New Manganese(II) Azido Coordination Polymers with Nicotinic/Isonicotinic Acids as Coligands: Synthesis, Structure, and Magnetic Properties

The reactions of Mn^II ions with azido ligands in the presence of nicotinic/isonicotinic acids gave two manganese(II) azido coordination polymers, [Mn₃(L¹)₂(N₃)₄]_n·nH₂O (1) and [Mn₂(L²)(N₃)₃]_n (2), where L¹ = nicotinate and L² = isonicotinate, with different topological structures. Complex 1 consists of 2D azido−Mn^II planes, which is further linked by L¹ to form a 3D framework with unprecedented 3,6-connected 4-nodal net topology, and complex 2 presents an unprecedented 3,4,6-connected 6-nodal 3D azido−Mn^II structure with L² as the coligand. Magnetic susceptibility measurements reveal dominant antiferromagnetic coupling existing in 1 and 2. Complex 1 is a spin-competitive system and enters into a weak ferromagnetic-to-magnetic phase transition at the critical temperature of 6 K due to spin canting. Complex 2 is an antiferromagnet and exhibits field-induced spin-flop behavior.