Positional isomeric tunable two Co(ii) 6-connected 3-D frameworks with pentanuclear to binuclear units: structures, ion-exchange and magnetic properties

Abstract

Two new Co(II) based metal–organic frameworks, namely {[Co₅(μ₃-OH)₂(m-pda)₃(bix)₄]·2ClO₄}_n (1) and {[Co₂(p-pda)₂(bix)₂(H₂O)]·H₂O}_n (2), were prepared by hydrothermal reactions of Co(II) salt with two isomeric dicarboxyl tectons 1,3-phenylenediacetic acid (m-pda) and 1,4-phenylenediacetic acid (p-pda), along with 1,3-bis(imidazol-L-ylmethyl)benzene (bix). Both complexes 1 and 2 have been characterized by elemental analysis, IR spectroscopy, single-crystal X-ray diffraction, powder X-ray diffraction (PXRD), and thermogravimetric analysis (TGA). 1 shows a 6-connected 3-D pcu cationic framework with pentanuclear [Co₅(μ₃-OH)₂(COO)₆(bix)₂]²⁺ units, while 2 exhibits a 6-connected 3-D msw net based on [Co₂(μ₂-H₂O)(COO)₂]²⁺ clusters. The results indicate that the different dispositions of the carboxylic groups of dicarboxylates have an important effect on the overall coordination frameworks. Perchlorate anions in 1 can be partly exchanged by thiocyanate and azide anions, however they are unavailable to nitrate anions. Magnetic susceptibility measurements indicate that both 1 and 2 show weak antiferromagnetic interactions between the adjacent Co(II) ions.