Rajca Andrzej, Wongsriratanakul Jirawat, Rajca Suchada, Cerny Ronald L
Department of Chemistry, University of Nebraska, Lincoln, 68588-0304, USA.
Chemistry. 2004 Jul 5;10(13):3144-57. doi: 10.1002/chem.200306036.
Synthesis and magnetic studies of annelated macrocyclic polyradicals and a related high-spin polymer with macrocyclic repeat units are described. Polyarylmethyl polyether precursors to the polyradicals and the related polymer are prepared by using Negishi cross-coupling of difunctionalized calix[4]arene-based macrocycles. The three lowest homologues, with high degree of monodispersity, are tetradecaether (14-ether) 3-(OCH(3))(14), octacosaether (28-ether) 4-(OCH(3))(28), and dotetracontaether (42-ether) 5-(OCH(3))(42), in which 2, 4, and 6 calix[4]arene-based macrocycles are annelated to the center macrocycle, respectively. The evidence for their annelated structures (ladder connectivities) is based upon FAB-MS and the (1)H NMR based end-group analysis. The absolute masses (4-12 kDa) were determined by FAB-MS and GPC/MALS. Small angle neutron scattering (SANS) provides the radii of gyration of 1.7, 2.0, and 3.2 nm for 4-(OCH(3))(28), 5-(OCH(3))(42), and polymer 6-(OCH(3))(n), respectively. The corresponding polyarylmethyl polyradicals 3 and 4, and polymer 6 possess average values of S approximately 6-7, S approximately 10, and S approximately 18, respectively, as determined by SQUID magnetometry and numerical fits to linear combinations of Brillouin functions. The quantitative values of magnetization at saturation and of magnetic susceptibilities indicate that about 40-60 % of unpaired electrons are present at low temperatures (T=1.8-5 K). For polyradical 3, the variable temperature magnetic data are fit to the Heisenberg Hamiltonian based model. The variable magnetic field data at low temperatures are also fit to a percolation-based model for organic spin cluster, with random distribution of chemical defects, and ferromagnetic versus antiferromagnetic couplings, providing quantitative agreement between the experiment and the theory. For polyradical 3 (with S approximately 6-7), annealing at room temperature for 0.5 h leads to a polyradical with S approximately 5.
本文描述了稠合大环多自由基及一种具有大环重复单元的相关高自旋聚合物的合成与磁性研究。通过基于杯[4]芳烃的双官能化大环的根岸交叉偶联反应制备了多自由基及相关聚合物的聚芳甲基聚醚前体。三种最低同系物具有高度单分散性，分别为十四醚（14 - 醚）3-(OCH(3))(14)、二十八醚（28 - 醚）4-(OCH(3))(28)和四十二醚（42 - 醚）5-(OCH(3))(42)，其中分别有2、4和6个基于杯[4]芳烃的大环稠合到中心大环上。它们稠合结构（梯状连接性）的证据基于快原子轰击质谱（FAB - MS）和基于核磁共振氢谱（(1)H NMR）的端基分析。通过FAB - MS和凝胶渗透色谱/多角度激光光散射（GPC/MALS）测定了绝对质量（4 - 12 kDa）。小角中子散射（SANS）分别给出了4-(OCH(3))(28)、5-(OCH(3))(42)和聚合物6-(OCH(3))(n)的回转半径为1.7、2.0和3.2 nm。通过超导量子干涉仪磁强计（SQUID）磁强测定以及对布里渊函数线性组合的数值拟合确定，相应的聚芳甲基多自由基3和4以及聚合物6的平均自旋值S分别约为6 - 7、约为10和约为18。饱和磁化强度和磁化率的定量值表明，在低温（T = 1.8 - 5 K）下约40 - 60%的未成对电子存在。对于多自由基3，变温磁性数据符合基于海森堡哈密顿量的模型。低温下的变磁场数据也符合基于有机自旋簇的渗流模型，该模型考虑了化学缺陷的随机分布以及铁磁与反铁磁耦合，实验与理论之间提供了定量一致性。对于多自由基3（S约为6 - 7），在室温下退火0.5小时会得到一个S约为5的多自由基。
