Two Polymorphs of (Anilinium)(18-Crown-6)[Ni(dmit)2]: Structure and Magnetic Properties

Two polymorphs of monovalent [Ni(dmit)₂]⁻ (dmit²⁻=2-thioxo-1,3-dithiole-4,5-dithiolate) crystals A and B, (anilinium)(18-crown-6)[Ni(dmit)₂], were prepared, and the structure and magnetic properties were investigated. In these crystals, the [Ni(dmit)₂]⁻ molecules form dimers, which arranged into chains between the supramolecular cation structure (anilinium)(18-crown-6). In crystal A, supramolecular cation formed a regular stack, inducing ladder structure of [Ni(dmit)₂], whose magnetism had been well fitted by spin ladder equation with the spin gap of Δ=190 K. Crystal B is ca. 3% more densely packed compared to crystal A. Due to the dense packing, supramolecular cation stack is distorted, which prevented the intermolecular interaction between [Ni(dmit)₂]⁻ dimers in direction corresponds to the ladder-leg direction in crystal A. Reflecting the [Ni(dmit)₂]⁻ arrangement, crystal B showed a temperature dependence of magnetic susceptibility well reproduced by the singlet-triplet thermal activation model, whose antiferromagnetic exchange interaction (2J) was 140 K.     

Proton Conduction at High Temperature in High-Symmetry Hydrogen-Bonded Molecular Crystals of RuIII Complexes with Six Imidazole-Imidazolate Ligands

A new H-bonded crystal [Ru^III(Him)₃(Im)₃] with three imidazole (Him) and three imidazolate (Im⁻) groups was prepared to obtain a higher-temperature proton conductor than a Nafion membrane with water driving. The crystal is constructed by complementary N−H⋅⋅⋅N H-bonds between the Ru^III complexes and has a rare Icy-c* cubic network topology with a twofold interpenetration without crystal anisotropy. The crystals show a proton conductivity of 3.08×10⁻⁵ S cm⁻¹ at 450 K and a faster conductivity than those formed by only HIms. The high proton conductivity is attributed to not only molecular rotations and hopping motions of HIm frameworks that are activated at ∼113 K, but also isotropic whole-molecule rotation of [Ru^III(Him)₃(Im)₃] at temperatures greater than 420 K. The latter rotation was confirmed by solid-state ²H NMR spectroscopy; probable proton conduction routes were predicted and theoretically considered.     

Novel Method for the Fabrication of a Charge‐Transfer Complex Crystal by Photoirradiation

A novel method for the fabrication of a charge‐transfer complex crystal was developed. Photoirradiation of a solution of TPP[Co(tbp)(CN)₂] and TPP[Co(Pc)(CN)₂] (tbp=tetrabenzoporphyrin, Pc=phthalocyanine, TPP=tetraphenylphosphonium) gave a molecular conducting crystal of a charge‐transfer complex TPP[Co(tbp)(CN)₂]₂, which was produced by the process in which the photoexcited electron in tbp was transferred from the LUMO of tbp to that of Pc.     

Electrical Network of Single‐Crystalline Metal Oxide Nanoclusters Wired by π‐Molecules

In a mixed‐valence polyoxometalate, electrons are usually delocalized within the cluster anion because of low level of inter‐cluster interaction. Herein, we report the structure and electrical properties of a single crystal in which mixed‐valence polyoxometalates were electrically wired by cationic π‐molecules of tetrathiafulvalene substituted with pyridinium. Electron‐transport characteristics are suggested to represent electron hopping through strong interactions between cluster and cationic π‐molecules.     

An obstruction to the positivity of relative Yamabe invariants

For a supergroup , we describe an obstruction to the existence of positive scalar curvature metrics with minimal boundary condition on a compact n-dimensional -manifold W with nonempty boundary M, , in terms of the bordism class [M] in the Stolz obstruction group associated to [St2]. In par ticular, when W is a 5-dimensional spin manifold and the -invariant of a connected component of M is nonzero, we prove that W does not admit a positive scalar curvature metric with minimal boundary condition. Received: 4 July 2001; in final form: 5 February 2002 / Published online: 8 November 2002 RID="*" ID="*" Partially supported by the Grants-in-Aid for Scientific Research (C), Japan Society for the Promotion of Science, No. 11640070.     

Yamabe metrics on cylindrical manifolds

We study a particular class of open manifolds. In the category of Riemannian manifolds these are complete manifolds with cylindrical ends. We give a natural setting for the conformal geometry on such manifolds including an appropriate notion of the cylindrical Yamabe constant/invariant. This leads to a corresponding version of the Yamabe problem on cylindrical manifolds. We find a positive solution to this Yamabe problem: we prove the existence of minimizing metrics and analyze their singularities near infinity. These singularities turn out to be of very particular type: either almost conical or almost cuspsingularities. We describe the supremum case, i.e., when the cylindrical Yamabe constant is equal to the Yamabe invariant of the sphere. We prove that in this case such a cylindrical manifold coincides conformally with the standard sphere punctured at a finite number of points. In the course of studying the supremum case, we establish a Positive Mass Theorem for specific asymptotically flat manifolds with two almost conical singularities. As a by-product, we revisit known results on surgery and the Yamabe invariant. Submitted: Submitted: August 2001. Revision: January 2003 RID="*" ID="*"Partially supported by the Grants-in-Aid for Scientific Research (C), Japan Society for the Promotion of Science, No. 14540072.     

Semiumbilic points for minimal surfaces in Euclidean 4-space

We show that locally conformally flat gradient Ricci solitons, possibly incomplete, are locally isometric to a warped product of an interval and a space form. Consequently, we get that complete gradient shrinking and steady Ricci solitons with vanishing Weyl tensor are rotationally symmetric, from which their classification follows.     

Exploring the thermochromism of sulfite-embedded polyoxometalate capsules

The Dawson-type polyanion [α-Mo(18)O(54)(SO(3))(2)](4-), with two SO(3)(2-) templates embedded inside a polyoxomolybdate(vi) cage, exhibits thermochromism over an exceptionally wide temperature range (～500 K). The temperature dependence of the cluster structure, established from X-ray crystallography, IR and Raman spectroscopy and DFT calculations, is related to a decreasing HOMO-LUMO gap in the near UV with increasing temperature. We postulate this is due to geometrical changes that affect both the occupied and unoccupied frontier molecular orbitals of this cluster anion.