Mondal Arpan, Kharwar Ajit Kumar, Konar Sanjit
Department of Chemistry , Indian Institute of Science Education and Research Bhopal , Bhopal Bypass Road, Bhauri , Bhopal 462066 , MP , India.
Inorg Chem. 2019 Aug 19;58(16):10686-10693. doi: 10.1021/acs.inorgchem.9b00615. Epub 2019 Aug 5.
We have demonstrated the effect of a solvent at the second coordination sphere on slow relaxation of magnetization for hepta-coordinated cobalt(II) complexes with the formulas Co(HL)(DMF)(HO)·(DMF) (), Co(HL)(MeOH)(HO)·(MeOH) (), and Co(HL)(DEF)(HO) () (HL = 2,2'-(pyridine-2,6-diylbis(ethan-1-yl-1-ylidene))bis(-phenylhydrazinecarboxamide). Structural analysis reveals that the presence of lattice solvent molecule in and dramatically changes the crystal packing and noncovalent interactions as compared to where no solvent molecule is present in the crystal lattice. The dc and ac magnetic susceptibility measurements reveal the presence of easy-plane magnetic anisotropy for all the complexes, and field induced slow relaxation behavior has been observed above 2 K for and in contrast to due to the availability of the solvent molecules in the crystal lattice. The calculations further support the sign of and the negligible effect of the first co-ordination sphere, as almost similar values were obtained for all the complexes. The field and temperature dependence of relaxation time confirm that quantum tunnelling of magnetization (QTM) plays a major role in slow magnetic relaxation, and thermal dependence like an optical or acoustic Raman pathway is also important. To further analyze the effect of dipole-dipole interaction on slow magnetic relaxation, a dilution experiment has been performed.
我们已经证明了在七配位钴（II）配合物Co(HL)(DMF)(HO)·(DMF)（）、Co(HL)(MeOH)(HO)·(MeOH)（）和Co(HL)(DEF)(HO)（）（HL = 2,2'-（吡啶-2,6-二基双（乙烷-1-亚基））双（-苯肼甲酰胺））中，第二配位层的溶剂对磁化强度缓慢弛豫的影响。结构分析表明，与晶格中不存在溶剂分子的相比，和中晶格溶剂分子的存在显著改变了晶体堆积和非共价相互作用。直流和交流磁化率测量表明，所有配合物都存在易面磁各向异性，并且由于晶格中存在溶剂分子，与相比，在2 K以上观察到了和的场诱导缓慢弛豫行为。计算进一步支持了的符号以及第一配位层的可忽略不计的影响，因为所有配合物获得的几乎相似。弛豫时间的场和温度依赖性证实，磁化强度的量子隧穿（QTM）在缓慢磁弛豫中起主要作用，并且像光学或声学拉曼途径那样的热依赖性也很重要。为了进一步分析偶极-偶极相互作用对缓慢磁弛豫的影响，进行了稀释实验。
