The complexes ( t BuNC)AuCl and ( t BuNC)AuI 13 C-labeled at the isocyanide group were prepared and investigated by concentration-and temperature-dependent IR and NMR spectroscopy in dichloromethane solution. No indication for association of the molecules was obtained. The crystal structure of the iodide complex was determined by X-ray diffraction methods and shown to feature only monomers with extremely large intermolecular Au-Au contacts of 4.162Å, well beyond the sum of the van der Waals radii. It therefore appears that ( t BuNC)AuI is a rare example of a sterically non-hindered L-Au-X complex which shows no aurophilic interactions whatsoever. In a quantum-chemical analysis (at the local MP2 level) of the dimerization of the model compounds (MeNC)AuCl and (MeNC)AuI in various dimer geometries it was demonstrated that the energy-balance of the dimerization is very delicate and not dominated solely by contributions from correlation / relativistic (aurophilic) effects.
Di(cyano)aurates(I), Gold(I) Cyanide Complexes, Bis(triphenylphosphoranylidene)ammonium SaltsPartially 13 C-labeled alkali dicyanoaurates M[Au(CN) 2 ] were prepared and investigated by NMR and IR spectroscopy in aqueous solution. For the range of concentration investigated the data obtained under standard conditions provided no evidence for anion association. The salt [Ph 3 PNPPh 3 ][Au(CN) 2 ] was also prepared and the crystal structure of the dichloromethane solvate determined. There is no anion aggregation in the crystal, and short contacts of the anions are only discernible with the solvent molecules. A literature survey of crystal structure data for dicyanoaurate(I) salts (almost 35 entries) show that inter-anionic contacts are only observed in structures with small cations or with cations exerting a directional influence.Alkali di(cyano)aurate(I) salts are the key intermediates in the recovery and processing of gold. Oxidative gold extraction from ores with aqueous alkali cyanide (NaCN or KCN) is followed by adsorption of the produced complexes Na[Au(CN) 2 ] or K[Au(CN) 2 on the surface of carbonaceous or resinous materials, for which the linear five-atomic anions [NC-Au-CN] appear to exhibit a specific affinity [1,2]. Although the details of this adsorption and desorption processes are still not perfectly understood on the molecular level, there is convincing evidence for anion aggregation both in solution, on the substrate surfaces, and in salts with small cations [3 -5]. During our own investigations [6 -8] in the supramolecular chemistry of neutral [L-Au-X], cationic [L-Au-L] + or anionic gold(I) complexes [X-Au-X] we noticed that anion aggregation to give oligomers or one-dimensional arrays is observed only in very special cases, and this is also true for the di(cyano)aurate(I) anion [9].With few exceptions [10, 11], most structural studies were carried out for compounds featuring the rod-like [Au(CN) 2 ] anion highly oriented between stacks of flat, plate-like cations [9b, 12 -24]. For several years these materials have been of considerable interest owing to their electrical conductor or semi-conductor properties.In the present study we tried to prepare and isolate a di(cyano)aurate(I) salt with a very bulky "inno-0932-0776/02/1000-1085 $ 06.00 c 2002 Verlag der Zeitschrift für Naturforschung, Tübingen www.znaturforsch.com K cent" cation with high flexibility and no directional influence to allow a spectrospic and structural characterization of anion association through aurophilic d 10 -d 10 interactions in an unperturbing environment both in solution and in the solid state.For precise NMR measurements, 13 C-enriched cyanide was used in the preparations. 13 C-labeled gold pseudohalides were investigated in the course of several earlier studies which provided fundamental data [25,26]. Previous spectroscopic and structural studies of simple di(cyano)aurates(I) are also summarized in the comprehensive Gmelin Handbook compilation [4]. Preparative and Spectroscopic StudiesFor the present investigation, th...
The concept of aurophilic bonding predicts an extended supramolecular chemistry of mono- and dinuclear gold acetylide complexes, but examples of the type (R3P)AuC⋮CAu(PR3) reported in the literature were all found to be monomeric owing to the influence of the auxiliary phosphine ligands employed. Compounds prepared with small tertiary phosphines have now been shown to exhibit the expected oligomerization: Complexes of the type (R3P)AuC⋮CAu(PR3) with R3P = Me3P and Me2PhP were found to have one-dimensional zigzag chain structures in which the molecular units are linked head-to-tail through short α,ω Au- -Au contacts. By contrast, (Et3P)AuC⋮CAu(PEt3), with its more bulky phosphines, shows monomeric units of D 3 symmetry in the crystal. The mononuclear complex (MePh2P)AuC⋮CH is a dimer in the solid state, with one short Au- -Au contact. This angular dimeric unit (C 2 symmetry) resembles the connectivity pattern in the zigzag chains of the aggregates of the dinuclear complexes. The compounds have also been characterized through their vibrational (IR/Raman), multinuclear NMR, and mass spectra.
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