Synthesis, structure, catalytic and magnetic properties of a pyrazole based five coordinated di-nuclear cobalt(II) complex

• DOI: 10.1016/j.poly.2015.12.062
• Publication Date: 2016-01-06T12:48:42Z
• Authors: Rabiul Alam; Kaberi Pal; Bikash Kumar Shaw; Malay Dolai; Nabanita Pal; Shyamal Kumar Saha; Mahammad Ali
• Keywords: Pyrazole

Abstract The reaction of 4-methyl-2,6- bis (3,5-dimethyl-1H-pyrazol-1-yl)methyl)phenol and Co(NO 3 ) 2 ·6H 2 O in MeCN gives rise to [Co 2 (L) 2 (N 3 ) 2 ] ( 1 ), a dinuclear five coordinated complex of Co(II), in satisfactory yield. The complex has been characterized by C, H and N microanalyses, FT-IR and UV–Vis spectral measurements. A single crystal X-ray diffraction study of 1 reveals that each Co(II) atom is in a distorted square-pyramidal geometry. Electrochemical studies in CH 3 CN showed that the Co(II)–Co(III)/Co(III)–Co(III) redox couple appears to be quasi-reversible ( E ½ = 0.409 V), while the corresponding Co(II)–Co(III)/Co(II)–Co(II) couple is mostly irreversible ( E ½ = −0.447 V). This complex displays modest catalytic activity toward the oxidation of various allylic compounds using TBHP as an oxidant in MeCN under mild conditions. A radical trapped experiment carried out in the presence of 4- tert- butylphenol clearly reveals that the epoxidation reactions occur purely through a radical pathway rather than a concerted one. Low temperature magnetic studies showed that the present Co(II) dimeric complex possesses a high positive magnetic anisotropy ( D = +29.8 cm −1 ) and a weak ferromagnetic exchange interaction (2 J = +10.3 cm −1 ).