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Revelation of Varying Bonding Motif of Alloxazine, a Flavin Analogue, in Selected Ruthenium(II/III) Frameworks

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Title Revelation of Varying Bonding Motif of Alloxazine, a Flavin Analogue, in Selected Ruthenium(II/III) Frameworks
 
Creator MONDAL, P
RAY, R
DAS, A
LAHIRI, GK
 
Subject DENSITY-FUNCTIONAL THEORY
BRIDGED DIRUTHENIUM COMPLEXES
OXIDATION-STATE COMBINATIONS
UNUSUAL COORDINATION MODE
BETA-DIKETONATE LIGAND
CRYSTAL-STRUCTURE
PERCHLORATE TETRAHYDRATE
METALLOFLAVIN COMPLEXES
ELECTRONIC-STRUCTURES
EXCITATION-ENERGIES
 
Description The reaction of alloxazine (L) and Ru-II(acac)(2)(CH3CN)(2) (acac(-) = acetylacetonate) in refluxing methanol leads to -the simultaneous formation of Ru-II(acac)(2)(L) (1 = bluish-green) and Ru-III(acac)(2)(L-) (2 = red) encompassing a usual neutral alpha-iminoketo chelating form of L and an unprecedented monodeprotonated alpha-iminoenolato chelating form of L-, respectively. The crystal structure of 2 establishes that N5,O4(-) donors of L- result in a nearly planar five-membered chelate with the {Ru-III(acac)(2)(+)} metal fragment. The packing diagram of 2 further reveals its hydrogen-bonded dimeric form as well as pi-pi interactions between the nearly planar tricyclic rings of coordinated alloxazirie ligands in nearby molecules. The paramagnetic 2 and one-electron-oxidized 1(+) display ruthenium(III)-based anisotropic axial EPR in CH3CN at 77 K with < g >/Delta g of 2.136/0.488 and 2.084/0.364, respectively (< g > = {1/3(g(1)(2) + g(2)(2) g(3)(2))}(1/2), and Delta g= g(1)-g(3)). The multiple electron-transfer processes of 1 and 2 in CH3CN -have been analyzed by DFT-calculated MO compositions and Mulliken spin density distributions at the paramagnetic states, which suggest successive two-electron uptake by the pi-system of the heterocyclic ring of L (L -> L center dot- -> L2-) or L- (L- -> L center dot 2- -> L3-) besides metal-based (Ru-II/Ru-III) redox process. The origin of the ligand as well as mixed metal-ligand-based multiple electronic transitions of 1(n) (n = +1, 0, -1, -2) and 2(n) (n = 0, -1, -2) in the UV and -visible regions, respectively, has been assessed by TD-DFT calculations in each redox state. The pK(a) values of 1 and 2 incorporating two and one NH protons of 6.5 (N3H, pK(a1))/8.16 (N1H, pK(a2)) and 8.43 (N1H, pK(a1)), respectively, are estimated by monitoring their spectral Changes as a function of pH in CH3CN-H2O (1:1). 1 and 2 in.CH3CN also participate in proton-driven internal reorganizations involving- the coordinated alloxatine moiety, i.e., transformation of an alpha-iminoketo chelating form to an alpha-iminoenolato chelating form and the reverse process without any electron-transfer step: Ru-II(acac)(2)(L) (1) -> Ru-II(acac)(2)(L-) (2(-)) and Ru-III(acac)(2)(L-) (2) -> Ru-III(acac)(2)(L) (1(+)).
 
Publisher AMER CHEMICAL SOC
 
Date 2016-01-15T06:03:43Z
2016-01-15T06:03:43Z
2015
 
Type Article
 
Identifier INORGANIC CHEMISTRY, 54(6)3012-3021
0020-1669
1520-510X
http://dx.doi.org/10.1021/acs.inorgchem.5b00122
http://dspace.library.iitb.ac.in/jspui/handle/100/17884
 
Language en