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

摘要

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 6(3)-topological coordination polymer [Co(H2L)(H2O)(2)]center dot H2O (1), where H4L is 3,5-bis(3',5'-dicarboxylpheny1)-1H-1,2,4-triazole. Upon thermal dehydration at 130 degrees C for 2 h, half lattice water in 1 can be released to form [Co (H2L)(H2O)(2)]center dot 0.5H(2)O (2). By increasing dehydration temperature to 150 degrees 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 degrees 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 (K-1)-(K-1)-(K-1)-mu(3)-H2L2-, (K-1)-(K-1)-(K-2)-mu(3)-H2L2- to (K-1-mu(2))-(K-1)-(K-2)-mu(4)-H2L2-; network topology ranges from 3 -connected 6(3)-hcb to (3,6) -connected kgd; magnetism changes from single-ion behavior of Co(II) to intradicobalt ferromagnetism.