Four‐Center Oxidation State Combinations and Near‐Infrared Absorption in [Ru(pap)(Q)₂]ⁿ (Q=3,5‐Di‐tert‐butyl‐N‐aryl‐1,2‐benzoquinonemonoimine, pap=2‐Phenylazopyridine)

Abstract

The complex series [Ru(pap)(Q)2](n) ([1](n)-[4](n); n = +2, +1, 0, -1, -2) contains four redox non-innocent entities: one ruthenium ion, 2-phenylazopyridine (pap), and two o-iminoquinone moieties, Q = 3,5-di-tert-butyl-N-aryl-1,2-benzoquinonemonoimine (aryl = C6H5 (1(+)); m-(Cl)2C6H3 (2(+)); m-(OCH3)2C6H3 (3(+)); m-(tBu)2C6H3 (4(+))). A crystal structure determination of the representative compound, [1]ClO4, established the crystallization of the ctt-isomeric form, that is, cis and trans with respect to the mutual orientations of O and N donors of two Q ligands, and the coordinating azo N atom trans to the O donor of Q. The sensitive C-O (average: 1.299(3) Å), C-N (average: 1.346(4) Å) and intra-ring C-C (meta; average: 1.373(4) Å) bond lengths of the coordinated iminoquinone moieties in corroboration with the N-N length (1.292(3) Å) of pap in 1(+) establish [Ru(III)(pap(0))(Q(·-))2 ](+) as the most appropriate electronic structural form. The coupling of three spins from one low-spin ruthenium(III) (t2g(5)) and two Q(·-) radicals in 1(+)-4(+) gives a ground state with one unpaired electron on Q(·-), as evident from g = 1.995 radical-type EPR signals for 1(+)-4(+). Accordingly, the DFT-calculated Mulliken spin densities of 1(+) (1.152 for two Q, Ru: -0.179, pap: 0.031) confirm Q-based spin. Complex ions 1(+)-4(+) exhibit two near-IR absorption bands at about λ = 2000 and 920 nm in addition to intense multiple transitions covering the visible to UV regions; compounds [1]ClO4-[4]ClO4 undergo one oxidation and three separate reduction processes within ±2.0 V versus SCE. The crystal structure of the neutral (one-electron reduced) state (2) was determined to show metal-based reduction and an EPR signal at g = 1.996. The electronic transitions of the complexes 1(n)-4(n) (n = +2, +1, 0, -1, -2) in the UV, visible, and NIR regions, as determined by using spectroelectrochemistry, have been analyzed by TD-DFT calculations and reveal significant low-energy absorbance (λmax >1000 nm) for cations, anions, and neutral forms. The experimental studies in combination with DFT calculations suggest the dominant valence configurations of 1(n)-4(n) in the accessible redox states to be [Ru(III)(pap(0))(Q(·-))(Q(0))](2+) (1(2+)-4(2+))→[Ru(III)(pap(0))(Q(·-))2](+) (1(+)-4(+))→[Ru(II)(pap(0))(Q(·-))2] (1-4)→[Ru(II)(pap(·-))(Q(·-))2](-) (1(-)-4(-))→[Ru(III)(pap(·-))(Q(2-))2](2-) (1(2-)-4(2-)).

Amphiphilicity in Oxygen Atom Transfer Reactions of Oxobis(iminoxolene)osmium Complexes

“…The cis geometry of ( H ap) 2 Os­(P­[OPh] 3 ) 2 implied by the presence of inequivalent, mutually coupled phosphorus atoms in its 31 P NMR spectrum is confirmed by X-ray crystallography (Figure ). A cis -bis­(iminoxo­lene)­osmium complex with neutral donors (intramolecularly coordinated thioethers), Os­(L N,O,S ) 2 , has been prepared, and cis -bis­(iminoxo­lene)­ruthenium complexes with neutral donors are also known. , In the trans geometry, the inversion center means that the ungerade ligand-centered combination is strictly nonbonding, giving rise to two filled dπ nonbonding orbitals, one filled metal–ligand π bonding orbital, and one filled ligand-centered nonbonding orbital in the metal complex. In contrast, in the C 2 - or pseudo- C 2 symmetry of the cis geometry, the dπ orbitals transform as 2 A + B , so both combinations of the ligand RAOs can interact with the dπ orbitals .…”

Ruthenium Derivatives of in Situ Generated Redox-Active 1,2-Dinitrosobenzene and 2-Nitrosoanilido. Diverse Structural and Electronic Forms

“…The radical complexes [Ru II (pap) 2 (L •– )] + , 1 + , and isomeric 3 + exhibit a weak and broad near-IR band in the range of 1100–1300 nm, involving SOMO of L •– and the vacant π* LUMO of pap . The intense visible and UV bands are originated via pap or L targeted mixed metal–ligand and intra/interligand transitions, respectively.…”

Analysis of Redox Series of Unsymmetrical 1,4-Diamido-9,10-anthraquinone-Bridged Diruthenium Compounds

“…The slightly distorted octahedral arrangements of the complexes are confirmed by the cis and trans angles around the metal ions (Tables S3, S5, S7, S9, and S11 in the Supporting Information). The metal–ligand (bpy, pap, H 3 L – /H 2 L 2– ) bond distances in [ 1 ]­ClO 4 –[ 3 ]­ClO 4 and [ 5 ]­(ClO 4 ) 2 are in good agreement with those reported for analogous complexes. , The NN (pap) distances of 1.302(4) Å and 1.293(7)/1.299(7) Å in [ 2 ]­ClO 4 and [ 5 ]­(ClO 4 ) 2 , respectively, confirm its unreduced state …”