264205-79-0Relevant articles and documents
Effects of metal co-ordination geometry on self-assembly: A dinuclear double belicate complex and a tetranuclear cage complex of a new bis-bidentate bridging ligand
Paul, Rowena L.,Couchman, Samantha M.,Jeffery, John C.,McClevcrty, Jon A.,Reeves, Zoc R.,Ward, Michael D.
, p. 845 - 851 (2000)
Reaction of 3-(2-pyridyl)pyrazole with 3, 3'-bis(bromomethyl)biphenyl resulted in the new ligand L1 which contains two bidentate chelating pyrazolyl/pyridine fragments separated by a /w/n-biphenyl spacer; this ligand is designed to act only as a bridging ligand, as the two bidentate sites are too far apart to co-ordinate to the same metal ion. The dinuclear copper(n) complex [Cu2(L')2(OAc)2][BF4]2 is a double helicate in which each copper(n) centre is in a square pyramidal co-ordination geometry, arising from two bidentate pyrazolyl/pyridine groups (one from each ligand L1) and a monodentate acetate. The structure is stabilised by extensive inter-ligand Tc-stacking interactions. The complex [Ag2(Ll)2][ClO4]2 is also assumed to be a double helicate. In contrast, reaction with Co afforded the tetranuclear cage complex [Co4(L')6][BF4]8, in which each bridging ligand links two metal centres by spanning one edge of the Co4 tetrahedron. Each metal is therefore in a pseudo-octahedral tris-chelate geometry, with the three bidentate chelating arms each coming from a different ligand L1. Again there is substantial inter-ligand K stacking. Unlike other complexes with the same {M4L6} tetrahedral cage structure, the central cavity is not occupied by a counter ion, showing that although the templating eflect of a counter ion can be beneficial in the assembly of such cages it is clearly not essential. 'H NMR spectroscopy suggests that there is a mixture of species in solution arising from other metal : ligand combinations; B NMR spectroscopy shows that at -40 °C a [BF4]~ anion can become trapped in the cavity of the cage, giving a characteristic high-field resonance in addition to that for the free [BF4]~ anions. Reaction of L1 with Pd afforded a mixture of products arising from ligand decomposition, of which [Pd2(L')(pypz)2][BF4][OH] was structurally characterised. It has a near-planar {Pd2(u-pypz)2}2+ core [Hpypz = 3-(2-pyridyl)pyrazole, which has arisen from decomposition of L1] with an additional bridging ligand L1 co-ordinating in a 'basket-handle' mode, straddling the central core. The Royal Society of Chemistry 2000.
