Intramolecular Aurophilic Interaction Research Articles

Structural and vibrational spectroscopic analysis of two Au(I) − NHC carbene complexes potential anticancer agents with intramolecular aurophilic interactions: A DFT study

Structural, electronic, and vibrational spectroscopic analysis using DFT/B3LYPD with LanL2DZ and SDD basis of two novel cationic gold(I) complexes with potential anticancer application exhibiting intramolecular aurophilic Au···H–N interactions, ranging from 2.74 to 2.84 Å. Both basis sets yielded equilibrium geometries and computed IR spectra in excellent agreement with X-ray structures and experimental IR spectra data. Despite structural differences in the thione co-ligand, both cationic complexes have remarkably similar dipole moments ranging from 6.4 to 6.6 D and HOMO-LUMO energy gaps, ranging from 5.0 to 5.3 eV, indicating that both possess almost identical solubility and similar chemical stability. Solvation free energies ranging from −35.9 to −39.0 kcal/mol were calculated using the implicit solvation SMD model, suggesting solvent effects play a significant role.

Diverse structural reactivity patterns of a POCOP ligand with coinage metals.

We have utilised the 4,6-di-tert-butyl resorcinol bis(diphenylphosphinite) (POCOP) ligand for exploring its coordination ability towards group 11 metal centres. The treatment of the bidentate ligand 1 with various coinage metal precursors afforded a wide range of structurally diverse complexes 2-12, depending upon the metal precursors used. This furnishes several multinuclear Cu(I) complexes with dimeric (2) and tetrameric cores (3, 4, and 5). The tetrameric stairstep complex 4 shows thermochromic behaviour, whereas the dimeric complex 2 and tetrameric complex 3 show luminescence properties at cryogenic temperatures. Interestingly, the halide substitution reaction of the dimeric complex 2 with KPPh2 produces a unique mixed phosphine-based tetrameric Cu(I) complex, 5. Treatment of the POCOP ligand with [CuBF4(CH3CN)4] in the presence of 2,2'-bipyridine afforded heteroleptic complex 6, consisting of tri- and tetra-coordinated cationic Cu(I) centres. Furthermore, we could also isolate cubane (8) and stairstep (9) complexes of Ag(I). The cationic Au(I) complex (12) was obtained from the dinuclear Au(I) complex of POCOP, 11. Complex 12 revealed the presence of a strong intramolecular aurophilic interaction with an Au⋯Au bond distance of 3.1143(9) Å. Subsequently, the photophysical properties of these complexes have been studied. All the complexes were characterised by single-crystal X-ray diffraction studies, routine NMR techniques, and mass spectroscopy.

Aurophilic Interactions of Dimeric Bisphosphine Gold(I) Complexes Pre-Organized by the Structure of the 1,5-Diaza-3,7-Diphosphacyclooctanes

The dimeric gold(I) chloride and gold(I) iodide complexes ([L2Au]Cl2 and L2AuI2) on the scaffold of the cyclic bisphosphine, namely 1,5-diaza-3,7-diphosphacyclooctane containing α-phenylbenzyl (benzhydryl) substituents at the nitrogen atoms, were synthesized. The obtained complexes were isolated as white crystalline powders. The single crystal XRD of the obtained complexes revealed the strong aurophilic interactions between two gold(I) atoms with the Au…Au distance values of 2.9977(6) and 3.1680(5) Å. The comparison of the gold complexes, based on the N,N-diaryl- and N,N-dibenzhydryl substituted 1,5-diaza-3,7-diphosphacyclooctanes, allowed to reveal the strong impact of the initial heterocycle conformation on the realization of the aurophilic interactions, where the geometry of N,N-dibenzhydryl substituted 1,5-diaza-3,7-diphosphacyclooctane, is pre-organized for the intramolecular aurophilic interactions of the complexes. The obtained complexes exhibit a bluish-green phosphorescence (λem 505 (-Cl) and 530(-I)) in the solid state at room temperature, originated by the metal-halide centered transitions, which was confirmed by the TDDFT calculations. It was found that the aurophilic interactions are realized in the ground and in the triplet excited states of the complexes. The slighter change of the geometry of the N,N-dibenzhydryl substituted gold(I) iodide complexes, under the transition from the ground state to the excited state, in comparison with their N,N-diaryl substituted analogues, results in the reduced values of the Stokes shift of luminescence (ca. 150 nm vs. 175 nm).

A neutral vicinal silylene/phosphane supported six-membered C2PSiAu2 ring and a silver(I) complex.

This work presents the different coordination nature of the bidentate ligand towards gold and silver complexes. The reaction of 1 with AuClSMe2 in dichloromethane resulted in two gold atoms containing six-membered ring PhC(NtBu)2Si-Au⋯Au-PPh2C6H4 (2). Compound 2 exhibits intramolecular aurophilic interaction (2.9987(7) Å), which is further supported by quantum chemical calculations. Moreover, the reduction of aluminium adduct 3 with AgSbF6 affords insertion of silver cation [{PhC(NtBu)2SiF2}-C6H4(PPh2)-Ag-(PPh2)C6H4{PhC(NtBu)2SiF2}]AlCl4- (4) between two phosphane. In compound 4 only two P(III) of two molecules of 1 coordinates to Ag(I), while two Si(II) remains uncoordinated and gives oxidative addition of Fluorine.

Aurophilic Interactions in Multi-Radical Species: Electronic-Spin and Redox Properties of Bis- and Tris-[(Nitronyl Nitroxide)-Gold(I)] Complexes with Phosphine-Ligand Scaffolds.

Multinuclear AuI complexes with two or three nitronyl nitroxide-2-ide radical anion and phosphine-ligand scaffolds, (NN-Au)2 -1 o, (NN-Au)2 -1 m, and (NN-Au)2 -1 p, have been synthesized to investigate the influence of AuI -AuI (aurophilic) interactions on the properties of multispin molecular systems. The desired complexes were successfully prepared in moderate yields in a one-pot synthesis from the corresponding phosphine ligand, AuI source, parent NN, and sodium hydroxide. Among the prepared complexes, (NN-Au)2 -1 o, in which an aurophilic interaction was clearly observed by crystal structure analysis, showed characteristic spin-spin interactions, electrochemical properties, and solvatochromic behavior. The results from theoretical calculations also suggested that the differences in properties between complex (NN-Au)2 -1 o and the other complexes are due to intramolecular aurophilic interactions.

Recent Progress on Supramolecular Luminescent Assemblies Based on Aurophilic Interactions in Solution

The development of supramolecular systems showing aurophilic interactions in solution is gaining much attention in the last years. This is due to the intriguing photophysical properties of gold(I) complexes, which usually confer to these supramolecular assemblies interesting luminescent properties, as well as the possibility of morphological modulation, through fine tuning of inter- and intramolecular aurophilic interactions, in synergy with the formation of other supramolecular contacts. In this work, an overview of the advances made in this area since 2015 is presented. A large variety of systems showing different spectroscopical and structural topologies has been reported. Moreover, these supramolecular assemblies have proven to be useful in a wide range of applications.

Reconstituting C-Centered Hexagold(I) Clusters with N-Heterocyclic Carbene Ligands

Abstract Ubiquitous intramolecular aurophilic interactions in gold clusters have usually been assigned as the main determinants of their molecular geometry and various properties. By utilizing N-heterocyclic carbene (NHC) ligands instead of phosphine ligands which have been exclusively used, we have developed ligand-specific photophysical properties of C-centered hexagold(I) (C@Au6) clusters. This account describes the recent development of carbene-protected C@Au6 clusters. First of all, a strong intramolecular C–H⋯Au interaction was found as a key structural feature of these clusters. These are also present in the newly emerged NHC-gold nanoclusters, but are negligible in the phosphine counterparts. Interestingly, the use of NHC ligands also produces clusters with a nearly identical metal kernel, but their luminescence changes significantly. In addition, a simple extension of the π-conjugated system of NHCs from imidazolylidene to benzimidazolylidene is expected to produce significant changes in both absorption coefficient and emission wavelength. These results show the promising potential of carbene ligands in character modulation of metal clusters, and may help in the rational design of carbene ligands for constructing functional metal clusters.

Rare Au···H Interactions in Gold(I) Complexes of Bulky Phosphines Derived from 2,6-Dibenzhydryl-4-methylphenyl Core.

Gold(I) complexes of sterically demanding phosphines derived from 2,6-dibenzhydryl-4-methylphenyl core viz: 2,6-dibenzhydryl-N,N-bis((diphenylphosphane)-methyl)-4-methylaniline (1), (2,6-dibenzhydryl-4-methylphenyl)-diphenylphosphane (2), N-(2,6-dibenzhydryl-4-methylphenyl)-1,1-diphenylphosphanamine (3), and (2,6-dibenzhydryl-4-methylphenoxy)-diphenylphosphane (4) are described. The reaction of 1 with 2 equiv of [AuCl(SMe2)] in dichloromethane yielded [{AuCl}2{Ar*N(CH2PPh2)2}] (5), which on further treatment with 2 equiv of AgSbF6 and 1 equiv of 1 produced 12-membered dimeric complex [Au2{μ-(Ar*N(CH2PPh2)2)2}][(SbF6)2] (6). A similar reaction of 5 with AgSbF6 in CH3CN afforded [{Au(NCCH3)}2{Ar*N(CH2PPh2)2}][(SbF6)2] (7). Equimolar reactions of bulky phosphines 2, 3, and 4 with [AuCl(SMe2)] resulted in [AuCl(PPh2Ar*)] (8), [AuCl(PPh2NHAr*)] (9), and [AuCl(PPh2OAr*)] (10). Complexes 9 and 10 on treatment with AgSbF6 in CH3CN produced the cationic complexes [Au(NCCH3)(PPh2NHAr*)][(SbF6)] (11) and [Au(NCCH3)(PPh2OAr*)][(SbF6)] (12), respectively. The molecular structure of complex 6 revealed the presence of a strong intramolecular aurophilic interaction with a Au···Au distance of 2.9720(4) Å. Careful analysis of molecular structure of 5 revealed the presence of rare Au···H-C (sp3) interactions between the gold(I) atom and one of the methylene protons of -NCH2PPh2 groups. The solution 1H NMR signals of the methylene protons of 5 showed a considerable downfield shift (∼1 ppm) compared to that of the free ligand indicating their interactions (Au···H) with the Au atom. Complexes 8 and 10 also showed Au···H interactions in their molecular structures. The existence of the Au···H interaction was studied by variable temperature 1H NMR data in the case of complex 5 and further evinced by the QTAIM analysis in complexes 5, 8, and 10.

Synthesis, structural characterization, and photophysical studies of hexanuclear gold(I) chalcogenido complexes

AbstractA hexanuclear gold(I) selenido cluster and its sulfido counterpart, [Au6{μ‐Ph2PN(CH2‐o‐Py)PPh2}3(μ3‐E)2](ClO4)2 (E = S, Se), with bridging bis(diphenylphosphino)amine ligands were synthesized and characterized. The X‐ray crystal structure of the selenido cluster was determined, with the gold core possessing a distorted heterocubane structure. Intramolecular aurophilic interactions with short Au(I)⋯Au(I) contacts of around 3.09–3.13 Å were observed. The complexes were found to emit strongly in the solid state with orange to red emission colors. Their electronic absorption and emission properties were also investigated.

Gold(I) Complexes of Ferrocenyl Polyphosphines: Aurophilic Gold Chloride Formation and Phosphine-Concerted Shuttling of a Dinuclear [ClAu···AuCl] Fragment.

A smart steric control of the metallocene backbone in bis- and poly(phosphino)ferrocene ligands favors intramolecular aurophilic interactions between [AuCl] fragments in polynuclear gold(I) complexes. We synthesized and characterized by multinuclear NMR and X-ray diffraction analysis mono-, di-, and polynuclear gold complexes of constrained ferrocenyl diphosphines, which bear either bulky tert-butyl groups or more flexible siloxane substituents at the cyclopentadienyl rings. The complexes meso-1,1'-bis(diphenylphosphino)-3,3'-di-tert-butylferrocene (4-m), rac-1,1'-bis[bis(5-methyl-2-furyl)phosphino]-3,3'-di-tert-butylferrocene (5-r), and rac-1,1'-bis(diphenylphosphino)-3,3'-bis[(tri-iso-propylsilyl)oxy]ferrocene (6-r) were used to form dinuclear gold complexes. Coordination of tert-butylated ferrocenyl phosphines generated aurophilic interactions in the corresponding dinuclear gold complexes, contrary to gold(I) complexes reported with 1,1'-bis(diphenylphosphino)ferrocene. The structurally related tetraphosphine 1,1',2,2'-tetrakis(diphenylphosphino)-4,4'-di-tert-butylferrocene (11) also gave access to mononuclear, dinuclear, and the original trinuclear gold chloride aurophilic complexes in which 14e- to 16e- gold centers coexist. In such complexes, nonbonded ("through-space") 31P-31P' nuclear spin couplings were evidenced by high-resolution NMR. In these interactions nuclear spin information is transferred between the lone-pair electron of an uncoordinated phosphorus P and a phosphorus P' that is involved in a σ covalent bond Au-P'. The dinuclear aurophilic complex displayed a concerted shuttling of its [ClAu···AuCl] fragment between the four phosphorus donors of the tetraphosphine ligand. Thus, an aurophilic Au···Au bond, which is assumed to be a weak energy interaction, can be conserved within a dynamic shuttling process at high temperature involving an intramolecular coordination-decoordination process of digold(I) at phosphorus atoms.

Steric effects and aurophilic interactions in crystals of Au2(μ-1,2-bis(diphenylphosphino)ethane)X2 and Au2(μ-1,2-bis(dicyclohexylphosphino)ethane)X2 (X = Cl, Br, I)

Crystals in the isostructural series Au2(μ-dppe)X2 (dppe is 1,2-bis(diphenylphosphino)ethane, X=Cl, Br, I) form centrosymmetric, dimeric structures with two short Au⋯Au contacts between the component molecules. We found no evidence for a second polymorph for any member of the Au2(μ-dppe)X2 series, although two polymorphs were observed previously for the related Au2(Ph2As(CH2)2AsPh2)X2 series. Crystals of Au2(μ-dcpe)X2 (where dcpe is 1,2-bis(dicyclohexylphosphino)ethane) show structures that differ appreciably from those of Au2(μ-dppe)X2. The bulky cyclohexyl substituents appear to be playing a major role in eliminating the formation of polymeric or dimeric structures. Au2(μ-dcpe)Cl2 has a monomeric structure without aurophilic interactions. In contrast, Au2(μ-dcpe)Br2 and Au2(μ-dcpe)I2 have similar structures with intramolecular aurophilic interactions. Au2(μ-dcpe)I2 displays a form of aggregation-induced emission. It displays a red-pink luminescence in crystalline form but is non-emissive in solution.

Aurophilicity in Action: Fine-Tuning the Gold(I)-Gold(I) Distance in the Excited State To Modulate the Emission in a Series of Dinuclear Homoleptic Gold(I)-NHC Complexes.

The solution-state emission profiles of a series of dinuclear Au(I) complexes 4-6 of the general formula Au2(NHC-(CH2)n-NHC)2Br2, where NHC = N-benzylbenzimidazol-2-ylidene and n = 1-3, were found to be markedly different from each other and dependent on the presence of excess bromide. The addition of excess bromide to the solutions of 4 and 6 leads to red shifts of ca. 60 nm, and in the case of 5, which is nonemissive when neat, green luminescence emerges. A detailed computational study undertaken to rationalize the observed behavior revealed the determining role aurophilicity plays in the photophysics of these compounds, and the formation of exciplexes between the complex cations and solvent molecules or counterions was demonstrated to significantly decrease the Au-Au distance in the triplet excited state. A direct dependence of the emission wavelength on the strength of the intracationic aurophilic contact allows for a controlled manipulation of the emission energy by varying the linker length of a diNHC ligand and by judicial choice of counterions or solvent. Such unique stimuli-responsive solution-state behavior is of interest to prospective applications in medical diagnostics, bioimaging, and sensing. In the solid, the investigated complexes are intensely phosphorescent and, notably, 5 and 6 exhibit reversible luminescent mechanochromism arising from amorphization accompanied by the loss of co-crystallized methanol molecules. The mechano-responsive properties are also likely to be related to changes in bromide coordination and the ensuing alterations of intramolecular aurophilic interactions. Somewhat surprisingly, the photophysics of NHC ligand precursors 2 and 3 is related to the formation of ground-state associates with bromide counterions through hydrogen bonding, whereas 1 does not appear to bind its counterions.

Synthesis, Characterization, and Luminescence Studies of Gold(I) Complexes with PNP- and PNB-Based Ligand Systems.

The synthesis, X-ray crystal structures, and spectroscopic studies of a series of PPh2N(2,6-iPr2C6H3)PPh2 (PNP) and PPh2N(2,6-iPr2C6H3)BCy2 (PNB; Cy = cyclohexyl) based gold(I) complexes are presented herein. The gold(I) chloride complexes 2 and 6 were treated with AgSbF6 to yield the corresponding dimeric dinuclear Au(I) cation (3) and dimeric mononuclear Au(I) cation (7) with PNP and PNB systems, respectively. The molecular structure of 3 revealed the presence of a strong intramolecular aurophilic interaction with a Au···Au bond distance of 2.7944(19) Å, one of the shortest aurophilic interactions known in the literature. However, complex 7 displays no aurophilic interaction. The reaction of 3 with diphenyl disulfide was performed, which led to a multinuclear tetragold(I) complex (4), keeping the aurophilic interaction intact. The effect of an aurophilic interaction is also illustrated through the study of the luminescent properties of these gold(I) complexes. Complexes 3 and 4 exhibit luminescence in solution as well as in the solid state, whereas the other gold(I) complexes remain nonluminescent.

Polymeric gold(I) diisobutyl dithiophosphate, [Au2{S2P(O-iso-C4H9)2}2]n: Synthesis, supramolecular self-organization (a role of aurophilic interaction), 13C and 31P MAS NMR spectroscopy, and thermal behavior

A new polymeric gold(I) diisobutyl dithiophosphate (Dtph), [Au2{S2P(O-iso-C4H9)2}2]n (I), was preparatively obtained and characterized by 13C and 31P MAS NMR spectroscopy and X-ray diffraction (CIF file CCDC no. 977818). Diagrams of the χ2 statistic were constructed from the complete 31P MAS NMR spectra and used to calculate the 31P chemical shift anisotropy (δaniso = δzz − δiso) and the asymmetry parameter η = (δyy − δxx)/(δzz − δiso). The main structural unit of complex I is the noncentrosymmetric dinuclear molecule [Au2{S2P(O-iso-C4H9)2}2], in which the gold atoms are linked by two bridging ligands Dtph. The central cyclic structural fragment of the dimer [Au2S4P2] is additionally stabilized by the intramolecular aurophilic interaction Au⋯Au. Further supramolecular self-organization of the complex involves intermolecular aurophilic bonds Au⋯Au that serve to unite adjacent dinuclear molecules [Au2{S2P(O-iso-C4H9)2}2] with different spatial orientations into the polymer chains ([Au2{S2P(O-iso-C4H9)2}2])n. The thermal behavior of complex I was examined by synchronous thermal analysis under argon. The character of the thermolysis of the complex to reduced metallic gold as a final product was determined.

Coordination Behaviour of a Hexadentate 1,1′‐Ferrocenylene‐Bridged Bisphosphole towards Coinage Metal Centres

AbstractWe describe the synthesis of a ferrocenylene‐bridged bis[2,5‐bis(2‐pyridyl)]phosphole ligand that shows additional rotational degrees of freedom relative to its previously described p‐phenylene‐bridged congener. The coordination behaviour of this ferrocenylene‐based bis‐N,P,N pincer towards coinage metal centres MI with M = Cu and Au was explored, revealing different coordination modes with and without involvement of N donation. Upon coordination of AuI metal centres, different isomers of a bimetallic AuI complex were isolated in the crystalline solid state that showed (or did not) intramolecular aurophilic interaction. Aurophilic as well as Au–N interactions have been investigated by means of ab initio calculations.

Synthesis, Structures, and Luminescence Properties of Interconvertible AuI2ZnIIand AuI3ZnIIComplexes with Mixed Bis(diphenylphosphino)methane andd-Penicillaminate

The reaction of the digold(I) complex [Au2(dppm)(D-pen)2](2-) ([1](2-); dppm = bis(diphenylphosphino)methane and D-pen = D-penicillaminate) with Zn(2+) in a 1:1 ratio gave the heterometallic Au(I)2Zn(II) trinuclear complex [Au2Zn(dppm)(D-pen)2] ([3]), in which the Zn(2+) ion is coordinated by [1](2-) in an N2O2S2 octahedral geometry with the trans(O) configuration, forming an 8-membered Au2ZnS2P2C metalloring. A similar reaction using the newly prepared and crystallographically characterized trigold(I) complex [Au3(dppm)2(D-pen)2](-) ([2](-)) produced the Au(I)3Zn(II) tetranuclear complex [Au3Zn(dppm)2(D-pen)2](+) ([4](+)), in which the Zn(2+) ion is coordinated by [2](-) in a similar octahedral geometry to form a Au3ZnS2P4C2 12-membered metalloring. Complex [3] was converted to [4](+) by treatment with [Au2(dppm)2](2+) in a 2:1 ratio, whereas [4](+) reverted to [3] upon treatment with a mixture of [Au(d-pen)2](2-) and Zn(2+) in a 1:1 ratio, indicative of the facile insertion/removal of the [Au(dppm)](+) moiety with retention of the geometry of the trans(O)-[Zn(D-pen-N,O,S)2](2-) unit. An analogous interconversion that requires the insertion/removal of the [Au(dppm)](+) moiety was also recognized between [1](2-) and [2](-). NMR spectroscopy revealed that [4](+) is in equilibrium with [3] and [Au2(dppm)2](2+) in solution, the ratio of which is largely dependent on the solvent polarity. The luminescence properties of these complexes were also investigated, revealing the importance of the intramolecular aurophilic interaction, as well as the Zn(II) coordination, for enhancement of the emission quantum efficiencies.

Aurophilicity versus Mercurophilicity: Impact of d10–d10 Metallophilic Interactions on the Structure of Metal‐Rich Supramolecular Assemblies

Treatment of U-shaped, binuclear Cu(I) complexes 1,1' (1, counterion: BF(4)(-); 1', counterion: PF(6)(-)) with metal cyanide linear linkers K[Au(CN)(2)] (3) and Hg(CN)(2) (4) lead to formation of new supramolecular assemblies 5,5' and 6,6', respectively, in good yield. These derivatives have been characterized by NMR spectroscopy, IR, and X-ray diffraction studies. Derivative 5,5' are supramolecular metallacycles in which intramolecular aurophilic interactions between the Au(I) metal centers of the linkers are observed. Derivative 5 crystallizes as a single solid phase, whereas derivative 5' is characterized in the solid state as four different pseudo-polymorphs (5'a-d). Notably in the case of phase 5'd, a dimer of supramolecular metallacycles bounded by intermolecular aurophilic interactions is formed. Conversely, derivatives 6,6' present large structural diversity depending on the nature of the counterion. Derivative 6 is a supramolecular rectangle in which the Hg(II)-Hg(II) metal distance suggests mercurophilic interaction, whereas 6' crystallizes as two different pseudo-polymorphs 6'a,b, that is, a one-dimensional coordination polymer and one oligomer with no short Hg(II)-Hg(II) metal contacts, respectively. In derivatives 6,6', short contacts between the Hg(II) metal centers and fluorine atoms of the counterions are also observed, which may explain the counterion structural dependence of these supramolecular assemblies based on Hg(II) metal cyanide linker. Comparison of the different solid-state structures characterized highlights the importance of weak secondary interactions between the linkers for the formation supramolecular metallacycles from molecular clips 1,1' and suggests the range of energies required for these interactions to form metallacycles and to induce self-aggregation.

Luminescence on–off switching via reversible interconversion between inter- and intramolecular aurophilic interactions

Reversible interconversion between inter- and intramolecular AuAu interactions induces luminescence on/off switching in solid state. For the gold(I) photoluminescence system, intermolecular aurophilic interaction is a more significant factor than intramolecular aurophilic interaction.

Bis[μ-1,2-bis(diphenylphosphino)ethane-κ2P:P′]digold(I)(Au—Au) bis(trifluoromethanesulfonate) acetonitrile disolvate

The title compound, [Au2(C26H24P2)2](CF3SO3)2·2CH3CN, comprises a cyclic cation with a short intra­molecular aurophilic inter­action of 2.9220 (3) Å. The trifluoro­methane­sulfonate anions and acetonitrile solvent mol­ecules are located in channels formed by the complex cations that run along the crystallographic c axis. Each counter-anion is also engaged in a C—H⋯O contact with one of the methyl­ene H atoms of a 1,2-bis­(diphenyl­phosphino)ethane (dppe) ligand; another C—H⋯O contact involving an aromatic H atom is also observed.

Syntheses, Structures, and Photophysical Properties of Mono- and Dinuclear Sulfur-Rich Gold(I) Complexes

The dinuclear gold complexes [{Au(PPh 3)} 2(mu- dmid)] ( 1) ( dmid = 1,3-dithiole-2-one-4,5-dithiolate) and [{Au(PPh 3)} 2(mu- dddt)] ( 2) ( dddt = 5,6-dihydro-1,4-dithiine-2,3-dithiolate) were synthesized and characterized by X-ray crystallography. Both complexes exhibit intramolecular aurophilic interactions with Au...Au distances of 3.1984(10) A for 1 and 3.1295(11) A for 2. A self-assembly reaction between 4,5-bis(2-hydroxyethylthio)-1,3-dithiole-2-thione ( (HOCH 2 CH 2 ) 2 dmit) and [AuCl(tht)] affords the complex [AuCl{ (HOCH 2 CH 2 ) 2 dmit}] 2 ( 4), which possesses an antiparallel dimeric arrangement resulting from a short aurophilic contact of 3.078(6) A. This motif is extended into two dimensions due to intra- and intermolecular hydrogen bonds via the hydroxyethyl groups, giving rise to a supramolecular network. Three compounds were investigated for their rich photophysical properties at 298 and 77 K in 2-MeTHF and in the solid state; [Au 2(mu- dmid)(PPh 3) 2] ( 1), [Au 2(mu- dddt)(PPh 3) 2] ( 2), and [AuCl{( HOCH 2 CH 2 ) 2 dmit}] ( 4). 1 exhibits relatively long-lived LMCT (ligand-to-metal charge transfer) emissions at 298 K in solution (370 nm; tau e approximately 17 ns, where M is a single gold not interacting with the other gold atom; i.e., the fluxional C-SAuPPh 3 units are away from each other) and in the solid state (410 nm; tau e approximately 70 mus). At 77 K, a new emission band is observed at 685 nm (tau e = 132 mus) and assigned to a LMCT emission where M is representative for two gold atoms interacting together consistent with the presence of Au...Au contacts as found in the crystal structure. In solution at 77 K, the LMCT emission is also red-shifted to 550 nm (tau e approximately 139 mus). It is believed to be associated to a given rotamer. 2 also exhibits LMCT emissions at 380 nm at 298 K in solution and at 470 nm in the solid state. 4 exhibits X/MLCT emission (halide/metal to ligand charge transfer) where M is a dimer in the solid state with obvious Au...Au interactions, resulting in red-shifted emission band, and is a monomer in solution in the 10 (-5) M concentration (i.e., no Au...Au interactions) resulting in blue-shifted luminescence. Both fluorescence and phosphorescence are observed for 4.