Stereoselective synthesis of cyclometalated iridium(III) complexes: characterization and photophysical properties

The stereoselective synthesis of a highly luminescent neutral Ir(III) complex comprising two bidentate chiral, cyclometalating phenylpyridine derivatives, and one acetylacetonate as ligands is described. The final complex and some intermediates were characterized by X-ray structural analysis, NMR-, CD-, and CPL-spectroscopy

Peculiar orientational disorder in 4-bromo-4′-nitrobiphenyl (BNBP) and 4-bromo-4′-cyanobiphenyl (BCNBP) leading to bipolar crystals

180° orientational disorder of molecular building blocks can lead to a peculiar spatial distribution of polar properties in molecular crystals. Here we present two examples [4-bromo-4′-nitrobiphenyl (BNBP) and 4-bromo-4′-cyanobiphenyl (BCNBP)] which develop into a bipolar final growth state. This means orientational disorder taking place at the crystal/nutrient interface produces domains of opposite average polarity for as-grown crystals. The spatial inhomogeneous distribution of polarity was investigated by scanning pyroelectric microscopy (SPEM), phase-sensitive second harmonic microscopy (PS-SHM) and selected volume X-ray diffraction (SVXD). As a result, the acceptor groups (NO2 or CN) are predominantly present at crystal surfaces. However, the stochastic process of polarity formation can be influenced by adding a symmetrical biphenyl to a growing system. For this case, Monte Carlo simulations predict an inverted net polarity compared with the growth of pure BNBP and BCNBP. SPEM results clearly demonstrate that 4,4′-dibromobiphenyl (DBBP) can invert the polarity for both crystals. Phenomena reported in this paper belong to the most striking processes seen for molecular crystals, demonstrated by a stochastic process giving rise to symmetry breaking. We encounter here further examples supporting the general thesis that monodomain polar molecular crystals for fundamental reasons cannot exist

Stereoselectivity in the formation of tris-diimine complexes of Fe(<small>II</small>), Ru(<small>II</small>), and Os(<small>II</small>) with a <i>C</i><small>₂</small>-symmetric chiral derivative of 2,2′-bipyridine

A C₂-symmetric enantiopure 4,5-bis(pinene)-2,2′-bipyridine ligand (–)-L was used to investigate the diastereoselectivity in the formation of [ML₃]²⁺ coordination species (M = Fe(II), Ru(II), Os(II), Zn(II), Cd(II), Cu(II), Ni(II)), and [ML₂Cl₂] (M = Ru(II), Os(II)). The X-ray structures of the [ML₃]²⁺ complexes were determined for Δ-[FeL₃](PF₆)₂, Δ-[RuL₃](PF₆)₂, Λ-[RuL₃](PF₆)₂, Δ-[OsL₃](PF₆)₂, and Λ-[OsL₃](TfO)₂. All of these compounds were also characterized by NMR, CD and UV/VIS absorption spectroscopy. The [FeL₃]²⁺ diastereoisomers were studied in equilibrated solutions at various temperatures and in several solvents. The [RuL₃]²⁺ complexes, which are thermally stable up to 200 °C, were photochemically equilibrated