Stereochemically non-rigid helical mercury(II) complexes

Reactions of the 1:2 condensate (L) of benzil dihydrazone and 2-acetylpyridine with Hg(ClO4)2 · xH2O and HgI2 yield yellow [HgL2](ClO4)2 (1) and HgLI2 (2), respectively. Homoleptic 1 is a 8-coordinate double helical complex with a Hg(II)N8 core crystallising in the space group Pbca with cell dimensions: a = 16.2250(3), b = 20.9563(7), c = 31.9886(11) Å. Complex 2 is a 4-coordinate single helical complex having a Hg(II)N2I2 core crystallising in the space group P21/n with cell dimensions a = 9.8011(3), b = 17.6736(6), c = 16.7123(6) Å and β = 95.760(3)o. In complex 1, the N-donor ligand L uses all of its binding sites to act as tetradentate. On the other hand, it acts as a bidentate N-donor ligand in 2 giving rise to a dangling part. From variable temperature 1H NMR studies both the complexes are found to be stereochemically non-rigid in solution. In the case of 2, the solution process involves wrapping up of the dangling part of L around the metal.