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 Qun 2019
Accepted
20 Cig 2019
First published
20 Cig 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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