Halogen Bond Mediated Self-Assembly of Mononuclear Lanthanide Complexes: Perception of Supramolecular Interactions, Slow Magnetic Relaxation, and Photoluminescence Properties.

Five new mononuclear lanthanide complexes, [LnL2][Et3NH]·THF/H2O (Ln = Nd, Tb, Dy) (H2LCl = 2-bis(2-hydroxy-3,5-dichloro benzyl)aminomethyl]pyridine), Ln = Nd (1), Tb (2), and Dy (3), and (H2LBr = 2-bis(2-hydroxy-3,5-dibromo benzyl)aminomethyl]pyridine), Ln = Nd (4, H2O) and Tb (5), were synthesized and structurally characterized by single-crystal X-ray diffraction analyses. Being isostructural in all the five cases, the metal center is octa-coordinated with a triangular dodecahedron (D2d symmetry) geometry, and it is independent of the halogen substitution (Cl/Br). This close similarity is due to the composite interplay of hydrogen/halogen bond interactions that control the overall crystal packing, yet notable differences in association patterns among the individual ones arise from the subtle stereo-electronic requirement of individual molecules in the three-dimensional (3D) architecture. Hirshfeld surface and density functional theory (DFT) calculations clearly vouch for the importance of the hydrogen bond and halogen bond interactions observed in the structure. Detailed magnetic measurements using direct-current and alternating-current susceptibility measurements show slow magnetic relaxation in 3, a characteristic feature of the single-molecule magnets (SMMs), which is not shown by 1 and 2. Steady-state and time-resolved photoluminescence of Tb(III) complexes shows a strong ligand-to-metal energy transfer that can be modulated by changing the substitution on phenolic ligands. The results from these analyses indicate that it may be advantageous to consider the subtle role of hydrogen bond (HB)/halogen bond (XB) intermolecular interactions judiciously for the design of SMMs and luminescent materials based on halogen-substituted ligands.

Inclusion of Ln(III) in the Complexes of Co(II) with a Mannich Base Ligand: Development of Atmospheric CO2 Fixation and Enhancement of Catalytic Oxidase Activities.

The reaction of the Mannich base ligand (H2L = N, N'-dimethyl- N, N'-bis(2-hydroxy-3-methoxy-5-methylbenzyl)ethylenediamine) with Co(OAc)2·4H2O and Ln(III) nitrate salts (Ln = Gd, Tb, and Dy) under basic conditions afforded three carbonato-bridged isostructural tetranuclear heterometallic Co(II)-Ln(III) complexes (Co2Gd2L2(µ4-CO3)2(NO3)2] (1), [Co2Tb2L2(µ4-CO3)2(NO3)2] (2), and [Co2Dy2L2(µ4-CO3)2(NO3)2] (3)) by atmospheric CO2 fixation. In all structures, two dinuclear [(CoIIL)LnIII(NO3)] units are linked via two µ4-carbonato groups to form the tetranuclear CoII2LnIII2 core. The geometry around two penta-coordinated Co(II) ions is distorted square pyramid, and that around two nona-coordinated Ln(III) ions is intermediate between "spherical tricapped trigonal prism" and "spherical capped square antiprism" in all complexes. The complexes (1-3) showed catecholase-like and phenoxazinone-synthase-like catalytic activities. The kcat values calculated for the catecholase-like reaction were 254.5, 272.4, and 291.3 h-1, and for the phenoxazinone-synthase-like reaction they were 2930.6, 2965.2, and 2998.5 h-1 for complexes 1-3, respectively. The probable pathways for these two oxidase reactions have been proposed by the analyses of mass spectral data. For all of the compounds, the variable temperature magnetic susceptibility and isothermal magnetization data were investigated. The complexes exhibited overall ferromagnetic behavior, which was evident from the isothermal magnetization curves. AC magnetic susceptibility measurements revealed the slow relaxation of magnetization in complexes 2 and 3 but very negligible in 1. The activation energy barriers ( Ueff) for the slow relaxation process were evaluated and found to be 1.99, 2.79, and 8.98 K for 1, 2, and 3, respectively.

Study of heterogeneous catalysis by iron-squarate based 3D metal organic framework for the transformation of tetrazines to oxadiazole derivatives.

We present here a simple, milder, and environmentally benign heterogeneous catalytic method for the transformation of tetrazines to oxadiazole derivatives at room temperature (25 °C) using our earlier synthesized iron-squarate based 3D metal organic framework, [Fe3(OH)3(C4O4)(C4O4)0.5]n (FeSq-MOF).

Insights into biomimetic system-ligand interaction of substituted isophthalic acid: A functionality induced photophysical study.

The present article attempts to interpret the modulation of photophysical properties of isophthalic acid (IPA) through its amino [5-amino isophthalic acid (5-amino IPA)] and azido [5-azido isophthalic acid (5-azido IPA)] substituted derivatives which are chemically potent organic ligands. The ground state structure-reactivity correlation of 5-amino IPA and 5-azido IPA has been deciphered through computational studies. The computed energetics show significant interaction feasibility of the substituted ligand systems with the biomimetic systems which is further validated experimentally. The binding interaction of the probes with oppositely polarized functionalization is studied to be significant with cetyltrimethylammonium bromide (CTAB) and bovine serum albumin (BSA) with the amino functionalized derivative having a comparatively stronger binding constant value. The steady-state absorption and fluorescence study establish significant modification of polarity of the heteronuclear probes. The micro polarity study in water-dioxane mixtures enables determination of polarity of 5-amino IPA in CTAB and BSA unlike 5-azido IPA. Presence of an overlapping region between the emission spectrum of BSA and the absorption spectrum of the probes as probable donor-acceptor pair are also scrutinized via the steady-state fluorescence studies. The photophysical behavior of 5-amino IPA is observed to be somewhat dissimilar to that of 5-azido IPA.

Influence of intrinsic spin ordering in La0.6Sr0.4Co0.8Fe0.2O3-δ and Ba0.6Sr0.4Co0.8Fe0.2O3-δ towards electrocatalysis of oxygen redox reaction in solid oxide cell.

The redox reaction of oxygen (OER & ORR) forms the rate determining step of important processes like cellular respiration and water splitting. Being a spin relaxed process governed by quantum spin exchange interaction, QSEI (the ground triplet state in O2 is associated with singlet oxygen in H2O/OH-), its kinetics is sluggish and requires inclusion of selective catalyst. Functionality and sustainability of solid oxide cell involving fuel cell (FC) and electrolyzer cell (EC) are also controlled by ORR (oxygen redox reaction) and OER (oxygen evolution reaction). We suggest that, presence of inherent spin polarization within La0.6Sr0.4Co0.8Fe0.2O3-δ (LSCF6482) (15.86 emu g-1) and Ba0.6Sr0.4Co0.8Fe0.2O3-δ (BSCF6482) (3.64 emu g-1) accounts for the excellent selective electrocatalysis towards ORR and OER. QSEI forms the atomic level basis for OER/ORR which is directly proportional to spin ordering (non-zero magnetization) of the active electrocatalyst. LSCF6482 exhibits (21.5 kJ mol-1@0.8 V for ORR compared to 61 kJ mol-1@0.8 V for OER) improved ORR kinetics whereas BSCF6482 (18.79 kJ mol-1@0.8 V for OER compared to 32.19 kJ mol-1 for ORR@-0.8 V) is best suited for OER under the present stoichiometry. The findings establish the presence of inherent spin polarization of catalyst to be an effective descriptor for OER and ORR kinetics in solid oxide cell (SOC).

Serendipitous assemblies of two large phosphonate cages: a Co15 distorted molecular cube and a Co12 butterfly type core structure.

This report describes the synthesis, characterization, and magnetic properties of two novel phosphonate-based Co(II) cages. Structural investigation reveals some interesting geometrical features in the molecular core that may provide new models in single molecular magnetic materials.

A 3D iron(II)-based MOF with squashed cuboctahedral nanoscopic cages showing spin-canted long-range antiferromagnetic ordering.

The reaction of dilithium squarate with Fe(II) perchlorate led to the formation of a new Fe(II)-based 3D MOF, [Fe3(OH)3(C4O4)(C4O4)0.5]n (1), with homoleptic squashed cuboctahedral cages. Complex 1 crystallizes in the monoclinic C2/c space group. Fe(II) centers in the complex are octahedrally coordinated by four squarate dianions in axial and equatorial positions and two hydroxyl groups in the remaining equatorial positions. The interesting structural feature of 1 is that the three-dimensional framework is an infinite extension of nanoscopic cuboctahedral cages. The framework also contains two types of voids; the larger hydrophobic ones are surrounded by aromatic squarate ligands, while the smaller ones are hydrophilic with hydroxyl groups on the surface connected by bifurcated hydrogen bonding interaction. A variable temperature magnetic study shows spin-canted long-range antiferromagnetic ordering in the low temperature regime.

Study of Drug Delivery Using Purely Organic Macrocyclic Containers-Cucurbit[7]uril and Pillararene.

An impaired immune system is the root of various human ailments provoking the urge to find vehicle-mediated quick delivery of small drug molecules and other vital metabolites to specific tissues and organs. Thus, drug delivery strategies are in need of improvement in therapeutic efficacy. It can be achieved only by increasing the drug-loading capacity, increasing the sustained release of a drug to its target site, easy relocation of drug molecules associated with facile complexation-induced properties of molecular vehicles, and high stimuli-responsive drug administration. Supramolecular drug delivery systems (SDDS) provide a much needed robust yet facile platform for fabricating innovative drug nanocarriers assembled by thermodynamically noncovalent interaction with the tunable framework and above-mentioned properties. Measures of cytotoxicity and biocompatibility are the two main criteria that lie at the root of any promising medicinal applications. This Review features significant advancements in (i) supramolecular host-guest complexation using cucurbit[7]uril (CB[7]), (ii) encapsulation of the drug and its delivery application tailored for CB[7], (iii) self-assembly of supramolecular amphiphiles, (iv) supramolecular guest relay using host-protein nanocavities, (v) pillararene (a unique macrocyclic host)-mediated SDDS for the delivery of smart nanodrugs for siRNA, fluorescent molecules, and insulin for juvenile diabetes. Furthermore, fundamental questions and future hurdles related to smart SDDS based on CB[7] and pillararenes and their future promising breakthrough implementations are also distinctly outlined in this Review.

Fabrication of morphologically modified strong supramolecular nanocomposite antibacterial hydrogels based on sodium deoxycholate with inverted optical activity and sustained release.

Low Molecular Weight (LMWG) gelators are small molecules that form supramolecular self-assembly involving physical forces and are highly biocompatible. However, fragility of these physical gels restricts their applicability where gels of higher mechanical strength are required. Herein, we have developed two different types of 2-D carbon nanomaterials viz. graphene oxide (GO) and carbon nanosheet (CNS) embedded sodium deoxycholate (NaDC) hydrogels. XRD, scanning electron microscopy (SEM), rheology and CD studies suggest significant modification of morphological, mechanical, viscoelastic and optical properties of the nanocomposite gels which is ascribed to the presence of the 2D nanotemplates and participation of different surface functionalities of GO and CNS in the gelation process. The overall shear resistance of both the nanocomposite hydrogels upto a shear rate of 300 shears/s-1 and above reveals tremendously improved mechanical stability with respect to the pure gels. The increased shear strength of the GO/NaDC and CNS/NaDC hydrogels is attributed to their 3-4 times broader and longer ribbon like structures in comparison to the fibrous structure of pure gels. The intact ribbon like morphology and greater entanglement impart 10 folds greater viscosity to GO-NaDC hydrogels as compared to better elasticity of CNS-NaDC hydrogels possessing broken ribbon edges. Most interestingly both GO and CNS influence the optical activity of the gels and presence of GO results in inversion of optical activity. The GO-NaDC gels are also found to demonstrate antibacterial activity against E. coli, and S. aureus. Thus, these extraordinarily modified mechanically strong gels have enhanced potential for use in tissue engineering, enantioselective and sustained drug delivery, topical antibiotics and other biomedical applications.

Dual release kinetics in a single dosage from core-shell hydrogel scaffolds.

The development of drug delivery systems with microencapsulated therapeutic agents is a promising approach to the sustained and controlled delivery of various drug molecules. The incorporation of dual release kinetics to such delivery devices further adds to their applicability. Herein, novel core-shell scaffolds composed of sodium deoxycholate and trishydroxymethylaminomethane (NaDC-Tris) have been developed with the aim of delivering two different drugs with variable release rates using the same delivery vehicle. Data obtained from XRD studies, sol-gel transition temperature measurement, rheology and fluorescence studies of the core-shell systems indicate a significant alteration in the core and the shell microstructural properties in a given system as compared to the pure hydrogels of identical compositions. The release of the model drugs Fluorescein (FL) and Rhodamine B (RhB) from the shell and the core, respectively, of the two core-shell designs studied exhibited distinctly different release kinetics. In the 25@250 core-shell system, 100% release of FL from the shell and 19% release of RhB from the core was observed within the first 5 hours, while 24.5 hours was required for the complete release of RhB from the core. For the 100@250 system, similar behaviour was observed with varied release rates and a sigmoidal increase in the core release rate upon disappearance from the shell. Cell viability studies suggested the minimal toxicity of the developed delivery vehicles towards NMuMG and WI-38 cells in the concentration range investigated. The reported core-shell systems composed of a single low molecular weight gelator with dual release kinetics may be designed as per the desired application for the consecutive release of therapeutic agents as required, as well as combination therapy commonly used to treat diseases such as diabetes and cancer.

Concomitant spin-canted antiferromagnetic ordering and proton conduction in homometallic and homoleptic coordination polymers.

Two unprecedented oxonate based 1D coordination polymers with Fe(II) and Co(II) have been synthesized. A detailed magnetic investigation revealed that these complexes are the first oxonate based systems to exhibit spin canted antiferromagnetic ordering at low temperatures. Proton conductivity studies of the complexes showed good proton conduction ability at elevated temperatures and under high humidity conditions.

Influence of the coordination environment on slow magnetic relaxation and photoluminescence behavior in two mononuclear dysprosium(III) based single molecule magnets.

The reaction of 2,6-bis(1-salicyloylhydrazonoethyl)pyridine [H4daps] with Dy(NO3)3·5H2O led to the formation of two new Dy(III) based complexes with formulae [Dy(H4daps)(H2O)3(NO3)] (NO3)2 (H2O) (1) and [Dy(H3daps)(H2O)2(NO3)] (NO3) (MeOH) (2). Complexes 1 and 2 were characterized by crystal structure determination, magnetic measurements and photoluminescence studies. In comparison with complex , complex 2 shows a slight difference of local symmetry around the Dy(III) center which is attributed to deprotonation of the ligand and also to different binding modes of the peripheral NO3(-) anion. AC magnetic susceptibility measurements reveal that both complexes exhibit single-molecule magnet (SMM) behavior, with the thermal energy barrier of 1 being higher than that of 2 (Ueff = 32.7 K for 1 and 23.8 K for 2). Our investigation discloses that small differences in the coordination environment around the metal centre played an important role in the difference in relaxation dynamics of the complexes. Solid state photoluminescence studies showed their photoluminescence behaviour with quantum yields of 0.98 and 1.44%.

Modulating the magnetic properties by structural modification in a family of Co-Ln (Ln = Gd, Dy) molecular aggregates.

Two types of heterometallic aggregates of the general formula [(Co(II))3(Co(III))2Ln3(µ3-OH)5(O2C(t)Bu)12(L)2]·2H2O (Ln = Gd(III) (), Dy(III) ()) and [(Co(III))3Ln3(µ3-OH)4(O2C(t)Bu)6(L)3](NO3)2·2CH3CN·2H2O (Ln = Gd(III) (), Dy(III) ()) were successfully isolated in reactions with [Co2(µ-OH2)(O2C(t)Bu)4]·(HO2C(t)Bu)4, Ln(NO3)3 and n-N-butyldiethanolamine (H2L) under ambient conditions by a change in the stoichiometry of the reactants from 1 : 1 : 1 to 1 : 1 : 2 in order. Bond Valence Sum (BVS) calculations and bond lengths indicate the presence of mixed valent Co (Co(II), Co(III)) centres in compounds and and only Co(III) centres in and as required for the charge balances and supported by the magnetic measurements. Isostructural crab shaped complexes and feature distorted cubane cores that edge share to each other whereas the metallic core of or displays hemicubane like arrangement of metal centres and oxygen atoms. Overall structural symmetry was found to enhance on moving from the former to the latter series of complexes. Magnetic studies reveal significant magnetic entropy changes for complexes and (-ΔSm = 21.57 and 19.39 J kg(-1) K(-1)) and single molecular magnetic behaviour for and .

A perception of ferro- and antiferromagnetic interactions in a two dimensional Ni(II) heterochiral coordination polymer showing unusual CO2 uptake behavior.

We present a robust two dimensional coordination polymer, [Ni2(L)2(N(CN)2)2]n (1) (LH = 2-((1-(pyridin-2-yl)ethylimino)methyl)phenol; N(CN)2(-) = dicyanamide ion) using a chiral Schiff base (LH), which shows diastereoselectivity in the structure via a chiral self-discrimination process, ferro- and antiferromagnetic interactions among the metal centers and unusual CO2 uptake behavior as a porous framework.

Observation of a large magnetocaloric effect in a 2D Gd(III)-based coordination polymer.

A new 2D Gd(III)-based coordination polymer has close to the highest cryogenic magnetocaloric effect of any MOF reported so far. The experimental results reveal its structural features and magnetic properties.

Lanthanide based coordination polymers chill, relax under magnetic field and also fluoresce.

Three lanthanide one-dimensional coordination polymers, obtained using Ln(3+) salts and croconate dianion, were structurally characterized. Magnetic studies reveal that the gadolinium analogue exhibits a large magnetocaloric effect while single-molecule magnet behaviour is observed in the dysprosium analogue.