Browsing by Author "Masahiro Yamashita"

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Novel Supramolecular Assemblies of Co(III) & Cu(II) with Diethylenetriamine and Azide: Synthesis, Structure, Spectroscopic and Magnetic Studies
(Wiley-Blackwell, 2018) Priyanka Pandey; Goulven Cosquer; Masahiro Yamashita; Sailaja S. Sunkari
In exploring the role of increased ligand basicity as well as denticity on moving from ethylenediamine (en) or 1,3-diaminopropane (1,3-dap), on supramolecular solid formation, complexation involving diethylenetriamine (det) and azide with CoII and CuII afforded three new complexes [Co(det)2](N3)3 (1), [Co(det)(N3)3] (2) and [Cu2(det)2(N3)5(H2O)2Na] (3) under self assembling conditions and are characterized structurally and magnetically. Formation of 1 and 2 is sensitive to temperature of crystallization, while such a temperature influence could not be observed for CuII system due to lack of crystals at low temperatures. As expected with a tridentate ligand, strong chelation stabilizes 1 at LT and is a thermodynamically stable product, while isolation of 2 at RT conditions is under kinetic control. Decomposition of 2 at high temperatures (above 70 °C) as revealed through temperature dependent UV-vis spectral studies also confirms its instability. Presence of three donor sites of det, leads to interesting structural pattern in Jahn-Teller active CuII, resulting in cationic chains of [Cu(det)(N3)]n + bridged by μ-1,3 azido bridges to the neighboring [Na(H2O)2(N3)2]− units, thus leading to a 2-D assembly of alternating layers of cationic and anionic chains in the unit cell of 3. Magnetic studies of 3 reveals anti-ferromagnetic interaction between the copper ions (J=– 0.479 cm–1), in conformity with the bridge angle dependent magnetic behavior in azido bridged copper complexes. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Slow magnetic relaxation in a ferromagnetic CuII chain complex, induced by a phonon bottleneck effect
(Royal Society of Chemistry, 2023) Sailaja S. Sunkari; Abhineet Verma; Om Pandey; Shraddha Gupta; Masanori Wakizaka; Shinya Takaishi; Hideyuki Kawasoko; Tomoteru Fukumura; Masahiro Yamashita
The first slow magnetic relaxation in a ferromagnetic Cu(ii) chain compound, Cu(dipic)(OH2)2 (dipicH2 = pyridine-2,6-dicarboxylic acid), induced by a phonon bottleneck effect under a magnetic field of 0.6 T, with a relaxation time of 2.2 s at 2.8 K, was observed. © 2023 The Royal Society of Chemistry.
Tetranuclear Copper(II) Complexes with Simultaneous Phenoxo and Azido Bridges - Synthesis, Structural and Magnetic Studies
(Wiley-Blackwell, 2018) Priyanka Pandey; Nidhi Dwivedi; Goulven Cosquer; Masahiro Yamashita; Sailaja Sunkari
Tetradentate Schiff base ligands with multiple coordinaton sites are one of the best choice for the construction of multinuclear metal complexes. Coupled with auxiliary ligands under self assembling conditions, the scope for generating new structures increases manifold due to various structure directing factors in operation. Though, phenoxo or azido bridged copper(II) systems have been investigated thoroughly from structural and magnetic aspects, the literature is scanty with combined phenoxo and azido bridged systems. In a study on the effect of synthetic conditions on the structures generated and associated magnetic properties, two new tetranuclear copper complexes, viz., [Cu4(L1)2(μ-N3)2(N3)2] (1) and [Cu4(L2)2(μ-N3)2(N3)2] (2) where L1=N,N′-Bis(salicylidene)diaminopropane (salpn) and L2=N,N′-Bis(salicylidene)diaminobenzene (salophen) with both phenoxo and azido bridges are reported. The tetranuclear cluster is made of two inversion related dimers built of phenoxo bridged Cu1 and Cu2 with distorted square planar and square pyramidal geometries respectively. These dimers are bridged by symmetrically bridging azides leading to a tetranuclear core. The contrasting magnetic behavior inspite of same coordination environments, antiferromagnetic in 1 (J1=−2.17 cm−1; J2=−28.15 cm−1) and ferromagnetic in 2 (J1=−74.7 cm−1; J2=146.5 cm−1), is understood in terms of lower bridge angles and closer separation between copper centers in 2 than in 1. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim