3,6-bis(2'-pyridyl)pyridazine (L) and its deprotonated form (L - H+)- as ligands for {(acac)2Ru(n+)} or {(bpy)2Ru(m+)}: investigation of mixed valency in [{(acac)2Ru}2(mu-L - H+)]0 and [{(bpy)2Ru}2(mu-L - H+)]4+ by spectroelectrochemistry and EPR.
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 Ru(II) 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)2Ru(III)(mu-L - H+)Ru(III)(acac)2](ClO4), [2](ClO4), and [(bpy)2Ru(II)(mu-L - H+)Ru(II)(bpy)2](ClO4)3, [4](ClO4)3. The different electronic characteristics of the co-ligands, sigma donating acac- and pi 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 Ru(III) centres (J = -11.5 cm(-1)) and of a luminescent diruthenium(II) species in [4](ClO4)3. The electrogenerated mixed-valent Ru(II)Ru(III) states 2 and [4]4+ with comproportionation constants Kc > 10(8) are assumed to be localised with the Ru(III) 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 (g1-g3 approximatly 0.5) in the EPR spectra. However, the individual g tensor components are distinctly higher for the pi acceptor ligated system [4]4+, signifying stabilised metal d orbitals.
Ghumaan
Sandeep
S
Department of Chemistry, Indian Institute of Technology-Bombay, Powai, Mumbai, 400076, India.
Sarkar
Biprajit
B
Patra
Srikanta
S
Parimal
Kumar
K
van Slageren
Joris
J
Fiedler
Jan
J
Kaim
Wolfgang
W
Lahiri
Goutam Kumar
GK
D018360:Crystallography, X-Ray; D004563:Electrochemistry; D004578:Electron Spin Resonance Spectroscopy; D008024:Ligands; D009682:Magnetic Resonance Spectroscopy; D010084:Oxidation-Reduction; D011522:Protons; D011724:Pyridazines / Q000737:chemistry*; D017975:Ruthenium Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D013056:Spectrophotometry, Ultraviolet
D008024:Ligands; D011522:Protons; D011724:Pyridazines; D017975:Ruthenium Compounds; C062482:pyridazine