatives to give polynuclear gold(I)-gold(I) or gold(I)-gold(III) complexes of the type [Au(4)(mu-SePh)(2)(PPh(3))(2)(mu-dppf)](OTf)(2), [Au(3)(C(6)F(5))(3)(mu-SePh)(2)(mu-dppf)], or [Au(4)(C(6)F(5))(6)(mu-SePh)(2)(mu-dppf)], with bridging selenolate ligands. The reaction of [Au(2)(SePh)(2)(mu-dppf)] with 1 equiv of AgOTf leads to the formation of the insoluble Ag(SePh) and the compound [Au(2)(mu-SePh)(mu-dppf)]OTf. The complexes [Au(4)(C(6)F(5))(6)(mu-SePh)(2)(mu-dppf)] and [Au(2)(mu-SePh)(mu-dppf)]OTf (two different solvates) have been characterized by X-ray diffraction studies and show the presence of weak gold(I)-gold(III) interactions in the former and intra- and intermolecular gold(I)-gold(I) inter-actions in the later.     

“Hummingbird” Behaviour of N‐Heterocyclic Carbenes Stabilises Out‐of‐Plane Bonding of AuCl and CuCl Units

An N‐heterocyclic carbene substituted by two expanded 9‐ethyl‐9‐fluorenyl groups was shown to bind an AuCl unit in an unusual manner, namely with the Au?X rod sitting out of the plane defined by the heterocyclic carbene unit. As shown by X‐ray studies and DFT calculations, the observed large pitch angle (21°) arises from an easy displacement of the gold(I) atom away from the carbene lone‐pair axis, combined with the stabilisation provided by weak CH???Au interactions involving aliphatic and aromatic H atoms of the NHC wingtips. Weak, intermolecular Cl???H bonds are likely to cooperate with the H???Au interactions to stabilise the out‐of‐plane conformation. A general belief until now was that tilt angles in NHC complexes arise mainly from steric effects within the first coordination sphere.     

Gold(I) Complexes Nuclearity in Constrained Ferrocenyl Diphosphines: Dramatic Effect in Gold‐Catalyzed Enyne Cycloisomerization

Di‐tert‐butylated‐bis(phosphino)ferrocene ligands bearing phosphino substituents R (R=phenyl, cyclohexyl, iso‐propyl, mesityl, or furyl) allow tuning the selective formation of Au(I) halide complexes. Thus, dinuclear linear two‐coordinate, but also rare mononuclear trigonal three‐coordinate and tetrahedral four‐coordinate complexes were formed upon tuning of the conditions. Both Au(I) chloride and rarer Au(I) iodide complexes were synthesized, and their X‐ray diffraction analysis are reported. The significance of the control of structure and nuclearity in Au(I) complexes is further illustrated herein by its strong effect on the efficiency and selectivity of gold‐catalysed cycloisomerization. Cationic linear digold(I) bis(dicyclohexylphosphino) ferrocenes outperform other catalysts in the demanding regioselective cycloisomerization of enyne sulphonamides into cyclohexadienes. Conversely, tetrahedral and trigonal cationic monogold(I) complexes were found incompetent for enyne cycloaddition. We used the two‐coordinate linear electron‐rich Au(I) complex 2 b (R=Cy) to extend the scope of selective intramolecular cycloaddition of different 1,6‐enyne sulfonylamines with high activity and excellent selectivity to the endo cyclohexadiene products.     

Dinuclear gold(I) isocyanide complexes with luminescent properties, and displaying thermotropic liquid crystalline behavior

Dinuclear gold(I) complexes [mu-(4,4'-CN-R-NC){Au(C6F4OC4H9)}2] [R = 1,4-phenylene, n = 8; R = 4,4'-biphenylene, 2,2'-dichloro-4,4'-biphenylene, 2,2'-dimethyl-4,4'-biphenylene, n = 4,6,8,10] have been prepared and their liquid crystal behavior and optical properties studied. Although the free ligands are not mesomorphic, all the gold(I) derivatives described, except the phenylisonitrilegold(I) derivative [mu-(1,4-CN-C6H4-NC){Au(C6F4OC8H17)}2], display liquid crystal behavior, giving rise to a nematic mesophase. The transition temperatures decrease in the order 4-4'-biphenylene > 2,2'-dichloro-4-4'-biphenylene > 2,2'dimethyl-4-4'-biphenylene. All compounds show photoluminescence in the solid state and in solution. The single-crystal X-ray diffraction structures of [mu-(4,4'-CN-R-NC){Au(C6F4OCnH2n+1)}2] (R = 4-4'-biphenylene and 2,2'-dichloro-4-4'-biphenylene) have been determined confirming the rodlike structure of the molecule, with a linear coordination around the gold atoms. There are Au...Au interactions in the 2,2'-dichlorobiphenyl derivative but not in the 4-4'-biphenyl compound.     

Adduct effects on structure and luminescence in a series of new dithiocarbamatogold(I) complexes

Reaction of [AuCl(SMe₂)] with NaL·H₂O (L = ethyl(pyridine-4-yl methyl)dithiocarbamate (epdtc) or methyl(2-(pyridin-2-yl)ethyl)dithiocarbamate (mpdtc)) affords a series of neutral dinuclear gold(I) complexes bridged by each dithiocarbamate ligand, [Au(L)]₂. The successive reaction of [Au(L)]₂ with organic acids such as isophthalic acid (m-pa) and maleic acid (ma) produces 1:1 adducts, [Au(L)]₂·(organic acid). The crystal structure of [Au(L)]₂·(m-pa) is a 1D polymer formed via hydrogen bonds between the free pyridyl and the carboxylic acid moiety. For the dinuclear moiety, strong intradinuclear aurophilic interactions (Au(I)–Au(I) = 2.7783(8) Å and 2.7525(7) Å) exist, but interdinuclear interactions are weak (3.2551(8)–3.2733(8) Å). The dinuclear gold(I) complexes, [Au(epdtc)]₂ and [Au(mpdtc)]₂, show a bright luminescence at 562.5 and 552.0 nm in solid state, respectively, but their organic acid adducts, [Au(L)]₂·(organic acid), have no luminescent properties. This dramatic difference in properties between the gold(I) complexes and their adducts may be ascribed to the weakness of the internuclear Au(I)–Au(I) interaction including crystal packing.     

Disproportionation of Gold(II) complexes. A density functional study of ligand and solvent effects

A computational study of gold(II) disproportionation is presented for the atomic ion as well as complexes with chloride and neutral ligands. The Au2+ atomic ion is stable to disproportionation, but the barrier is more than halved to 119 kcal/mol in an aqueous environment vs 283 kcal/mol in the gas phase. For dissociative disproportionation of chloride complexes, the loss of chlorine, either as an atom (Delta G(aq) = +20 kcal/mol) or as an anion (Delta G(aq) = +15 kcal/mol) represents the largest calculated barrier. The calculated transition state for associative disproportionation is only 9 kcal/mol above separated Au(II)Cl3(-) anions. For the disproportionation of Au(II)L3 complexes with neutral ligands, disproportionation is highly endergonic in the gas phase. Calculations imply that for synthesis of a monometallic Au(II) complex, a nonpolar solvent is preferred. With the exception of [Au(CO)3]2+, disproportionation of Au(II)L3 complexes to Au(I)L and Au(III)L3 is exergonic in solution phase for the ligands investigated. The driving force is provided by the very favorable solvation free energy of the trivalent gold complex. The solvation free energy contribution to the reaction (Delta G(solv)) is very large for small and polar ligands such as ammonia and water. Furthermore, calculations imply that choosing ligands that would yield neutral species upon disproportionation may provide an effective route to thwart this decomposition pathway for Au(II) complexes. Likewise, bulkier ligands that yield larger, more weakly solvated complex ions would appear to be desirable.     

Dative Au→Al Interactions: Crystallographic Characterization and Computational Analysis

Hitherto unknown Au→Al interactions have been evidenced upon coordination of the geminal phosphorus–aluminum Lewis pair Mes₂PC(?CHPh)AltBu₂ (Mes=2,4,6‐trimethylphenyl). Four different gold(I) complexes featuring alkyl (Me), aryl (Ph, C₆F₅), and alkynyl (C?CPh) co‐ligands have been prepared. X‐ray diffraction analyses show that P→Au→Al bridging coordination induces noticeable bending of the ligand (the PCAl bond angle shrinks by 13°). This new type of transition metal→Lewis acid interaction has been analyzed by DFT calculations.     

Syntheses and structures of dinuclear gold(I) dithiophosphonate complexes and the reaction of the dithiophosphonate complexes with phosphines: diverse coordination types

The dinuclear gold(I) dithiophosphonate complex, [Au(2)(dtp)(2)] (1), where dtp = [S(2)P(R)(OR')](-) with R = p-C(6)H(4)OCH(3); R'= c-C(5)H(9), has been synthesized and its reaction studied with the phosphine ligands PPh(3) and Ph(2)P(CH(2))(n)PPh(2) (n = 1-4). Compound 1 contains two gold atoms homobridged by the anionic dithiophosphonate ligand, forming an eight-membered ring complex in a chair form. After the reaction of 1 with diphosphine ligands, the dinuclear open-ring complexes Au(2)(dppm)(dtp)(2) (2), Au(2)(dppe)(dtp)(2) (3), Au(2)(dppp)(dtp)(2) (4), Au(2)(dppb)(dtp)(2) (5) were formed (dppm = diphenylphosphinomethane; dppe = diphenylphosphinoethane; dppp = diphenylphosphinopropane; dppb = diphenylphosphinobutane). The reaction with dppm is stoichiometry-dependent. Thus, when 1 reacts with 2 equiv of dppm, the ionic complex [Au(2)(dppm)(2)(dtp)]dtp forms. This dtp counterion was exchanged with tetrafluoroborate to yield [Au(2)(dppm)(2)(dtp)]BF(4), the crystallization of which afforded two interconvertible isomers, 6-yellow and 7-white. Reaction of 1 with PPh(3) affords the tetracoordinate mononuclear complex [Au(dtp)(PPh(3))(2)] (8). The molecular structures of 1-8 were confirmed by X-ray crystallography and show multiple coordination modes and geometries. The crystal structures of 1 and its reaction products with dppm (2, 6, 7) show short intramolecular Au.Au aurophilic bonding interactions of 2.95-3.10 A while no intermolecular interactions were discernible. However, reaction products of 1 with longer-chain Ph(2)P(CH(2))(n)PPh(2) ligands, n = 2-4, exhibit structures that lack both intra- and intermolecular Au.Au interactions.     

Aurophilicity in gold(I) thiosemicarbazone clusters

The reaction of the phosphine thiosemicarbazone ligands HLPH and HLPMe with Au(I) ions yields the gold complexes [Au(3)(HLPH)(2)Cl(2)]Cl·2MeOH (1·2MeOH) and [Au(2)(HLPMe)Cl(2)] (2). The structures determined by X Ray diffraction, [Au(3)(HLPH)(2)Cl(2)]Cl·4MeOH (1·4MeOH) and [Au(2)(HLPMe)Cl(2)](2) (2), are the first examples of gold(I) thiosemicarbazone clusters showing aurophilicity. The structure of the trinuclear cation 1 contains the Au(1) atom located in an inversion centre, being connected to another gold(I) atom, Au(2), through a phosphino thiosemicarbazone molecule which acts as a S,P-bridging ligand. Additionally, every gold(I) atom in the trinuclear cation 1 assembles into trinuclear linear cluster units by means of close gold-gold interactions, being connected through the crystal cell in a 2D zigzag mode. The crystal structure of [Au(2)(HLPMe)Cl(2)](2) (2) contains one discrete molecule [(AuCl)(2)(HLPMe)] in the asymmetric unit, which is further assembled into tetranuclear [(AuCl)(2)(HLPMe)](2) units by means of close gold-gold interactions. Both clusters are highly luminescent in solution.     

Synthesis and structures of cyclic gold complexes containing diphosphine ligands and luminescent properties of the high nuclearity species

A mixture of cyclic gold(I) complexes [Au(2)(μ-cis-dppen)(2)]X(2) (X = OTf 1, PF(6)3) and [Au(cis-dppen)(2)]X (X = OTf 2, PF(6)4) is obtained from the reaction of [Au(tht)(2)]X (tht = tetrahydrothiophene) with one equivalent of cis-dppen [dppen = 1,2-bis(diphenylphosphino)ethylene]. The analogous reaction with trans-dppen or dppa [dppa = bis(diphenylphosphino)acetylene] affords the cyclic trinuclear [Au(3)(μ-trans-dppen)(3)]X(3) (X = OTf 11, PF(6)12) and tetranuclear [Au(4)(μ-dppa)(4)]X(4) (X = OTf 13, PF(6)14, ClO(4)15) gold complexes, respectively. Recrystallization of 15 from CH(2)Cl(2)/MeOH yielded a crystal of the octanuclear gold cluster [Au(8)Cl(2)(μ-dppa)(4)](ClO(4))(2)16. Attempts to prepare dicationic binuclear gold(II) species from the reaction of a mixture of 3 and 4 with halogens gave a mixture of products, the components of which confirmed to be acyclic binuclear gold(I) [Au(2)X(2)(cis-dppen)] (X = I 5, Br 7) and cyclic mononuclear gold(III) [AuX(2)(cis-dppen)]PF(6) (X = I 6, Br 8) complexes. Complexes 11-14 reveal weak emission in butyronitrile glass at 77 K, but they are non-emissive at room temperature. Ab initio modelling was performed to determine the charge state of the gold atoms involved. Extensive structural comparisons were made to experimental data to benchmark these calculations and rationalize the conformations.     

Metallophilic bonding and agostic interactions in gold(I) and silver(I) complexes bearing a thiotetrazole unit

Gold(I) and silver(I) complexes of 1-methyl-5-thio-tetrazole (1) have been prepared and the coordination chemistry of this ligand toward metal-phosphine frameworks has been explored. As indicated by IR and Raman data, ligand 1 is deprotonated and the resulted anion acts as a bidentate (S,N)-tetrazole-5-thiolato unit in the new gold(I) complexes, [Au(SCN(4)Me)(PPh(3))] (2), [{Au(SCN(4)Me)}(2)(μ-dppm)] (3), and [{Au(SCN(4)Me)}(2)(μ-dppe)] (4), while it is coordinated only through the sulfur atom as its neutral tetrazole-5-thione form in the silver(I) derivative, [Ag(HSCN(4)Me)(PPh(3))](2)(OTf)(2) (5). Further characterization of the new compounds was performed using multinuclear ((1)H, (13)C, (31)P, (19)F) NMR spectroscopy, mass spectrometry, and DSC measurements. Single-crystal X-ray diffraction studies revealed basically linear P-M-S arrangements in complexes 3-5. The bidentate (S,N) coordination pattern results in a T-shaped (S,N)PAu core in 3 and 4, whereas, in 5, a similar coordination geometry is achieved in the dimer association based on S-bridging ligand 1. Herein, weak (C)H···Au and (C)H···Ag agostic interactions were observed. An intramolecular Au···Au contact occurs in 3, while in 4 intermolecular aurophilic bonds lead to formation of a chain polymer. An intermolecular Ag···Ag contact is also present in the dimer unit of 5. Low-temperature (31)P NMR data for 5 evidenced the presence of monomer and dimer units in solution. Theoretical calculations on model of the complexes 2 and 4 are consistent with the geometries found by X-ray diffraction studies.     

Mononuclear, dinuclear, and hexanuclear goldI complexes with (aza-15-crown-5)dithiocarbamate

The reactions of sodium (aza-15-crown-5)dithiocarbamate with [AuClL] precursors lead to mono-, di-, or hexanuclear derivatives depending on L. The homoleptic hexanuclear gold(I) cluster [Au6(S2CNC10H20O4)6] is formed by displacement of the chloride and isocyanide ligands in [AuCl(CN(2,6-Me2C6H3))]. X-ray diffraction studies show a novel geometry in gold cluster chemistry where the six gold atoms display a cyclohexane-like geometry in a chair conformation with Au-Au-Au angles of 117.028(9) degrees, two short gold-gold distances of 2.9289(5) A, and bidentate bridging dithiocarbamate ligands. The molecular structure shows a crown of gold atoms surrounded by crown ethers. This derivative luminesces at 569 nm at room temperature in the solid state. A dinuclear isomer [Au2(S2CNC10H20O4)2] had been reported previously and was obtained by reaction with [AuCl(SMe2)]. The mechanism to obtain the hexanuclear derivative involves a mononuclear intermediate [Au(S2CNC10H20O4)(CNR)] for which the X-ray structure shows a short gold-gold distance of 3.565 A with the two molecules in an anti configuration. Phosphine gold(I) mononuclear derivatives [Au(S2CNC10H20O4)(PR3)] (R = Me, Ph, both characterized by X-ray diffraction) and dinuclear diphosphine derivatives [{Au(S2CNC10H20O4)}2(mu-P-P)] (P-P = dppm, bis(diphenylphosphinomethane); dppp, 1,3-bis(diphenylphosphinopropane); and dppf, 1,1'-bis(diphenylphosphinoferrocene)) are also reported. In the mononuclear complexes, the molecular structure confirms that the dithiocarbamato ligand is mainly acting as monodentate, with a second longer Au-S distance of 3.197 (PMe3), 2.944(4) (PPh3), and 2.968 A (CNR). Three phosphine complexes are emissive at 562 (PMe3), 528 (PPh3), and 605 nm (dppm), at 77 K. X-ray diffraction studies of the dppm derivative show gold-gold intramolecular contacts of 3.0972(9) A (3.2265(10) A for a second independent molecule) and basically monodentate coordination of the dithiocarbamato ligands. All the complexes extract sodium and potassium salts from aqueous solutions. The diphosphine derivatives are noticeably better extractors than the monophosphino derivatives, mainly for potassium salts.     

Supramolecular aggregation of mononuclear triorganophosphinegold(I) 2-mercaptobenzamides: solution structures, thermal decomposition, and photoluminescence

The crystal structures of R3PAu[SC6H4C(=O)NH2-2], R = Et (1), Ph (2), and Cy (3) show linear coordination geometries for gold defined by sulfur and phosphorus atoms. Supramolecular aggregation via {...H-N-C=O}2 synthons lead to dimeric aggregates in each case. In (1) and (2), the aggregates are spherical, but steric effects exerted by cyclohexyl rings in (3) dictate a rodlike form; no Au...Au interactions were noted in the crystal structures. Solvent dependence in their NMR spectra is correlated with intra- and intermolecular hydrogen bonding. The compounds uniformly decompose under controlled conditions to give gold. The complexes excited by UV light produce strong blue-green luminescence. The configuration interaction singles (CIS) post-Hartree-Fock (HF) calculations for the compounds indicate that it is the charge transfer from the sulfur and pi-orbitals of SC6H4C(=O)NH2-2 to gold that produce the emission from gold. The assignment of the observed luminescence is presented in terms of the relaxed excited states of gold, in which the vibronic interactions for three p-orbitals of gold are taken into account.