Coordination Polymers with End-On Azido and Pyridine CarboxylateN-Oxide Bridges Displaying Long-Range Magnetic Ordering with Low Dimensional Character

Abstract

A series of 2D and one 3D transition-metal−azido coordination polymers with pyridine carboxylate N-oxide, isonicotinate N-oxide (INO), and nicotinate N-oxide (NNO) as the coligands were synthesized by a hydrothermal method and structurally and magnetically characterized. These complexes have the formulas [M(L)(N₃)(H₂O)]_n (L = INO and M = Mn, 1 · Mn; Co, 2 · Co; Ni, 3 · Ni and L = NNO and M = Mn, 4 · Mn; Co, 5 · Co; Ni, 6 · Ni) and [Cu(L)(N₃)(H₂O)_0.5]_n (L = INO, 7 · Cu; NNO, 8 · Cu). All complexes consist of end-on azido and syn-syn carboxylato mixed-bridged M−N₃/COO chains that are further linked by the pyridine N-oxide group of the INO or NNO to give rise to 2D layered structures for 1 · Mn, 2 · Co, 3 · Ni, 4 · Mn, 5 · Co, 6 · Ni, and 8 · Cu and a 3D framework for 7 · Cu. The high-temperature magnetic susceptibilities are dominated by low-dimensional behavior while long-range ordering sets in at low temperatures. The Mn complexes are antiferromagnets, and the others are metamagnets. In addition, 5 · Co exhibits slow magnetic relaxation behavior at low temperatures. The metamagnetism in each case is due to strong intrachain ferromagnetic interactions and weak interchain antiferromagnetic ones.