Tunability in Metal Coordination Sphere, Ligand Coordination Mode, Network Topology, and Magnetism via Stepwise Dehydration Induced Single-Crystal to Single-Crystal Transformation

Abstract

Stimuli-responsive solid-state crystal dynamics or flexibility in metal–organic frameworks (MOFs) showing multiple structure changes is an arising interest for understanding the structure–property relationship and designing functional materials. In this article, dehydration-induced stepwise single-crystal to single-crystal (SC–SC) transformations are observed in two-dimensional 63-topological coordination polymer [Co­(H2L)­(H2O)2]·H2O (1), where H4L is 3,5-bis­(3′,5′-dicarboxylphenyl)-1H-1,2,4-triazole. Upon thermal dehydration at 130 °C for 2 h, half lattice water in 1 can be released to form [Co­(H2L)­(H2O)2]·0.5H2O (2). By increasing dehydration temperature to 150 °C for 3 h, the third phase [Co­(H2L)­(H2O)2] (3) that is free of lattice water molecule is gained. Further increasing the dehydration temperature to 160 °C for 6 h, one of coordination water molecule can be released, giving rise to dicobalt-based 2D (3,6)-connected kgd double layer [Co­(H2L)­(H2O)] (4). During stepwise dehydration SC–SC transformation courses, coordination sphere of Co­(II) changes from penta-coordinate trigonal bipyramid to hexa-coordinate octahedra; H2L2– ligates from (κ1)–(κ1)–(κ1)−μ3–H2L2–, (κ1)–(κ1)–(κ2)−μ3–H2L2– to (κ1–μ2)–(κ1)–(κ2)−μ4–H2L2–; network topology ranges from 3-connected 63-hcb to (3,6)-connected kgd; magnetism changes from single-ion behavior of Co­(II) to intradicobalt ferromagnetism.

Cyclic Structural Transformations from Crystalline to Crystalline to Amorphous Phases and Magnetic Properties of a Mn(II)-Based Metal–Organic Framework

“…In terms of host–guest interactions, solvent molecules incorporated into the interior of the framework trigger structural flexibility of the dynamic soft crystals. Substantial structural variations in soft coordination networks are accompanied by changes in the ligand conformation and deformation of the metal nodes when guest molecules enter or exit the pores of the framework. − Solvent inclusion in or removal from the framework often engenders single crystal-to-single crystal transformations. − The structural dynamics in flexible coordination systems also promotes crystal-to-amorphous structural conversions upon solvation–desolvation. − Thus, most structural transformations involve reversible or irreversible phase exchange between two crystalline states or between crystalline and amorphous states. In fact, structural nonrigidity of soft frameworks is more diverse, and even three states are mutually transformable upon various sample treatments (solvent exchange, activation, and resolvation, for instance). − In these examples, phase conversions from crystalline to another crystalline to other crystalline states occur upon incorporation of guest solvent molecules into the frameworks or elimination of the introduced solvent molecules.…”

R-Substituent-Induced Structural Diversity and Single-Crystal to Single-Crystal Transformation of Coordination Polymers: Synthesis, Luminescence, and Magnetic Behaviors

“…So far, SCSC transformation induced by guest removal/inclusion without bond cleavage has been studied extensively. In contrast, examples involving cleavage and formation of covalent or coordinative bonds, which result in a change of coordination number, geometry, dimensionality, etc., are less common . The metal–ligands (M–L) coordination bonds always will break, deform, and reorganize new M–L bonds after exposure to the above factors .…”

“…In contrast, examples involving cleavage and formation of covalent or coordinative bonds, which result in a change of coordination number, geometry, dimensionality, etc., are less common. 25 The metal−ligands (M−L) coordination bonds always will break, deform, and reorganize new M−L bonds after exposure to the above factors. 26 Compared with the original compound, the new compound caused by the change of the M−L bond often has a different coordination number, geometry, dimensionality, and physical or chemical properties.…”

Elucidating phase transformation of Eu-based metal organic framework with intermediate isolation and theoretical calculations

“…36 The transformation probably involves the removal of coordinated solvent molecules, partial breaking or formation of coordination bonds. [37][38][39] Fortunately, many cases of MOF phase transformation proceed through singlecrystal-to-single-crystal (SC-SC) conversion, and this allows clear structural characterization of both reactants and products using X-ray crystallography for detailed structural comparison. [40][41][42][43] It is insightful that the phase transformation can be traced closely for the crystal-clear depiction of the process.…”