Slow diffusion of AgX with O(SiMe 2 (4-Py)) 2 (L) yields unique molecular rectangles consisting of [Ag(L)] 2 X 2 (X -) NO 3 -, ClO 4 -, PF 6 -, and CF 3 SO 3 -). For the rectangular system, the transannular argentophilic (Ag-Ag) interaction competes with the interaction between Ag(I) and its anions, while the π-π interactions are constantly preserved. The strength of the argentophilic interaction is in the following order: NO 3 -> ClO 4 -> PF 6 -> CF 3 SO 3and is reversibly stretched via the anion exchange from 3.20(1) to 3.81(1) Å without the destruction of the cyclic skeleton.

A view (Farrugia, 1997) showing the atom labelling and the hydrogen bonding (dashed lines) in (I); ellipsoids are at the 30% probability level [symmetry code: (i) 1 2 + x, 1 2 À y, 1 À z].

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In the title compound, [NiCl(2)(C(15)H(26)N(2))], the chiral alkaloid (6R,7S,8S,14S)-(-)-L-sparteine acts as a bidentate ligand, with two chloride ligands occupying the remaining coordination sites, producing a slightly distorted tetrahedron. The N-Ni-N plane in the title complex is twisted by 81.31 (11) degrees from the Cl-Ni-Cl plane. Other distortions of the tetrahedron are discussed.

No abstract