Steric Effect of a Capping Ligand on the Formation of Supramolecular Coordination Networks of Ni(II): Solid-State Entrapment of Cyclic Water Dimer.

Supramolecular dimer of water is the simplest of the small water clusters [(HO) , = 2-10]. During the course of our work on supramolecular coordination networks of three-component systems (divalent metal ion, tridentate capping ligand, and ditopic carboxylate linker), a cyclic water dimer is found to be entrapped in the network of [Ni(6-Mebpta)(adc)]·2HO () (6-Mebpta = 2-methyl--((6-methylpyridin-2-yl)methyl)--(pyridin-2-ylmethyl)propan-2-amine and adc = acetylenedicarboxylate). Based on the single-crystal structure of , the water dimer plays an important role in connecting the bis(adc) bridged dinickel synthons to form a one-dimensional (1D) supramolecular network. To emphasize the role of 6-Mebpta in the judicious choice of components for , one simple modification to it by having another methyl group in the second pendant pyridyl group to make 6,6'-Mebpta (2-methyl-,-bis((6-methylpyridin-2-yl)methyl)propan-2-amine) did not allow the formation of any water cluster in [Ni(6,6'-Mebpta)(adc)(HO)]·HO (), where a different coordination environment around Ni(II) is also observed. Further quantification of the difference in supramolecular interactions observed in and has been assessed by Hirshfeld surface analysis. Both and are obtained in good yields at room temperature (methanol as solvent) and are further characterized by elemental analysis, Fourier transform infrared (FTIR) and Raman spectroscopy, powder X-ray diffraction, and thermogravimetric analysis.