Strong metal-metal coupling in a dinuclear (terpyridine)(bipyridine)ruthenium mixed-valence complex incorporating the bridging ligand 1,4-dicyanamidobenzene dianion

The complex, [{Ru(terpy)(bpy)}2(μ-dicyd)][PF6]2.2, where terpy = 2,2′,2″-terpyridine, bpy = 2,2′-bipyridine, and dicyd2− = 1,4-dicyanamidobenzene dianion, has been synthesized and characterized by cyclic voltammetry and spectroelectrochemical methods. A quantitative absorption spectrum of the radical anion dicyd− has also been determined. The mixed valence ion, [{Ru(terpy)(bpy)}2(μ-dicyd)]3+ is strongly coupled with Kc = 2.7 × 107 and has an intervalence band at λ = 1090 nm (∈max = 3000 M−1 cm−1, v1/2 = 1800 cm−1). The mixed-valence properties of this complex were compared to its ammine analogue [{(NH3)5Ru}2(μ-dicyd)]3+ and rationalized by the perturbation of spectator ligands on the interaction of ruthenium ions with the dicyd2− superexchange pathway. The dependence of intervalence oscillator strength on the nature of the mixed-valence complex was also discussed

Effect of conjugation on the oscillator strength of the ruthenium(III)-cyanamide chromophore

The complexes, [(NH3)5Ru(L)][ClO4]2, where L− = cyanamide, phenylcyanamide, 4-cyanamidobiphenyl, 1-cyanamidonaphthalene, 2-cyanamidonaphthalene, 2-cyanamidophenanthrene, and 1-cyanamidopyrene anions, were synthesized and characterized by cyclic voltammetry and electronic absorption spectroscopy. The Ru(III/ II) couple was shown to shift positively with increasing conjugation of the group attached to the cyanamide moiety and indicated withdrawal of cyanamide electron density onto the conjugated group. Extended Hueckel calculations of the free anion ligands permitted estimates of transition dipole moment lengths, R, for the b1 * ← b1 transition of the cyanamide complexes. Only an approximate positive correlation was shown between oscillator strength and R2

The photodecomposition product μ-oxalato-lκ 2O,O′:2κ 2O′,O‴-bis{bis[2-(2-pyridyl)phenyl-κ 2C,N]iridium(III)}-acetone (1/1.974)

An attempt to grow crystals of [Ir(ppy)2(vacac)], (I), from an acetone-d6 solution formed instead crystals of [(Ir(ppy) 2)2(μ-oxalato)] acetone solvate, (II), [Ir 2C11H8N)4(C2O 4)]·-1.974C3H6O, where ppy is the phenylpyridine anion and vacac is vinylacetylacetonate. Each IrIII ion in (II) is in a pseudooctahedral coordination environment, where the pyridine N atoms are trans to each other and the phenyl C atoms are trans to the O atoms of the oxalate bridging ligand. There are two crystallographically independent dimer molecules, each lying on an inversion centre. It is suggested that the oxalate ligand is formed in a series of steps initiated by the aldol condensation of acetone with vacac

Metal-Ligand Coupling Elements and Antiferromagnetic Superexchange in Ruthenium Dimers

Antiferromagnetic exchange constants were calculated by using the Mulliken-Hush treatment for metal-ligand coupling elements (J. Photochem, Photobiol. A: Chem. 1994, 82, 47) and the valence bond model of antiferromagnetic exchange (Inorg. Chem. 1993, 32, 2850), from the spectral data of the solvent-dependent ligand-to-metal charge-transfer bands of [{(NH3)5Ru}2(μ-L)]4+ complexes, where L is a substituted 1,4-dicyanamidobenzene dianion derivative. These calculated values were compared to the corresponding experimental exchange constants that were estimated from the complexes' solvent-dependent room-temperature magnetic moments. The correlation between these values is quite good, and this in turn implies that a relatively unsophisticated level of theory in conjunction with spectroscopy may be all that is necessary to predict trends in molecular properties derived from frontier orbitals

Iridium luminophore complexes for unimolecular oxygen sensors

In this study, a series of novel luminescent cyclometalated Ir(III) complexes has been synthesized and evaluated for use in unimolecular oxygen-sensing materials. The complexes Ir(C6)2(vacac), 1, Ir(ppy)2-(vacac), 2, fac-Ir(ppy)2(vppy), 3, and mer-Ir(ppy)2(vppy), 4, where C6 = Coumarin 6, vacac = allylaceto-acetate, ppy = 2-phenylpyridine, and vppy = 2-(4-vinylphenyl) pyridine, all have pendent vinyl or allyl groups for polymer attachment via the hydrosilation reaction. These luminophore complexes were characterized by NMR, absorption, and emission spectroscopy, luminescence lifetime and quantum yield measurements, elemental analysis, and cyclic voltammetry. Complex 1 was structurally characterized using X-ray crystallography, and a series of 1-D (1H, 13C) and 2-D (1H-1H, 1H-13C) NMR experiments were used to resolve the solution structure of 4. Complexes 1 and 3 displayed the longest luminescence lifetimes and largest quantum efficiencies in solution (τ = 6.0 μs, φ = 0.22 for 1; τ = 0.4 μs, φ = 0.2 for 3) and, as result, are the most promising candidates for future luminescence-quenching-based oxygen-sensing studies

Synthesis, characterization, and evaluation of [Ir(ppy)2(vpy)Cl] as a polymer-bound oxygen sensor

This study reports new luminescent oxygen sensors in which the luminophore is covalently bound to the polymer matrix and compares their behavior to related sensors in which the luminophore is dispersed within the matrix. The cyclometalated iridium complex [Ir(ppy)2(vpy)CI], 1, has been synthesized and characterized spectroscopically (absorption and emission) and by 1-D and 2-D 1H NMR, elemental analysis, and X-ray crystallography. Complex 1 was attached via hydrosilation to hydride-terminated poly(dimethylsiloxane) (PDMS), yielding material 2. Successful luminophore attachment was determined spectroscopically from the emission properties, and through the altered physical behavior of 2 compared to a dispersion of 1 in PDMS. Hydrosilation of 1 with dimethylphenylsilane yielded [Ir(ppy)2(DMPSEpy)CI], 3, which was fully characterized and used to probe the effect of hydrosilation on the spectroscopic properties of the luminophore. Evaluation of 2 as a luminescent oxygen sensor revealed significantly improved sensitivity over dispersions of 1 in PDMS. Material 2 was also blended with polystyrene (PS) to improve the physical properties of the sensor films. The blend sensors exhibited increased sensitivity relative to films of 2 alone and maintained short response times to rapid changes in air pressure. In contrast, 1 partitioned into the PS phase when dispersed in a PDMS/PS blend, resulting in longer sensor response times