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41.
Sen TK Sau SCh Mukherjee A Modak A Mandal SK Koley D 《Chemical communications (Cambridge, England)》2011,47(43):11972-11974
The recently isolated abnormal N-heterocyclic carbene (aNHC) has been established as an efficient organocatalyst in ring opening polymerization of three different cyclic esters rac-lactide (rac-LA), ε-caprolactone (ε-CL), and δ-valerolactone (δ-VL). Preliminary DFT calculations indicate that aNHC can be a better organocatalyst than the corresponding nNHC counterpart. 相似文献
42.
Two new noncentrosymmetric (NCS) polar oxides, BaMgTe(2)O(7) and BaZnTe(2)O(7), have been synthesized and characterized, with their crystal structures determined by single crystal X-ray diffraction. The iso-structural materials exhibit structures consisting of layers of corner-shared MgO(5) or ZnO(5), Te(6+)O(6), and Te(4+)O(4) polyhedra that are separated by Ba(2+) cations. The Te(4+) cation is found in a highly asymmetric and polar coordination environment attributable to its stereoactive lone-pair. The alignment of the individual TeO(4) polar polyhedra results in macroscopic polarity for BaMgTe(2)O(7) and BaZnTe(2)O(7). Powder second-harmonic generation (SHG) measurements revealed a moderate SHG efficiency of approximately 5 × KDP (or 200 × α-SiO(2)) for both materials. Piezoelectric charge constants of 70 and 57 pm/V, and pyroelectric coefficients of -18 and -10 μC·m(-2)·K(-1) were obtained for BaMgTe(2)O(7) and BaZnTe(2)O(7), respectively. Although the materials are polar, frequency dependent polarization measurements indicated that the materials are not ferroelectric, that is, the observed macroscopic polarization cannot be reversed. Infrared, UV-vis diffuse spectroscopy, and thermal properties were also measured. Crystal data: BaMgTe(2)O(7), orthorhombic, space group Ama2 (No. 40), a = 5.558(2) ?, b = 15.215(6) ?, c = 7.307(3) ?, V = 617.9(4) ?(3), and Z = 4; BaZnTe(2)O(7), orthorhombic, space group Ama2 (No. 40), a = 5.5498(4) ?, b = 15.3161(11) ?, c = 7.3098(5) ?, V = 621.34(8) ?(3), and Z = 4. 相似文献
43.
We derive an integro-differential equation for the joint probability density function in phase space associated with the continuous-time random walk, with generic waiting time probability density function and external force. This equation permits us to investigate whole diffusion processes covering initial-, intermediate-, and long-time ranges, which can distinguish the evolution details for systems having the same behavior in the long-time limit with different initial- and intermediate-time behaviors. Moreover, we obtained analytic solutions for probability density functions both in velocity and phase spaces, and interesting dynamic behaviors are discovered. 相似文献
44.
Kallol Mukherjee Nicolas Grimblat Somratan Sau Koushik Ghosh Majji Shankar Vincent Gandon Akhila K. Sahoo 《Chemical science》2021,12(44):14863
A direct Pd(ii)-catalyzed kinetic resolution of heteroaryl-enabled sulfoximines through an ortho-C–H alkenylation/arylation of arenes has been developed. The coordination of the sulfoximine pyridyl-motif and the chiral amino acid MPAA ligand to the Pd(ii)-catalyst controls the enantio-discriminating C(aryl)–H activation. This method provides access to a wide range of enantiomerically enriched unreacted aryl-pyridyl-sulfoximine precursors and C(aryl)–H alkenylation/arylation products in good yields with high enantioselectivity (up to >99% ee), and selectivity factor up to >200. The coordination preference of the directing group, ligand effect, geometry constraints, and the transient six-membered concerted-metalation–deprotonation species dictate the stereoselectivity; DFT studies validate this hypothesis.A Pd/MPAA catalysed KR of heteroaryl substituted sulfoximines through C–H alkenylation and arylation (up to >99% ee) is developed. In-depth DFT studies uncover the salient features. 相似文献
45.
J. Sau 《Hyperfine Interactions》1985,22(1-4):125-130
An evolution equation for the relaxation of a nucleus in a metal is derived, assuming that the electronic thermostat is the vacuum of quasi-particles. The relaxation originates in the successive creations of quasi-boson excitations of the electronic system.The author's interest in this subject was aroused through a collaboration with Prof. I. Berkes. He wishes to thank him. It is pleasure to thank also Prof. R. Coussement and Dr. P. Put for many helpfull discussions and for their hospitality at the I.K.S. Leuven. 相似文献
46.
O. Scholten K. Heyde P. van Isacker J. Jolie J. Moreau M. Waroquier J. Sau 《Nuclear Physics A》1985,438(1):41-77
States of mixed proton-neutron symmetry are investigated in different dynamical symmetries of the interacting boson model. We discuss in each of the limits the energy spectrum, the wave functions and the B(M1; 01+ → 1 1+) values. We also study three classes of transitional nuclei namely the Pd nuclei [U(5) → O(6)], the Sm nuclei [U(5) → SU(3)] and the Pt nuclei [O(6) → SU(3)] with respect to the energy of the lowest non-symmetric Jπ = 1+, 3+ levels as well as the M1 and M3 strengths for exciting these levels from the ground state. For 98Pd we compare this calculation with a shell-model calculation. Finally, we adress the problem of the mixing of the non-symmetric Jπ = 1+ state with nearby hexadecapole (g-boson) configurations. 相似文献
47.
Sau Dhiman Kumar Saha Nityananda Butcher Ray J. Chaudhuri Siddhartha 《Transition Metal Chemistry》2004,29(1):75-80
The coordination behaviour of a new pyrazolyl thiosemicarbazone, HMPz4MCy, synthesized and characterized (elemental analyses, mass spectrum, i.r. and 1H-n.m.r) for the first time, is reported via solid state isolation of NiII complexes, [Ni(HMPz4MCy)2]X2·nH2O (X = Cl, Br, NO3, ClO4 and BF4; n = 2–3). The complex species were spectroscopically and structurally characterized. I.r. data for the free ligand and its NiII complexes indicate that the ligand, HMPz4MCy, exhibits a neutral NNS tridentate function via the pyrazolyl nitrogen (tertiary), azomethine nitrogen and thione sulphur. Electronic spectral data are suggestive of a distorted octahedral environment for the six-coordinate NiII species. X-ray crystallography of a representative species, [Ni(HMPz4MCy)2]Cl2·2.5H2O (P21/c, monoclinic) has shown unambiguously that the crystallographic asymmetric unit consists of a [Ni(HMPz4MCy)2]2+ cation and two Cl– anions with the solvent of crystallization consisting of two H2O molecules with full occupancy and a third H2O molecule with half occupancy. The two NNS ligands orthogonally coordinate to the central nickel(II) ion with two azomethine nitrogen atoms in trans and the pyrazolyl nitrogen and the thione sulphur atoms in cis-positions. The crystal structure is stabilized by an extensive network of hydrogen bonds and is also additionally stabilized by C—HS contacts restricting free rotation about the N—C single bonds. 相似文献
48.
Nityananda Saha Dhiman Kumar Sau Siddhartha Chaudhuri Parikshit Chandra Mandal 《Transition Metal Chemistry》2005,30(5):532-540
New iron(III) complexes of 5-methyl-3-formylpyrazole 3-hexamethyleneiminylthiosemicarbazone (HMPz3Hex), [Fe(MPz3Hex)2]X · nH2O (where X = Cl, NO3or ClO4 and n = 1–2) have been synthesized and physico-chemically characterized by magnetic data (polycrystalline state), electronic, i.r. and e.p.r. spectral studies. The reported complexes are all cationic electrolytes (1:1) containing two moles of monodeprotonated title ligand and an anionic counterpart. I.r. spectra (4000–200 cm?1) indicate coordination to the central iron(III) ion via the pyrazolyl (tertiary) ring nitrogen, azomethine nitrogen and thiolato sulphur atoms of the primary ligand molecule. E.p.r. data (r.t. and l.n.t.) show the presence of a low-spin iron(III) cation with d xz 2 d xz 2 d xz 1 configuration. Cyclic voltammograms of iron(III) complexes indicate a reversible Fe+3/Fe+2 couple. X-ray data of [Fe(MPz3Hex)2]ClO4 · 2H2O (P1, triclinic) authenticate a FeN4S2 distorted octahedral coordination with the two azomethine nitrogens trans to each other; the pyrazolyl nitrogens and thiolato sulphurs are in cis-positions, indicating an unusual rotation about the azomethine (C=N) double bond of the free HMPz3Hex during complexation with iron(III). 相似文献
49.
Lai CY Mak WL Chan EY Sau YK Zhang QF Lo SM Williams ID Leung WH 《Inorganic chemistry》2003,42(19):5863-5870
Treatment of 2-(methylsulfinyl)benzaldehyde (1) with ethylenediamine or (1R,2R)-(-)-1,2-diaminocyclohexane afforded N,N'-bis[2-(methylsulfinyl)benzylidene]ethylenediamine (L(1)) or (1R,2R)-N,N'-bis[2-(methylsulfinyl)benzylidene]-1,2-cyclohexanedia mine (L(2)), respectively. Lithiation of 2-bromobenzaldehyde diethylacetal with n-BuLi/TMEDA followed by reaction with (1R,2S,5R)-(-)-menthyl-(S)-p-toluenesulfinate afforded 2-(S)-(p-tolylsulfinyl)benzaldehyde diethyl acetal (2). Deprotection of 2 with pyridinium tosylate followed by condensation with ethylenediamine, (1R,2R)-(-)-diaminocyclohexane, or (S,S)-(+)-diaminocyclohexane afforded N,N'-bis[2-(S)-(p-tolylsulfinyl)benzylidene]ethylenediamine (L(3)), (1R,2R)-N,N'-bis[2-(S)-(p-tolylsulfinyl)benzylidene]-1,2-cyclohexanediamine ((R,R)-L(4)), or (S,S)-N,N'-bis[2-(S)-(p-tolylsulfinyl)benzylidene]-1,2-cyclohexanediamine ((S,S)-L(4)), respectively. Treatment of [Ru(PPh(3))(3)Cl(2)] with L afforded trans-[Ru(L)Cl(2)] [L = L(1) (3), L(2) (4), L(3) (5), (R,R)-L(4) ((R,R)-6), (S,S)-L(4) ((S,S)-6)]. The X-ray structures of (S(S),R(S))-4, (R,R)-6, and (S,S)-6 have been determined. The average Ru-N, Ru-S, and Ru-Cl distances in (S(S),R(S))-4 are 2.063, 2.2301, and 2.4039 A, respectively. The corresponding distances in (R,R)-6 are 2.071, 2.256, and 2.411 A, and those in (S,S)-6, 2.058, 2.2275, and 2.3831 A. Compound 3 exhibited a reversible Ru(III/II) couple at 0.56 V vs Cp(2)Fe(+/0) in CH(2)Cl(2). Treatment of 3 with AgNO(3) in water afforded the aqua compound trans-[Ru(L(1))Cl(H(2)O)][PF(6)] (7), which has been characterized by X-ray crystallography. The Ru-Cl, Ru-O, average Ru-N, and average Ru-S distances in 7 are 2.3733(6), 2.1469(16), 2.071, and 2.2442 A, respectively. Treatment of 3 with AgNO(3) followed by reaction with PPh(3) afforded [Ru(L(1))(PPh(3))(2)][PF(6)](2) (8). Treatment of [Os(PPh(3))(3)Cl(2)] with L(1) resulted in deoxygenation of one sulfoxide group of L(1) and formation of [Os(L(5))Cl(2)(PPh(3))] (9) (L(5) = N-[2-(methylsulfinyl)benzylidene]-N'-[2-(methylthio)benzylididene]ethylenediamine), which has been characterized by X-ray crystallography. The average Os-S(O), Os-N(trans to P), Os-N(trans to S), Os-P, and Os-Cl distances are 2.1931, 2.085, 2.175, 2.3641, and 2.4266 A, respectively. 相似文献
50.
I. Berkes G. Marest J. Sau H. Sayouty P. Put R. Coussement G. Scheveneels 《Hyperfine Interactions》1983,15(1-4):233-236
195,197mHg has been oriented at low temperature in a cadmium single crystal. From the orientation pattern of the 388 keV gamma ray VZZ (HgCd) =+1.82(25).1018 V/cm2 has been deduced. Using the dipole-relaxation mechanism on the gold isomeric state, the relaxation constant CK=0.044(5)Ks, the quadrupole interaction frequencies
Q
(195m-AuCd)=+395(18) MHz,
Q
(197m-AuCd)=+380(58) MHz and (E2/M1; 261 keV) < 0 are obtained from the orientation pattern of the 261 and 279 keV gamma rays. Using literature electric field gradient of gold in cadmium, Q(195m-Au,11/2)=(+) 1.41(1.0)b and Q(197m-Au,11/2)=(+)1.35(22)b can be deduced. 相似文献