%0 Journal Article %1 Ghumaan.2006 %A Ghumaan, Sandeep %A Sarkar, Biprajit %A Chanda, Nripen %A Sieger, Monika %A Fiedler, Jan %A Kaim, Wolfgang %A Lahiri, Goutam Kumar. %D 2006 %J Inorganic Chemistry %K dipyridylketone electrochem prepn pyridylpyrazine ruthenium spectroelectrochem %N 19 %P 7955--7961 %R 10.1021/ic060887l %T 2,2'-Dipyridylketone (dpk) as Ancillary Acceptor and Reporter Ligand in Complexes [(dpk)(Cl)Ru(m-tppz)Ru(Cl)(dpk)]n+ where tppz = 2,3,5,6-Tetrakis(2-pyridyl)pyrazine %V 45 %X The tppz-bridged diruthenium(II) complex [(dpk)(Cl)RuII(m-tppz)RuII(Cl)(dpk)](ClO4)2, [2](ClO4)2, and mononuclear [(dpk)(Cl)RuII(tppz)](ClO4), [1](ClO4) [tppz = 2,3,5,6-tetrakis(2-pyridyl)pyrazine, dpk = 2,2'-dipyridylketone], were synthesized. The 260 mV sepn. between successive 1-electron oxidn. couples in [2]2+ translates to a relatively small comproportionation const., Kc, of 2.5 $\times$ 104 for the intermediate. Electrochem. data (Eox, Ered, Kc) reflect the donor/acceptor effects of ancillary ligands L in systems [(L)ClRu(m-tppz)RuCl(L)]n, particularly the competition between L and tppz for electron d. from the metal. According to EPR (g1 = 2.470, g2 = 2.195, and g3 = 1.873 at 4 K) the intermediate [2]3+ is a mixed-valent RuIIRuIII species which shows a rather narrow intervalence charge transfer (IVCT) band at 1800 nm (e = 1500 M-1 cm-1). The width at half-height (Dn1/2) of 700 cm-1 of the IVCT band is much smaller than the calcd. value of 3584 cm-1, obtained by using the Hush formula Dn1/2 = (2310Eop)1/2 (Eop = 5556 cm-1, energy of the IVCT transition) which would be applicable to localized (Class II) mixed-valent RuIIRuIII systems. Valence delocalization in [2]3+ is supported by the uniform shift of the nC:O band of the N,N'-coordinated dpk ligands from 1676 cm-1 in the RuIIRuII precursor to 1690 cm-1 in the Ru2.5Ru2.5 form, illustrating the use of the dpk acceptor to act as reporter ligand via the free but p-conjugated org. carbonyl group. The apparent contradiction between the moderate value of Kc and the narrow IVCT band is discussed considering borderline or hybrid Class II-III concepts of mixed-valency, as well as coordination aspects, i.e., the bis-tridentate nature of the p-acceptor bridging ligand. Altogether, [1]+ and [2]2+ display four and five successive redn. processes, resp., involving both tppz- and dpk-based unoccupied p* orbitals. The 1-electron reduced form [2]+ was assigned as a tppz.bul.- radical-anion-contg. species which exhibits a free-radical-type EPR signal at 4K (g|| = 2.002, g$\bot$ = 1.994) and one moderately intense ligand-based low-energy band at 965 nm (e = 1100 M-1 cm-1). [on SciFinder(R)]

@article{Ghumaan.2006, abstract = {The tppz-bridged diruthenium(II) complex [(dpk)(Cl)RuII(\textgreek{m}-tppz)RuII(Cl)(dpk)](ClO4)2, [2](ClO4)2, and mononuclear [(dpk)(Cl)RuII(tppz)](ClO4), [1](ClO4) [tppz = 2,3,5,6-tetrakis(2-pyridyl)pyrazine, dpk = 2,2'-dipyridylketone], were synthesized. The 260 mV sepn. between successive 1-electron oxidn. couples in [2]2+ translates to a relatively small comproportionation const., Kc, of 2.5 $\times$ 104 for the intermediate. Electrochem. data (Eox, Ered, Kc) reflect the donor/acceptor effects of ancillary ligands L in systems [(L)ClRu(\textgreek{m}-tppz)RuCl(L)]n, particularly the competition between L and tppz for electron d. from the metal. According to EPR (g1 = 2.470, g2 = 2.195, and g3 = 1.873 at 4 K) the intermediate [2]3+ is a mixed-valent RuIIRuIII species which shows a rather narrow intervalence charge transfer (IVCT) band at 1800 nm (\textgreek{e} = 1500 M-1 cm-1). The width at half-height (\textgreek{Dn}1/2) of 700 cm-1 of the IVCT band is much smaller than the calcd. value of 3584 cm-1, obtained by using the Hush formula \textgreek{Dn}1/2 = (2310Eop)1/2 (Eop = 5556 cm-1, energy of the IVCT transition) which would be applicable to localized (Class II) mixed-valent RuIIRuIII systems. Valence delocalization in [2]3+ is supported by the uniform shift of the \textgreek{n}C:O band of the N,N'-coordinated dpk ligands from 1676 cm-1 in the RuIIRuII precursor to 1690 cm-1 in the Ru2.5Ru2.5 form, illustrating the use of the dpk acceptor to act as reporter ligand via the free but \textgreek{p}-conjugated org. carbonyl group. The apparent contradiction between the moderate value of Kc and the narrow IVCT band is discussed considering borderline or hybrid Class II-III concepts of mixed-valency, as well as coordination aspects, i.e., the bis-tridentate nature of the \textgreek{p}-acceptor bridging ligand. Altogether, [1]+ and [2]2+ display four and five successive redn. processes, resp., involving both tppz- and dpk-based unoccupied \textgreek{p}* orbitals. The 1-electron reduced form [2]+ was assigned as a tppz.bul.- radical-anion-contg. species which exhibits a free-radical-type EPR signal at 4K (g|| = 2.002, g$\bot$ = 1.994) and one moderately intense ligand-based low-energy band at 965 nm (\textgreek{e} = 1100 M-1 cm-1). [on SciFinder(R)]}, added-at = {2022-06-15T11:26:56.000+0200}, author = {Ghumaan, Sandeep and Sarkar, Biprajit and Chanda, Nripen and Sieger, Monika and Fiedler, Jan and Kaim, Wolfgang and Lahiri, Goutam Kumar.}, biburl = {https://puma.ub.uni-stuttgart.de/bibtex/22a013f68481ab2131c5e2f17bbf4099d/huebleriac}, doi = {10.1021/ic060887l}, interhash = {18a6fc614c7a6ddb92eb7ec84938089e}, intrahash = {2a013f68481ab2131c5e2f17bbf4099d}, issn = {0020-1669}, journal = {Inorganic Chemistry}, keywords = {dipyridylketone electrochem prepn pyridylpyrazine ruthenium spectroelectrochem}, number = 19, pages = {7955--7961}, timestamp = {2022-06-15T09:26:56.000+0200}, title = {2,2'-Dipyridylketone (dpk) as Ancillary Acceptor and Reporter Ligand in Complexes [(dpk)(Cl)Ru(\textgreek{m}-tppz)Ru(Cl)(dpk)]n+ where tppz = 2,3,5,6-Tetrakis(2-pyridyl)pyrazine}, volume = 45, year = 2006 }