Three-Dimensional Open-Framework Neodymium Oxalates with Organic Functional Groups Protruding in 12-Member Channels

Two open-framework neodymium oxalates, [NH3CH2CH(NH3)CH3][Nd(C2O4)2(HCOO)]·H2O (I) and [OC(CH3)NCH2CH(CH3)NH3][Nd(C2O4)2]·H2O (II), have been synthesized hydrothermally in the presence of 1,2-diaminopropane
(1,2-DAP) and formic (I) and acetic (II) acids. The Nd atoms in both these oxalates have 9-fold coordination with
respect to the oxygens, with the Nd atom in a distorted monocapped square antiprism coordination in I and in an
idealized D3h triply capped trigonal prism coordination in II. The three-dimensional framework structures of I and II
are built up by in-plane linkages between the Nd and the oxalate moieties, forming layers with 12-membered
honeycomb-like apertures, pillared by an out-of-plane oxalate unit. The 12-memberd channel in I contains a dangling
formate group in addition to the disordered amine molecule, while in II, the channel has N-(2-aminopropyl acetimide)
molecules formed by the in situ reaction of 1,2-DAP and acetic acid. The accessibility of the formate and N-(2-aminopropyl acetimide) functional groups in I and II, respectively, uniformly distributed within the channels enables
chemical manipulation. Crystal data:  I, monoclinic, space group P21/c (no. 14), M = 459.5, a = 9.0279(4) Å, b
= 18.1362(8) Å, c = 8.5631(4) Å, β = 102.735(10)°, V = 1367.56(11) Å3, Z = 4, R1 = 0.0229, wR2 = 0.0599
[1782 observed reflections with I > 2σ(I)]; II, triclinic, space group P1̄ (no. 2), M = 454.5, a = 8.6222(9) Å, b =
9.5683(10) Å, c = 9.5712(10) Å, α = 109.388(2)°, β = 98.508(10)°, γ = 102.361(12)°, V = 706.73(13) Å3, Z
= 2, R1 = 0.0446, wR2 = 0.115 [1730 observed reflections with I > 2σ(I)].

本工作通过水热法，以1,2-丙二胺（1,2-DAP）分别与甲酸、乙酸为辅助试剂，成功合成两款开放骨架草酸钕化合物：[NH3CH2CH(NH3)CH3][Nd(C2O4)2(HCOO)]·H2O（记为I）与[OC(CH3)NCH2CH(CH3)NH3][Nd(C2O4)2]·H2O（记为II）。

两款化合物中的钕（Nd）原子均与氧原子形成九配位结构：其中化合物I中的Nd原子处于畸变单帽四方反棱柱配位环境，化合物II中的Nd原子则为理想化D3h对称三帽三角棱柱配位环境。

I与II的三维骨架结构由钕原子与草酸根基团的面内连接构筑，形成带有12元环类蜂窝状孔道的层状结构，再通过面外草酸单元进行柱撑。化合物I的12元环孔道中除无序分布的胺分子外，还包含悬挂式甲酸根基团；而化合物II的孔道中则存在由1,2-DAP与乙酸原位反应生成的N-(2-氨基丙基)乙酰胺分子。

两款化合物孔道内分别均匀分布的甲酸根基团与N-(2-氨基丙基)乙酰胺官能团具备良好可及性，可支撑后续化学修饰操作。

晶体学数据：
I：单斜晶系，空间群P21/c（序号14），摩尔质量M=459.5，晶胞参数a=9.0279(4) Å，b=18.1362(8) Å，c=8.5631(4) Å，β=102.735(10)°，晶胞体积V=1367.56(11) ų，Z=4，R1=0.0229，wR2=0.0599（基于I>2σ(I)的1782个观测衍射点）；
II：三斜晶系，空间群P1̄（序号2），摩尔质量M=454.5，晶胞参数a=8.6222(9) Å，b=9.5683(10) Å，c=9.5712(10) Å，α=109.388(2)°，β=98.508(10)°，γ=102.361(12)°，晶胞体积V=706.73(13) ų，Z=2，R1=0.0446，wR2=0.115（基于I>2σ(I)的1730个观测衍射点）。