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)]center dot 2H(2)O (1) and [Ni(cyclam)(H2O)(2)][Ni(dipic)(2)]center dot 2.5H(2)O (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 Nil 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. (C) 2007 Elsevier B.V. All rights reserved.