Seven-Coordination versus Six-Coordination in Divalent First-Row Transition-Metal Complexes Derived from 1,10-Diaza-15-crown-5

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• 作者：Lea Vaiana ; Mart&iacute ; n Regueiro-Figueroa ; Marta Mato-Iglesias ; Carlos Platas-Iglesias ; David Esteban-Gó ; mez ; André ; s de Blas ; Teresa Rodr&iacute ; guez-Blas
• 刊名：Inorganic Chemistry
• 出版年：2007
• 出版时间：October 1, 2007
• 年：2007
• 卷：46
• 期：20
• 页码：8271 - 8282
• 全文大小：234K
• 年卷期：v.46,no.20(October 1, 2007)
• ISSN：1520-510X

文摘

The complexes of the heptadentate receptor N,N'-bis(benzimidazol-2-ylmethyl)-1,10-diaza-15-crown-5 (L²) with Mn^II,Co^II, Ni^II, Cu^II, and Zn^II are reported. The X-ray crystal structures of the Zn^II and Ni^II complexes show that whereasthe Zn^II ion is seven-coordinated in a (distorted) pentagonal-bipyramidal coordination environment, the Ni^II ion isonly six-coordinated in a distorted octahedral coordination environment. Theoretical calculations on the [M(L²)]²⁺systems (M = Mn, Co, Ni, Cu, or Zn) performed at the density functional theory (DFT; B3LYP) level have beenused to obtain information about the structure and electronic properties of these complexes, as well as to rationalizetheir preferences for a pentagonal-bipyramidal or an octahedral coordination. We have found that for the Mn^II, Co^II,Cu^II, and Zn^II complexes, geometry optimizations lead systematically to pentagonal-bipyramidal coordinationenvironments around the metal ions. However, for the Ni^II complex, two minimum-energy conformations were obtained,with the metal ion being in octahedral (o-[Ni(L²)]²⁺) or pentagonal-bipyramidal (pb-[Ni(L²)]²⁺) coordination. Thestabilization of the octahedral geometry in the Ni^II complex can be considered as the result of the Jahn-Tellereffect operating in pentagonal-bipyramidal geometry, which in an extreme case leads to an octahedral coordination.Spectrophotometric titrations carried out in dimethyl sulfoxide (DMSO) and CH₃CN/DMSO (9:1) solutions indicatethe following stability sequence for the complexes of L²: Co^II Ni^II > Zn^II Mn^II. The variations in the geometryand stability of the complexes may be rationalized in terms of the different occupations of the frontier molecularorbitals along the first-row transition-metal series. Finally, a time-dependent DFT approach was used to investigatethe absorption spectrum of the [Cu(L²)]²⁺ complex based on the optimized geometries at the B3LYP level, alsoconfirming a pentagonal-bipyramidal coordination in solution for this compound.