Syntheses, structures and spectroscopy of uni- and bi-dentate nitrogen base complexes of silver(i) trifluoromethanesulfonate

Abstract

In extension of recent synthetic and crystallographic studies of adducts of silver(I) oxyanion salts with uni- and bi-dentate nitrogen-donor ligands, AgX : L (1 : n), a parallel series of complexes formed with silver(I) trifluoromethanesulfonate (‘tfs’, ‘triflate’) has been similarly defined, showing rather more divergence from tendencies established with the previous ClO₄, NO₃, F₃CCO₂ core arrays than might be expected from basicity arguments. Thus, while silver triflate crystallised from neat base forms 1 : 2 mononuclear adducts with 2,4,6-trimethylpyridine and quinoline which comprise essentially linear two-coordinate [LAgL]⁺ cations, perturbed by approaches of the anions, 1 : 2 adducts obtained similarly from pyridine and 2-methylpyridine are [L₂Ag(μ-tfs)₂AgL₂] dimers, with central four- and eight-membered rings arising from μ-OSO₂CF₃ and extended μ-(O,O′SOCF₃) anion bridging modes, respectively. With piperidine, a single-stranded polymer reminiscent of the arrays [(pip)₂AgX]_∞|∞, X = Cl, NCS, is formed, the triflate bridging through two of its oxygen atoms, rather than via a single atom bridge. With 2- and 4-cyanopyridine, the former a 1 : 1 adduct (being an acetonitrile solvate (MeCN coordinated)), and the latter 1 : 2, both are more complex structures in which the nitrile functionalities now coordinate weakly. The 1 : 2 adduct with 2-acetylpyridine parallels its perchlorate analogue, the ligands being bidentate in a mononuclear complex [L₂AgOSO₂CF₃], while adducts of 2,9-dimethylphenanthroline and 2,2′-biquinolyl, both acetonitrile monosolvates, take the form [LAg(NCMe)]tfs. Agtfs : dpk (8 : 8)_∞|∞·EtOH (‘dpk’ = bis(2-pyridyl)ketone) is a complex polymer. The nature of the interactions is explored by way of spectroscopy (IR, NMR and ESI MS) and a density functional theory approach.