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

Abstract

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-salicylaldehyde (3-OCH3-saloH) under argon atmosphere: [Co(dpamH)2(5-NO2-salo)]NO3 (1) and [Co(dpamH)2(3-OCH3-salo)]NO3·1.3 EtOH·0.4H2O (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···O and C-H···O hydrogen bonds. In turn, these dimers are assembled into (100) layers through π-π 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 π-π 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···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 Δr/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 °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.

Synthesis, Electronic, Magnetic and Structural Characterization of New Trinuclear Mixed‐Valence CoIII‐CoII‐CoIII Complex.

“…The diffuse reflectance was recorded (Supplementary Information, Figure S4). It was observed the ligand, charge‐transfer and d‐d transitions this information confirm that in solution and solid is the same …”

“…Inside of Figure shows the band for the d‐d transitions in the range of 550 nm to 1000 nm. The two λ max at 552 nm (18,094 cm −1 ) and the shoulder with λ max at 659 nm (15,157 cm −1 ), support the presence of both octahedral Co II and octahedral Co III ions in the complexes . The higher energy d‐d transitions are due to the 1 A 1g → 1 T 1g and the 4 T 1g (F)→ 4 T 1g (P) and the shoulder is probably due to the 4 T 1g (F)→ 4 A 2g .…”

Cycloheptatrienyl trianion: an elusive bridge in the search of exchange coupled dinuclear organolanthanide single-molecule magnets

“…This type of behaviour has been similarly noted in Single-Chain Magnets (SCMs), where inter-chain spin–spin interactions give rise to decreasing susceptibility values. 49,50 Even under the optimal field of 1000 Oe, there is a decrease in intensity of the peaks for the out-of-phase component (Fig. S11†).…”

A toolbox of building blocks, linkers and crystallisation methods used to generate single-chain magnets

“…[23]. [62,63]. Indeed, the first ever SCM to be reported in the literature, by Gatteschi and co-workers, used a simple [Co II (hfac) 2 ] complex (hfac = hexafluoroacetylacetonate, Figs.…”

“…The second is by H-bond interactions from coordinated water molecules to the salpn ligand (Fig. 41) [139], and the third is by -stacking interactions [62,108].…”