Quantitative analysis of the magnetism of the meta-(methoxy)phenyl nitronyl nitroxide crystal: A bottom–up analysis of a crystal presenting competing ferro and antiferromagnetic interactions

• Published in: Polyhedron 2005-11, Vol.24 (16), p.2368-2376
• Main Authors: Deumal, Mercè, Robb, Michael A., Novoa, Juan J.
• Format: Article
• Language: English
• Subjects: m-(Methoxy)phenyl nitronyl nitroxide; Magnetic exchange pathways; Magnetic susceptibility simulation; Molecule-based magnetism; Theoretical calculations
• ISSN: 0277-5387
• DOI: 10.1016/j.poly.2005.03.110

The magnetic topology of the m-(OMe)PhNN crystal consists of bent bc-planes defined by FM J(d3) and AFM J(d4) pair interactions that form a three-dimensional network by means of AFM J(d2) exchange interactions. This complex network of competing FM and AFM pathways does not allow a sounding prediction of the macroscopic magnetic susceptibility χ( T) using qualitative arguments. Our first principles bottom-up theoretical procedure numerically computes the χT versus T curve that fully reproduces the experimental shape. Preliminary tests have been carried out in order to uncover the changes needed to modify the dominant AFM behavior of the m-(OMe)PhNN crystal into a dominant FM behavior. Crystals of the meta isomer of the (methoxy)phenyl nitronyl nitroxide radical, m-(OMe)PhNN, present the characteristics of an antiferromagnet (paramagnetic θ = −0.97 K, | J| = 1.6 cm −1, [L. Angeloni, A. Caneschi, L. David, A. Fabretti, F. Ferraro, D. Gatteschi, A. le Lirzin, R. Sessoli, J. Mater. Chem. 4 (1994) 1047]). Using our quantitative bottom–up approach, we analyze here the magnetism of this crystal by first computing its magnetic topology and, then, using this information, the macroscopic magnetic susceptibility χ( T) of the crystal. The crystal presents one ferro and two antiferromagnetic exchange interactions, J AB , of similar strength (+0.20, −0.20 and −0.11 cm −1) that create a complex three-dimensional magnetic topology of interacting planes. This complex network of competing ferro and antiferromagnetic pathways does not allow a sounding prediction of the macroscopic magnetic susceptibility using qualitative considerations. Our approach computes the χT versus T curve that fully reproduces the experimental shape.