1D Helix, 2D Brick-Wall and Herringbone, and 3D Interpenetration d¹⁰ Metal−Organic Framework Structures Assembled from Pyridine-2,6-dicarboxylic Acid <i>N</i>-Oxide

Five novel interesting d10 metal coordination polymers, [Zn(PDCO)(H2O)2]n (PDCO = pyridine-2,6-dicarboxylic acid
N-oxide) (1), [Zn2(PDCO)2(4,4‘-bpy)2(H2O)2·3H2O]n (bpy = bipyridine) (2), [Zn(PDCO)(bix)]n (bix = 1,4-bis(imidazol-1-ylmethyl)benzene) (3), [Zn(PDCO)(bbi)·0.5H2O]n (bbi = 1,1‘-(1,4-butanediyl)bis(imidazole)) (4), and [Cd(PDCO)(bix)1.5·1.5H2O]n (5), have been synthesized under hydrothermal conditions and structurally characterized. Polymer
1 possesses a one-dimensional (1D) helical chainlike structure with 41 helices running along the c-axis with a pitch
of 10.090 Å. Polymer 2 has an infinite chiral two-dimensional (2D) brick-wall-like layer structure in the ac plane
built from achiral components, while both 3 and 4 exhibit an infinite 2D herringbone architecture, respectively
extended in the ac and ab plane. Polymer 5 features a most remarkable and unique three-dimensional (3D) porous
framework with 2-fold interpenetration related by symmetry, which contains channels in the b and c directions, both
distributed in a rectangular grid fashion. Compounds 1−5, with systematic variation in dimensionality from 1D to 2D
to 3D, are the first examples of d10 metal coordination polymers into which pyridinedicarboxylic acid N-oxide has
been introduced. In addition, polymers 1, 4, and 5 display strong blue fluorescent emissions in the solid state.
Polymer 3 exhibits a strong SHG response, estimated to be approximately 0.9 times that of urea.