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

Four succinato-bridged complexes of copper(II) have been synthesized. Complex 1, [Cu-2(mu-OH2)(2)L(bpy)(2)(NO3)(2)](n) and 2, [Cu-2(mu-OH2)(2)L(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).8H(2)O 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)pi-pi interactions forming the multidimensional supramolecular architectures. Interestingly, the appearance of edge-to-face pi-pi 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 (mu-H2O). Complex 3 also shows antiferromagnetic (syn-syn mu-OCO), and ferromagnetic coupling (mu-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.