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121.
Sourav Biswas Dr. Sourav Das Tulika Gupta Dr. Saurabh Kumar Singh Dr. Michael Pissas Dr. Gopalan Rajaraman Prof. Vadapalli Chandrasekhar 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(51):18532-18550
A family of five isostructural butterfly complexes with a tetranuclear [Ln4] core of the general formula [Ln4(LH)2(μ2‐η1η1Piv)(η2‐Piv)(μ3‐OH)2]?x H2O?y MeOH?z CHCl3 ( 1 : Ln=DyIII, x=2, y=2, z=0; 2 : Ln=TbIII, x=0, y=0, z=6; 3 : Ln=ErIII, x=2, y=2, z=0; 4 : Ln=HoIII, x=2, y=2, z=0; 5 : Ln=YbIII, x=2, y=2, z=0; LH4=6‐{[bis(2‐hydroxyethyl)amino]methyl}‐N′‐(2‐hydroxy‐3‐methoxybenzylidene)picolinohydrazide; PivH=pivalic acid) was isolated and characterized both structurally and magnetically. Complexes 1 – 5 were probed by direct and alternating current (dc and ac) magnetic susceptibility measurements and, except for 1 , they did not display single‐molecule magnetism (SMM) behavior. The ac magnetic susceptibility measurements show frequency‐dependent out‐of‐phase signals with one relaxation process for complex 1 and the estimated effective energy barrier for the relaxation process was found to be 49 K. We have carried out extensive ab initio (CASSCF+RASSI‐SO+SINGLE_ANISO+POLY_ANISO) calculations on all the five complexes to gain deeper insights into the nature of magnetic anisotropy and the presence and absence of slow relaxation in these complexes. Our calculations yield three different exchange coupling for these Ln4 complexes and all the extracted J values are found to be weakly ferro/antiferromagentic in nature (J1=+2.35, J2=?0.58, and J3=?0.29 cm?1 for 1 ; J1=+0.45, J2=?0.68, and J3=?0.29 cm?1 for 2 ; J1=+0.03, J2=?0.98, and J3=?0.19 cm?1 for 3 ; J1=+4.15, J2=?0.23, and J3=?0.54 cm?1 for 4 and J1=+0.15, J2=?0.28, and J3=?1.18 cm?1 for 5 ). Our calculations reveal the presence of very large mixed toroidal moment in complex 1 and this is essentially due to the specific exchange topology present in this cluster. Our calculations also suggest presence of single‐molecule toroics (SMTs) in complex 2 . For complexes 3 – 5 on the other hand, the transverse anisotropy was computed to be large, leading to the absence of slow relaxation of magnetization. As the magnetic field produced by SMTs decays faster than the normal spin moments, the concept of SMTs can be exploited to build qubits in which less interference and dense packing are possible. Our systematic study on these series of Ln4 complexes suggest how the ligand design can help to bring forth such SMT characteristics in lanthanide complexes. 相似文献
122.
We have synthesized nanoparticles of hexagonal CdS in the diameter range 3-13 nm by the reaction of cadmium acetate dihydrate with thioacetamide in imidazolium [BMIM]-based ionic liquids. We have obtained three different particle sizes of CdS by changing the anion of the ionic liquid. Addition of trioctylphosphine oxide (TOPO) to the reaction mixture causes greater monodispersity as well as smaller particle size, while addition of ethylenediamine produces nanorods of 7 nm average diameter. Hexagonal ZnS and cubic PbS nanoparticles with average diameters of 3 and 10 nm, respectively, have been prepared by the reaction of the metal acetates with thioacetamide in [BMIM][BF4]. Hexagonal CdSe nanoparticles with an average diameter 12 nm were obtained by the reaction of cadmium acetate dihydrate with dimethylselenourea in [BMIM][BF4]. In this case also we observe the same effect of the addition of TOPO as in the case of CdS. Addition of ethylenediamine to the reaction mixture gives rise to nanorods. ZnSe nanowires with a cubic structures, possible diameters in the range 70-100 nm by the reaction of zinc acetate dihydrate with dimethylselenourea in [BMIM][MeSO4]. The nanostructures obtained are single crystalline in all the cases. Most of the nanostructures show characteristic UV/Vis absorption and photoluminescence emission spectra. The thermodynamically most stable structures are generally produced in the synthesis carried out in ionic liquids. 相似文献
123.
Chary KV Sagar GV Naresh D Seela KK Sridhar B 《The journal of physical chemistry. B》2005,109(19):9437-9444
A series of copper catalysts supported on TiO2-ZrO2 with copper loading varying from 1.0 to 21.6 wt % were prepared by a wet impregnation method. The catalysts were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), UV-vis diffuse reflectance spectroscopy, electron spin resonance (ESR), temperature programmed reduction (TPR), and Brunauer-Emmett-Teller specific surface area measurements. Copper dispersion and metal area were determined by N2O decomposition by the passivation method. XRD results suggest that the copper oxide is present in a highly dispersed amorphous state at copper loadings <16.8 wt % in the sample and as a crystalline CuO phase at higher Cu loadings. Copper dispersion increases with Cu loading up to 5.1 wt % and levels off at higher loadings. The XPS peak intensity ratios of Cu 2p(3/2)/Ti 2p(3/2) and Cu 2p(3/2)/Zr 3d(5/2) were compared with the copper dispersion calculated from N2O decomposition. ESR results suggest the presence of two types of copper species on the TiO2-ZrO2 support. TPR profiles reveal the presence of highly dispersed copper oxide at lower temperatures and bulk CuO at higher temperatures. The catalytic properties were evaluated for the vapor-phase dehydrogenation of cyclohexanol to cyclohexanone and related to the dispersion of Cu on TiO2-ZrO2. 相似文献
124.
Biswas P Panja SS Manogaran S Chakraborty T 《The journal of physical chemistry. A》2005,109(14):3225-3234
Laser-induced fluorescence excitation and resolved fluorescence spectra following excitations of the single vibronic levels (SVL) of p-vinyltoluene (p-VT) and p-vinylfluorobenzene (p-VFB) have been measured in a seeded supersonic free-jet expansion. A complete vibronic assignment of the fluorescence spectrum measured following excitation of the 0(0)0-band of p-VT has been presented. Normal vibrational modes in the S0 and S1 states of the molecule have been calculated by CASSCF method, and the correlation between the two set of modes is made by expressing the excited-state normal modes in terms of those of the ground state. The calculations predict that in the excited state methyl and vinyl torsional motions of p-VT are extensively mixed with many of the out-of-plane modes of the aromatic ring. Our resolved fluorescence spectral data measured following SVL excitations essentially agree with such predictions. In the excited state, the molecule exhibits a dramatically low threshold for the rotor-induced IVR in a supersonic jet expansion. Several mechanisms have been discussed to explain the phenomenon. 相似文献
125.
Shipra Sagar Binitendra Naath Mongal Abhijit Dutta Paritosh Mondal William Lewis Nadis Saba 《Journal of Coordination Chemistry》2016,69(15):2364-2376
Schiff base pyridin-2-ylimino methyl naphthanol (HL) was synthesized and characterized by spectroscopic (FTIR, ESIMS, and NMR) techniques. The ligand was reacted with perchlorate salts of Mn+2, Co+2, and Ni+2. ESIMS mass spectra indicate the formation of mononuclear complex ML2 for all three complexes. CoL2 crystallizes in P21/n space group, adopting a distorted tetrahedral geometry where Co is in a N2O2 donor environment. Structure of the Co complex was optimized by DFT calculation. Solution-phase complexation between the ligand and the three metals ions: Mn+2, Co+2, and Ni+2 (pH 7.2 in tris buffer), in CH3CN–H2O was performed spectrophotometrically by UV–vis spectral study. Job’s plot from each titration suggests a 1 : 2 metal to ligand combination. The association constants for the formation of ML2 are as follows: Mn (19.80 × 103 M?1), Co (14.54 × 103 M?1) and Ni (19.04 × 103 M?1). 相似文献
126.
A highly atom-efficient synthetic protocol for hydroarylation of terminal-aryl alkynes and styrene through the regioselective CC bond formation via the electrophilic addition of naphthols and substituted phenols has been developed using alumina-sulfuric acid as a heterogeneous supported solid acid catalyst. This methodology shows excellent regioselectivity and affords the desired product in good to excellent yield. The heterogeneous catalyst can also be recycled efficiently without much loss of activity. 相似文献
127.
Effects of chain length and heat treatment on the nanotribology of alkylsilane monolayers self-assembled on a rough aluminum surface 总被引:1,自引:0,他引:1
The conformational order of alkylsilane monolayers self-assembled on a rough aluminum surface is affected by the molecular chain length and the thermal history of the sample. These monolayers have been characterized by grazing angle FTIR spectroscopy. Tribological mechanisms were explored using initial molecular conformation order, sliding distance, normal load, and substrate compliance as experimental variables. Results indicate that the initial conformational disorder of the molecules determines the level of friction at the commencement of sliding. Adverse changes in dynamic friction and monolayer life during sliding are not thermally induced but are related to substrate roughness and local plasticity. Plastic deformation reduces the spatial density of the alkylsilane monolayer and is accentuated by an increase in the normal load. 相似文献
128.
Prathima N Harini M Rai N Chandrashekara RH Ayappa KG Sampath S Biswas SK 《Langmuir : the ACS journal of surfaces and colloids》2005,21(6):2364-2374
The thermal stability of short alkanethiol CH(3)(CH(2))(7)SH (C(8)) and long C(18) self-assembled monolayers (SAMs) is investigated using grazing angle reflection-absorption infrared spectroscopy, cyclic voltammetry, and molecular dynamics simulation. We track the disordering of SAM by untilting and gauche defect accumulation with increasing temperature in the 300-440 K range, a range of interest to tribology. Molecular dynamics simulation with both fully covered and partially covered C(6), C(8), and C(18) monolayers brings out the morphological changes in the SAM, which may be associated with the observed thermal stability characteristics. The molecular dynamics simulations reveal that short-chain C(6) and C(8) alkanethiols are more defective at lower temperature than the long-chain C(18) alkanethiol. With increasing temperature disorder in the SAM, as reflected in both untilting and gauche defect accumulation, tends to saturate at temperatures below 360 K for short-chain SAMs such that any further increase in temperature, until desorption, does not lead to any significant change in conformational order. In contrast the disorder in the long-chain C(18) SAM increases monotonically with temperature beyond 360 K. Thus, in a practical range of temperature, the ability of a SAM to retain order with increasing thermal perturbations is governed by the state of disorder prior to heat treatment. This deduction derived from molecular dynamics simulation helps to rationalize the significant difference we have observed experimentally between the thermal response of short- and long-chain thiol molecules. 相似文献
129.
Biswas I Peisert H Schwieger T Dini D Hanack M Knupfer M Schmidt T Chassé T 《The Journal of chemical physics》2005,122(6):064710
In this work we have investigated the electronic structure and the molecular orientation of (t-Bu)(4)PcMg (tetra-t-butyl magnesium phthalocyanine) on polycrystalline and single crystalline gold substrates using photoemission spectroscopy and x-ray absorption spectroscopy, and we compare the results to the unsubstituted PcCu (copper phthalocyanine). The C 1s photoemission spectrum is described similar to unsubstituted relatives with an additional component for the aliphatic substituents. The variation of the excitation energy causes distinct differences in the shape of the C 1s spectrum, which is very useful for the analysis of the molecular orientation in the uppermost layer. It is shown that despite of the sterically demanding substituents, ordered sublimed films of (t-Bu)(4)PcMg are accessible, the orientation of the molecules, however, is different from the orientation of the unsubstituted relatives. 相似文献
130.
Subhendu?Biswas Kamala?Mitra Bibhutosh?AdhikaryEmail author C.?Robert.?Lucas 《Transition Metal Chemistry》2005,30(5):586-592
Synthesis of six hydroxo-bridged binuclear manganese(III) complexes of formulae [MnL-X-MnL](ClO4) [X = OH (1–6)] along with a mononuclear manganese(III) complex (7) [Mn(L)(L′)(MeOH)2] [HL′ = 2-(2-hydroxy-phen-yl)benzimidazole] and two carboxylate-bridged binuclear manganese(III) complexes (8) and (9) are described. The complexes have been characterized by the combination of i.r., u.v.-vis spectroscopy, magnetic moments and by their redox properties. The electronic spectra of all the complexes exhibit almost identical features consisting of two d–d bands at ca. 550 and 600 nm, one MLCT band at ca.400 nm, together with two π–π* intra-ligand transitions at ca. 250 nm and ca.300 nm. Room temperature magnetic data range from μ = 2.7–3.0 BM indicates some super-exchange between the binuclear metal centers via bridging hydroxo/carboxylato groups. The X-ray crystal structure of the binuclear complex (5) revealed that it has a symmetric MnIIIN2O2 core bridged by a hydroxyl group. The X-ray analysis of the mononuclear complex (7) showed that the manganese-center possesses a distorted octahedral geometry. Electrochemical properties of hydroxo-bridged manganese(III) complexes (1–6) show identical features consisting of an irreversible and a quasi-reversible reduction corresponding to the Mn2III → MnIIMnIII → MnIIMnII couples in the voltammogram. It was found that electron withdrawing substituents on the ligand result in easier reduction. Complex (7) displays an irreversible reduction at 0.08 V and a reversible oxidation at 0.45V assignable to the MnIII → MnII reduction and MnIII → MnIV oxidation, respectively. The carboxylate-bridged compound (8) exhibits two irreversible oxidations at 0.4 and 0.6 V, probably due to Mn2III → MnIIIMnIV → MnIVMnIV oxidations and shows a quasi-reversible reductive wave at −0.85 V, tentatively assigned to Mn2III → MnIIMnIII reduction. 相似文献