Variable coordination behavior of new hybrid pyrazole ligand: Synthesis and characterization of several Zn^II, Cd^II, Hg^II, Pd^II, Pt^II, and Ni^II complexes

In this paper we describe the synthesis of the new mixed-donor ligand 1,8-bis(3,5-dimethyl-1H-pyrazol-1-yl)-3,6dioxaoctane (L). The complexes [MCI2(L)] (M=Zn" (1), CdII (2), HgII (3), PdII (4), PtII (6), NiII (7)) and [PdCl 2(L)]2 (5) were prepared and fully characterized. X-ray crystal structures of complexes 1,2,4,6, and 7 have been determined. The L ligand behaves either as a NN-bidentate (chelate or bridge) and NOON-tetradentate (equatorial or planar) ligand. In these structures, C-H ⋯ X (X=O, N or CI/CI) intermolecular interactions have been identified and studied. Moreover, the 113Cd{1H}, 195Pt{1H}, and 199Hg{1H} NMR spectra were measured to investigate the coordination environment of the metal in solution. Diffusion NMR studies have also been performed to characterize monomeric and dimeric species of PdII. Finally, we have observed that the dimeric complex 5 is converted into the corresponding monomeric complex 4. © 2009 American Chemical Society.