两例配位聚合物MCl2(β-ala)n(M=Co,Ni；β-ala=3-氨基丙酸)的结构相变

摘要

利用3-氨基丙酸(β-ala)和过渡金属氯化物构筑了2例互为异质同晶的配位聚合物[MCl2(β-ala)]n(M=Co2+ (1),Ni2+(2)),并通过差示扫描量热法、变温X射线单晶衍射以及变温介电测试研究了它们的结构相变.配合物1和2的结构中,相邻的M2+离子通过2个氯离子和1个双齿羧基的桥联作用形成一维配位链.在升/降温过程中,1和2分别在236、224 K和309、302 K附近发生高温相(Pnam)与低温相(Pna21)之间的温致结构相变;该相变主要是由配体的铵乙基由高温相中的两重无序状态冻结为低温相中的有序状态而引起的,该有序-无序型相变使这两个化合物在相变温度附近都表现出介电台阶及介电弛豫的共存现象.%Two new isomorphic coordination polymers,[MCl2(β-ala)],n (M=Co2+ (1) or Ni2+ (2),β-ala=3-aminopropionic acid),were constructed by assembling 3-aminopropionic acid and transition metal chlorides.Their reversible structural phase transitions were disclosed by differential scanning calorimetry (DSC),variable-temperature single -crystal X-ray diffraction and dielectric measurements.In 1 and 2,the adjacent M2+ ions are mix-bridged by two μ2-Cl-ions and a syn-syn carboxylate group fromβ3-ala ligand,resulting in one-dimensional polymeric coordination chains.Both 1 and 2 undergo reversible phase transitions,which occur at critical temperature (Tc-heating,Tc-cooling of 236,224 K and 309,302 K,respectively,with a change of space group between Pnam at the hightemperature phase (HTP) and Pna21 at the low-temperature phase (LTP).The phase transitions are mainly related to the dynamic change of ammonium ethyl group from two-fold disorder in HTP to static ordered state in LTP.Such order-disorder structural phase transitions lead to the coexistence of step-like dielectric anomaly and dielectric relaxation in the vicinity of the phase transition.CCDC:1555337,1_LTP;1555336,1_HTP;1555339,2_LTP;1555338,2_HTP.