Issue 21, 2019

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

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

Supplementary files

Article information

Article type
Paper
Submitted
04 1 2019
Accepted
20 3 2019
First published
20 3 2019

Dalton Trans., 2019,48, 7378-7387

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

J. Rajpurohit and M. Shanmugam, Dalton Trans., 2019, 48, 7378 DOI: 10.1039/C9DT00056A

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