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Issue 36, 2014
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Ruthenium, osmium and rhodium complexes of 1,4-diaryl 1,4-diazabutadiene: radical versus non-radical states

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Abstract

Ruthenium, osmium and rhodium complexes of 1,4-di(3-nitrophenyl)-1,4-diazabutadiene (LDAB) of types trans-[RuII(LDAB)(PPh3)2Cl2] (1), trans-[OsII(LDAB)(PPh3)2Br2] (2) and trans-[Rh(LDAB)(PPh3)2Cl2] (3) are isolated and characterized by elemental analyses, IR, mass and 1H NMR spectra including the single crystal X-ray structure determination of 1·2toluene. The α-diimine fragment of the LDAB ligand in 1·2toluene is deformed, showing a relatively longer –C[double bond, length as m-dash]N– bond, 1.320 Å, and a shorter [double bond, length as m-dash]CH–CH[double bond, length as m-dash] bond, 1.395 Å. Density functional theory (DFT) calculations on trans-[Ru(LDAB)(PMe3)2Cl2] (1Me) and trans-[Os(LDAB)(PMe3)2Br2] (2Me) with singlet spin states authenticated that the closed shell singlet state (CSS) solutions of 1 and 2 are stable and no perturbation occurs because of the diradical open shell singlet (OSS) state. The EPR spectra of 3 and the Mulliken spin density distribution obtained from the DFT calculation on trans-[Rh(LDAB)(PMe3)2Cl2] (3Me) imply that the ground electronic state of 3 can be defined by the [RhIII(LDAB˙)(PPh3)2Cl2] (3RhL˙) ↔ [RhII(LDAB)(PPh3)2Cl2] (3Rh˙L) resonating states. In solid, the contribution of 3RhL˙ is higher and the gav is 2.018 with Δg = 0.10, whereas in frozen glasses the contribution of 3Rh˙L is higher and the gav is 2.026 with Δg (frozen glasses) = 0.13. The g parameters of the electrogenerated [1]+ (g1 = 2.456, g2 = 2.128 and g3 = 1.624, Δg = 0.824), [2]+ (g1 = 2.599, g2 = 2.041 and g3 = 1.965, Δg = 0.634), [1] (g1 = 2.138, g2 = 2.109, g3 = 1.978 and Δg = 0.160) and [2] (g1 = 2.168, g2 = 2.097, g3 = 1.987 and Δg = 0.181) ions and the spin density distributions obtained from the DFT calculations on [1Me]+, [2Me]+, [1Me] and [2Me] reveal that the reversible anodic peaks of 1 and 2 at 0.11 and 0.34 V, referenced versus Fc+/Fc couple, are due to the M(III)/M(II) redox couple, while the reversible cathodic waves at −1.27 V and −0.82 V of 1 and 2 are caused by the LDAB/LDAB˙ redox couple. Both [MII(LDAB˙)(PPh3)2Br2] and [MI(LDAB)(PPh3)2Br2] tautomers contribute to the ground electronic states of [1] (g = 2.075) and [2] (g = 2.084) ions, which are isoelectronic to 3. Time dependent (TD) DFT calculations and spectroelectrochemical measurements elucidated that lower energy absorption bands of 1 and 2 are caused by the metal to ligand charge transfer (MLCT) that disappears upon oxidation or reduction.

Graphical abstract: Ruthenium, osmium and rhodium complexes of 1,4-diaryl 1,4-diazabutadiene: radical versus non-radical states

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Publication details

The article was received on 28 Apr 2014, accepted on 23 Jul 2014 and first published on 23 Jul 2014


Article type: Paper
DOI: 10.1039/C4DT01241K
Author version available: Download Author version (PDF)
Citation: Dalton Trans., 2014,43, 13731-13741
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    Ruthenium, osmium and rhodium complexes of 1,4-diaryl 1,4-diazabutadiene: radical versus non-radical states

    S. Chandra Patra, A. Saha Roy, V. Manivannan, T. Weyhermüller and P. Ghosh, Dalton Trans., 2014, 43, 13731
    DOI: 10.1039/C4DT01241K

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