Magneto-Structural Correlations in Cu(tn)Cl₂ (tn = 1,3-Diaminopropane): Two-Dimensional Spatially Anisotropic Triangular Magnet Formed by Hydrogen Bonds

A novel polymeric one-dimensional compound Cu(tn)Cl2 (tn = 1,3-diaminopropane) was prepared and structurally characterized, and its spectral, magnetic, thermodynamic, and thermal properties were studied. The unique structure shows ladderlike chains composed of CuII atoms and chloro bridging ligands [Cu(−μ3-Cl−)Cu2] running along the crystallographic c axis. The coordination geometry about copper (4 + 2) approximates that of a strongly elongated octahedron. The equatorial plane of the coordination octahedron is formed by a chelate N-bonded tn ligand and two chloro ligands. One of the chloro ligands is terminal, and the other one, μ3-Cl-, forms two additional longer bonds to the neighboring copper atoms and thus occupies the axial octahedral positions. The electronic ground state of the CuII ion is of dz2 symmetry and suggests the activation of intraladder and interladder Cl···H−N hydrogen bonds as exchange paths that form a two-dimensional pattern of a triangular symmetry. The interaction due to the hydrogen bonds seems to play an important role in molecular packing and magnetic coupling. The studies of magneto-structural correlations including electron paramagnetic resonance measurements and thermodynamic and magnetic properties revealed a two-dimensional character of magnetic correlations with the effective intralayer exchange coupling J/kB ≈ −3 K. No phase transition to the ordered state has been observed down to 60 mK. Cu(tn)Cl2 with the interlayer coupling J‘ ≈ 10-3J and moderate intralayer interaction represents an excellent example of a two-dimensional magnetic system.本研究合成了一种新型聚合型一维化合物Cu(tn)Cl₂（tn=1,3-丙二胺，1,3-diaminopropane），并对其进行了结构表征，同时研究了该化合物的光谱、磁学、热力学及热学性能。 该化合物的独特结构呈现出沿晶体学c轴延伸的梯状链，链结构由二价铜原子（CuII）与氯桥配体构成，其结构单元为[Cu(−μ3-Cl⁻)Cu₂]。 铜原子的配位几何构型为(4+2)型，近似于严重拉长的八面体结构。 配位八面体的赤道平面由一个螯合N配位的tn配体与两个氯配体构成。其中一个氯配体为端基配体，另一个为三桥联氯负离子（μ3-Cl⁻），该配体通过额外两个较长的配位键与相邻铜原子结合，从而占据八面体的轴向位置。 二价铜离子的电子基态具有dz²轨道对称性，这表明梯内与梯间的Cl···H−N氢键可作为磁交换路径，进而形成具有三角对称特征的二维网络结构。 氢键相互作用似乎在分子堆积与磁耦合过程中发挥了重要作用。 针对该化合物的磁构关系开展的研究（包括电子顺磁共振（electron paramagnetic resonance）测量以及热力学与磁学性能表征）结果显示，其磁关联具有二维特征，有效层内交换耦合常数J/k_B≈−3 K。 在低至60 mK的温度范围内未观测到有序态相变。 该Cu(tn)Cl₂体系具有约为10⁻³J的层间耦合强度与适中的层内相互作用，是二维磁系统的优秀研究范例。