Principles of melting in hybrid organic-inorganic perovskite and polymorphic ABX3 structures.

Four novel dicyanamide-containing hybrid organic-inorganic ABX3 structures are reported, and the thermal behaviour of a series of nine perovskite and non-perovskite [AB(N(CN)2)3] (A = (C3H7)4N, (C4H9)4N, (C5H11)4N; B = Co, Fe, Mn) is analyzed. Structure-property relationships are investigated by varying both A-site organic and B-site transition metal cations. In particular, increasing the size of the A-site cation from (C3H7)4N → (C4H9)4N → (C5H11)4N was observed to result in a decrease in T m through an increase in ΔS f. Consistent trends in T m with metal replacement are observed with each A-site cation, with Co < Fe < Mn. The majority of the melts formed were found to recrystallise partially upon cooling, though glasses could be formed through a small degree of organic linker decomposition. Total scattering methods are used to provide a greater understanding of the melting mechanism.

Melting of hybrid organic-inorganic perovskites.

Several organic-inorganic hybrid materials from the metal-organic framework (MOF) family have been shown to form stable liquids at high temperatures. Quenching then results in the formation of melt-quenched MOF glasses that retain the three-dimensional coordination bonding of the crystalline phase. These hybrid glasses have intriguing properties and could find practical applications, yet the melt-quench phenomenon has so far remained limited to a few MOF structures. Here we turn to hybrid organic-inorganic perovskites-which occupy a prominent position within materials chemistry owing to their functional properties such as ion transport, photoconductivity, ferroelectricity and multiferroicity-and show that a series of dicyanamide-based hybrid organic-inorganic perovskites undergo melting. Our combined experimental-computational approach demonstrates that, on quenching, they form glasses that largely retain their solid-state inorganic-organic connectivity. The resulting materials show very low thermal conductivities (~0.2 W m-1 K-1), moderate electrical conductivities (10-3-10-5 S m-1) and polymer-like thermomechanical properties.

Storing redox equivalent in the phenalenyl backbone towards catalytic multi-electron reduction.

Storing and transferring electrons for multi-electron reduction processes are considered to be the key steps in various important chemical and biological transformations. In this work, we accomplished multi-electron reduction of a carboxylic acid via a hydrosilylation pathway where a redox-active phenalenyl backbone in Co(PLY-O,O)2(THF)2, stores electrons and plays a preponderant role in the entire process. This reduction proceeds by single electron transfer (SET) from the mono-reduced ligand backbone leading to the cleavage of the Si-H bond. Several important intermediates along the catalytic reduction reaction have been isolated and well characterized to prove that the redox equivalent is stored in the form of a C-H bond in the PLY backbone via a ligand dearomatization process. The ligand's extensive participation in storing a hydride equivalent has been conclusively elucidated via a deuterium labelling experiment. This is a rare example where the ligand orchestrates the multielectron reduction process leaving only the metal to maintain the conformational requirements and fine tunes the electronics of the catalyst.

Phenalenyl Based Aluminum Compound for Catalytic C-H Arylation of Arene and Heteroarenes at Room Temperature.

Main group metal based catalysis has been considered to be a cost-effective alternative way to the transition metal based catalysis, due to the high abundance of main group metals in the Earth's crust. Among the main group metals, aluminum is the most abundant (7-8%) in the Earth's crust, making the development of aluminum based catalysts very attractive. So far, aluminum based compounds have been popularly used as Lewis acids in a variety of organic reactions, but chemical transformation demanding a redox based process has never utilized an Al(III) complex as a catalyst. Herein, we tuned the redox noninnocence behavior of a phenalenyl ligand by coupling with Al(III) ion, which subsequently can store the electron upon reduction with K to carry out direct C-H arylation of heteroarenes/mesitylene at ambient temperature. A mechanistic investigation revealed that a three-electron reduced phenalenyl based triradical aluminum(III) complex plays the key role in such catalysis. The electronic structure of the catalytically active triradical species has been probed using EPR spectroscopy, magnetic susceptibility measurements, and electronic structure calculations using a DFT method.

Graphene oxide-phenalenyl composite: transition metal-free recyclable and catalytic C-H functionalization.

An efficient route towards a heterogeneous transition metal-free catalytic C-H functionalization using a covalently linked graphene oxide-phenalenyl conjugate is described herein (28 examples, which include a core of some biologically relevant biaryl and hetero-biaryls). It is an environmentally benign, economical and heterogeneous platform, whose catalytic activity can easily be regenerated through a simple washing-drying technique and the catalytic activity can be retained even after 10 cycles.

An Iron-Based Long-Lived Catalyst for Direct C-H Arylation of Arenes and Heteroarenes.

Direct C-H arylation of arenes and heteroarenes to biaryls at ambient temperature has been accomplished using a phenalenyl-supported iron(III) catalyst. The present catalyst requires a chemical reductant such as potassium and functions without any light stimulation. C-H arylation of various heteroarenes including pyridine as well as unactivated arene such as benzene delivered good to excellent yield (28 examples, up to 92 %) at room temperature. A combined effort based on experiments and theoretical calculations established that a phenalenyl-based radical species (generated by chemical reduction of the iron(III) coordinated phenalenyl complex) plays key role during the catalysis. Furthermore, this catalyst displayed remarkable stability during the catalysis, as evident from the fact that it was still usable over ten consecutive catalytic runs without losing its catalytic efficiency.

Tuning the redox non-innocence of a phenalenyl ligand toward efficient nickel-assisted catalytic hydrosilylation.

In this report, a ligand-redox assisted catalytic hydrosilylation has been investigated. A phenalenyl ligand coordinated nickel complex has been utilized as an electron reservoir to develop a base metal-assisted catalyst, which very efficiently hydrosilylates a wide variety of olefin substrates under ambient conditions. A mechanistic investigation revealed that a two-electron reduced phenalenyl based biradical nickel complex plays the key role in such catalysis. The electronic structure of the catalytically active biradical species has been interrogated using EPR spectroscopy, magnetic susceptibility measurements, and electronic structure calculations using a DFT method. Inhibition of the reaction by a radical quencher, as well as the mass spectrometric detection of two intermediates along the catalytic loop, suggest that a single electron transfer from the ligand backbone initiates the catalysis. The strategy of utilising the redox reservoir property of the ligand ensures that the nickel is not promoted to an unfavorable oxidation state, and the fine tuning between the ligand and metal redox orbitals elicits smooth catalysis.

Accessing Heterobiaryls through Transition-Metal-Free C-H Functionalization.

Herein we report a transition-metal-free synthetic protocol for heterobiaryls, one of the most important pharmacophores in the modern drug industry, employing a new multidonor phenalenyl (PLY)-based ligand. The current procedure offers a wide substrate scope (24 examples) with a low catalyst loading resulting in an excellent product yield (up to 95%). The reaction mechanism involves a single electron transfer (SET) from a phenalenyl-based radical to generate a reactive heteroaryl radical. To establish the mechanism, we have isolated the catalytically active SET initiator, characterizing by a magnetic study.

Unique trapping of paddlewheel copper(ii) carboxylate by ligand-bound {Cu2} fragments for [Cu6] assembly.

The bridging nature of in situ generated hydroxide ions and carboxylates (RCOO(-); R = CH3, C2H5, CH2Ph) has been utilized to design a new family of [Cu6] coordination complexes: [Cu6(µ3-OH)2(µ-H2L)2(µ1,1,3-O2CCH3)2(µ1,3-O2CCH3)2(µ-ClO4)2](ClO4)2·H2O (), [Cu6(µ3-OH)2(µ-H2L)2(µ1,1,3-O2CC2H5)4(µ-ClO4)2](ClO4)2·2H2O () and [Cu6(µ3-OH)2(µ-H2L)2(µ1,3-O2CCH2Ph)4(ClO4)2](ClO4)2·2H2O (). Tetracarboxylate bridged {Cu2} core units are trapped between two ligand-bound {Cu2(µ-H2L)(µ-OH)}(2+) subunits forming the [Cu6] complexes. The hexanuclear {Cu6(µ3-OH)2(H2L)2(µ-O2CR)4}(4+) cores having six interconnected Cu(II) ions assume a hitherto unknown dumbbell-shaped topology. Detailed characterizations have been done using X-ray crystallography and variable temperature magnetic measurements. For complexes , the dominant coupling constant (J') values between carboxylate bridged copper centers are -36.2 to -45.2 cm(-1) for short CuCu separations of 2.540-2.578 Å. In MeCN solutions all three complexes showed catalytic oxidation of 3,5-di-tert-butyl catechol (3,5-DTBCH2) in air.

Thymine Functionalized Graphene Oxide for Fluorescence "Turn-off-on" Sensing of Hg2+ and I- in Aqueous Medium.

Selective detection of either mercury (Hg2+) or iodide (I-) ion using fluorescence turn-on or turn-off processes is an important area of research. In spite of intensive research, simultaneous detection of both mercury and iodide using fluorescence turn-off-on processes, high sensitivity and theoretical support concerning the mechanisms are still lacking. In the present work, graphene oxide is functionalized by thymine to realize simultaneous detection of both Hg2+ and I- selectively using fluorescence turn-off-on mechanism. Ultra high sensitivity to the extent of ppb level exploiting large surface area of graphene is achieved. DFT calculations also assist to realize the detailed mechanisms involving this PL quenching and also its regain during sensing of these ions in aqueous solution.

Field-induced ferromagnetism and multiferroic behavior in end-on pseudohalide-bridged dinuclear copper(II) complexes with tridentate Schiff base blocking ligands.

Four new end-on pseudohalide-bridged dinuclear copper(II) complexes, [Cu2(L(1))2(N3)2]·DMF (1), [Cu2(L(2))2(N3)2] (2), [Cu2(L(3))2(NCS)2] (3), and [Cu2(L(4))2(N3)2] (4) {where HL(1), HL(2), HL(3), and HL(4) are tridentate N2O donor Schiff bases}, are synthesized and characterized. Complexes 1, 2, and 3 possess π···π stacking interactions, while in addition hydrogen-bonding interactions are present in 1 and 3. However, by contrast, complex 4 contains neither type of interaction. Field-induced long-range ferromagnetic ordering beyond 0.9 T is observed in complexes 1 and 2 due to π···π stacking interactions, while ferroelectric ordering is observed in complexes 1 and 3 due to hydrogen-bonding interactions. Most interestingly, complex 1, which contains both π···π stacking and hydrogen-bonding interactions, shows multiferroic behavior as a result of coupling between the dielectric and magnetic fields with 8% change in the magneto-dielectric effect at room temperature. We believe that from this study will emerge a new class of multiferroic materials.

Highly selective detection of trinitrophenol by luminescent functionalized reduced graphene oxide through FRET mechanism.

Among different nitro compounds, trinitrophenol (TNP) is the most common constituent to prepare powerful explosives all over the world. A few works on the detection of nitro explosives have already been reported in the past few years; however, selectivity is still in its infant stage. As all the nitroexplosives are highly electron deficient in nature, it is very difficult to separate one from a mixture of different nitro compounds by the usual photoinduced electron transfer (PET) mechanism. In the present work, we have used a bright luminescent, 2,6-diamino pyridine functionalized graphene oxide (DAP-RGO) for selective detection of TNP in the presence of other nitro compounds. The major advantage of using this material over other reported materials is not only to achieve very high fluorescence quenching of ∼96% but also superior selectivity >80% in the detection of TNP in aqueous medium via both fluorescence resonance energy transfer and PET mechanisms. Density functional theory calculations also suggest the occurrence of an effective proton transfer mechanism from TNP to DAP-RGO, resulting in this tremendous fluorescence quenching compared to other nitro compounds. We believe this graphene based composite will emerge a new class of materials that could be potentially useful for selective detection, even for trace amounts of nitro explosives in water.