New Type of Single Chain Magnet: Pseudo-One-Dimensional Chain of High-Spin Co(II) Exhibiting Ferromagnetic Intrachain Interactions

作者：Tangoulis V^*; Lalia Kantouri M; Gdaniec M; Papadopoulos Ch; Miletic V; Czapik A

来源：Inorganic Chemistry, 2013, 52(11): 6559-6569.

DOI：10.1021/ic400557f

Two new six-coordinated high-spin Co(II) complexes have been synthesized through the reactions of Co(II) salts with dipyridylamine (dpamH) and 5-nitro-salicylaldehyde (5-NO2-saloH) or 3-methoxy-salicylal-dehyde (3-OCH3-saloH) under argon atmosphere: [Co(dpamH)(2)(5-NO2-salo)]NO3 (1) and [Co(dpamH)(2)(3-OCH3-salo)]NO3 center dot 1.3 EtOH center dot 0.4H(2)O (2). According to the crystal packing of compound 1, two coordination cations are linked with two nitrate anions into a cyclic dimeric arrangement via N-H center dot center dot center dot O and C-H center dot center dot center dot O hydrogen bonds. In turn, these dimers are assembled into (100) layers through pi-pi stacking interactions between inversion center related pyridine rings of the dpamH ligands. The crystal packing of compound 2 reveals a 1D assembly consisting solely from the coordination cations, which is formed by pi-pi stacking interactions between pyridine rings of one of the dpamH along the [010] and another 1D assembly of the coordination cations and nitrate anions through the N-H center dot center dot center dot O hydrogen bonding interactions along the [001] direction. All complexes were magnetically characterized, and a new approximation method was used to fit the magnetic susceptibility data in the whole temperature range 2-300 K on the basis of an empirical expression which allows the treatment of each cobalt(II) ion in axial symmetry as an effective spin S-eff = 1/2. In zero field, dynamic magnetic susceptibility measurements show slow magnetic relaxation below 5.5 K for compound 2. The slow dynamics may originate from the motion of broad domain walls and is characterized by an Arrhenius law with a single energy barrier Delta(r)/k(B) = 55(1) K for the [10-1488 Hz] frequency range. In order to reveal the importance of the crystal packing in the SCM behavior, a gentle heating process to 180 degrees C was carried out to remove the solvent molecules. The system, after heating, undergoes a major but not complete collapse of the network retaining to a small percentage its SCM character.

• 出版日期2013-6-3