%0 Journal Article %1 Das.2009d %A Das, Dipanwita %A Das, Atanu Kumar %A Sarkar, Biprajit %A Mondal, Tapan Kumar %A Mobin, Shaikh M. %A Fiedler, Jan %A Zalis, Stanislav %A Urbanos, Francisco A. %A Jimenez-Aparicio, Reyes %A Kaim, Wolfgang %A Lahiri, Goutam Kumar. %D 2009 %J Inorganic Chemistry %K acac crystal electronic iminobenzosemiquinone magnetic prepn property redox ruthenium series;electrochem series;ruthenium structure substitution %N 24 %P 11853--11864 %R 10.1021/ic901900g %T The Semiquinone-Ruthenium Combination as a Remarkably Invariant Feature in the Redox and Substitution Series Ru(Q)n(acac)3-nm, n = 1-3; m = (-2), -1, 0, +1, (+2); Q = 4,6-Di-tert-butyl-N-phenyl-o-iminobenzoquinone %V 48 %X Three new compds., Ru(Q·-)(acac)2 (1), Ru(Q·-)2(acac) (2), and Ru(Q·-)3 (3), were obtained and characterized as RuIII complexes with 4,6-di-tert-butyl-N-phenyl-o-iminobenzosemiquinone (Q·-) ligands. All three systems show multiple electron transfer behavior, which was analyzed using EPR and UV-visible-near-IR (NIR) spectroelectrochem. 1H NMR spectroscopy and a crystal structure anal. suggest antiferromagnetically spin-spin coupled RuIII and Q·- in 1, similar to that in the compd. with unsubstituted o-iminobenzosemiquinone (4). However, in contrast to 4n, the system 1m exhibits unambiguously metal-centered electron transfer, producing ions RuIV(Q·-)(acac)2+ = 1+ and RuII(Q·-)(acac)2- = 1-, both with EPR-evidenced ligand-based spin, as also supported by DFT calcns. Compared with the related redox system Ru(Q)(bpy)2k (5k) (k = 0-3), the spectroelectrochem. similarity suggests corresponding electronic structures except for the 1+/53+ pair RuIV(Q·-)(acac)2+ (1+) vs. RuIII(Q)(bpy)23+ (53+). Compd. 2, a three-spin system RuIII(Q·-)2(acac) obtained in the all-cis configuration, possesses a complicated magnetic behavior including strong intramol. antiferromagnetic coupling (JRu-q, $\sim$-103 cm-1 and Jq-q, -102 cm-1) and weak intermol. antiferromagnetic and ferromagnetic interactions. Strong intramol. coupling leads to one unpaired electron at low temps., supported by the radical-type EPR signal of the solid and solns., diminishing at higher temps. The up-down-up spin arrangement for the ground state of (Q·-)-RuIII-(Q·-) (S = 1/2) is confirmed by DFT calcns. for 2. Oxidn. to 2+ leaves the UV-visible-NIR spectrum almost unchanged, whereas redn. to 2- and 22- produces low-energy absorptions. The ligand-centered spin for 22- = RuII(Q·-Q2-)(acac)2- suggests the RuII(Q·-)2(acac)- formulation for 2-. 3, Obtained as a structurally characterized mer isomer, has a predominantly ligand-centered HOMO, evident from the EPR signal of 3+ and as supported by DFT calcns. In contrast, electron addn. proceeds to yield a metal/ligand mixed spin intermediate 3- according to EPR, with $\sim$25\% calcd. metal character of the LUMO. The near-IR absorption of 3 at 1280 nm corresponds to the HOMO-LUMO transition (ligand-to-metal/ligand-to-ligand charge transfer). Oxidn. to 3+ produces a weak broad band at $\sim$2500 nm, while the redn. to 3- gives rise to an intense absorption feature at 816 nm. The valence state alternatives are being discussed for all spectroelectrochem. accessible species, and the individual results are compared across this unique substitution and redox series involving a highly non-innocent ligand/metal combination. All established oxidn. state formulations involve the iminosemiquinone-Ru entity, illustrating the remarkable stability of that arrangement, which corroborates the use of this combination in H2O oxidn. catalysis. on SciFinder(R)

@article{Das.2009d, abstract = {Three new compds., [Ru(Q·-)(acac)2] (1), [Ru(Q·-)2(acac)] (2), and [Ru(Q·-)3] (3), were obtained and characterized as RuIII complexes with 4,6-di-tert-butyl-N-phenyl-o-iminobenzosemiquinone (Q·-) ligands. All three systems show multiple electron transfer behavior, which was analyzed using EPR and UV-visible-near-IR (NIR) spectroelectrochem. 1H NMR spectroscopy and a crystal structure anal. suggest antiferromagnetically spin-spin coupled RuIII and Q·- in 1, similar to that in the compd. with unsubstituted o-iminobenzosemiquinone (4). However, in contrast to 4n, the system 1m exhibits unambiguously metal-centered electron transfer, producing ions [RuIV(Q·-)(acac)2]+ = 1+ and [RuII(Q·-)(acac)2]- = 1-, both with EPR-evidenced ligand-based spin, as also supported by DFT calcns. Compared with the related redox system [Ru(Q)(bpy)2]k (5k) (k = 0-3), the spectroelectrochem. similarity suggests corresponding electronic structures except for the 1+/53+ pair [RuIV(Q·-)(acac)2]+ (1+) vs. [RuIII(Q)(bpy)2]3+ (53+). Compd. 2, a three-spin system [RuIII(Q·-)2(acac)] obtained in the all-cis configuration, possesses a complicated magnetic behavior including strong intramol. antiferromagnetic coupling (JRu-q, $\sim$-103 cm-1 and Jq-q, -102 cm-1) and weak intermol. antiferromagnetic and ferromagnetic interactions. Strong intramol. coupling leads to one unpaired electron at low temps., supported by the radical-type EPR signal of the solid and solns., diminishing at higher temps. The up-down-up spin arrangement for the ground state of {(Q·-)-RuIII-(Q·-)} (S = 1/2) is confirmed by DFT calcns. for 2. Oxidn. to 2+ leaves the UV-visible-NIR spectrum almost unchanged, whereas redn. to 2- and 22- produces low-energy absorptions. The ligand-centered spin for 22- = [RuII(Q·-Q2-)(acac)]2- suggests the [RuII(Q·-)2(acac)]- formulation for 2-. 3, Obtained as a structurally characterized mer isomer, has a predominantly ligand-centered HOMO, evident from the EPR signal of 3+ and as supported by DFT calcns. In contrast, electron addn. proceeds to yield a metal/ligand mixed spin intermediate 3- according to EPR, with $\sim$25{\%} calcd. metal character of the LUMO. The near-IR absorption of 3 at 1280 nm corresponds to the HOMO-LUMO transition (ligand-to-metal/ligand-to-ligand charge transfer). Oxidn. to 3+ produces a weak broad band at $\sim$2500 nm, while the redn. to 3- gives rise to an intense absorption feature at 816 nm. The valence state alternatives are being discussed for all spectroelectrochem. accessible species, and the individual results are compared across this unique substitution and redox series involving a highly non-innocent ligand/metal combination. All established oxidn. state formulations involve the iminosemiquinone-Ru entity, illustrating the remarkable stability of that arrangement, which corroborates the use of this combination in H2O oxidn. catalysis. [on SciFinder(R)]}, added-at = {2022-06-15T11:26:56.000+0200}, author = {Das, Dipanwita and Das, Atanu Kumar and Sarkar, Biprajit and Mondal, Tapan Kumar and Mobin, Shaikh M. and Fiedler, Jan and Zalis, Stanislav and Urbanos, Francisco A. and Jimenez-Aparicio, Reyes and Kaim, Wolfgang and Lahiri, Goutam Kumar.}, biburl = {https://puma.ub.uni-stuttgart.de/bibtex/263b32427a658555985c90794b1695777/huebleriac}, doi = {10.1021/ic901900g}, interhash = {47f3fe831ddc95cc72f24ccc3a8a40b3}, intrahash = {63b32427a658555985c90794b1695777}, issn = {0020-1669}, journal = {Inorganic Chemistry}, keywords = {acac crystal electronic iminobenzosemiquinone magnetic prepn property redox ruthenium series;electrochem series;ruthenium structure substitution}, number = 24, pages = {11853--11864}, timestamp = {2022-06-15T09:26:56.000+0200}, title = {The Semiquinone-Ruthenium Combination as a Remarkably Invariant Feature in the Redox and Substitution Series [Ru(Q)n(acac)3-n]m, n = 1-3; m = (-2), -1, 0, +1, (+2); Q = 4,6-Di-tert-butyl-N-phenyl-o-iminobenzoquinone}, volume = 48, year = 2009 }