title: Metallacryptate single-molecule magnets: effect of lower molecular symmetry on blocking temperature.
abstract: 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.
authors.affiliation: Department of Chemistry, University of Michigan, Ann Arbor, Michigan 48109-1055, USA.
authors.forename: Curtis M
authors.initials: CM
authors.lastname: Zaleski
authors.forename: Ezra C
authors.initials: EC
authors.lastname: Depperman
authors.forename: Catherine
authors.initials: C
authors.lastname: Dendrinou-Samara
authors.forename: Maria
authors.initials: M
authors.lastname: Alexiou
authors.forename: Jeff W
authors.initials: JW
authors.lastname: Kampf
authors.forename: Dimitris P
authors.initials: DP
authors.lastname: Kessissoglou
authors.forename: Martin L
authors.initials: ML
authors.lastname: Kirk
authors.forename: Vincent L
authors.initials: VL
authors.lastname: Pecoraro
mesh_terms: 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
chemical_list: D009942:Organometallic Compounds; D008345:Manganese