Structural isomerism in silver thioether macrocyclic chemistry: the synthesis, redox properties and crystal structures of [Agn([15]aneS5)n][PF6]n′[Ag2([15]aneS5)2][BPh4]2 and [Ag([15]aneS5)][B(C6F5)4]([15]aneS5= 1,4,7,10,13-pentathiacyclopentadecane)

Abstract

Reaction of AgNO₃ with 1 molar equivalent of [15]aneS₅(1,4,7,10,13-pentathiacyclopentadecane) in refluxing MeOH–water gives a colourless solution. Addition of excess of counter ion [PF₆^–, BPh₄^– or B(C₆F₅)₄^–] affords the colourless complexes [Ag_n([15]aneS₅)_n][PF₆]_n′[Ag₂([15]aneS₅)₂][BPh₄]₂ and [Ag([15]aneS₅)][B(C₆F₅)₄] respectively in high yield. Single-crystal X-ray structural studies on these systems have revealed different cation stereochemistries as the counter ion is altered. Thus, [Ag_n([15]aneS₅)_n][PF₆]_n crystallises in the orthorhombic space group lba2 with a= 25.713(3), b= 25.749(3), c= 11.6989(19)Å and Z= 16. The two independent infinite chains of cations in the structure are antiparallel. The stereochemistry at Ag¹ is severely distorted octahedral through an [S₄+ S₂] donor set, Ag(1)⋯ S(1) 3.219(5), Ag(1)–S(4) 2.659(5), Ag(1)–S(7) 2.651(6), Ag(1)⋯ S(10) 3.075(7), Ag(1)–S(13) 2.564(6)Å, with one thioether donor from an adjacent [Ag([15]aneS₅)]⁺ fragment asymmetrically bridging two metal centres, Ag(1)–S(1B) 2.742(5)Å. A similar geometry is observed at the second Ag ion, Ag(2)⋯ S(1′) 3.263(5), Ag(2)–S(4′) 2.605(5), Ag(2)⋯ S(7′) 2.964(8), Ag(2)–S(10′) 2.713(7), Ag(2)–S(13′) 2.637(6), Ag(2)–S(1D) 2.714(5)Å. The complex [Ag₂([15]aneS₅)₂][BPh₄]₂ crystallises in the triclinic space group P with a= 11.462(3), b= 11.895(3), c= 27.019(10)Å, α= 78.503(18), β= 84.729(13), γ= 67.118(18)°, and Z= 2. The structure of the [Ag₂([15]aneS₅)₂]²⁺ cation shows an unusual binuclear stereochemistry with [4 + 1] thioether donation to one silver(I) centre, Ag(2)–S(7′) 2.558(4), Ag(2)–S(10′) 2.623(5), Ag(2)–S(13′) 2.716(5), Ag(2)–S(1) 2.486(3), Ag(2)⋯ S(1′) 3.131(3)Å, and [3 + 1] thioether donation to the other, Ag(1)–S(7) 2.529(3), Ag(1)–S(10) 2.608(4), Ag(1)–S(1′) 2.537(3), Ag(1)⋯ S(1) 2.907(3)Å. Thus, one S-donor [S(1) and S(1′)] of each macrocycle bridges asymmetrically between the two metal centres. The complex [Ag([15]aneS₅)][B(C₆F₅)₄] crystallises in the triclinic space group P with a= 12.476(5), b= 13.658(7), c= 15.608(6)Å, α= 108.300(22), β= 108.467(17), γ= 100.518(21)° and Z= 2. The structure contains discrete mononuclear [Ag([15]aneS₅)]⁺ cations and [B(C₆F₅)₄]^– anions. The geometry at Ag¹ is asymmetric with all five thioether donors of the macrocycle interacting with the metal centre: Ag–S(1) 2.4712(19), Ag ⋯ S(4) 2.7262(20), Ag–S(7) 2.6847(21), Ag–S(10) 2.5621(19), Ag ⋯ S(13) 2.8813(19)Å. In MeCN solution [Ag([15]aneS₅)]⁺ shows a chemically reversible Ag^I–Ag^II redox couple at E_½= 0.76 V and a quasi-reversible Ag^I–Ag^o couple at –0.37 V vs. ferrocene–ferrocenium. The intensely coloured d⁹ silver(II) oxidation product has been observed by X- and Q-band ESR spectroscopy and the oxidation of Ag^I to Ag^II monitored spectroelectrochemically.