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)]_<i>n</i> (<b>2</b>), {[Cd­(L)­(1,4-bbi)]·(H₂O)}_<i>n</i> (<b>3</b>), {[Cd­(L)­(<i>m</i>-bix)­(H₂O)]·(H₂O)₂}_<i>n</i> (<b>4</b>), [Zn­(L)­(4,4′-bpy)_0.5]_<i>n</i> (<b>5</b>), and [Zn­(L)­(bpp)]_<i>n</i> (<b>6</b>) (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), <i>m</i>-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 <b>2</b> displays a layered structure containing two kinds of (Cd–L)_<i>n</i> and (Cd–PA)_<i>n</i> helical chains. Compound <b>3</b> features a 3D supramolecular framework embodying a type of supramolecular helical chain. Compound <b>4</b> exhibits a metal–organic ribbon structure with two kinds of helical chains. Compound <b>5</b> features a 3D architecture in which a 1D lemniscate shape pseudo meso-helix chain is observed. Compound <b>6</b> exhibits a 2D achiral layer in which the 1D (Zn–bpp)_<i>n</i> 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