Magnetic anisotropy in octahedral Dy(III) and Yb(III) complexes

New organophosphate complexes [Ln(dippH)3(dippH2)3]·(H2O)6, (Ln = Dy, Yb and Y; dippH2 = 2,6-diisopropylphenyl phosphate), displaying octahedral coordination geometry around the metal ion, exhibit unusual slow relaxation of magnetisation, which is investigated through experimental studies and ab initio CASSCF calculations.

Tuning Magnetic Anisotropy in Co(II) Tetrahedral Carbazole-Modified Phosphine Oxide Single-Ion Magnets: Importance of Structural Distortion versus Heavy-Ion Effect

Three mononuclear cobalt(II) tetrahedral complexes [Co(CzPh2PO)2X2] (CzPh2PO = (9H-carbazol-9-yl)diphenylphosphine oxide and X = Cl (1), Br (2), I (3)) have been synthesized using a simple synthetic approach to examine their single-ion magnetic (SIM) behavior. A detailed study of the variation in the dynamic magnetic properties of the Co(II) ion in a tetrahedral ligand field has been carried out by the change of the halide ligand. The axial zero-field splitting parameter D was found to vary from -16.4 cm-1 in 1 to -13.8 cm-1 in 2 and +14.6 cm-1 in 3. All the new complexes exhibit field-induced SIM behavior. The results obtained from ab initio CASSF calculations match well with the experimental data, revealing how halide ions induce a change in the D value as we move from Cl- to I-. The ab initio calculations further reveal that the change in the sign of D is due to the multideterminant characteristics of the ground state wave function of 1 and 2, while single-determinant characteristics are instead observed for 3. To gain a better understanding of the relationship between the structural distortion and the sign and magnitude of D values, magnetostructural D correlations were developed using angular relationships, revealing the importance of structural distortions over the heavy halide effect in controlling the sign of D values. This study broadens the scope of employing electronically and sterically modified phosphine oxide ligands in building new types of air-stable Co(II) SIMs.

Field-induced SIM behaviour in early lanthanide(III) organophosphates containing 18-crown-6

Single-ion magnets (SIMs) have attracted wide attention in recent years. Despite tremendous progress in late lanthanide SIMs, reports on early lanthanides exhibiting SIM characteristics are scarce. A series of five novel 18-crown-6 encapsulated mononuclear early lanthanide(III) organophosphates, [{(18-crown-6)Ln(dippH)₃}{(18-crown-6)Ln(dippH)₂(dippH₂)}]·[I₃] [Ln = Ce (1), Pr (2), Nd (3)] and [{Ln(18-crown-6)(dippH)₂(H₂O)}·{I₃}] [Ln = Sm (4) and Eu (5)], have been synthesised in the present study. 18-crown-6 coordinates to Ln(III) ions in an equatorial position while the axial positions are occupied by either three phosphate moieties as in 1-3 or two phosphate moieties and one water molecule as in 4 and 5, resulting in a muffin-shaped coordination geometry around the Ln(III) centres. Magnetic susceptibility measurements reveal that Ce and Nd complexes are field-induced single-ion magnets with significant barrier heights. Furthermore, the ab initio CASSCF/RASSI-SO/SINGLE_ANISO calculations on complexes 1 and 3 reveal significant QTM in the ground state rationalising the field-induced single-ion magnetism behaviour of these complexes.

Electron Paramagnetic Resonance Spectra of Pentagonal Bipyramidal Gadolinium Complexes

Gadolinium is a special case in spectroscopy because of the near isotropic nature of the 4f⁷ configuration of the +3 oxidation state. Gd³⁺ complexes have been studied in several symmetries to understand the underlying mechanisms of the ground state splitting. The abundance of information in Gd³⁺ spectra can be used as a probe for properties of the other rare earth ions in the same complexes. In this work, the zero-field splitting (ZFS) of a series of Gd³⁺ pentagonal bipyramidal complexes of the form [GdX₁X₂(L_eq)₅]ⁿ⁺ [n = 1, X = axial ligands: Cl^-, ^-O^tBu, ^-OArF₅ or n = 3, X = ^tBuPO(NHⁱPr)₂, L_eq = equatorial ligand: Py, THF or H₂O] with near fivefold symmetry axes along X¹-Gd-X² was investigated. The ZFS parameters were determined by fitting of room-temperature continuous wave electron paramagnetic resonance (EPR) spectra (at X-, K-, and Q-band) to a spin Hamiltonian incorporating extended Stevens operators compatible with C₅ symmetry. Examination of the acquired parameters led to the conclusion that the ZFS is dominated by the B₂⁰ term and that the magnitude of B₂⁰ is almost entirely dependent on, and inversely proportional to, the donor strength of the axial ligands. Surveying the continuous shape measure and the X¹-Gd-X² angle of the complexes showed that there is some correlation between the proximity of each complex to D_5h symmetry and the magnitude of the B₆⁵ parameter, but that the deformation of the X¹-Gd-X² angle is more significant than other distortions. Finally, the magnitude of B₂⁰ was found to be inversely proportional to the thermal barrier for the reversal of the magnetic moment (U_eff) of the corresponding isostructural Dy³⁺ complexes.

A rigid calcium 2-ethylhexylphosphate one-dimensional polymer: synthesis, structure, thermal behaviour and decomposition chemistry

The reactivity of two different phosphate esters has been explored with calcium ions. The reaction of calcium oxide with a mixture of mono/bis 2-ethylhexyl phosphate and 1,10-phenanthroline leads to the formation of the 1-D polymer [(phen)Ca(ehpH)₂]_n (1). On the other hand, the reaction of Ca(OAc)₂ with trimethyl phosphate in the presence of 1,10-phenanthroline however yields needle-shaped colourless crystals of [(phen)Ca(OAc)₂]_n (2). Compounds 1 and 2 have been characterized by various spectroscopic and analytical techniques. The solid-state structures have been determined by single crystal X-ray diffraction studies. The arrangement of rigid and flexible parts in 1 makes it an interesting compound to be studied for its thermal behaviour. DSC experiments performed above and below room temperature reveal thermal transitions in both the ranges, where below room temperature transition is prominent. A combination of variable temperature powder and single crystal X-ray diffraction experiments provides further insights into these transitions. Solid-state bulk thermolysis of 1 at 500 °C leads to an amorphous material contaminated with graphitic carbon which upon further heating to 600 °C produces crystalline α-Ca(PO₃)₂.

4,4′-Methylenebis[N-(2-hydroxy-3-methoxybenzylidene)-2,6-diisopropylaniline]

In the V-shaped title Schiff base, C41H50N2O4, the planes of the benzene rings of the central diphenylmethane unit make a dihedral angle of 70.40 (5)°, whereas the planes of the neighbouring benzene and ortho-vanilin rings are twisted with respect to one another by dihedral angles of 75.76 (5) and 73.89 (6)°. The Schiff base displays intramolecular O—H...N hydrogen bonds and weak intermolecular C—H...O contacts.

Alkali Metal Di-tert-butyl Phosphates: Single-Source Precursors for Homo- and Heterometallic Inorganic Phosphate Materials

The reaction of alkali metal acetates, M(OAc)·nH₂O (M = Li, Na, K), with thermally and hydrolytically unstable di-tert-butylphosphate ((^tBuO)₂PO₂H, dtbp-H) in a 1:1 molar ratio in MeOH at room temperature leads to clean formation of group 1 metal phosphates [Li(μ-dtbp)]_n (1), [Na(μ-dtbp)]_n (2), and [K₄(μ-dtbp)₄(μ-H₂O)₃]_n (3). All three compounds are essentially M/L 1:1 complexes. Owing to the presence of larger potassium ions, additional coordinated water molecules are found in 3, which has been further employed as a precursor for the synthesis of a mixed-metal phosphate polymer [CaK(μ-H₂O)₃(μ-dtbp)₃]_n (4) by reacting 3 with Ca(OAc)₂. Compounds 1-4 have been characterized by various analytical and spectroscopic techniques. Molecular structures of 1-4 have been established in the solid state by single-crystal X-ray diffraction studies, which reveal them to be one-dimensional polymers, where the adjacent metal centers are connected through -O-P-O- bridges formed by the dtbp ligand. These complexes are rare examples of analytically pure alkali metal alkyl phosphates bearing no additional N-donor ligands (other than dtbp ligands, only water molecules are coordinated to the metal centers). Therefore, these compounds can be employed as single-source precursors (SSPs) for nano-sized ceramic phosphates. The thermogravimetric analysis of 1-4 reveals the loss of thermally labile tert-butyl substituents of the organophosphate ligands to form organic-free phosphate materials in the temperature range 300-500 °C. Solvothermal decomposition of 1-3 in boiling toluene leads to the formation of corresponding dihydrogen phosphates M(H₂PO₄) (M = Li, Na, and K). The thermal decomposition of heterometallic 4 in the temperature range 400-800 °C leads to the formation of phase-pure mixed-metal calcium potassium metaphosphate CaK(PO₃)₃.

Supramolecular aggregation in sterically encumbered monoarylphosphates and their H-bonded adducts: multigram synthesis of elusive 2,6-di-tert-butylphenyl phosphate

A viable synthetic methodology has been developed for multigram synthesis of bulky 2,6-di-tert-butyphenyl phosphate; its supramolecular association behaviour and those of adducts formed with N-bases is established.

Deciphering the Role of Anions and Secondary Coordination Sphere in Tuning Anisotropy in Dy(III) Air-Stable D5h SIMs*

Precise control of the crystal field and symmetry around the paramagnetic spin centre has recently facilitated the engineering of high-temperature single-ion magnets (SIMs), the smallest possible units for future spin-based devices. In the present work, we report a series of air-stable seven coordinate Dy(III) SIMs {[L₂ Dy(H₂ O)₅ ][X]₃ ⋅L₂ ⋅n(H₂ O), n = 0, X = Cl (1), n=1, X = Br (2), I (3)} possessing pseudo-D_5h symmetry or pentagonal bipyramidal coordination geometry with high anisotropy energy barrier (U_eff ) and blocking temperature (T_B ). While the strong axial coordination from the sterically encumbered phosphonamide, ^t BuPO(NHⁱ Pr)₂ (L), increases the overall anisotropy of the system, the presence of high symmetry significantly quenches quantum tunnelling of magnetization, which is the prominent deactivating factor encountered in SIMs. The energy barrier (U_eff ) and the blocking temperature (T_B ) decrease in the order 3>2>1 with the change of anions from larger iodide to smaller strongly hydrogen-bonded chloride in the secondary coordination sphere, albeit the local coordination geometry and the symmetry around the Dy(III) display only slight deviations. Ab initio CASSCF/RASSI-SO/SINGLE_ANISO calculations provide deeper insights into the dynamics of magnetic relaxation in addition to the role of the secondary coordination sphere in modulating the anisotropy of the D_5h systems, using diverse models. Thus, in addition to the importance of the crystal field and the symmetry to obtain high-temperature SIMs, this study also probes the significance of the secondary coordination sphere that can be tailored to accomplish novel SIMs.

The Redox Journey of Iconic Ferrocene: Ferrocenium Dications and Ferrocenate Anions

The recent discoveries of both dicationic and monoanionic ferrocene derivatives throw light on the effect of the substituents on the C₅ ring as well as the choice of redox agents and solvent system in the preparation of previously believed to be difficult synthetic targets. These oxidized and reduced forms of ferrocene are of interest to spectroscopists, magnetochemists, and theoreticians.

Enhancing the barrier height for Yb(III) single-ion magnets by modulating axial ligand fields

The effect of systematic modification of the axial ligand field X on Ueff values in Yb(iii)-based SIMs, [Yb(Ph3PO)4X2]X' (X, X' = NO3 (1), OTf (2) and X = I/Br/Cl; X' = I3 (3)), whose equatorial Ph3PO ligation remains unchanged, has been investigated. Combined magnetic studies coupled with ab initio calculations reveal weakening of the axial ligand fields leading to the increase in the energy barrier, apart from suggesting the operation of different relaxation pathways.

Di-tert-butylphosphate Derived Thermolabile Calcium Organophosphates: Precursors for Ca(H2PO4)2, Ca(HPO4), α-/β-Ca(PO3)2, and Nanocrystalline Ca10(PO4)6(OH)2

Thermally and hydrolytically unstable di-tert-butyl phosphate (dtbp-H) has been used as synthon to prepare discrete and polymeric calcium phosphates that are convenient single-source precursors for a range of calcium phosphate ceramic biomaterials. The reactivity of dtbp-H toward two different calcium sources has been found to vary significantly, e.g., the reaction of Ca(OMe)₂ with dtbp-H in a 1:6 molar ratio in petroleum ether forms a mononuclear calcium hexa-phosphate complex [Ca(dtbp)₂(dtbp-H)₄] (1), whereas the change of calcium source to CaH₂, in a 1:2 molar ratio under otherwise similar reaction conditions, yields the calcium phosphate polymer, [Ca(μ-dtbp)₂(H₂O)₂·H₂O]_n(2). Compounds 1 and 2 have been extensively characterized by various spectroscopic and analytical techniques. The solid-state structures of both 1 and 2 have been determined by single-crystal X-ray diffraction studies. In discrete molecule 1, the central calcium ion is surrounded by two anionic dtbp and four neutral dtbp-H ligands in an octahedral coordination environment. Compound 2 is a one-dimensional polymer in which adjacent calcium ions are connected through double dtbp bridges. Solid-state thermolysis of bulk 1 in air leads to the exclusive formation of calcium metaphosphate β-Ca(PO₃)₂ in the entire temperature range of 400-800 °C. Thermal decomposition of polymer 2, however, can be fine-tuned to produce either α-Ca(PO₃)₂ or β-Ca(PO₃)₂ depending on the thermolysis conditions employed. Although the sample sintered at 600 °C produces exclusively α-form of Ca(PO₃)₂, the sample annealed at 800 °C or above produces β-form. Both α- and β-forms can also be successively formed one after other by a slow heating of a freshly prepared 2 on the powder diffractometer sample holder. Additional forms of ceramic phosphates have been prepared by solvothermal conditions because of the highly labile nature of the tert-butoxy groups of dtbp in 1 and 2. Solution decomposition of either 1 or 2 in boiling toluene at 140 °C in a sealed tube produces calcium dihydrogen phosphate [Ca(H₂PO₄)₂·H₂O] as the only product in the form of single crystals. Solution thermolysis of 2 in protic solvents such as water and methanol can be biased to produce other calcium phosphate biomaterials such as hydroxyapatite [Ca₁₀(PO₄)₆(OH)₂]and calcium monohydrogen phosphate [Ca(HPO₄)] in the presence of additional calcium precursors such as CaO and Ca(OMe)₂, respectively.

Compositional Control as the Key for Achieving Highly Efficient OER Electrocatalysis with Cobalt Phosphates Decorated Nanocarbon Florets

Compositional interplay of two different cobalt phosphates (Co(H₂ PO₄ )₂ ; Co-DP and Co(PO₃ )₂ ; Co-MP) loaded on morphologically engineered high surface area nanocarbon leads to an increased electrocatalytic efficiency for oxygen evolution reaction (OER) in near neutral conditions. This is reflected as significant reduction in the onset overpotential (301 mV) and enhanced current density (30 mA cm^-2 @ 577 mV). In order to achieve uniform surface loading, organic-soluble thermolabile cobalt-bis(di-tert-butylphosphate) is synthesized in situ inside the nanocarbon matrix and subsequently pyrolyzed at 150 °C to produce Co(H₂ PO₄ )₂ /Co(PO₃ )₂ (80:20 wt%). Annealing this sample at 200 or 250 °C results in the redistribution of the two phosphate systems to 55:45 or 20:80 (wt%), respectively. Detailed electrochemical measurements clearly establish that the 55:45 (wt%) sample prepared at 200 °C performs the best as a catalyst, owing to a relay mechanism that enhances the kinetics of the 4e^- transfer OER process, which is substantiated by micro-Raman spectroscopic studies. It is also unraveled that the engineered nanocarbon support simultaneously enhances the interfacial charge-transfer pathway, resulting in the reduction of onset overpotential, compared to earlier investigated cobalt phosphate systems.

A single-ion single-electron cerrous magnet

Herein, we present monometallic Ln(iii) complexes [L₃Ln(NO₃)₃] [where Ln = Ce (1) and La (2)] assembled from a simple reaction of the respective lanthanide nitrate hydrate and a bulky phosphonic diamide ^tBuPO(NHⁱPr)₂ ligand (L), where complex 1 behaves as a single-ion single-electron magnet under a small applied magnetic field. The Ce(iii) ion occupies a nine-coordinate distorted muffin-like coordination environment. The combination of direct and Raman process dominates the relaxation dynamics in 1 under the applied dc field. The low-temperature measurements performed with oriented crystals on a micro-SQUID setup exhibits strong tunnelling at zero-field, consistent with the theoretical results where strong mixing of the ground state with higher excited m_J levels is detected and also throws additional insights on the relaxation dynamics of 1. Ab initio calculations have been performed to understand the origin of anisotropy and models have been proposed for future directions.

Hitherto unknown eight-connected frameworks formed from A4B4O12 metal organophosphate heterocubanes

Modulation of a functional group on the distal part of a phosphate ester has been prudently exploited to selectively switch between the formation of D4R SBUs and 3-D framework structures. While amino substitution at the para-position of an aryl phosphate results in the isolation of tetra-amino functionalized discrete D4R zinc phosphate or its 4-connected 3-D framework, the introduction of an acetylamino substituent leads to a single-step assembly of a rare eight-connected 3-D framework solid.

Bimetallic Nanoparticles Anchored on Core-Shell Support as an Easily Recoverable and Reusable Catalytic System for Efficient Nitroarene Reduction

We report an easily recoverable and reusable versatile magnetic catalyst (Fe3O4@CS_AgNi, where CS = chitosan) for organic reduction reactions. The catalytic system is prepared by dispersing AgNi bimetallic nanoparticles on the magnetite core-shell (Fe3O4@CS). The as-synthesized catalyst has been characterized by spectroscopic techniques, such as IR, UV-vis, and X-ray photoelectron spectroscopy (XPS), and analytical tools, such as thermogravimetric analysis, powder X-ray diffraction, Brunauer-Emmett-Teller adsorption, FEG-scanning electron microscopy, high-resolution transmission electron microscopy (HR-TEM), inductively coupled plasma-atomic emission spectroscopy, and magnetic measurements. HR-TEM studies indicate the core-shell structure of Fe3O4@CS and confirm the presence of AgNi nanoparticles on the surface of Fe3O4@CS spheres. IR spectral and XPS studies lend evidence for the occurrence of a strong chemical interaction between the amino groups of CS and AgNi nanoparticles. The nano-catalyst Fe3O4@CS_AgNi rapidly reduces p-nitrophenol to p-aminophenol using NaBH4 as the reductant within a few minutes under ambient conditions (as monitored by UV-visible spectroscopy). The utility of this catalytic system has also been extended to the reduction of other nitroarenes. A strong interaction between Fe3O4@CS and AgNi nanoparticles impedes the leaching of AgNi nanoparticles from the core-shell support, leading to excellent reusability of the catalyst.

Selective formation of discrete versus polymeric copper organophosphates: DNA cleavage and cytotoxic activity

Copper phosphate metalloligands [Cu(X-dipp)(Pyterpy)]₂ [X = H (1), Br (2)], exemplifying expanded 4,4'-bipyridine type molecules, have been synthesized by reacting 4'-(4-pyridyl)-2,2':6',2''-terpyridine (Pyterpy) and para substituted 2,6-diisopropylphenyl phosphate (X-dippH₂) with copper acetate. The pendant N,N-ends of dimeric copper phosphates 1 and 2 have been forced to engage in further coordination by limiting the concentration of Pyterpy in the reaction mixture to yield rare Pyterpy bridged corner-shared polymeric copper phosphates [Cu₂(X-dippH)(X-dipp)(Pyterpy)(H₂O)]_n [X = Cl (3), Br (4), I (5)]. The formation of 1-5 is supported by spectroscopic and analytical data. The solid state structures of these compounds have further been confirmed by single-crystal X-ray diffraction studies. Soluble dimeric complexes 1 and 2 have been assessed for their in vitro anti-tumour properties against human breast and colorectal cancer cell lines. The DNA cleavage, protein cleaving and cytotoxicity assays revealed that these compounds are effective in cleaving DNA, while the activity of 1 as an anti-tumor agent is better than 2.

A decade of "Chemical Frontiers Goa"

We are delighted to present this collection of open access articles in RSC Advances to celebrate the Decennial Year of the "Chemical Frontiers Goa" meetings.

Thermolabile Organotitanium Monoalkyl Phosphates: Synthesis, Structures, and Utility as Epoxidation Catalysts and Single-Source Precursors for TiP2O7

The reaction of [Cp*TiCl₃] (Cp* = C₅Me₅) with monoalkyl phosphates (RO)PO₃H₂ (R = Me, Et, and ⁱPr) in tetrahydrofuran (THF) at 25 °C leads to the formation of binuclear complexes [Cp*₂Ti₂(μ-O₂P(OH)OR)₂(μ-O₂P(O)OR)₂] [R = Me (1), Et (2), and ⁱPr (3)]. On the other hand, the reaction of ( ^tBuO)₂PO₂K with [Cp*TiCl₃] in acetonitrile or THF results in isolation of either the dinuclear [Cp*₂Ti₂(μ-O₂P(OH)O ^tBu)₂(μ-O₂P(O)O ^tBu)₂] (4) or the trinuclear titanophosphate [Cp*₃Ti₃(μ-O₃PO ^tBu)₂(μ-O)₂(μ-O₂P(O ^tBu)₂)] (5), respectively. The formation of compounds 4 and 5 is facilitated by partial hydrolysis of the tert-butoxy groups of ( ^tBuO)₂PO₂K. New titanophosphates 1-5 have been characterized by spectroscopic and analytical methods, and the molecular structures have further been confirmed by single-crystal X-ray diffraction studies. Thermal decomposition studies of 1-5 reveal the initial loss of thermally labile alkyl substituents of the organophosphate ligands, followed by the loss of C₅Me₅ groups to form an organic-free amorphous titanophosphate in the temperature range 300-500 °C. This material transforms to highly crystalline titanium pyrophosphate TiP₂O₇ at 800 °C. Compounds 1-5 and the TiP₂O₇ materials obtained at 300, 500, and 800 °C through the thermal decomposition of 3 have been employed as efficient homogeneous catalysts for the alkene epoxidation reaction. Using hydrogen peroxide as the oxidant in an acetonitrile medium, these catalysts exhibit >90% alkene conversion with >90% epoxide selectivity in 4 h at temperatures below 100 °C.

Enriching lanthanide single-ion magnetism through symmetry and axiality

Rapidly growing modern information technology demands energy and cost efficient tools that can efficiently store and process a large amount of data. However, the miniaturization technology that was being used to boost the performance of the electronic devices, keeping up with the pace as estimated by Moore's law, is reaching its limit. To overcome these challenges, several alternative routes that can eventually mimic the modern electronics fabrication using silicon have been proposed. Single molecule magnets (SMMs), being considered as one of the potential alternatives, have gone through significant progress and the focus has shifted from the use of polynuclear clusters to mononuclear complexes in the last few years. The recent frenzy in the field of SMMs is driven by a better understanding of the effects of crystal field (CF) and molecular symmetry on the magnetic properties, especially in the case of mononuclear paramagnetic complexes, apart from other controlling factors. This has led to the advent of highly anisotropic single-ion magnets (SIMs) with magnetic blocking temperatures as high as 60 K and anisotropic energy barriers over 1800 K. This article overviews our recent research in the light of the emergence of the importance of CF and symmetry in 4f ion based single-ion magnets (SIMs), especially in the context of SIMs with D5h symmetry, apart from commenting on the synthetic efforts adopted to place these metal ions in unusual coordination geometries.

Is a strong axial crystal-field the only essential condition for a large magnetic anisotropy barrier? The case of non-Kramers Ho(iii) versus Tb(iii )

A monometallic non-Kramers Ho(iii) complex with a strong uniaxial ligand field displays a record high energy barrier of 355 K with hysteresis opening up to 4 K at a sweep rate of 0.027 T s^-1, while the isomorphous, more anisotropic non-Kramers Tb(iii) complex displays strong quantum tunnelling between the ground states. Ab initio calculations reveal that the presence of strong axial ligands and moderately weaker equatorial ligands is sufficient to quench the QTM between the ground pseudo doublets (m_J = ±8) in the case of Ho(iii) complex, where the relaxation is found to proceed via the first excited state. However, the equatorial field disrupts the stabilization of ground pseudo doublets in Tb(iii), inducing QTM and inhibiting SIM behaviour. Further insights into the decisive role played by the secondary coordination sphere and hydrogen-bonding in the SIM characteristics of these two non-Kramers ions were also gained. This combined experimental and computational approach highlights that although strong axiality holds the key for designing high temperature SIMs based on oblate non-Kramers ions, the strength of the equatorial ligand field also cannot be ignored.

1,3,5-Triphenylbenzene: a versatile photoluminescent chemo-sensor platform and supramolecular building block

Rich and diverse chemistry of 1,3,5-triphenylbenzene is discussed with emphasis on fluorescence based chemo-sensors, apart from a discussion on its use in building a number of supramolecular assemblies and fluorescent covalent-organic-frameworks.

[Am]Mn(H2POO)3: A New Family of Hybrid Perovskites Based on the Hypophosphite Ligand

A family of five hybrid ABX₃ perovskites has been synthesized using hypophosphite (H₂POO)^- as the X-site ion. These compounds adopt the general formula [Am]Mn(H₂POO)₃, where Am = guanidinium (GUA), formamidinium (FA), imidazolium, triazolium, and dabconium. We explore the diverse structural and phase transition behavior of these materials through single-crystal diffraction measurements and demonstrate contrasting magnetism in two of the phases, Am = GUA and FA, that arises from structural distortions. The results show that hypophosphite perovskites offer a promising platform for generating new functional materials.

Bulky Isopropyl Group Loaded Tetraaryl Pyrene Based Azo-Linked Covalent Organic Polymer for Nitroaromatics Sensing and CO2 Adsorption

An azo-linked covalent organic polymer, Py-azo-COP, was synthesized by employing a highly blue-fluorescent pyrene derivative that is multiply substituted with bulky isopropyl groups. Py-azo-COP was investigated for its sensing and gas adsorption properties. Py-azo-COP shows selective sensing toward the electron-deficient polynitroaromatic compound picric acid among the many other competing analogs that were investigated. Apart from its chemosensing ability, Py-azo-COP (surface area 700 m2 g-1) exhibits moderate selectivity toward adsorption of CO2 and stores up to 8.5 wt % of CO2 at 1 bar and 18.2 wt % at 15.5 bar at 273 K, although this is limited due to the electron-rich -N=N- linkages being flanked by isopropyl groups. Furthermore, the presence of a large number of isopropyl groups imparts hydrophobicity to Py-azo-COP, as confirmed by the increased adsorption of toluene compared to that of water in the pores of the COP.

Triphenylbenzene Sensor for Selective Detection of Picric Acid

A C ₃-symmetric triphenylbenzene based photoluminescent compound, 1,3,5-tris(4'-(N-methylamino)phenyl) benzene ([NHMe]₃TAPB), has been synthesized by mono-N-methylation of 1,3,5-tris(4'-aminophenyl) benzene (TAPB) and structurally characterized. [NHMe]₃TAPB acts as a selective fluorescent sensor for picric acid (PA) with a detection limit as low as 2.25 ppm at a signal to noise ratio of 3. Other related analytes (i.e. TNT, DNT and DNB) show very little effect on the fluorescence intensity of [NHMe]₃TAPB. The selectivity is triggered by proton transfer from picric acid to the fluorophore and ground-state complex formation between the protonated fluorophore and picrate anion through hydrogen bonding interactions. The fluorescence lifetime measurements reveal static nature of fluorescence quenching.

Intriguing structural chemistry of neutral and anionic layered monoalkylphosphates: single-source precursors for high-yield ceramic phosphates

A simple protocol for multi-gram synthesis of unstable and normally inaccessible phosphate monoesters ROPO₃H₂ is reported, apart from demonstration of their thermal instability and utility as starting materials for metal phosphate single source precursors.