Magnetic properties of six-coordinated high-spin cobalt(II) complexes:: Theoretical background and its application

In this contribution we study and analyse the influence of the different parameters involved in the magnetic susceptibility of six-coordinated high-spin Co(II) complexes. We propose an empirical expression to fit the magnetic susceptibility of polycrystalline samples of mononuclear Co(II) complexes with an axial distortion, the variable parameters being Delta (axial distortion), alpha (orbital reduction factor) and lambda (spin-orbit coupling). This expression avoids solving the 12 x 12 matrix associated to the distortion of the T-4(1g) term. In order to take into account the magnetic coupling (J) in the polynuclear Co(II) complexes, a perturbational approach is proposed to describe their magnetic susceptibility in the whole temperature range (2-300 K) as a function of J, Delta, alpha and lambda. This approach is valid in the limit of the weak magnetic coupling as compared to the spin-orbit coupling, vertical bar J/lambda vertical bar < 0.1. The model allows the treatment of each cobalt(II) ion in axial symmetry as an effective spin S-eff = 1/2. That causes a drastic reduction of the matrix size of the polynuclear compounds from 12(n) x 12(n) to 2(n) x 2(n), n being the number of Co(II) ions in the complex. The main advantage of the model is to make possible the fit of the magnetic susceptibility data of those polynuclear Co(II) complexes whose high nuclearity involved intractable matrices. (c) 2008 Elsevier B. V. All rights reserved.