Different coordination modes of Hdipic and dipic ligands to nickel(II) ions in a same environment (dipic = 2,6-pyridinedicarboxylate, dipicolinate)

Two new nickel(II) complexes of the composition [Ni(cyclam)(Hdipic)2] · 2H2O (1) and [Ni(cyclam)(H2O)2][Ni(dipic)2] · 2.5H2O (2) (cyclam = 1,4,8,11-tetraazacyclotetradecane) have been prepared and structurally characterized by a combination of analytical, spectroscopic, thermogravimetric, and crystallographic methods. The structure of 1 shows that the central nickel(II) ion is coordinated axially by two monodentate Hdipic ligands. The discrete neutral complex 1 further extends its structure by hydrogen bonding interactions to form a one-dimensional supramolecule. The structure of 2 consists of two independent nickel(II) centers. Water molecules instead of dipic ligands prefer to coordinate to the Ni1 ion forming a divalent cation [Ni(cyclam)(H2O)2]2+. Two dipic ligands coordinate to the second Ni2 ion forming a divalent anion [Ni(dipic)2]2−. The divalent cations and anions are charge-balanced, resulting in a molecular salt. The divalent cations and anions are interconnected by multiple types of hydrogen bonding interactions.

Graphical abstractTwo new macrocyclic nickel(II) complexes 1 and 2 have been prepared and structurally characterized by a combination of analytical, spectroscopic, thermogravimetric, and crystallographic methods. The Hdipic and dipic ligands in 1 and 2 show different coordination modes to nickel(II) ions in a same environment.Figure optionsDownload full-size imageDownload as PowerPoint slide