Azadipyrromethene cyclometalation in neutral Ru(II) complexes: photosensitizers with extended near-infrared absorption for solar energy conversion applications.

In the on-going quest to harvest near-infrared (NIR) photons for energy conversion applications, a novel family of neutral ruthenium(ii) sensitizers has been developed by cyclometalation of an azadipyrromethene chromophore. These rare examples of neutral ruthenium complexes based on polypyridine ligands exhibit an impressive panchromaticity achieved by the cyclometalation strategy, with strong light absorption in the 600-800 nm range that tails beyond 1100 nm in the terpyridine-based adducts. Evaluation of the potential for Dye-Sensitized Solar Cells (DSSC) and Organic Photovoltaic (OPV) applications is made through rationalization of the structure-property relationship by spectroscopic, electrochemical, X-ray structural and computational modelization investigations. Spectroscopic evidence for photo-induced charge injection into the conduction band of TiO2 is also provided.

Two fac-tricarbonylrhenium(I) azadipyrromethene (ADPM) complexes: ligand-substitution effect on crystal structure.

The crystal structures of fac-(acetonitrile-κN)(2-{[3,5-bis(4-methoxyphenyl)-2H-pyrrol-2-ylidene-κN(1)]amino}-3,5-bis(4-methoxyphenyl)-1H-pyrrol-1-ido-κN(1))tricarbonylrhenium(I)-hexane-acetonitrile (2/1/2), [Re(C36H30N3O4)(CH3CN)(CO)3]·0.5C6H14·CH3CN, (2), and fac-(2-{[3,5-bis(4-methoxyphenyl)-2H-pyrrol-2-ylidene-κN(1)]amino}-3,5-bis(4-methoxyphenyl)-1H-pyrrol-1-ido-κN(1))tricarbonyl(dimethyl sulfoxide-κO)rhenium(I), [Re(C36H30N3O4)(C2H6OS)(CO)3], (3), at 150 K are reported. Both complexes display a distorted octahedral geometry, with a fac-Re(CO)3 arrangement and one azadipyrromethene (ADPM) chelating ligand in the equatorial position. One solvent molecule completes the coordination sphere of the Re(I) centre in the remaining axial position. The ADPM ligand shows high flexibility upon coordination, while retaining its π-delocalized nature. Bond length and angle analyses indicate that the differences in the geometry around the Re(I) centre in (2) and (3), and those found in three reported fac-Re(CO)3-ADPM complexes, are dictated mainly by steric factors and crystal packing. Both structures display intramolecular C-H...N hydrogen bonding. Intermolecular interactions of the Csp(2)-H...π and Csp(2)-H...O(carbonyl) types link the discrete monomers into extended chains.

Red-emitting [Ru(bpy)2(N-N)]2+ photosensitizers: emission from a ruthenium(II) to 2,2'-bipyridine (3)MLCT state in the presence of neutral ancillary "super donor" ligands.

The synthesis and characterization of a novel family of [Ru(II)(bpy)2(N-N)](PF6)2 (bpy = 2,2'-bypyridine) complexes are reported, where N-N = pyridine/pyrimidine/pyrazine functionalized in different positions with the electron-donating bicyclic hexahydropyrimidopyrimidine (hpp) unit. A series of bidentate ligands 1a-5a were synthesized in good to high yields (55-96%). The corresponding complexes 1b, 2b, and 5b were prepared in n-butanol, while complexes 3b and 4b were prepared in a mixture of n-butanol and water (1/1, v/v) in modest to good yields (23-76%). Both ligand and complex structures were fully characterized by a variety of techniques, including X-ray crystallography. In cyclic voltammetric studies, all the complexes exhibit a Ru(III/II) couple, which is ∼500 mV less positive than the Ru(III/II) couple in Ru(bpy)3(2+). The (1)MLCT and (3)MLCT states of all of the complexes (530-560 nm/732-745 nm) are shifted bathochromically in comparison to those of Ru(bpy)3(2+) (450 nm/620 nm). These values are in good agreement with DFT and TD-DFT calculations.

A new ring-like arrangement of vanadyl(IV) groups bridged by monodentate alkoxides: cyclo-decakis(µ-cyclohexylmethanolato)pentakis[oxidovanadium(IV)].

The pentanuclear title compound, [V(5)(C(7)H(13)O)(10)O(5)], has a metal-oxygen core that consists of five vanadyl(IV) centres bridged by the O atoms of cyclohexylmethanolate ligands. This particular ring topology is new to oxovanadium(IV) chemistry and resembles the structure proposed for [V(5)O(15)](5-) on the basis of (51)V NMR studies in aqueous solution. The bulky cyclohexylmethanolate ligands adopt chair-like conformations and project outwards from the central cyclic core. The title compound crystallizes in a centrosymmetric triclinic unit cell, which contains four independent but chemically identical molecules in the asymmetric unit. The crystal structure is devoid of any significant intermolecular interactions.

Azadipyrromethene dye derivatives in coordination chemistry: the structure-property relationship in homoleptic metal(II) complexes.

As a chromophore closely related to dipyrromethene (DPM), the azadipyrromethene (ADPM) family has attracted much interest in the life sciences and optoelectronic fields. A high-yielding microwave-assisted synthesis is reported for new homoleptic complexes of cobalt(II), nickel(II), copper(II) and zinc(II) based on the tetrakis(p-methoxyphenyl)azadipyrromethene ligand 1b. These complexes are compared with other homoleptic complexes of the same metal(II) series based on the tetraphenylazadipyrromethene 1a and also with related BF2(+) chelates (Aza-BODIPYs 6a and 6b) for a better understanding of trends arising from substitution of the chelate and/or the electron-donating effect of the p-methoxy substituents. The electrochemical behavior of the new compounds 2b, 3b, and 5b in dichloromethane revealed two pseudoreversible reductions (2b, -1.09 and -1.25 V vs SCE; 3b, -1.05 and -1.29 V; 5b, -1.13 and -1.25 V) followed by a third irreversible process (2b, -1.78 V; 3b, -1.80 V; 5b, -1.77 V) along with two pseudoreversible oxidations (2b, 0.55 and 0.80 V; 3b, 0.56 and 0.80 V; 5b, 0.55 and 0.80 V) followed by two closely spaced irreversible processes (2b, 1.21 and 1.27 V; 3b, 1.21 and 1.28 V; 5b, 1.22 and 1.25 V). On its side, copper(II) homoleptic complex 4b revealed only one pseudoreversible reduction at -0.59 V followed by three irreversible processes at -0.95, -1.54, and -1.74 V, respectively. The oxidation behavior of this complex exhibited two pseudoreversible processes (0.55 and 0.82 V) and two irreversible processes (1.19 and 1.25 V). The redox processes are assigned and discussed in relation to their photophysical properties. X-ray structures for 1b and related copper(II) complex 2b are also discussed.

Supramolecular interactions in a copper(II) 4'-(4-bromophenyl)-2,2':6',2''-terpyridine complex.

The title compound, [4'-(4-bromophenyl)-2,2':6',2''-terpyridine]chlorido(trifluoromethanesulfonato)copper(II), [Cu(CF(3)O(3)S)Cl(C(21)H(14)BrN(3))], is a new copper complex containing a polypyridyl-based ligand. The Cu(II) centre is five-coordinated in a square-pyramidal manner by one substituted 2,2':6',2''-terpyridine ligand, one chloride ligand and a coordinated trifluoromethanesulfonate anion. The Cu-N bond lengths differ by 0.1 Å for the peripheral and central pyridine rings [2.032 (2) (mean) and 1.9345 (15) Å, respectively]. The presence of the trifluoromethanesulfonate anion coordinated to the metal centre allows Br···F halogen-halogen interactions, giving rise to the formation of a dimer about an inversion centre. This work also demonstrates that the rigidity of the ligand allows the formation of other types of nonclassical interactions (C-H···Cl and C-H···O), yielding a three-dimensional network.

Changing the role of 2,2'-bipyridine from secondary ligand to protagonist in [Ru(bpy)2(N-N)]2+ complexes: low-energy, red emission from a ruthenium(II)-to-2,2'-bipyridine 3MLCT state.

Two new bidentate ligands (1 and 2) with bicyclic guanidine moieties were synthesized and attached to a Ru(II)(bpy)(2) core (bpy = 2,2'-bipyridine) to afford complexes 3 and 4, which were characterized by spectroscopic and electrochemical methods. Complex 4 was further characterized by X-ray crystallography. In cyclic voltammetric studies, both complexes show a Ru(II/III) couple, which is 500 mV less positive than the Ru(II/III) couple of Ru(bpy)(3)(2+). The (1)MLCT and (3)MLCT states of 3 (560 nm/745 nm) and 4 (550 nm/740 nm) are significantly red-shifted with respect to Ru(bpy)(3)(2+) (440 nm/620 nm). Compounds 3 and 4 exhibit emission from a Ru(II)-to-bpy (3)MLCT state, which is rarely the emitting state at λ > 700 nm in [Ru(bpy)(2)(N-N)](2+) complexes.

4-Bromo-N-phenyl-benzamidoxime.

The title compound, C(13)H(11)BrN(2)O, a hydroxy-amidine derivative (an amidoxime), was obtained by addition of the corresponding imidoyl chloride to hydroxy-lamine. The benzene and phenyl rings are twisted from the mean plane of the hydroxy-amidine group by 34.4 (1) and 59.2 (1)°, respectively. In the crystal structure, inter-molecular O-H⋯N hydrogen bonds link pairs of mol-ecules, forming centrosymmetric dimers.