Coupled High Spin Co(II) Ions Linked by Symmetrical Double Hydrogen Bonds: Role of a Slow Relaxing Cu(II) Impurity in Interrupting the Co-Co Exchange interaction

REY, MARILIN A.; PASSEGGI, MARIO; PEREZ, ANA L.; DALOSTO, SERGIO D.; RIZZI, ALBERTO; KEMMERER, AXEL; RAMOS, CARLOS; BRONDINO, CARLOS D.

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY

WILEY-V C H VERLAG GMBH

Lugar: Weinheim; Año: 2018 vol. 2018 p. 4604 - 4613

1434-1948

Co(II) and Cu(II) ions are two paramagnetic transition metal ions showingdifferent relaxation rates (ν), with νCo(II) >> νCu(II). To measure the isotropic exchange constant (J) between high spin Co(II) ions and between Cu(II) and high spin Co(II) ions, we performed magnetic and EPR measurements complemented with computational calculations on pure trans-diaqua-bis(picolinato-N,O)-cobalt(II) dihydrate (1), on theCu(II) ion doped compound of 1 (2), and on the Cu(II) ion doped compound in a Zn(II) matrix isomorphous to 1. The dependence with temperature of the Cu(II) EPR resonance lines of 2 induced by the fast relaxing Co(II) ion host as well as the evaluation of thetemperature-independent Co-Co and Cu-Co isotropic exchange interaction are analyzed. We determined JCo-Co= −1.07 cm-1 associated with a double symmetrical hydrogen bond bridge, and |J|Co-Cu= 0.0015 cm-1associated with a double but asymmetrical hydrogen bond bridge, which are in line with the values determined from computational calculations. This work shows that EPR can advantageously be used to evaluate weak exchange interactions between distinct metal ions with different relaxation rates by using the fact that those metal-metal interactions thatbroaden the EPR resonance line which are described by matrices with a trace of zero, are averaged out at high temperatures.