Structures and Related Properties of AgX Bearing 3,3‘-Thiobispyridine (X- = NO3-, BF4-, ClO4-, and PF6-)

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Abstract
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) Å3, 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) Å3, 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) Å3, 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) Å3, 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.