Variable solid state aggregations in a series of (isocyanide)gold(i) halides with the novel trimethylamine-isocyanoborane adduct

Abstract

This paper provides evidence that the degree of aurophilic character and resulting solid state arrangement observed in (isocyanide)gold(I) halides is in part dependent on the nature of halide substituent. In particular, we report here the synthesis of a series of novel (isocyanide)gold(I) halides involving trimethylamine-isocyanoborane, an unusual 'zwitterionic' isocyanide that is comparable to the more familiar methyl isocyanide, but potentially more strongly Lewis basic. The reaction of chloro(dimethyl sulfide)gold(I) and the isocyanoborane species, (RNC)(R =(H3C)3NB(H)2), gives the novel crystalline adduct [(RNC)AuCl] (1). Treatment of 1 in an organic phase with aqueous KBr effected substitution of the chloride to give the bromide analogue [(RNC)AuBr] (2). The structures of 1 and 2 were determined by X-ray crystallography to be isostructural, consisting of a zigzag topology of chains of monomers, where adjacent gold(I) centres interact aurophilically. However, similar reaction of 1 with KI solution affords the unusual and unexpected compound, [(RNC)2Au][AuI2] (3). This iodide 3, is a linear chain polymer of alternating anion, cation units that is formed via ligand redistribution. The complexes 1-3 all fluoresce in the presence of UV light; the fluorescence of 3 being most prevalent at room temperature. The free trimethylamine-isocyanoborane ligand, the dimeric structures of compounds 1,2 and the thermodynamic stabilities of the dimers in the gas phase were studied by density functional and ab initio calculations at various levels of theory. The theoretical results are compared to the corresponding experimental data.

Luminescence, structural, and bonding trends upon varying the halogen in isostructural aurophilic dimers

“…E-mail: omary@unt.edu, tomc@unt.edu There has been much attention given to understanding the nature of the aurophilic character and its effect on the photophysical, photochemical and redox behavior of Au(I) compounds in the last few years. [15][16][17][18][19][20][21] The degree of association in these complexes is dependent on several factors among which the steric and electronic effects of the ligands are the most apparent. Despite the significant research focus upon luminescent Au(I) compounds, establishing a clear structure-luminescence relationship remains an elusive goal in this area.…”

Electronic and steric control over Au⋯Au, C–H⋯O and C–H⋯π interactions in the crystal structures of mononuclear triarylphosphinegold(i) carbonimidothioates: R3PAu[SC(OMe)=NR′] for R = Ph, o-tol, m-tol or p-tol, and R′ = Ph, o-tol, m-tol, p-tol or C6H4NO2-4

“…6,7 Such considerations generated crystal engineering studies investigating the competition of hydrogen-bonding versus aurophilic interactions. [8][9][10][11][12][13][14][15][16][17][18][19] By themselves, aurophilic interactions are known to give rise to a rich diversity of supramolecular architectures [20][21][22][23][24][25][26][27] and to stabilise supramolecular chains and oligomers. [28][29][30][31][32] Over and above structural considerations, interest in gold complexes, with and without aurophilic interactions, relates to their photophysical properties, i.e.…”

“…[63][64][65] It appears that steric effects play an important role, however. This is evidenced by the observation that gold complexes with small ligands such as cyanide, 66,67 isocyanide, 26,[68][69][70] and thiocyanide 71 usually form aurophilic interactions. Phosphinegold(I) complexes are ubiquitous in gold chemistry and given that steric profiles of the molecules are easily moderated by simple substitution at the phosphorous atom, they provide a relatively large data base of structures from which trends may be discerned.…”

Bromide ion binding by a dinuclear gold(i) N-heterocyclic carbene complex: a spectrofluorescence and X-ray absorption spectroscopic study

“…Cl − , Br − , I − ) can have a profound effect on the degree of aurophilicity. 25 Here, coordination of an anion (which is electron donating and/or easily polarisable) to the Au(I) atoms, causes an increase in the nephalauxetic effect for the Au(I) atoms. The nephalauxetic effect is characterised by radial orbital expansion (already significant for Au(I) due to relativistic effects), 26 and a decrease in the positive charge on the Au(I) centres, thereby favouring weak (aurophilic) interactions between the Au(I) atoms.…”