Structural and Magnetic Studies on Two-Dimensional Square Planar Lattice Magnets Composed of Organic Radical Cation Salts (Benzo[1,2-d:4,5-d′]Bis[1,3,2]dithiazolyl-2-zolium)·X (X = TlBr₄, TlI₄, and InI₄)

The magnetostructural correlation was investigated in three organic radical cation salts based on the monocation of benzo[1,2-d:4,5-d′]bis[1,3,2]dithiazolyl (BBDTA), which is an S = 1/2 system, and the tetrahedral diamagnetic monoanions, TlBr4− (1), TlI4− (2), and InI4− (3), by analysis of their crystal structures and magnetic properties. X-ray diffraction studies showed that these three salts consisted of alternatively stacked layers of the diamagnetic anions layers and the organic cation layers in which BBDTA+ formed a square planar lattice, which is rare in organic radical crystals. 1 exhibited canted antiferromagnetism with an antiferromagnetic interaction in the organic cation layer below 11.6 K, whereas 2 and 3 showed metamagnetism with a ferromagnetic interaction in the organic cation layer below 8.9 and 11.3 K, respectively. Their intra- and interlayer magnetic coupling constants, 2J/kB and zJ′/kB, were estimated to be −11.2 and −4.1 K for 1, +11.4 and −3.7 K for 2, and +12.8 and −2.3 K for 3, respectively, using a two-dimensional square planar S = 1/2 Heisenberg model with mean field approximation. A consideration of the molecular orbitals showed that the differences in the intralayer magnetic interactions in 1 and, 2 or 3, originate in the molecular orientation of BBDTA+ in the organic cation layer. Overlap relation between the singly occupied molecular orbitals (SOMOs) of the nearest neighbor BBDTA+ pairs was found in 1, whereas an orthogonal relation was found in 2 and 3.本研究针对三种基于苯并[1,2-d:4,5-d′]双[1,3,2]二噻唑基（benzo[1,2-d:4,5-d′]bis[1,3,2]dithiazolyl，BBDTA）一价阳离子的有机自由基阳离子盐，开展磁结构关联研究。该体系自旋状态为S=1/2，分别结合三种四面体抗磁性一价阴离子：TlBr4−（1）、TlI4−（2）与InI4−（3），研究通过晶体结构与磁性能分析完成。X射线衍射研究表明，这三种盐均由抗磁性阴离子层与有机阳离子层交替堆叠构成，其中BBDTA+形成了有机自由基晶体中较为罕见的正方形平面晶格。在11.6 K以下，化合物1表现出倾斜反铁磁性，其有机阳离子层内存在反铁磁相互作用；而化合物2与3则分别在8.9 K和11.3 K以下呈现变磁性，其有机阳离子层内存在铁磁相互作用。采用二维正方形平面S=1/2海森堡模型结合平均场近似，我们估算得到三种化合物的层内与层间磁耦合常数2J/kB和zJ′/kB分别为：化合物1的−11.2 K与−4.1 K，化合物2的+11.4 K与−3.7 K，以及化合物3的+12.8 K与−2.3 K。对分子轨道的分析显示，化合物1与2、3之间的层内磁相互作用差异，源于有机阳离子层内BBDTA+的分子取向差异：在化合物1中，最近邻BBDTA+离子对的单电子占据分子轨道（singly occupied molecular orbitals，SOMOs）存在轨道重叠关系；而在化合物2与3中则呈现正交关系。