Emergent Spin-Glass Behavior in an Iron(II)-Based Metal–Organic Framework Glass
Das C., Salamon S., Landers J., Weiss J.-B., Xue W.-L., Kolodzeiski P., Pallach R., Wende H., Henke S.
Article, Advanced Functional Materials, 2025, DOI Link
View abstract ⏷
Metal–organic framework (MOF) glasses combine the structural tunability of crystalline MOFs with the processability of amorphous materials, offering exciting opportunities for functional hybrid materials. Here, a one-pot, solvent-free synthesis is reported of an Fe2+-based MOF glass, gFe-tBubipy, with the composition [Fe2(im)3.12(bim)0.88(tBubipy)0.11]·[Fe(Cp)2]0.09 (im− = imidazolate, bim− = benzimidazolate, tBubipy = 4,4′-di-tert-butyl-2,2′-bipyridine, Cp− = cyclopentadienyl anion). This material forms a continuous random network structure of four-connected tetrahedral and octahedral Fe2+ nodes and exhibits an exceptionally low glass transition temperature (Tg = 87 °C). Despite its amorphous nature and complex composition, gFe-tBubipy exhibits a high degree of local structural order that enables strong antiferromagnetic exchange interactions between Fe2+ centers. Remarkably, it exhibits clear signatures of spin-glass behavior, with a well-defined magnetic freezing transition ≈14 K. This combination of a MOF glass exhibiting a distinct glass transition with spin-glass magnetism arising from topological disorder and frustrated, short-range magnetic interactions represent a significant advance. This discovery underscores the transformative potential of MOF glasses as a versatile platform for exploring the interplay between structural disorder and cooperative magnetic phenomena in hybrid materials.
Hybrid polysaccharide–NaI derived transparent and flexible solid-state electrolyte films for sustainable design of supercapacitors
Wakekar S., Jana B., Yarramsetti S., Ghosh S., Patro L.N., Maram P.S., Shanmugam M., Das C.
Article, Journal of Materials Chemistry A, 2025, DOI Link
View abstract ⏷
Conventional liquid electrolytes utilized in supercapacitors suffer from leakage, flammability, and poor adaptability making them unsuitable to design flexible, wearable, and portable devices. Despite the significant advancements in designing flexible electrode materials towards the fabrication of safer and integrated energy storage systems, the development of optically transparent and mechanically flexible polysaccharide-based solid-state electrolytes remains comparatively limited. Herein, we report a series of flexible solid-state electrolyte (FSSENaI-x; where x = 27, 43, 53, 60, 65, and 69 wt%) films, composed of konjac glucomannan (KGM), hydroxypropyl methylcellulose (HPMC), and sodium iodide (NaI). Among them, the FSSENaI-65 film exhibits optimal properties in terms of mechanical, optical, and ionic conductivity suitable for designing supercapacitor devices. It achieves a Young's modulus of ∼2.5 MPa with an exceptional elongation at break at 118%, along with an optical transparency of 88% at 800 nm. It delivers a high ionic conductivity of 2.77 mS cm−1 at room temperature and a wide electrochemical stability window of 2.4 V. A solid-state supercapacitor assembled with the FSSENaI-65 film shows a specific capacitance of 159 F g−1 at 1 A g−1, with an excellent cycling stability retaining 87.5% of its specific capacitance over 4000 cycles at 5 A g−1. It maintains a stable performance under bending conditions with a capacitance retention of 72.2% over 2000 cycles at 5 A g−1. The device furnishes a high energy density of 22.1 Wh kg−1 and power density of 500.6 W kg−1 at 1 A g−1 confirming its potential for next-generation flexible energy storage systems.
Konjac glucomannan derived biodegradable superionic solid-state electrolyte films for devising economically viable supercapacitor
Wakekar S., Pasupuleti L., Jana B., Yarramsetti S., Maram P.S., Shanmugam M., Patro L.N., Das C.
Article, Chemical Communications, 2025, DOI Link
View abstract ⏷
We synthesized biodegradable and economically viable solid-state electrolyte films based on konjac glucomannan (KG) and sodium iodide (NaI). Among the KGNaI-x (x = 31–69 wt%) films, KGNaI-69 exhibits superior flexibility, biodegradability, and sodium superionic conductivity of 77.9 mS cm−1. The KGNaI-69-based supercapacitor delivers outstanding electrochemical efficiency and cycling stability, retaining 84.4% capacitance after 5000 cycles establishing its potentiality toward flexible energy storage devices.
Deciphering the functions of metal-organic frameworks and their derived composites towards atmospheric water harvesting: A comprehensive review
Review, Sustainable Materials and Technologies, 2024, DOI Link
View abstract ⏷
To address water scarcity globally, recently atmospheric water harvesting (AWH) has emerged as an intriguing and sustainable solution. This comprehensive review critically investigates how diversity in MOFs and their composite materials shapes the effectiveness and practicality of AWH technologies. These materials range from pristine MOFs to functionalized MOFs-based composites to attain the sophisticated hydrophilic behavior to perform as water harvesters. The multifaceted effects of MOFs and their composite materials on the kinetics of sorption and condensation, the feasibility of water uptake and release, the overall performance of the materials, the theoretical understanding of water uptake, and various instrumentation techniques have been demonstrated in this comprehensive review. It contributes to the ongoing discourse on sustainable water sourcing by emphasizing the pivotal role of materials diversity in shaping the future of AWH technologies.
Insights Into the Mechanochemical Glass Formation of Zeolitic Imidazolate Frameworks
Xue W.-L., Das C., Weiss J.-B., Henke S.
Article, Angewandte Chemie - International Edition, 2024, DOI Link
View abstract ⏷
Metal–organic framework (MOF) glasses, known for their potential in gas separation, optics, and solid-state electrolytes, benefit from the processability of their (supercooled) liquid state. Traditionally, MOF glasses are produced by heating MOF crystals to their melting point and then cooling the liquid MOF to room temperature under an inert atmosphere. While effective, this melt-quenching technique requires high energy due to the high temperatures involved. It also limits the scope of new material development by restricting the compositional range to only those combinations of metal ions and linkers that are highly thermally stable. An alternative, mechanical milling at room temperature, has demonstrated its capability to transform MOF crystals into amorphous phases. However, the specific conditions under which these amorphous phases exhibit glass-like behavior remain uncharted. In this study, we explore the mechanochemical amorphization and vitrification of a variety of zeolitic imidazolate frameworks (ZIFs) with diverse linkers and different metal ions (Zn2+, Co2+ and Cu2+) at room temperature. Our findings demonstrate that ZIFs capable of melting can be successfully converted into glasses through ball-milling. Remarkably, some non-meltable ZIFs can also be vitrified using the ball-milling technique, as highlighted by the preparation of the first Cu2+-based ZIF glass.
Mechanochemically-induced glass formation from two-dimensional hybrid organic-inorganic perovskites
Ye C., Lampronti G.I., McHugh L.N., Castillo-Blas C., Kono A., Chen C., Robertson G.P., Nagle-Cocco L.A.V., Xu W., Stranks S.D., Martinez V., Brekalo I., Karadeniz B., Uzarevic K., Xue W., Kolodzeiski P., Das C., Chater P., Keen D.A., Dutton S.E., Bennett T.D.
Article, Chemical Science, 2024, DOI Link
View abstract ⏷
Hybrid organic-inorganic perovskites (HOIPs) occupy a prominent position in the field of materials chemistry due to their attractive optoelectronic properties. While extensive work has been done on the crystalline materials over the past decades, the newly reported glasses formed from HOIPs open up a new avenue for perovskite research with their unique structures and functionalities. Melt-quenching is the predominant route to glass formation; however, the absence of a stable liquid state prior to thermal decomposition precludes this method for most HOIPs. In this work, we describe the first mechanochemically-induced crystal-glass transformation of HOIPs as a rapid, green and efficient approach for producing glasses. The amorphous phase was formed from the crystalline phase within 10 minutes of ball-milling, and exhibited glass transition behaviour as evidenced by thermal analysis techniques. Time-resolved in situ ball-milling with synchrotron powder diffraction was employed to study the microstructural evolution of amorphisation, which showed that the crystallite size reaches a comminution limit before the amorphisation process is complete, indicating that energy may be further accumulated as crystal defects. Total scattering experiments revealed the limited short-range order of amorphous HOIPs, and their optical properties were studied by ultraviolet-visible (UV-vis) spectroscopy and photoluminescence (PL) spectroscopy.
Creating glassy states of dicarboxylate-bridged coordination polymers
Fan Z., Wei Y.-S., Das C., Kanamori K., Yamada H., Ohara K., Horike S.
Article, Chemical Communications, 2023, DOI Link
View abstract ⏷
We report the direct formation of dicarboxylate-based coordination polymer glasses through thermal dehydration. The rearrangement of the coordination networks caused by dehydration was monitored by in situ powder X-ray diffraction, infrared spectroscopy, and synchrotron X-ray characterizations. The microporosity and mechanical properties of these glasses were investigated.
Formation of Porosity toward Acetylene upon Vitrification of Non-porous Photochromic Coordination Polymer Crystals
Fan Z., Wei Y.-S., Tabe H., Nakatani T., Das C., Yamada H., Horike S.
Article, Chemistry of Materials, 2023, DOI Link
View abstract ⏷
Designing permanent microporosity in a glassy state of coordination polymer (CP) and metal-organic framework (MOF) has been challenging due to densification of the structures upon vitrification. Here, we propose a new approach to create porosity in CP/MOF glasses derived from nonporous 1D crystal structures. Glassy states of two dense 1D crystal structures [Ag2(cis-dbe) (CF3SO3)2] and [Ag2(cis-dbe) (CF3CO2)2], where cis-dbe = cis-1,2-dicyano-1,2-bis(2,4,5-trimethyl-3-thienyl)ethene, were prepared by ball milling. Glass structures and dynamics were characterized by synchrotron X-ray, solid-state NMR, and thermal analyses. Loosened assembly of 1D chains through glass formation enabled representation of permanent microporosity and resulted in selective gas sorption behaviors of acetylene over CO2. It elucidated that the property of gas uptake is affected by the glass dynamics and interaction with anions. Reversible photochromism of cis-dbe is preserved in the glasses, leading to multi-functional glass materials.
Smoke in the MOF liquid
Note, Nature Materials, 2023, DOI Link
Breathing porous liquids based on responsive metal-organic framework particles
Koutsianos A., Pallach R., Frentzel-Beyme L., Das C., Paulus M., Sternemann C., Henke S.
Article, Nature Communications, 2023, DOI Link
View abstract ⏷
Responsive metal-organic frameworks (MOFs) that display sigmoidal gas sorption isotherms triggered by discrete gas pressure-induced structural transformations are highly promising materials for energy related applications. However, their lack of transportability via continuous flow hinders their application in systems and designs that rely on liquid agents. We herein present examples of responsive liquid systems which exhibit a breathing behaviour and show step-shaped gas sorption isotherms, akin to the distinct oxygen saturation curve of haemoglobin in blood. Dispersions of flexible MOF nanocrystals in a size-excluded silicone oil form stable porous liquids exhibiting gated uptake for CO2, propane and propylene, as characterized by sigmoidal gas sorption isotherms with distinct transition steps. In situ X-ray diffraction studies show that the sigmoidal gas sorption curve is caused by a narrow pore to large pore phase transformation of the flexible MOF nanocrystals, which respond to gas pressure despite being dispersed in silicone oil. Given the established flexible nature and tunability of a range of MOFs, these results herald the advent of breathing porous liquids whose sorption properties can be tuned rationally for a variety of technological applications.
A robust low coordinate Co(II) catalyst for efficient conversion of CO2 into methanol under mild conditions
Sharma V., Rasamsetty A., Das C., Borah D., Shanmugam M.
Article, Chemical Engineering Journal, 2023, DOI Link
View abstract ⏷
Compared to the Run+ (where n = 2 or 3) homogenous catalysts that convert CO2 into methanol, 3d metal catalysts (such as Fen+, Con+, and Mnn+) exhibit poor activity due to catalyst poisoning and/or instability. Overcoming the hurdles observed in the case of 3d metal catalysts, in this article, we have unveiled a robust, cheap, and abundant Co(II) catalyst ([Li(DME)3][Co(L1)3]; 1, where L1 = 2,6-diisopropylanilide) which efficiently converts the CO2 into its methanol equivalent (B(OMe)3) in the presence of NaBH4, which upon hydrolysis yields methanol under mild conditions (0.1 bar CO2 and 60 °C) with the unprecedented TON and TOF of 11,171 and 508 h−1, respectively compared to any 3d metal catalyst reported to date. Further, we noticed that the activity of 1 was maintained for weeks, which is reflected in the overall TON of 54,000 obtained after 7 cycles. Moreover, we have shown that 1 can selectively reduce CO2 into methanol even from the “vehicle exhaust” directly. Systematic investigations were performed to shed light on the likely intermediates involved in the catalytic cycle, based on that we have proposed a mechanism for this reaction.
Crystallization Kinetics of a Liquid-Forming 2D Coordination Polymer
Das C., Nishiguchi T., Fan Z., Horike S.
Article, Nano Letters, 2022, DOI Link
View abstract ⏷
We investigated a mechanism of crystal melting and crystallization behavior of a two-dimensional coordination polymer [Ag2(L1)(CF3SO3)2] (1, L1 = 4,4′-biphenyldicarbonitrile) upon heating-cooling processes. The crystal showed melting at 282 °C, and the following gentle cooling induced the abrupt crystallization at 242 °C confirmed by DSC. A temperature-dependent structural change has been discussed through calorimetric, spectroscopic, and mechanical measurements. They indicated that the coordination-bond networks are partially retained in the melt state, but the melt showed a significantly low viscosity of 9.8 × 10-2Pa·s at Tmwhich is six orders lower than that of ZIF-62 at Tm(435 °C). Rheological studies provided an understanding of the fast relaxation dynamics for the recrystallization process, along with that the high Tmprovides enough thermal energy to crossover the activation energy barrier for the nucleation. The isothermal crystallization kinetics through calorimetric measurements with applying the Avrami equation identified the nature of the nuclei and its crystal growth mechanism.
Cyclic Solid-State Multiple Phase Changes with Tuned Photoemission in a Gold Thiolate Coordination Polymer
Veselska O., Vaidya S., Das C., Guillou N., Bordet P., Fateeva A., Toche F., Chiriac R., Ledoux G., Wuttke S., Horike S., Demessence A.
Article, Angewandte Chemie - International Edition, 2022, DOI Link
View abstract ⏷
The discovery of a universal memory that exhibits fast access speed, high-density storage, and non-volatility has fuelled research into phase-change materials over the past decades. In spite of the efficiency of the inorganic chalcogenides for phase-change random access memory (PCRAM), they still have some inherent drawbacks, such as high temperature required for phase change and difficulty to control the domain size of the phase change, because of their brittleness. Here we present a AuI–thiolate coordination polymer which undergoes two successive phase changes on application of mild heating (<200 °C) from amorphous-to-crystalline1-to-crystalline2 phases. These transitions are reversible upon soft hand grinding. More importantly, each phase exhibits different photoluminescent properties for an efficient optical read-out. We believe that the ability of the AuI–thiolate coordination polymer to have reversible phase changes under soft conditions and at the same time to display distinct optical signals, can pave the way for the next generation of PCRAM.
Photoluminescent coordination polymer bulk glasses and laser-induced crystallization†
Fan Z., Das C., Demessence A., Zheng R., Tanabe S., Wei Y.-S., Horike S.
Article, Chemical Science, 2022, DOI Link
View abstract ⏷
We synthesized luminescent coordination polymer glasses composed of d10 metal cyanides and triphenylphosphine through melt-quenching and mechanical milling protocols. Synchrotron X-ray total scattering measurements and solid-state NMR revealed their one-dimensional chain structures and high structural dynamics. Thermodynamic and photoluminescence properties were tunable by the combination of heterometallic ions (Ag+, Au+, and Cu+) in the structures. The glasses are moldable and thermally stable, and over centimeter-sized glass monoliths were fabricated by the hot-press technique. They showed high transparency over 80% from the visible to near-infrared region and strong green emission at room temperature. Furthermore, the glass-to-crystal transformation was demonstrated by laser irradiation through the photothermal effect of the glasses.
Materials breaking the rules: General discussion
Addicoat M., Bennett T.D., Brammer L., Craig G., Das C., Dichtel W., Doan H., Evans A.M., Evans J., Goodwin A., Horike S., Jiang J., Kaskel S., Kato M., Kitagawa S., Kobayashi A., Krause S., Lavenn C., Lee J.-S.M., Phillips A.E., Roseveare T.M., Schmid R., Shivanna M., Sirbu D., Tashiro S., Ting V.P., Van Der Veen M.A., Wilson B., Zhao P.
Note, Faraday Discussions, 2021, DOI Link
Crystal melting and vitrification behaviors of a three-dimensional nitrile-based metal-organic framework
Article, Faraday Discussions, 2021, DOI Link
View abstract ⏷
A three-dimensional (3D) metal-organic framework [Ag(pL2)(CF3SO3)]·2C6H6 (pL2 = 1,3,5-tris(4-cyanophenylethynyl)benzene), composed of Ag+ and tripodal nitrile ligands, was prepared to enable the investigation of its crystal melting and vitrification behaviors. The guest-free state showed a crystal melting at 271 °C, and the liquid state transformed into a glassy state via cooling. The vitrification of the crystalline compound into an amorphous glassy state was also obtained by mechanical hand-grinding. The structure of the glassy state retained the 3D networked structure, confirmed by FT-IR, X-ray absorption, and scattering measurements. The mechanically induced glass showed a small uptake of CO2 and a strong affinity for benzene and H2O vapors, confirmed by gas sorption isotherms. Powder X-ray diffraction studies have revealed that the vitrified structure returned to the original 3D crystalline structure by exposure to these vapors.
Stable melt formation of 2D nitrile-based coordination polymer and hierarchical crystal-glass structuring
Das C., Ogawa T., Horike S.
Article, Chemical Communications, 2020, DOI Link
View abstract ⏷
Crystal melting and vitrification of nitrile-based two-dimensional coordination polymer (CP) were studied. The crystal melts at 169 °C and has a wide liquid-state temperature window of over 110 °C. The crystalline state transformed to a glassy state by melt-quench or mechanical milling. The mechanically induced glass showed permanent porosity, and it also showed glass-to-crystal transformation upon solvent treatment. Surface crystallization on top of the grain-boundary-free glass monolith was demonstrated.
Magnetization relaxation dynamics of a rare coordinatively unsaturated Co(ii) complex: Experimental and theoretical insights
Das C., Rasamsetty A., Tripathi S., Shanmugam M.
Article, Chemical Communications, 2020, DOI Link
View abstract ⏷
A robust and unusual three coordinate Co(ii) complex [Li(DME)3][Co(L)3] (1, where L = Lithium (2,6-diisopropylphenyl) amide and DME = Dimethoxyethane) shows easy plane magnetic anisotropy (D) which is validated by variable temperature X-band EPR studies. 1 also registered with the largest anisotropic barrier (51.1 K, τ0 = 1.98 × 10-8 s; Hdc ≠ 0) to the magnetization reversal among the three coordinate Co(ii) complexes. The role of its geometry on the SH parameters and the experimental observations are rationalized by theoretical calculations including the origin of magnetic anisotropy. This journal is
Chiral tetranuclear copper(ii) complexes: Synthesis, optical and magnetic properties
Ahmed N., Tripathi S., Sarkar A., Ansari K.U., Das C., Prajesh N., Horike S., Boomishankar R., Shanmugam M.
Article, New Journal of Chemistry, 2020, DOI Link
View abstract ⏷
Treating the enantiomerically pure Schiff base ligand (R-H2L1 or S-H2L1) with equimolar copper nitrate led to the isolation of two chiral tetranuclear Cu(ii) cubane complexes with the general molecular formula [Cu4(R-L1)4] (R-1) and [Cu4(S-L1)4] (S-1), which are characterized by single-crystal X-ray diffraction. Both R-1 and S-1 are structurally analogous to each other, which is reflected from their unit cell parameters. The chiral ligands employed efficiently transfer the chirality to the metal complex, which is reflected from their flack parameters and the complex R-1 crystallizes in the chiral, polar point/space group (C2). The chirality is maintained not only in the solid-state but also in the solution state for both R/S-H2L1 and R/S-1. The direct current magnetic susceptibility measurements performed on a polycrystalline sample of a representative complex R-1 exhibits a dominant ferromagnetic interaction resulting in an S = 2 ground state, which is in contrast to the other alkoxide bridged [Cu4O4] complexes reported. The electronic structure and the observed ferromagnetic exchange coupling in R-1 are rationalized by detailed theoretical calculations. This journal is
Glass-phase coordination polymer displaying proton conductivity and guest-accessible porosity
Inukai M., Nishiyama Y., Honjo K., Das C., Kitagawa S., Horike S.
Article, Chemical Communications, 2019, DOI Link
View abstract ⏷
We describe the preparation of the crystalline and glassy state of a coordination polymer displaying proton conduction and guest-accessible porosity. EXAFS and solid-state NMR analyses indicated that pyrophosphate and phosphate ions are the main proton transporters in the glass and that homogeneously distributed 5-chloro-1H-benzimidazole in the glass provides the porosity.
Stabilizing Terminal Ni(III)-Hydroxide Complex Using NNN-Pincer Ligands: Synthesis and Characterization
Shanmugam M., Rajpurohit J., Shukla P., Kumar P., Das C., Vaidya S., Sundararajan M., Shanmugam M.
Article, Inorganic Chemistry, 2019, DOI Link
View abstract ⏷
The reaction of [Ni(COD)2] (COD; cyclooctadiene) in THF with the NNN-pincer ligand bis(imino)pyridyl (L1) reveals a susceptibility to oxidation in an inert atmosphere ([O2] level <0.5 ppm), resulting in a transient Ni:dioxygen adduct. This reactive intermediate abstracts a hydrogen atom from THF and stabilizes an uncommon Ni(III) complex. The complex is crystallographically characterized by a molecular formula of [NiIII(L1··)2-(OH)] (1). Various isotopically labeled experiments (16O/18O) assertively endorse the origin of terminal oxygen based ligand in 1 due to the activation of molecular dioxygen. The presence of proton bound to the terminal oxygen in 1 is well supported by NMR, IR spectroscopy, DFT calculations, and hydrogen atom transfer (HAT) reactions promoted by 1. The observation of shakeup satellite peaks for the primary photoelectron lines of Ni(2p) in the X-ray photoelectron spectroscopy (XPS) unambiguously confirms the paramagnetic signature associated with the distorted square planar nickel ion, which is consistent with the trivalent oxidation state assigned for the nickel ion in 1. The variable temperature magnetic susceptibility data of 1 shows dominant antiferromagnetic interactions exist among the paramagnetic centers, resulting in an overall S = 1/2 ground state. Variable temperature X-band EPR studies performed on 1 show evidence for the S = 1/2 ground state, which is consistent with magnetic data. The unusual g-tensor extracted for the ground state S = 1/2 is analyzed under a strong exchange limit of spin-coupled centers. The electronic structure predicted for 1 is in good agreement with theoretical calculations.
Unusual Methylenediolate Bridged Hexanuclear Ruthenium(III) Complexes: Syntheses and Their Application
Rajpurohit J., Upadhyay A., Das C., Dubey R., Vaidya S., Krishnan V., Kumar A., Shanmugam M.
Article, Inorganic Chemistry, 2018, DOI Link
View abstract ⏷
Three structurally analogous hexanuclear ruthenium(III) complexes were isolated with the general molecular formula of [Ru 6 III (O) 2 (μ 4 -η 2 -η 2 -CH 2 O 2 )(t-BuCO 2 ) 12 (L) 2 ] where L = pyridine (1) or 4-dimethylamino pyridine (DMAP; 2) or 4-cyanopyridine (3). Complexes 1 and 3 were solved in the tetragonal I4c2 and P4 1 2 1 2 space group, respectively, while 2 crystallized in the monoclinic system with P2 1 /c space group. In all three complexes, two oxo-centered Ru(III) triangles were bridged by a unique and a rare methylenediolate (CH 2 O 2 ) 2- ) ligand. This (CH 2 O 2 ) 2- group is reported to be an intermediate, which is not isolated in its metal-free form, to date, as it is unstable. Control experiments performed evidently reveal that the unique reaction condition followed is mandatory to isolate 1-3 and the origin of (CH 2 O 2 ) 2- is unknown at the moment, as no precursor was used to form this intermediate. The presence of (CH 2 O 2 ) 2- identified through X-ray diffraction was further unambiguously confirmed by various 1D ( 1 H and 13 C) and 2D-NMR (HSQC, TOCSY, NOESY, and DEPT) spectroscopies. Direct current (dc) magnetic susceptibility measurements performed on 1 and 2 reveal the predominant antiferromagnetic exchange interaction between the Ru(III) centers result in a diamagnetic ground state at 2.0 K. The paramagnetic influence of 1-3 at room temperature evidently felt by the 1 H nuclei of the (CH 2 O 2 ) 2- unit predominates compared to other NMR active nuclei in the complexes. The presence of an electron donating or withdrawing substituent on the terminal pyridine results in significant change in the dihedral angle of two oxo-centered triangular (Ru 3 O) planes. The change in the structural parameters of 1-3 due to the substituents markedly reflected on the absorption profile and redox behavior, which are systematically investigated. Preliminary galvanostatic charge/discharge cycling experiments performed on a representative complex (3) suggest that 3 can be a promising candidate to employ as an effective multiple electron charge carrier in a nonaqueous redox flow battery.
Effect of coordination geometry on the magnetic properties of a series of Ln2 and Ln4 hydroxo clusters
Rasamsetty A., Das C., Sanudo E.C., Shanmugam M., Baskar V.
Article, Dalton Transactions, 2018, DOI Link
View abstract ⏷
A series of three isostructural tetranuclear complexes with the general molecular formula [Ln4(μ3-OH)4(L)4(μ2-piv)4(MeOH)4] (Ln = Gd 1, Dy 2 and Ho 3; LH = [1,3-bis(o-methoxyphenyl)-propane-1,3-dione]) were isolated and unambiguously characterized by single crystal XRD. Under similar reaction conditions, simply changing the co-ligand from pivalate to 2,6-bis(hydroxymethyl)-p-cresol (LH′3) led to the isolation of dinuclear Ln(iii) complexes with the general molecular formula [Ln2(L)4(μ2-LH′2)2]·4DMF (Ln = Gd 4, Dy 5 and Ho 6). Direct current magnetic susceptibility data studies on the polycrystalline sample of 1-6 and the results reveal the existence of weak antiferromagnetic exchange interactions between the lanthanide ions in 1 which is evident from the spin Hamiltonian (SH) parameters (J1 = -0.055 cm-1 and g = 2.01) extracted by fitting χMT(T). On the other hand, though complex 4 exhibits weak antiferromagnetic coupling (J1 = -0.048 cm-1 and g = 1.99) between the Gd(iii) ions, the χMT(T) data of complexes 5 and 6 unambiguously disclose the presence of ferromagnetic interactions between Dy(iii) and Tb(iii) ions at lower temperature. Magnetization relaxation dynamics studies performed on 2 show frequency dependent out-of-phase susceptibility signals in the presence of an optimum external magnetic field of 0.5 kOe. In contrast, complex 5 shows slow magnetization relaxation with an effective energy barrier (Ueff) of 38.17 cm-1 with a pre-exponential factor (τ0) of 1.85 × 10-6 s. The magnetocaloric effect (MCE) of complexes 1 and 4 was extracted from the detailed magnetization measurement and the change in the magnetic entropy (-ΔSm) of 1 and 4 was found to be 25.57 J kg-1 K-1 and 12.93 J kg-1 K-1, respectively, at 3.0 K for ΔH = 70 kOe.
Lanthanide-Based Porous Coordination Polymers: Syntheses, Slow Relaxation of Magnetization, and Magnetocaloric Effect
Das C., Upadhyay A., Ansari K.U., Ogiwara N., Kitao T., Horike S., Shanmugam M.
Article, Inorganic Chemistry, 2018, DOI Link
View abstract ⏷
Two lanthanide-containing structurally analogous porous coordination polymers (PCPs) have been isolated with the general molecular formula [Ln2(L1)2(H2O)4(ox)]n.4nH2O (where L1 = fumarate, ox = oxalate; Ln = Dy (1), Gd (2)). Thermogravimetric analysis (TGA) and TG-MS measurements performed on 1 and 2 suggest that not only the solvated water molecules in the crystal lattice but also the four coordinated water molecules on the respective lanthanides in 1 and 2 are removed upon activation. Due to the removal of the waters, 1 and 2 lost their crystallinity and became amorphous, as confirmed by powder X-ray diffraction (PXRD). We propose the molecular formula [Ln2(L1)2(ox)]n for the amorphous phase of 1 and 2 (where Ln = Dy (1′), Gd (2′)) on the basis of XANES, EXAFS, and other experimental investigations. Magnetization relaxation dynamics probed on 1 and 1′ reveal two different relaxation processes with effective energy barriers of 53.5 and 7.0 cm-1 for 1 and 45.1 and 6.4 cm-1 for 1′, which have been rationalized by detailed ab initio calculations. For the isotropic lanthanide complexes 2 and 2′, magnetocaloric effect (MCE) efficiency was estimated through detailed magnetization measurements. We have estimated -ΔSm values of 52.48 and 41.62 J kg1- K-1 for 2′ and 2, respectively, which are one of the largest values reported for an extended structure. In addition, a 26% increase in -ΔSm value in 2′ in comparison to 2 is achieved by simply removing the passively contributing (for MCE) solvated water molecule in the lattice and coordinated water molecules.
Influence of Radicals on Magnetization Relaxation Dynamics of Pseudo-Octahedral Lanthanide Iminopyridyl Complexes
Das C., Upadhyay A., Shanmugam M.
Article, Inorganic Chemistry, 2018, DOI Link
View abstract ⏷
Controlling quantum tunneling of magnetization (QTM) is a persistent challenge in lanthanide-based single-molecule magnets. As the exchange interaction is one of the key factors in controlling the QTM, we targeted lanthanide complexes with an increased number of radicals around the lanthanide ion. On the basis of our targeted approach, a family of pseudo-octahedral lanthanide/transition-metal complexes were isolated with the general molecular formula of [M(L•-)3] (M = Gd (1), Dy (2), Er (3), Y (4)) using the redox-active iminopyridyl (L•-) ligand exclusively, which possess the highest ratio of radicals to lanthanide reported for discrete metal complexes. Direct current magnetic susceptibility studies suggest that dominant antiferromagnetic interactions exist between the radical and lanthanide ions in all of the complexes, which is strongly corroborated by magnetic data fitting using a Heisenberg-Dirac-Van Vleck (HDVV) Hamiltonian (-2J Hamiltonian). A good agreement between the fit and the experimental magnetic data obtained using g = 2, Jrad-rad = -111.9 cm-1 for 4 and g = 1.99, Jrad-rad = -111.9 cm-1, JGd-rad = -1.85 cm-1 for 1. Complex 2 shows frequency-dependent slow magnetization relaxation dynamics in the absence of an external magnetic field, while 3 shows field-induced frequency-dependent χM′′ signals. An ideal octahedral geometry around the lanthanide ion is predicted to be unsuitable for the design of a single-molecule magnet (SMM); nevertheless, complex 2 exhibits slow relaxation of magnetization with a record high anisotropy barrier for a six-coordinate Dy(III) complex. A rationale for this unusual behavior is detailed and reveals the strength of the synthetic methodology developed.
Influence of the Ligand Field on the Slow Relaxation of Magnetization of Unsymmetrical Monomeric Lanthanide Complexes: Synthesis and Theoretical Studies
Upadhyay A., Vignesh K.R., Das C., Singh S.K., Rajaraman G., Shanmugam M.
Article, Inorganic Chemistry, 2017, DOI Link
View abstract ⏷
A series of monomeric lanthanide Schiff base complexes with the molecular formulas [Ce(HL)3(NO3)3] (1) and [Ln(HL)2(NO3)3], where LnIII = Tb (2), Ho (3), Er (4), and Lu (5), were isolated and characterized by single-crystal X-ray diffraction (XRD). Single-crystal XRD reveals that, except for 1, all complexes possess two crystallographically distinct molecules within the unit cell. Both of these crystallographically distinct molecules possess the same molecular formula, but the orientation of the coordinating ligand distinctly differs from those in complexes 2-5. Alternating-current magnetic susceptibility measurement reveals that complexes 1-3 exhibit slow relaxation of magnetization in the presence of an optimum external magnetic field. In contrast to 1-3, complex 4 shows a blockade of magnetization in the absence of an external magnetic field, a signature characteristic of a single-ion magnet (SIM). The distinct magnetic behavior observed in 4 compared to other complexes is correlated to the suitable ligand field around a prolate ErIII ion. Although the ligand field stabilizes an easy axis of anisotropy, quantum tunnelling of magnetization (QTM) is still predominant in 4 because of the low symmetry of the complex. The combination of low symmetry and an unsuitable ligand-field environment in complexes 1-3 triggers faster magnetization relaxation; hence, these complexes exhibit field-induced SIM behavior. In order to understand the electronic structures of complexes 1-4 and the distinct magnetic behavior observed, ab initio calculations were performed. Using the crystal structure of the complexes, magnetic susceptibility data were computed for all of the complexes. The computed susceptibility and magnetization are in good agreement with the experimental magnetic data [XMT(T) and M(H)] and this offers confidence on the reliability of the extracted parameters. A tentative mechanism of magnetization relaxation observed in these complexes is also discussed in detail.
Role of the Diamagnetic Zinc(II) Ion in Determining the Electronic Structure of Lanthanide Single-Ion Magnets
Upadhyay A., Das C., Vaidya S., Singh S.K., Gupta T., Mondol R., Langley S.K., Murray K.S., Rajaraman G., Shanmugam M.
Article, Chemistry - A European Journal, 2017, DOI Link
View abstract ⏷
Four complexes containing DyIII and PrIII ions and their LnIII–ZnII analogs have been synthesized in order to study the influence that a diamagnetic ZnII ion has on the electronic structure and hence, the magnetic properties of the DyIII and PrIII single ions. Single-crystal X-ray diffraction revealed the molecular structures as [DyIII(HL)2(NO3)3] (1), [PrIII(HL)2(NO3)3] (2), [ZnIIDyIII(L)2(CH3CO2)(NO3)2] (3) and [ZnII2PrIII(L)2(CH3CO2)4(NO3)] (4) (where HL=2-methoxy-6-[(E)-phenyliminomethyl]phenol). The dc and ac magnetic data were collected for all four complexes. Compounds 1 and 3 display frequency dependent out-of-phase susceptibility signals (χM“), which is a characteristic signature for a single-molecule magnet (SMM). Although 1 and 3 are chemically similar, a fivefold increase in the anisotropic barrier (Ueff) is observed experimentally for 3 (83 cm−1), compared to 1 (16 cm−1). To rationalize the larger anisotropic barrier (1 vs. 3), detailed ab initio calculations were performed. Although the ground state Kramer's doublet in both 1 and 3 are axial in nature (gzz=19.443 for 1 and 18.82 for 3), a significant difference in the energy gap (Ueff) between the ground and first excited Kramer's doublet is calculated. This energy gap is governed by the electrostatic repulsion between the DyIII ion and the additional charge density found for the phenoxo bridging ligand in 3. This extra charge density was found to be a consequence of the presence of the diamagnetic ZnII ion present in the complex. To explore the influence of diamagnetic ions on the magnetic properties further, previously reported and structurally related Zn–DyIII complexes were analyzed. These structurally analogous complexes unambiguously suggest that the electrostatic repulsion is found to be maximal when the Zn-O-Dy-O dihedral angle is small, which is an ideal condition to maximize the anisotropic barrier in DyIII complexes.
Structural and magnetic properties of semiquinonate based Al(III) and Ga(III) complexes
Das C., Shukla P., Sorace L., Shanmugam M.
Article, Dalton Transactions, 2017, DOI Link
View abstract ⏷
The reaction of anhydrous MCl3 (M = Al(iii) or Ga(iii)) with one-electron-reduced 3,5-di-tert-butyl-1,2-ortho-benzoquinone (using metallic sodium) led us to isolate two distinct metal complexes of Al(iii) and Ga(iii), which were structurally and magnetically characterized. Complex 1 crystallized in the monoclinic P21/n space group, whereas 2 crystallized in the triclinic P1 space group. Interestingly, whereas the Al(iii) derivative was obtained as a dimer with the molecular formula [Al2(μ-HL-)2(L-)4] (1) (where L- is a semiquinonate radical and HL- is a monoanionic catecholate ligand), the Ga(iii) derivative crystallized as [Ga(L-)3] (2), which is a polymorph of a previously reported complex. The presence of both catecholate and/or semiquinonate ligands in 1 and 2 was confirmed by single-crystal X-ray diffraction, mass spectrometry, and NMR and infrared spectroscopy techniques. The crystalline phase purity of the complexes was confirmed by powder X-ray diffraction (PXRD). Measurements of direct-current magnetic susceptibility, which were performed on a polycrystalline samples, revealed that in both complexes the semiquinonate radical anions are coupled ferromagnetically via the diamagnetic metal ion. The magnetism data of both complexes were modelled using the Heisenberg-Van Vleck-Dirac (HDVV) Hamiltonian, and the extracted parameters are consistent with the literature reports. The details of the electronic structures of the ground states of 1 and 2 were further investigated via X-band (ca. 9 GHz) electron paramagnetic resonance (EPR). The EPR spectrum of 2 could be reproduced by considering a quartet ground state with zero-field splitting and hyperfine coupling, whereas attempts to simulate all the EPR spectral features observed in a frozen solution of 1 by assuming it was a pure phase failed. A correct simulation required the simultaneous inclusion of contributions from a quartet and a triplet state. This evidently suggests that the dimeric complex of 1 is in equilibrium with a monomeric [Al(L-)3] complex in solution.
Heteronuclear Ni(ii)-Ln(iii) (Ln = La, Pr, Tb, Dy) complexes: Synthesis and single-molecule magnet behaviour
Upadhyay A., Das C., Langley S.K., Murray K.S., Srivastava A.K., Shanmugam M.
Article, Dalton Transactions, 2016, DOI Link
View abstract ⏷
The reaction of hydrated nickel(ii) salts (chloride or nitrate) and hydrated lanthanide nitrate salts with the Schiff base ligand 2-methoxy-6-[(E)-phenyliminomethyl] phenol (HL) in methanol resulted in the isolation of three isostructural linear heterometallic trinuclear complexes and a heterometallic tetranuclear complex. The molecular structures of these complexes were determined via single crystal X-ray diffraction revealing molecular structures of formulae [Ni2La(L-)6](NO3)0.55(OH)0.45 (1), [Ni2Pr(L-)6](NO3)0.48(OH)0.52 (2), [Ni2Tb(L-)6](NO3)0.5(Cl)0.5 (3) and [Ni2Dy2(L-)2(o-vanillin)2(CO3)2(NO3)2(MeOH)2] (4). Structural analysis for 1-3 reveals that the lanthanide ion is sandwiched between two Ni(ii) ions and the Ni⋯Ln⋯Ni metallic core displays a linear arrangement, with an average ∠Ni⋯Ln⋯Ni bond angle of 179.7°. Analysis of 4 reveals the metal ions are arranged such that two Ni-Dy subunits are bridged by two carbonate ligands via the Dy sites. Direct current magnetic susceptibility measurements for complexes 1-4 reveal that the Ni(ii) ions are coupled ferromagnetically with the Tb(iii) (3) and Dy(iii) (4) ions, and antiferromagnetically with the Pr(iii) ion (2). For complex 1 a long range intramolecular ferromagnetic interaction is witnessed between the Ni(ii) ions (Ni⋯Ni = 6.873(9) Å) via a closed shell La(iii) ion. The magnetic data of 1 were fitted using the HDVV Hamiltonian revealing the following parameters; J = +0.46 cm-1, g = 2.245, D = +4.91 cm-1. Alternating current magnetic susceptibility measurements performed on complexes 2-4 revealed that 3 and 4 displayed frequency dependent χ′′M signals (Hac = 3.5 Oe and Hdc = 0 Oe) which is a characteristic signature of a single-molecule magnet behaviour.
Single-Molecule Magnetism, Enhanced Magnetocaloric Effect, and Toroidal Magnetic Moments in a Family of Ln4 Squares
Das C., Vaidya S., Gupta T., Frost J.M., Righi M., Brechin E.K., Affronte M., Rajaraman G., Shanmugam M.
Article, Chemistry - A European Journal, 2015, DOI Link
View abstract ⏷
Three cationic [Ln4] squares (Ln=lanthanide) were isolated as single crystals and their structures solved as [Dy4(μ4-OH)(HL)(H2L)3(H2O)4]Cl2·(CH3OH)4·(H2O)8 (1), [Tb4(μ4-OH)(HL)(H2L)3(MeOH)4]Cl2·(CH3OH)4·(H2O)4 (2) and [Gd4(μ4-OH)(HL)(H2L)3(H2O)2(MeOH)2]Br2·(CH3OH)4·(H2O)3 (3). The structures are described as hydroxo-centered squares of lanthanide ions, with each edge of the square bridged by a doubly deprotonated H2L2- ligand. Alternating current magnetic susceptibility measurements show frequency-dependent out-of-phase signals with two different thermally assisted relaxation processes for 1, whereas no maxima in χM" appears above 2.0 K for complex 2. For 1, the estimated effective energy barrier for these two relaxation processes is 29 and 100 K. Detailed ab initio studies reveal that complex 1 possesses a toroidal magnetic moment. The ab initio calculated anisotropies of the metal ions in complex 1 were employed to simulate the magnetic susceptibility by using the Lines model (POLY-ANISO) and this procedure yields J1=+0.01 and J2=-0.01 cm-1 for 1 as the two distinct exchange interactions between the DyIII ions. Similar parameters are also obtained for complex 1 (and 2) from specific heat measurements. A very weak antiferromagnetic super-exchange interaction (J1=-0.043 cm-1 and g=1.99) is observed between the metal centers in 3. The magnetocaloric effect (MCE) was estimated by using field-dependent magnetization and temperature-dependent heat-capacity measurements. An excellent agreement is found for the -ΔSm values extracted from these two measurements for all three complexes. As expected, 3 shows the largest -ΔSm variation (23 J Kg-1 K-1) among the three complexes. The negligible magnetic anisotropy of Gd indeed ensures near degeneracy in the (2S+1) ground state microstates, and the weak super-exchange interaction facilitates dense population of low-lying excited states, all of which are likely to contribute to the MCE, making complex 3 an attractive candidate for cryogenic refrigeration.
Origin of SMM behaviour in an asymmetric Er(iii) Schiff base complex: A combined experimental and theoretical study
Das C., Upadhyay A., Vaidya S., Singh S.K., Rajaraman G., Shanmugam M.
Article, Chemical Communications, 2015, DOI Link
View abstract ⏷
An asymmetric erbium(iii) Schiff base complex [Er(HL)2(NO3)3] was synthesized which shows SMM behaviour with an Ueff of 5.2 K. Dipolar interaction in 1 significantly reduced upon dilution which increases the barrier height to 51.5 K. Ab initio calculations were performed to shed light on the mechanism of magnetization relaxation.
Probing the magnetic and magnetothermal properties of M(ii)–Ln(iii) complexes (where M(ii) = Ni or Zn; Ln(iii) = La or Pr or Gd)
Ahmed N., Das C., Vaidya S., Srivastava A.K., Langley S.K., Murray K.S., Shanmugam M.
Article, Journal of the Chemical Society. Dalton Transactions, 2014, DOI Link
View abstract ⏷
We establish the coordination potential of the Schiff base ligand (2-methoxy-6-[(E)-2′-hydroxymethyl-phenyliminomethyl]-phenolate (H2L)) via the isolation of various M(ii)–Ln(iii) complexes (where M(ii) = Ni or Zn and Ln(iii) = La or Pr or Gd). Single crystals of these five complexes were isolated and their solid state structures were determined by single crystal X-ray diffraction. Structural determination revealed molecular formulae of [NiGd(HL)2(NO3)3] (1), [NiPr(HL)2(NO3)3] (2) and [Ni2La(HL)4(NO3)](NO3)2 (3), [Zn2Gd(HL)4(NO3)](NO3)2 (4), and [Zn2Pr(HL)4(NO3)](NO3)2 (5). Complexes 1 and 2 were found to be neutral heterometallic dinuclear compounds, whereas 3–5 were found to be linear heterometallic trinuclear cationic complexes. Direct current (dc) magnetic susceptibility and magnetization measurements conclusively revealed that complexes 1 and 4 possess a spin ground state of S = 9/2 and 7/2 respectively. Empirically calculated ΔχM T derived from the variable temperature susceptibility data for all complexes undoubtedly indicates that the Ni(ii) ion is coupled ferromagnetically with the Gd(iii) ion, and antiferromagnetically with the Pr(iii) ion in 1 and 2 respectively. The extent of the exchange interaction for 1 was estimated by fitting the magnetic susceptibility data using the parameters (g = 2.028, S = 9/2, J = 1.31 cm−1 and zJ = +0.007), supporting the phenomenon observed in an empirical approach. Similarly using a HDVV Hamiltonian, the magnetic data of 3 and 4 were fitted, yielding parameters g = 2.177, D = 3.133 cm−1, J = −0.978 cm−1, (for 3) and g = 1.985, D = 0.508 cm−1 (for 4). The maximum change in magnetic entropy (−ΔSm) estimated from the isothermal magnetization data for 1 was found to be 5.7 J kg−1 K−1 (ΔB = 7 Tesla) at 7.0 K, which is larger than the −ΔSm value extracted from 4 of 3.5 J kg−1 K−1 (ΔB = 7 Tesla) at 15.8 K, revealing the importance of the exchange interaction in increasing the overall ground state of a molecule for better MCE efficiency. © 2014 the Partner Organisations.
Nickel(II)-lanthanide(III) magnetic exchange coupling influencing single-molecule magnetic features in {Ni2Ln2} complexes
Ahmed N., Das C., Vaidya S., Langley S.K., Murray K.S., Shanmugam M.
Article, Chemistry - A European Journal, 2014, DOI Link
View abstract ⏷
Four isostructural [Ni2Ln2(CH3CO2)3(HL)4(H2O)2]3+ (Ln3+=Dy (1), Tb (2), Ho (3) or Lu (4)) complexes and a dinuclear [NiGd(HL)2(NO3)3] (5) complex are reported (where HL = 2-methoxy-6-[(E)-2'-hydroxymethyl-phenyliminometh-yl]-phenolate). For compounds 1-3 and 5, the Ni2+ ions are ferromagnetically coupled to the respective lanthanide ions. The ferromagnetic coupling in 1 suppresses the quantum tunnelling of magnetisation (QTM), resulting in a rare zero dc field Ni-Dy single-molecule magnet, with an anisotropy barrier Ueff of 19 K.
Enhancing the effective energy barrier of a Dy(iii) SMM using a bridged diamagnetic Zn(ii) ion
Upadhyay A., Singh S.K., Das C., Mondol R., Langley S.K., Murray K.S., Rajaraman G., Shanmugam M.
Article, Chemical Communications, 2014, DOI Link
View abstract ⏷
Field induced single-molecule-magnet behaviour is observed for both a heterodinuclear [ZnDy(L-)2]3+ complex (1) and a mononuclear [Dy(HL)2]3+ complex (2), with effective energy barriers of 83 cm-1 and 16 cm-1, respectively. Insights into the relaxation mechanism(s) and barrier heights are provided via ab initio and DFT calculations. Our findings reveal an interesting observation that the Ueff of SMMs can be enhanced by incorporating diamagnetic metal ions. This journal is © the Partner Organisations 2014.
Synthesis and magnetic properties of a 1-D helical chain derived from a Nickel-Sodium Schiff base complex
Upadhyay A., Das C., Meera S.N., Langley S.K., Murray K.S., Shanmugam M.
Article, Journal of Chemical Sciences, 2014, DOI Link
View abstract ⏷
The reaction of the deprotonated form of the Schiff base ligand; (E)-2-methoxy-6-((phenylimino) methyl)phenol (L) with nickel chloride hydrate results in the formation of the 1-dimentional coordination polymer; Na[Ni(L)2(OMe)(MeOH)]n (1). The structure was determined via single crystal X-ray diffraction measurements. A careful analysis of the complex shows that the polymer exists as a helical structure, where the helicity is brought about by the presence of an alkali metal ion which is observed for the first time. Moreover the helical structure in 1 is maintained predominantly through covalent bond rather than supramolecular interactions. Direct current magnetic susceptibility measurement suggests that complex 1 obeys the Curie law. The fitting of magnetic data using the PHI software package yields parameters of S = 1, g = 2.26 and D = +4.51 (or D = -7.24 cm-1) for 1.
Electronic and magnetic properties of a Gadolinium(III) schiff base complex
Upadhyay A., Das C., Shanmugam M., Langley S.K., Murray K.S., Shanmugam M.
Article, European Journal of Inorganic Chemistry, 2014, DOI Link
View abstract ⏷
A mononuclear GdIII Schiff base complex of formula [Gd(HL)2(NO3)3] (1), where HL = 2-methoxy-6-[(E)-phenyliminomethyl]phenol, has been isolated and its structure was determined by single-crystal X-ray diffraction. 1H NMR spectroscopic data reveal the zwitterionic nature of the HL ligand upon coordination with the GdIII ion. Direct current (dc) magnetic susceptibility and X-band EPR measurements were performed to probe the electronic and magnetic properties of complex 1. The susceptibility and magnetization data were fitted simultaneously, resulting in spin-Hamiltonian parameters: S = 7/2, g = 2.018, and D = 0.108 cm-1. The extracted parameters are in good agreement with the values obtained by fitting the temperature-dependent polycrystalline X-band EPR spectra of 1 (S = 7/2, g = 2.005, and D = 0.0815 cm-1; E/D = 0.08). EPR dilution experiments performed on 1 indicates strongly that the anisotropy arises solely from the GdIII ion with undetectably small or no contribution from spin-spin exchange interactions.
Carboxymethyl tamarind-g-poly(acrylamide)/silica: A high performance hybrid nanocomposite for adsorption of methylene blue dye
Pal S., Ghorai S., Das C., Samrat S., Ghosh A., Panda A.B.
Article, Industrial and Engineering Chemistry Research, 2012, DOI Link
View abstract ⏷
Here, synthesis of an efficient nanocomposite based on a polyacrylamide grafted carboxymethyl tamarind (CMT-g-PAM) and a SiO2 nanoparticle is presented. The synthesized nanocomposites are characterized using FT-IR, SEM, TEM, 13C NMR, elemental analysis, viscosity, rheological measurement, and molecular weight determination. Various characterizations reveal the existence of an excellent polymer matrix-nanoparticle interaction, which is at a maximum when 1.5 wt % of SiO2 is introduced in the polymer matrix (i.e., CMT-g-PAM/SiO2-3). Nanocomposites show tremendous methylene blue (MB) dye adsorption capacity, because of their higher hydrodynamic radius as well as hydrodynamic volume, which originates from proper polymer matrix-SiO2 nanoparticle interaction. CMT-g-PAM/SiO2-3 exhibited a maximum adsorption capacity (Qmax) of 43.859 mg•g-1. The adsorption behavior of the nanocomposite shows that adsorption kinetics and isotherms are in good agreement with pseudo-second-order and Langmuir equations, respectively. Negative values of ΔG° confirmed the spontaneous nature of adsorption. Further, desorption experiments affirmed that the developed nanocomposite has excellent regenerative efficacy. © 2012 American Chemical Society.
