The Ferromagnetic Coupling Between Cu II Ions via the m -Phenylene bridge May be Tuned:

1. INTRODUCTION The m-phenylene bridge has been suggested as a convenient way to induce ferromagnetic coupling between metallic spin carriers. This is to occur, presumably, through a spin polarization mechanism. Three synthetic [CuII2] complexes displaying this bridge, including ours, showed very different type of magnetic couplings. This behavior could be well simulated by DFT calculations. The theoretical studies have been extended to a series of model complexes, where the electronic properties of the ligand were modified. A correlation between the strength of the coupling and the total spin population on the central bridge is found, and this can be modulated by choosing appropiately the external substituents of the ligand. Predictions of very strong ferromagnetic interactions with certain ligands offer an attractive challenge to experimetal chemists. EXPERIMENT The three ligands and the corresponding [CuII2] complexes below where prepared and the magnetic coupling determined. The large differences are not obvious to explain. The couplig within the three experimental systems was simulated correctly by DFT. The coupling within a series of model complexes was also calculated. MODEL A J = +1.7 cm1 H2L1 H4L2 H2L3 MODEL B J = +4.4 cm1 MODEL E J = +39.1 cm1 MODEL C J = +12.3 cm1 [Cu2(L1)2] (1) [Cu2(L2)2]4+ (24+) [Cu2(L3)2] (3) MODEL D Jexp= -1.0 cm-1 Jexp= +16.8 cm-1 Jexp= +14.6 cm-1 J = +14.5 cm1 Hendrickson et al. Inorg. Chem. 1978, 17, 1834 Journaux et al. Angew. Chem. Int. Ed. 2001, 40, 3039 For Complex 3 This work Heisenberg Spin Hamiltonian J=+14.56 cm-1 zJ’=-0.98 cm-1 g=2.13 Bleaney-Bowers Equation and Molecular field approximation MODEL F PERSPECTIVES J = +325 cm1 This work suggests the possibility of tuning the coupling between CuII ions through a m-phenylene bridge using chemical tools. Ligand in MODEL F is predicted to give a J value of +325 cm-1. A correlation is found between the strength of the ferromagnetic coupling and the total spin population Σ|ρi| of the phenylene bridge. This is enhanced for ligands favouring localization of charge on the donor atom near the bridge (right form in the scheme below) ACKNOWLEDGEMENTS 350 300 Ministerio de Ciencia y Tecnología (Spain) and the Council of Scientific and Industrial Research (India) are kindly acknowledged 250 J / cm-1 200 150 100 50 0 0.2 0.4 0.6 0.8 1.0 1.2 Σ|ρi| The Ferromagnetic Coupling Between CuII Ions via the m-Phenylene bridge May be Tuned: Perspectives from Theory and Experiment Guillem Aromí, Joan Ribas, Juan J. Novoa, Jordi Ribas-Ariño, Debashis Ray Universitat de Barcelona, Departament de Química Inorgànica i CERQT, Diagonal 647, 08028 BARCELONA, Spain Department of Chemistry, Indian Institute of Technology, Kharagpur 721 302, India THEORY This work is featured in the recent publication; Chem. Commun. 2005, 5172-5174