title: Molecule-Based Magnets: Ferro- and Antiferromagnetic Interactions in Copper(II)-Polyorganosiloxanolate Clusters.
abstract: The magnetic behavior of the clusters [(PhSiO(2))(6)Cu(6)(O(2)SiPh)(6)].6EtOH (1), Na(4)[(PhSiO(2))(12)Cu(4)].8(n)()BuOH (2), and K(4)[(C(2)H(3)SiO(2))(12)Cu(4)].6(n)()BuOH (3) has been investigated by combined magnetic susceptibility measurements and variable-temperature EPR techniques (9.25 and 245 GHz). The six copper(II) ions in the core of 1, which approaches 6/mmm symmetry, are ferromagnetically coupled as a result of the geometry at the bridging siloxanolate oxygen atoms (Cu-O-Cu = 91.5-94.6 degrees; J = -42 cm(-)(1) with H = J S(i)().S(i)()(+1), S(7) = S(1)). The ground S = 3 spin state is split in zero field mainly due to anisotropic exchange contributions (D = 0.30 cm(-)(1)). Notably, both the magnitude and the sign of the zero-field splitting parameter have been determined from HF-EPR spectra. Large antiferromagnetic Cu-Cu interactions (J approximately 200 cm(-)(1)) and an S = 0 ground state have been detected in the tetranuclear clusters 2 and 3 as a consequence of the larger Cu-O-Cu angles. The results presented in the paper are relevant to the search for new molecule-based magnetic materials.
authors.affiliation: Department of Chemistry, University of Florence, via Maragliano 75, 50144 Firenze, Italy, Department of Chemistry, University of Modena, via G. Campi 183, 41100 Modena, Italy, Laboratoire des Champs Magnetiques Intenses, CNRS, Grenoble, France, and A. N. Nesmeyanov Institute of Organoelement Compounds (INEOS), 28 Vavilov St., Moscow 117813, Russia.
authors.forename: Eva
authors.initials: E
authors.lastname: Rentschler
authors.forename: Dante
authors.initials: D
authors.lastname: Gatteschi
authors.forename: Andrea
authors.initials: A
authors.lastname: Cornia
authors.forename: Antonio C.
authors.initials: AC
authors.lastname: Fabretti
authors.forename: Anne-Laure
authors.initials: AL
authors.lastname: Barra
authors.forename: Olga I.
authors.initials: OI
authors.lastname: Shchegolikhina
authors.forename: Alexandr A.
authors.initials: AA
authors.lastname: Zhdanov