Cyclo-[Ni(μ2-SPh)2]9 and cyclo-[Ni(μ2-SPh)2]11: new oligomeric types of toroidal nickel(ii) thiolates containing geometrically unprecedented 9- and 11-membered ring systems

Abstract

Two new oligomeric types of toroidal nickel(II) monothiolate ring systems, cyclo-[Ni(SPh)₂]₁₁ (1) and cyclo-[Ni(SPh)₂]₉ (2), containing heretofore unknown 11-membered (n = 11) and 9-membered (n = 9) ring-geometries, respectively, are reported. Our initial isolation of 1 was as an unexpected by-product that resulted from unsuccessful attempts to produce crystalline nanostructural gold thiolate clusters from reactions of alkyl/phenyl thiols with the recently prepared nanostructural [Au₁₆Ni₂₄(CO)₄₀]⁴⁻ cluster. The unique architecture of 1 led to a designed preparation of it by a direct synthetic route involving reactions of PhSNa with Ni(ClO₄)₂ in THF or DMF. Slow addition of the reactants at low temperature afforded two crystal forms of 1: namely, the previously isolated triclinic crystals (P) as well as solvated monoclinic crystals (C2/c) (1a). Normal mixing of the reactants at room temperature gave rise to a trigonal crystal form (P12/c) that was determined to be cyclo-[Ni(SPh)₂]₉ (2). The atomic arrangements and stoichiometries of both 1 and 2 were unequivocally established from low-temperature CCD area-detector X-ray diffractometry studies; particularly noteworthy is that the structures of both crystal forms of 1 possess nearly identical molecular geometries (including the phenyl-ring orientations) along with an encapsulated THF molecule. These new air-stable molecular additions to the cyclo-[Ni(μ₂-SR)₂]_n family (with n = 4, 5, 6, and 8) are of particular stereochemical interest in that: (1) in sharp contrast to the previously known monodentate thiolate-bridged members which ideally possess regular convex Ni–S toroids, the assembled n-localized edge-fused square-planar [NiS₄] subunits found in the triclinic and monoclinic crystal forms of undecanickel 1 and in the trigonal crystal form of nonanickel 2 have irregularly-shaped mixed concave/convex toroidal pseudo-C_2v and pseudo-D_3h ring geometries, respectively, that are geometrically unique; (2) 1 is the first host member of any known cyclo-[Ni(SR)₂]_n oligomer to have a co-crystallized solvated guest molecule (viz., THF); and (3) the observed orientations of adjacent phenyl rings attached to the highly pyramidal sulfur atoms in both 1 and 2 suggest the occurrence of weakly attractive pairwise phenyl⋯phenyl dispersion forces that are presumed to stabilize these novel nickel(II) phenylthiolate oligomers. A comparative analysis of the salient solid-state structural features of the idealized Ni–S ring geometries of the resulting entire cyclo-[Ni(SPh)₂]_n family (n = 4, 5, 6, 8, 9, and 11) is presented (under the assumed absence of sterically crowded R-substituents and/or abnormal packing effects). The unsymmetrical enlargement of the pseudo-threefold 9-membered ring in 2 by the formal insertion of two adjacent [Ni(SPh)₂] units to give an otherwise analogous Ni–S framework of the 11-membered ring in 1 is attributed to the elongated template-geometry of the guest molecule coupled with the maintenance of attractive pairwise phenyl ring interactions.