Controlled Synthesis and Magnetic Properties of 2D and 3D Iron Azide Networks 2 1 [Fe(N 3 ) 2 (4,4'-bpy)] and 3 1 [Fe(N 3 ) 2 (4,4'-bpy)] Aihua Fu, [a, c] Xiaoying Huang, [a] Jing Li,* [a] Tan Yuen, [b] and Chyan Long Lin [b] Abstract: Controlled synthesis of tran- sition metal complexes with mixed li- gands has led to two new compounds with the same empirical formula [Fe(N 3 ) 2 (4,4'-bpy)] (4,4'-bpy  4,4'- bipyridine). The compound 2D- [Fe(N 3 ) 2 (4,4'-bpy)] (I) contains end-on (EO) bridging azido ligands. It crystal- lizes in the orthorhombic crystal system, space group Cmmm (No. 65): a  11.444(2) ä, b  15.181(3) ä, c  3.458(1) ä, V  600.8(2) ä 3 , and Z  2. The compound 3D-[Fe(N 3 ) 2 (4,4'-bpy)] (II) contains end-to-end (EE) azido bridges. It belongs to the tetragonal crystal system, space group P4 1 2 1 2 (No. 92): a  8.132(1) ä, b  8.132(1) ä, c  16.708(3) ä, V  1104.9(5) ä 3 , 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 solu- tion 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,inthelow- field region, multiple transitions at T N1  20Kand T N2  5 K were observed, and these indicated the existence of Fe moment reorientation. Heat capacity measurements on II confirmed ferro- magnetic transition at T C  20 K. Keywords: controlled synthesis ¥ iron ¥ magnetic properties ¥ polymers Introduction A significant amount of re- search has been dedicated to the study of molecular-based magnets, the structures of which are built upon inorganic motifs bridged by organic compo- nents. [1] Inthelightofcontrolled synthesis, we have recently pro- posed and successfully prepared a group of two-dimensional layered networks based on six-coordinate, divalent metal centers, [M(ox)(4,4'-bpy)] (M  Fe, Co, Ni, Zn; ox  C 2 O 4 2 , 4,4'-bpy  4,4'-bipyridine) and [MCl 2 (4,4'-bpy)] (M  Fe, Co, Ni, Co/Ni). [2] In these structures, metal centers are bonded by a m 2 -bridging ligand, L, to form one-dimensional magnetic chains, as illustrated in Figure 1 (left). A second, lengthier and rigid bridging ligand, such as 4,4'-bpy (approx. length:  7.1 ä), is used to complete the metal coordination and to interconnect the parallel chains, which generates a two- dimensional network structure. The intrachain metal±metal interactions constitute the primary cause for the magnetic ordering in these compounds, whereas interchain interactions are usually secondary. Evidently, the magnetic properties are directly affected by the nature of the bridging ligand, L. While comparisons have been made between the two structures, with L being C 2 O 4 2 and Cl  , from which some interesting conclusions have been derived, the two ligands are quite different in a number of ways. Synthesis of related structures containing ligands (L) with similar properties and bonding nature would therefore be of great value for understanding the ligand effect on the magnetic interactions and the structure±property correlation. The investigation of transition metal azide coordination complexes has become an area of increasing interest. This is primarily due to the versatility of the azido ligand in the self- [a] Prof. J. Li, A. Fu, X. Huang Department of Chemistry, Rutgers University, Camden New Jersey 08102 (USA) Fax: ( 1)856-225-6506 E-mail: jingli@crab.rutgers.edu [b] Prof. T. Yuen, Prof. C.L. Lin Department of Physics, Temple University, Philadelphia Pennsylvania 19122 (USA) [c] A. Fu Current address: Department of Chemistry University of California, Berkeley, CA 94720 (USA) FULL PAPER Chem. Eur. J. 2002, 8, No. 10 ¹ WILEY-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002 0947-6539/02/0810-2239 $ 20.00+.50/0 2239 Figure 1. One-dimensional magnetic chains of ML 2 (left, M  metal center, L  m 2 ligand) are interconnected by another rigid and lenthier ligand to form a two-dimensional crystal structure (right).