Iron(II) and zinc(II) monohelical binaphthyl salen complexes

A new chiral binaphthyl salen ligand with rigid polyaromatic sidearms gives monohelical complexes (Fe(II) and Zn(II)) of predetermined handedness.     

Iron(II) and zinc(II) monohelical binaphthyl-salen complexes with overlapping benz[a]anthryl sidearms

The synthesis of the polyaromatic aldehyde 1-hydroxybenz[a]anthracene-2-carboxaldehyde is reported via a seven step protocol from 9,10-dihydroanthracene, with an overall yield of 30%. Two equivalents of the aldehyde are condensed with (R)-1,1'-binaphthyl-2,2'-diamine to produce a new binaphthyl-salen ligand, which is subsequently complexed to iron(II) and zinc(II) ions. The ligand and complexes are characterized by single-crystal X-ray crystallography. The complexes have distinct helical structures with overlapping benz[a]anthryl sidearms, and only M-helices are observed. The ligand and complexes are further characterized by solution (1)H and (13)C NMR spectroscopy as well as UV-visible and ECD spectroscopies. These studies indicate that there is a single component in solution, consistent with the solid state characterization.     

Synthesis of symmetric bis(imidazole-4,5-dicarboxamides) substituted with amino acids

A series of symmetric bis(imidazole-4,5-dicarboxamides) (bis-I45DCs) were prepared with amino acid esters and a variety of linker groups. The critical pyrazine intermediates, substituted with amino acid esters, were synthesized by stoichiometric control of the amino acid ester, even though primary alkanamines, in comparison, generally offer less selectivity for this reaction. Diamines are added to subsequently react with and open the remaining acyl imidazole bonds in the pyrazine intermediates and thereby yield the bis-I45DCs.     

Electrical transport and magnetic ordering in R 2Ti3Ge4 (R=Dy, Ho and Er) compounds

New R ₂Ti₃Ge₄ (R=Dy, Ho and Er) intermetallic compounds have been synthesized and characterized by X-ray diffraction and low temperature ac magnetic susceptibility, electrical resistivity and thermoelectric power measurements were carried out. The compounds crystallize in the parent, Sm₅Ge₄-type orthorhombic structure (space group Pnma) and lanthanide contraction is observed as one moves along the rare-earth series. The changeover from paramagnetic to antiferromagnetic phase happens at low temperatures and the ordering temperature scales with the de Gennes factor. The electrical resistivity is metallic with a negative curvature above 100 K. Thermopower displays a weak maximum at temperatures less than 50 K signifying the possible phonon and magnon drag effects.     

Elastic properties of the Ta–V system: bcc Ta0.33V0.67 and C15 TaV2

Resonant ultrasound spectroscopy was used to measure the elastic constants of bcc Ta_0.33V_0.67 over the temperature range 3.5–300?K; the results were compared to earlier measurements on C15 TaV₂. The temperature dependence of the polycrystalline shear modulus is completely different in the two phases; that of the bcc phase decreases with temperature whereas that of the C15 phases increases in an anomalous fashion. This difference is consistent with a model involving doubly-degenerate levels at the X point of the Brillouin zone in the C15 phase with the Fermi level lying near the doubly degenerate level. This model accounted for the unusual behaviour of the C15 phase. Debye temperatures were determined from the ultrasonic measurements: 295?K for the C15 phase and 315?K for the bcc phase.     

An improved method for the synthesis of dissymmetric N,N'-disubstituted imidazole-4,5-dicarboxamides

Symmetrically and dissymmetrically disubstituted imidazole-4,5-dicarboxamides (I45DCs) have diverse bioactivities and therefore represent useful small molecules for lead structure identification in drug discovery. For this reason, an improved synthesis was developed as a first step in the preparation of greater numbers of analogues. The method involves the transformation of imidazole-4,5-dicarboxylic acid into dissymmetrically disubstituted I45DCs in four steps and in a minimum yield of 51%. This reflects an overall reduction of one synthetic step and a greater than 30% improvement in yield over the known method.     

Dinuclear zinc(II) complexes of symmetric Schiff-base ligands with extended quinoline sidearms

The synthesis of two 2-formylquinolines is reported via the Skraup method followed by SeO(2) oxidation. Each aldehyde is condensed with (1R,2R)-diaminocyclohexane and (R)-BINAM, yielding four enantiomerically-pure bis(imine-quinoline) ligands. The neutral ligands are reacted with ZnCl(2) to give complexes with bis(bidentate) coordination of ZnCl(2) units. X-Ray structural characterization of three complexes shows them to have a single-stranded helical motif, with M helicity, except in one case where a 1:1 mixture of M and P helices is seen. The ligands and complexes are further characterized spectroscopically by solution (1)H and (13)C NMR, UV-vis and ECD.     

Monohelical Iron(II) and Zinc(II) complexes of a (1R,2R)-cyclohexyl salen ligand with benz[a]anthryl sidearms

An enantiomerically pure C2-symmetric salen ligand with benz[a]anthracene siderams produces M helical complexes (FeII and ZnII) in solution. Interconversion to produce a 1:1 mixture of helical conformers in the solid state is possible, despite overlapped sidearms.