Influence of Semirigidity and Diverse Binding Modes of an Asymmetric Pyridine-pyrazole Based Bis-Chelating Ligand in Controlling Molecular Architectures and Their Properties

Abstract

We report herein the synthesis, characterization, and properties of some metal directed architectures using a new asymmetric, semirigid, and bis-chelating pyridine-pyrazole based ligand, {N′-(amino (pyrimidin-2-yl)methylene)-3-(pyridin-2-yl)-1H-pyrazole-5-carbohydrazide (H2APPC)}. The H2APPC ligand forms multinuclear cage complexes with different transition metal salts ranging from discrete mononuclear complex to nonanuclear with different kinds of network topologies. The semirigid ligand molecule not only changes the conformation but also exhibits variable coordination behavior, depending on the metal ions used. For instance, the reaction of manganese salt with H2APPC results in a truncated [3 × 3] grid network, whereas the nickel salt forms a highly unusual hexanuclear cage complex. Interestingly, in the presence of copper salt, H2APPC forms a different kind of structure along with an in situ generated new ligand. The zinc salts form a mononuclear complex. Most interestingly, reaction with cadmium salts leads to an intriguing [3 × 3] grid network, with a highly unusual occurrence of multiple variants of coordination environments around the metal centers. It is imperative to note here that the above display of metal-directed architectures is quite uncommon for an asymmetric semirigid ligand and cadmium complex that shows four kinds of coordination geometries which are not known in the literature, to the best of our knowledge. The variable temperature magnetic measurements of manganese, nickel, and copper complex showed strong antiferromagnetic interactions between the neighboring metal centers. Furthermore, the Cd9 framework showed promising solvent-dependent luminescent properties.