Solvent Directed Synthesis of Molecular Cage and Metal Organic Framework of Copper(II) Paddlewheel Cluster

A solvothermal reaction of a clip-type dicarboxylic acid H(2)DCA 3,3-((5-nitroisophthaloyl)bis(azanediyl))-dibenzoic acid] and Cu(NO3)(2) in equimolar ratio in dimethylformamide (DMF) yielded MOF(CuCG1) which was formed by interlinking 4+2] self-assembled polyhedral cages via coordination between amide moiety present in the linker and the axial position of copper paddlewheel Cu-2(CO2)(4). Upon a change in the solvent from DMF to DMA dimethylacetamide] the interlinking among the polyhedra was successfully terminated to get single crystals of a discrete coordination cage with DMA bound to axial position of Cu(II) (CuCG2). Similar termination of the interlinking was also achieved by a fast crystallization process to get discrete architecture CuCG1

Face and edge directed self-assembly of Pd-12 tetrahedral nano-cages and their self-sorting

Reactions of a cis-blocked Pd(II) 90 degrees acceptor cis-(tmeda) Pd(NO3)(2)] (M) with 1,4-di(1H-tetrazol-5-yl) benzene (H2L1) and 1,3,5-tri(1H-tetrazol-5-yl) benzene] (H3L2) in 1 : 1 and 3 : 2 molar ratios respectively, yielded soft metallogels G1 and G2 tmeda = N, N, N', N'-tetramethylethane-1,2-diamine]. Post-metalation of the gels G1 and G2 with M yielded highly water-soluble edge and face directed self-assembled Pd-12 tetrahedral nano-cages T1 and T2, respectively. Such facile conversion of Pd(II) gels to discrete tetrahedral metallocages is unprecedented. Moreover, distinct self-sorting of these two tetrahedral cages of similar sizes was observed in the self-assembly of M with a mixture of H2L1 and H3L2 in aqueous medium. The edge directed tetrahedral cage (T1) was successfully used to perform Michael reactions of a series of water insoluble nitro-olefins assisted by encapsulation into the cage in aqueous medium

Mechano-fluorochromic Pt-II Luminogen and Its Cysteine Recognition

A new triphenylamine-based organometallic Pt-II luminogen (1) and its analogous organic compound (2) are reported. The molecules are decorated with aldehyde functionality to improve their photophysical properties by utilising donor-acceptor interactions. The single crystal X-ray structure analysis of PtII analogue 1 revealed that the neighbouring molecules were loosely organised by weak intermolecular C-H center dot center dot center dot pi interactions. Because of the twisted nature of the triphenylamine backbone the compounds showed aggregation-induced emission enhancement in THF/water mixture. Due to their loose crystal packing, upon application of external stimuli these luminogens exhibited mechano-fluorochromic behaviour. The crystalline forms of the compounds displayed a more superior emission efficiency than the grinded samples. Moreover, the compounds showed crystallization-induced emission enhancement (CIEE) and exhibited chemodosimetric response towards cysteine under physiological condition

Aggregation-Induced Emission of Platinum(II) Metallacycles and Their Ability to Detect Nitroaromatics

Two new acceptors containing platinum-carbazole (1) and platinum-triphenylamine (2) backbones with bite angles of 908 and 1208, respectively, have been synthesised and characterised. Reactions of the rigid acceptor 1 with linear dipyridyl-based donors (3 and 4) generated 4+4] self-assembled molecular squares (5 and 6), and similar treatments with acceptor 2 instead of 1 yielded 6+6] self-assembled molecular hexagons (7 and 8). The metallacycles were characterised by multinuclear NMR spectroscopy (H-1 and P-31) and ESI-MS. The geometries of the metallacycles were optimised by using the PM6 method. When aggregates of the metallacycles were formed by adding hexane solutions in dichloromethane, aggregation-induced emission was observed for metallacycles 5 and 7, and aggregation-caused quenching was observed for metallacycles 6 and 8. The formation of aggregates was verified by dynamic light scattering and TEM analyses. Macrocycles 5 and 7 are white-light emitters in THF. Moreover, their high luminescence in both solution and the solid state was utilised for the recognition of nitroaromatic explosives

Conformation-selective coordination-driven self-assembly of a ditopic donor with Pd-II acceptors

Coordination-driven self-assembly of 3-(5-(pyridin-3-yl)-1H-1,2,4-triazol-3-yl)pyridine (L) was investigated with 90 degrees cis-blocked Pd(II) acceptors and tetratopic Pd(NO3)(2). Although the ligand is capable of binding in several different conformations (acting as a ditopic donor through the pyridyl nitrogens), the experimental results (including X-ray structures) showed that it adopts a particular conformation when it binds with 90 degrees cis-blocked Pd(II) acceptors (two available sites) to yield 2 + 2] self-assembled macrocycles. On the other hand, with Pd(NO3)(2) (where four available sites are present) a different conformer of the same donor was selectively bound to form a molecular cubic cage. The experimental findings were corroborated well with the density functional theory (B3LYP) calculations. The tetratopic Pd(NO3)(2) yielded a 6 + 12] self-assembled Pd6L12 molecular cube, which contains a potential void occupied by nitrate and perchlorate ions. Being a triazole based ligand, the free space inside the cage is enriched with several sp(2) hybridised nitrogen atoms with lone pairs of electrons to act as Lewis basic sites. Knoevenagel condensation reactions of several aromatic aldehydes with active methylene compounds were successfully performed in reasonably high yields in the presence of the cage

A Self-Assembled Trigonal Prismatic Molecular Vessel for Catalytic Dehydration Reactions in Water

A water-soluble Pd-6 trigonal prism (A) was synthesized by two-component coordination-driven self-assembly of a Pd-II 90 degrees acceptor with a tetraimidazole donor. The walls of the prism are constructed by three conjugated aromatic building blocks, which means that the confined pocket of the prism is hydrophobic. In addition to the hydrophobic cavity, large product egress windows make A an ideal molecular vessel to catalyze otherwise challenging pseudo-multicomponent dehydration reactions in its confined nanospace in aqueous medium. This study is an attempt at selective generation of the intermediate tetraketones and xanthenes by fine-tuning the reaction conditions employing a supramolecular molecular vessel. Moreover, either poor or no yield of the dehydrated products in the absence of A under similar reaction conditions supports the ability of the confined space of the barrel to promote such reactions in water. Furthermore, we focused on the rigidification of the tetraphenylethylene-based tetraimidazole unit anchored within the Pd-II coordination architecture; enabling counter-anion dependent aggregation induced emission in the presence of water

Self-assembly of a ``cationic-cage'' via the formation of Ag-carbene bonds followed by imine condensation

A new strategy for the synthesis of a ``cationic-cage'' (CC-Ag) has been developed via metal-carbene (M-CNHC) bond formation followed by imine bond condensation. Reaction of a trigonal trisimidazolium salt H3L(PF6)(3) functionalized with three flexible N-phenyl-aldehyde pendants with silver oxide yielded a trinuclear tricationic organometallic cage (OC-Ag). Subsequent treatment of the organometallic cage (OC-Ag) with 1,4-diaminobutane links the two tris-NHC ligands via imine bond condensation, which thus generates a 3D `cationiccage' (CC-Ag). Furthermore, post-synthetic replacement of the Ag(I) with Au(I) leading to the formation of CC-Au was achieved via trans-metalation, with the retention of the molecular architecture

Self-assembly of a Pd8 macrocycle and Pd12 homochiral tetrahedral cages using poly(tetrazolate) linkers

A two-dimensional molecular square () was obtained by the self-assembly of a bis(tetrazole) linker, 4,4'-bis(1-tetrazol-5-yl)-1,1'-biphenyl (H), with a square-planar metal acceptor [ = (tmeda)Pd(NO), where tmeda = ,,','-tetramethylethane-1,2-diamine] in dimethyl sulfoxide (DMSO) followed by crystallization. The uncommon 2,3-binding mode through N atoms of the tetrazole rings in this assembly leads to the formation of an octanuclear molecular square. The molecular square [Pd()(NO)] is unstable in DMSO and slowly converts to a dynamic mixture of a 3D tetrahedral cage [Pd()(NO)] and the macrocycle . A tetrahedral cage () is formed by the usual 1,3-binding mode of the tetrazole rings. However, self-assembly of the [Pd()(PF)] was possible to access in the pure form in a less polar solvent like acetonitrile. The pure [Pd()(PF)] also converts to a mixture of and in DMSO. Interestingly, when a tris(tetrazole) linker, tris(4-(1-tetrazol-5-yl)phenyl)amine (H), was treated with the acceptor , it produced a tetrahedral nanocage [Pd()(NO)] through 1,3-binding mode of the tetrazole rings without any trace of an octahedral cage through 2,3-binding mode of the tetrazole moieties

Self-Assembled Pd(II) Barrels as Containers for Transient Merocyanine Form and Reverse Thermochromism of Spiropyran

Self-assembly of a cis-blocked Pd(II) 90\ub0 ditopic acceptor [cis-(tmeda)Pd(NO3)2] (M) with a tetradentate donor L1 [benzene-1,4-di(4-terpyridine)] in 2:1 molar ratio yielded two isometric molecular barrels MB1 and MB3 in DMSO [tmeda = N,N,N\u2032N\u2032-tetramethylethane-1,2-diamine]. Exclusive formation of the symmetrical tetrafacial barrel (MB1) was achieved when the self-assembly was performed in aqueous medium. The presence of a large confined cavity makes MB1 a potential molecular container. Spiropyran (SP) compounds exist in stable closed spiro form in visible light and convert to transient open merocyanine (MC) form upon irradiation with UV-light or upon strong heating. The transient MC form readily converts to the stable closed SP form in visible light. MB1 has been employed as a safe container to store the planar and unstable merocyanine isomers (MC1/2) of different spiropyran molecules (SP1/2) [SP1/2 = 6-bromo-spiropyran and 6- nitrospiropyran] for several days. The transient MC forms (MC1 and MC2) were found to be stable inside the molecular container MB1 under visible light and even in the presence of different stimuli such as heat and UV light for a long time. Such stabilization of MC forms inside the confined cavity of MB1 is noteworthy. This phenomenon was generalized by utilizing a carbazole-based molecular barrel (MB2) as a host, which also showed a similar stabilization of transient MC form in visible light at room temperature. Moreover, reverse thermochromism was observed as a result of heating of the MC1 82 MB2 complex, which de-encapsulates the guest in the form of SP1 to give a colorless solution. Moreover, both the host molecules (MB1, MB2) were capable of stabilizing transient MC2 even in the solid state. Such stabilization of transient MC forms in the solid state and transformation of SP forms to MC forms in the solid state in the presence of molecular barrel are remarkable, and these properties have been employed in developing a magic ink