Ligand-ligand redox interaction through some metal-cluster units

Journal of Chemical Sciences, 2012

Electronic structural forms of selected mononuclear and dinuclear ruthenium complexes encompassing redox non-innocent terminal as well as bridging ligands have been addressed. The sensitive valence and spin situations of the complexes have been established in the native and accessible redox states via detailed analysis of their crystal structures, electrochemistry, UV/VIS/NIR spectroelectrochemistry, EPR signatures at the paramagnetic states and DFT calculations. Mononuclear complexes exhibit significant variations in valence and spin distribution processes based on the simple modification of the non-innocent ligand frameworks as well as electronic nature of the co-ligands, σ-donating or π-accepting. Dinuclear complexes with modified pyrazine, p-quinone and azo-derived redox-active bridging ligands show complex features including redoxinduced electron-transfer (RIET), remote metal to metal spin-interaction in a three-spin metal-bridge-metal arrangement as well as electron-transfer driven chemical transformation (EC).

Indian Journal of …, 2011

Synthesis and characterisation of the ruthenium complexes, [Ru II (Q)(tppz)(Cl)]ClO 4 (1) and [{Ru II (Q)Cl} 2 -(µ-tppz)](ClO 4 ) 2 (2), incorporating redox noninnocent ligands, (Q = o-benzoquinonediimine, tppz = 2,3,5,6-tetrakis-(2-pyridyl)pyrazine) are reported. The crystal structure of (1) and DFT optimized structure of (2) in comparison with the reported structures of analogous molecules establish that their valence configurations comprise the fully oxidized Q o and tppz o along with the Ru(II) center as well as non-planarity of the coordinated tppz. The reversible Ru II /Ru III oxidation of (1) and two successive Ru II /Ru III couples for (2) appear at 0.95 V and 0.96, 1.11 V vs SCE in CH 3 CN, respectively. The separation in potential of 0.15 V between the two successive oxidation processes in (2) leads to the comproportionation constant, K c value of 3.5×10 2 , which implies a rather weakly coupled (electrochemical) valence localized class II mixed valent Ru II Ru III state in (2) + . However, the DFT calculated Mulliken spin densities of (2) + (Ru1, Ru2, Q, tppz and Cl of 0.333, 0.412, 0.070, −0.006 and 0.221, respectively) suggest an almost valence averaged situation. The compositions of molecular orbitals of (1) and (2) suggest appreciable (dπ)Ru II →π * (tppz)/π * (Q) back-bonding. Both the complexes exhibit multiple close-by reductions within the potential range of 0 to −2.0 V vs SCE in CH 3 CN which are assigned to be the ligand (Q/tppz) based reductions. The molecular orbital compositions predict Q based first reduction followed by tppz-based successive reductions in (1), whereas in (2) first reduction primarily takes place at the bridging tppz center followed by the reduction of Q. (1) and (2) exhibit multiple metal-to-ligand charge transfer transitions in the visible region due to the presence of two and three acceptor ligands, respectively. The key transitions in the visible region are assigned based on the TD-DFT calculations on optimized structures of (1) and .

Inorganica Chimica Acta, 2005

In quest of ruthenium complexes having [RuN 3 S 2 ] cores, a non-flexible configuration, trans-thiolate donors and exchangeable coligand L, [Ru(L)(pyN 2 H 2 S 2)] complexes have been synthesized ½pyN 2 H 2 S 2 2À ¼ 2; 6-bisð2-mercaptophenylaminomethylÞ pyridine ð2ÀÞ. Treatment of [RuCl 2 (CH 3 CN) 4 ] with pyN 2 H 2 S 2 2À gave [Ru(py)(pyN 2 H 2 S 2)] (1). The pyridine coligand in 1 proved to be labile and could be substituted by either CO or DMSO under normal conditions to give [Ru(CO)(pyN 2 H 2 S 2)] (2) and [Ru(DMSO)(pyN 2 H 2 S 2)] (3), respectively. Alternatively, 2 could be obtained directly from [RuCl 2 (CH 3 CN) 4 ] and pyN 2 H 2 S 2 2À in the presence of CO, whereas the reaction in the absence of CO gave the dinuclear [Ru(pyN 2 H 2 S 2)] 2 (8). Treatment of either 2 or 3 with NOBF 4 afforded [Ru III (CO)(pyN 2 H 2 S 2)]BF 4 ([4]BF 4) and [Ru(NO)(pyN 2 H 2 S 2)]BF 4 ([5]BF 4), respectively. Treatment of [5]BF 4 with either NEt 4 N 3 or N 2 H 4 afforded the amide [Ru(NO)(pyN 2 HS 2)] (6) and the hydrazine [Ru(N 2 H 4)(pyN 2 H 2 S 2)] (7), respectively. Treatment of the dinuclear 8 with either one or two equivalents of NOBF 4 afforded the mixed-valence diruthenium (II,III) [Ru III Ru II (pyN 2 H 2 S 2) 2 ]BF 4 ([9]BF 4) and the diruthenium (III) [Ru III Ru III (pyN 2 H 2 S 2) 2 ](BF 4) 2 {[10](BF 4) 2 }, respectively. The diruthenium (III) complex [10](BF 4) 2 is diamagnetic, which can be ascribed to spin-spin pairing between the two Ru III atoms. A preliminary structure determination of [10](BF 4) 2 supports this observation, indicating a single bond between the two Ru III atoms. Novel diruthenium complex of this type could be synthesized more generally by treatment of [RuCl 3 (MeSPh) 3 ] with pyN 2 H 2 S 2 2À. All complexes were characterized by spectroscopic methods and elemental analysis. The cations [9] + and [10] 2+ were characterized by X-ray structure analysis.

Dalton Transactions, 2013

A combined experimental and theoretical approach has been used to investigate the redox properties of two dinuclear Ru(II) complexes, 2a and 2b, containing the planar dpt-ph-dpt bridging ligand (dpt-phdpt = 1'',4''-bis(2,4-dipyrid-2'-yl-1,3,5-triazin-6-yl)benzene). The redox properties of the free bridging ligand and the X-ray structure of 2a have also been reported, together with the X-ray structure of a related mononuclear compound, for comparison purposes. The photophysical processes of 2a and 2b have also been studied by pump-probe transient absorption spectroscopy. Compounds 2a and 2b are able to reversibly collect six and eight electrons, respectively, upon electrochemical reduction at mild potentials (>−2.0 V vs. SCE). A detailed assignment of the various reduction processes to specific subunits of the dinuclear arrays has been made possible by calculation of the HOMOs and LUMOs of native and bireduced species. For example, computation allowed us to clarify the redox behavior of 2b: the first reduction processes of this compound occur at almost coincident potentials, with successive electrons added on the same subunit (namely, the bridging ligand). Charge redistribution towards the other subunits of the molecular framework upon second reduction, revealed by calculation performed on the bireduced species, is the key to interpreting this peculiar behavior. Inter-ligand electron hopping interconverts the MLCT state involving the peripheral ligand to that of the (lower-lying) MLCT state that involves the bridging ligand. This process is faster than 350 fs in 2a, where its driving force is higher than 0.2 eV, whereas it occurs with a time constant of about 6 ps in 2b, having a smaller driving force for the process. Both compounds decay to the ground state, with MLCT emission on the nanosecond time scale, however a faster component of such decay is kinetically evidenced, indicating a process of about 200-250 ps in both cases, which is tentatively assigned to relatively slow diffusive solvent dynamics.

Inorganic Chemistry, 1989

Syntheses are described for the ligand-bridged complexes [(tpm)Ru"'(p-O)(p-L),Ru"'(tpm)"+ (L = 02P(0)(OH), n = 0 (1); L = 0 2 C 0 , n = 0 (2); L = 02CCH3, n = 2 (3); tpm is the tridentate, facial ligand tris(1-pyrazoly1)methane. The X-ray crystal structure of [(tpm)Ru(p-O)(p-O2P(O)(0H)),Ru(tpm)].8H2O was determined from three-dimensional X-ray counter data. The com lex crystallizes in the trigonal space group P3221 with three molecules in a cell of dimensions (I = 18.759 (4) A and c = 9.970 ( 6 ) 1. The structure was refined to a weighted R factor of 0.042 based on 1480 independent reflections with I 1 3 4 . The structure reveals that the complex consists of two six-coordinate ruthenium atoms that are joined by a p-oxo bridge (rRu4 = 1.87 A; LRuORu = 1 2 4 . 6 O ) and two p-hydrogen phosphato bridges (average rRu+ = 2.07 A) which are capped by two tpm ligands.

Bulletin of the Chemical Society of Japan, 2007

Two consecutive one-electron reductions of the mixedmetal trinuclear complexes [Ru III 2 M II (3-O)(-CH 3 COO) 6-(S)(bzpy) 2 ] {(M ¼ Co, S ¼ H 2 O) and (M ¼ Ni, S = N,N 0dimethylformamide); bzpy = 4-benzoylpyridine} in acetonitrile give stable ''double'' mixed-valence states where both Ru 2 II,III and (bzpy À)(bzpy) states coexist. Splitting of the ligand-based redox waves, (bzpy) 2 /(bzpy À)(bzpy)/(bzpy À) 2 , is 0.35 and 0.34 V for the Co and Ni complexes, respectively.

Journal of The Chemical Society-dalton Transactions, 1994

The reaction between 4-methoxyphenol and Ru,(CO)~~ in cyclohexane has been investigated and found to afford a hexaruthenium 'raft' cluster Ru,(p-H)&-q7-0C~H~OMe-4)(CO& (3a), together with tetraruthenium clusters incorporating three (Ru&-OC,H,OMe-4),(@lX~-OCsH.,OMe-4XCO),, (3bN or four (Ru&-OC,H,OMe-4),(LL-OC,H,OMe-4),(CO~u, (3~)) aryloxo ligands; similarly, reaction of Ru,(CO),, with 2-naphthol afforded the analogous Ru,(~~-H)~(IL~-~'-OC~~H~XCO)~~ &I), Ru&-0C,,H7)2(11-CIX~-OC10H7MC0)10 (4b) and Ru.,(~~-OC~~H~)~(~-OC~~H~)~(CO~~,, (4e). The source of chloride in 3b and 4b is believed to be carbon tetrachloride contaminant in the cyclohexane. An X-ray diffraction study reveals that 3b contains an Ru,(CO), unit linked to an Ru(CO), moiety by two asymmetric triply-bridging and one asymmetric doubly-bridging 4methox-yphenoxo ligands, and an asymmetric doubly-bridging chloro ligand; this interaction is strongly suggestive of a higher oxidation state ruthenium linked to a trinuclear cluster of formally zero oxidation state. The dynamic 13C NMR spectra of 4c have been recorded, and are consistent with restricted rotation about the Ar-0 linkage of the p+oordinated naphthoxo ligands at low temperature.

fe: el acceso a las órdenes religiosas de los no europeos en el las Monarquías Ibéricas (siglos XVI-XVIII)" Directores: María López Barquero y Eleuterio Santos Candela.