Preparation and characterisation of tetraphenylphosphonium and tetraphenylarsonium halogenoargentates(I), including a new lodoargentate(I) cluster, [Ag4I8]4–, containing three- and four-co-ordinated silver(I)

A new iodoargentate(I) cluster [Ag4I8]4–, containing three- and four-co-ordinated silver(I) has been isolated with the tetraphenylphosphonium and tetraphenylarsonium cations and characterised by means of crystal structure determination. Tetrakis(tetraphenylphosphonium) and tetrakis(tetraphenylarsonium) hexa-µ-iodo-di-iodotetra-argentate(I)[(1) and (2)] are isostructural and crystallise in the triclinic space group P, with a= 13.453(7), b= 16.607(9), c= 11.068(7)A, α= 102.83(4), β= 103.94(4), γ= 82.96(4)°, Z= 1, and a= 13.446(3), b= 16.712(3), c= 11.293(4)A, α= 103.36(2), β= 103.84(2), γ= 83.43(2)°, Z= 1, respectively. The initial phases crystallising from solution during formation of [PPh4]4[Ag4I8] and [AsPh4]4[Ag4I8] are [PPh4][Ag3I4](3) and [AsPh4][Ag3I4](4), respectively. The latter compounds are also isostructural with one another and crystallise in the monoclinic space group P21/c with Z= 4 and a= 13.380(5), b= 26.536(5), c= 8.504(4)A, β= 108.09(4)° for (3), and a= 13.448(7), b= 26.723(4), c= 8.546(4), β= 107.99(4)° for (4). With tetraphenylarsonium as cation, discrete chloroargentate(I) and bromoargentate(I) anions, [Ag2X4]2–, X = Cl (5) or Br (6), containing distorted trigonal-planar co-ordinated silver(I), have been obtained. Bis(tetraphenylarsonium)di-µ-chloro-dichlorodiargentate(I)(5) and bis(tetraphenylarsonium) di-µ-bromo-dibromodiargentate(I)(6) both crystallise in the monoclinic space group P21/n with Z= 2 and a= 14.280(6), b= 8.200(4), c= 19.118(8)A, β= 101.19(3)°, and a= 14.546(4), b= 8.072(2), c= 19.854(5)A, β= 102.73(2)°, respectively. The tetranuclear [Ag4I8]4– anion is centrosymmetric and can be described in terms of two edge-sharing silver(I)–iodide tetrahedra, each linked via a common edge to an approximately planar silver(I)–iodide triangle. In the latter the silver(I) atom is displaced 0.054(1)(1) and 0.026(1)A(2) from the plane through the three iodide ligands. The Ag–I distances associated with the three-co-ordinated centre are 2.727(2), 2.763(2), and 2.765(2)A(1), and 2.721 (1), 2.757(1), and 2.766(1)A(2), while those involving the four-co-ordinated centre range from 2.842(2) to 2.991 (2)(1) and 2.846(1) to 2.973(1)A(2). The Ag ⋯ Ag separations are 3.171 (2) and 3.256(2), and 3.198(1) and 3.306(2)A in (1) and (2), respectively. The [Ag3I4]– polymers in [PPh4][Ag3I4](3) and [PPh4][Ag3I4](4) consist of triple chains of edge-sharing Ag–I tetrahedra, Ag–I distances ranging from 2.796(2)–2.972(3)(3) and 2.798(4)–2.966(4)A(4). The anions in [AsPh4]2[Ag2Cl4] and [AsPh4]2[Ag2Br4] are centrosymmetric, approximately planar entities in which silver(I) is displaced 0.004(1)(5) and 0.048(1)A(6) from the ligand plane, and the Ag ⋯ Ag separations are 3.659(2)(5) and 3.549(2)A(6). In [Ag2Cl4]2–, the bridging Ag–Cl distances differ considerably from one another, i.e. 2.446(2) and 2.809(2)A, the terminal Ag–Cl bond being 2.359(2)A. In [Ag2Br4]2–, there is less discrepancy between bridging distances: 2.614(1) and 2.741 (1)A; Ag–Br(terminal) is 2.481 (1)A.