Insertion of Functional Groups into a Nd<sup>3+</sup> Metal–Organic Framework via Single-Crystal-to-Single-Crystal Coordinating Solvent Exchange

Single-crystal-to-single-crystal (SCSC) transformations represent some of the most fascinating phenomena in chemistry. They are not only intriguing from a basic science point of view but also provide a means to modify or tune the properties of the materials via the postsynthetic introduction of suitable guest molecules or organic functional groups into their structures. Here, we describe <b>UCY-2</b>, a new flexible Nd<sup>3+</sup> metal–organic framework (MOF), which exhibits a unique capability to undergo a plethora of SCSC transformations with some of them being very uncommon. These structural alterations involve the replacement of coordinating solvent molecules of <b>UCY-2</b> by terminally ligating solvents and organic ligands with multiple functional groups including −OH, −SH, −NH–, and −NH<sub>2</sub> or their combinations, chelating ligands, anions, and two different organic compounds. The SCSC coordinating solvent exchange is thus demonstrated as a powerful method for the functionalization of MOFs.