Magnetic properties of octa- and heptadeca-nuclear heterometallic Co^II-Ln^III complexes derived from the ligand 6-chloro-2-hydroxypyridine

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• 作者：Stuart K. Langley ; Nicholas F. Chilton ; Boujemaa Moubaraki ; Keith S. Murray
• 关键词：Heterometallic ; Lanthanide ; Cobalt(II) ; Magnetism ; Single-molecule-magnetism
• 刊名：Polyhedron
• 出版年：13 December, 2013
• 年：2013
• 卷：66
• 期：Complete
• 页码：48-55
• 全文大小：1650 K

文摘

Four isostructural heterometallic octanuclear complexes have been synthesized of general formulae [Co^II₄Ln^III₄(OH)₄(chp)₁₀(acac)₆]路solv (Ln = Y (1), Gd (2), Tb (3) and Dy (4); solv = 0.5MeCN for 1, 2 and 4 and Et₂O for 3), where Hchp = 6-chloro-2-hydroxypyridine and acac^{鈭?/sup> = acetylacetonate. A fifth complex of formula [CoII₁₁DyIII₆(OH)₁₄(chp)₁₄(piv)₈(NO₃)₄(MeCN)₄]路2H₂O (5) was also isolated using the Hchp ligand with pivalic acid as a co-ligand. X-ray crystallographic studies reveal that complexes 1-4 all display a central planar butterfly motif consisting of the four LnIII ions, with the CoII ions 鈥渃apping鈥?around the periphery of the butterfly. Compound 5 displays a complex metallic core with an unusual disc-like motif capped by two non-planar butterfly units. DC magnetic susceptibility measurements for the {CoII₄LnIII₄} family of compounds (1-4) reveals that the diamagnetic Y analogue {CoII₄YIII₄} (1) displays antiferromagnetic exchange interactions between the Co-Co ions. An overall decrease in the susceptibility (蠂_MT) is then observed upon lowering the temperature for {CoII₄GdIII₄} (2) and {CoII₄TbIII₄} (3), while the {CoII₄DyIII₄} (4) complex displays a decrease before a small increase at the lowest temperatures measured, indicating a ferrimagnetic ground state. AC susceptibility measurements reveal an absence of any SMM behaviour for 1-3 but show the onset of slow magnetic relaxation below 4 K in the case of 4. The DC and AC behaviour of complex 5 {CoII₁₁DyIII₆} follows a similar profile to compound 4 revealing a small increase in 蠂_MT at low temperatures, with the observation of possible SMM behaviour as observed via low temperature 鈥榯ails鈥?of peaks in the out-of-phase susceptibilities.}