کد مقاله کد نشریه سال انتشار مقاله انگلیسی نسخه تمام متن
1309003 1499211 2008 12 صفحه PDF دانلود رایگان
عنوان انگلیسی مقاله ISI
New dinuclear cobalt(II) octaaza macrocyclic complexes with high oxidation redox potentials: Their crystal structure and unusual magnetic properties
موضوعات مرتبط
مهندسی و علوم پایه شیمی شیمی معدنی
پیش نمایش صفحه اول مقاله
New dinuclear cobalt(II) octaaza macrocyclic complexes with high oxidation redox potentials: Their crystal structure and unusual magnetic properties
چکیده انگلیسی

Dinuclear cobalt(II) complexes were synthesised from 1,4,8,11-tetrakis-(2-pyridylmethyl)-1,4,8,11-tetraazacyclotetradecane (tmpc), [Co2(tmpc)Cl2][CoCl4] (1), [Co2(tmpc)Cl2][PF6]2 (1a) and [Co2(tmpc)(NO3)2][NO3]2 · MeOH (2) and characterised by magnetic, spectroscopic and electrochemical techniques and by single-crystal X-ray diffraction. The X-ray structures of 1 and 2 demonstrate that in both complexes the metal ion is exo-coordinated with respect to the macrocyclic ligand. In 1, the Co(II) ions are fivefold coordinated with trigonal bipyramidal geometry, while in 2 they are sixfold coordinated with a distorted octahedral geometry. The high magnetic moments obtained for these complexes are explained in terms of a spin–orbit coupling. Magnetic measurements show a deviation from the Curie–Weiss law at low temperatures. Two magnetic orderings were observed, at high temperatures an antiferromagnetic coupling was found, below 20 K a change to a weak ferromagnetic coupling was observed. Isothermal magnetic measurements at low temperature show a weak hysteresis, which was confirmed by the small coercive field found at low temperature. In addition, for the first time an explanation for the observation that these cobalt(II) compounds are very stable towards oxidation is offered in terms of the high redox potential values obtained for 1, 1a, and 2.

Dinuclear cobalt(II) complexes were synthesised and characterised. Two magnetic orderings were observed, an antiferromagnetic coupling at high temperatures, below 20 K a change to a weak ferromagnetic coupling was observed. Isothermal magnetic measurements show hysteresis for these complexes. The half wave potentials for the oxidation of Co(II) to Co(III) accounts for the observation that these complexes are very stable towards oxidation.Figure optionsDownload as PowerPoint slide

ناشر
Database: Elsevier - ScienceDirect (ساینس دایرکت)
Journal: Inorganica Chimica Acta - Volume 361, Issues 9–10, 27 June 2008, Pages 2747–2758
نویسندگان
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