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Solution structure of a pentachromium(II) single molecule magnet from DFT calculations, isotopic labelling and multinuclear NMR spectroscopy

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Abstract

The structure of pentachromium(II) extended metal atom chain [Cr5(tpda)4Cl2] (2), which behaves as a single molecule magnet at low temperature, was investigated by Density Functional Theory (DFT) calculations and spectroscopic studies without the constraints of a crystal lattice (H2tpda = N2,N6-bis(pyridin-2-yl)pyridine-2,6-diamine). DFT studies both in the gas phase and including CH2Cl2 solvent effects indicate that an unsymmetric structure (C4 point group), with pairs of formally quadruply-bonded metal ions and one terminal metal center, is slightly more stable (2.9 and 3.9 kcal mol−1) than a symmetric structure (D4 point group). Isotopically-labelled samples (2-d8 and 2-d16) have then been prepared to aid in molecular symmetry determination by combined 1H and 2H NMR studies in dichloromethane solution. The spectra are strongly suggestive of a symmetric (D4) framework, indicating fast shuttling between the two unsymmetric forms over the timescale of NMR experiments. Procedures for a high-yield Pd-free synthesis of H2tpda and for site-selective post-synthetic H/D exchange of aromatic H2tpda hydrogens are also reported.

Graphical abstract: Solution structure of a pentachromium(ii) single molecule magnet from DFT calculations, isotopic labelling and multinuclear NMR spectroscopy

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Publication details

The article was received on 18 Oct 2017, accepted on 04 Dec 2017 and first published on 05 Dec 2017


Article type: Paper
DOI: 10.1039/C7DT03931J
Citation: Dalton Trans., 2018, Advance Article
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    Solution structure of a pentachromium(II) single molecule magnet from DFT calculations, isotopic labelling and multinuclear NMR spectroscopy

    A. Dirvanauskas, R. Galavotti, A. Lunghi, A. Nicolini, F. Roncaglia, F. Totti and A. Cornia, Dalton Trans., 2018, Advance Article , DOI: 10.1039/C7DT03931J

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