Browsing by Author "Nattamai Bhuvanesh"

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Confocal Raman microscopic evidence for cyclic water Pentamer, at high temperatures in a supramolecular host of [Cu(cyclam)(N3)2]·4H2O
(Elsevier B.V., 2022) Abhineet Verma; Nattamai Bhuvanesh; Joseph Reibenspies; Satyen Saha; Sailaja S. Sunkari
Here, we report the existence of a pentameric water cluster in the host framework of [Cu(cyclam)(N3)2]·4H2O, that is stable upto 167 °C, well above the boiling point of water. The pentameric cluster structure embedded in the host framework is evident from the single crystal studies. The high thermal stability is confirmed by TGA and temperature dependent confocal Raman microscopic studies, where loss of water bands is well captured between 167 and 170 °C, besides its existence through SCXRD studies. To the best of our knowledge, this is the first report where temperature dependent confocal Raman microscopic investigation is used to study the stability of water in crystal environment. The study promises that temperature dependent confocal Raman microscopy can be an efficient tool to investigate the existence and stability of small water clusters, precisely in restricted environments. © 2022 Elsevier B.V.
Counterion Influenced Metal-Organic Frameworks of Cyclam with CuII
(John Wiley and Sons Inc, 2023) Abhineet Verma; Nattamai Bhuvanesh; Joseph Reibenspies; Sailaja S. Sunkari
Cyclam is one of the simplest macrocycle that forms stable metal chelates, much explored for their material and biological applications. Varying anion shape is an effective strategy to modulate the supramolecular structure, inspite of same molecular structure. Here, we report six new complexes of cyclam with CuII bound to counterions of different shapes viz., linear (NCS−/N3−), bent (N(CN)2−) or spherical (Cl−/Br−/I−) in which the shape of the anion leads to distinctly different supramolecular structures (ladder/linear chains with linear anions), braid like (with bent anion) and 3-D hydrogen bonded networks (with spherical anions) due to changes in the non-covalent interactions, inspite of the same molecular structure. The variations in packing are responsible for their different thermal properties. With metallo-cyclams being explored for their efficacy in medical and material fields, studies of this type may offer potential candidates to explore. © 2023 Wiley-VCH GmbH.
Structurally characterised new twisted conformer for cyclen, controlled by metal ion complexation as seen in NiIIand CuIIcomplexes with halides and pseudohalides
(Royal Society of Chemistry, 2022) Abhineet Verma; Nattamai Bhuvanesh; Joseph Reibenspies; Sakharam B. Tayade; Avinash S. Kumbhar; Kateryna Bretosh; Jean-Pascal Sutter; Sailaja S. Sunkari
Serendipitous self-assembly is a potential approach for achieving structurally versatile and unexpected solids with chosen metal-ligand combinations. Cyclen (1,4,7,10-tetraazacyclododecane) is an interesting flexible molecule, well explored for biological and material applications of its metal complexes. The dihedral angle (θ) between four nitrogen atoms of free cyclen is close to 0°. Still, it may vary upon complexation, allowing flexibility to adopt any two conformers,viz., (i) planar and (ii) twisted. The present work establishes the crucial role of metal ions in controlling the conformation adopted by cyclen through metal complexation. SCXRD studies of the complexes of cyclen with CuIIand NiIIwith halides and pseudohalides as counterions reveal the existence of a planar conformation (θ= ∼0-3°) for cyclen in CuIIsystems and a highly twisted conformation (hitherto unreported) in NiIIsystems (θ= ∼52-55°). Further, SQUID magnetic studies for the dimeric [Ni1] complex reveal antiferromagnetic interactions between the two Ni centres. © The Royal Society of Chemistry 2021.