Controlled synthesis and magnetic properties of 2D and 3D iron azide networks ∞ 2[Fe(N3)2(4,4′-bpy)] and ∞ 3[Fe(N3)2(4,4′-bpy)]

Controlled synthesis of transition metal complexes with mixed ligands has led to two new compounds with the same empirical formula Fe(N₃)₂(4,4′-bpy)] (4,4′-bpy = 4,4′-bipyridine). The compound 2D-Fe(N₃)₂(4,4′-bpy)] (I) contains end-on (EO) bridging azido ligands. It crystallizes in the orthorhombic crystal system, space group Cmmm (No. 65): a = 11.444(2) Å, b = 15.181(3) Å, c = 3.458(1) Å, V = 600.8(2) ų, and Z = 2. The compound 3D-[Fe(N₃)₂(4,4′-bpy)] (II) contains end-to-end (EE) azido bridges. It belongs to the tetragonal crystal system, space group P4₁2₁2 (No. 92): a = 8.132(1) Å, b = 8.132(1) Å, c = 16.708(3) Å, V = 1104.9(5) ų, and Z = 4. Crystals of I and II have been grown by the diffusion method. Phase-pure samples of both compounds have been obtained by means of an optimal solution synthesis. Spontaneous long-range magnetic ordering was found in both I and II, with I being a metamagnet, and II being a ferromagnet. For I, in the low-field region, multiple transitions at T_N1 = 20 K and T_N2 = 5 K were observed, and these indicated the existence of Fe moment reorientation. Heat capacity measurements on II confirmed ferromagnetic transition at T_C = 20 K.