systems are good spin linkers. Indeed, our analysis shows that the spin delocalization extent in the ligand is severely damped by bond alternation and therefore
reduces the interference effects between the spin waves of remote magnetic sites.
One should note that the spin-polarizability of hydrocarbon bridging ligands
increases with the near degeneracy of the lowest spin states. These ligands might
finally behave as non-innocent ligands.
From a conceptual point of view, this chapter also recalls the essential difference
between the spin delocalization and spin polarization mechanisms [71, 72]. The
former is governed by mono-electronic operators while the latter is a bi-electronic.
This is a matter of frequent confusion. Indeed one sometimes unduly speaks of spin
polarization of the ligand as soon as its atoms bear some spin densities [68–70]. In
most cases this is simply a delocalization effect as the magnetic orbitals have
delocalization tails on the ligand. Happily enough the spin delocalization and the
spin polarization quite often work in the same direction, regarding the sign and
magnitude of the magnetic couplings. The spin polarization may concern subsets of
orbitals which, for symmetry reasons, are not affected by the spin delocalization, for
instance the σ MOs of π radicals. When it affects the subsystems of MOs already
concerned by the spin delocalization (for instance the π MOs of π radicals) the spin
polarization reinforces the contrast in the spin density distribution on the ligand,
increasing the positive spin densities and introducing negative spin densities on the
atoms which were on nodal positions of the Hückel SOMOs.
References
1. Gatteschi D, Kahn O, Miller JS, Palacio F (eds) (1991) Magnetic molecular materials. Kluwer,
Dordrecht
2. Kahn O (1993) Molecular magnetism. VCH, Weinheim
3. Gatteschi D (1994) Adv Mater 6:635–645
4. Miller JS, Epstein AJ (1994) Angew Chem Int Ed Engl 33:385–415
5. (1996) Molecule-based magnetic materials. ACS Symposium series, vol 644
6. Itoh K, Kinoshita M (2000) Molecular magnetism. Gordon and Breach, Tokyo
7. Long J (2003) In: Yang P (ed) Chemistry of nanostructured materials. World Scientific
Publishing, Hong Kong
8. (2005) Coord Chem Rev 249. Special issue “Molecular magnetism”
9. Gatteschi D, Bogani L, Cornia A, Mannini M, Sorace L, Sessoli R (2008) Solid State Sci
10:1701–1709
10. Malrieu J-P, Caballol R, Calzado CJ, de Graaf C, Guihéry N (2014) Chem Rev 114:429
11. Moreira I de PR, Illas F (2006) Phys Chem Chem Phys 8:1645
12. Bencini V (2008) Inorg Chim Acta 361:3820
13. Neese F (2009) Coord Chem Rev 253:526
14. Iwamura H (2013) Polyhedron 66:3–14
15. Makarova TL, Palacio F (eds) (2006) Carbon-based magnetism: an overview of metal-free
carbon-based compounds and materials. Elsevier, Amsterdam
16. Nakano M, Fukui H, Minami T, Yoneda K, Shigeta Y, Kishi R, Champagne B, Botek E,
Kubo T, Ohta K, Kamada K (2011) Theor Chem Acc 130:711–724
14 Magnetic Properties of Conjugated Hydrocarbons …
393
reduces the interference effects between the spin waves of remote magnetic sites.
One should note that the spin-polarizability of hydrocarbon bridging ligands
increases with the near degeneracy of the lowest spin states. These ligands might
finally behave as non-innocent ligands.
From a conceptual point of view, this chapter also recalls the essential difference
between the spin delocalization and spin polarization mechanisms [71, 72]. The
former is governed by mono-electronic operators while the latter is a bi-electronic.
This is a matter of frequent confusion. Indeed one sometimes unduly speaks of spin
polarization of the ligand as soon as its atoms bear some spin densities [68–70]. In
most cases this is simply a delocalization effect as the magnetic orbitals have
delocalization tails on the ligand. Happily enough the spin delocalization and the
spin polarization quite often work in the same direction, regarding the sign and
magnitude of the magnetic couplings. The spin polarization may concern subsets of
orbitals which, for symmetry reasons, are not affected by the spin delocalization, for
instance the σ MOs of π radicals. When it affects the subsystems of MOs already
concerned by the spin delocalization (for instance the π MOs of π radicals) the spin
polarization reinforces the contrast in the spin density distribution on the ligand,
increasing the positive spin densities and introducing negative spin densities on the
atoms which were on nodal positions of the Hückel SOMOs.
References
1. Gatteschi D, Kahn O, Miller JS, Palacio F (eds) (1991) Magnetic molecular materials. Kluwer,
Dordrecht
2. Kahn O (1993) Molecular magnetism. VCH, Weinheim
3. Gatteschi D (1994) Adv Mater 6:635–645
4. Miller JS, Epstein AJ (1994) Angew Chem Int Ed Engl 33:385–415
5. (1996) Molecule-based magnetic materials. ACS Symposium series, vol 644
6. Itoh K, Kinoshita M (2000) Molecular magnetism. Gordon and Breach, Tokyo
7. Long J (2003) In: Yang P (ed) Chemistry of nanostructured materials. World Scientific
Publishing, Hong Kong
8. (2005) Coord Chem Rev 249. Special issue “Molecular magnetism”
9. Gatteschi D, Bogani L, Cornia A, Mannini M, Sorace L, Sessoli R (2008) Solid State Sci
10:1701–1709
10. Malrieu J-P, Caballol R, Calzado CJ, de Graaf C, Guihéry N (2014) Chem Rev 114:429
11. Moreira I de PR, Illas F (2006) Phys Chem Chem Phys 8:1645
12. Bencini V (2008) Inorg Chim Acta 361:3820
13. Neese F (2009) Coord Chem Rev 253:526
14. Iwamura H (2013) Polyhedron 66:3–14
15. Makarova TL, Palacio F (eds) (2006) Carbon-based magnetism: an overview of metal-free
carbon-based compounds and materials. Elsevier, Amsterdam
16. Nakano M, Fukui H, Minami T, Yoneda K, Shigeta Y, Kishi R, Champagne B, Botek E,
Kubo T, Ohta K, Kamada K (2011) Theor Chem Acc 130:711–724
14 Magnetic Properties of Conjugated Hydrocarbons …
393