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Bar A.K.,Indian Institution of Science
Chemistry (Weinheim an der Bergstrasse, Germany) | Year: 2012

Three new nanoscopic trigonal prisms, [(tmen)(6) Pd(6) (H(2)L)(3)](NO(3))(12) (1), [(Meen)(6) Pd(6)(H(2) L)(3)](NO(3))(12) (2), and [(2,2'-bipy)(6)Pd(6) (H(2)L)(3)](NO(3))(12) (3), have been synthesized in excellent yields through single-step metal-ligand-coordination-driven self-assembly using 5,10,15,20-tetrakis(3-pyridyl)porphyrin (H(2)L) as a donor and cis-blocked Pd(II) 90° acceptors. These complexes were fully characterized by spectroscopic studies and single-crystal X-ray diffraction. All of these barrels quantitatively bind Zn(II) ions in the N(4) pockets of the porphyrin walls at room temperature. Their corresponding zinc-embedded complexes, [(tmen)(6)Pd(6)(ZnL)(3)](NO(3))(12) (1 a), [(Meen)(6) Pd(6)(ZnL)(3)](NO(3))(12) (2 a), and [(2,2'-bipy)(6)Pd(6)(ZnL)(3)](NO(3))(12) (3 a), were synthesized under ambient conditions by the post-synthetic binding of Zn(II) ions into the H(2)N(4) pockets of the porphyrin walls of these complexes. These zinc-embedded complexes were characterized by electronic absorption, fluorescence emission, (1)H NMR spectroscopy, as well as elemental analysis. Complexes 1-3 exhibited considerable microporosity in their solid state. Complex 1 was an efficient adsorbent for nitrogen gas and EtOH, MeOH, and water vapors. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


The two-component self-assembly of a 90° Pd(II) acceptor and a triimidazole donor led to the formation of a water-soluble semi-cylindrical cage with a hydrophobic cavity, which was separately crystallized with hydrophilic- and hydrophobic guests. The parent cage was found to catalyze the Knoevenagel condensation reaction of a series of aromatic mono-aldehydes with active methylene compounds, such as Meldrum's acid or 1,3-dimethylbarbituric acid. The confined hydrophobic nanospace within this cage was also used in the catalytic Diels-Alder reactions of 9-hydroxymethylanthracene with N-phenylmaleimide or N-cyclohexylmaleimide. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Bar A.K.,Indian Institution of Science | Raghothama S.,Indian Institution of Science | Moon D.,Pohang Accelerator Laboratory | Mukherjee P.S.,Indian Institution of Science
Chemistry - A European Journal | Year: 2012

Template-assisted formation of multicomponent Pd 6 coordination prisms and formation of their self-templated triply interlocked Pd 12 analogues in the absence of an external template have been established in a single step through Pd-N/Pd-O coordination. Treatment of cis-[Pd(en)(NO 3) 2] with K 3tma and linear pillar 4,4′-bpy (en=ethylenediamine, H 3tma=benzene-1,3,5-tricarboxylic acid, 4,4′-bpy=4,4′-bipyridine) gave intercalated coordination cage [{Pd(en)} 6(bpy) 3(tma) 2] 2[NO 3] 12 (1) exclusively, whereas the same reaction in the presence of H 3tma as an aromatic guest gave a H 3tma- encapsulating non-interlocked discrete Pd 6 molecular prism [{Pd(en)} 6(bpy) 3(tma) 2(H 3tma) 2][NO 3] 6 (2). Though the same reaction using cis-[Pd(NO 3) 2(pn)] (pn=propane-1,2-diamine) instead of cis-[Pd(en)(NO 3) 2] gave triply interlocked coordination cage [{Pd(pn)} 6(bpy) 3(tma) 2] 2[NO 3] 12 (3) along with non-interlocked Pd 6 analogue [{Pd(pn)} 6(bpy) 3(tma) 2](NO 3) 6 (3′), and the presence of H 3tma as a guest gave H 3tma-encapsulating molecular prism [{Pd(pn)} 6(bpy) 3(tma) 2(H 3tma) 2][NO 3] 6 (4) exclusively. In solution, the amount of 3′ decreases as the temperature is decreased, and in the solid state 3 is the sole product. Notably, an analogous reaction using the relatively short pillar pz (pz=pyrazine) instead of 4,4′-bpy gave triply interlocked coordination cage [{Pd(pn)} 6(pz) 3(tma) 2] 2[NO 3] 12 (5) as the single product. Interestingly, the same reaction using slightly more bulky cis-[Pd(NO 3) 2(tmen)] (tmen=N,N,N′,N′-tetramethylethylene diamine) instead of cis-[Pd(NO 3) 2(pn)] gave non-interlocked [{Pd(tmen)} 6(pz) 3(tma) 2] [NO 3] 6 (6) exclusively. Complexes 1, 3, and 5 represent the first examples of template-free triply interlocked molecular prisms obtained through multicomponent self-assembly. Formation of the complexes was supported by IR and multinuclear NMR ( 1H and 13C) spectroscopy. Formation of guest-encapsulating complexes (2 and 4) was confirmed by 2D DOSY and ROESY NMR spectroscopic analyses, whereas for complexes 1, 3, 5, and 6 single-crystal X-ray diffraction techniques unambiguously confirmed their formation. The gross geometries of H 3tma-encapsulating complexes 2 and 4 were obtained by universal force field (UFF) simulations. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Acharyya K.,Indian Institution of Science | Mukherjee P.S.,Indian Institution of Science
Chemistry - A European Journal | Year: 2014

A supramolecular approach that uses hydrogen-bonding interaction as a driving force to accomplish exceptional self-sorting in the formation of imine-based covalent organic cages is discussed. Utilizing the dynamic covalent chemistry approach from three geometrically similar dialdehydes (A, B, and D) and the flexible triamine tris(2-aminoethyl)amine (X), three new [3+2] self-assembled nanoscopic organic cages have been synthesized and fully characterized by various techniques. When a complex mixture of the dialdehydes and triamine X was subjected to reaction, it was found that only dialdehyde B (which has OH groups for H-bonding) reacted to form the corresponding cage B3X2 selectively. Surprisingly, the same reaction in the absence of aldehyde B yielded a mixture of products. Theoretical and experimental investigations are in complete agreement that the presence of the hydroxyl moiety adjacent to the aldehyde functionality in B is responsible for the selective formation of cage B3X2 from a complex reaction mixture. This spectacular selection was further analyzed by transforming a nonpreferred (non-hydroxy) cage into a preferred (hydroxy) cage B3X2 by treating the former with aldehyde B. The role of the H-bond in partner selection in a mixture of two dialdehydes and two amines has also been established. Moreover, an example of unconventional imine bond metathesis in organic cage-to-cage transformation is reported. Marriage guidance: Controlled self-sorting in covalent cage formation, including cage-to-cage transformation, has been achieved by using hydrogen bonding as a driving force (see figure). Unconventional imine bond metathesis in organic cages is also reported. Copyright © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Mukherjee S.,Indian Institution of Science | Mukherjee P.S.,Indian Institution of Science
Chemistry - A European Journal | Year: 2013

Four new oxo-centered MnIII-salicylaldoximate triangle-based extended complexes [MnIII 6O2(salox) 6(EtOH)4(phda)]n×(saloxH 2)n×(2H2O)n (1), [Mn III 6O2(salox)6(MeOH) 5(5-I-isoph)]n×(3 MeOH)n (2), [Mn III 6O2(salox)6(MeOH) 4(H2O) (5-N3-isoph)]n×(4 MeOH)n (3) and [MnIII 3NaO(salox) 3(MeOH)4(5-NO2-isoph)]n×(MeOH) n (H2O)n (4) [salox=salicylaldoximate, phda=1,3-phenylenediacetate, isoph=isophthalate] have been synthesized under similar reaction conditions. Single crystal X-ray structures show that in 1, only one type of Mn6 cluster is arranged in 1 D, whereas in 2 and 3 there are two types of clusters, differing in the way the triangle units are joined and assembled. In complex 4, however, the basic building structure is heteronuclear and based on Mn3 units extended in 2 D. Susceptibility measurements (dc and ac) over a wide range of temperatures and fields show that the complexes 1, 2, and 3 behave as single molecule magnets (SMMs) with S=4 ground state, while 4 is dominantly antiferromagnetic with a ground spin state S=2. Density functional theory calculations have been performed on model complexes to provide a qualitative theoretical interpretation for their overall magnetic behavior. Four new MnIII-salox extended complexes were synthesized and found to differ in their basic and overall structures depending upon the bridging dicarboxylates (see scheme). The Mn6 cluster-based complexes showed single molecular magnet (SMM) behavior, while the Mn 3-based complex is dominantly antiferromagnetic, which was confirmed by DFT calculations. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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