Browsing by Author "Kalyani, M."

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    An Intricate Balance of Ionicity and Covalency: Metal-Like Conduction in All-Inorganic Halide Double Perovskite Cs2AgSbCl6
    (American Chemical Society, 2025) Kalyani, M.; Ananthram, K.S.; Saha, S.; Ninawe, P.; Tarafder, K.; Ballav, N.
    Halide perovskites have recently evolved as attractive materials with enormous technological significance due to synthetic control over the structure-property relationship. Halide perovskites are often realized to be either electrical insulators or semiconductors. We present an unusual metal-like conduction (thermally deactivated) in a Pb-free all-inorganic halide double perovskite, Cs2AgSbCl6. The experimental results were understood using density functional theory studies, combined with molecular dynamics simulations and electron localization function calculations, revealing retention of the predominant ionicity of the Ag-Cl bond and an increase in the covalency of the Sb-Cl bond at an elevated temperature, which resulted in a significant change of the electronic band structure, including the density of states, thereby exhibiting an intricate balance of ionicity and covalency. A significant modulation of the electrical conductivity (more than 3 orders of magnitude) without any noticeable structural change will stimulate the investigation of hitherto unknown electronic phase transitions in halide double perovskites. Additionally, light-induced unidirectional rectification of current in Cs2AgSbCl6 was ascribed to a dynamic internal polarization effect. © 2025 American Chemical Society.
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    Synergistic Photoconductivity and Ultralow Thermal Conductivity upon Stabilizing Iron(III)-tris(2,2?-bipyridine) in a Two-Dimensional Haloargentate Network
    (American Chemical Society, 2025) Jose, T.M.; Hassan, N.; Ananthram, K.S.; Kalyani, M.; Tarafder, K.; Ballav, N.
    Crystalline organic–inorganic halometallate hybrids have emerged as promising materials for optoelectronic applications due to their structural diversity and tunable properties. We report a three-dimensional (3D) hybrid organic–inorganic crystal?[Fe(bpy)3]2Ag6Br11·NO3(bpy = 2,2? bipyridine)?consisting of two-dimensional (2D) Ag(I)-based (Ag6Br11)n5n–anionic sheets, zero-dimensional (0D) [Fe(bpy)3]3+complexes (acting as the structure-directing agent), and interlayer disordered NO3–anions. Specifically, the thermodynamically unstable cation [Fe(bpy)3]3+is stabilized under ambient conditions by the two-dimensional (2D) inorganic anionic scaffold. The crystal exhibits strong ligand-supported argentophilic interactions (Ag···Ag bond distance of 2.98 Å), forming an extended (Ag6Br11)n5n–network, and displays broad UV–visible absorption with a band gap of 1.90 eV. Remarkably, this organic–inorganic hybrid shows a ?103-fold increase in photocurrent under 532 nm light illumination. Density functional theory calculations provided the mechanistic insights, and such a remarkable photoconductivity is attributed to an efficient charge delocalization and inorganic-to-organic charge transfer. Additionally, the crystal exhibits an ultralow thermal conductivity over a broad temperature range (?0.3 W/m·K; 300–400 K), making it an excellent candidate for heat management applications. © 2025 American Chemical Society
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    Thermally-driven conformational twist in organic azobenzene linker activates molecular doping effect in thin films of lanthanide MOFs
    (Royal Society of Chemistry, 2025) Bhoi, U.; Kalyani, M.; Ananthram, K.S.; Saha, S.; Acharya, A.; Hassan, N.; Raj, M.; Tarafder, K.; Ballav, N.
    Azobenzene-based photo-switchable molecules have shown significant potential in stimuli-responsive systems, especially when incorporated into metal–organic frameworks (MOFs). This study reports thin films of lanthanide-based metal–organic frameworks (Ln-MOFs) with 4,4?-azobenzene dicarboxylic acid (H2ADA) as the organic linker – Tb-ADA, Eu-ADA, and Gd-ADA – using an electrodeposition method. Upon heating to 400 K, a reversible structural transition was observed via variable temperature grazing-incidence X-ray diffraction (GIXRD) and Raman spectroscopy, not due to trans–cis isomerization but rather a thermally-induced conformational twist of the ADA linker. Density functional theory (DFT) combined with molecular dynamics (MD) simulations supports this interpretation, revealing high-energy atropisomeric states stabilized by MOF confinement. Molecular doping of these films with 7,7,8,8-tetracyanoquinodimethane (TCNQ) significantly enhanced their electrical conductivity, increasing by two orders of magnitude at 400 K. This enhancement is attributed to improved ?–? stacking and charge-transfer interactions facilitated by the conformational twist. Temperature-dependent X-ray photoelectron spectroscopy (XPS) confirmed redox activity in TCNQ@Tb-ADA films, showing reversible conversion between Tb(iii) and Tb(iv), with back electron transfer at 400 K restoring Tb(iii). These findings introduce a new mechanism of thermally-driven conformational switching in MOFs and open avenues for developing responsive electronic materials based on azobenzene linkers. This journal is © The Royal Society of Chemistry, 2025