Lanthanide-Aromatic Iminodiacetate Frameworks with Helical Tubes: Structure, Properties, and Low-Temperature Heat Capacity

Abstract

A series of lanthanide coordination polymers [LnL(H 2 O) 2 ] n [Ln = Pr ( 1 ), Nd ( 2 ), Sm ( 3 ), Eu ( 4 ), and Gd ( 5 ), H 3 L = N -(4-carboxy-benzyl)iminodiacetic acid] was hydrothermally prepared and structurally characterized. All the five compounds have been confirmed as 3D Ln-CPs with one-dimensional helical tunnels composed of four helical chains, although there are different coordination geometries around Ln 3+ . Enantiomeric helixes in 1–3 , and absolute left-handed and right-handed helical chains in 4 and 5 , respectively, lead to different tunnel spaces. Their conformations can also be featured by different space groups and unit cell dimensions. Photoluminescence measurement on 3 and 4 show characteristic emission peaks of Sm 3+ and Eu 3+ ions, respectively. The low-temperature heat capacity of 1–4 has been investigated in the temperature range of 1.9–300 K. Their heat capacity values are nearly equal below 10 K and display a crossover with the value order C p,m ( 2) > C p,m ( 1) ≈ C p,m ( 4) > C p,m ( 3) above 10 K. The measured heat capacities have been fitted, and the corresponding thermodynamic functions were consequently calculated based on the fitting parameters. The standard molar entropies at 298.15 K have been determined to be (415.71 ± 4.16), (451.32 ± 4.51), (308.53 ± 3.09), and (407.62 ± 4.08) J·mol –1 ·K –1 for 1 , 2 , 3 , and 4 , respectively.

Assembly of Lanthanide-Containing 3D [MnMo9O32]6–-Based Metal–Organic Frameworks and Oxidative Desulfurization Performance

“…As depicted in Figures c and S8 (viewed in the c -axis and b -axis direction, respectively), the left-handed and right-handed helical chains are staggered, with parallel 2 1 screw axis but opposite handedness, forming a two-dimensional layer structure, which leads to chiral racemization. Similar double helical chains have been commonly observed in Ln-containing MOFs. − Furthermore, it is worth noting that each Waugh-type [MnMo 9 O 32 ] 6– anion is bound to two Pr2 ions as well as two Pr3 ions through six terminal O atoms (Figure S7). Thus, a fascinating phenomenon is observed: the L -[MnMo 9 O 32 ] 6– anion is encapsulated in the left-handed helical chains, while the R -[MnMo 9 O 32 ] 6– anion fills the right-handed helical chains (Figure d).…”