Polymeric networks of copper(II) using succinate and aromatic N–N donor ligands: synthesis, crystal structure, magnetic behaviour and the effect of weak interactions on their crystal packing

Abstract

Four succinato-bridged complexes of copper(II) have been synthesized. Complex 1, [Cu₂(μ-OH₂)₂L(bpy)₂(NO₃)₂]_n and 2, [Cu₂(μ-OH₂)₂L(phen)₂(NO₃)₂]_n (bpy = 2,2′-bipyridine; phen = 1,10-phenanthroline and LH₂ = succinic acid) exhibit 1D coordination polymer structures where both the nitrate ions are directly linked to the copper(II) producing synthons in a 2D sheet. A novel 2D grid-like network, {[Cu₄L₂(bpy)₄(H₂O)₂](ClO₄)₄(H₂O)}_n 3, is obtained upon changing the nitrate by perchlorate anion in complex 1, where the channels are occupied by the anions. On changing the nitrate by tetrafluoroborate anion in complex 2, a novel octanuclear complex, [Cu₈L₄(phen)₁₂](BF₄)8·8H₂O 4, is isolated. The coligand bpy and phen in these complexes show face-to-face (in 1, 2, 3, 4) or edge-to-face (in 4) π–π interactions forming the multidimensional supramolecular architectures. Interestingly, the appearance of edge-to-face π–π interactions in complex 4 facilitates the formation of discrete octanuclear entities. Variable-temperature (300–2 K) magnetic measurements of complexes have been done. Complexes 1 and 2 show very weak antiferromagnetic (OOC–CH₂–CH₂–COO) and ferromagnetic coupling (μ-H₂O). Complex 3 also shows antiferromagnetic (syn–syn μ-OCO), and ferromagnetic coupling (μ-O of the -COO group). Complex 4 with two types (syn–syn and syn–anti) of binding modes of the carboxylate group shows strong antiferromagnetic interaction.