Corey Seward

Luminescent Star-Shaped Zinc(II) and Platinum(II) Complexes Based on Star-Shaped 2,2′-Dipyridylamino-Derived Ligands

New ZnII and PtII complexes of the star-shaped ligands 2,4,6-tris(2,2′-dipyridylamino)-1,3,5-triazine (tdat), 1,3,5-tris(2,2′-dipyridylamino)benzene (tdab), 2,4,6-tris[p-(2,2′-dipyridylamino)phenyl]-1,3,5-triazine (tdapt) and 1,3,5-tris[p-(2,2′-dipyridylamino)phenyl]benzene (tdapb) have been synthesized and characterized. 1:1, 1:2 and 1:3 (ligand vs. the number of Zn atoms) ZnII complexes of the tdat ligand have been identified. The 1:1 and 1:2 ZnII complexes of tdat are dynamic in solution. For the tdab, tdapt and tdapb ligands, only 1:3 complexes of PtII and ZnII have been isolated. Single-crystal X-ray diffraction analyses have been carried out for some of these new complexes, which revealed that there is a distinct difference in the arrangement of star-shaped ligands in the complexes of ZnII and those of PtII. The PtII complexes of tdat and tdab adopt an unusual “bowl” shape and stack in a “head-to-tail” fashion in the crystal lattice. In contrast, the corresponding ZnII complexes do not have a “bowl” shape. The difference between the ZnII complexes and the PtII complexes can be attributed to the different coordination geometry preferred by the two metal ions. The ZnII complex of tdapb displays several crystal motifs, two of which contain benzene molecules in the crystal lattices. All complexes are luminescent in the blue region, attributable to ligand-based π ⇄ π* transitions. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

1-D Chain and 3-D grid green luminescent terbium(III) coordination polymers: {Tb(O2CPh)3(CH3OH)2(H2O)}n and {Tb2(O2CPh)6(4,4′-bipy)}n

Two lanthanide coordination polymers {Tb(O2CPh)3(CH3OH)2(H2O)}n1 and {Tb2(O2CPh)6(4,4′-bipy)}n2 have been identified and isolated from a methanol solution A of Tb(OAc)3·4H2O, benzoic acid and 4,4′-bipyridine in a 1∶3∶2 ratio. Their structures have been determined by single-crystal X-ray diffraction analyses, which revealed that 1 has a covalent, 1-D linear chain structure while 2 has a covalent, 3-D grid architecture. When irradiated by UV light, 1 and 2 are brightly green luminescent, facilitated by a ligand (benzoate or 4,4′-bipy) to TbIII inter-system energy transfer process. Solution A has been found to be suitable for the formation of transparent films containing terbium(III) ions by spin coating. The polymeric structures of 1 and 2 and their co-existence are believed to be responsible for the good film forming property of solution A. The amorphous film produced by using solution A and spin coating has a green emission similar to those of 1 and 2. p

STARBURST COMPLEXES OF DI-2-PYRIDYLAMINE DERIVATIVES WITH A BENZENE OR 1,3,5-TRIAZINE CORE

ABSTRACT Luminescent starburst organic molecules have attracted much recent attention primarily because of their potential applications in organic light emitting diodes. Starburst organic molecules that are functionalized by donor groups such as pyridyl are especially interesting because they can bind to metal ions to form unusual structures and supramolecular assemblies in addition to the introduction of redox properties and catalytic capability associated with the metal ions. This review focuses on starburst molecules that contain 2,2′-dipyridylamino groups with a C 3 symmetry. The smallest members of this group of starburst molecules involve a central benzene core or a 1,3,5-triazine core which are covered in this review. Larger starburst molecules that involve 1,3,5-triphenylbenzene, 1,3,5-tris(biphenyl)benzene, 2,4,6-triphenyltriazine or 2,4,6-tris(biphenyl)triazine as the central core are not discussed in the present review. The structural variation and luminescent properties of various metal complexes involving the small starburst ligands are described.

New red–orange phosphorescent/electroluminescent cycloplatinated complexes of 2,6-bis(2′-indolyl)pyridine

Three novel cyclometalated complexes of 2,6-bis(2′-indolyl)pyridine (H2BIP), Pd(BIP)(Py) (Py = pyridine) (1), Pt(BIP)(SMe2) (2) and Pt(BIP)(Py) (3) have been synthesized and characterized structurally. The Pd and Pt centers in these compounds are four-coordinate with a square planar geometry. The BIP ligand acts as a tridentate chelate to the metal center, and the dimethyl sulfide and the pyridine ligand bind to the metal center as terminal ligands. Compound 1 has no luminescence. Compounds 2 and 3 display bright orange luminescence either at 77 K in a frozen CH2Cl2 solution or at ambient temperature in a polymer matrix (e.g. poly(carbonate) or PVK). The emission maxima for 2 and 3 in the frozen CH2Cl2 solution are at λ = 572 and 589 nm, respectively. The emission spectra of 2 and 3 in the polymer matrix are very similar with λmax = 585 nm. The luminescence of 2 and 3 is phosphorescent as supported by the emission lifetimes of 2 (94(1) μs in CH2Cl2 at 77 K, 22.1(1) μs in poly(carbonate) at 298 K) and 3 (44(1) μs in CH2Cl2 at 77 K, 19(1) μs in poly(carbonate) at 298 K). Based on the luminescence properties of the free ligand and the results of molecular orbital calculations, we propose that the luminescence of 2 and 3 is most likely due to a π → π* transition with a significant dπ orbital contribution from the Pt(II) center to the π level. Electroluminescent devices using compound 3 as the emitter and PVK as the host and hole transport material have been fabricated successfully.

Chromium Compounds with CO or Isocyanides

A review with 684 references covering the period 1993–2004 summarising the syntheses, structures and reactivity of molecules possessing a chromium carbonyl or chromium isonitrile linkage. The major topics discussed are complexes in which there is a chromium–main group element bond, and arene chromium tricarbonyl complexes with emphasis on the stereochemical and electronic effects of complexation on the chemistry of the arene. Recent work on chromium hydrides and on (cyclopentadienyl)Cr(CO)3 radicals and the formation of fulvalene complexes is also discussed. The use of carbene complexes as precursors to polycyclic aromatics is summarised, and the interconversion of chromium isonitriles and their isomeric nitrogen-stabilised Fischer-type carbenes is outlined. Potential applications such as chromium-containing conducting polymers, materials with novel non-linear optical properties, biological labelling, and molecular machines are discussed.