EPR and XANES studies of anaerobic photolysis of iso-propilpyridinecobaloxime: Elucidation of the reactivity of the Co(II) primary product

• Type: Article in International Scientific Journal
• Date: 2014

Authors

Maria Rangel (Author) ICBAS; Andreia Leite (Author) Other; Andre Silva (Author) Other; Baltazar de Castro (Author) FCUP; Walkiria Schlindwein (Author) Other; Loretta Murphy (Author) Other

Journal

Title: Journal of Organometallic Chemistry

Vol. 760

Pages: 11-18

ISSN: 0022-328X

Publisher: Elsevier

Indexing

ISI Web of Knowledge - 2 Citations

Scopus - 2 Citations

Scientific classification

FOS: Natural sciences > Chemical sciences

Other information

Authenticus ID: P-009-AZF

DOI: 10.1016/j.jorganchem.2014.01.033

Abstract (EN): Anaerobic photolysis of iso-propilpyridinecobaloxime was monitored by EPR and X-ray Absorption Near Edge spectroscopy (XANES). The spectra of the cobalt(II) photolysis products were analyzed and compared with those obtained for parent cobalt(II) dimethylglyoximato complexes in order to rationalize the involvement of photolysis primary products in further reactions in solution. The results obtained upon photolysis in frozen matrix, confirm that the photolysis primary product is the five coordinate cobalt(II) complex, [Co(DH)(2)py], and that this species is only observable in frozen solution. As the matrix is relaxed to room temperature the five coordinate species evolves to give rise to a six coordinate cobalt(II) complex, [Co(DH)(2)py(2)], that persists at room temperature and that is observable in EPR upon re-cooling to frozen solution. When monitoring the warming up of the irradiated frozen solution we observe an EPR signal which is assigned to a square planar species, [Co(DH)(2)], providing evidence for the source of pyridine molecules to originate the compound with two bound pyridine molecules. Since the latter signal is lost upon warming we hypothesize that the four coordinate species polymerizes or packs into diamagnetic forms at room temperature. The supposition is corroborated by comparison of the values of the magnetic moments of compounds [Co(DH)(2)py(2)], [Co(DH)(2)py] and [Co(DH)(2)] as powders and in solution. EPR titration of compound [Co(DH)(2)] with pyridine substantiates the latter results and shows that the complex with two bound pyridine molecules is the predominant species from a 1: 1 M ratio. The XANES profiles of powder and solution samples of compound [Co(DH)(2)] are meaningfully different and indicative that substantial axial interactions are present in solution while the powder's profile is closely related with those described for square planar complexes. The presence of two solvent molecules bound to [Co(DH)(2)] in solution is confirmed by the values of the spin-Hamiltonian parameters obtained for the same sample. The use of XANES spectroscopy was particularly valuable to provide independent evidence that the structure of [Co(DH)(2)] and [Co(DH)(2)py] is different in powder and in solution and to monitor the change in oxidation state and geometry during the progression of the photolysis process. (C) 2014 Published by Elsevier B. V.

Language: English

Type (Professor's evaluation): Scientific

No. of pages: 8