A New Alternating Ferro‐Antiferromagnetic One‐Dimensional Azido‐Bridged (Arylazoimidazole)manganese(<scp>II</scp>), [Mn(TaiEt)(N₃)₂]_<i>n</i> [TaiEt = 1‐Ethyl‐2‐(<i>p</i>‐tolylazo)imidazole], Exhibiting Bulk Weak Ferromagnetic Long‐Range Ordering

Abstract

Abstract 1‐Ethyl‐2‐( p ‐tolylazo)imidazole [ p ‐Me−C 6 H 4 −N=N−C 3 H 2 N 2 − Et‐1; TaiEt], an unsymmetrical N,N′‐blocker, and azide (N 3 − ), a versatile intermediary, coordinate to manganese( II ) forming an alternating chain with the formula [Mn(TaiEt)(N 3 ) 2 ] n ( 1 ). The compound crystallizes in the triclinic P $\bar 1$ space group with a = 7.9297(7) Å, b = 9.5883(9) Å, c = 11.8366(11) Å, α = 103.555(2)°, β = 105.811(2)°, γ = 104.280(2)°, and Z = 2. The structure consists of neutral chains in which each manganese( II ) center is alternately bridged by two end‐on and two end‐to‐end azide ligands. The unsymmetrical arylazo heterocycle chelator creates a strong distortion around the metal center [N−Mn−N′ bite 67.7°; Mn−N′(azo) distance 2.562 Å]. The magnetic properties of 1 have been investigated over the temperature range 2−300 K. Magnetic data are analyzed on the basis of an alternating ferro‐ and antiferromagnetic Heisenberg chain of the manganese( II ) ions, described by the spin Hamiltonian H = − J 1 Σ S 2 i S 2 i +1 − J 2 Σ S 2 i +1 S 2 i +2 . The J exchange parameters are 2.65 ± 0.12 cm −1 and −14.5 ± 0.15 cm −1 , respectively. Magnetic studies at low temperatures indicate long‐range ordering (canting) with a remnant magnetism that vanishes above 40 K. The canting phenomenon has been studied by various techniques including an EPR spectroscopic investigation at different temperatures and appears to be due to the local distortion around each metal center and the π‐π stacking in the 3‐D network. (© Wiley‐VCH Verlag GmbH &amp; Co. KGaA, 69451 Weinheim, Germany, 2004)