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

Two novel Cu-II coordination polymers, [Cu4O(L-1)(4)(N-3)(2)](n)(ClO4)(4n)center dot 3nH(2)O (1) and [Cu-7(L-2)(2)(N-3)(14)](n) (2), have been synthesized from two zwitterionic carboxylate ligands, 1-carboxylatomethyl-4,4'-bipyridinium (L-1) and 1-carboxylatomethyl-4,4'-dimethylenedipyridinium (L-2). Compound 1 exhibits interpenetrated 3D diamond networks in which the unusual mu(4)-O-centred tetrahedral Cu-4 clusters with peripheral 1,1-N-3 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 mu(3)-1,1,3-N-3, (1,1-N-3)(COO) and the organic backbone of the zwitterionic ligand. Magnetic studies reveal that compound 1 exhibits ferromagnetic coupling through (mu(4)-O)(1,1-N-3) and antiferromagnetic coupling through the mu(4)-O-only and (mu(4)-O)(COO)(2) pathways. Compound 2 exhibits ferromagnetic coupling within the (1,1-N-3)(2) bridged polynuclear units and weak antiferromagnetic coupling through mu(3)-1,1,3-N-3, and (1,1-N-3)(COO) between the units.