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The molecular and electronic structure of an unusual cobalt NNO pincer ligand complex

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Abstract

The reaction of two equivalents of [Co(PMe3)4] (1) with one equivalent of a neutral NNO pincer ligand (L1) led to the formation of purple-coloured single crystals. The crystal structure determination reveals the molecular structure as a cobalt dimer [Co2(L1)(PMe3)5], which is solved in the triclinic P[1 with combining macron] space group. Although this species appears to have a formal zero oxidation state on cobalt ions, careful analysis of the structural parameters of the L1 reveals that the NNO ligand is reduced by three electrons; this observation has rarely been reported in the literature. Therefore, herein, more accurate description of the molecular formula [(PMe3)2CoII4-L13−)CoI(PMe3)3] (2) was proposed. In 2, we observed an unusual η3-π-allyl-type binding mode of the pyridine ring carbon atoms of the L13− ligand with the cobalt ion. X-ray photoelectron spectroscopy not only reveals the presence of the mixed valent cobalt ion within 2 but also unambiguously discloses the spin state of these metal ions (Co(I) diamagnetic (low-spin) and Co(II) paramagnetic (high-spin)). The proposed electronic structure is consistent with the magnetic moment measured at room temperature. The electronic structure of 2 was further supported by the Q-band EPR measurements performed on polycrystalline sample of 2 at 5.0 K, and the presence of two independent S = ½ states was revealed. This has been qualitatively rationalized based on the super-exchange coupling pathway observed in 2. The NMR studies performed for 2 (C6D6 solvent) evidently showed that the solid-state structure of 2 was maintained in solution.

Graphical abstract: The molecular and electronic structure of an unusual cobalt NNO pincer ligand complex

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Publication details

The article was received on 04 Jan 2019, accepted on 20 Mar 2019 and first published on 20 Mar 2019


Article type: Paper
DOI: 10.1039/C9DT00056A
Citation: Dalton Trans., 2019, Advance Article

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    The molecular and electronic structure of an unusual cobalt NNO pincer ligand complex

    J. Rajpurohit and M. Shanmugam, Dalton Trans., 2019, Advance Article , DOI: 10.1039/C9DT00056A

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