Calculation of current densities using gauge-including atomic orbitals

A method for calculating the various components of the magnetically induced current-density tensor using gauge-including atomic orbitals is described. The method is formulated in the framework of analytical derivative theory, thus enabling implementation at the Hartree-Fock self-consistent-field (HF-SCF) as well as at electron-correlated levels. First-order induced current densities have been computed up to the coupled-cluster singles and doubles level (CCSD) augmented by a perturbative treatment of triple excitations [CCSD(T)] for carbon dioxide and benzene and up to the full coupled-cluster singles, doubles, and triples (CCSDT) level in the case of ozone. The applicability of the gauge including magnetically induced current method to larger molecules is demonstrated by computing first-order current densities for porphin and hexabenzocoronene at the HF-SCF and density-functional theory level. Furthermore, a scheme for obtaining quantitative values for the induced currents in a molecule via numerical integration over the current flow is presented. For benzene, a perpendicular magnetic field induces a (field dependent) ring current of 12.8 nA T(-1) at the HF-SCF level using a triple-zeta basis set augmented with polarization functions (TZP). At the CCSD(T)/TZP level the induced current was found to be 11.4 nA T(-1). Gauge invariance and its relation to charge-current conservation is discussed.     

Coordination Chemistry of Acrylamide 4. Crystal Structures and IR Spectroscopic Properties of Acrylamide Complexes with CoII,NiII, and ZnII nitrates

Acrylamide complexes of metal nitrates: [M(O‐OC(NH₂)CHCH₂)_n(H₂O)_m][NO₃]₂ (M = Co( 1 ), Ni( 2 ) (n = 6 and m = 0) and Zn( 3 ) (n = 4 and m = 2)) have been determined by using single crystal X‐ray diffraction analysis. All complexes crystallize in the triclinic space group . The structures of 1 and 2 represent octahedral species [M(AAm)₆]²⁺ (AAm = O‐OC(NH₂)CHCH₂ and M = Co or Ni) and uncoordinated nitrate ions. The structure of 3 involves the octahedral cation [Zn(AAm)₄(H₂O)₂]²⁺ in which the Zn²⁺ environment includes oxygen atoms of four acrylamide and two water molecules that are stabilized using ionic nitrate ions. The observations of the solid‐state IR spectroscopic vibrational frequencies of these acrylamide complexes are in agreement with the crystal structures.     

(2S,5S)-2,5-dibenzyl-1,4-dimethylpiperazine, a novel alkaloid from zanthoxylum arborescens

The isolation and structure determination of (2S,5S)-2,5-dibenzyl-1,4-dimethylpiperazine ($\text{1}$), a new alkaloid biogenetically related to L-phenylalanine diketopiperazine, is described.     

Synthesis and characterization of dinuclear ruthenium complexes covalently linked to Ru(II) tris-bipyridine: an approach to mimics of the donor side of photosystem II

To mimic the electron-donor side of photosystem II (PSII), three trinuclear ruthenium complexes (2, 2a, 2b) were synthesized. In these complexes, a mixed-valent dinuclear Ru2(II,III) moiety with one phenoxy and two acetato bridges is covalently linked to a Ru(II) tris-bipyridine photosensitizer. The properties and photoinduced electron/energy transfer of these complexes were studied. The results show that the Ru2(II,III) moieties in the complexes readily undergo reversible one-electron reduction and one-electron oxidation to give the Ru2(II,III) and Ru2(III,III) states, respectively. This could allow for photooxidation of the sensitizer part with an external acceptor and subsequent electron transfer from the dinuclear ruthenium moiety to regenerate the sensitizer. However, all trinuclear ruthenium complexes have a very short excited-state lifetime, in the range of a few nanoseconds to less than 100 ps. Studies by femtosecond time-resolved techniques suggest that a mixture of intramolecular energy and electron transfer between the dinuclear ruthenium moiety and the excited [Ru(bpy)3]2+ photosensitizer is responsible for the short lifetimes. This problem is overcome by anchoring the complexes with ester- or carboxyl-substituted bipyridine ligands (2a, 2b) to nanocrystalline TiO2, and the desired electron transfer from the excited state of the [Ru(bpy)3]2+ moiety to the conduction band of TiO2 followed by intramolecular electron transfer from the dinuclear Ru2(II,III) moiety to photogenerated Ru(III) was observed. The resulting long-lived Ru2(III,III) state decays on the millisecond timescale.     

Compensation of steric demand by cation-pi interactions,cobaltocenium cations as guests in tetraurea calix[4]arene dimers

The affinities of ferrocene (2) and the cobaltocenium cation (3+), which have roughly the same size and differ in their charge, towards the inner cavity of the dimeric capsule formed by tetraurea calix[4]arene (1) were studied in C2D4Cl2 solutions. While 3+, which occupies more than 75% of the internal volume of the dimer, is readily encapsulated this is not the case for 2. This is probably due to cation-pi interactions, which operate only between 3+ and the aromatic rings of the calix[4]arene dimer. We found that the affinity of the cobaltocenium cation is higher than that of the tropylium cation (4+) and is only 2-3 times less than that of the tetraethylammoniun cation (5+). From the variable temperature 1H NMR spectra of this capsule, the free energy of activation at 298 K (deltaGdouble dagger(298K)) for the reorientation of the hydrogen bonded belt between the two parts of the dimer could be determined by total line shape analysis for the aromatic protons of the calixarene. The value of 14.3 +/- 0.2 kcal mol(-1) for the dimeric capsules of 3+ PF6- is very similar to the free activation energy found for dimeric capsules of 1 with 4+ PF6- and 5+ PF6- in C2D4Cl2. It becomes significantly lower, if PF6- is replaced by BF4-. We also found that ten times more DMSO is needed to disrupt the capsule 1 x 3+ x 1 than the corresponding 1 x 1 dimer containing benzene as guest. This demonstrates again the importance of the cation-pi interactions for the stability of such hydrogen-bonded dimeric capsules.     

Self-assembly of tetrahedral and trigonal antiprismatic clusters [Fe4(L4)4] and [Fe6(L5)6] on the basis of trigonal tris-bidentate chelators

In a one-pot reaction, the tetranuclear iron chelate complex [Fe4(L4)4] 6 was generated from benzene-1,3,5-tricarboxylic acid trichloride (4), bis-tert-butyl malonate (5a), methyllithium, and iron(II) dichloride under aerobic conditions. Alternatively, hexanuclear iron chelate complex [Fe(L5)6] 7 was formed starting from bis-para-tolyl malonate (5b) by employing identical reaction conditions to those applied for the synthesis of 6. The clusters 6 and 7 are present as racemic mixtures of homoconfigurational (delta,delta,delta,delta)/(lambda,lambda,lambda,lambda)-fac or (delta,delta,delta,delta,delta,delta)/(lambda,lambda,lambda,lambda,lambda,lambda)-fac stereoisomers. The structures of 6 and 7 were unequivocally resolved by single-crystal X-ray analyses. The all-iron(III) character of 6 and 7 was determined by M?ssbauer spectroscopy.     

Preparation and characterization of fibres from a thermotropic liquid crystal polyester with non-coplanar biphenylene units

Abstract

Fibres were prepared from the nematic melt of poly(2,2′-dimethyl-4,4′-biphenylene phenylterephthalate). The phenyl substitution in the terephthalic acid moiety in combination with the non-coplanar biphenyl moiety prevent crystallization of this thermotropic polyester. Oriented fibres were prepared by two different methods. Similarly to other thermotropic liquid crystal polymer fibres, chain orientation can be achieved by an elongational flow in a down draw process. This polyester also allows tensile deformation of the spun fibres around the glass transition temperature. In both routes similar degrees of orientation and mechanical properties were obtained. Tensile moduli in the order of 40–45 GPa and tensile strengths up to 550–650 MPa were obtained. The orientation function values were determined to be in the order of 0·8–0·9. A comparison with other unsubstituted thermotropic liquid crystal polyesters at the same level of orientation revealed that the moduli are the same, although the substituents increase the chain diameter. This result may be attributed to an increase of the apparent shear modulus due to an interlocking mechanism of the rigid lateral substituents.