Two azido-bridged copper(II) coordination polymers with isonicotinate-N-oxide and picolinate-N-oxide acting as co-ligands

Two one-dimensional coordination polymers [Cu-1.5(L-1)(N-3)(2)(H2O)](n) (1) and [Cu-1.5(L-2)(N-3)(2)](n) (2) were synthesized by hydrothermal reactions of Cu(II) salt with NaN3 in the presence of two secondary ligands, isonicotinate-N-oxide (L-1) and its isomer, picolinate-N-oxide (L-2). Single-crystal X-ray diffraction studies reveal that azide anions adopt a mu-1,1 bridging coordination mode linking the metal ions by both double and single azide bridges in 1, but they adopt both mu-1,1 and mu-1,1,1 bridging modes in 2. The magnetic measurements showed strong ferromagnetic coupling and the onset of magnetic ordering in 1 (a metamagnet with a small glass behaviour), but antiferromagnetic interactions between the ferromagnetic trimers in 2. This result indicates that the judicious selection of co-ligands can effectively tune the formation of metal-azide coordination polymers and thereby, their magnetic properties.