Technical Report of ISSP Ser. A: Number 2791

Abstract

The crystal of p-fluorophenyl nitronyl nitroxide (2-(4-fluorophenyl) 4,4,5,5-tetramethyl 4,5-dihydro-1H-imidazol 1-oxyl 3-N-oxide, abbreviated as p-FPNN) radical has been found to possess a dimeric structure. Each dimer is related to adjacent ones by four-fold screw symmetry to form a three-dimensional network. The temperature dependence of the paramagnetic susceptibility is explained by the formation of a triplet state within the dimer and additional interdimer ferromagnetic interactions. The intra-and interdimer exchange interactions are estimated to be J/k(sub B) = 5.0 K and J'/k(sub B) = 0.02 K, respectively. The molecular arrangement in the dimer suggests that the intermolecular interactions between the NO group and the phenyl ring are favorable to ferromagnetic coupling. Slight structural change below about 100 K has been studied by use of EPR (Electron Paramagnetic Resonance) and X-ray diffraction.

p-フルオロフェニル・ニトロニル・ニトロキシド・ラジカルの結晶が2量体構造をもつことがわかった。各2量体は4重ら施対称性によって近接のものに関係付けられ、3次元ネットワークを形成する。常磁性磁化率の温度依存性は、2量体内の3重項状態の形成と2量体間強磁性相互作用によって説明される。2量体内および2量体間交換相互作用は、それぞれJ/κB=5.0KおよびJ/κB=0.02Kと推定された。2量体内の分子配置は、NO基とフェニル環の分子間相互作用が強磁性結合をもたらすことを示唆している。約100K以下の若干の構造変化を電子常磁性共鳴(EPR)およびX線回折によって調べた。