Darpandeep Aulakh

Metal–Organic Frameworks as Platforms for the Controlled Nanostructuring of Single-Molecule Magnets

The prototypical single-molecule magnet (SMM) molecule [Mn12O12(O2CCH3)16(OH2)4] was incorporated under mild conditions into a highly porous metal-organic framework (MOF) matrix as a proof of principle for controlled nanostructuring of SMMs. Four independent experiments revealed that the SMM clusters were successfully loaded in the MOF pores, namely synchrotron-based powder diffraction, physisorption analysis, and in-depth magnetic and thermal analyses. The results provide incontrovertible evidence that the magnetic composite, SMM@MOF, combines key SMM properties with the functional properties of MOFs. Most importantly, the incorporated SMMs exhibit a significantly enhanced thermal stability with SMM loading advantageously occurring at the periphery of the bulk MOF crystals with only a single SMM molecule isolated in the transverse direction of the pores.

The structural diversity and properties of nine new viologen based zwitterionic metal–organic frameworks

The neutral flexible viologen based ligand 1,1′-bis(4-carboxybenzyl)-4,4′-bipyridinium dibromide (H2LBr2) and its self-assembly with first-row transition metals in an aqueous media leads to the formation of nine new zwitterionic (ZW) MOF materials with the following compositions: {[CuBr(L)]·(OH)·7H2O}n (1); {[M4(L)6(OH2)12]·2Br·3(bdc)·33H2O}n with M = Mn (2), Co (3) and Ni (4), {[M(bdc)(L)1.5]·9H2O}n with M = Cd (5) and Zn (6); {[Cu2(3-pzc)2(L)(OH2)]·5H2O}n (7); {[ZnCl2(L)0.5]·0.33H2O}n (8) and [Pd(HL)(Br)2(NO2)2(OH2)2] (9) (bdc = 1,4-benzenedicarboxylate, pzc = 3-pyrazole carboxylate). These compounds were characterized by single-crystal X-ray diffraction (SCXRD), powder X-ray diffraction (PXRD), infrared spectrometry (IR), elemental analyses, thermogravimetric analyses (TGA) and differential scanning calorimetry (DSC). Interestingly, when the samples are exposed to UV irradiation, photochromic behavior is observed for the ligand only, whereas the ZW MOFs are found to be photochemically inert. The fundamental structural origin for this photo reactivity is discussed in detail, as well as an in-depth CSD analysis of important intra- and intermolecular parameters of L-based MOFs.

Organosilatranes with thioester-anchored heterocyclic ring assembly: Cu2+ ion binding and fabrication of hybrid silica nanoparticles

This work presents the design, synthesis, UV-Vis absorption properties and Cu2+ ion binding of the organo-silicon complexes (3a–h) with different coordination abilities that are derived from mercaptopropylsilatrane (MPS) and respective heteroaromatic carboxylic acids (1a–h). The prepared thioester based organosilatranes (ThE-OS) have been meticulously characterized by a series of characterization techniques such as elemental analyses, FT-IR, NMR (1H, 13C), LC-MS, and structure of 3e was unambiguously determined by X-ray single crystal analyses. All the compounds have shown judicious absorption enhancement in the intensity as well as λmax values on binding with Cu2+ ions compared to other surveyed metal ions. In addition, it is for the first time that the hybrid silica nanoparticles (H-SiNPs) bearing a thioester linkage in the silica framework are reported. The synthesis was achieved conveniently by an in situ co-condensation reaction of tetraethyl orthosilicate (TEOS) with the corresponding ThE-OS. The derivatization of silica is confirmed by FT-IR, 13C and 29Si solid state CP-MAS NMR, UV-Vis, TEM, XRD, TGA and EDX techniques. Furthermore, the H-SiNPs have exhibited greater affinity towards Cu2+ ions than the parent ThE-OS.

Unrivaled combination of surface area and pore volume in micelle-templated carbon for supercapacitor energy storage

We created Immense Surface Area Carbons (ISACs) by a novel heat treatment that stabilized the micelle structure in a biological based precursor prior to high temperature combined activation – pyrolysis. While displaying a morphology akin to that of commercial activated carbon, ISACs contain an unparalleled combination of electrochemically active surface area and pore volume (up to 4051 m2 g−1, total pore volume 2.60 cm3 g−1, 76% small mesopores). The carbons also possess the benefit of being quite pure (combined O and N: 2.6–4.1 at%), thus allowing for a capacitive response that is primarily EDLC. Tested at commercial mass loadings (∼10 mg cm−2) ISACs demonstrate exceptional specific capacitance values throughout the entire relevant current density regime, with superior rate capability primarily due to the large fraction of mesopores. In the optimized ISAC, the specific capacitance (Cg) is 540 F g−1 at 0.2 A g−1, 409 F g−1 at 1 A g−1 and 226 F g−1 at a very high current density of 300 A g−1 (∼0.15 second charge time). At intermediate and high currents, such capacitance values have not been previously reported for any carbon. Tested with a stable 1.8 V window in a 1 M Li2SO4 electrolyte, a symmetric supercapacitor cell yields a flat energy–power profile that is fully competitive with those of organic electrolyte systems: 29 W h kg−1 at 442 W kg−1 and 17 W h kg−1 at 3940 W kg−1. The cyclability of symmetric ISAC cells is also exceptional due to the minimization of faradaic reactions on the carbon surface, with 80% capacitance retention over 100 000 cycles in 1 M Li2SO4 and 75 000 cycles in 6 M KOH.

The Importance of Polymorphism in Metal–Organic Framework Studies

Polymorphic phase transitions remain frequently undetected in routine metal-organic framework (MOF) studies; however, their discovery is of major importance in interpreting structure-property relationships. We herein report a reversible enantiotropic single-crystal to single-crystal polymorphic phase transition of a new microporous MOF [Eu(BDC)(NO3)(DMF)2]n (H2BDC = 1,4-benzenedicarboxylic acid; DMF = dimethylformamide). While modification 1LT at 170 K crystallizes in the monoclinic space group P21/c with unit cell dimensions of a = 17.673(2) Å, b = 20.023(2) Å, c = 10.555(9) Å, β = 90.129(4)°, modification 1HT at 290 K crystallizes in higher symmetry space group C2/c with unit cell dimensions of a = 17.200(7) Å, b = 10.737(4) Å, c = 10.684(4) Å, β = 90.136(2)°. This temperature-induced phase transition is accompanied by a small change in the solvent-accessible voids from 46.8 in 1LT to 49.8% in 1HT, which triggers a significant change in the adsorption properties as compared to a reported isostructural compound. Detailed investigations on the phase transition were studied with variable-temperature single-crystal X-ray diffraction (SCXRD), powder X-ray diffraction, and differential scanning calorimetry measurements. The herein-presented investigations emphasize the importance of polymorphic phase transitions in routine MOF studies originating from low-temperature SCXRD data and high-temperature physical property characterizations in avoiding the use of a wrong structure in interpreting structure-property relationships.

Thioester-appended organosilatranes: synthetic investigations and application in the modification of magnetic silica surfaces

The present investigation discloses a series of new organosilicon derivatives (3a–k) tailored with substituted benzoic acid modules (1a–k) via thioesterification with 3-mercaptopropylsilatrane (MPS). Product formation was authenticated using elemental analyses and different spectroscopic methods comprising FT-IR, NMR [1H, 13C] and LC-MS (Q-TOF). Thereafter, complete structural elucidation of compounds 3c and 3f was achieved by the single crystal X-ray technique. Photo-electronic inspection of all compounds by UV-Vis spectroscopy revealed their sensitivity towards substitution patterns. In addition, this is the first time that the potential of a silatranyl moiety has been tested for the modification of a silica surface pre-decorated with a magnetite core. The synthesis was achieved through a facile methodology involving chemical bonding at each stage, which proceeded without any external surfactant or template. The course of the reaction was followed by FT-IR, UV-Vis, XRD, TEM, FESEM, EDX and TGA techniques. Furthermore, the hybrid nanomaterial possessed significant sensorial ability toward copper ions, which makes the present protocol favourable for the construction of a new class of chelating ligands with an in-built multifunctional nanodevice.

Systematic Investigation of Controlled Nanostructuring of Mn12 Single-Molecule Magnets Templated by Metal–Organic Frameworks

This is the first systematic study exploring metal-organic frameworks (MOFs) as platforms for the controlled nanostructuring of molecular magnets. We report the incorporation of seven single-molecule magnets (SMMs) of general composition [Mn12O12(O2CR)16(OH2)4], with R = CF3 (1), (CH3)CCH2 (2), CH2Cl (3), CH2Br (4), CHCl2 (5), CH2But (6), and C6H5 (7), into the hexagonal channel pores of a mesoporous MOF host. The resulting nanostructured composites combine the key SMM properties with the functional properties of the MOF. Synchrotron-based powder diffraction with difference envelope density analysis, physisorption analysis (surface area and pore size distribution), and thermal analyses reveal that the well-ordered hexagonal structure of the host framework is preserved, and magnetic measurements indicate that slow relaxation of the magnetization, characteristic of the corresponding Mn12 derivative guests, occurs inside the MOF pores. Structural host-guest correlations including the bulkiness and polarity of peripheral SMM ligands are discussed as fundamental parameters influencing the global SMM@MOF loading capacities. These results demonstrate that employing MOFs as platforms for the nanostructuration of SMMs is not limited to a particular host-guest system but potentially applicable to a multitude of other molecular magnets. Such fundamental findings will assist in paving the way for the development of novel advanced spintronic devices.

Heteroaryl chalcone allied triazole conjugated organosilatranes: synthesis, spectral analysis, antimicrobial screening, photophysical and theoretical investigations

A series of heteroaryl tethered triazole conjoined organosilatranes were synthesized following an archetypal click reaction. The reaction sequence follows the initial generation of acetylinic Schiff bases (3a–3c, 4a–4c) which undergo 3 + 2 cycloaddition with 3-azidopropyltriethoxysilane (3-AzPTES) to give organotriethoxysilanes (5a–5c, 6a–6c) which were ultimately amended into their five-membered organosilatrane descendants (7a–7c, 8a–8c). The synthesized compounds were fully characterized by IR, 1H, 13C, mass spectrometry techniques and elemental analysis. Also, the complete structure elucidation of 7a and 8a was achieved via X-ray crystallography. The photophysical studies of the entire sequence of organosilatranes were performed in solvents of varying polarity to gain an insight into their solvatochromic behaviour. The results reveal that the molecules display trivial positive solvatochromism suggesting a high dipole moment of the excited state that has also been concurrently supported by the results derived from the Lippert–Mataga equation. Further, the molecular structures and photophysical properties of the organosilatranes were also studied theoretically by applying the IEFPCM model that mimics the desired solvent in combination with the TDDFT approach. Theoretical results were found to be in absolute accord with the experimental values. Additionally, several DFT based reactivity descriptors are reported presenting a meticulous view into the relative stability and reactivity of the chalcone linked organosilatranes. Further, all the organosilatranes were screened for their physiochemical and pharmacokinetic delineation by computational analysis and then investigated for their antimicrobial activities against different strains of bacteria and fungi. Compounds 8b and 8c were found to be the most potent antibacterial and antifungal agents, respectively.

Porous substrates as platforms for the nanostructuring of molecular magnets

Single molecule magnets (SMMs) and single ion magnets (SIMs), also known as molecular magnets (MMs), exhibit magnetic bistability and slow relaxation of their magnetization, characteristics which are representative of nanodomain particles whose origin is attributed to individual molecular spins. MMs have been receiving significant attention due to their potential applications in (1) ultra-high-density information storage devices, where each molecule can be used as a magnetic bit of information, and (2) quantum computing applications, taking advantage of lengthy coherence intervals. Any practical applications of MMs however, requires their controlled organization in different dimensionality architectures to allow for read-and-write processes, which is a challenge given that their chemical integrity and unique magnetic properties must be preserved during the nanostructuration process. This feature article highlights recent advances in this newly emerging field on the nanostructuration of MMs, and provides a comprehensive review of MM composites derived from various porous substrates, with particular emphases on synthetic approaches and characterization strategies.

First synthesis of pyrene-functionalized silatranes for mechanistic insights into their potential anti-parasitic and anti-oxidation activities

The known silatranes have attached substituents such as hydrogen, organyl, organoxy, aminoalkyl, thioorganyl, acyloxy, halogen, pseudohalogen, and other groups; however, their functionalization with any polycyclic aromatic hydrocarbon substituent is not recognized; this creates a niche in silatrane chemistry. The current study involves the first synthesis of pyrene-functionalized silatranes starting from 1-pyrenecarboxaldehyde and aminopropylsilane, fulfilling the niche. These newly synthesized silatranes were structurally characterized by IR spectroscopy, multinuclear NMR (1H and 13C) spectroscopy, electrospray ionization time-of-flight mass spectrometry (ESI-TOF-MS), and thermogravimetric analysis, and the structure of one of the silatranes was further confirmed by single crystal XRD analysis. The protozoans Giardia lamblia and Trichomonas vaginalis are responsible for a significant number of intestinal infections, and antioxidants are needed to prevent the formation of reactive species in the body. In the present study, anti-oxidant, anti-giardiasis, and anti-trichomoniasis potential of the synthesized compounds were assessed. Both compounds displayed significant activity against G. lamblia and T. vaginalis and showed potential anti-oxidant activity. The results indicate that one of the compounds is even more active against G. lamblia than metronidazole, a standard drug. Moreover, a theoretically and electrochemically supported mechanism for the anti-oxidant activity of the compounds has been reported in this study.