Imidazo[1,2-a]pyridin-2-ylacetic acid and two pairs of isomorphous ML2(H2O)2 dihydrates (M = Ni, Co and Mn, Cd) based on its anion: Syntheses, crystal structures and properties

Imidazo[1,2-a]pyridin-2-ylacetic acid (HL, 1) and four ML2(H2O)(2)center dot 2H(2)O (M = Ni (2), Co (3), Mn (4), Cd (5)) complexes formed by its anion were synthesized, structurally characterized by single-crystal X-ray diffraction and investigated in terms of their thermal stability. In addition, magnetic properties of 2-4 are reported and the NIR-Vis-UV spectra of 2 and 3 are discussed in details. The crystal of 1 comprises 20 hydrogen bonded networks held in the crystal lattice by weak C-H center dot center dot center dot O and pi-pi contacts. The ML2(H2O)(2)center dot 2H(2)O complexes crystallize as isomorphous pairs (2, 3 and 4, 5) with slightly distorted hexa-coordinated environment around M(II) ion formed by two N,O-chelated imidazo[1,2-a]pyridin-2-ylacetate anions and two water molecules. In all 2-5, coordinated and lattice water molecules join discrete octahedral complexes into 2D hydrogen-bonded networks, held in the crystal lattice by weak C-H center dot center dot center dot O and pi-pi contacts. The Co(II) and Ni(II) complexes (2 and 3) are thermally less stable than Mn(II) and Cd(II) complexes (4 and 5). These differences are discussed in view of Hirshfeld surface analysis of reported compounds. The magnetic properties of 2 and 3 are largely determined by a tetragonal distortion of coordinated polyhedron, which stays in good agreement with observed and calculated transitions energies and their assignments in the electronic spectra of both compounds. Compound 4 displays almost ideal Curie-Weiss paramagnetism over the whole temperature range. Additionally, in all 2-4, weak magnetic exchange interactions mediated by H-bonds play a role with absolute values off coupling parameter increasing in the order: Mn < Co < Ni. (C) 2014 Elsevier Ltd. All rights reserved.