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.