Copper Coordination Polymers Based on Single-Chain or Sheet Structures Involving Dinuclear and Tetranuclear Copper(II) Units: Synthesis, Structures, and Magnetostructural Correlations

Abstract

Reactions between the potentially pentadentate (N(2)O(3)), trianionic double Schiff-base ligand 2,6-bis[[(2-hydroxyethyl)imino]methyl]-4-methylphenol (H(3)L) and Cu(CH(3)CO(2))(2) or Cu(ClO(4))(2), in the presence of NaN(3), give novel coordination polymers with chain {[Cu(2)(H(2)L)(N(3))(3)](2).H(2)O}(n) (1) or sheet [Cu(2)(H(2)L)(N(3))(3)](n) (2) and [Cu(2)(HL)(N(3))](n)[ClO(4)](n) (3) structures, respectively. These clusters are comprised of repeating dinuclear units (1) or their dimers (2 and 3). In these compounds, H(3)L acts as a tridentate (N(2)O) monoanionic (1), tetradentate (ON(2)O) monoanionic (2), or pentadentate (O(3)N(2)) dianionic (3) ligand. Compound [Cu(2)(HL)(N(3))(2)(H(2)O)].0.5CH(3)OH (4) formed from the reaction of Cu(CH(3)CO(2))(2) with H(3)L under reflux, which did not afford crystals suitable for X-ray studies. X-ray structure determinations have revealed that the basic building block in 1-3 comprises two copper centers bridged through one mu-phenolate O atom from H(2)L(-) or HL(2-) and one mu-azido(N1,N1) ion. Compounds 1-3 unveil three different ways in which this Cu(2) basic unit may be organized in the crystalline phase at the supramolecular level through a variety of bridging interactions involving additional azide ligands or alkoxide groups from the side arms of the ligand H(3)L. Bulk magnetization measurements have served to demonstrate that the magnetic interactions are completely dominated by the strong antiferromagnetic coupling occurring within the Cu(2) building block, with coupling constants ranging from 330 to 560 cm(-1) (in the H = -JS(1)S(2) convention). These results together have been incorporated with data from the few related copper dimers reported exhibiting the same bridging pattern into a study aimed at extracting possible magnetostructural correlations within this Cu(2) unit. An earlier predicted correlation between J and the angle formed by the phenoxide bridge and the Cu(2) core has been identified for the first time.