Ahmed A. Mohamed

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.

CYCLIC TRINUCLEAR GOLD(I) COMPOUNDS: SYNTHESIS, STRUCTURES AND SUPRAMOLECULAR ACID-BASE π-STACKS

Trinuclear 9-membered rings can be formed by gold(I) ions with exobidentate C,N or N,N monoanionic ligands. They are generally slightly irregular and puckered unless the metallocycle is imposed by intramolecular crystallographic symmetry. Gold-gold intramolecular interactions are always present and the complexes exhibit a roughly D3h symmetry. Crystal structures of these trinuclear complexes show individual complexes, dimers supramolecular columnar packing or more complex supramolecular aggregates. Dimers and supramolecular structures are held together by aurophilic intermolecular gold-gold interactions. Bulky substituents on the ligands can prevent intermolecular metal-metal interactions or the formation of supramolecular architectures. It is well established that the Au(I) center in many linear 2-coordinate Au(I) complexes displays electrophilic tendencies in reaction chemistry while also often accepting electron donors to expand the coordination. Trinuclear Au(I) pyrazolates, carbeniates and benzylimidazolates are well known and undergo electron loss through oxidative addition forming first Au(I,III) mixed valence species and ultimately (with the carbeniates, TR(carb), the benzylimidazolates, TR(bzim) and the chlorinated pyrazolate TR(Cl-pz) trinuclear Au(III) species. Surprisingly, these Au(I) carbeniates and benzylimidazolates also are excellent bases for the metals cations Tl(I) and Ag(I). The acidic, neutral [Hg(C6F4)3]3 interacts with TR(carb) and TR(bzim) as seen by X-ray solid state and solution NMR measurements. Recently it has been shown that the neutral pi acids C6F6 and TCNQ also form stacked pi-acid, pi-base solid state products with TR(carb) and TR(bzim). The TR(bzim) and TR(carb) products are luminescent as solids but C6F6 intercalation quenches the luminescence of the p-tol, ethoxy TR(carb), which is a dimer in the solid state. It is interesting that pi-acid, pi-base stacking can involve either a ABAB pattern or an ABBABBA pattern of the molecules, where B is base, TR(carb) or TR(bzim). The B units are aurophilically bonded to each other by two Au…Au linkages. DFT calculations demonstrate that the basicity of the BB dimer is increased relative to the molecular species.

Synthesis and X-ray structures of silver and gold guanidinate-like complexes. A Au(II) complex with a 2.47 A Au-Au distance.

The structures of the tetranuclear silver(I), [Ag4(hpp)4], and the dinuclear gold(II), [Au2(hpp)2Cl2], (hpp = 1,3,4,6,7,8-hexahydro-pyrimido[1,2-a]pyrimidinate) guanidinate-like bases are reported and show a silver-silver distance of 2.8614(6) A and a gold-gold distance of 2.4752(9) A, the shortest Au-Au bond heretofore reported.

Halide and nitrite recognizing hexanuclear metallacycle copper(II) pyrazolates.

Halide-centered hexanuclear, anionic copper(II) pyrazolate complexes [trans-Cu(6)((3,5-CF(3))(2)pz)(6)(OH)(6)X](-), X = Cl, Br, I are isolated in a good yield from the redox reaction of the trinuclear copper(I) pyrazolate complex [μ-Cu(3)((3,5-CF(3))(2)pz)(3)] with a halide source such as PPh(3)AuCl or [Bu(4)N]X, X = Cl, Br, or I, in air. X-ray structures of the anion-centered hexanuclear complexes show that the six copper atoms are bridged by bis(3,5-trifluoromethyl)pyrazolate and hydroxyl ligands above and below the six copper atom plane. The anions are located at the center of the cavity and weakly bound to the six copper atoms in a μ(6)-arrangement, Cu-X = ~3.1 Å. A nitrite-centered hexanuclear copper(II) pyrazolate complex [trans-Cu(6)((3,5-CF(3))(2)pz)(6)(OH)(6)(NO(2))](-) was obtained when a solution of [PPN]NO(2) in CH(3)CN was added dropwise to the trinuclear copper(I) pyrazolate complex [μ-Cu(3)((3,5-CF(3))(2)pz)(3)] dissolved in CH(3)CN, in air. Blue crystals are produced by slow evaporation of the acetonitrile solvent. The X-ray structure of [PPN][trans-Cu(6)((3,5-CF(3))(2)pz)(6)(OH)(6)(NO(2))] complex shows the nitrite anion sits in the hexanuclear cavity and is perpendicular to the copper plane with a O-N-O angle of 118.3(7)°. The (19)F and (1)H NMR of the pyrazolate ring atoms are sensitive to the anion present in the ring. Anion exchange of the NO(2)(-) by Cl(-) can be observed easily by (1)H NMR.

Three-coordinate, luminescent, water-soluble gold(I) phosphine complexes: structural characterization and photoluminescence properties in aqueous solution

Abstract The trigonal planar Au(I) complex Cs8[Au(TPPTS)3]·5.25H2O, TPPTS=tris-sulfonatophenyl phosphine, has been structurally characterized. The X-ray data for the triclinic crystal, P 1 , are a=13.7003(4) A, b=18.0001(6) A, c=18.2817(2) A, α=100.249(2)°, β=99.593(2)°, γ=109.818(2)°, V=4046.3(2) A3, Z=2. The complex has AuP distances of 2.374(6), 2.394(5), and 2.417(5) A. A network of bonding has been found involving the Cs+ ions, the sulfonate groups of the ligands, and the H2O solvent molecules. Luminescence studies of [Au(TPPTS)3]8− and (TPA)3AuCl, TPA=1,3,5-triaza-7-phosphaadamantane, in the solid state and in solution are discussed and quenching studies of the luminescence of [Au(TPPTS)3]8− are reported with alkyl halides and oxygen.

Novel metallamacrocyclic gold(I) thiolate cluster complex: structure and luminescence of [Au9(μ-dppm)4(μ-p-tc)6](PF6)3

The structure of a novel metallamacrocyclic phosphine gold(I) thiolate cluster, [Au9(mu-dppm)4(mu-p-tc)6](PF6)3, where dppm = bis(diphenylphosphine)methane and p-tc = p-thiocresolate, is reported and shows AuAu attractions of approximately 3.0 A and gold(I) atoms linked to thiolate and phosphine ligands in distorted trigonal and nearly linear geometries.

Perspectives in Inorganic and Bioinorganic Gold Sulfur Chemistry

A detailed picture of the chemical and electrochemical oxidation of a series of mononuclear and dinuclear phosphine Au(I) thiolates is presented. The medicinal implications of the results are illustrated by redox studies on the anti-rheumatoid drug, auranofin, [(2,3,4,6-tetra-acetyl-1-thio- g -D-glucopyranosato)(triethylphosphine) gold(I)]. The phosphine Au(I) thiolate complexes undergo a broad irreversible oxidation in the range, +0.6 to +1.1 V, and a second irreversible oxidation at more positive potentials from +1.2 to +1.6 V (vs. SCE). Chemical oxidation of the Au(I) thiolate complexes with (Cp 2 Fe)(PF 6 ) results in disulfide and tetragold(I) clusters with bridging thiolate ligands, except for the unusual nine Au(I) atoms cluster obtained by oxidation of [(dppm)Au 2 (p-SC 6 H 4 CH 3 ) 2 ]. Chemical oxidation of auranofin with (Cp 2 Fe)(PF 6 ) results in disulfide and a cationic Au(I) cluster with bridging thiolate ligands, [(Et 3 PAu) 2 ( w -SATg)] 2 2+ , typical of mononuclear gold(I) thiolates. The Au(I) clusters react with disulfide to undergo thiolate/disulfide exchange. Comparative rates show clusters react much faster than the mononuclear complex, Ph 3 PAu(SC 6 H 4 CH 3 ). A mechanism for the oxidation of auranofin and related complexes, and possible biological implications are discussed.

Fine-tuning the luminescence and HOMO-LUMO energy levels in tetranuclear gold(I) fluorinated amidinate complexes.

Tetranuclear gold(I) fluorinated amidinate complexes have been synthesized and their photophysical properties and structures described. DFT calculations were carried out to illustrate how a minor change in the ligand resulted in a loss of emission in the perfluorophenyl amidinate complex compared with nonfluorinated phenyl amidinate complexes reported previously. The fluorinated complexes reported here [Au(ArN)(2)C(H)](4) (1, Ar = 4-FC(6)H(4); 2, 3,5-F(2)C(6)H(3); 3, 2,4,6-F(3)C(6)H(2); 4, 2,3,5,6-F(4)C(6)H) emit in the blue-green region at 470, 1, 478, 2, 508, 3, and 450 nm, 4, by excitation at ca. 375 nm at room temperature with nanosecond lifetimes. The emissions observed at 77 K in the solid state show structured emission for complexes 1 and 2, with a vibrational spacing of ca. 1200 and 1500 cm(-1), corresponding to the vibrational modes of the amidinate ligand. The pentafluorophenyl derivative 5, Ar = C(6)F(5,) shows no photoluminescence in the solid state nor in the solution. This result is different from results in which the pentafluorophenyl group is attached to a phenylpyridine ligand in an Ir(III) complex and other organics. This quenching appears to be related to a nonradiative de-excitation process caused by the ππ*-πσ* crossover in the excited state of the pentafluorophenyl amidinate ligand. With increasing numbers of fluorine atoms, there is a progressive decrease in the contribution of the amidinate ligands to the corresponding HOMO orbital. There also is a slight decrease in the ligand contribution to the LUMO with increased numbers of fluorine atoms and an exchange of the character of the orbitals of the gold centers.

Cyclic Voltammetry of Auranofin

The oxidative behavior of Auranofin, 2,3,4,6-tetra-O-acetyl-1-thio-β-D-glucopyranosato- S(triethylphosphine)gold(I), was investigated by using cyclic voltammetry (CV) in 0.1 M Bu4NPF6/CH2Cl2 and 0.1 M Bu4NPF4/CH2Cl2 solutions using Pt working and auxiliary electrodes and a Ag/AgCI reference. CV studies at scan rates from 50-2,000 mV/s and Auranofin concentrations between 1 and 4 mM, show two irreversible oxidation processes occurring at +1.1 V and +1.6 V vs. Ag/AgCl. Ph3 (p-thiocresolate) was also investigated as a reference for comparison of the oxidation processes in Auranofin to that of other phosphine gold thiolate complexes previously reported. The electrochemical response appears to be sensitive to adsorption at the electrode as well as to the nature of the supporting electrolyte solution. Repeated cycling shows a build up of products at the electrode.

Gold(III) diazonium complexes for electrochemical reductive grafting.

Gold(III) diazonium complexes were synthesized for the first time and studied for electrochemical reductive grafting. The diazonium complex [CN-4-C(6)H(4)N≡N]AuCl(4) was synthesized by protonating CN-4-C(6)H(4)NH(2) with chloroauric acid H[AuCl(4)]·3H(2)O to form the ammonium salt [CN-4-C(6)H(4)NH(3)]AuCl(4), which was then oxidized by the one-electron oxidizing agent [NO]PF(6) in CH(3)CN. The highly irreversible reduction potential of 0.1 mM [CN-4-C(6)H(4)N≡N]AuCl(4) observed at -0.06 V versus Ag/AgCl in CH(3)CN/0.1 M [Bu(4)N]PF(6) encompasses both gold(0) deposition and diazonium reduction. Repeated scans showed the absence of the reduction peak on the second run, which indicates that surface modification with a blocking gold aryl film has occurred and is largely complete.