251 research outputs found
High-spin low-spin transition
Temperature dependent nuclear inelastic-scattering (NIS) of synchrotron
radiation was applied to investigate both spin states of the spin-crossover
complex [Fe(tpa)(NCS)(2)] (tpa = tris(2-pyridylmethyl)amine). A remarkable
increase of the iron-ligand bond stretching upon spin crossover has
unambiguously been identified by comparing the measured NIS spectra with
theoretical simulations based on density-functional calculations
Perchlorato[N,N,N′,N′-tetrakis(2-pyridylmethyl)cyclohexane-1,2-diamine]manganese(II) perchlorate
The asymmetric unit of the title compound, [Mn(ClO4)(C30H34N6)]ClO4, consists of a cationic [Mn(ClO4)(C30H34N6)]+ complex and a perchlorate anion. In the complex, the Mn2+ ion is seven-coordinated in an approximately pentagonal–bipyramidal environment by six N atoms from the hexadentate N,N,N′,N′-tetrakis(2-pyridylmethyl)cyclohexane-1,2-diamine (tpdach) ligand and one O atom from a perchlorate anion. The complex displays intermolecular π–π interactions between adjacent pyridine rings (centroid-to-centroid distance 4.133 Å). Moreover, there are weak intra- and intermolecular C—H⋯O hydrogen bonds. The Cl atom and two O atoms of the perchlorate are disordered, with a site-occupancy factor of 0.59 (2) for the major component
Pressure-induced changes of the vibrational modes of spin-crossover complexes studied by nuclear resonance scattering of synchrotron radiation
Nuclear inelastic scattering (NIS) spectra were recorded for the
spin-crossover complexes STP and ETP (STP =
[Fe(1,1,1-trisf[N-(2-pyridylmethyl)-N-methylamino]methylg- ethane)](ClO4)2 and
ETP =
[Fe(1,1,1-trisf[N-(2-pyridylmethyl)-N-methylamino]methylg-butane)](ClO4)2) at
30 K and at room temperature and also at ambient pressure and applied pressure
(up to 2.6 GPa). Spin transition from the high-spin (HS) to the low-spin (LS)
state was observed by lowering temperature and also by applying pressure at
room temperature and has been assigned to the hardening of iron-bond stretching
modes due to the smaller volume in the LS isomer
Broken-Symmetry Ground States of Halogen-Bridged Binuclear Metal Complexes
Based on a symmetry argument, we study ground states of what we call
MMX-chain compounds, which are the new class of halogen-bridged metal
complexes. Commensurate density-wave solutions of a relevant multi-band
Peierls-Hubbard model are systematically revealed within the Hartree-Fock
approximation. We numerically draw ground-state phase diagrams, where various
novel density-wave states appear.Comment: 5 pages, 4 figures embedded, to appear in Phys. Lett.
Wide-and narrow-rim functionalised calix[4]arenes: synthesis and characterisation
Functionalisation of calix[4]arene at both the wide and narrow rims leads to the formation of compounds containing bipyridyl, via an amide linkage, at the wide rim and having either a butyl chain, a benzyl group or an alkyl ester functionality at the narrow rim. All compounds were characterised using 1H and 13C NMR spectroscopies. Initial binding studies with Ru(bipy)2Cl2 are reported.
Graphical abstract
Functionalisation of calix[4]arene was carried out such that metal complexation could occur at both the wide and narrow rims, a rare occurrence in calixarene chemistry
Novel Density-Wave States of Two-Band Peierls-Hubbard Chains
Based on a symmetry argument we systematically reveal Hartree-Fock
broken-symmetry solutions of the one-dimensional two-band extended
Peierls-Hubbard model, which covers various materials of interest such as
halogen-bridged metal complexes and mixed-stack charge-transfer salts. We find
out all the regular-density-wave solutions with an ordering vector or
. Changing band filling as well as electron-electron and electron-phonon
interactions, we numerically inquire further into the ground-state phase
diagram and the physical property of each state. The possibility of novel
density-wave states appearing is argued.Comment: 10 pages, 6 PS figures, to appear in Phys. Lett.
Competing Ground States of the New Class of Halogen-Bridged Metal Complexes
Based on a symmetry argument, we study the ground-state properties of
halogen-bridged binuclear metal chain complexes. We systematically derive
commensurate density-wave solutions from a relevant two-band Peierls-Hubbard
model and numerically draw the the ground-state phase diagram as a function of
electron-electron correlations, electron-phonon interactions, and doping
concentration within the Hartree-Fock approximation. The competition between
two types of charge-density-wave states, which has recently been reported
experimentally, is indeed demonstrated.Comment: 4 pages, 5 figures embedded, to appear in J. Phys. Soc. Jp
Ground-state properties of a Peierls-Hubbard triangular prism
Motivated by recent chemical attempts at assembling halogen-bridged
transition-metal complexes within a nanotube, we model and characterize a
platinum-halide triangular prism in terms of a Peierls-Hubbard Hamiltonian.
Based on a group-theoretical argument, we reveal a variety of valence
arrangements, including heterogeneous or partially metallic charge-density-wave
states. Quantum and thermal phase competitions are numerically demonstrated
with particular emphasis on novel insulator-to-metal and insulator-to-insulator
transitions under doping, the former of which is of the first order, while the
latter of which is of the second order.Comment: 9 pages, 7 figures. to be published in J. Phys. Soc. Jpn. Vol. 79,
No.
Quantum and Thermal Phase Transitions of Halogen-Bridged Binuclear Transition-Metal Complexes
Aiming to settle the controversial observations for halogen-bridged binuclear
transition-metal (MMX) complexes, finite-temperature Hartree-Fock calculations
are performed for a relevant two-band Peierls-Hubbard model. Thermal, as well
as quantum, phase transitions are investigated with particular emphasis on the
competition between electron itinerancy, electron-phonon interaction and
electron-electron correlation. Recently observed distinct thermal behaviors of
two typical MMX compounds Pt_2(CH_3CS_2)_4I and
(NH_4)_4[Pt_2(P_2O_5H_2)_4I]2H_2O are supported and further tuning of their
electronic states is predicted.Comment: 5 pages, 3 figures embedded, to be published in J. Phys. Soc. Jpn.
Vol.70, No.5 (2001
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