Discrete and polymeric complexes of a macrocyclic pillar ligand in the absence and presence of dicarboxylic acid coligands

Abstract

The macrocyclic pillar ligand, dipyridyldibenzotetraaza[14]annulene (H2L), in the absence and presence of the dicarboxylate coligands, biphenyl-4,4′-dicarboxylic acid (H2bpdc) or benzene-1,3-dicarboxylic acid (H2bdc), reacts with nickel(II), cobalt(II) and zinc(II) to yield [Ni(L)] (1), [Co(L)] (2), [Co(L)]n (3), {[Zn(H2L)(bdc)]·0.5DMF·1.5H2O}n (4) and {[Co4(L)2(bpdc)2]·2DMF·H2O}n (5) displaying both discrete and polymeric structures. Complexes 1 and 2 are isostructural, with the respective low-spin, square-planar metal ions occupying the macrocyclic cavity and bound to the N4-donor set of the macrocycle in its doubly deprotonated form. In 3, the cobalt(II) centre again occupies the macrocyclic cavity, but in this case one axial site is occupied by a pyridyl nitrogen from a second ligand complex, resulting in the formation of an infinite zigzag one-dimensional (1D) structure. Solvothermal reaction between Zn(NO3)2·4H2O, H2L and H2bdc afforded the 2D coordination polymer {[Zn(H2L)(bdc)]·0.5DMF·1.5H2O}n (4) in which H2L ligands crosslink 1D (bdc-Zn)n wavy backbones via Zn–Npyd bonds. In contrast, the solvothermal reaction of H2L with Co(NO3)2·6H2O in the presence of H2bpdc resulted in formation of the 2-fold interpenetrated 3D coordination polymer, {[Co4(L)2(bpdc)2]·2DMF·H2O}n (5), exhibiting a pillared-layer structure. The 3D framework of 5 is based on dicobalt(II) cluster secondary building units (SBUs) to yield a rob net in which the bpdc/Co-based 2D nets are cross-linked by CoL macrocyclic pillar units; the framework of 5 is thermally stable until 350 °C.