EPR en un compuesto de Co(II) de alto espin

PEREZ, A. L.; KEMMERER, A.; REY, MARILIN A.; DALOSTO S; RAMOS, C; PASSEGGI, MARIO; RIZZI, A.; BRONDINO, C

Buenos Aires

Workshop; Taller; IV Taller de Resonancia Magnética; 2018; 2018

Magnetic studies on high spin Co (II) coordination compounds are of interest not only because they are part of many biological systems of central importance in nature [1], but also because of their application as molecular magnetic materials [2], as they provide information on the electronic structure and interactions between Co(II) ions and allow to establish correlations between magnetism and structure [3].In this work we study the complex Co(II)-picolinic acid which crystallizes in the monoclinic system P21/n, Z = 2. The two symmetry related Co(II) ions of the unit cell, designated as A (x, y, z) and B (1/2-x, 1/2+y, 1/2-z), are in a slightly distorted octahedral environment coordinated to two water oxygen atoms, two carboxylic oxygen atoms, and two pyridine nitrogen atoms of picolinic acid moieties. CoA (or CoB), are linked by double hydrogen bond bridges (dCo-Co, 5.130 Å) and by  hydrophobic interactions, which gives rise to Co(II) ion chains running along the b crystal axis (Figure). These two magnetically inequivalent Co(II) chains, symmetry related by the monoclinic C2 rotation around the b axis, are held together by hydrogen bond interactions mediated by reticular water molecules (Figure). The shortest CoA-CoB distance is 9.096 Å.Magnetization data were analyzed assuming Co(II) ions in a high spin configuration (S=3/2) with a spin Hamiltonian that included the Zeeman interaction and ZFS parameters. Magnetic susceptibility measurements showed a Curie-Weiss behavior, indicating the presence of exchange interactions between Co(II) ions in the crystal lattice. EPR experiments showed typical spectra of Co(II) ions in high spin configuration (S = 3/2), with absence of resolved hyperfine structure. The absence of hyperfine interaction observed in the EPR spectra, together with the Curie-Weiss behavior observed in the magnetic susceptibility measurement, evidence the presence of exchange interactions between Co (II) ions transmitted by hydrogen bonds connecting metallic sites in the crystal lattice.References:[1] P. A. Frey, A. D. Hegeman. Enzymatic Reaction Mechanisms, Oxford University Press, ed., 670?677, 2007.[2] L. Bogani, A. Vindigni, R. Sessoli, D. Gatteschi. J. Mater. Chem, 2008, 18, 4750-4758.[3] R Boča. Structure & Bonding, 2006, 117: 1-264.