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Issue 4, 2005
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3,6-Bis(2′-pyridyl)pyridazine (L) and its deprotonated form (L − H+) as ligands for {(acac)2Run+} or {(bpy)2Rum+}: investigation of mixed valency in [{(acac)2Ru}2(μ-L − H+)]0 and [{(bpy)2Ru}2(μ-L − H+)]4+ by spectroelectrochemistry and EPR

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Abstract

Crystallographically characterised 3,6-bis(2′-pyridyl)pyridazine (L) forms complexes with {(acac)2Ru} or {(bpy)2Ru2+} via one pyridyl-N/pyridazyl-N chelate site in mononuclear RuII complexes (acac)2Ru(L), 1, and [(bpy)2Ru(L)](ClO4)2, [3](ClO4)2. Coordination of a second metal complex fragment is accompanied by deprotonation at the pyridazyl-C5 carbon {L → (L − H+)} to yield cyclometallated, asymmetrically bridged dinuclear complexes [(acac)2RuIII(μ-L − H+)RuIII(acac)2](ClO4), [2](ClO4), and [(bpy)2RuII(μ-L − H+)RuII(bpy)2](ClO4)3, [4](ClO4)3. The different electronic characteristics of the co-ligands, σ donating acac and π accepting bpy, cause a wide variation in metal redox potentials which facilitates the isolation of the diruthenium(III) form in [2](ClO4) with antiferromagnetically coupled RuIII centres (J = −11.5 cm−1) and of a luminescent diruthenium(II) species in [4](ClO4)3. The electrogenerated mixed-valent RuIIRuIII states 2 and [4]4+ with comproportionation constants Kc > 108 are assumed to be localised with the RuIII ion bonded via the negatively charged pyridyl-N/pyridazyl-C5 chelate site of the bridging (L − H+) ligand. In spectroelectrochemical experiments they show similar intervalence charge transfer bands of moderate intensity around 1300 nm and comparable g anisotropies (g1g3 ≈ 0.5) in the EPR spectra. However, the individual g tensor components are distinctly higher for the π acceptor ligated system [4]4+, signifying stabilised metal d orbitals.

Graphical abstract: 3,6-Bis(2′-pyridyl)pyridazine (L) and its deprotonated form (L − H+)− as ligands for {(acac)2Run+} or {(bpy)2Rum+}: investigation of mixed valency in [{(acac)2Ru}2(μ-L − H+)]0 and [{(bpy)2Ru}2(μ-L − H+)]4+ by spectroelectrochemistry and EPR

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Publication details

The article was received on 17 Nov 2004, accepted on 14 Dec 2004 and first published on 17 Jan 2005


Article type: Paper
DOI: 10.1039/B417530A
Citation: Dalton Trans., 2005,0, 706-712
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    3,6-Bis(2′-pyridyl)pyridazine (L) and its deprotonated form (L − H+) as ligands for {(acac)2Run+} or {(bpy)2Rum+}: investigation of mixed valency in [{(acac)2Ru}2(μ-L − H+)]0 and [{(bpy)2Ru}2(μ-L − H+)]4+ by spectroelectrochemistry and EPR

    S. Ghumaan, B. Sarkar, S. Patra, K. Parimal, J. van Slageren, J. Fiedler, W. Kaim and G. K. Lahiri, Dalton Trans., 2005, 0, 706
    DOI: 10.1039/B417530A

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