Influence of a Single Catenane on the Solid-State Properties of Mechanically Linked Polymers.

We report on mechanically linked polymers containing a single catenane in the middle of the chain. These polymers were synthesized by a simple procedure consisting in "clicking" polymer chains onto a functionalized palladium-templated [2]catenane, allowing the preparation of a variety of mechanically linked polymers. The flexibility of the catenane junction was modulated by removing the Pd ion from the catenane to unlock the macrocycles and increase their mobility. We show that this mobility change has a strong impact on the solid-state properties of the polymers. This is illustrated by studying the glass transition temperature of polystyrene-based polymers and the crystallization behavior of poly(ethylene oxide)-based polymers. Our study proves that a change of flexibility of a single catenane inserted into a polymer chain drastically influences the polymer behavior in the solid state.

Role of wingtip substituents on benzene-platform-based tetrapodal ligands toward the formation of a self-assembled silver carbene cage.

Tetrapodal imidazolium ligands L(1)-L(3) as their PF6(-) salts are synthesized in good yields by reacting 1,2,4,5-tetrakis(bromomethyl)benzene with N-methylimidazole, N-benzylimidazole, and N-ethylimidazole, respectively. Single-crystal X-ray diffraction studies of L(1)·4PF6, L(2)·4PF6, and L(3)·4PF6 show the chair conformation of the tetrapodal imidazoliums (L(1)-L(3)), where 1,5- and 2,4-imidazolium moieties are oriented in opposite directions of the benzene plane. The PF6(-) salts of L(1)-L(3) are reacted with Ag2O to synthesize different silver complexes of N-heterocyclic carbene (NHC), 1-3, respectively, in good yields. Crystals of all three complexes suitable for single-crystal X-ray diffraction study are also isolated. Structural analysis of 1, i.e., the complex of L(1)·4PF6 containing methyl as a wingtip substituent, and Ag2O shows the formation of a bimetallic silver NHC (NHC-Ag) complex, [(L(1)-4H)·2Ag]·2PF6, which is rotationally disordered over an inversion of symmetry of the space group P2(1)/c. Elemental analysis and solution-state (1)H and (13)C NMR studies confirm the above molecular formula of complex 1. When L(2)·4PF6 functionalized with the benzyl wingtip moiety is explored for similar complexation with Ag2O, the isolated complex 2 shows the formation of a simple NHC-Ag complex with molecular formula [(L(2)-4H)·2Ag]·2PF6, as observed in the case of 1. Interestingly, the reaction of L(3)·4PF6 containing ethyl as the wingtip substituent and Ag2O shows the formation of a silver-ion-assisted tetranuclear molecular box of [Ag4(L(3)-4H)2](4+) (3).

A chelation enhanced selective fluorescence sensing of Hg2+ by a simple quinoline substituted tripodal amide receptor.

Two tris(2-aminoethyl)amine (tren) based tripodal amide fluoroionophores, 1 and 2, functionalized with quinoline (chelating fluorophore) and naphthalene (non-chelating fluorophore) respectively, are synthesized in good yields. Fluoroionophore 1 shows a selective UV-Vis spectral shift in the case of Hg(2+) in acetonitrile among different metal ions like Li(+), Na(+), Ca(2+), Mg(2+), Cr(2+), Mn(2+), Fe(2+), Co(2+), Ni(2+), Cu(2+), Zn(2+), Cd(2+), Hg(2+), Pb(2+), and Ag(+). On the other hand, fluoroionophore 2 shows no selectivity towards any of the above metal ions in the UV-Vis study. Furthermore, 1 shows a selective chelation induced fluorescence enhancement in the presence of Hg(2+) whereas 2 shows the enhancement of fluorescence with most of the metal ions via a photoinduced charge transfer mechanism. The naked eye detection of Hg(2+) in an acetonitrile solution of 1 shows a greenish fluorescence upon UV light irradiation. The isolated Hg(2+) complex of 1, 3, shows a similar UV-Vis and fluorescence spectral output as observed from in situ spectroscopic studies of 1 in the presence of Hg(2+). Infra-red (IR) and (1)H- NMR studies also reveal the interaction of Hg(2+) with the quinoline nitrogen atoms as well as with the amide functionality.

Mercaptothiazolinyl functionalized hexapodal and tripodal receptors on benzene platform: formation of silver ion assisted hexanuclear metallocage vs metal-organic polymer.

Mercaptothiazolinyl functionalized hexapodal (L(1)) and tripodal (L(2)) receptors on the benzene platform have been synthesized easily in good yields and structurally characterized by a single-crystal X-ray crystallographic study. In the solid state, L(1) shows an orientation of six arms in 1,3,5 vs 2,4,6 facial steric gearing fashion, whereas L(2) adopted C(2v) symmetry where two of its thiazolinyl arms are oriented in one direction and the third arm in the another direction. Two silver complexes of L(1), 1 ([2(L(1))·6(AgClO(4))·2(CHCl(3))·HClO(4)]) and 2 ([2(L(1))·6(AgClO(4))]), that are suitable for single-crystal X-ray studies are isolated upon the slow diffusion of a dimethylformamide solution of AgClO(4) to the solution of L(1) in chloroform and dichloromethane, respectively. Similarly, upon the slow diffusion of an acetonitrile solution of AgClO(4) to the chloroform solution of L(2), colorless crystals of the silver complex of L(2), 3, are successfully isolated. The structural analyses of 1 and 2 show the formation of a silver ion assisted hexanuclear metallocage Ag(6)(L(1))(2) via dimeric assembly of L(1) with multiple clefts and pockets toward guests binding. In 1, two chloroform molecules sit in top and bottom pockets, whereas six perchlorate counteranions are bound in six clefts between the silver ion pillared side arms of the metallocage. Though complex 2 shows the formation of a metallocage like 1, the single crystal structural analysis depicts perchlorate counteranions bonded to the silver atoms of the metallocage. On the contrary, the silver complex of tripodal receptor L(2), 3, shows the formation of a metallo-organic polymeric network of L(2) and Ag(+). To the best of our knowledge, this work represents the first report on the formation of an M(6)L(2) type metallosupramolecular cage topology with multiple clefts for guest binding by a semirigid hexapodal receptor.

Selective colorimetric and fluorometric sensing of Cu(II) by iminocoumarin derivative in aqueous buffer.

A new iminocoumarin based receptor L (C(27)H(26)N(4)OS) is synthesized with pyridyl and benzothiazolyl functionality. Synthesis of L is easy and it is isolated in good yield. L shows a selective and distinct color change from yellow to orange with Cu(2+) over Li(+), Na(+), Ca(2+), Mg(2+), Cr(2+), Mn(2+), Fe(2+), Co(2+), Ni(2+), Cu(2+), Zn(2+), Cd(2+), Pb(2+), and Ag(+) whereas a slight change in color is also observed in the case of Hg(2+) but L shows selective fluorescent quenching only in the presence of Cu(2+) in aqueous HEPES buffer (pH 7.0). The naked eye detection limit of Cu(2+) is determined at 2 µM whereas an emission experiment shows a lower detection limit at 200 nM. Selectivity studies of L in presence of 50 equivalents of other ion(s) by emission experiment show no interference toward the detection of 1 equivalent of Cu(2+). Both UV-Vis and fluorescence studies in the presence of Cu(2+)-salts of different counter anions with various sizes and shapes (Cl(-), ClO(4)(-), NO(3)(-), CF(3)SO(3)(-), SO(4)(2-) and BF(4)(-)) show almost similar spectral output in buffer media irrespective of the nature of the counter anions. The detailed UV-Vis and fluorescence titration experiments suggest the existence of both 1:1 and 2:1 (L:Cu(2+)) complexation stoichiometry and EPR study shows d(x(2)-y(2)) ground state of the Cu(II) centre in the complex. Furthermore the formation of a mononuclear [Cu(L)(CH(3)CN)].2ClO(4) complex and the flexible conformation of L in the solid state are confirmed by the single-crystal X-ray structural study.

Functionalized guanidinium chloride based colourimetric sensors for fluoride and acetate: single crystal X-ray structural evidence of -NH deprotonation and complexation.

A series of new symmetrically functionalized guanidinium chlorides (S1-S10) are synthesized in good yields and their sensing ability toward anions is studied in MeCN-DMF (24 : 1) (v/v). The absorption bands of these molecules in the presence of anions are tuned by varying the functional groups attached to the guanidinium moiety (which resembles urea) with respect to (i) aromaticity (S1-S4), (ii) electron induction effect (S1, S5-S9), (iii) positional isomeric effect (S7-S9), (iv) indole functionality (S10) of the conjugated aryl units. Anions that are above Cl(-) in the Hofmeister series (F(-), AcO(-), H(2)PO(4)(-)) are eligible as an analyte in this series of molecules whereas less basic anions than Cl(-) do not cause any interference. Thus, this series of molecules are suitable for the detection of anions in the narrow window of the Hofmeister series. Out of all the anions, only fluoride causes vivid colour changes from yellow to red to reddish orange and finally to blue, irrespective of the increasing aromaticity, induction and positional isomeric effect of the substituent that is attached to the guanidinium moiety. Interestingly, S9 has shown the ability to sense distinctly both F(-) and AcO(-) colourimetrically. Further S10, a sensor attached with indole functionality shows selective sensing of F(-) colourimetrically with a NIR signature at ∼930 nm though both these outputs are very unstable in nature. Stability constants for complex formation of S1-S10 (except S5) with F(-), AcO(-) are calculated by UV-vis titration experiments. Finally single crystal X-ray structural studies on the species 1 formed upon treating S6 with sodium fluoride confirms -NH deprotonation, whereas the reaction of S6 and S2 with sodium benzoate shows 1:1 host:guest binding that results in complexes 2 and 3 respectively.

Binding of ammonium hexafluorophosphate and cation-induced isolation of unusual conformers of a hexapodal receptor.

The pyrazole-based hexa-host receptor showed the preference of an unusual conformation via 1:1 hydrogen bonding with ammonium hexafluorophosphate over steric gearing. Two different unusual conformers of the receptor are also isolated upon complexation with Cu(2+) and Cd(2+) ions.

Thiomethoxychalcone-functionalized ferrocene ligands as selective chemodosimeters for mercury(II): single-crystal X-ray structural signature of the [Hg8(mu8-S)(SCH3)12]2+ cluster.

Thiomethoxychalcone-based ligands bis[3,3-bis(methylsulfanyl)]-1,1'-eta(5)-ferrocenyl-2-propen-1-one (L(1)), 3,3-bis(methylsulfanyl)-1-eta(5)-ferrocenyl-2-propen-1-one (L(2)), and 3-methylsulfanyl-3-sulfanyl-1-eta(5)-ferrocenyl-2-propen-1-one (L(3)) have been synthesized on the ferrocene backbone by varying the number of chalcone arms and thiomethoxy substitutents. The single-crystal X-ray crystallographic analyses of all three ligands are reported in which crystals of L(1) were obtained as both syn and anti conformers and showed the conformational freedom of the two cyclopentadienyl (Cp) units. L(1)-L(3) are studied extensively toward their applicability in the colorimetric sensing of metal ions in solution. The solution-state study of mono- and bis(thiomethoxy)ferrocenylchalcone-functionalized ligands L(1) and L(2) showed selective colorimetric sensing for Hg(2+) over Li(+), Na(+), Ca(2+), Mg(2+), Cr(2+), Mn(2+), Fe(2+), Co(2+), Ni(2+), Cu(2+), Zn(2+), Cd(2+), and Au(3+) in acetonitrile. In both cases, a selective color change from orange to purple was observed with Hg(2+) and the resultant solution showed the appearance of a new peak at 565 nm (epsilon = 3920 M(-1) cm(-1)) for L(1) and 600 nm (epsilon = 1140 M(-1) cm(-1)) for L(2) in the UV/vis experiments. The UV/vis titration profiles of L(1) and L(2) indicate the formation of 2:1 (L(1)/Hg(2+)) and 1:1 (L(2)/Hg(2+)) initial complexations in solution. On the other hand, L(3) with thiomethoxy- and thiol-functionalized ferrocenylchalcone showed no appreciable color change with Hg(2+) under the same experimental conditions. Attempts were made to isolate single crystals of the resulting purple solution obtained in the cases of L(1) and L(2) with Hg(2+). In both cases, crystals suitable for a single-crystal X-ray diffraction study were isolated in very low yield by a layer diffusion technique. The single-crystal structural investigations demonstrated the formation of a sulfide-encapsulated mercury thiolate cuboctahedron cluster, [Hg(8)S(SCH(3))(12)](2+), upon a selective chemodosimetric desulfurization reaction between Hg(2+) and L(1) or L(2). Cyclic voltammetric studies also support the Hg(2+)-induced cleavage of thiomethoxy groups.