Coordination polymers built from 1,4-bis(imidazol-1-ylmethyl)benzene : from crystalline to amorphous

The supramolecular chemistry of the bis-imidazole ligand 1,4-bis(imidazol-1-ylmethyl)benzene, popularly known as bix, has been explored by various researchers in order to synthesize functional coordination polymers (CPs). The flexibility of the bix ligand, its unpredictable conformation and its coordination behaviour with transition metal ions have resulted in a huge number of structurally diverse and functionally intriguing CPs. In this perspective review we discuss the progress in CPs of bix between 1997 and today. More precisely, this review emphasizes the developments in functional supramolecular coordination polymers built from the bix ligand, from crystalline materials to amorphous nanomaterials

New bis-pyrazole-bis-acetate based coordination complexes: influence of counter-anions and metal ions on the supramolecular structures

A new flexible bis-pyrazol-bis-acetate ligand, diethyl 2,2’-(pyridine-2,6-diylbis (5-methyl-1H-pyrazole-3,1-diyl))diacetate (L), has been synthesised, and three coordination complexes, namely, [Zn(L)2](BF4)2 (1), [MnLCl2] (2) and [CdLCl2] (3) have been obtained. All ligands and complexes were characterised by IR, mass spectroscopy, thermogravimetric analysis and single-crystal X-ray diffraction. Single crystal X-ray diffraction experiment revealed that the primary supramolecular building block of 1 is a hexagonal chair shaped 0D hydrogen bonded synthon (stabilised by C–H∙∙∙O hydrogen bonding and C=O∙∙∙π interactions), which further built into a 2D corrugated sheet-like architecture having a 3-c net honeycomb topology, and finally extended to a 3D hydrogen bonded network structure having a five nodal 1,3,3,3,7-c net, through C–H∙∙∙F interactions. On the other hand, the two crystallographically independent molecules of 2 exhibited two distinct supramolecular structures such as 2D hydrogen bonded sheet structure and 1D zigzag hydrogen bonded chain, sustained by C–H∙O and C–H∙∙∙Cl interactions, which are further self-assembled into a 3,4-c network structure, and 3 showed a 2D hydrogen bonded sheet structure. The supramolecular structural diversity in these complexes is due to the different conformations adopted by the ligands, which are mainly induced by different metal ions with coordination environments controlled by different anions. Hirshfeld surface analysis was explored for the qualitative and quantitative analysis of the supramolecular interactions

Ligand and solvent effects in the formation and self-assembly of a metallosupramolecular cage

Two bis-pyridyl-bis-urea ligands namely N,N'-bis-(3-pyridyl)diphenylmethylene-bis-urea (L1) and N,N'-bis-(3-picolyl)diphenylmethylene-bis-urea (L2) have been reacted with a Cu(ii) salt resulting in the formation of a metallosupramolecular cage [{Cu(μ-L1)(DMSO)(HO)}·SO·X] (1) and a one-dimensional coordination polymer [{Cu(1)(μ-L2)(HO)}{Cu(2)(μ-L2)(HO)}·2SO·9HO·X] (2) (where DMSO = dimethylsulfoxide, and X = disordered lattice included solvent molecules), respectively. The single crystal structures of 1 and 2 are discussed in the context of the effect of the ligands, particularly the hydrogen bonding functionality of the ligand, on the supramolecular structural diversities observed in these metal organic compounds. The supramolecular packing of 1 is clearly influenced by the nature of the solvent and ligand used; mixtures of DMSO/MeOH or DMSO/HO lead to the formation of blue crystals or a hydrogel, respectively

Pt(IV)-based nanoscale coordination polymers : antitumor activity, cellular uptake and interactions with nuclear DNA

Cisplatin has been for many years the gold standard chemotherapeutic drug for the treatment of a wide range of solid tumors, even though its use is commonly associated with serious side effects including non-selective toxicity, myelosuppression or development of cisplatin resistance, among others complications. Over the last decade, a number of nanoparticle formulations were developed to reduce its side effects and improve the selectivity and efficacy of this drug. In this study, we have developed a novel nanoparticle platform based on nanoscale coordination polymer named (Zn-Pt(IV)-NCPs) which contains a Pt(IV) prodrug, Zn and the linker ligand 1,4-Bis(imidazol-1-ylmethyl)benzene (bix). The main objective has been to gain insights into the mechanism of action of this nanostructured material in comparison with cisplatin and the free Pt(IV) prodrug in order to establish a correlation between nanostructuration and therapeutic activity. Zn-Pt(IV)-NCPs nanoparticles displayed an average size close to 200 nm as determined by DLS, a good stability in physiologic environments, and a controlled drug release of Pt. In vitro studies demonstrated that Pt(IV)-NCPs showed an enhanced cytotoxic effect against cell culture of cervical cancer, neuroblastoma and human adenocarcinoma cells in comparison with free Pt(IV) prodrug. Although no difference in cell uptake of Pt was observed for any of the three cell lines assayed, a higher amount of Pt bound to the DNA was found in the cells treated with the nanostructured Pt(IV) prodrug. These studies suggest that the nanostructuration of the prodrug facilitate its activation and induce a change in the mechanism of action related to an increased interaction with the DNA as corroborated by the studies of direct interaction of the Pt(IV) prodrug, nanostructured or not, with DNA

Coordination polymers built from 1,4-bis(imidazol-1-ylmethyl)benzene: From crystalline to amorphous

The supramolecular chemistry of the bis-imidazole ligand 1,4-bis(imidazol-1-ylmethyl)benzene, popularly known as bix, has been explored by various researchers in order to synthesize functional coordination polymers (CPs). The flexibility of the bix ligand, its unpredictable conformation and its coordination behaviour with transition metal ions have resulted in a huge number of structurally diverse and functionally intriguing CPs. In this perspective review we discuss the progress in CPs of bix between 1997 and today. More precisely, this review emphasizes the developments in functional supramolecular coordination polymers built from the bix ligand, from crystalline materials to amorphous nanomaterials.NNA thanks the EU for a Marie Curie Intra-European Fellowship. FN and DRM thank ICN2-CSIC, Spain for financial support, and especially the students and collaborators for their contributions to amorphous CPPs. This work was supported by project MAT2015-70615-R from the Spanish Government and by FEDER funds. ICN2 acknowledges support from the Severo Ochoa Program (MINECO, Grant SEV-2013-0295).Peer Reviewe

A hexa-quinoline based C 3-symmetric chemosensor for dual sensing of zinc(ii) and PPi in an aqueous medium via chelation induced "oFF-ON-OFF" emission

A quinoline-based C-symmetric fluorescent probe (1), N,N',N''-((2,4,6-trimethylbenzene-1,3,5-triyl)tris(methylene))tris(1-(quinolin-2-yl)-N-(quinolin-2-ylmethyl)methanamine), has been developed which can selectively detect Zn without the interference of Cdvia significant enhancement in emission intensity (fluorescence "turn-ON") associated with distinct fluorescence colour changes and very low detection limits (35.60 × 10 M in acetonitrile and 29.45 × 10 M in 50% aqueous buffer (10 mM HEPES, pH = 7.4) acetonitrile media). Importantly, this sensor is operative with a broad pH window (pH 4-10). The sensing phenomenon has been duly studied through UV-vis, steady-state, and time-resolved fluorescence spectroscopic methods indicating 1:3 stoichiometric binding between 1 and Zn which is further corroborated by H NMR studies. Density functional theoretical (DFT) calculations provide the optimized molecular geometry and properties of the zinc complex, 1[Zn(ClO)] , which is proposed to be formed in acetonitrile. The results are in line with the solution-state experimental findings. The single crystal X-ray study provides the solid state structure of the trinuclear Zn complex showing solubility in an aqueous buffer (10 mM HEPES, pH = 7.4). Finally, the resulting trinuclear Zn complex has been utilized as a fluorescence "turn-OFF" sensor for the selective detection of pyrophosphate in a 70% aqueous buffer (10 mM HEPES, pH = 7.4) acetonitrile solvent with a nanomolar detection limit (45.37 × 10 M)

A hexa-quinoline based C3-symmetric chemosensor for dual sensing of zinc(ii) and PPi in an aqueous medium via chelation induced “OFF–ON–OFF” emission

A quinoline-based C3-symmetric fluorescent probe (1), N,N′,N′′-((2,4,6-trimethylbenzene-1,3,5-triyl)tris(methylene))tris(1-(quinolin-2-yl)-N-(quinolin-2-ylmethyl)methanamine), has been developed which can selectively detect Zn2+ without the interference of Cd2+via significant enhancement in emission intensity (fluorescence “turn-ON”) associated with distinct fluorescence colour changes and very low detection limits (35.60 × 10−9 M in acetonitrile and 29.45 × 10−8 M in 50% aqueous buffer (10 mM HEPES, pH = 7.4) acetonitrile media). Importantly, this sensor is operative with a broad pH window (pH 4–10). The sensing phenomenon has been duly studied through UV-vis, steady-state, and time-resolved fluorescence spectroscopic methods indicating 1 : 3 stoichiometric binding between 1 and Zn2+ which is further corroborated by 1H NMR studies. Density functional theoretical (DFT) calculations provide the optimized molecular geometry and properties of the zinc complex, 1[Zn(ClO4)]33+, which is proposed to be formed in acetonitrile. The results are in line with the solution-state experimental findings. The single crystal X-ray study provides the solid state structure of the trinuclear Zn2+ complex showing solubility in an aqueous buffer (10 mM HEPES, pH = 7.4). Finally, the resulting trinuclear Zn2+ complex has been utilized as a fluorescence “turn-OFF” sensor for the selective detection of pyrophosphate in a 70% aqueous buffer (10 mM HEPES, pH = 7.4) acetonitrile solvent with a nanomolar detection limit (45.37 × 10−9 M).P. G. gratefully acknowledges the Science and Engineering Research Board (SERB; EMR/2016/000900), India, for financial support and the Alexander von Humboldt Foundation for donating a fluorometer. S. S. would like to thank CSIR, India, for SRF.Peer reviewe

Light-Triggered Metal Coordination Dynamics in Photoswitchable Dithienylethene–Ferrocene System

The C-2-symmetric photochromic molecule 3, containing dithienylethene (DTE) and ferrocene units connected by an alkyne bridge, represents a unique probe where a metal (Hg2+) binds with the central DTE moiety. Both photoisomerized states of 3 (open, 3o; closed, 3c) are found to interact with Hg2+ ion by the S atoms of the DTE core; however, the binding constants (from a UV-vis study) and DFT calculations suggest that the open isomer (3o) binds with the metal ion more strongly than that of the closed isomer (3c). Notably, the course of metal binding does not perturb the inherent photoisomerization properties of the DTE core and the photoswitchability persists even in the metal-coordinated form of 3, however, with a comparatively slower rate. The quantum yields for photocyclization (Phi(o -> c)) and photocycloreversion (Phi(c -> o)) in the free form are 0.56 and 0.007, respectively, whereas the photocyclization quantum yield in the Hg2+ complexed species is 0.068, 8.2 times lower than the photocyclization quantum yield (Phi(o -> c)) of free 3o. Thus, the rate of photoisomerization can be modulated by a suitable metal coordination to the DTE core. The dynamics of photoswitchability in the metal-coordinated form of DTE has been explored by experimental means (UV-vis and electrochemical studies) as well as quantum chemical calculations

Exploring the effect of morphologies of Fe(III) metal-organic framework MIL-88A(Fe) on the photocatalytic degradation of rhodamine B

Metal-organic frameworks built from [Fe3(μ3-O)(COO)6] clusters and fumaric acid ligand, the so-called MIL-88 A(Fe) is a well-known environment-friendly promising material for many applications. In this paper, three different morphologies of MIL-88 A(Fe) such as rod, diamond and spindle have been synthesized separately by reacting FeCl3•6H2O and fumaric acid in 1 : 1 metal-ligand stoichiometric ratio using two different solvents such as water and DMF via hydrothermal method. The morphology of the products and their particle sizes were obtained using SEM and three distinct morphologies viz., rod, diamond and spindle were clearly distinguished by TEM. All the three samples were characterized by FT-IR, PXRD, UVDRS, PL, XPS and BET, and the effect of the morphologies of MIL-88 A(Fe) on the photocatalytic degradation of Rhodamine B (RhB) was studied under sunlight. The addition of an H2O2 electron acceptor can markedly enhance the photocatalytic Rhodamine B degradation of MIL-88 A(Fe). Among these three, rod-shaped morphology of MIL-88 A(Fe) shows the higher photocatalytic effect for the degradation of Rhodamine B under sunlight due to its lower band gap, high surface area, and lower electron-hole recombination rate which enable them the transfer of electrons for the photocatalytic degradation. We found that 98% degradation of RhB in 50 min has taken place by using r-MIL-88 A(Fe) as the catalyst under sunlight.</p

A 0D/2D Heterojunction Composite of Polymeric Carbon Nitride and ZIF-8-Derived ZnO for Photocatalytic Organic Pollutant Degradation

Solar photocatalytic technology based on semiconducting materials has gained the attention of the scientific community to solve the energy crisis and environmental remediation. Zeolitic imidazolate frameworks (ZIFs) are a subfamily of metal–organic frameworks (MOFs) with the isomorphic topologies of zeolites and coordinative compositions of MOFs. Owing to high specific surface areas, tunable channels and high thermal stabilities, zeolitic imidazolate frameworks (ZIFs) have been used in catalytic applications. In this paper, ZIF-8 was used as a matrix to synthesize 0D/2D heterojunction photocatalysts, viz., ZnO/C3N4-x% (x = 2.5, 5 and 10), for the photocatalytic degradation study of rhodamine B (RhB). The synthesized composite materials were characterized using FTIR, PXRD, UVDRS, PL, TEM, and BET analyses. TEM images showed the nearby contacts between ZnO and C3N4 in the hybrid and the uniform distribution of ZnO on the surface of the C3N4 nanosheet, thus increasing the development of 0D/2D heterojunction. The hybrid system ZnO/C3N4-5% (ZCN-5) showed good photocatalytic activity for the degradation of RhB under sunlight. A possible mechanism for the improved photocatalytic activity of the ZnO/C3N4 composite is also suggested. This exploratory study demonstrates the effective separation and migration of photo-induced electron–hole pairs between the 2D C3N4 sheet and 0D ZnO for the improved performance of heterojunction photocatalysts