For the first time, fully characterized and stable trinuclear "double sandwich" molecules are reported with Hg(II) ion using a highly flexible porphyrin dimer. The molecules display interesting and intense luminescence properties at room temperature. The present investigation clearly demonstrates that attractive mercurophilic interactions do play an essential role in bringing two porphyrin macrocycles exactly on top of each other with an unfavorable fully eclipsed geometry to produce short Hg•••Hg distances. Interactions between Hg(II) dz 2 orbitals provide the directionality with a linear Hg 3 core having short Hg•••Hg distances despite the fact that ligand framework is highly flexible.
Addition of 2,4,6-trinitrophenol (HTNP) to an ethene-bridged diiron(III) μ-oxo bisporphyrin (1) in CH Cl initially leads to the formation of diiron(III) μ-hydroxo bisporphyrin (2⋅TNP) with a phenolate counterion that, after further addition of HTNP or dissolution in a nonpolar solvent, converts to a diiron(III) complex with axial phenoxide coordination (3⋅(TNP) ). The progress of the reaction from μ-oxo to μ-hydroxo to axially ligated complex has been monitored in solution by using H NMR spectroscopy because their signals appear in three different and distinct spectral regions. The X-ray structure of 2⋅TNP revealed that the nearly planar TNP counterion fits perfectly within the bisporphyrin cavity to form a strong hydrogen bond with the μ-hydroxo group, which thus stabilizes the two equivalent iron centers. In contrast, such counterions as I , I , BF , SbF , and PF are found to be tightly associated with one of the porphyrin rings and, therefore, stabilize two different spin states of iron in one molecule. A spectroscopic investigation of 2⋅TNP has revealed the presence of two equivalent iron centers with a high-spin state (S=5/2) in the solid state that converts to intermediate spin (S=3/2) in solution. An extensive computational study by using a range of DFT methods was performed on 2⋅TNP and 2 , and clearly supports the experimentally observed spin flip triggered by hydrogen-bonding interactions. The counterion is shown to perturb the spin-state ordering through, for example, hydrogen-bonding interactions, switched positions between counterion and axial ligand, ion-pair interactions, and charge polarization. The present investigation thus provides a clear rationalization of the unusual counterion-specific spin states observed in the μ-hydroxo bisporphyrins that have so far remained the most outstanding issue.
Two isomers of a nickel(ii)porphyrinato dication diradical, isolated selectively in pure form, are stabilized exclusively by anion–π interactions, have unique and distinct electronic and spectroscopic features and display an anion-induced charge/electron transfer phenomenon.
In this article, we are introducing the synthesis of two naphthalene derivatives (NPBU (butyl 2‐(naphthalene‐2‐yl)acetate) and NPME (methyl 2‐(naphthalene‐2‐yl)acetate)) having different length of aliphatic tail. These two newly synthesized naphthalene derivative are used as a fluorophore to understand the binding interaction with surfactants (SDS (sodium dodecyl sulfate), CTAB (cetrimonium bromide) and Triton X‐100) and also with β‐CD (β‐cyclodextrin). Because of long hydrophobic tail, NPBU is more hydrophobic in nature and showed self‐aggregation properties in aqueous medium. Whereas, the short aliphatic tail containing NPME not showed any self‐aggregation property in an aqueous medium. Because of hydrophobicity NPBU could binds with the hydrophobic inner core of micelles of SDS, CTSB and Triton X‐100. NPBU also formed inclusion complex with inner hydrophobic cavity of β‐CD. However, because of low hydrophobicity NPME, could not able to binds with hydrophobic inner core of micelles and also it was not able to bind with hydrophobic cavity of β‐CD. The calculated CMC (critical micelle concentration) values of SDS, CTAB and Triton X‐100 by using NPBU fluorophore are ∼12 mM, ∼0.8 mM and ∼0.12 mM respectively. The NPME binds with β‐CD and formed inclusion complexes NPBU@β‐CD and calculated binding constant was 0.22 × 102 M−1. Thus this presented comparative study is showing the importance of a hydrophobic tail, attached to naphthalene molecule. The attachment of a long hydrophobic tail makes the fluorophore sensitive towards microenvironment of surfactants and make naphthalene molecules suitable for investigation of structure and dynamics of micellization of different types of surfactants.
The multiheme cytochrome c involves extensive interaction among the heme centers to enable them to perform a wide variety of enzymatic activities. In an attempt to exploit such heme-heme interactions in the synthetic diheme, an ethane-bridged diiron(III) porphyrin dimer has been utilized that can switch easily between syn and anti conformations due to highly flexible nature of the bridge. Upon protonation using 5% aqueous Brønsted acid, the dichloromethane solution of diiron(III)-µ-oxo porphyrin dimer immediately changes its color from green to red leading to the formation of a series of µ-hydroxo complexes. However, long exposure of the Brønsted acid converts the µ-hydroxo complex to five-coordinate diiron(III) porphyrin dimer in which the counter anion switches its position to act as an axial ligand. In the present study, the investigation has been extended further using Brønsted acids containing strongly coordinating anions such as HN 3 , HNCS and l-(+)-Lactic acid (HLA) in which the anions eventually coordinate to iron centers directly as axial ligands. A comprehensive account of the anion-mediated spin state change in the ethane-bridged diiron(III) porphyrin dimer has also been presented here.
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