Publication details

New molecular heptanuclear cobalt phosphonates: synthesis, structures and magnetic properties



Year of publication 2018
Type Article in Periodical
Magazine / Source New Journal of Chemistry
MU Faculty or unit

Faculty of Science

Keywords cobalt; complex; magnetic; phosphonate
Description The synthesis, structures and magnetic properties of two novel heptanuclear homoleptic molecular cobalt phosphonates are described. Reactions between CoCl26H(2)O and (2-{[(E)-(2-hydroxyphenyl)methylidene]amino}propan-2-yl)phosphonate ligand (HSAA(2-)) in methanol lead to the crystalline products [Co-7(SAA)(2)(HSAA)(4)] (1) and [Co-7(SAA)(2)(NaSAA)(4)] (2), which crystallize in the space groups P2(1)/n (1) and P1 (2). Complexes show a similar structure motif - a centered trigonal antiprism composed of seven Co2+ ions with different coordination environments for the central and peripheral atoms. These heptanuclear molecular cages {Co-7} are held together by six phosphonate ligands. The main difference in their molecular cores is the presence of four sodium cations in 2 instead of four phenolic protons in 1. Magnetic measurements reveal a strong magnetic anisotropy for both structures 1 and 2. Above 50 K, both complexes follow the Curie-Weiss law. The low temperature susceptibility data indicate differences in the intramolecular exchange coupling, as ferromagnetic and antiferromagnetic interactions are observed for 1 and 2, respectively. This can be related to structural differences leading to variations in the Co-O-Co bridging angles between the central octahedral and the six peripheral trigonal-bipyramidal Co2+ ions.
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