Metallacryptate Single-Molecule Magnets: Effect of Lower Molecular Symmetry on Blocking Temperature
作者:Curtis M. Zaleski、Ezra C. Depperman、Catherine Dendrinou-Samara、Maria Alexiou、Jeff W. Kampf、Dimitris P. Kessissoglou、Martin L. Kirk、Vincent L. Pecoraro
DOI:10.1021/ja050951i
日期:2005.9.1
The structural characterization of complexes [(Mn4Mn22III)-Mn-II(pdol)(12)(OCH3)(12)(O)(16)(N-3)(6)] (1) and [Mn-4(II)-Mn-22(III)(pdol)(12)(OCH3)(12)(O)(16)(OH)(2)(H2O)(OCH3)(3)]center dot CIO4 center dot 5CH(3)OH (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 chi T values decreasing from 300 K (51.2 cm(3) K mol(-1)) to 2 K (19.8 cm(3) 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, U-eff, 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.
A Tetranuclear Mixed-Valent Mn$\rm{^{II}_{3}}$MnIV Compound with a (μ4-O)Mn4 Core This work was carried out in the frame of WG0010 of D21 COST action. The authors thank Prof. V. L. Pecoraro for his valuable suggestions. V.T. thanks Dr. Claudio Sangregorio and the Department of Chemistry, Florence, Italy for taking the magnetic measurements.
作者:Tereza Afrati、Catherine Dendrinou-Samara、Catherine P. Raptopoulou、Aris Terzis、Vassilis Tangoulis、Dimitris P. Kessissoglou
Synthesis and structure of : A new member of anion encapsulating metallamacrocyles
作者:Tereza Afrati、Catherine Dendrinou-Samara、Curtis M. Zaleski、Jeff W. Kampf、Vincent L. Pecoraro、Dimitris P. Kessissoglou
DOI:10.1016/j.inoche.2005.09.024
日期:2005.12
The reaction of copper(II) perchlorate with di-2-pyridyl ketone oxime yields the first 18-MC-6 complex with M-N-O connectivity, [Cu-6(pko)(6)ClO4(CH3CN)(6)] [Cu-6(pko)(6)(ClO4)(3)(CH3CN)(4)]- 8ClO(4) (.) 14CH(3)CN - H2O 1. In the solid state the cationic complex encapsulates a perchlorate anion within the central cavity. Magnetic susceptibility measurements reveal that the complex is diamagnetic. EPR measurements indicate that the complex dissociates in DMF. (c) 2005 Elsevier B.V. All rights reserved.