Self-assembly of a metal-ion-bound monolayer of trigonal connectors on mercury: an electrochemical Langmuir trough

Coordination nanosheets (CONASHs): strategies, structures and functions

Nanosheets, which are two-dimensional polymeric materials, remain among the most actively researched areas of chemistry and physics this decade. Generally, nanosheets are inorganic materials created from bulk crystalline layered materials and have fascinating properties and functionalities. An emerging alternative is molecule-based nanosheets containing organic molecular components. Molecule-based nanosheets offer great diversity because their molecular, ionic, and atomic constituents can be selected and combined to produce a wide variety of nanosheets. The present article focuses on coordination nanosheets (CONASHs), a class of molecule-based nanosheets comprising organic ligand molecules and metal ions/atoms in a framework linked with coordination bonds. Following the Introduction, Section 2 describes CONASHs, including their definition, design, synthetic procedures, and characterisation techniques. Section 3 introduces various examples of CONASHs, and Section 4 explores their functionality and possible applications. Section 5 describes an outlook for the research field of CONASHs.

Inclusion compound based approach to forming arrays of artificial dipolar molecular rotors: a search for optimal rotor structures

Hexagonal tris(o-phenylenedioxy)cyclotriphosphazene (TPP) is used as ahost for organizing dipolar molecular rotor guests into regular trigonal arrays. Inclusion of molecular rotors with transversely dipolar rotators into TPP channels is followed by solid-state nuclear magnetic resonance, diifferential scanning calorimetry, X-ray diffraction, and dielectric spectroscopy. The more polar of the two rotors does not form an inclusion. The second rotor forms two different inclusions differing in crystallite size and the rotational barriers.

Friction in carborane-based molecular rotors driven by gas flow or electric field: classical molecular dynamics

Friction in molecular rotors is examined by classical molecular dynamics simulations for grid-mounted azimuthal dipolar molecular rotors, whose rotation is either allowed to decay freely or is driven at GHz frequencies by a flow of rare gas or by a rotating electric field. The rotating parts (rotators) are propeller-shaped. Their two to six blades consist of condensed aromatic rings and are attached to a deltahedral carborane hub, whose antipodal carbons carry [n]staffane axles mounted on a square molecular grid. The dynamic friction constant η has been derived in several independent ways with similar results. Analysis of free rotation decay yields η as a continuous exponentially decreasing function of rotor frequency. The calculated dependence of friction torque on frequency resembles the classical macroscopic Stribeck curve. Its relation to rotational potential energy barriers and the key role of the rate of intramolecular vibrational redistribution (IVR) of energy and angular momentum from rotator rotation to other modes are considered in two limiting regimes. (i) In the strongly overdamped regime, rotation is much slower than IVR, and effective friction can be expressed through potential barriers to rotation. (ii) In the strongly underdamped regime, rotation is much faster than IVR, whose rate then determines friction.

Alkyl-thiol Langmuir films on the surface of liquid mercury

The coverage dependent phase behavior of monolayers of alkyl thiols (CH3(CH2)(n-1)SH, denoted as CnSH) on mercury was studied for chain lengths 9 <or= n <or= 22, using surface tensiometry and surface-specific X-ray scattering methods. At low coverage, a disordered single layer of surface-parallel molecules is found for all n. At high coverage, a monolayer of standing-up molecules is formed, exhibiting well-ordered phases, the structure of which is n- and coverage-dependent. The molecular chains pack in a centered rectangular unit cell, with an approximately 27 degrees tilt from the surface normal toward nearest neighbors. The strong sulfur-mercury bond induces a noncentered unit cell for the headgroups, incorporating one mercury atom per two thiol molecules. The small but significant differences in structure of these films on gold and on mercury are discussed and assigned to the different structure of the subphase: long-range-ordered crystal for gold and short-range-ordered liquid for mercury.

Adsorption of tentacled tetragonal star connectors, C4R4-Co-C5(HgX)5, on mercury

For future use in self-assembly of surface structures, the adsorption on the surface of mercury of a series of tetraphenylcyclobutadienecyclopentadienylcobalt double-decker sandwich complexes with five mercury and sulfur containing "tentacles" on the cyclopentadienyl deck has been examined by combined electrochemical and Langmuir trough techniques.

Dipolar and Nonpolar Altitudinal Molecular Rotors Mounted on an Au(111) Surface

We describe the preparation of a compound whose molecules consist of two metal sandwich stands carrying tentacles with affinity to metal surfaces and holding an axle that carries a dipolar or a nonpolar rotator. The dipolar rotor exists as three pairs of enantiomers, rapidly interconverting at room temperature. When mounted on a gold surface, each molecule represents a chiral altitudinal rotor, with the rotator axle parallel to the surface. The surface-mounted rotor molecules are characterized by several spectroscopic and imaging techniques. At any one time, in about one-third of the dipolar rotors the rotator is free to turn and the direction of its dipole can be flipped by the electric field applied by an STM tip, as revealed by differential barrier height imaging. Molecular dynamics calculations suggest that electric field normal to the surface causes members of one pair of enantiomers to rotate unidirectionally.

Molecular Dynamics Simulation of an Electric Field Driven Dipolar Molecular Rotor Attached to a Quartz Glass Surface

Molecular dynamics simulations of the response of a dipolar azimuthal 3-chloroprop-1-ynyl rotor mounted on the surface of quartz glass to a rotating electric field were performed. The rotor motion was classified as synchronous, asynchronous, random, or hindered, based on the value of the average lag of the rotor behind the field and a comparison of the intrinsic rotational barrier V(b) with kT. A phase diagram of rotor behavior was deduced at 10, 300, and 500 K as a function of field strength and frequency. A simple model for the rotor motion was developed, containing the driving force, the temperature, the height of the torsional barrier, and the friction constant of the rotor. Defining E(bo) to be the electric field strength necessary to get rotational response from the rotor ("breakoff field") and mu to be the rotor dipole moment component in the plane of rotation, we find that E(bo) is frequency independent when 2 microE(bo) is less than either V(b) or kT (the driving force needs to overcome the more important of the two, the intrinsic barrier or random thermal motion). At higher frequencies, E(bo) is a quadratic function of the frequency and the driving force fights friction, which is dictated by intramolecular vibrational redistribution (IVR) from the pumped rotational mode to all others. Fitting the simple model to simulation data, we derived a friction constant of 0.26 ps eV x (nu - 0.5)/THz between 500 and 1000 GHz.

Supramolecular assembly at interfaces: formation of an extended two-dimensional coordinate covalent square grid network at the air-water interface

Reaction of a Langmuir monolayer of an amphiphilic pentacyanoferrate(3+) complex with Ni(2+) ions from the subphase results in the formation of a two-dimensional iron-nickel cyanide-bridged network at the air-water interface. The network can be transferred to various supports to form monolayer or multilayer lamellar films by the Langmuir-Blodgett (LB) technique. The same network does not form from homogeneous reaction conditions. Therefore, the results demonstrate the potential utility of an interface as a structure director in the assembly of low dimensional coordinate covalent network solids. Characterization of the LB film extended networks by X-ray photoelectron spectroscopy (XPS), FT-IR spectroscopy, SQUID magnetometry, X-ray absorption fine structure (XAFS), and grazing incidence synchrotron X-ray diffraction (GIXD) revealed a face-centered square grid structure with an average domain size of 3600 A(2). Magnetic measurements indicated that the network undergoes a transition to a ferromagnetic state below a T(c) of 8 K.