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Structure of Methanol Solvated Iodozinc(II) Complexes in Solution.

ABSTRACT: The structures of the solvated zinc ion and the solvated zinc-iodide complexes in methanol solution have been determined by EXAFS. The zinc ion is six-coordinated in an octahedral fashion with a mean Zn-O bond distance of 2.071(4) Å. According to the stability constants of the zinc-iodide system in methanol solution the first complex, ZnI+, is suppressed, which may indicate that a coordination change takes place at this step. On the other hand, the second complex, ZnI2, predominates at excess of iodide. The methanol solvated ZnI2 complex has a tetrahedral structure with mean Zn-I and Zn-O bond distances of 2.55(1) and 1.99(1) Å, respectively. The mean Zn-I bond distance in a solution containing a maximal content of ZnI+, ca. 12%, strongly indicates that the first complex also has a tetrahedral structure.

SUBMITTER: Persson I

PROVIDER: S-EPMC5871641 | biostudies-literature | 2018

REPOSITORIES: biostudies-literature

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Structure of Methanol Solvated Iodozinc(II) Complexes in Solution.

Persson Ingmar I

Journal of solution chemistry 20180319 3

The structures of the solvated zinc ion and the solvated zinc-iodide complexes in methanol solution have been determined by EXAFS. The zinc ion is six-coordinated in an octahedral fashion with a mean Zn-O bond distance of 2.071(4) Å. According to the stability constants of the zinc-iodide system in methanol solution the first complex, ZnI<sup>+</sup>, is suppressed, which may indicate that a coordination change takes place at this step. On the other hand, the second complex, ZnI<sub>2</sub>, pre ...[more]

PMID: 29606778

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Project description:We report a complex with a rare Cu(II)-O-Cu(II) structural motif that is stable at room temperature, which allows its in-depth characterization by a variety of spectroscopic methods. Interest in such compounds is fueled by the recent discovery that a Cu(II)-O-Cu(II) species on the surface of Cu-ZSM-5 is capable of oxidizing methane to methanol, and this in turn ties into mechanistic discussions on the methane oxidation at the dicopper site within the particulate methane monooxygenase. For the synthesis of our Cu2O complex we have developed a novel, neutral ligand system, FurNeu, exhibiting two N-(N',N'-dimethylaminoethyl)(2-pyridylmethyl)amino binding pockets connected by a dibenzofuran spacer. The reaction of FurNeu with CuCl yielded [FurNeu](Cu2(μ-Cl))(CuCl2), 1, demonstrating the geometric potential of the ligand to stabilize Cu-X-Cu moieties. A Cu(I) precursor with weakly coordinating anions was chosen in the next step, namely [Cu(NCCH3)4]OTf, which led to the formation of [FurNeu](Cu(NCCH3))2(OTf)2, 3. Treatment of 3 with O2 or PhIO led to identical green solutions, whose UV-vis spectra were markedly different from the one displayed by [FurNeu](Cu)2(OTf)4, 4, prepared independently from FurNeu and Cu(OTf)2. Further investigations including PhIO consumption experiments, NMR and UV-vis spectroscopy, HR-ESI mass spectrometry, and protonation studies led to the identification of the green product as [FurNeu](Cu2(μ-O))(OTf)2, 5. DOSY NMR spectroscopy confirmed its monomeric character. Over longer periods of time 5 decomposes to give [Cu(picoloyl)2], formed through an oxidative N-dealkylation reaction followed by further oxidation of the ligand. Due to its slow decomposition reaction, all attempts to crystallize 5 failed. However, its structure in solution could be determined by EXAFS analysis in combination with DFT calculations, which revealed a Cu-O-Cu angle that amounts to 105.17°. Moreover, TDDFT calculations helped to rationalize the UV-vis absorptions of 5. The reactivity of complex 5 with 2,4-di-tert-butylphenol, DTBP, was also investigated; the initially formed biphenol product, TBBP, was found to further react in the presence of excessive O2 to yield 2,4,7,9-tetra-tert-butyloxepino[2,3-b]benzofuran, TBOBF, via an intermediate diphenoquinone. It turned out that 5, or its precursor 3, can even be employed as a catalyst for the oxidation of DTBP to TBBP or for the oxidation of TBBP to TBOBF.

Dataset Information

Structure of Methanol Solvated Iodozinc(II) Complexes in Solution.

Publications

Structure of Methanol Solvated Iodozinc(II) Complexes in Solution.

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