Yasutaka Kitagawa

Electroconductive Porous Coordination Polymer Cu[Cu(pdt)2] Composed of Donor and Acceptor Building Units

We synthesized a new porous coordination polymer Cu[Cu(pdt)2], which shows relatively high electrical conductivity (6 x 10(-4) S cm(-1) at 300 K) by the introduction of electron donors and acceptors as building units. This compound is applicable as a porous electrode with high power density. In addition, this compound forms a triangular spin lattice and shows spin frustration.

A photofunctional bottom-up bis(dipyrrinato)zinc(II) complex nanosheet

Two-dimensional polymeric nanosheets have recently gained much attention, particularly top-down nanosheets such as graphene and metal chalcogenides originating from bulk-layered mother materials. Although molecule-based bottom-up nanosheets manufactured directly from molecular components can exhibit greater structural diversity than top-down nanosheets, the bottom-up nanosheets reported thus far lack useful functionalities. Here we show the design and synthesis of a bottom-up nanosheet featuring a photoactive bis(dipyrrinato)zinc(II) complex motif. A liquid/liquid interfacial synthesis between a three-way dipyrrin ligand and zinc(II) ions results in a multi-layer nanosheet, whereas an air/liquid interfacial reaction produces a single-layer or few-layer nanosheet with domain sizes of >10 μm on one side. The bis(dipyrrinato)zinc(II) metal complex nanosheet is easy to deposit on various substrates using the Langmuir–Schäfer process. The nanosheet deposited on a transparent SnO2 electrode functions as a photoanode in a photoelectric conversion system, and is thus the first photofunctional bottom-up nanosheet.

DFT studies of interaction between O2 and Au clusters. The role of anionic surface Au atoms on Au clusters for catalyzed oxygenation

Abstract Density functional and ab initio molecular orbital (MO) calculations have been carried out for the AuO, AuO2, AuO2−, and the Au13O2 clusters. The results show that the surface atoms of the icosahedral Au13 cluster are negatively charged and the anionic Au atoms in the cluster have a stronger interaction with O2 than a neutral Au atom. These findings suggest that the negatively charged surface Au atoms on the surface of the Au clusters are the active sites for oxygenation on the supported and unsupported Au catalysts.

Theoretical studies on effective spin interactions, spin alignments and macroscopic spin tunneling in polynuclear manganese and related complexes and their mesoscopic clusters

Abstract Theoretical efforts to investigate molecular magnetic materials are reviewed mainly from the viewpoint of our interest. Ab initio calculations of effective exchange interactions between spins are performed for HH, HHeH and simplified models of binuclear manganese and related complexes by using the spin unrestricted Hartree–Fock (UHF) and spin-polarized density functional (DFT), and UHF plus DFT hybrid methods. The scope and limitation of these broken-symmetry approaches are briefly discussed in relation to several computational schemes of effective exchange integrals ( J ab ). The calculated J ab values for the three systems are summarized for comparison of the computational methods. The natural orbitals (UNO or DNO) of the UHF and DFT solutions for magnetic clusters are determined by diagonalizing their first-order density matrices. They are used for MO-theoretical interpretation of superexchange interactions. The effective spin Hamiltonians such as the Heisenberg model are constructed for polynuclear complexes assuming the calculated and experimental effective exchange integrals. The macroscopic quantum tunneling (MQT) and coherence (MQC) of spins in the manganese oxide clusters are analyzed using the Heisenberg model, and the tunneling rate of spins is calculated by the coherent state path integral method. The topological rules for MQT and MQC are derived from this analysis. The path integral formulations are extended to tunneling probabilities for clusters of clusters and spin lattices with mesoscopic size. The resulting ideas are also applied to the molecular design of mesoscopic clusters of clusters in intermediate and strong correlation regimes. The active control of spins are finally discussed from the viewpoint of functionalities in molecular and biological materials, and technological applications of mesoscopic molecular magnets to quantum computing.

Theoretical study of the magnetic interaction for M–O–M type metal oxides. Comparison of broken-symmetry approaches

Abstract The unrestricted Hartree–Fock (UHF) and hybrid-density functional theory (DFT) calculations have been carried out for the metal oxides such as copper oxides and nickel oxides. In order to elucidate magnetic properties of the species, the effective exchange integrals ( J ab ) have been obtained by the total energy difference between the highest and lowest spin states in several computational schemes with and without spin projection. The mixing ratios of the exchange correlation functionals in the hybrid DFT method have been reoptimized so as to reproduce the J ab values for strongly correlated oxides. The natural orbital analysis has also been performed for elucidation of symmetry and occupation numbers of the magnetic orbitals. From these calculated results, we discuss characteristics of the magnetic interactions for metal oxides in the strong correlation regime.

Spin Contamination Error in Optimized Geometry of Singlet Carbene (1A1) by Broken-Symmetry Method†

Spin contamination errors of a broken-symmetry (BS) method in optimized structural parameters of the singlet methylene ((1)A(1)) molecule are quantitatively estimated for the Hartree-Fock (HF) method, post-HF methods (CID, CCD, MP2, MP3, MP4(SDQ)), and a hybrid DFT (B3LYP) method. For the purpose, the optimized geometry by the BS method is compared with that of an approximate spin projection (AP) method. The difference between the BS and the AP methods is about 10-20 degrees in the HCH angle. In order to examine the basis set dependency of the spin contamination error, calculated results by STO-3G, 6-31G*, and 6-311++G** are compared. The error depends on the basis sets, but the tendencies of each method are classified into two types. Calculated energy splitting values between the triplet and the singlet states (ST gap) indicate that the contamination of the stable triplet state makes the BS singlet solution stable and the ST gap becomes small. The energy order of the spin contamination error in the ST gap is estimated to be 10(-1) eV.

Density-functional study of intramolecular ferromagnetic interaction through m-phenylene coupling unit (II): Examination of functional dependence

As a first step toward examination of ferromagnetic polymers and dendrimers by ab initio crystal orbital methods, we elucidated candidates for monomer units with the high-spin ground states in the previous study of Part I [J. Chem. Phys. 113, 4035 (2000)] by employing density-functional (DFT) methods using Becke’s and Becke’s three parameter exchanges with Lee–Yang–Parr correlation or Hartree–Fock (HF) molecular orbital and post HF approximations. However, it was found that further computations applying other DFT functionals should be carried out to clarify the level of approximations which appropriately describe the electronic structures of magnetic molecules. In this part II, we present details of numerical results concerning magnetic properties and electronic structures for m-phenylene molecules with three neutral and one cation radicals by spin-polarized density functional methods using variety of local and nonlocal functionals and unrestricted molecular orbital methods including Mo/ller–Plesset and c...

Heteroleptic [Bis(oxazoline)](dipyrrinato)zinc(II) Complexes: Bright and Circularly Polarized Luminescence from an Originally Achiral Dipyrrinato Ligand

Heteroleptic zinc(II) complexes synthesized using achiral dipyrrinato and chiral bis(oxazoline) ligands show bright fluorescence with quantum efficiencies of up to 0.70. The fluorescence originates from the (1)π-π* photoexcited state localized exclusively on the dipyrrinato ligand. Furthermore, the luminescence is circularly polarized despite the achirality of the dipyrrinato ligand. Single-crystal X-ray structure analysis discloses that the chiral bis(oxazoline) ligand undergoes intramolecular π-π stacking with the dipyrrinato ligand, inducing axial chirality in the dipyrrinato moiety.

Syntheses, structures and solid-state properties of MMX mixed-valence chains, [Ni(II/III)2(RCS2)4I]infinity (R = Et, n-Pr and n-Bu): evidence of a spin-Peierls transition.

The partial oxidation of [Ni(II/II)(2)(RCS(2))(4)] (R = Et (1), n-Pr (2), and n-Bu (3)) with iodine affords the MMX chain compounds [Ni(II/III)(2)(RCS(2))(4)I](infinity) (R = Et (4), n-Pr (5), and n-Bu (6)), respectively. The crystal structures of 4-6 consist of neutral one-dimensional (1-D) chains with a repeating -Ni-Ni-I- unit. The room-temperature (RT) structure of 4 indicates a charge-polarization (CP) state {-Ni((2.5-delta)+)-Ni((2.5+delta)+)-I(-)-Ni((2.5-delta)+)-Ni((2.5+delta)+)-I(-)- (delta << 0.5)} close to an averaged valence state judged by the Ni-I distances. In contrast, 5 and 6 exhibit a 3-fold periodicity of a -Ni-Ni-I- unit due to the disorder of the dithiocarboxylato ligands. Compounds 4-6 show typical semiconducting behavior and exhibit an intense sharp absorption band centered at 5400 cm(-1), which is attributed to a Mott-Hubbard gap due to a relatively large on-site Coulomb repulsion energy U of the nickel atoms. The high-temperature magnetic susceptibilities of 4-6 can be described by a 1-D Heisenberg antiferromagnetic chain model with |J|/k(B) ranging from 898(2) to 939(3) K. Compounds 4 and 5 undergo a spin-Peierls (SP) transition at relatively high T(sp) = 47 and 36 K, respectively, which are accompanied by superlattice reflections corresponding to a 2-fold -Ni-Ni-I- period below T(sp). By determining the superstructure of 4 at 26 K, we conclude that the valence-ordered state changes from the CP in the RT phase to the alternate charge-polarization (ACP) state of -Ni((2.5-delta)+)-Ni((2.5+delta)+)-I(-)-Ni((2.5+delta)+)-Ni((2.5-delta)+)-I(-)- in the SP phase. Such a spin-Peierls transition could not be observed for 6.

Theoretical study of H2O and O2 adsorption on Au small clusters

Hybrid Density functional calculations have been carried out for Au10, Au10-H2O, Au10-O2, and Au10-H2 O-O2 model clusters. The results show that all the Au10 clusters examined have a weak interaction with H2O and neutral and negatively charged Au10 clusters have a weak interaction with O2. Moreover, it is also found that the negative charge densities of O2 were greatly increased in the case of the coadsorption of O2 and H2O on the surface of the negatively charged Au10. These findings suggest that the presence of H2O enhances the activation of O2 on the surface of an Au cluster.