Das, Dipanwita ; Mondal, Tapan Kumar ; Mobin, Shaikh M. ; Lahiri, Goutam Kumar (2009) Sensitive valence structures of [(pap)2Ru(Q)]n (n = +2, +1, 0, -1, -2) with two different redox noninnocent ligands, Q = 3,5-di-tert-butyl-n-aryl-1,2-benzoquinonemonoimine and pap = 2-Phenylazopyridine Inorganic Chemistry, 48 (20). pp. 9800-9810. ISSN 0020-1669
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Official URL: http://pubs.acs.org/doi/abs/10.1021/ic901343j
Related URL: http://dx.doi.org/10.1021/ic901343j
Abstract
The complexes [(pap)2Ru(Q)]ClO4, [1]ClO4-[4]ClO4, with two different redox noninnocent ligands, Q = 3,5-di-tert-butyl-N-aryl-1,2-benzoquinonemonoimine (-aryl = m-(Cl)2C6H3 (1+), C6H5 (2+), m-(OCH3)2C6H3 (3+), and m-(tBu)2C6H3 (4+)) and pap = 2-phenylazopyridine, have been synthesized and characterized using various analytical techniques. The single-crystal X-ray structure of the representative [2]ClO4.C7H8 exhibits multiple intermolecular C-H...O hydrogen bondings and C-H...p interactions. The C1-O1 = 1.287(4) (density functional theory, DFT, 1.311) and C6-N1 = 1.320(4) (DFT, 1.353) Å and intraring bond distances associated with the sensitive quinine (Q) moiety along with the azo(pap) bond distances, N3-N4 = 1.278(4) (DFT, 1.297) and N6-N7 = 1.271(4) (DFT, 1.289)Å , in 2+ justify the [(pap)2RuII(Q·-)]+ valence configuration at the native state of 1+-4+. Consequently, Mulliken spin densities on Q, pap, and Ru in 2+ are calculated to be 0.8636, 0.1040, and 0.0187, respectively, and 1+-4+ exhibit free radical sharp EPR spectra and one weak and broad transition around 1000 nm in CH3CN due to interligand transition involving a singly occupied molecular orbital (SOMO) of Q·- and the vacant π orbital of pap. Compounds 1+-4+ undergo a quasi-reversible oxidation and three successive reductions. The valence structure of the electron paramagnetic resonance (EPR)-inactive oxidized state in 12+-42+ has been established as [(pap)2RuII(Q°)]2+ instead of the alternate formalism of antiferromagnetically coupled [(pap)2RuIII(Q·-)]2+ on the basis of the DFT calculations on the optimized 2+, which predict that the singly occupied molecular orbital is primarily composed of Q with 77% contribution. Accordingly, the optimized structure of 22+ predicts shorter C1-O1 (1.264) and C6-N1 (1.317 Å) distances and longer Ru1-O1 (2.080) and Ru1-N1 (2.088 Å) distances. Compounds 12+-42+ exhibit the lowest energy transitions around 600 nm, corresponding to Ru(dπ )/Q(π )→pap(π). The presence of two sets of strongly p-acceptor ligands, pap and Q, in 12+-42+ stabilizes the Ru(II) state to a large extent such that the further oxidation of {RuII-Q°}→{RuIII-Q°} has not been detected within +2.0 V versus a saturated calomel electrode. The EPR-inactive reduced states 1-4 have been formulated as [(pap)2RuII(Q2-)] over the antiferromagnetically coupled alternate configuration, [(pap)(pap·-)RuII(Q·-)]. The optimized structure of 2 predicts sensitive C1-O1 and C6-N1 bond distances of 1.337 and 1.390 Å, respectively, close to the doubly reduced Q2- state, whereas the N-N distances of pap, N3-N4 = 1.299 and N6-N7 = 1.306 Å, remain close to the neutral state. In corroboration with the doubly reduced Q2- state, 1-4 exhibit a moderately strong interligand p(Q2-) → π (pap) transition in the near-IR region near 1300 nm. The subsequent two reductions are naturally centered around the azo functions of the pap ligands.
Item Type: | Article |
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Source: | Copyright of this article belongs to American Chemical Society. |
ID Code: | 88373 |
Deposited On: | 29 Mar 2012 04:45 |
Last Modified: | 29 Mar 2012 04:45 |
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