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 $q=0$ or $q=\pi$. 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