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

Abstract

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) Å 3, 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) Å ³, 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.