A new silver(I) aggregate having an octagonal Ag4S4 core where μ3-S bonding interactions lead to a nanotube assembly that exhibits quasiaromaticity

Silver(I) chloride reacts with 2-mercapto-3,4,5,6-tetrahydropyrimidine (StpmH(2), C4H8N2S) in DMSO with excess triethylamine to give a complex of formula {[Ag4Cl4(mu(3)-StpmH(2))(4)](n)} (1). The product was characterized by elemental analyses, FTIR far-IR, UV/Vis, and H-1 and Ag-109 NMR spectroscopic techniques. The Ag-109 NMR spectroscopic data of the complexes {[Ag-6(mu(2)-Br)(6)(mu(2)-StpmH(2))(4)(mu(3)-StpmH(2))(2)](n)} (2) and {[Ag-4(mu(2)-StpmH(2))(6)](NO3)(4)}(n) (3) are also reported here for comparison. Crystal structure of complex 1 was determined by X-ray diffraction at 100(1) K. Complex 1, C4H8AgClN2S, crystallized in the tetragonal system, space group P4cc, a = 15.7761(9) angstrom, b = 15.7761(9) angstrom, c = 6.9624(8) angstrom, V = 1732.8(2) angstrom(3), Z = 2. Each metal ion is bonded to one terminal Cl atom and three mu(3)-S atoms from three StpmH(2) ligands. Four silver ions are bridged by four sulfur atoms forming an octagonal Ag4S4 core. Each Ag-1 ion of one core is also bridged to an Ag-1 ion of another core through a sulfur atom, which forms an infinite nanotube structure. A computational study utilizing the method of nucleus-independent chemical shifts (NICS) showed that the Ag4S4 core exhibits strong quasiaromaticity at the geometric cage center. To the best of our knowledge, this is the first example of an Ag-1 cluster that presents quasiaromaticity and stacking interactions. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)