Metallacryptate single-molecule magnets: effect of lower molecular symmetry on blocking temperature.
The structural characterization of complexes [Mn(II)4Mn(III)22(pdol)12(OCH3)12(O)16(N3)6] (1) and [Mn(II)4Mn(III)22(pdol)12(OCH3)12(O)16(OH)2(H3O)(OCH3)3].ClO4.5CH3OH (2), where pdol(2-) is di-2-pyridyl methanediol, reveals that each has a metallacryptand shell that encapsulates a manganese oxide core. Variable-temperature direct current magnetic susceptibility measurements on 2 indicate a paramagnetic ground state that results from an overall antiferromagnetic interaction in the cluster, with chiT values decreasing from 300 K (51.2 cm3 K mol(-1)) to 2 K (19.8 cm3 K mol(-1)). Variable-temperature alternating current magnetic susceptibility measurements imply that both 1 and 2 behave as single-molecule magnets. Fitting the frequency-dependent out-of-phase magnetic susceptibility to the Arrhenius equation yields an effective energy barrier, Ueff, to magnetization relaxation of 16.5 +/- 0.7 K (11.5 +/- 0.5 cm(-1)) for 1 and 36.2 +/- 2.0 K (25.1 +/- 1.4 cm(-1)) for 2. The larger value for 2 is in agreement with the lower molecular symmetry, larger magnetoanisotropy, and higher ground spin state of 2 compared to those of 1. This observation suggests a new strategy for increasing the blocking temperatures in high-nuclearity manganese clusters.
Zaleski
Curtis M
CM
Department of Chemistry, University of Michigan, Ann Arbor, Michigan 48109-1055, USA.
Depperman
Ezra C
EC
Dendrinou-Samara
Catherine
C
Alexiou
Maria
M
Kampf
Jeff W
JW
Kessissoglou
Dimitris P
DP
Kirk
Martin L
ML
Pecoraro
Vincent L
VL
D018360:Crystallography, X-Ray; D008280:Magnetics; D008345:Manganese / Q000737:chemistry*; D008958:Models, Molecular; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D013237:Stereoisomerism; D013696:Temperature
D009942:Organometallic Compounds; D008345:Manganese