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Huge Dielectric Response and Molecular Motions in Paddle‐Wheel [Cu II 2 (Adamantylcarboxylate) 4 (DMF) 2 ]⋅(DMF) 2
Author(s) -
Ye Qiong,
Takahashi Kiyonori,
Hoshino Norihisa,
Kikuchi Takemitsu,
Akutagawa Tomoyuki,
Noro Shinichiro,
Takeda Sadamu,
Nakamura Takayoshi
Publication year - 2011
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201101743
Subject(s) - chemistry , crystal (programming language) , molecule , crystallography , dielectric , crystal structure , carboxylate , analytical chemistry (journal) , stereochemistry , organic chemistry , materials science , optoelectronics , computer science , programming language
Abstract The temperature‐dependent dynamic properties of [Cu II 2 (ADCOO) 4 (DMF) 2 ]⋅(DMF) 2 ( 1 ) and [Cu II 2 (ADCOO) 4 (AcOEt) 2 ] ( 2 ) crystals were examined by X‐ray crystallography, 1 H 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 II 2 (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 II 2 (ADCOO) 4 ] moiety, forming [Cu II 2 (ADCOO) 4 (DMF) 2 ] and [Cu II 2 (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 increasing 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 ).