Showing papers by "Sanjit Konar published in 2023"

Pressure-Induced Hysteretic and Abrupt Spin Transition in Amine Functionalized Isoquinoline-Based Two-Dimensional FeII Hofmann Frameworks

Abstract: Two two-dimensional (2D) Hofmann-type coordination frameworks are synthesized by employing the square planar tetracyanometallate building blocks and an amine-functionalized isoquinoline ligand with the general formula of [Fe(L)2{M(CN)4}] (L = 5-amino isoquinoline) (M = Pt (1Pt) and Pd (1Pd)) to explore the spin-state switching behavior. The inclusion of the amine functional group in the isoquinoline ligand plays a major role in exhibiting a complete spin crossover (SCO) behavior under ambient atmospheric pressure. The effective host–host supramolecular interaction such as strong π···π stacking and N–H···C interactions between interlayer 2D sheets of {FeII[Pt (CN)4]}n is responsible for the abrupt hysteretic spin transition behavior. Interestingly, the applied external pressure enhances the stabilization of the low spin states revealing a one-step abrupt and hysteretic spin transition near room temperature.

NaGaSe2: A Water-Loving Multifunctional Non-van der Waals Layered Selenogallate.

Abstract: A missing member of well-known ternary chalcometallates, a sodium selenogallate, NaGaSe2, has been synthesized by employing a polyselenide flux and stoichiometric reaction. Crystal structure analysis using X-ray diffraction techniques reveals that it contains supertetrahedral adamantane-type Ga4Se10 secondary building units. These Ga4Se10 secondary building units are further connected via corners to form two-dimensional (2D) [GaSe2]∞- layers stacked along the c-axis of the unit cell, and the Na ions reside in the interlayer space. The compound has an unusual ability to absorb water molecules from the atmosphere or a nonanhydrous solvent to form distinct hydrated phases, NaGaSe2·xH2O (where x can be 1 and 2), with an expanded interlayer space, as verified by X-ray diffraction (XRD), thermogravimetric-differential scanning calorimetry (TG-DSC), desorption, and Fourier transform infrared spectroscopy (FT-IR) studies. The in situ thermodiffractogram indicates the emergence of an anhydrous phase before 300 °C with the decrease of interlayer spacings and reverting to the hydrated phase within a minute of re-exposure to the environment, supporting the reversibility of such a process. Structural transformation induced through water absorption results in an increase of Na ionic conductivity by 2 orders of magnitude compared to that of the pristine anhydrous phase, as verified by impedance spectroscopy. Na ions from NaGaSe2 can be exchanged in the solid-state route with other alkali and alkaline earth metals in a topotactic or nontopotactic way, leading to 2D isostructural and three-dimensional networks, respectively. Optical band gap measurements show a band gap of ∼3 eV for the hydrated phase, NaGaSe2·xH2O, which is in good agreement with the calculated band gap using a density functional theory (DFT)-based method. Sorption studies further confirm the selective absorption of water over MeOH, EtOH, and CH3CN with a maximum water uptake of 6 molecules/formula unit at a relative pressure, P/P0, of 0.9.

Dinuclear iron(II) triple helicates exhibiting room temperature spin transition behaviour in solid and solution phase.

Abstract: In this work, three dinuclear iron (II) helicates (complexes 1-3 ) have been synthesized using imidazole and pyridine-imine-based ligands having fluorene moiety in the backbone. A change in the ligand field strength by terminal modulation led to a change in the spin transition behaviour from incomplete, multi-step to complete, around room temperature in the solid state. Spin transition behaviour has also been observed in the solution phase characterized using variable temperature 1 H nuclear magnetic resonance spectroscopy (Evans method) and correlated using UV-visible spectroscopy. Fitting the NMR data using the ideal solution model provided the transition temperature in the order T½ ( 1 ) < T½ ( 2 ) < T½ ( 3 ), which indicates an increase in the ligand field strength from complexes 1 to 3 . This study accentuates the interplay between the ligand field strength, crystal packing, and supramolecular interactions in fine-tuning the spin transition behavior effectively.

Competitive electronic and steric effects in spin-state modulation of a 3D-Hofmann framework and its extension toward nanoscale

Abstract: Modulating the spin-crossover behaviour in porous coordination polymers is not only an excellent way to address the challenges associated with high-order data storage and processing, but the colour change involved...

Significant Control on Zero-field Quantum Tunneling of Magnetization in Dysprosium Based Single-Molecule Magnets via Orientation of the Anilato Ligand.

Abstract: Tuning the bridging fashion of anilato ligand in dinuclear DyIII complexes, reveals a sizable effect on the slow relaxation of magnetization. Combined experimental and theoretical studies divulge that the geometry with high order axial symmetry (pseudo square antiprism) reduces the transverse crystal fields corresponding to QTM resulting in a significant increase in energy barrier (Ueff = 518 cm-1) through the Orbach relaxation process whereas the geometry with lower symmetry (triangular dodecahedron, pseudo D2d) enhances the transverse crystal fields that accelerate the ground state QTM process. Notably, the value 518 cm-1 represents the highest energy barrier among anilato ligand based SMMs.

[α-AsW9O33]9- bridged hexagonal clusters of Ln(III) showing field induced SMM behavior: experimental and theoretical insight.

Abstract: Polyoxometalates (POM), as inorganic polydentate oxygen donors, provide binding opportunities for oxophilic lanthanide metal centers to construct novel Ln-substituted POM materials with exciting structures and attractive properties. Herein, we have reported four arsenotungstate [α-AsW9O33]9- based lanthanide-containing polyoxometalates [CsxK36-x{Ln6(H2O)12(α-AsW9O33)6}]·yH2O (Ln = Er (1), Gd (2), Ho (3), and Tb (4)), which are synthesized in an alkaline medium. Complexes 1-3 are the dimeric structures of [Ln3(H2O)6(α-AsW9O33)3]18- polyanions, whereas complex 4 is a hexamer of the polyanion [Tb (H2O)2(α-AsW9O33)]6- as a building unit. In all the complexes, [α-AsW9O33]9- units are staggered up and down and give rise to the chair conformation, where one [α-AsW9O33]9- unit bridges two Ln(III) centers through four μ2-oxygen and two terminal oxygen atoms, resulting in the hexagonal arrangement of lanthanides. The dynamic magnetic measurement indicates that only complex 1 exhibits slow relaxation of magnetization with an applied dc field (1500 Oe). To gain insight into the slow relaxation of magnetization in complex 1, the ligand-field parameters and the splitting of the ground-state multiplet of the Er(III) ions have been estimated. The ab initio calculation results confirm that the ground state wave function of these molecules (1, 3, and 4) is mainly composed of a mixture of mJ states, and the non-axial crystal field (CF) terms are more predominant than the axial CF term. The solid-state fluorescence spectra of 1-4 reveal that the photoexcitation O → M ligand-to-metal charge-transfer (LMCT) of arsenotungstate fragments is effectively quenched due to the spatial coordination environment around the Ln(III) ion.