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

摘要

Two novel Cu~(II) coordination polymers, [Cu_4O(L~1)_4(N_3)_2]_n(ClO_4)_(4n)·3nH_2O (1) and [Cu7_(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 μ_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 μ_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 (μ_4-O)(1,1-N_3) and antiferromagnetic coupling through the μ_4-O-only and (μ_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 μ_3-1,1,3-N_3, and (1,1-N_3)(COO) between the units.