A Series of Cd(II) and Zn(II) Coordination Polymers with Helical Subunits Assembled from a Versatile 3‑(4-hydroxypyridinium-1-yl) Phthalic Acid and N‑Donor Ancillary Coligands

A series of coordination polymers with various helical subunits, namely, [Cd­(L)­(CH3OH)­(H2O)]n (2), {[Cd­(L)­(1,4-bbi)]·(H2O)}n (3), {[Cd­(L)­(m-bix)­(H2O)]·(H2O)2}n (4), [Zn­(L)­(4,4′-bpy)0.5]n (5), and [Zn­(L)­(bpp)]n (6) (H2L = 3-(4-hydroxypyridinium-1-yl) phthalic acid; PA = phthalic acid, a part of 3-(4-hydroxypyridinium-1-yl) phthalic acid)), have been hydro­(solvo)­thermally synthesized through the reaction of 3-(4-hydroxypyridinium-1-yl) phthalic acid with divalent zinc and cadmium salts in the presence or absence of N-donor ancillary coligands (1,4-bbi = 1,1′-(1,4-butanediyl)­bis­(imidazole), m-bix = 1,3-bis­(imidazol-1-ylmethyl)­benzene, 4,4′-bpy = 4,4′-bipyridine, bpp = 1,3-bi­(4-pyridyl)­propane). As a result of various coordination modes of the versatile 3-(4-hydroxypyridinium-1-yl) phthalic acid and different coligands, these compounds exhibit structural diversity. Compound 2 displays a layered structure containing two kinds of (Cd–L)n and (Cd–PA)n helical chains. Compound 3 features a 3D supramolecular framework embodying a type of supramolecular helical chain. Compound 4 exhibits a metal–organic ribbon structure with two kinds of helical chains. Compound 5 features a 3D architecture in which a 1D lemniscate shape pseudo meso-helix chain is observed. Compound 6 exhibits a 2D achiral layer in which the 1D (Zn–bpp)n helical chains are alternately arranged in a right- and left-handed sequence. These compounds have been characterized by powder X-ray diffractions (PXRD) and thermal gravimetric analyses (TGA). In addition, their photochemical properties have also been investigated.