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Inui, Yuji,Shiro, Motoo,Kusukawa, Takahiro,Fukuzumi, Shunichi,Kojima, Takahiko The Royal Society of Chemistry 2013 Dalton transactions Vol.42 No.8
<P>[Ir<SUB>6</SUB>(μ-alloCl<SUB>2</SUB><SUP>2−</SUP>)<SUB>3</SUB>(Cp*)<SUB>6</SUB>(OH)<SUB>3</SUB>](PF<SUB>6</SUB>)<SUB>3</SUB> (<B>1</B>) having 7,8-dichloroalloxazine dianion (alloCl<SUB>2</SUB><SUP>2−</SUP>) as bridging ligands was synthesized and characterized by X-ray crystallography, spectroscopic and electrochemical measurements. The alloxazine ligands showed unprecedented coordination modes to link the six Ir(<SMALL>III</SMALL>) centres. The complex exhibited remarkable stability and reversible six-electron redox processes at the bridging alloxazine ligands in organic solvents. The first reversible reduction process occurred on each of three alloxazine ligands in <B>1</B> to produce a three-electron-reduced species, [Ir<SUP>III</SUP><SUB>6</SUB>Cp*<SUB>6</SUB>(μ-alloCl<SUB>2</SUB>&z.rad;<SUP>3−</SUP>)<SUB>3</SUB>(OH)<SUB>3</SUB>], and was observed as an apparent one-step reduction process at −0.65 V (<I>vs</I>. Fc<SUP>0/+</SUP>). The second reversible reduction process on each of the three alloxazine ligands in <B>1</B> was recorded at almost the same potential, −0.78 V (<I>vs</I>. Fc<SUP>0/+</SUP>), to afford the six-electron-reduced form, [Ir<SUP>III</SUP><SUB>6</SUB>Cp*<SUB>6</SUB>(μ-alloCl<SUB>2</SUB><SUP>4−</SUP>)<SUB>3</SUB>(OH)<SUB>3</SUB>]<SUP>3−</SUP>. The radical anion of the alloxazine derivative was detected by EPR measurements at room temperature. After the six-electron reduction of <B>1</B> with cobaltocene, the backward oxidation processes of reduced forms with <I>p</I>-chloranil were traced by UV-Vis spectroscopy to confirm the recovery of the original spectrum of <B>1</B>.</P> <P>Graphic Abstract</P><P>An alloxazine-bridged hexanuclear Ir(<SMALL>III</SMALL>) complex was synthesized and characterized. The complex exhibited two-step reversible reduction processes in CH<SUB>3</SUB>CN solution. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c2dt32535g'> </P>
Inui, Yuji,Shiro, Motoo,Fukuzumi, Shunichi,Kojima, Takahiko The Royal Society of Chemistry 2013 Organic & biomolecular chemistry Vol.11 No.5
<P>The formation of guanine quartets with 9-isopropylguanine (<SUP>i</SUP>PG) is discussed in organic solvents. Crystal structures of the <SUP>i</SUP>PG quartets were determined by X-ray crystallography with template cations (Na<SUP>+</SUP> and Ca<SUP>2+</SUP>) and the structure without a template cation was also obtained by virtue of the stabilization by intermolecular hydrogen bonding with water molecules of crystallization. The difference in the quartet formation of <SUP>i</SUP>PG in the presence and absence of a template cation was clearly demonstrated by <SUP>1</SUP>H NMR measurements in CDCl<SUB>3</SUB>–CH<SUB>3</SUB>OH mixed solvents. The quartet formation is mainly governed by the enthalpy gain due to the electrostatic interaction between the O6 oxygen in <SUP>i</SUP>PG and the template cations in the presence of the cations rather than the intermolecular hydrogen bonding, while desolvation of <SUP>i</SUP>PG is the dominant factor for the formation in the absence of cations. In the presence of Na<SUP>+</SUP> and Ca<SUP>2+</SUP>, Δ<I>H</I> and Δ<I>S</I> values in the formation of <SUP>i</SUP>PG-4–Na<SUP>+</SUP> and <SUP>i</SUP>PG-4–Ca<SUP>2+</SUP> complexes were determined to be Δ<I>H</I> = −8.4 kcal mol<SUP>−1</SUP> and Δ<I>S</I> = +50 cal mol<SUP>−1</SUP> K<SUP>−1</SUP> for Na<SUP>+</SUP> and Δ<I>H</I> = −12.9 kcal mol<SUP>−1</SUP> and Δ<I>S</I> = +34 cal mol<SUP>−1</SUP> K<SUP>−1</SUP> for Ca<SUP>2+</SUP> on the basis of van't Hoff plots attained from the results of temperature-dependent UV-Vis spectroscopic measurements.</P> <P>Graphic Abstract</P><P>Formation of ‘naked’ G-quartets was elucidated on the basis of crystal structures and thermodynamic analysis. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c2ob26877a'> </P>
Kojima, Takahiko,Inui, Yuji,Miyazaki, Soushi,Shiro, Motoo,Fukuzumi, Shunichi Royal Society of Chemistry 2009 Chemical communications Vol.2009 No.43
<P>A novel tetranuclear Ir(<SMALL>III</SMALL>) complex involving unprecedented coordination modes of alloxazine formed a closed π-space by intermolecular hydrogen bonding and the counter anions encapsulated in the space could be exchanged <I>via</I> self-assembly.</P> <P>Graphic Abstract</P><P>A novel tetranuclear Ir(<SMALL>III</SMALL>) complex involving unprecedented coordination modes of alloxazine formed a closed π-space by intermolecular hydrogen bonding; counter anions encapsulated in the space could be exchanged <I>via</I> self-assembly. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=b911033j'> </P>
Rekharsky, Mikhail V.,Yamamura, Hatsuo,Mori, Tadashi,Sato, Akihiro,Shiro, Motoo,Lindeman, Sergey V.,Rathore, Rajendra,Shiba, Kouhei,Ko, Young Ho,Selvapalam, Narayanan,Kim, Kimoon,Inoue, Yoshihisa WILEY-VCH Verlag 2009 Chemistry Vol.15 No.8
<P>Water seeds: Complex stoichiometry/composition and degree of oligomerization (oligomeric supramolecular complex formation) of cucurbit[6]uril (CB[6]) with N-alkyl- and N,N′-dialkylpiperazine were investigated in aqueous solutions by means of isothermal titration calorimetry (ITC), ESI-MS, NMR and light scattering measurements. <img src='wiley_img/09476539-2009-15-8-CHEM200800398-content.gif' alt='wiley_img/09476539-2009-15-8-CHEM200800398-content'> </P><P>Complex stoichiometry/composition and degree of oligomerization (oligomeric supramolecular complex formation) of cucurbit[6]uril (CB[6]) with N-alkyl- and N,N′-dialkylpiperazine were investigated in aqueous solutions by means of isothermal titration calorimetry (ITC), ESI-MS, NMR and light scattering measurements. It was found that the complex stability and the degree of oligomerization increase with elongating the alkyl chain attached to the piperazine core. X-ray crystallographic studies revealed a clear correlation between the structure of CB[6]–alkylpiperazine crystals obtained from aqueous solutions and the molecular weight/properties of host–guest oligomers existed in the solution as supramolecular “seeds” of crystal formation.</P> <B>Graphic Abstract</B> <P>Water seeds: Complex stoichiometry/composition and degree of oligomerization (oligomeric supramolecular complex formation) of cucurbit[6]uril (CB[6]) with N-alkyl- and N,N′-dialkylpiperazine were investigated in aqueous solutions by means of isothermal titration calorimetry (ITC), ESI-MS, NMR and light scattering measurements. <img src='wiley_img/09476539-2009-15-8-CHEM200800398-content.gif' alt='wiley_img/09476539-2009-15-8-CHEM200800398-content'> </P>