Synthesis, magnetic, thermal and structural properties of Co(II), Ni(II) and Cu(II) complexes containing isophthalato ligands

Abstract

A series of novel ternary Co(II), Ni(II) and Cu(II) complexes containing 2,2'-dipyridylamine (dipya), 2,2'-bipyridine (bipy), and 1,10-phenanthroline (phen), as aromatic diamine ligands, and dianion of isophthalic acid (ipht) have been prepared by ligand exchange reactions from diluted H2O/EtOH solutions. The complexes were characterized by elemental analysis, IR spectroscopy, magnetic susceptibility measurements and TG and DSC analysis. Three complexes, Cu(dipya)(ipht)center dot H2O (1), Co(dipya)(ipht)center dot 2H(2)O (2) and Cu(ipht)(phen)center dot 2H(2)O (5) are polymeric with bis-monodentate ipht, while the other two complexes M(bipy)(iPht)center dot 4H(2)O, M=Co(II) (3) and Ni(II) (4), contain ipht as a counter ion. All Co(II) and Ni(II) complexes are (pseudo)octahedral, while Cu(II) complexes have square-pyramidal or distorted octahedral geometry. The variable temperature magnetic susceptibility measurements showed very weak antiferromagnetic behaviour for all complexes. Dehydration processes, decomposition mechanisms and thermal stability of 1-5 are assumed. One complex from the above series, [Ni(bipy)(H2O)(4)](iPht) (4), and one additional complex, [Co(bipy)(iPht)](n) (6), are obtained as single-crystals and their structures are determined from X-ray diffraction data. In both structures M(II) centers are in deformed octahedral environment and they are linked by hemi-ipht ligands (4) and two different bridging ipht ligands (6). Three-dimensional networks in 4 and 6 are governed by strong noncovalent interactions. The cations and ipht anions in 4 are connected by hydrogen bonds building double layers parallel to ab-plane that are further packed by pi-pi interactions. In 6 double chains extending along b-axis are strengthened by interchain pi-pi interactions constructing a three-dimensional framework.