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|標題:||First stable reduced form of Co-5 (+10): fine tuning of linear pentacobalt(II) complexes containing delocalized metal-metal bonds through ligand modification||作者:||Wang, W.Z.
|關鍵字:||di(2-pyridyl)amide dpa ligands;string complexes;magnetic-properties;structural versatility;trimetallic complexes;tricobalt compounds;stretch isomerism;chain complexes;dft;oxidation||Project:||Dalton Transactions||期刊/報告no：:||Dalton Transactions, Issue 47, Page(s) 6808-6816.||摘要:||
Pentacobalt EMACs [Co-5(mu(5)-dpzpda)(4)X-2] (X=Cl- (1), NCS- (2)) with fine-tuning of the supporting ligand based on the tripyridyldiamine ligand, N,N'-di(pyrazin-2-yl) pyridine-2,6-diamine (H(2)dpzpda), and their reduced form (Ph4P)[Co-5(mu(5)-dpzpda)(4)X-2] (X = Cl- (3), NCS- (4)) were first synthesized and structurally characterized. The structures of 1-4 showed direct Co-Co bonds with Co-Co distances in the range 2.2385(7)-2.2888(15) angstrom, and valence electrons delocalized through the whole metal chain with distances of longer than 9.06 angstrom. The distances of the inner Co-Co bonds and the Co-axial ligands became longer after reduction, whereas no significant change was observed in the distances of the outer Co-Co bonds and Co-N (supporting ligand) bonds, which was consistent with the MO analysis. Electrochemical studies on both 1 and 2 showed one reversible oxidation and one reversible reduction at E-1/2 = +0.82 and -0.05 V for 1, and at E-1/2 = +0.89 and +0.02 V for 2, respectively. The redox reactions of the thiocyanate complex 4 happened at higher potentials than the chloride complex 3. A magnetism study of 1-4 revealed anomalous magnetic behaviour similar to that of heptacobalt EMACs, and a deviation from the Curie-Weiss law was observed. The chi T-M value at 300 K is 0.84 and 1.16 emu K mol(-1) for 1 and 2, respectively, suggesting spin-equilibrium or a spin-admixture between doublet and quartet states arising from the Boltzmann distribution over different energy levels. Similar results were obtained for 3 and 4, showing intermediate cMT values between a diamagnetic and a triplet state of 0.15-0.96 emu K mol(-1) in the temperature range 5-300 K. The structural and magnetic results were interpreted through an EHMO study.
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