Combined Magnetic and Single-Crystal X-ray Structural Study of the Linear Chain Antiferromagnet [(CH₃)₄N][MnCl₃] under Varying Pressure

The magnetic susceptibility and single-crystal X-ray structure of the one-dimensional Heisenberg antiferromagnetic chain tetramethylammonium manganese trichloride (TMMC) have been studied under pressure as a facile route to develop structure−property relationships. The X-ray structure of TMMC was determined at 0, 2.1, 3.8, 6.8, 12.2, and 17.0 kbar using diamond−anvil cell techniques and synchrotron radiation. The space group is confirmed to be P63/m up to 17 kbar, and structural refinement shows that the Mn−Mn separations between and along the chains change by about 3.4 and 2.5%, respectively, over 17 kbar. A structural transition from hexagonal to monoclinic symmetry possibly occurs at 17 kbar, associated with a loss of crystal quality. Variable-temperature magnetic susceptibility data were taken at 0, 0.3, 1.5, 2.9, 4.0, 5.2, and 6.5 kbar and show that the intrachain coupling constant changes from −6.85 to −7.81 K over this range. The interchain coupling constant of −0.54 K can also be extracted from the Fisher model modified for interacting chains. The pressure−temperature diagram shows the slope of the intrachain antiferromagnetic coupling with pressure, ΔTIAF/ΔP, changes from 0.5 to 1.6 K/kbar at 2 kbar where the structure changes from P21/a to P21/m. Comparison of the magnetic and structural data are consistent with the power−law relationship developed by Bloch where J ∝ r-n, r = Mn···Mn separation and n ≈ 10.本研究针对一维海森堡反铁磁链化合物四甲基铵三氯化锰（tetramethylammonium manganese trichloride，缩写TMMC）开展压力下的磁化率与单晶X射线晶体结构表征，以期建立其结构与性能的关联关系。本研究借助金刚石对顶砧技术与同步辐射光源，在0、2.1、3.8、6.8、12.2及17.0 kbar的压力条件下测定了TMMC的X射线晶体结构。结果确认，在17 kbar以内其空间群均为P63/m；结构精修结果显示，在17 kbar的压力区间内，链间与沿链方向的Mn-Mn间距分别变化约3.4%与2.5%。在17 kbar处，样品可能发生从六方晶系到单斜晶系的结构相变，同时伴随晶体质量下降。本研究在0、0.3、1.5、2.9、4.0、5.2及6.5 kbar的压力下开展了变温磁化率测试，结果表明，该压力区间内链内耦合常数从-6.85 K变化至-7.81 K。针对考虑链间相互作用的修正费舍尔模型（Fisher model），还可提取得到链间耦合常数为-0.54 K。压力-温度相图显示，链内反铁磁耦合随压力变化的斜率ΔTIAF/ΔP在2 kbar处发生突变，从0.5 K/kbar变为1.6 K/kbar，该压力点对应结构从P21/a相变至P21/m。对磁学与结构数据的对比分析表明，其符合布洛赫（Bloch）提出的幂律关联关系：*J* ∝ *r*⁻ⁿ，其中*r*为Mn···Mn间距，*n*≈10。