Structural and spectroscopic characterization of silver(I) tribenzylphosphane complexes including chloro and bromo derivatives with unusual stoichiometries and an iodo complex with a Ag13I13 cluster core

The reaction of tribenzylphosphane (PBn3) with silver(I) halides, AgX (X = Cl, Br and I), afforded the cluster compound, [Ag13I13(PBn3)6 ] (1), a low-yielding ionic salt, [Ag(PBn3)2]8[AgCl3]Cl6·6H2O (2), and a non-stoichiometric compound, Ag∼11.5Br∼11.5(PBn3)16·∼5.5H2O (3). As well, reactions with the appropriate Ag salt and PBn3 in a 1:2 M ratio yielded [Ag(PBn3)2]PF6 (4), [Ag(PBn3)2]BF4 (5) and [Ag(PBn3)2Cl]·0.33CHCl3 (6) while [Ag(PBn3)2I] (7) was obtained when the ratio was 4:1. The iodo-cluster 1 has an onion-like structure with an iodide ion at its center surrounded trigonal-prismatically by an inner core of six silver ions. These silver ions are tetrahedrally coordinated to the innermost iodide ion and by six iodides that bridge to an outer layer of six silver ions which themselves are tetrahedrally coordinated by six bridging iodides and capped by the six PBn3 ligands. The top of the onion features a silver ion with three iodo ligands arranged in a near-planar trigonal arrangement around it. Single crystal X-ray crystallography shows the complexes 2 and 3 to contain columns of discrete [Ag(PBn3)2]+ cations with a linear P–Ag–P coordination, as also observed in the simple salts, 4 and 5, where the anion is [PF6]− and [BF4]−. The phenyl groups of PBn3 swing back over the silver to generate a sixfold phenyl embrace. However, in 3, although the PBn3 sites are fully occupied, about a quarter of the sixfold phenyl embraces are devoid of the object of their attention, the encapsulated silver ion. For 2, the [AgCl3]2− anions are trigonal-planar, three-coordinated. For 3, the AgBr32- appear as motifs in an approximately 25% silver-deficient Ag4Br62- cluster. The crystal structures of the three-coordinate halides, 6 and 7, show that the geometry around the silver is close to a T-shape, with the chloride and iodide ions bound. The far-IR and 31P CP MAS NMR spectra of a selection of the new complexes confirm aspects of their symmetry as deduced from the crystallographic studies.

Graphical abstractTribenzylphosphane (PBn3) reacts with silver(I) halides to afford the onion-like cluster, [Ag13I13(PBn3)6], the ionic salt, [Ag(PBn3)2]8[AgCl3]Cl6·6H2O, and the non-stoichiometric complex, Ag∼11.5Br∼11.5(PBn3)16·∼5.5H2O as well as mononuclear [Ag(PBn3)2]PF6, [Ag(PBn3)2]BF4, [Ag(PBn3)2Cl] and [Ag(PBn3)2I]. Cationic [Ag(PBn3)2]+ species with a linear P–Ag–P coordination are a feature of many of the compounds as a result of the driving force of the ‘sextuple phenyl embrace’.Figure optionsDownload full-size imageDownload as PowerPoint slideResearch highlights► Tribenzylphosphane (PBn3) reacts with AgI to afford the onion-like cluster, [Ag13I13(PBn3)6]. ► AgCl reacts to form the ionic salt, [Ag(PBn3)2]8[AgCl3]Cl6·6H2O. ► AgBr reacts to form the non-stoichiometric complex, Ag∼11.5Br∼11.5(PBn3)16·∼5.5H2O. ► Mononuclear 2- and 3-coordinate complexes have also been characterized. ► Cationic [Ag(PBn3)2]+ species with a linear P–Ag–P coordination are a feature.