Reasons behind the Relative Abundances of Heptacoordinate Complexes along the Late First-Row Transition Metal Series

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• 作者：Mart铆n Regueiro-Figueroa ; Lu铆s M. P. Lima ; V铆ctor Blanco ; David Esteban-G贸mez ; Andr茅s de Blas ; Teresa Rodr铆guez-Blas ; Rita Delgado ; Carlos Platas-Iglesias
• 刊名：Inorganic Chemistry
• 出版年：2014
• 出版时间：December 15, 2014
• 年：2014
• 卷：53
• 期：24
• 页码：12859-12869
• 全文大小：540K
• ISSN：1520-510X

文摘

A series of transition metal complexes [ML¹] (H₂L¹ = 1,4,10-trioxa-7,13-diazacyclopentadecane-N,N鈥?diacetic acid, M = Co, Ni, Cu, or Zn) have been prepared and characterized. The X-ray structures of the [CoL¹] and [CuL¹] complexes reveal that the metal ions are seven-coordinated with a distorted pentagonal bipyramidal coordination. The five donor atoms of the macrocycle define the pentagonal plane of the bipyramid, while two oxygen atoms of the carboxylate groups coordinate apically. The [NiL¹] complex presents a very distorted structure with long Ni鈥揙 distances involving two oxygen atoms of the crown moiety [2.544(3) 脜]. This distortion is related to the Jahn鈥揟eller effect that is expected to operate in d⁸ pentagonal bipyramidal complexes. The spectroscopic characterization of the [ZnL¹] and [CuL¹] complexes using NMR and EPR and the theoretical calculation of the ¹³C NMR shifts and g- and A-tensors using DFT confirm that these complexes retain the pentagonal bipyramidal coordination in aqueous solution. The stability trend of the [ML¹] complexes (Co²⁺ > Ni²⁺ < Cu²⁺ > Zn²⁺), which is in contradiction with the Irving鈥揥illiams order, has been analyzed using DFT calculations (TPSSh functional). The free energy values calculated in the gas phase for [CoL¹](g) + [M(H₂O)₆]²⁺(g) 鈫?[ML¹](g) + [Co(H₂O)₆]²⁺(g) (M = Ni, Cu, Zn) reproduce fairly well the stability trend observed experimentally, the agreement being improved significantly upon inclusion of solvent effects. Our results indicate that the pentagonal bipyramidal coordination is particularly unfavorable for Ni²⁺, and thus preorganized ligands that favor this geometry such as L¹ are selective for Co²⁺ over Ni²⁺ cations.