Structural and spectroscopic characterization of silver(I) tribenzylphosphane complexes including chloro and bromo derivatives with unusual stoichiometries and an iodo complex with a Ag 13I 13 cluster core

Abstract

The reaction of tribenzylphosphane (PBn 3) with silver(I) halides, AgX (X = Cl, Br and I), afforded the cluster compound, [Ag 13I 13(PBn 3) 6 ] ( 1), a low-yielding ionic salt, [Ag(PBn 3) 2] 8[AgCl 3]Cl 6·6H 2O ( 2), and a non-stoichiometric compound, Ag ∼11.5Br ∼11.5(PBn 3) 16·∼5.5H 2O ( 3). As well, reactions with the appropriate Ag salt and PBn 3 in a 1:2 M ratio yielded [Ag(PBn 3) 2]PF 6 ( 4), [Ag(PBn 3) 2]BF 4 ( 5) and [Ag(PBn 3) 2Cl]·0.33CHCl 3 ( 6) while [Ag(PBn 3) 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 PBn 3 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(PBn 3) 2] + cations with a linear P–Ag–P coordination, as also observed in the simple salts, 4 and 5, where the anion is [PF 6] − and [BF 4] −. The phenyl groups of PBn 3 swing back over the silver to generate a sixfold phenyl embrace. However, in 3, although the PBn 3 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 [AgCl 3] 2− anions are trigonal-planar, three-coordinated. For 3, the AgBr 3 2 - appear as motifs in an approximately 25% silver-deficient Ag 4 Br 6 2 - 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.