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Issue 7, 2013
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Thermochromic organometallic complexes: experimental and theoretical studies of 16- to 18-electron interconversions of adducts of arene Ru(II) carboranes with aromatic amine ligands

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Abstract

A series of 18-electron complexes of general formula [Ru(p-cym)(1,2-dicarba-closo-dodecaborane-1,2-dithiolato)(L)] (p-cym = para-cymene; L = 4-dimethylaminopyridine (2), nicotinamide (3), 3-ethynylpyridine (4), N-methylimidazole (5), 4-cyanopyridine (6), and pyridine (7)) were synthesised by reactions between the 16-electron precursor [Ru(p-cym)(1,2-dicarba-closo-dodecaborane-1,2-dithiolato)] (1) and corresponding heterocyclic bases. X-ray crystal structures of complexes 2 and 5 were determined. In dichloromethane and chloroform solutions at ambient temperature, the 18-electron complexes 2–7 are in equilibrium with the 16-electron precursor 1. Each equilibrium is displaced towards the formation of the blue 16-electron or yellow 18-electron complex by increasing or decreasing the temperature of the solution, respectively, which results in controlled and reversible thermochromism. Binding constants (K) and Gibbs free energies (ΔG°) of the six equilibria have been determined by a combination of experiments (Job plots, UV-visible titrations, NMR studies) and also by computation (time-dependent density functional theory, TD-DFT). A linear free energy relationship for log K versus pKa for the pyridine and imidazole ligands was established. The predicted strong interactions of 1 with other aromatic amine ligands, such as amphetamine derivatives, were verified experimentally. This appears to be the first report of reversible 16/18-electron interconversions with associated thermochromic properties for a well-known family of complexes.

Graphical abstract: Thermochromic organometallic complexes: experimental and theoretical studies of 16- to 18-electron interconversions of adducts of arene Ru(ii) carboranes with aromatic amine ligands

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Publication details

The article was received on 06 Nov 2012, accepted on 23 Nov 2012 and first published on 06 Dec 2012


Article type: Paper
DOI: 10.1039/C2DT32650G
Dalton Trans., 2013,42, 2580-2587
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    Thermochromic organometallic complexes: experimental and theoretical studies of 16- to 18-electron interconversions of adducts of arene Ru(II) carboranes with aromatic amine ligands

    N. P. E. Barry, R. J. Deeth, G. J. Clarkson, I. Prokes and P. J. Sadler, Dalton Trans., 2013, 42, 2580
    DOI: 10.1039/C2DT32650G

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