Unique (3,9)-connected porous coordination polymers constructed by tripodal ligands with bent arms

Abstract

Solvothermal reactions of Co(NO₃)₂ with tripodal ligands 3,3′-([3,4′-bipyridine]-2′,6′-diyl)dibenzoic acid (H₂L4), 3,3′-([4,4′-bipyridine]-2,6-diyl)dibenzoic acid (H₂L5), and 2,6-bis(4-(1H-tetrazol-5-yl)phenyl)-4,4′-bipyridine (H₂L6) possessing one to three bent arms, yielded three new porous coordination polymers, namely [Co₃(μ₃-OH)(L4)₃] (1), [Co₃(μ₃-OH)(L5)₃] (2), and [Co₃(μ₃-OH)(L6)₃] (3), respectively. Single-crystal X-ray crystallography showed that 1–3 are all three-dimensional (3,9)-connected coordination networks interconnected by the tripodal ligands and the classical tricapped trigonal-prismatic [Co₃(μ₃-OH)(RCOO)₆(Py)₃] (Py = pyridyl) or new tricapped trigonal-prismatic [Co₃(μ₃-OH)(Rtz)₆(Py)₃] (Rtz⁻ = tetrazolate) clusters. However, instead of the classical xmz topology for such a kind of 3-connected ligands and 9-connected clusters, 1 and 2 show a new (3,9)-connected topology, wys, with a point symbol of {4²·6}₃{4⁶·6²⁷·8³}, while 3 has a (3,9)-connected eee topology. Thermogravimetry, powder X-ray diffraction, and gas adsorption measurements demonstrated that the desolvated forms of 1–3 are all porous, but different framework flexibilities were observed.