Joydeb Goura
Indian Institute of Technology Kanpur
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Featured researches published by Joydeb Goura.
Inorganic Chemistry | 2014
Joydeb Goura; James P. S. Walsh; Floriana Tuna; Vadapalli Chandrasekhar
The reaction of 2-methoxy-6-(pyridin-2-ylhydrazonomethyl)phenol (LH) with Ln(III) (Ln = Gd, Tb, Dy, Ho) salts in the presence of an excess of triethylamine afforded [Gd4(L)4(μ4-OH)(μ3-OH)2(NO3)4]·(NO3)·4CH3CN·CH3OH·2H2O (1), [Tb4(L)4(μ4-OH)(μ3-OH)2(NO3)4]·(NO3)·4CH3CN·3H2O (2), [Dy4(L)4(μ4-OH)(μ3-OH)2(NO3)4]·(NO3)·6CH3CN·H2O (3), and [Ho4(L)4(μ4-OH)(μ-OH)2(NO3)4]·(NO3)·8CH3CN·3CH3OH·2H2O (4). All four complexes contain a monocationic tetranuclear core with a unique seesaw topology. The tetranuclear assembly is formed through the coordination of four [L](-), one μ4-OH, two μ3-OH, and four chelating nitrate ligands, with a charge-balancing nitrate counteranion. Magnetic studies reveal a weak antiferromagnetic coupling throughout the series. Compound 1 can be modeled well with an isotropic exchange between all centers parametrized by J = -0.09 cm(-1). Compound 3 exhibits slow magnetic relaxation at low temperatures.
Inorganic Chemistry | 2012
Vadapalli Chandrasekhar; Joydeb Goura; E. Carolina Sañudo
The reaction of manganese(II) salts with organophosphonic acid [t-BuPO(3)H(2) or cyclopentyl phosphonic acid (C(5)H(9)PO(3)H(2))] in the presence of ancillary nitrogen ligands [1,10-phenanthroline (phen) or 2,6-bis(pyrazol-3-yl)pyridine (dpzpy)], afforded, depending on the stoichiometry of the reactants and the reaction conditions, dinuclear, trinuclear, and tetranuclear compounds, [Mn(2)(t-BuPO(3)H)(4)(phen)(2)]·2DMF (1), [Mn(3)(C(5)H(9)PO(3))(2)(phen)(6)](ClO(4))(2)·7CH(3)OH (2), [Mn(3)(t-BuPO(3))(2)(dpzpy)(3)](ClO(4))(2)·H(2)O (3), [Mn(4)(t-BuPO(3))(2)(t-BuPO(3)H)(2)(phen)(6)(H(2)O)(2)](ClO(4))(2) (4), and [Mn(4)(C(5)H(9)PO(3))(2)(phen)(8)(H(2)O)(2)](ClO(4))(4) (5). Magnetic studies on 1, 2, and 4 reveal that the phosphonate bridges mediate weak antiferromagnetic interactions between the Mn(II) ions have also been carried out.
Chemistry: A European Journal | 2015
Joydeb Goura; Jamie Brambleby; Paul Goddard; Vadapalli Chandrasekhar
We report a Co(III) 2 Dy(III) complex, which shows single-ion-magnet behaviour. AC susceptibility data of this compound reveals the presence of slow relaxation of the magnetization in zero-field below 15 K. The relaxation barrier is 88 K.
Inorganic Chemistry | 2013
Vadapalli Chandrasekhar; Joydeb Goura; Andrew Duthie
Two novel indium(III) phosphonates, [In2(t-BuPO3H)4(phen)2Cl2] (1) and [In3(C5H9PO3)2(C5H9PO3H)4(phen)3]·NO3·3.5H2O (2) with phen = 1,10-phenanthroline, have been synthesized by solvothermal reactions involving indium(III) salts and organophosphonic acids. 1 is a dinuclear compound where the two indium centers are bridged by a pair of isobidentate phosphonate ligands, [t-BuP(O)2OH](-), resulting in an eight-membered (In2P2O4) puckered ring. Compound 2 is trinuclear; the In3 platform is held together by two bicapping tripodal phosphonate ligands from the top and bottom of the indium plane. In addition, two bridging monoanionic phosphonate ligands serve to bind two pairs of indium centers. Both 1 and 2 also contain monodentate monoanionic phosphonate ligands. The solid-state MAS (31)P NMR spectrum of complex 1 shows two signals at 21.9 and 29.3 ppm. Compound 2 contains signal maxima at 25.8 and 28.9 ppm, with a shoulder at 31.5 ppm. Room temperature solid-state fluorescence spectra of 1 and 2 are characterized by strong emission bands at 385 nm (λex = 350 nm) and 395 nm (λex = 350 nm), respectively, which are red-shifted with respect to the emission of free phenanthroline.
Inorganic Chemistry | 2016
Sourav Biswas; Joydeb Goura; Sourav Das; Craig V. Topping; Jamie Brambleby; Paul Goddard; Vadapalli Chandrasekhar
Octanuclear heterobimetallic complexes, [Ln4Ni4(H3L)4(μ3-OH)4(μ2-OH)4]4Cl·xH2O·yCHCl3 (Dy(3+), x = 30.6, y = 2 (1); Tb(3+), x = 28, y = 0 (2) ; Gd(3+), x = 25.3, y = 0 (3); Ho(3+), x = 30.6, y = 3 (4)) (H5L = N1,N3-bis(6-formyl-2-(hydroxymethyl)-4-methylphenol)diethylenetriamine) are reported. These are assembled by the cumulative coordination action of four doubly deprotonated compartmental ligands, [H3L](2-), along with eight exogenous -OH ligands. Within the core of these complexes, four Ln(3+)s are distributed to the four corners of a perfect square grid while four Ni(2+)s are projected away from the plane of the Ln4 unit. Each of the four Ni(2+)s possesses distorted octahedral geometry while all of the Ln(3+)s are crystallographically equivalent and are present in an elongated square antiprism geometry. The magnetic properties of compound 3 are dominated by an easy-plane single-ion anisotropy of the Ni(2+) ions [DNi = 6.7(7) K] and dipolar interactions between Gd(3+) centers. Detailed ac magnetometry reveals the presence of distinct temperature-dependent out-of-phase signals for compounds 1 and 2, indicative of slow magnetic relaxation. Magnetochemical analysis of complex 1 implies the 3d and the 4f metal ions are engaged in ferromagnetic interactions with SMM behavior, while dc magnetometry of compound 2 is suggestive of an antiferromagnetic Ni-Tb spin-exchange with slow magnetic relaxation due to a field-induced level crossing. Compound 4 exhibits an easy-plane single-ion anisotropy for the Ho(3+) ions and weak interactions between spin centers.
Inorganic Chemistry | 2014
Joydeb Goura; Prasenjit Bag; Valeriu Mereacre; Annie K. Powell; Vadapalli Chandrasekhar
The reaction of Fe(ClO4)2·6H2O with t-BuPO3H2 or Cl3CPO3H2 in the presence of an ancillary pyrazole phenolate as a coligand, H2phpzH [H2phpzH = 3(5)-(2-hydroxyphenyl)pyrazole], afforded tetra- and pentanuclear Fe(III) phosphonate complexes [Fe4(t-BuPO3)4(HphpzH)4]·5CH3CN·5CH2Cl2 (1) and [HNEt3]2[Fe5(μ3-O)(μ-OH)2 (Cl3CPO3)3(HphpzH)5(μ-phpzH]·3CH3CN·2H2O (2). Single-crystal X-ray structural analysis reveals that 1 possesses a cubic double-4-ring (D4R) core similar to what is found in zeolites. The molecular structure of 2 reveals it to be pentanuclear. It crystallizes in the chiral P1 space group. Magnetic studies on 1 and 2 have also been carried out, which reveal that the bridging phosphonate ligands mediate weak antiferromagnetic interactions between the Fe(III) ions. Magnetization dynamics of 1 and 2 have been corroborated by a Mössbauer spectroscopy analysis.
Dalton Transactions | 2016
Amit Chakraborty; Joydeb Goura; Prasenjit Bag; Arun Kumar Bar; Jean-Pascal Sutter; Vadapalli Chandrasekhar
Utilizing a new ferrocene-based compartmental ligand, H4L (1), a series of novel heterometallic complexes [{LZn(μ-OAc)Dy}4(μ4-H2O)] (2), [{LZn(μ-OAc)Tb}4(μ4-H2O)] (3), [{LZn(μ-OAc)Ho}4(μ4-H2O)] (4), [L = Fe[(C5H4){-C(Me)[double bond, length as m-dash]N-N[double bond, length as m-dash]C6H3-(o-O)(m-O)}]2] were synthesized and characterized. 2 and 3 crystallize in the monoclinic crystal system in the I2/m space group, whereas 4 crystallizes in the tetragonal crystal system in the I4/m space group. The tetra deprotonated ligand L4- has two distinct coordination compartments: one pocket (2N, 2O) suitable for the transition metal (3d) ions and another pocket (4O) suitable for lanthanide (4f) metal ions. Additionally, the terminal phenoxo group can be utilized for cluster expansion. In all the complexes, the ZnII ion is in a perfect square pyramidal (2N, 3O) geometry whereas the lanthanide ion has a coordination number of eight (8O) in a distorted biaugmented trigonal-prism geometry. The electrochemical properties of 2 and 3 along with ligand H4L (1) were studied by cyclic voltammetry (CV). All the complexes display a similar type of electrochemical behavior viz., one quasi-reversible oxidation typical of a ferrocene/ferrocenium motif. The magnetic properties of all the complexes have also been investigated.
ACS Omega | 2018
Pankaj Kalita; Joydeb Goura; Juan Manuel Herrera; Enrique Colacio; Vadapalli Chandrasekhar
The reaction of 2-methoxy-6-[{2-(2-hydroxyethylamino)ethylimino}methyl] phenol (LH3) with lanthanide metal salts followed by the addition of nickel acetate allowed isolation of a family of octanuclear complexes, [Ni4Ln4(μ2-OH)2(μ3-OH)4(μ-OOCCH3)8(LH2)4]·(OH)2·xH2O. Single crystal X-ray diffraction studies of these complexes reveal that their central metallic core consists of two tetranuclear [Ni2Ln2O4] cubane subunits fused together by acetate and hydroxide bridges. The magnetic study of these complexes reveals a ferromagnetic interaction between the LnIII and the NiII center. The magnitude of exchange coupling between the NiII and LnIII center, parametrized from the magnetic data of the Gd analogue, gives J = +0.86 cm–1. The magneto caloric effect, studied for the NiII4GdIII4 complex, shows a maximum of magnetic entropy change, −ΔSm = 22.58 J kg–1 K–1 at 3 K for an applied external field of 5 T.
Inorganic Chemistry | 2014
Joydeb Goura; Rogez Guillaume; Eric Rivière; Vadapalli Chandrasekhar
Crystal Growth & Design | 2015
Amit Chakraborty; Prasenjit Bag; Joydeb Goura; Arun Kumar Bar; Jean-Pascal Sutter; Vadapalli Chandrasekhar