Excited state localization and internuclear interactions in asymmetric ruthenium(II) and osmium(II) bpy/tpy based dinuclear compounds.

The synthesis of two asymmetric dinuclear complexes with the formula [M(bpy)(2)(bpt)Ru(tpy)Cl](2+), where M = Ru (1a), Os(2a); bpy = 2,2'-bipyridyl; Hbpt = 3,5-bis(pyridin-2-yl)1,2,4-triazole and tpy = 2,2',6',2''-terpyridine, is reported. The compounds obtained are characterized by mass spectrometry, (1)H NMR, UV/vis/NIR absorption, luminescence, and resonance Raman spectroscopy. Deuterium isotope labeling facilitates assignment of the (1)H NMR and resonance Raman spectra. The interaction between the two metal centers, mediated by the bridging 1,2,4-triazolato moiety in the mixed valent state, is assigned as type II based on the observation of metal to metal charge transfer absorption bands at 7090 and 5990 cm(-1) for 1a and 2a, respectively. The extent of localization of the emissive excited state was determined by transient resonance Raman and emission spectroscopy. Both 1a and 2a show phosphorescence at the same wavelengths; however, whereas for compound 1a the emission is based on the Ru(tpy)Cl- center, for 2a the emissive state is localized on the Os(bpy)(2)- unit. This indicates that also in the excited state there is efficient interaction between the two metal centers.

Synthesis of asymmetric supramolecular compounds using a Ni(0) catalysed homo-coupling approach.

The synthesis and characterisation of a series of dinuclear ruthenium and osmium polypyridyl metal complexes based on the bridging ligands [5-(5'-bipyridin-2',2''-yl)-3-(pyridin-2-yl)]-1,2,4-triazole (Hpytr-bipy), 2,2'-bis(pyridin-2''yl)-5,5'-bis(pyridin-3''-yl) (bipy-bipy) and 5,5'-bis(pyridin-2''-yl)-3,3'-bis(1,2,4-triazole) (Hpytr-Hpytr) are reported. The dinuclear complexes have been synthesised via a Ni(0) catalysed cross-coupling reaction from brominated precursors. With this approach a mixture of three products is obtained, which are separated by chromatographic methods. The compounds obtained are characterised by elemental analysis, (1)H NMR, absorption and emission spectroscopy. The synthetic approach developed offers a new route to asymmetric multinuclear supramolecular structures that is complimentary to the complexes as ligands/complexes as metal approaches.

Spectroelectrochemical properties of homo- and heteroleptic ruthenium and osmium binuclear complexes: intercomponent communication as a function of energy differences between HOMO levels of bridge and metal centres.

A series of binuclear ruthenium and osmium complexes [(bipy)(2)Ru(qpy)Ru(bipy)(2)](4+) (1), [(bipy)(2)Os(qpy)Os(bipy)(2)](4+) (2), [(bipy)(2)Ru(pytr-bipy)Ru(bipy)(2)](3+) (3), [(bipy)(2)Ru(pytr-bipy)Os(bipy)(2)](3+) (4), [(bipy)(2)Os(pytr-bipy)Ru(bipy)(2)](3+)(5) and [(bipy)(2)Os(bpbt)Os(bipy)(2)](2+) (6) {bipy = 2,2'-bipyridyl; qpy = 2,2':5',5'':2'',2'''-quaterpyridyl; pytr-bipy = 3-(2,2'-bipyrid-6-yl)-5-(pyrid-2-yl)-1,2,4-triazolato, and bpbt = 5,5'-bis-(pyrid-2''-yl)-3,3'-bis-1,2,4-triazolato} are reported. Analysis of the electrochemical data focuses on structural factors and on determining the extent of electronic communication between the metal centres in the mixed valence oxidation state. Intervalence charge transfer (IT) bands could be identified in the spectra of the complexes 4 and 6 only. Analysis of their spectroelectrochemical data leads to the conclusion that the IT is superexchange mediated through the HOMO of the bridging ligand.

A density functional theory study of the electronic properties of Os(II) and Os(III) complexes immobilized on Au(111).

We present a density functional theory (DFT) study of an osmium polypyridyl complex adsorbed on Au(111). The osmium polypyridyl complex [Os(bpy)2(P0P)Cl]n+ [bpy is 2,2'-bipyridine, P0P is 4,4'-bipyridine, n = 1 for osmium(II), and n = 2 for osmium(III)] is bound to the surface through the free nitrogen of the P0P ligand. The calculations illuminate electronic properties relevant to recent comprehensive characterization of this class of osmium complexes by electrochemistry and electrochemical scanning tunneling microscopy. The optimized structures for the compounds are in close agreement with crystallographic structures reported in the literature. Oxidation of the complex has little effect on these structural features, but there is a substantial reordering of the electronic energy levels with corresponding changes in the electron density. Significantly, the highest occupied molecular orbital shifts from the metal center to the P0P ligand. The surface is modeled by a cluster of 28 gold atoms and gives a good description of the effect of immobilization on the electronic properties of the complexes. The results show that the coupling between the immobilized complex and the gold surface involves electronic polarization at the adsorbate/substrate interface rather than the formation of a covalent bond. However, the cluster is too small to fully represent bulk gold with the result that, contrary to what is experimentally observed, the DFT calculation predicts that the gold surface is more easily oxidized than the osmium(II) complex.