Theoretical and computational investigation of meta-phenylene as ferromagnetic coupler in nitronyl nitroxide diradicals

• Published in: Theoretical chemistry accounts Vol. 133; no. 4
• Main Authors: Pal, Arun K., Mañeru, Daniel Reta, Latif, Iqbal A., Moreira, Ibério de P. R., Illas, Francesc, Datta, Sambhu N.
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 01.04.2014
• Subjects: Atomic/Molecular Structure and Spectra; Chemistry; Chemistry and Materials Science; Inorganic Chemistry; Organic Chemistry; Physical Chemistry; Regular Article; Theoretical and Computational Chemistry; Inductive effect; Dihedral angle; Diradical; Magnetic coupling constant; DFT; NICS
• ISSN: 1432-881X; 1432-2234
• DOI: 10.1007/s00214-014-1472-y

We predict the magnetic exchange coupling constant ( J ) for 27 m -phenylene-based nitronyl nitroxide (NN) diradicals with nine different substituents in three unique (common ortho , ortho – meta and common meta ) positions on the coupler unit by using the broken-symmetry density functional methodology. For all investigated diradicals, J values are computed using B3LYP, B3LYP-D3 and M06-2X functionals with 6–311+G(d,p) basis set. The J M06-2X value is larger than J B3LYP and closer to the observed value for the unsubstituted species. Substitutions at common ortho position always produce a greater angle of twist between the spin source and the coupler units. When the twist angle is very large, the nature of intramolecular magnetic interaction changes from ferromagnetic to antiferromagnetic. In these cases, the coupler–NN bond order becomes small. Substitution at the common meta position of m -phenylene in the diradical has little steric and hydrogen-bonding effects. Electron-withdrawing groups reveal a specific trend for single-atom substitution. An ortho substitution generally decreases J and a meta substitution always increases J with a decreasing −I effect. Variation of J with planarity as well as Hammett constant is investigated. The nucleus-independent chemical shift value is found to decrease from the corresponding mono-substituted phenyl derivatives. The dependence of J on these factors is explored.