Water dimers connect [Cu(cda)(py)3] (cda = pyridine-4-hydroxy-2,6-dicarboxylate, py = pyridine) complex units to left- and right-handed helices that form a tubular coordination polymer through supramolecular bonding

The reaction between pyridine-4-hydroxy-2,6-dicarboxylic acid (cdaH2) and Cu(NO3)2 · 3H2O afford products that depend on the reaction conditions applied. In presence of excess of aqueous pyridine (1:2 v/v), equimolar amounts of the reactants form {[Cu(cda)(py)3]2 · 5H2O}n (1). In this complex, dimeric water clusters are H-bonded to carboxylate O atoms forming both left- and right-handed helices. These helices are further H-bonded to form a tubular coordination polymer. It crystallizes in the monoclinic space group P21/a with a = 14.235(5), b = 23.097(4), c = 15.542(6) Å, β = 114.392(5)°, V = 4654(2) Å3, Z = 4, R1 = 0.0422, wR2 = 0.0992, S = 0.899. When pyridine is used in place of aqueous pyridine, a new coordination polymer, {Cu(cda)(py)}n(2) is formed that crystallizes in the monoclinic space group P21/c with a = 12.391(5), b = 12.770(5), c = 7.135(5) Å, β = 95.155(5)°, V = 1124(1) Å3, Z = 4, R1 = 0.0415, wR2 = 0.0882, S = 1.190. The structure of 2 consists of carboxylate-bridged [Cu(cda)(py)] units extending as a zigzag infinite chain where each metal ion shows square-pyramidal geometry. Variable temperature magnetic susceptibility measurements in the temperature range, 2–300 K for 2 is also reported.

Pyridine-4-hydroxy-2,6-dicarboxylic acid reacts with Cu(NO3)2 · 3H2O in excess of aqueous pyridine to form a complex where dimeric water clusters are H-bonded to carboxylate O atoms forming both left- and right-handed helices. These helices are further H-bonded to form a tubular metal–organic open framework structure.Figure optionsDownload as PowerPoint slide