Aurophilic Contacts Research Articles

Aurophilicity vs. thiophilicity: directing the crystalline supramolecular arrangement in luminescent gold compounds

The fluorination of thiolate ligands is applied as a tool that allows control of the prevalence of thiophilic (Au–S) interactions over the expected aurophilic contacts in luminescent gold compounds.

Gold(I) Alkynyls Supported by Mono- and Bidentate NHC Ligands: Luminescence and Isolation of Unprecedented Ionic Complexes.

Reactions of NHC·HX (NHC = 1-benzyl-3-methylbenzimidazol-2-ylidene, X = Br-, PF6-) and (AuC≡CR)n (R = Ph, C3H6OH) in the presence of Cs2CO3 initially afford compounds of the general formula [(NHC)2Au]2[(RC2)2Au]X, which can be isolated by crystallization. With increased reaction time, only the expected mononuclear complexes of the type [NHCAuC≡CR] are produced. The crystal structure of [(NHC)2Au]2[(PhC2)2Au]PF6 reveals an unprecedented triple-decker array upheld by a remarkably short (2.9375(7) Å) unsupported Au···Au···Au contact. The mononuclear complex [NHCAuC≡CPh] was found to crystallize as three distinct polymorphs and a pseudopolymorph, which depending on the intermolecular Au···Au distances emit blue, green, or yellow light. Two synthetic approaches were employed for the preparation of a series of dinuclear NHC-ligated Au(I) alkynyl complexes of the general formula [NHC-(CH2)n-NHC(AuC≡CR)2], where NHC = N-benzylbenzimidazol-2-ylidene, R = Ph, C3H6OH, C6H10OH, and n = 1-3. In solution, the complexes with aliphatic substituents on the alkynyl fragment are nonemissive, whereas their phenyl-bearing congeners demonstrate characteristic metal-perturbed 3[IL(C≡CPh)] emission. In the solid state, a clear correlation between intermolecular aurophilic interactions and luminescence was established, including their role in the luminescent thermochromism of the phenylalkynyl complexes. The relationship between the Au···Au distance and emission energy was found to be inverse: i.e., the shorter the aurophilic contact, the higher the emission energy. We tentatively attribute this behavior to a smaller extent of excited-state distortion for a structure with a shorter Au···Au separation.

Modulation of supramolecular gold(I) aggregates by anion’s interaction

The gold complexes [Au(4-pyridylethynyl)(PTA)] and [Au(4-pyridylethynyl)(DAPTA)] (PTA = 1,3,5-triaza-7-phosphaadamantane; DAPTA = 3,7-diacetyl-1,3,7-triaza-5-phosphabicyclo[3.3.1]nonane) were used as host in molecular recognition processes of sodium hexametaphosphate (HMP) and a single-stranded 24-long oligonucleotide. Experiments were performed by absorption titrations and looking at the resulting host:guest adducts by polarised optical, fluorescence and scanning electron microscopy. The resulting information indicates that different types of interactions are present with the two different guest molecules. In the case of HMP, the compounds aggregate giving rise to larger structures, favouring exciton splitting coupling and the formation of head to tail interactions. In the case of oligonucleotide studies, the formation of smaller supramolecular structures is observed, with less contribution of aurophilic contacts and organised in a parallel way (head to head interactions organised by the presence of the oligonucleotide).

Homoleptic Gold Acetonitrile Complexes with Medium to Very Weakly Coordinating Counterions: Effect on Aurophilicity?

A series of gold acetonitrile complexes [Au(NCMe)2 ]+ [WCA]- with weakly coordinating counterions (WCAs) was synthesized by the reaction of elemental gold and nitrosyl salts [NO]+ [WCA]- in acetonitrile ([WCA]- =[GaCl4 ]- , [B(CF3 )4 ]- , [Al(ORF )4 ]- ; RF =C(CF3 )3 ). In the crystal structures, the [Au(NCMe)2 ]+ units appeared as monomers, dimers, or chains. A clear correlation between the aurophilicity and the coordinating ability of counterions was observed, with more strongly coordinating WCAs leading to stronger aurophilic contacts (distances, C-N stretching frequencies of [Au(NCMe)2 ]+ units). An attempt to prepare [Au(L)2 ]+ units, even with less weakly basic solvents like CH2 Cl2 , led to decomposition of the [Al(ORF )4 ]- anion and formation of [NO(CH2 Cl2 )2 ]+ [F(Al(ORF )3 )2 ]- . All nitrosyl reagents [NO]+ [WCA]- were generated according to an optimized procedure and were thoroughly characterized by Raman and NMR spectroscopy. Moreover, the to date unknown species [NO]+ [B(CF3 )3 CN]- was prepared. Its reaction with gold unexpectedly produced [Au(NCMe)2 ]+ [Au(NCB(CF3 )3 )2 ]- , in which the cyanoborate counterion acts as an anionic ligand itself. Interestingly, the auroborate anion [Au(NCB(CF3 )3 )2 ]- behaves as a weakly coordinating counterion, which becomes evident from the crystallographic data and the vibrational spectral characteristics of the [Au(NCMe)2 ]+ cation in this complex. Ligand exchange in the only room temperature stable salt of this series, [Au(NCMe)2 ]+ [Al(ORF )4 ]- , is facile and, for example, [Au(PPh3 )(NCMe)]+ [Al(ORF )4 ]- can be selectively generated. This reactivity opens the possibility to generate various [AuL1 L2 ]+ [Al(ORF )4 ]- salts through consecutive ligand-exchange reactions that offer access to a huge variety of AuI complexes for gold catalysis.

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.

N‐Heterocyclic Carbene–Phosphinidene Complexes of the Coinage Metals

Coinage metal complexes of the N-heterocyclic carbene-phosphinidene adduct IPr⋅PPh (IPr=1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene) were prepared by its reaction with CuCl, AgCl, and [(Me2 S)AuCl], which afforded the monometallic complexes [(IPr⋅PPh)MCl] (M=Cu, Ag, Au). The reaction with two equivalents of the metal halides gave bimetallic [(IPr⋅PPh)(MCl)2 ] (M=Cu, Au); the corresponding disilver complex could not be isolated. [(IPr⋅PPh)(CuOTf)2 ] was prepared by reaction with copper(I) trifluoromethanesulfonate. Treatment of [(IPr⋅PPh)(MCl)2 ] (M=Cu, Au) with Na(BAr(F) ) or AgSbF6 afforded the tetranuclear complexes [(IPr⋅PPh)2 M4 Cl2 ]X2 (X=BAr(F) or SbF6 ), which contain unusual eight-membered M4 Cl2 P2 rings with short cuprophilic or aurophilic contacts along the chlorine-bridged M⋅⋅⋅M axes. Complete chloride abstraction from [(IPr⋅PPh)(AuCl)2 ] was achieved with two equivalents of AgSbF6 in the presence of tetrahydrothiophene (THT) to form [(IPr⋅PPh){Au(THT)}2 ][SbF6 ]2 . The cationic tetra- and dinuclear complexes were used as catalysts for enyne cyclization and carbene transfer reactions.

Aminkomplexe des Golds, Teil 8: Zwei Pyridinderivate des Gold(I)-thiocyanats [1] / Amine Complexes of Gold, Part 8: Two Pyridine Derivatives of Gold(I) Thiocyanate

Abstract The reaction between (tht)AuCl (tht = tetrahydrothiophene) and KSCN leads to a mixture possibly consisting of gold(I) thiocyanate and [Au(tht)2]+ [Au(SCN)2]-. This can be treated with pyridine to give the ionic derivative [Au(py)2]+ [Au(SCN)2]- (1), for which the structures of two polymorphs were determined. Orthorhombic polymorph 1a (space group Pbcn, Z = 4) consists of infinite chains of alternating cations and anions with all gold atoms lying on a twofold axis, whereas triclinic polymorph 1b (space group P1̅, Z = 2) contains isolated tetranuclear units cation···anion···anion···cation with inversion symmetry. In both patterns the gold atoms are linked by short aurophilic contacts. Attempts to recrystallize 1b from dichloromethane-diethyl ether led to small quantities of tetrapyridinium bis(dithiocyanatogold(I)) sulfate (2), (pyH)4[Au(SCN)2]2(SO4), which was identified by crystal structure analysis. The cations are associated with the sulfate ions by classical hydrogen bonds; aurophilic interactions between the anions lead to dimers, which further associate to chains by Au···S contacts.

Synthesis, Characterization, and Luminescence Studies of Discrete Polynuclear Gold(I) Sulfido and Selenido Complexes with Intramolecular Aurophilic Contacts

The synthesis, characterization, and photophysical and photochemical properties of a family of high-nuclearity gold(I) chalcogenides, specifically, the gold(I) sulfido and selenido complexes containing different bridging diphosphine ligands with nuclearities of ten ([Au10{μ-Ph2PN(R)PPh2}4(μ3-E)4](2+)) and six ([Au6{μ-Ph2PN(R)PPh2}3(μ3-E)2](2+)), are reported. The X-ray crystal structures of the complex cations of Au10 and Au6 are found to be propeller-like structures and distorted cubane structures, respectively, with the presence of short intramolecular gold···gold distances. The complexes show intense green and/or orange phosphorescence upon photoexcitation in the solid state and in solution at ambient and low temperature. The emission properties are found to be strongly dependent on the nuclearities and the chalcogenido ligands, but are rather insensitive to the substituents on the bis(diphenylphosphino)amines. The emissions are tentatively assigned to originate from the excited states derived from the phosphine-centered intraligand (IL) transition or metal-centered (ds/dp) mixed with ligand-to-metal-metal charge transfer (LMMCT) (E→Au) transition. The photochemical properties of the complexes were also studied by transient absorption spectroscopy.

Primary amino-functionalized N-heterocyclic carbene ligands as support for Au(i)⋯Au(i) interactions: structural, electrochemical, spectroscopic and computational studies of the dinuclear [Au2(NH2(CH2)2imMe)2][NO3

The N-heterocyclic carbene (NHC) precursor, 1-(2-aminoethyl)-3-methylimidazolium nitrate, [NH(2)(CH(2))(2)imMe)]NO(3) ([3][NO(3)]) reacted with Ag(2)CO(3) in dimethyl sulfoxide readily yielding a Ag(I)-(NHC-NH(2)) complex presenting limited stability in solution. The in situ carbene transfer reaction of the latter with [Au(tht)Cl] afforded the first example of a dinuclear gold(I) complex [Au(2)(NH(2)(CH(2))(2)imMe)(2)][NO(3)](2) ([5][NO(3)](2)) bearing a primary amino-functionalized NHC ligand. The complex has been characterized by NMR, mass spectrometry, X-ray crystallography and cyclic voltammetry; the electrochemical behaviour and photophysical properties of [5][NO(3)](2) have been also investigated and the experimental data have been compared with density functional theory (DFT) and Time Dependent (TDDFT) calculations. Single-crystal structural studies showed that the Au(I)-carbene compound contains dinuclear (AuL)(2) cations in which pairs of gold(I) centres are linked by a pair of bridging ligands, with a Au···Au aurophilic contact of 3.2332(17) Å that is maintained in solution as documented by the DFT calculations. Complex [5][NO(3)](2) is photoluminescent in solution at room temperature and the high energy emission peak at 410 nm is remarkably shifted with respect to the absorption band centered at 260 nm.

Structural relationships between o-, m- and p-tolyl substituted R3EI2 (E = As, P) and [(R3E)AuX] (E = As, P; X = Cl, Br, I)

The compounds R3EI2 (R = o-tolyl, E = As, 1a; R = m-tolyl, E = P 1c; R = p-tolyl, E = As, 1d, P, 1e), which display the charge transfer spoke structure, and [(o-tolyl3As)AuCl] 2 have been synthesised and their solid state structures compared to the related complexes [(R3P)AuX] (R = o-tolyl, X = Cl, I, Ia; Br, II; I, III; R = m-tolyl, X = Cl, IV; R = p-tolyl, X = Cl, V, Va; Br, VI; I, VII) on the basis of a similarity of their molecular shape and volume. All of the new compounds 1a, 1c–1e and 2 have been fully spectroscopically characterised and by single crystal X-ray crystallography. The sterically demanding exo3o-tolyl ring conformation is observed for 1a, which is comparable to that reported for o-tolyl3PI21b, with a long As–I bond 2.7351(14) Å and short I⋯I distance 2.9528(11) Å. The exo3o-tolyl ring conformation is maintained on complexation to gold(I) in 2, but has no significant impact on the expected bond lengths, with As–Au 2.3443(15) Å and Au–Cl 2.284(4) Å. The exo3 conformation appears to be stabilised in both cases by the formation of a six-fold edge-to-face (EF)6 embrace. It is found that in some cases the structures of the dihalogen adducts and the gold(I) complexes are isomorphous indicating that ligand packing requirements are most significant i.e. for 1c and IV. Where the structures digress this is due either to the greater ability of the dihalogen adduct to engage in hydrogen bonding 1a, b and I–III; or subtle changes in the nature of the tolyl ring embraces 1d, e and V–VII. Subtle changes in the nature of the tolyl ring embraces also account for the different polymorphs I and Ia and V and Va. There is no credible evidence to suggest that the aurophilic contact, seen in only one polymorph Va, exerts any influence on the overall crystal packing. The structural comparisons presented here add further to the applicability of the recently recognised structural mimicking ability of the R3PX2 systems and [R3PAuX] complexes, and that the aurophilic contact is a poor supramolecular synthon.

Isolation of 1,4-Li2-C6H4 and its reaction with [(Ph3P)AuCl

The difficulty in generating 1,4-Li2-C6H4 utilising the lithium halogen exchange reaction on 1,4-Br2-C6H4, 1,4-I2-C6H4 and 1-Br-4-I-C6H4 is revisited and only on treatment of 1,4-I2-C6H4 with 2 molar equivalents of n-BuLi can 1,4-Li2-C6H4 1 be isolated in excellent yield. Treatment of 1 with two equivalents of [ClAu(PPh3)] gives [1,4-(Ph3PAu)2-C6H4] 2a in excellent yield. Subsequent treatment of 2a with 2.5 molar equivalents of PPh2Me, PPhMe2 or PMe3 affords the PPh3 substituted compounds [1,4-(LAu)2-C6H4] (L = PPh2Me 2b, PPhMe2 2c, PMe3 2d) in essentially quantitative yields. On treatment of 1,4-Br2-C6H4 or 1-Br-4-I-C6H4 with 2 molar equivalents of n-BuLi only mono-lithiation takes place to give 1-Br-4-Li-C6H4 3 as shown through the isolation of essentially 1:1 molar equivalents of Ph2PC6H4-4-Br and Ph2PBu on treatment with 2 molar equivalents of ClPPh2. Treatment of 3, prepared by lithium/iodine exchange on 1-Br-4-I-C6H4, with [ClAu(PPh3)] affords [(Ph3P)Au(C6H4-4-Br)] 4 as expected and in addition [(Ph3P)Au(n-Bu)(C6H4-4-Br)2] 5, indicating the straightforward chloride/aryl exchange at gold may proceed in competition with oxidative addition of the n-BuI, generated in the initial lithium/iodine exchange reaction, to some aurate complex Li[Au(C6H4-4-Br)2] 6 formed in situ followed by reductive elimination of Br-C6H4-4-n-Bu in a manner that mimics lithium diorganocuprate chemistry. All of the gold-containing compounds have been spectroscopically characterised by 1H and 31P-{1H} NMR and in addition compounds 2a-d and 5 by single crystal X-ray diffraction studies. The solid state structures observed for 2a-d are dictated by non-conventional hydrogen bonding and the packing requirements of the phosphine ligands. For 2a and 2b there is no close Au...Au approach, however for 2c and 2d the reduction in the number of phenyl rings allows the formation of Au...Au contacts. For 2c and 2d the extended structures appear to be helical chains with Au...Au contact parameters of 3.855(5) A and C-Au-Au-C 104.1(3)degrees for 2c and 3.139(4) A and C-Au-Au-C -92.0(2)degrees for 2d. The Au...Au approach in 2c is longer than is normally accepted for an AuAu contact and is dictated by ligand directed non-conventional hydrogen bonding to the aurated benzene ring and the pi-stacking requirements of the phosphine ligand. By comparison of the structures 2a-2d with other structures in the database it is evident that the aurophilic interaction is a poor supramolecular synthon in the presence of non-conventional hydrogen bond donors. Searches of the CCDC database suggest that the observed parameters for the Au...Au contact in 2c sit close to the cut-off point for observing this type of contact. In addition to aurophilic contacts and non-conventional hydrogen bonds there are a number of halogenated solvent C-Cl...Au contacts observed in the structures of 2a and 2d. The nature of these contacts have implications for the accepted van der Waals radius of gold which should be extended to 2 A.

The Smallest “Aurophilic Species”

The existence of the C2v symmetric closed-shell di[gold(I)]hydronium cation [Au2H]+ (1), is predicted. It is shown that 1 is the smallest possible molecular species containing aurophilic contacts. Equilibrium structural parameters, vibrational frequencies and formation energies of 1 from Au+ and AuH, have been calculated, employing a series of highly correlated but available standard relativistic ab initio methods up to CCSD(T) level of theory and all-electron basis sets of quadruple-ζ quality with double polarizations. Relativistic effects have been taken into account by employing pseudorelativistic electron core potentials (ECP) or a scalar relativistic treatment using a Douglas-Kroll-Heß Hamiltonian of 2nd, 3rd and 4th order (DKH2, DKH3, DKH4).

Vapochromic Behavior of {Ag2(Et2O)2[Au(C6F5)2]2}n with Volatile Organic Compounds

The vapochromic behaviors of {Ag2L2[Au(C6F5)2]2}n (L = Et2O (1), Me2CO (2), THF (3), CH3CN (4)) were studied. {Ag2L2[Au(C6F5)2]2}n (L = Et2O (1)) was synthesized by the reaction of [Bu4N][Au(C6F5)2] with AgOClO3 in 1:1 molar ratio in CH2Cl2/Et2O (1:2). 1 was used as starting material with THF to form {Ag2L2[Au(C6F5)2]2}n (L = THF (3)). 3 crystallizes in the monoclinic space group C2/c and consists of tetranuclear units linked together via aurophilic contacts resulting in the formation of a 1D polymer that runs parallel to the crystallographic z axis. The gold(I) atoms are linearly coordinated to two pentafluorophenyl groups and display additional Au...Ag close contacts within the tetranuclear units with distances of 2.7582(3) and 2.7709(3) A. Each silver(I) center is bonded to the two oxygen atoms of the THF molecules with a Ag-O bond distance of 2.307(3) A. TGA analysis showed that 1 loses two molecules of the coordinated solvent per molecular unit (1st one: 75-100 degrees, second one: 150-175 degrees C), whereas 2, 3, and 4 lose both volatile organic compounds (VOCs) and fluorinated ligands in a less well defined manner. Each complex loses both the fluorinated ligands and the VOCs by a temperature of about 325 degrees C to give a 1:1 gold/silver product. X-ray powder diffraction studies confirm that the reaction of vapors of VOCs with 1 in the solid state produce complete substitution of the ether molecules by the new VOC. The VOCs are replaced in the order CH3CN > Me2CO > THF > Et2O, with the ether being the easiest to replace. {Ag2(Et2O)2[Au(C6F5)2]2}n and {Ag2(THF)2[Au(C6F5)2]2} n both luminesce at room temperature and at 77 K in the solid state. Emission maxima are independent of the excitation wavelength used below about 500 nm. Emission maxima are obtained at 585 nm (ether) and 544 nm (THF) at room temperature and at 605 nm (ether) and 567 nm (THF) at 77 K.

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.

Spin-Crossover Behavior in Cyanide-bridged Iron(II)−Gold(I) Bimetallic 2D Hofmann-like Metal−Organic Frameworks

The synthesis and characterization of new two-dimensional (2D) cyanide-bridged iron(II)-gold(I) bimetallic coordination polymers formulated, {Fe(3-Xpy)2[Au(CN)2]2} (py = pyridine; X = F (1), Cl (2), Br (3), and I (4)) and the clathrate derivative {Fe(3-Ipy)2[Au(CN)2]2}.1/2(3-Ipy) (5), are reported. The iron(II) ion lies in pseudoctahedral [FeN6] sites defined by four [Au(CN)2](-) bridging ligands and two 3-Xpy ligands occupying the equatorial and axial positions, respectively. Although only compounds 2 and 4 can be considered strictly isostructurals, all of the components of this family are made up of parallel stacks of corrugated {Fe[Au(CN)2]2}n grids. The grids are formed by edge sharing of {Fe4[Au(CN)2]4} pseudosquare moieties. The stacks are constituted of double layers sustained by short aurophilic contacts ranging from 3.016(2) to 3.1580(8) A. The Au...Au distances between consecutive double layers are in the range of 5.9562(9)-8.790(2) A. Compound 5, considered a clathrate derivative of 4, includes one-half of a 3-Ipy molecule per iron(II) atom between the double layers. Compound 1 undergoes a half-spin transition with critical temperatures Tc downward arrow = 140 K and Tc upward arrow = 145 K. The corresponding thermodynamic parameters derived from differential scanning calorimetry (DSC) are Delta H = 9.8 +/- 0.4 kJ mol(-1) and Delta S = 68.2 +/- 3 J K mol(-1). This spin transition is accompanied by a crystallographic phase transition from the monoclinic P2(1)/c space group to the triclinic P1 space group. At high temperatures, where 1 is 100% high-spin, there is only one crystallographically independent iron(II) site. In contrast, the low temperature structural analysis shows the occurrence of two crystallographically independent iron(II) sites with equal population, one high-spin and the other low-spin. Furthermore, 1 undergoes a complete two-step spin transition at pressures as high as 0.26 GPa. Compounds 2- 4 are high-spin iron(II) complexes according to their magnetic and [FeN6] structural characteristics. Compound 5, characterized for having two different iron(II) sites, displays a two-step spin transition with critical temperatures of Tc(1) = 155 K, Tc(2) downward arrow = 97 K, and Tc(2) upward arrow = 110 K. This change of spin state takes place in both sites simultaneously. All of these results are compared and discussed in the context of other {Fe(L) x [M(I)(CN)2]} coordination polymers, particularly those belonging to the homologous compounds {Fe(3-Xpy)2[Ag(CN)2]2} and their corresponding clathrate derivatives.

Gold(i) and silver(i) complexes containing a tripodal tetraphosphine ligand: influence of the halogen and stoichiometry on the properties. The X-ray crystal structure of two gold(i) dimeric aggregates

Complexes of the type [Au2(micro-PP3)2]X2 [X=Cl (), Br (), I ()], [Ag2(micro-PP3)2](NO3)2 (), Ag(PP3)Cl (), M3(micro-PP3)X3 [M=Au, X=Cl (), Br (), I (); M=Ag, X=NO3 ()] and Au4(micro-PP3)X4 [X=Cl (), Br (), I ()] have been prepared by interaction between gold(I) or silver(I) salts and the ligand tris[2-(diphenylphosphino)ethyl]phosphine (PP3) in the appropriate molar ratio. Microanalysis, mass spectrometry, IR and NMR spectroscopies and conductivity measurements were used for characterization. and are ionic dinuclear species containing four-coordinate gold(i) and four/three coordinate silver(i), respectively. Solutions of behave as mixtures of complexes in a 2:1 [Au2(micro-PP3)X2; X=Cl(), Br(), I()] and 4:1 () metal to ligand ratio. and react with free PP(3) in solution to generate the ionic compounds and , respectively. Complexes and , with four linear PAuX fragments per molecule, were shown by X-ray diffraction to consist of dimeric aggregates via close intermolecular gold(I)gold(I) contacts of 3.270 A () and 3.184 A (). The resultant octanuclear systems have an inversion center with two symmetry-related gold(I) atoms being totally out of the aurophilic area and represent a new form of aggregation compared to that found in other halo complexes of gold(I) containing polyphosphines. The luminescence properties of the ligand and complexes, in the solid state, have been studied. Most of the gold systems display intense luminescent emission at room and low temperature. The influence of the halogen on the aurophilic contacts of compounds with a 4:1 metal to ligand ratio results in different photophysical properties, while and are luminescent complex is nonemissive. The luminescence increases with increasing the phosphine/metal ratio affording for complexes , without aurophilic contacts, the stronger emissions. Silver complexes and are nonemissive at room temperature and show weaker emissions than gold(I) species at 77 K.

Conformational analysis of a helically distorted gold(I) macrocycle derived from xantphos: evidence for the aurophilic Au… Au interaction from NMR

Variable-temperature solution (1)H- and (31)P-NMR experiments are reported for [Au(2)(xantphos)(2)](NO(3))(2) gold(I) complex incorporating a 16-membered Au(2)P(4)C(8)O(2) macrocycle derived from the 9,9-dimethyl-4,5-bis(diphenylphosphino)xanthene (xantphos) ligand. These NMR studies provide detailed structural information about its solution structure in comparison to the solid-state structure available from single crystal X-ray diffraction. Two-dimensional (1)H-NOESY spectroscopy at low temperatures allowed the full assignment of proton resonances, which are severely exchange-broadened at room temperature. The (1)H--(1)H spatial connectivities of the large number of non-equivalent protons unravel the complete stereochemistry of the gold(I) macrocycle in its symmetrically twisted conformation. Chemical exchange between particular proton pairs has allowed understanding the molecular dynamics and ruled out formation of coordination oligomers. Spectral analysis of the unique phosphorous AA'BB' spin system has revealed three-bond (31)P--(31)P scalar couplings mediated through the Au--Au bond, and has confirmed the existence of the aurophilic contact in low-temperature solutions. The solution (13)C and (31)P spectra are compared to the solid state (31)P-MAS and (13)C--CP/MAS spectra, where signal doubling effects due to the crystal packing have been discovered.

Factors affecting luminescence and aurophilicity on digold(I) complexes and their potential as cation probes

In the last few years we have analysed the factors that affect the structures and luminescence properties of Au(I) compounds, specifically in relation with the presence of aurophilic contacts and their application as cation probes. EXAFS studies have allowed us to obtain for the first time direct structural data of dissolved Au(I) compounds. An overview of the work reported to date is presented here. The optical properties of complex [Au2Cl2(μ-dpephos)] (dpephos =bis(2-diphenylphosphino) phenylether, 1) have been revisited and new results are now included. New aspects on the use of the complexes as Ag(I) probes are also discussed.

Unexpected Structural Preference for Aggregates with Metallophilic Ag- - -Au Contacts in (Trimethylphosphine)silver(I) and -gold(I) Phenylethynyl Complexes. An Experimental and Theoretical Study

(Me3P)AuC⋮CPh is a molecular compound associated into chains through aurophilic contacts, while its silver analogue exists as the ionic isomer [(Me3P)2Ag]+[Ag(C⋮CPh)2]-. Equivalent mixtures of the two compounds (Au:Ag = 1:1) in dichloromethane yield the ionic mixed-metal compound [(Me3P)2Ag]+[Au(C⋮CPh)2]-, which is stable in solution only in the presence of an excess of the Me3P ligand. Under these conditions it can be crystallized, and in the crystals the cations and the anions (with idealized D3d and D2h symmetry, respectively) are aggregated via heterometallophilic bonding, generating linear −Ag−Au−Ag−Au− chains. The solid was found to be also unstable at room temperature, owing to a rapid loss of four out of six tertiary phosphines, which leads to a product of the composition [(Me3P)2Ag]+[Ag2Au3(C⋮CPh)6]-. By crystal structure analysis, the anion was shown to have three [PhC⋮CAuC⋮CPh]- anions associated via two Ag+ cations to give a Ag2Au3 core unit of quasi-D3h symmetry. Structure and bonding in this anion have been analyzed through density functional calculations of the [Ag2Au3(C⋮CH)6]- model and shown to be largely ionic in nature. Deviations of the experimental and calculated geometrical details could be traced to the electrostatic field in the crystal. In the unit cell, the cluster anions are associated with the [(Me3P)2Ag]+ cations (of idealized D3h symmetry) via heterometallophilic contacts in which two of the three gold atoms are involved.

Complexes self‐associate by hydrogen bonding and metallophilic attraction: Theoretical study

AbstractHydrogen bonding and metallophilic attractions are studied in the model systems: [(AuNH3Cl)2], [(AuNH(CH3)2Cl)2], [{Au2(μ‐SH)(PH2O)(PH2OH)}2], [(CuNH3Cl)2], and [{Cu(NH3)Cl}4] at the Hartree–Fock (HF) and second‐order Møller–Plesset (MP2) levels. The two interactions are found to be comparable and prevailing in the final structure. It is determined that the aurophilic contact has a same magnitude that the hydrogen bonding, and is stronger than the cuprophilic interaction. The presence of hydrogen bond directs the growth of the crystal. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2006