Dinuclear Species versus Zigzag or Helical Polymers in Palladium, Zinc, and Copper Complexes with Ditopic Bis(pyrazolyl)methane Ligands



Two new all-nitrogen donor ditopic ligands, namely, p-bis[bis(pyrazol-1-yl)methyl]biphenyl (L3) and p-bis[bis(3,5-dimethylpyrazol-1-yl)methyl]biphenyl (L4), have been synthesized. Their coordination chemistry, along with that of the previously described ligands p-bis[bis(pyrazol-1-yl)methyl]benzene (L1) and p-bis[bis(3,5-dimethylpyrazol-1-yl)methyl]benzene (L2), has been explored with different metallic fragments. The reactions of L1–L4 with PdCl2(PhCN)2, Pd(OAc)2 and Zn(NO3)2 led to the formation of dinuclear species with anti orientation of the metallic fragments and bis(bidentate) chelation of the coordinated ligands. The reactions of L1 or L3 with Cu(OAc)2 produced zigzag polymers with Cu2(OAc)4 paddle-wheel units alternating with ligands that coordinate through one pyrazolyl ring at each end. The reaction between L3 and [Cu(CH3CN)4][BF4] leads to a helical racemic coordination polymer. The presence of methyl groups on the pyrazolyl rings and the geometry of the metal centres influence the parameters of the metallacycles formed by chelate coordination of the ligands. The discrete molecules and the polymers organize to give three-dimensional structures through different noncovalent interactions including hydrogen bonding, CH–π, anion–π and π–π interactions that are influenced by the presence or absence of methyl groups on the pyrazolyl rings.