Polynuclear Complexes Containing Ditopic Bispyrazolylmethane Ligands. Influence of Metal Geometry and Supramolecular Interactions

The new ligands bis(pyrazol-1-yl)(pyridine-4-yl)methane (bpzm4py) (L1) and bis(3,5-dimethylpyrazol-1-yl)(pyridine-4-yl)methane (bpz*m4py) (L2) were synthesized and were made to react with different metallic starting materials. In the case of Pd(II), chloride or allyl trinuclear complexes were synthesized, in which the central palladium is bonded to two ligands through the pyridine moiety. Mononudear [Pd(allyl)L]X complexes were also isolated. On using other M(II) centers (M = Co, Ni, Zn), which could adopt an octahedral geometry, box-like cyclic dimers formed by the self-assembly of two metal centers and two ligands in a head-to-tail disposition were obtained. All metal ions exhibited a distorted octahedral geometry. A complex of Ag(I) with similar cyclic dimers connected through difluorophosphate anions to generate zigzag chains was also crystallized. The silver center was five-coordinate and the chain interactions gave rise to the formation of sheets. In the solid state, different noncovalent interactions were present in the molecular and supramolecular structures, including hydrogen bonds, pi-pi. stacking and anion -pi or CH-pi interactions. Examples of possible synergy between some of these interactions were found. Where possible, the solution chemistry was analyzed and correlated with the solid state structure. The existence of polynuclear species in solution was evaluated and the effect of some noncovalent interactions on the NMR resonances was observed.