Spectroscopic and structural studies on adducts of silver(I) cyanide with ER3 ligands (E = P, As or Sb)

Abstract

The adducts AgCN∶EPh₃ (E = P, As or Sb) (1∶2) and AgCN∶PPh₃ (1∶1) have been characterized by room temperature single crystal structure determination and low frequency vibrational spectroscopy. The compounds AgCN∶EPh₃ (E = P or As) (1∶2) [as pyridine (py) monosolvates] are isomorphous and of the form [(Ph₃E)₃Ag(CN)Ag(EPh₃)₃][Ag(CN)₂], an aqua–2-methylpyridine solvate and an acetonitrile solvate also being structurally characterized for the E = P adduct. For E = Sb the complex is a simple single stranded polymer · · ·Ag(SbPh₃)₂(CN)Ag(SbPh₃)₂(CN)· · · as is AgCN∶PPh₃ (1∶1), · · ·Ag(PPh₃)₂(CN)Ag(CN)Ag(PPh₃)₂· · ·. An adduct of the form AgCN∶PR₃ (1∶1) is also obtained for tris(2,4,6-trimethoxyphenyl)phosphine (tmpp) as a pyridine hemisolvate, now ionic but with the pyridine loosely co-ordinated to the anion, [Ag(tmmp)₂][Ag(CN)₂(py)]. By contrast, in the AgCN∶P(o-tol)₃ (tol = o-tolyl)∶py(1∶0.5∶0.5) adduct, Ag{P(o-tol)₃}(py) moieties are linked in a single-stranded polymer by NCAgCN units, · · ·Ag[P(o-tol)₃](py)(NCAgCN)· · ·. The structural characterization of [Ag(PPh₃)₃(CN)] has also been made. The far-infrared spectra of AgCN·2AgNO₃, [Ag(SbPh₃)₂(CN)] and [Ag(SbPh₃)₃(CN)] show ν(AgX) bands (X = CN) at 435, 358 and 310 cm^–1. The relationship between the ν(AgX) wavenumbers and the Ag–X bond lengths r(AgX) for the case of terminally bound CN groups has been established, and this has the same form as that found previously for a range of AgX complexes (X = Cl, Br or I) with phosphine and arsine ligands. The ν(AgX) wavenumbers for the CN-bridged compounds AgCN·2AgNO₃ and [Ag(SbPh₃)₂(CN)] are about 50 cm^–1 higher than those for compounds with terminal Ag–CN bonds of similar bond length. Similar behaviour is observed for the bridging CN groups in the cations of the ionic 1∶2 complexes [{Ag(EPh₃)₃}₂CN]⁺[Ag(CN)₂]^–·3py (E = P or As), where the ν(AgX) wavenumbers (301, 354 cm^–1 respectively) are about 80 cm^–1 higher than those predicted for terminal bonding.