INVESTIGADORES
BRONDINO Carlos Dante
artículos
Título:
Magnetic Properties of Weakly Exchange-Coupled High Spin Co(II) Ions in Pseudooctahedral Coordination Evaluated by Single Crystal X-band EPR and Magnetic Measurements
Autor/es:
N. I. NEUMAN; E. WINKLER; O. PEÑA; M.C.G. PASSEGGI; A. C. RIZZI; C. D. BRONDINO
Revista:
INORGANIC CHEMISTRY
Editorial:
AMER CHEMICAL SOC
Referencias:
Lugar: Washington; Año: 2014 vol. 53 p. 2535 - 2544
ISSN:
0020-1669
Resumen:
We report single-crystal X-band EPR and magnetic
measurements of the coordination polymer catena-(trans-(µ2-Fumarato)-tetraaqua-cobalt(II)), 1, and the Co(II)-doped Zn(II) analogue, 2, in different Zn:Co ratios. 1
presents two magnetically inequivalent high spin S = 3/2 Co(II) ions per unit cell, named A and B, in a distorted
octahedral environment coordinated to four water oxygen atoms and trans coordinated to two carboxylic
oxygen atoms from the fumarate anions, in which the Co(II) ions are linked by
hydrogen bonds and fumarate molecules. Magnetic susceptibility and
magnetization measurements of 1 indicate
weak antiferromagnetic exchange interactions between the S = 3/2 spins of the Co(II) ions in the crystal lattice. Oriented
single crystal EPR experiments of 1
and 2 were used to evaluate the
molecular g-tensor and the different
exchange coupling constants between the Co(II) ions, assuming an effective spin
S´= 1/2. Unexpectedly, the eigenvectors
of the molecular g-tensor were not
lying along any preferential bond direction, indicating that in high spin Co(II) ions in roughly
octahedral geometry with approximately axial EPR signals, the presence of
molecular pseudo axes in the metal site does not determine preferential
directions for the molecular g-tensor.
The EPR experiment and magnetic measurements, together with a theoretical
analyses relating the coupling constants obtained from both techniques, allowed
us to evaluate selectively the exchange coupling constant associated with
hydrogen bonds that connect magnetically inequivalent Co(II) ions (|JAB1/2|=0.55(2) cm-1) and the exchange coupling constant associated
with a fumarate bridge connecting equivalent Co(II) ions (|JAA1/2| ~ 0.25 (1) cm-1), in good agreement with the average J3/2 value determined from magnetic measurements.