title: Varying electronic structural forms of ruthenium complexes of non-innocent 9,10-phenanthrenequinonoid ligands.
abstract: Bis(acetylacetonato)ruthenium complexes [Ru(acac)2(Q1-3)], 1-3, incorporating redox non-innocent 9,10-phenanthrenequinonoid ligands (Q1 = 9,10-phenanthrenequinone, 1; Q2 = 9,10-phenanthrenequinonediimine, 2; Q3 = 9,10-phenanthrenequinonemonoimine, 3) have been characterised electrochemically, spectroscopically and structurally. The four independent molecules in the unit cell of 2 are involved in intermolecular hydrogen bonding and π-π interactions, leading to a 2D network. The oxidation state-sensitive bond distances of the coordinated ligands Q(n) at 1.296(5)/1.289(5) Å (C-O), 1.315(3)/1.322(4) Å (C-N), and 1.285(3)/1.328(3) Å (C-O/C-N) in 1, 2 and 3, respectively, and the well resolved (1)H NMR resonances within the standard chemical shift range suggest DFT supported variable contributions from valence formulations [Ru(III)(acac)2(Q˙(-))] (spin-coupled) and [Ru(II)(acac)2(Q(0))], respectively. Complexes 1-3 exhibit one oxidation and two reduction steps with comproportionation constants Kc∼ 10(7)-10(22) for the intermediates. The electrochemically generated persistent redox states 1(n) (n = 0, 1-, 2-) and 2(n)/3(n) (n = 1+, 0, 1-, 2-) have been analysed by UV-vis-NIR spectroelectrochemistry and by EPR for the paramagnetic intermediates in combination with DFT and TD-DFT calculations, revealing significant differences in the oxidation state distribution at the {Ru-Q} interface for 1(n)-3(n). In particular, the diminished propensity of the NH-containing systems for reduction results in the preference for Ru(II)(Q(0)) relative to Ru(III)(Q˙(-)) (neutral compounds) and for Ru(II)(Q˙(-)) over the Ru(III)(Q(2-)) alternative in the case of the monoanionic complexes.
authors.affiliation: Department of Chemistry, Indian Institute of Technology Bombay, Powai, Mumbai 400076, India. lahiri@chem.iitb.ac.in.
authors.forename: Abhishek
authors.initials: A
authors.lastname: Mandal
authors.forename: Tanaya
authors.initials: T
authors.lastname: Kundu
authors.forename: Fabian
authors.initials: F
authors.lastname: Ehret
authors.forename: Martina
authors.initials: M
authors.lastname: Bubrin
authors.forename: Shaikh M
authors.initials: SM
authors.lastname: Mobin
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Kaim
authors.forename: Goutam Kumar
authors.initials: GK
authors.lastname: Lahiri
mesh_terms: D000042:Absorption; D004563:Electrochemistry; D004583:Electrons; D008024:Ligands; D008958:Models, Molecular; D008968:Molecular Conformation; D009942:Organometallic Compounds / Q000737:chemistry*; D010616:Phenanthrenes / Q000737:chemistry*; D012428:Ruthenium / Q000737:chemistry*
chemical_list: D008024:Ligands; D009942:Organometallic Compounds; D010616:Phenanthrenes; C005399:9,10-phenanthrenequinone; D012428:Ruthenium