Roland Bircher

Studies of Finite Molecular Chains: Synthesis, Structural, Magnetic and Inelastic Neutron Scattering Studies of Hexa- and Heptanuclear Chromium Horseshoes

We report the synthesis and structural characterisation of a family of finite molecular chains, specifically [{[R(2)NH(2)](3)[Cr(6)F(11)(O(2)CCMe(3))(10)]}(2)] (in which R=nPr 1, Et 2, nBu 3), [{Et(2)NH}(2){[Et(2)NH(2)](3)[Cr(7)F(12)(O(2)CCMe(3))(12)][HO(2)CCMe(3)](2)}(2)] (4), [{[Me(2)NH(2)](3)[Cr(6)F(11)(O(2)CCMe(3))(10)]2.5 H(2)O}(4)] (5) and [{[iPr(2)NH(2)](3)[Cr(7)F(12)(O(2)CCMe(3))(12)]}(2)] (6). The structures all contain horseshoes of chromium centres, with each Cr...Cr contact within the horseshoe bridged by a fluoride and two pivalates. The horseshoes are linked through hydrogen bonds to the secondary ammonium cations in the structure, leading to di- and tetra-horseshoe structures. Through magnetic measurements and inelastic neutron scattering studies we have determined the exchange coupling constants in 1 and 6. In 1 it is possible to distinguish two exchange interactions, J(A)=-1.1 meV and J(B)=-1.4 meV; J(A) is the exchange interactions at the tips of the horseshoe and J(B) is the exchange within the body of the horseshoe (1 meV=8.066 cm(-1)). For 6 only one interaction was needed to model the data: J=-1.18 meV. The single-ion anisotropy parameters for Cr(III) were also derived for the two compounds as: for 1, D(Cr)=-0.028 meV and |E(Cr)|=0.005 meV; for 6, D(Cr)=-0.031 meV. Magnetic-field-dependent inelastic neutron scattering experiments on 1 allowed the Zeeman splitting of the first two excited states and level crossings to be observed. For the tetramer of horseshoes (5), quantum Monte Carlo calculations were used to fit the magnetic susceptibility behaviour, giving two exchange interactions within the horseshoe (-1.32 and -1.65 meV) and a weak inter-horseshoe coupling of +0.12 meV. Multi-frequency variable-temperature EPR studies on 1, 2 and 6 have also been performed, allowing further characterisation of the spin Hamiltonian parameters of these chains.

Pressure dependence of the magnetic anisotropy in the single-molecule magnet Mn 4 O 3 Br ( O Ac ) 3 ( dbm ) 3

The anisotropy splitting in the ground state of the single-molecule magnet

New family of ferric spin clusters incorporating redox-active ortho-dioxolene ligands.

{\mathrm{Mn}}_{4}{\mathrm{O}}_{3}\mathrm{Br}{(\mathrm{O}\mathrm{Ac})}_{3}{(\mathrm{dbm})}_{3}

Transverse magnetic anisotropy in Mn12 acetate: Direct determination by inelastic neutron scattering

is studied by inelastic neutron scattering as a function of hydrostatic pressure. This allows a tuning of the anisotropy and thus the energy barrier for slow magnetization relaxation at low temperatures. The value of the negative axial anisotropy parameter

Exchange-coupling constants, spin density map, and Q dependence of the inelastic neutron scattering intensity in single-molecule magnets

{D}_{\text{cluster}}

Standing spin waves in an antiferromagnetic molecular Cr6 horseshoe

changes from

Single-Molecule Magnets Under Pressure

\ensuremath{-}0.0627(1)\phantom{\rule{0.3em}{0ex}}\mathrm{meV}

Ferromagnetic and Antiferromagnetic Intermolecular Interactions in a New Family of Mn4 Complexes with an Energy Barrier to Magnetization Reversal

at ambient to

Mixed-Valent Cobalt Spin Clusters: a Hexanuclear Complex and a One-Dimensional Coordination Polymer Comprised of Alternating Hepta- and Mononuclear Fragments

\ensuremath{-}0.0603(3)\phantom{\rule{0.3em}{0ex}}\mathrm{meV}

Magnetic Polyoxometalates: Anisotropic Exchange Interactions in the Moiety of [(NaOH2)Co3(H2O)(P2W15O56)2]17-

at