Structural diversity and properties of M(II) 4-carboxyl phenoxyacetate complexes with 0D-, 1D-, 2D- and 3D M-cpoa framework

Nine new metal complexes with an asymmetric H(2)cpoa ligand, [Co(Hcpoa)(2)(bpe)(2)(H2O)(2)] (1), [Co(cpoa)(bpe)(1.5)(H2O)]center dot H2O (2), [Co(Hcpoa)(2)(4,4'-bpy)(2)] (3), [Co(4,4'-bpy)(H2O)(4)]center dot [Co(cpoa)(2)(H2O)(2)]center dot 2H(2)O (4), [Ni(cpoa)(4,4'-bpy)(H2O)(2)] (5), [Ni(cpoa)(bpe)(1.5)(H2O)]center dot H2O (6), [Zn-2(cpoa)(2)(bpe)(H2O)] (7), [Zn(cpoa)(bpe) (.5)]center dot 0.5(i-C3H7OH) (8) and [Zn(cpoa)(bpe)(0.5)]center dot 0.5(n-C3H7OH) (9) (H(2)cpoa = 4-carboxyphenoxy acetic acid, bpe = 1,2-bis(4-pyridyl) ethane, 4,4'-bpy = 4,4'-bipyridine) were synthesized under hydro/solvothermal conditions. X-ray single-crystal structural analyses reveal that they have metal -organic frameworks ranging from 0D (1), 1D (3, 4), 2D (5, 7, 8) to 3D structure (2, 6, 9). The reaction of the CoCl2/H(2)cpoa/bpe (1 : 1 : 1) system results in the formation of complex 1 at the starting pH of ca. 8, and complex 2 at 12. The reaction of CoCl2/H(2)cpoa/4,4'-bpy (1 : 1 : 1) forms complex 3 with a 1D chain structure, while a molar ratio of 1 : 1 : 0.5 leads to the formation of complex 4 with two 1D metal -organic frameworks of rarely reported homometal complex ion pairs. By changing the added organic solvent, the 2D layer framework of complex 8 and the microporous 3D framework of complex 9 were obtained under the same reaction conditions. The guest n-C3H7OH molecules occupy 1D channels in 9. Thermogravimetric and powder X-ray diffraction analyses show that the microporous 3D framework of 9 is maintained after the removal of the guest molecule. And a reversible dealcoholization/realcoholization process can be observed. The magnetic measurements show antiferromagnetic interactions between the metal ions in 2, 4 and 5, and antiferromagnetic interaction in the range of 300-18 K and ferromagnetic interaction between Ni(II) ions below 18 K in 6.