S. S. Tandon

Bio: S. S. Tandon is an academic researcher from Guru Nanak Dev University. The author has contributed to research in topics: Palladium & Platinum. The author has an hindex of 4, co-authored 9 publications receiving 45 citations.

[Cu2{1,4-bis[(3-methyl-2-pyridyl)amino]phthalazine-H}(N3)3] at 40K

Abstract: The structure of the title compound, μ-azido-1:2κ 2 N 1 -[μ-4-(3-methyl-2-pyridyl-2κN-amino)-1-(3-methyl-2-pyridyl-1κN-imino)-1,2-dihydrophthalazin-2-yl-1:2κ 2 N 2 :N 3 ]bis[(azido-κN 1 )copper(II)], [Cu 2 (C 20 H 17 N 6 )(N 3 ) 3 ], (I), determined from data recorded at 40 (1) K using a new open-flow He gas cryostat, is presented here as part of an extended study program on dicopper(II) azide-bridged compounds. Each pair of Cu II centres in (I) is equatorially bridged by a μ 2 -1,1-azide, with a bridge angle of 107.2 (1)°. The dinuclear centres form tetranuclear clusters through two μ 2 -1,3-azide bridges, which in turn form chains along the a axis. Two C-H...N intermolecular interactions interlink these chains along the [110] and [110] directions.

Ligating properties of model bioheterocyclics. Part IV. synthesis and characterization of palladium(II), platinum(II) and platinum(IV) halide complexes with 3,8-Diphenyl-4,5,6,9-tetrahydro1,4,7-thiadiazonines

Abstract: Palladium(II) halides form five-coordinate PdC2,(TDAN) complexes with 1,4,7-thiadiazonines (TDAN), whereas platinum(II) chloride yields five coordinate [PtC2,(TDAN)] · n H2O complexes in the solid state and four-coordinate square planar [PtCl(TDAN)]CI · n H2O complexes in DMF solution. Platinum(IV) chloride reacts with TDAN to form six-coordinate [PtCl3(TDAN)]CI · n H2O octahedral complexes. 1.4.7-Thiadiazonine behaves as a tridentate ligand and coordinatesvia all three heteroatoms (S. N and N) forming three mutually adjacent five membered chelate rings with the metal ion.

Thermal- and photoinduced spin-state switching in an unprecedented three-dimensional bimetallic coordination polymer.

Abstract: The compound {Fe(pmd)[Ag(CN)2][Ag2(CN)3]} (pmd=pyrimidine) was synthesized and characterized. Magnetic, calorimetric and single crystal visible spectroscopic studies demonstrate the occurrence of a two-step high-spin (HS) right arrow over left arrow low-spin (LS) transition. The critical temperatures are T(c1)=185 and T(c2)=148 K. Each step involves approximately 50 % of the iron centers, with the low-temperature step showing a hysteresis of 2.5 K. The enthalpy and entropy variations associated with the two steps are DeltaH(1)=3.6+/-0.4 kJ mol(-1) and DeltaS(1)=19.5+/-3 J K(-1) mol(-1); DeltaH(2)=4.8+/-0.4 kJ mol(-1) and DeltaS(2)=33.5+/-3 J K(-1) mol(-1). Photomagnetic and visible spectroscopy experiments show that below 50 K, where the LS state is the thermodynamically stable state, the compound can be switched quantitatively to the HS state using green-red light (550-650 nm). HS-to-LS relaxation experiments in the dark at temperatures between 15 and 55 K show that the relaxation takes place via a two-step cooperative process, which was analyzed in the context of the mean field theory. The crystal structure has been studied at 290, 220, 170, 90 and 30 K together with 30 K after irradiation. The compound adopts monoclinic symmetry (P2(1)/c, Z=16) at all temperatures. There are five [FeN6] pseudo-octahedral sites linked by pmd, [Ag(CN)2]- and [Ag2(CN)3]- bridging ligands to form an unprecedented three-dimensional (6,6) topology. The structural analysis allows for an understanding of the microscopic mechanism of the two-step behavior of the thermally induced spin transition as well as the corresponding relaxation of the photoexcited compound based on the individual changes of the five sites. Synergy between metallophilic interactions and the spin transition is also shown by the variation of the AgAg distances. Correlations between the variation of the unit-cell volume and the change of AgAg interactions within each step with the asymmetric change of the anomalous heat capacity have also been inferred.

Interplay between kinetically slow thermal spin-crossover and metastable high-spin state relaxation in an iron(II) complex with similar T1/2 and T(LIESST).

Abstract: This paper describes the first material to show the well-known light-induced excited spin-state trapping (LIESST) effect, the metastable excited state of which relaxes at a temperature approaching its thermal spin-crossover. Cooling polycrystalline [FeL(2)][BF(4)](2).x H(2)O (L=2,6-bis[3-methylpyrazol-1-yl]pyridine; x=0-1/3) at 1 K min(-1) leads to a cooperative spin transition, taking place in two steps centered at 147 and 105 K, that is only 54 % complete by magnetic susceptibility. Annealing the sample at 100 K for 2 h results in a slow decrease in chi(M)T to zero, showing that the remainder of the spin-crossover can proceed, but is kinetically slow. The crystalline high- and fully low-spin phases of [FeL(2)][BF(4)](2).x H(2)O are isostructural (C2/c, Z=8), but the spin-crossover proceeds via a mixed-spin intermediate phase that has a triple unit cell (C2/c, Z=24). The water content of the crystals is slowly lost on exposure to air without causing decomposition. However, the high-spin/mixed-spin transition in the crystal proceeds at 110+/-20 K when x=1/3 and 155+/-5 K when x=0, which correspond to the two spin-crossover steps seen in the bulk material. The high-spin state of the compound is generated quantitatively by irradiation of the low-spin or the mixed-spin phase at 10 K, and in approximately 70 % yield by rapidly quenching the sample to 10 K. This metastable high-spin state relaxes back to the low-spin ground state at 87+/-1 K in one, not two, steps, and without passing through the intermediate phase. This implies that thermal spin-crossover and thermally activated high-spin-low-spin relaxation in this material become decoupled, thus avoiding the physical impossibility of T(LIESST) being greater than T(1/2).

Dicyanometallates as Model Extended Frameworks

Abstract: We report the structures of eight new dicyanometallate frameworks containing molecular extra-framework cations. These systems include a number of hybrid inorganic–organic analogues of conventional ceramics, such as Ruddlesden–Popper phases and perovskites. The structure types adopted are rationalized in the broader context of all known dicyanometallate framework structures. We show that the structural diversity of this family can be understood in terms of (i) the charge and coordination preferences of the particular metal cation acting as framework node, and (ii) the size, shape, and extent of incorporation of extra-framework cations. In this way, we suggest that dicyanometallates form a particularly attractive model family of extended frameworks in which to explore the interplay between molecular degrees of freedom, framework topology, and supramolecular interactions.

Multi-Temperature Crystallographic Studies of Mixed-Valence Polynuclear Complexes; Valence Trapping Process in the Trinuclear Oxo-Bridged Iron Compound, [Fe3O(O2CC(CH3)3)6(C5H5N)3]

Abstract: Single-crystal X-ray diffraction data have been collected on five different crystals at 12 different temperatures (10, 28, 35, 60, 85, 100, 118, 135, 160, 200, 240, 295 K) on a trinuclear, oxo-bridged, mixed-valence iron complex, Fe3O(O2CC(CH3)3)6(C5H5N)3, using both synchrotron and conventional radiation sources. The present study for the first time provides structural information for an oxo-bridged trinuclear compound below the boiling point of nitrogen (77 K). The use of very low-temperature crystallographic data is crucial for understanding the physical properties of the complex. No change of space group is observed in the whole temperature range, although a reversible broadening of the Bragg peaks is observed around 85 K. The structure has ordering processes involving the tert-butyl groups, and above 85 K, four tert-butyl groups become disordered. Around 150 K, a fifth tert-butyl becomes disordered, whereas the last tert-butyl is ordered at all temperatures. Very significant temperature-dependent cha...

A study of the thermal and light induced spin transition in [FeL2](BF4)2 and [FeL2](ClO4)2 L = 2,6-di(3-methylpyrazol-1-yl)pyrazine

Abstract: The spin crossover compounds [FeL2](BF4)2, L = 2,6-di(3-methylpyrazol-1-yl)pyrazine and [FeL2](ClO4)2 have very unusual two stage spin transitions which are initially steep and then become more gradual. A detailed variable temperature single crystal X-ray diffraction study has shown that the course of the spin transition is controlled by an order–disorder transition in the counter anions. The high and low spin states both crystallise in the tetragonal space group I, the structures of the high and low spin states are presented at 290 and 30 K, respectively. The title compounds are shown to undergo LIESST (Light Induced Excited Spin State Trapping) under irradiation with either red or green laser light with wavelengths of 632.8 and 532.06 nm, respectively, at 30 K. The cell parameters for the tetragonal photo-induced metastable high spin state at this temperature are a = 9.169(6), c = 17.77(1) A for [FeL2](ClO4)2 with an increase in unit cell volume of 21 A3, and a = 9.11(1), c = 17.75(2) A and an increase in volume of 42.8 A3 for [FeL2](BF4)2.