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

• Published in: Dalton transactions : an international journal of inorganic chemistry 2022-08, Vol.51 (32), p.12258-1227
• Main Authors: Milani, Jorge Luiz Sônego, da Mata, Álvaro Farias Arruda, Oliveira, Igor Santos, Valdo, Ana Karoline Silva Mendanha, Martins, Felipe Terra, Rabelo, Renato, Cangussu, Danielle, Cano, Joan, Lloret, Francesc, Julve, Miguel, das Chagas, Rafael Pavão
• Format: Article
• Language: English
• Subjects: Carbonates; Catalysts; Chlorides; Cobalt compounds; Coupling (molecular); Cryomagnetic properties; Crystal structure; Curie temperature; High temperature; Ligands; Low temperature; Magnetic anisotropy; Magnetic induction; Magnetic permeability; Magnetic properties; Magnetic relaxation; Single crystals
• ISSN: 1477-9226; 1477-9234
• DOI: 10.1039/d2dt01440h

Five cobalt( ii ) complexes of formula [CoCl 2 (L n ) 2 ] [ 1 with L 1 = 1-benzyl-2-phenyl-1 H -benzimidazole, 2 with L 2 = 2-(furan-2-yl)-1-(furan-2-ylmethyl)-1 H -benzimidazole, 3 with L 3 = 1-(4-chlorobenzyl)-2-(4-chlorophenyl)-1 H -benzimidazole, 4 with L 4 = 1-(2-methoxybenzyl)-2-(2-methoxyphenyl)-1 H -benzimidazole and 5 with L 5 = 2-(thiophen-2-yl)-1-(thiophen-2-ylmethyl)-1 H -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 CO 2 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 . Field-induced SMM behaviour in a series of tetrahedral 1,2-disubstituted benzimidazole cobalt( ii ) complexes and their catalytic properties for an eco-friendly cycloaddition of CO 2 with epoxides.