title: Huge dielectric response and molecular motions in paddle-wheel [Cu(II)2(adamantylcarboxylate)4(DMF)2]⋅(DMF)2.
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).
authors.affiliation: Ordered Matter Science Research Center, Southeast University, Nanjing 211189, PR China.
authors.forename: Qiong
authors.initials: Q
authors.lastname: Ye
authors.forename: Kiyonori
authors.initials: K
authors.lastname: Takahashi
authors.forename: Norihisa
authors.initials: N
authors.lastname: Hoshino
authors.forename: Takemitsu
authors.initials: T
authors.lastname: Kikuchi
authors.forename: Tomoyuki
authors.initials: T
authors.lastname: Akutagawa
authors.forename: Shin-ichiro
authors.initials: S
authors.lastname: Noro
authors.forename: Sadamu
authors.initials: S
authors.lastname: Takeda
authors.forename: Takayoshi
authors.initials: T
authors.lastname: Nakamura
mesh_terms: D000218:Adamantane / Q000737:chemistry*; D002264:Carboxylic Acids / Q000737:chemistry*; D003300:Copper / Q000737:chemistry*; D018360:Crystallography, X-Ray; D004126:Dimethylformamide; D005559:Formamides / Q000737:chemistry*; D008024:Ligands; D008958:Models, Molecular; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000737:chemistry*
chemical_list: D002264:Carboxylic Acids; D005559:Formamides; D008024:Ligands; D009942:Organometallic Compounds; D003300:Copper; D004126:Dimethylformamide; D000218:Adamantane