| Popis: |
In most magnetic molecular clusters studied in the literature, localized moments of metal ions are coupled by superexchange interactions via ligand entities which are parts of molecular clusters. There is a limited number of studies where magnetic behaviour arises from unfilled molecular orbitals delocalized over the entire metal cores of molecular metal clusters [J. Sinzing et al., Phys. Rev. Lett. 81 (1998) 3211]. This type of magnetism is present in compounds with paramagnetic hexanuclear tantalum halide clusters. Temperature dependent magnetic susceptibility measurements for the compound [Ta_6Cl_12(CH_3OH)_6]Br_3 (I) and temperature dependent magnetic susceptibility anisotropy measurements for the compound [Ta_6Cl_12(CH_3OH)_6]Br_3· ; ; 4H_2O (II) can be interpreted as Bonner-Fisher one-dimensional model of interacting magnetic centres [J. C. Bonner, M. E. Fisher, Phys. Rev. A, 135 (1964) 640]. Structural data for compounds (I) and (II) are available from the literature [N. Brničević et al., Inorg. Chem. 31 (1992) 3294]. Compound (I) crystallizes in space group, a = b = 19.127 (4) Å ; ; , c = 8.565 (1) Å ; ; , and compound (II) in C2/m space group, a = 12.187 (14) Å ; ; , b = 15.793 (4) Å ; ; , c = 9.182 (6) Å ; ; , β = 99.05 (3)o. Magnetic measurements will be discussed in view of the structural data with special attention to the crystallographic origin of anisotropy for compound (II). |
