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A series of paracyclophane (PC) bridged mixed-valence (MV) bis-triarylamine radical cations with different ([2.2], [3.3], [4.4]) linkers, with and without additional ethynyl spacers, have been studied by quantum-chemical calculations (BLYP35-D3/TZVP/COSMO) of ground-state structures, thermal electron-transfer barriers, hyperfine couplings, and lowest-lying excited states. Such PC-bridged MV systems are important intra-molecular model systems for inter-molecular electron transfer (ET) via π-stacked aromatics, since they allow enforcement of a more or less well-defined geometrical arrangement. Closely comparable ET barriers and electronic couplings for all [2.2] and [3.3] bridges are found for these class-II MV systems, irrespective of the use of pseudo- para and pseudo- meta connections. While the latter observation contradicts notions of quantum interference for off-resonant conduction through molecular wires, it agrees with the less intricate nodal structures of the highest occupied molecular orbitals. The ET in such MV systems may be more closely connected with hole conduction in the resonant regime. Computations on model cations, in which the [2.2] linkers have been truncated, confirm predominant through-space π-π electronic coupling. Systems with [4.4] PC bridges exhibit far more structural flexibility and concomitantly weaker electronic interactions between the redox centers. © 2015 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

The reaction of trans-RuCl(CCC6H4R1-4)(dppe)2(2:R1= Me (a), C5H11(b), OMe (c), CO2Me (d), NO2(e), CCSiMe3(f), CCBut(g), NH2(h)), prepared in situ from reactions of [RuCl(dppe)2]OTf ([1]OTf) with terminal alkynes in CH2Cl2solutions containing 1,8-diazabicycloundec-7-ene(DBU) and TlBF4, provides a convenient and rapid routeto bis(acetylide) complexes trans-Ru(CCC6H4R1-4)2(dppe)2(3a–h) and trans-Ru(CCC6H4R1-4)(CCC6H4R2-4)(dppe)2(4, R1= CCSiMe3, R2= NH2; 5, R1= CO2Me, R2= NH2; 6, R1= CO2Me, R2= OMe). However, even in the absence of the chlorideabstracting reagent, more strongly electron donating substituents(e.g., R1= OMe (2c), NH2(2h)) promote sufficient ionization of the Ru–Cl bondin trans-RuCl(CCC6H4R1-4)(dppe)2to lead to slow conversion tobis(alkynyl) complexes 3c,hin the presenceof excess alkyne and DBU. Desilylation of 2fand 3faffords 2iand 3i(R1= CCH), respectively. The molecular structures of 3a–d,f–ihave been determined and are reported together with the structuresof the monoalkynyl complexes 2f,g,iand compared with related compounds from the literature.Complexes 3a–iand 4–6undergo one reversible electrochemical oxidationprocess, which can be attributed to depopulation of an orbital withsignificant alkynyl ligand character. The one-electron-oxidation products[3f]•+, [3h]•+, [4]•+, and [5]•+, chosen to serve as representative examples of thisfamily of complexes, each exhibit a series of NIR absorptions between15000 and 5000 cm–1which on the basis of TDDFTcalculations cannot be attributed to a single, static lowest energymolecular structure. Rather, the transitions that are responsiblefor the absorption band envelope have varying degrees of LMCT andinter-alkynyl ligand IVCT or MLCT character that depend not only onthe nature of the Rngroups but also on the ensemble ofthermally populated molecular conformers in solution with variousrelative orientations of the metal fragment and arylethynyl moieties. [ABSTRACT FROM AUTHOR]

The conformational energy landscape and the associated electronic structure and spectroscopic properties (UV/Vis/near-infrared (NIR) and IR) of three formally d5/d6 mixed-valence diruthenium complex cations, [{Ru(dppe)Cp*}2(μ-C≡CC6H4C≡C)]+, [ 1]+, [ trans-{RuCl(dppe)2}2(μ-C≡CC6H4C≡C)]+, [ 2]+, and the Creutz-Taube ion, [{Ru(NH3)5}2(μ-pz)]5+, [ 3]5+ (Cp=cyclopentadienyl; dppe=1,2-bis(diphenylphosphino)ethane; pz=pyrazine), have been studied using a nonstandard hybrid density functional BLYP35 with 35 % exact exchange and continuum solvent models. For the closely related monocations [ 1]+ and [ 2]+, the calculations indicated that the lowest-energy conformers exhibited delocalized electronic structures (or class III mixed-valence character). However, these minima alone explained neither the presence of shoulder(s) in the NIR absorption envelope nor the presence of features in the observed vibrational spectra characteristic of both delocalized and valence-trapped electronic structures. A series of computational models have been used to demonstrate that the mutual conformation of the metal fragments-and even more importantly the orientation of the bridging ligand relative to those metal centers-influences the electronic coupling sufficiently to afford valence-trapped conformations, which are of sufficiently low energy to be thermally populated. Areas in the conformational phase space with variable degrees of symmetry breaking of structures and spin-density distributions are shown to be responsible for the characteristic spectroscopic features of these two complexes. The Creutz-Taube ion [ 3]5+ also exhibits low-lying valence-trapped conformational areas, but the electronic transitions that characterize these conformations with valence-localized electronic structures have low intensities and do not influence the observed spectroscopic characteristics to any notable extent. [ABSTRACT FROM AUTHOR]

The character of the electronic transitions in the ultraviolet-visible--near infrared (UV--vis--NIR) spectra of platinum-bis(alkynyl) bridged, bis-triarylamine mixed-valence systems trans-[Pt(C = CC6H4NAr2)2 (PR3)2]n+ (R = ethyl, Ar = C6H4CH3-4 (l) or C6H4OCH3-4 (2); R = Ph, Ar = C6H4CH3-4 (3) or C6H4OCH3-4 (4), n = 0, 1, 2) has been determined from a combination of spectroscopic measurement and density functional theory calculations. The hybrid functional BLYP35 in combination with a suitable solvent model (i.e., conductor-like screening model (COSMO)) has been used to model the UV--vis--NIR and IR spectroscopic properties of [l--4]+, to confirm the description of [l--4]+ as examples of metal-bridged organic mixed-valence compounds, and to assign the principal features of the electronic spectra, including the triarylamine-based intervalence charge transfer transition located in the NIR region. The successful modeling of the charge distribution within the system demonstrates the utility of the BLYP35-COSMO protocol as a tool for use in the study of intramolecular charge transfer properties in mixed-valence complexes. [ABSTRACT FROM AUTHOR]

Spinning to improve (band) shape: A blend of theoretical and experimental work demonstrates that the rotational conformation of mixed‐valence complexes influences the low‐energy (NIR) transitions in such molecules. Interpretations of the NIR band shapes are presented. [ABSTRACT FROM AUTHOR]