Structural diversity in tetranuclear ytterbium-based metal–organic frameworks and their divided net analysis

Abstract

Lanthanides such as ytterbium have high and various coordination numbers, which lead to the generation of versatile secondary building units (SBUs) for metal–organic framework (MOF) synthesis. However, the versatility also tends to impose relatively low symmetry and uncertainty on the structures, thus understanding the connectivity modes between the inorganic units and the linkers is essential. In this work, a ditopic linker with an α-amino group is employed to regulate the hydrolysis of Yb(III) to facilitate the generation of SBUs with [Yb4(μ3-OH)4] cores, which further reticulate with the linkers to afford three kinds of MOFs. Analysis of the coordination linkages reveals that the linkers can be divided into three different modes, and the arrangement of the linkers with different modes around the SBUs leads to the structures with completely different nets. Furthermore, linker vacancies are found and quantified in the real crystal structures. In addition, a divided net strategy is used to analyze the nets of the two 8-connected MOFs. By dividing each 8-connected node into a 6-connected node and a 2-connected node, the underlying nets of the two MOFs can be regarded as an integration of a pcu net with infinite zig-zag chains or straight rods.