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

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

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY

WILEY-V C H VERLAG GMBH

Lugar: Weinheim; Año: 2018

1434-1948

Co(II)and Cu(II) ions are two paramagnetic transition metal ions showing differentrelaxation rates (n), with nCo(II) >> nCu(II). To measure the isotropic exchange constant (J) between high spin Co(II) ions andbetween Cu(II) and high spin Co(II) ions, we performed magnetic and EPR measurementscomplemented with computational calculations on pure trans-diaqua-bis(picolinato-N,O)-cobalt(II) dihydrate (1), on the Cu(II) ion doped compound of 1 (2), and on the Cu(II) ion doped compound in a Zn(II) matrix isomorphousto 1. The dependence withtemperature of the Cu(II) EPR resonance lines of 2 induced by the fast relaxing Co(II) ion host as well as theevaluation of the temperature-independent Co-Co and Cu(II)-Co(II)isotropic exchangeinteraction are analyzed. We determined an antiferromagnetic interaction JCo-Co= -1.07(1) cm-1 associated with a double symmetrical hydrogen bondbridge, and |J|Co-Cu= 0.0015(2) cm-1 associated with a double but asymmetrical hydrogenbond bridge, which are in line with the values obtained from computationalcalculations. This work shows that EPR can advantageously be usedto evaluate weak exchange interactions between distinct metal ions withdifferent relaxation rates by using the fact that those metal-metal interactions thatbroaden the EPR resonance line which are described by matrices with a trace ofzero, are averaged out at high temperatures.