Humidity Sensitive Structural Dynamics and Solvatomagnetic Effects in a 3D Co(II)-Based Coordination Polymer

Abstract

A chiral Co(II)-based coordination polymer, [Co(pimda)(HO)] (1, Hpimda = 2-propyl-1H-imidazole-4,5-dicarboxylic acid) with 3D hyperkagomé topology is reported. Upon heating/cooling, the water molecules which are coordinated to a pair of crystallographically symmetric Co(II) ions are removed/recovered discretely in two steps, giving [Co(pimda)(HO)] (2) and [Co(pimda)(HO)] (3), which is evidenced by the reversible single-crystal-to-single-crystal (SCSC) structural transformations. As the coordination geometry of the two Co(II) ions changes from octahedron to trigonal bipyramid, obvious color change from pink for 1 to dark violet for 2 and 3 is observed. Further magnetic measurements demonstrate the presence of a solvatomagnetic effect from paramagnets for 1 and 2 to weak ferromagnet for 3. Moreover, as revealed by the variable-temperature crystallographic measurements, the first and second dehydration temperatures could be controlled from 298 K (25 °C) and 383 K (110 °C) sealed in a capillary (high humidity) to 255 K (-18 °C) and 307 K (34 °C) in dry N (low humidity), indicating the strong humidity sensitivity of the structural dynamics.

Humidity-Induced Structural Transformation in Pseudopolymorph Coordination Polymers

“…Over the past few decades, wide research in the field of coordination polymers (CPs) has been conducted . The high potential of CPs in gas storage and separation, sensing, − catalysis, and other areas like magnetic properties , and electrical conductivity , is the main reason that this field has been of great interest among scientists and crystal engineers.…”

New 2D and 3D Coordination Polymers by Dehydration of 1∞[MII(tF‐BDC)(H2O)4] (MII = Zn2+, Co2+, Ni2+ and tF‐BDC2– = Tetrafluoroterephthalate)

“…This is accompanied by a drastic color change of the resulting compounds: pale rose for 1 ∞ [Co II ( tF ‐BDC)(H 2 O) 4 ] and deep blue for 3 ∞ [Co II ( tF ‐BDC)] (Figure ). This well‐known solvatochromic effect for Co II complexes and Co II ‐based coordination polymers can be followed upon heating of 1 ∞ [Co II ( tF ‐BDC)(H 2 O) 4 ] (Figure S8, Supporting Information), where between 185 °C and 195 °C the strongest color change is observed. Upon exposure of blue 3 ∞ [Co II ( tF ‐BDC)] to humid air the pale rose color of 1 ∞ [Co II ( tF ‐BDC)(H 2 O) 4 ] is obtained again within minutes indicating the reversibility of the dehydration/hydration process.…”

Metal–Metalloligand Coordination Polymer Embedding Triangular Cobalt–Oxo Clusters: Solvent- and Temperature-Induced Crystal to Crystal Transformations and Associated Magnetism

“…Magnetic studies reveal that both II and III display long-range ordered weak ferromagnetism, unlike I , which remains paramagnetic down to 2 K. A dynamic cantilever magnetometry measurement on III suggests a weak magnetic anisotropy. It is worth mentioning that there are only limited examples where the magnetic ground state is changed and associated with a SC-SC transformation. , …”