Four new cobalt(II) coordination complexes: thermochromic switchable behavior in the process of dehydration and rehydration

Four cobalt(II) coordination complexes, {[Co-11(L1)(6)(HL1)(2)(H2O)28]center dot 12H(2)O}(n) (1), [Co-4(H(2)L1)(4)(HL1)(2)(H2O)(8)]center dot 2H(3)L1 center dot 2H(2)O (2), {[Co(H(2)L3)(H2O)(3)]center dot 2H(2)O}(n) (3) and [Co(HL1)(4,4'-bpy)(H2O)(2)](n) (4), (H(3)L1 = 2,4,6-tri(3-carboxyphenylthio)-1,3,5-triazine, H(4)L3 = 2,4-bis(3-carboxyphenylthio)-6-(4-carboxyphenylamino -1,3,5-triazine, 4,4'-bpy = 4,4'-bipyridine), was synthesized hydrothermally and characterized by single-crystal X-ray diffraction, powder X-ray diffraction, IR, thermal analysis, UV-vis spectroscopy and magnetic measurements. Complex 1 shows a 2D layer structure composed of three types of secondary building units (SBUs), [M-1], [M-3] and [M-4] bridged by [HL1](2-) and [L1](3-) linkers. While complex 2 is a tetranuclear compound and further forms a 3D supramolecular network structure based on eight types of hydrogen-bonding interactions between the molecules. The 2D framework of complex 3 can be described as 1D infinite chains interconnected by [H(2)L3](2-) ligands. Furthermore, the hydrogen-bonding interactions between the adjacent layers along the ac plane makes the 2D layer structure extend to a 3D network. The structure of complex 4 can be illustrated as a 1D zigzag infinite chain with 4,4'-bipyridine as the secondary ligand. Additionally, the pi center dot center dot center dot pi stacking interactions can be observed between the adjacent chains. An aquo-accessible thermochromic change in complexes 1-4 was induced by means of the reversible dehydration and rehydration of the crystals. Magnetic measurements showed antiferromagnetic coupling between the Co2+ ions in all of the four complexes.