Structures and related properties of AgX bearing 3,3′-thiobispyridine (X^- = NO₃^-, BF₄^-, ClO₄^-, and PF₆^-)

Infinite molecular helices [Ag(3,3′-Py₂S)]X (3,3′-Py₂S = 3,3′-thiobispyridine; X^- = BF₄^-, ClO₄^-, and PF₆^-) have been rationally constructed or induced. Crystallographic characterization (X^- = BF₄^-, monoclinic P2₁/n, a = 8.946(3) Å, b = 14.130(2) Å, c = 10.124(2) Å, β = 107.83(2)°, V = 1218.3(5) ų, Z = 4, R = 0.0351; X^- = ClO₄^-, monoclinic P2₁/n, a = 8.884(1) Å, b = 14.305(3) Å, c = 10.110(1) Å, β = 106.78(1)°, V = 1230.1(3) ų, Z = 4, R = 0.0417; X^- = PF₆^-, monoclinic P2₁/c, a = 10.959(2) Å, b = 9.808(2) Å, c = 14.065(3) Å, β = 112.03(2)°, V = 1401.4(5) ų, Z = 4, R = 0.0442) reveals that the skeletal structure is an oblong cylindrical cationic helix consisting of alternating Ag(I) and 3,3′-Py₂S species and that its counteranions are pinched in two columns inside each helix. The formation of the helical coordination polymer appears to be primarily associated with a suitable combination of the skewed conformer of 3,3′-Py₂S and the potential linear geometry of the N-Ag(I)-N bond. However, the framework of the nitrate analogue [Ag(3,3′-Py₂S)NO₃] (monoclinic P2₁/c, a = 8.177(2) Å, b = 10.291(1) Å, c = 14.771(2) Å, β = 102.19(1)°, V = 1214.9(4) ų, Z = 4, R = 0.0300) is a two-dimensional network consisting of an 18-membered ring unit, where each 3,3′-Py₂S acts as a N,N′,S- tridentate ligand connecting three tetrahedral silver(I) ions with the monodentate nitrate weakly bonded to the silver (Ag···O = 2.65(1) Å) rather than acting as a counteranion. The anion exchange of [Ag(3,3′-Py₂S)-NO₃] with BF₄^-, ClO₄^-, or PF₆^- has been accomplished in aqueous media. The two-dimensional networks are easily converted into the helices via the anion exchange, but the reverse anion exchange proceeds slightly. Thermal analyses indicate a relationship between the thermal stabilities and the structural properties.