Fluoride Bridges as Structure-Directing Motifs in 3d-4f Cluster Chemistry

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• 作者：Torben Birk ; Kasper S. Pedersen ; Christian Aa. Thuesen ; Thomas Weyherm眉ller ; Magnus Schau-Magnussen ; Stergios Piligkos ; H枚gni Weihe ; Susanne Mossin ; Marco Evangelisti ; Jesper Bendix
• 刊名：Inorganic Chemistry
• 出版年：2012
• 出版时间：May 7, 2012
• 年：2012
• 卷：51
• 期：9
• 页码：5435-5443
• 全文大小：469K
• 年卷期：v.51,no.9(May 7, 2012)
• ISSN：1520-510X

文摘

The use of kinetically robust chromium(III) fluorido complexes as synthons for mixed 3d-4f clusters is reported. The tendency toward linear {Cr^III鈥揊鈥揕n^III} units dictates the cluster topology. Specifically, we show that reaction of cis-[Cr^IIIF₂(NN)₂]NO₃ (NN = 1,10-phenanthroline (鈥減hen鈥? or 2,2鈥?bipyridine (鈥渂py鈥?) with Ln(NO₃)₃路xH₂O produces isostructural series of molecular {Ln₂Cr₂} squares (1鈥?b>9) with linear fluoride bridges. In a parallel fashion, fac-[Cr^IIIF₃L], where L = N,N鈥?/i>,N鈥?trimethyl-1,4,7-triazacyclononane (鈥淢e₃tacn鈥?, reacts with Nd(NO₃)₃路6H₂O to form a fluoride-centered penta-nuclear complex and fac-[Cr^IIIF₃L鈥瞉, with L鈥?= 1,1,1-tris-((methylamino)methylethane) (鈥淢e₃tame鈥?, reacts with [Ln(hfac)₃(H₂O)₂] (hfacH = 1,1,1,5,5,5-hexafluoroacetylacetone) to yield an isostructural series of {Ln₃Cr₂} (10鈥?b>14) trigonal bipyramids with no central ligand. The formation of the latter is accompanied by a partial solvolysis of the Cr(III) precursor but without formation of insoluble LnF₃. The magnetic properties of the gadolinium containing clusters allow quantification of fluoride-mediated, antiferromagnetic Gd鈥揅r exchange interactions of magnitude between 0.14 cm^鈥? and 0.71 cm^鈥? (膜 = J₁₂艤₁路艤₂ formalism) and vanishingly small J_Gd鈥揋d of 0.06(0) cm^鈥?. The large spin and small anisotropy together with weak exchange interactions in the {Gd₃Cr₂} (11) cluster give rise to a very large magneto-caloric effect of 鈭捨?i>S_m = 28.7 J kg^鈥? K^鈥? (渭₀H = 90 to 0 kOe).