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(N₃)₂]_n(ClO ₄)_4n·3nH₂O (1) and [Cu ₇(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-N ₃, (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.