Synthesis, crystal structure and thermal properties of bis-(aceto-nitrile-κN)bis-(3-bromo-pyridine-κN)bis-(thio-cyanato-κN)cobalt(II)

Single crystals of the title compound, [Co(NCS)₂(C₅H₄BrN)₂(C₂H₃N)₂], were obtained by the reaction of Co(NCS)₂ with 3-bromo-pyridine in aceto-nitrile. The Co^II cations lie on crystallographic inversion centers and are coordinated by two N-bonded thio-cyanate anions, two 3-bromo-pyridine and two aceto-nitrile ligands thereby forming slightly distorted CoN₆ octa-hedra. In the crystal, these complexes are linked by C-H⋯S and C-H⋯N hydrogen bonds into a three-dimensional network. In the direction of the crystallographic b-axis, the complexes are arranged into columns with neighboring 3-bromo-pyridine ligands stacked onto each other, indicating π-π inter-actions. The CN stretching vibration of the thio-cyanate anions is observed at 2066 cm^-1, in agreement with the presence of only N-bonded anionic ligands. TG-DTA measurements reveal that in the first mass loss the aceto-nitrile ligands are removed and that in the second step, half of a 3-bromo-pyridine ligand is lost, leading to the formation of a polymeric compound with the composition [(Co(NCS)₂)₂(C₅H₄BrN)₃] _n already reported in the literature.

Single-molecule magnet behaviour and catalytic properties of tetrahedral Co(II) complexes bearing chloride and 1,2-disubstituted benzimidazole as ligands

Five cobalt(II) complexes of formula [CoCl₂(Lⁿ)₂] [1 with L1 = 1-benzyl-2-phenyl-1H-benzimidazole, 2 with L2 = 2-(furan-2-yl)-1-(furan-2-ylmethyl)-1H-benzimidazole, 3 with L3 = 1-(4-chlorobenzyl)-2-(4-chlorophenyl)-1H-benzimidazole, 4 with L4 = 1-(2-methoxybenzyl)-2-(2-methoxyphenyl)-1H-benzimidazole and 5 with L5 = 2-(thiophen-2-yl)-1-(thiophen-2-ylmethyl)-1H-benzimidazole] have been synthesised, spectroscopically characterised and cryomagnetically investigated. The crystal structures of 1, 3, 4 and 5 have been determined by X-ray diffraction on single crystals. Each cobalt(II) ion is four-coordinate in a distorted tetrahedral environment built by two chloride anions and two benzimidazole ligands. The neutral molecules are well separated from each other, shortest intermolecular cobalt⋯cobalt distances being greater than 9.0 Å. Static (dc) magnetic susceptibility measurements in the temperature range 2.0-300 K of 1-5 reveal the occurrence of a Curie law behaviour of magnetically non-interacting spin quadruplets in the high-temperature domain with a downturn at low temperatures due to magnetic anisotropy. The values of the D and E/D parameters for these compounds vary in the ranges -8.75 to +8.96 cm^-1 and 0.00140 to 0.23, respectively. Dynamic (ac) magnetic susceptibility measurements of 1-5 show slow magnetic relaxation in the lack (1) or under the presence (1-5) of applied dc magnetic fields, a feature which is typical of single-molecule magnet behaviour (SMM). The analysis of the ac data shows that a thermally activated Orbach relaxation mechanism dominates this behaviour. Complexes 1-5 also act as efficient and highly selective eco-friendly catalysts in the coupling reaction between CO₂ and epoxides to produce cyclic carbonates under solvent-free conditions. Under optimized reaction conditions, different epoxides were converted to the respective cyclic carbonate, with excellent conversions, using catalyst 4.

Slow magnetic relaxation for cobalt(II) complexes in axial bipyramidal environment: an S = 1/2 spin case

A new family of magnetically mononuclear cobalt(II) complexes with formula [{Ni^II(L)Co^II(H₂O)₂(MeOH)}{Ni^II(L)}₂](ClO₄)₂ where H₂L1 = bis(N,N'-bis(3-methoxysalicylidene)ethylene-1,2-diamine) (1), H₂L2 = bis(N,N'-bis(3-methoxysalicylidene)propane-1,2-diamine) (2) and [{Cu^II(L4)}₂Co^II](ClO₄)₂ (3) where H₂L4 = bis(N,N'-bis(3-ethoxysalicylidene)cyclohexane-1,2-diamine) have been obtained employing non chiral or enantiomerically pure Schiff bases. The structural studies have been carried out by single crystal X-ray and powder diffraction. Dynamic magnetic studies indicate that some members of this family present field induced slow relaxation of the magnetization and its response has been compared with the magnetically diluted [Zn_0.9Co_0.1] complex 1D. Ultra-low frequency Raman spectroscopy has been used to relate the slow relaxation with lattice vibrations.

Field-induced single ion magnet behaviour of discrete and one-dimensional complexes containing [bis(1-methylimidazol-2-yl)ketone]-cobalt(II) building units

We describe herein the first examples of six-coordinate Co^II single-ion magnets (SIMs) based on the β-diimine ^Mebik ligand [^Mebik = bis(1-methylimidazol-2-yl)ketone]: two mononuclear [Co^II(^Rbik)₂L₂] complexes and one mixed-valence {CoIII2Co^II}_n chain of formulas [Co^II(^Mebik)(H₂O)(dmso)(μ-NC)₂CoIII2(μ-2,5-dpp)(CN)₆]_n·1.4nH₂O (3) [L = NCS (1), NCSe (2) and 2,5-dpp = 2,5-bis(2-pyridyl)pyrazine (3)]. Two bidentate ^Mebik molecules plus two monodentate N-coordinated pseudohalide groups in cis positions build somewhat distorted octahedral surroundings around the high-spin cobalt(II) ions in 1 and 2. The diamagnetic [CoIII2(μ-2,5-dpp)(CN)₈]^2- metalloligand coordinates the paramagnetic [Co^II(^Mebik)(H₂O)(dmso)]²⁺ complex cations in a bis-monodentate fashion to afford neutral zigzag heterobimetallic chains in 3. Ab initio calculations, and cryomagnetic dc (2.0-300 K) and ac (2.0-12 K) measurements as well as EPR spectroscopy for 1-3 show the existence of magnetically isolated high-spin cobalt(II) ions with D values of 59.84-89.90 (1), 66.32-93.90 (2) and 70.40-127.20 cm^-1 (3) and field-induced slow relaxation of the magnetization, being thus new examples of SIMs with transversal magnetic anisotropy. The analysis of their relaxation dynamics reveals that the relaxation of the magnetization occurs by the Raman (with values of the n parameter covering the range 6.0-6.8) and direct spin-phonon processes.

Dimeric Mn(ii), Co(ii), Ni(ii) and Cu(ii) complexes of a common carboxylate-appended (2-pyridyl)alkylamine ligand: structure, magnetism and DFT study

Weak anti- (1) and ferro-magnetic (2–4) interactions are observed in [MII2(L3)2(S)2]2+ (Mn 1, Co 2, Ni 3) (S = MeOH) and Cu 4 (S = none).

Non-traditional thermal behavior of Co(ii) coordination networks showing slow magnetic relaxation

Three new Co(ii) coordination polymers show the DC magnetic data consistent with the S = 3/2 spin system with large zero-field splitting D > 0, which was confirmed by HF EPR and FIRMS measurements.