TY - JOUR
T1 - Studies of finite molecular chains
T2 - Synthesis, structural, magnetic and inelastic neutron scattering studies of hexa- And heptanuclear chromium horseshoes
AU - Ochsenbein, Stefan T.
AU - Tuna, Floriana
AU - Rancan, Marzio
AU - Davies, Rachel S.G.
AU - Muryn, Christopher A.
AU - Waldmann, Oliver
AU - Bircher, Roland
AU - Sieber, Andreas
AU - Carver, Graham
AU - Mutka, Hannu
AU - Fernandez-Alonso, Felix
AU - Podlesnyak, Andrew
AU - Engelhardt, Larry P.
AU - Timco, Grigore A.
AU - Güdel, Hans U.
AU - Winpenny, Richard E.P.
PY - 2008/6/9
Y1 - 2008/6/9
N2 - We report the synthesis and structural characterisation of a family of finite molecular chains, specifically [{[R2NH2] 3[Cr6F11(O2CCMe3) 10]}2] (in which R = nPr 1, Et 2, nBu 3), [{Et 2NH}2{[Et2NH2]3[Cr 7F12(O2C-CMe3)12][HO 2CCMe3]2}2] (4), [{[Me 2-NH2]3[Cr6F11(O 2CCMe3)10]·2.5 H2O} 4] (5) and [{[iPr2NH2]3[Cr 7F12(O2C-CMe3)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 tetrahorseshoe 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, JA = -1.1 meV and JB = -1.4 meV; JA is the exchange interactions at the tips of the horseshoe and JB 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 CrIII were also derived for the two compounds as: for 1, D Cr=-0.028 meV and |ECr| = 0.005 meV; for 6, DCr =-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.
AB - We report the synthesis and structural characterisation of a family of finite molecular chains, specifically [{[R2NH2] 3[Cr6F11(O2CCMe3) 10]}2] (in which R = nPr 1, Et 2, nBu 3), [{Et 2NH}2{[Et2NH2]3[Cr 7F12(O2C-CMe3)12][HO 2CCMe3]2}2] (4), [{[Me 2-NH2]3[Cr6F11(O 2CCMe3)10]·2.5 H2O} 4] (5) and [{[iPr2NH2]3[Cr 7F12(O2C-CMe3)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 tetrahorseshoe 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, JA = -1.1 meV and JB = -1.4 meV; JA is the exchange interactions at the tips of the horseshoe and JB 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 CrIII were also derived for the two compounds as: for 1, D Cr=-0.028 meV and |ECr| = 0.005 meV; for 6, DCr =-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.
KW - Chain complexes chromium
KW - EPR spectroscopy
KW - Magnetic measurements
KW - Neutron scattering
UR - http://www.scopus.com/inward/record.url?scp=53849136277&partnerID=8YFLogxK
U2 - 10.1002/chem.200800227
DO - 10.1002/chem.200800227
M3 - Article
AN - SCOPUS:53849136277
SN - 0947-6539
VL - 14
SP - 5144
EP - 5158
JO - Chemistry - A European Journal
JF - Chemistry - A European Journal
IS - 17
ER -