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Indian Journal of Chemistry -Section A (IJC-A) >
IJC-A Vol.50A [2011] >
IJC-A Vol.50A(09-10) [September-October 2011] >
| Title: | Ruthenium complexes of two different non-innocent ligands. Investigation of electronic structural aspects by experimental and DFT analysis |
| Authors: | Kundu, Tanaya
Chowdhury, Abhishek Dutta
Laha, Biswajit
Mobin, Shaikh M
Lahiri, Goutam Kumar |
| Keywords: | Coordination chemistry
Electronic structures
Crystal structure
Non-innocent ligands
DFT calculations
Ruthenium
Redox properties |
| Issue Date: | Sep-2011 |
| Publisher: | NISCAIR-CSIR, India |
| Abstract: | Synthesis
and characterisation of the ruthenium complexes, [RuII(Q)(tppz)(Cl)]ClO4
(1) and [{RuII(Q)Cl}2-
(m-tppz)](ClO4)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 Qo and tppzo along with the
Ru(II) center as well as non-planarity of the coordinated tppz. The reversible
RuII/RuIII oxidation of (1) and two successive RuII/RuIII couples for
(2) appear at 0.95 V and
0.96, 1.11 V vs SCE in CH3CN, respectively. The separation in
potential of 0.15 V between the two successive oxidation processes in (2) leads to the comproportionation
constant, Kc value of 3.5X102, which implies a rather weakly
coupled (electrochemical) valence localized class II mixed valent RuIIRuIII
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 (d )RuII->*(tppz)/*(Q) back-bonding. Both the complexes exhibit multiple
close-by reductions within the potential range of 0 to -2.0
V vs SCE in CH3CN 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 (2). |
| Page(s): | 1324-1333 |
| CC License: |  CC Attribution-Noncommercial-No Derivative Works 2.5 India |
| ISSN: | 0975-0975(Online); 0376-4710(Print) |
| Source: | IJC-A Vol.50A(09-10) [September-October 2011]
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