Copper(II) coordination polymers with azide and bipyridine-based zwitterionic carboxylate ligands: structures and magnetism

Two novel CuII coordination polymers, [Cu4O(L1)4(N3)2]n(ClO4)4n·3nH2O (1) and [Cu7(L2)2(N3)14]n (2), have been synthesized from two zwitterionic carboxylate ligands, 1-carboxylatomethyl-4,4′-bipyridinium (L1) and 1-carboxylatomethyl-4,4′-dimethylenedipyridinium (L2). Compound 1 exhibits interpenetrated 3D diamond networks in which the unusual μ4-O-centred tetrahedral Cu4 clusters with peripheral 1,1-N3 and COO bridges are cross-linked by 4,4′-dipyridinium-1-methylene spacers. In compound 2, pentanuclear and dinuclear units with double azide bridges are linked into a unique 2D layer by μ3-1,1,3-N3, (1,1-N3)(COO) and the organic backbone of the zwitterionic ligand. Magnetic studies reveal that compound 1 exhibits ferromagnetic coupling through (μ4-O)(1,1-N3) and antiferromagnetic coupling through the μ4-O-only and (μ4-O)(COO)2 pathways. Compound 2 exhibits ferromagnetic coupling within the (1,1-N3)2 bridged polynuclear units and weak antiferromagnetic coupling through μ3-1,1,3-N3, and (1,1-N3)(COO) between the units.