Journal
CHEMISTRY-A EUROPEAN JOURNAL
Volume 17, Issue 51, Pages 14442-14449Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/chem.201101743
Keywords
carboxylate ligands; copper; dielectric constants; metal-metal interactions; molecular devices
Categories
Funding
- Ministry of Education, Culture, Sports, Science, and Technology of Japan
- Management Expenses Grants for National Universities Corporations
- National Natural Science Foundation of China [20701007, 91022003]
- Outstanding Young Teachers of Southeast University
- Japan Society for the Promotion of Science [JSPSP08040]
- Grants-in-Aid for Scientific Research [23655109, 23350085] Funding Source: KAKEN
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The temperature-dependent dynamic properties of [Cu-2(II)(ADCOO)(4)(DMF)(2)]center dot(DMF)(2) (1) and [Cu-2(II)(ADCOO)(4)(AcOEt)(2)] (2) crystals were examined by X-ray crystallography, H-1 NMR spectroscopy, and measurements of the dielectric constants and magnetic susceptibilities (ADCOO = adamantane carboxylate, DMF = N,N-dimethylformamide, and AcOEt = ethyl acetate). In both crystals, four ADCOO groups bridged a binuclear Cu-II-Cu-II bond, forming a paddle-wheel [Cu-2(II)(ADCOO)(4)] structure. The oxygen atoms of two DMF molecules in crystal 1 and two AcOEt molecules in crystal 2 were coordinated at axial positions of the [Cu-2(II)(ADCOO)(4)] moiety, forming [Cu-2(II)-(ADCOO)(4)(DMF)(2)] and [Cu-2(II)(ADCOO)(4)(AcOEt)(2)], respectively. Two additional DMF molecules were included in the unit cell of crystal 1, whereas AcOEt was not included in the unit cell of crystal 2. The structural analyses of crystal 1 at 300 K showed three-fold rotation of the adamantyl groups, whereas rotation of the adamantyl groups of crystal 2 at 300 K was not observed. Thermogravimetric measurements of crystal 1 indicated a gradual elimination of DMF upon in-creasing the temperature above 300 K. The dynamic behavior of the crystallized DMF yielded significant temperature-dependent dielectric responses in crystal 1, which showed a huge dielectric peak at 358 K in the heating process. In contrast, only small frequency-dependent dielectric responses were observed in crystal 2 because of the freezing of the molecular rotation of the adamantyl groups. The magnetic behavior was dominated by the strong antiferromagnetic coupling between the two S = 1/2 spins of the Cu-II-Cu-II site, with magnetic exchange energies (J) of -265 K (crystal 1) and -277 K (crystal 2).
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