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The NIR and IR spectroscopic properties of the cyanide-bridged complex, trans-[Ru(dmap)4{(μ-CN)Ru(py)4Cl}2]3+ (py=pyridine, dmap=4-dimethylaminopyridine) provide strong evidence that this trimetallic ion behaves as a Class III mixed-valence species, the first example reported of a cyanide-bridged system. This has been accomplished by tuning the energy of the fragments in the trimetallic complex to compensate for the intrinsic asymmetry of the cyanide bridge. Moreover, (TD)DFT calculations accurately predict the spectra of the trans-[Ru(dmap)4{(μ-CN)Ru(py)4Cl}2]3+ ion and confirms its delocalized nature. [ABSTRACT FROM AUTHOR]

The NIR donor-acceptor charge transfer (DACT) bands of the series of trinuclear complexes trans-[(NC)5FeII/III-(μ-CN)RuIIL4μ-NC)FeIII(CN)5]5/4- (L= pyridine, 4-tert-butylpyridine, and 4-methoxypyridine) are analyzed in terms of a simplified molecular orbital picture that reflects the interaction between the donor and acceptor fragments. The degree of electronic coupling between the fragments is estimated by a full fit of the DACT band profiles according to a three-state model inspired in the Mulliken-Hush formalism. The information is complemented with determinations performed on the asymmetric heterotrinuclear species trans-[(NC)5CoIII(μ-CN)RuII(py)4(μ-NC)FeIII(CN)5]4-, whose preparation is reported here for the first time. The analysis of the NIR spectra of the symmetric trans-[(NC)5FeIII-(μ-CN)RuIIL4(μ-NC)FeIII(CN)5]4- species reveals a low degree of mixing between the terminal acceptor fragments and the bridging moiety containing RuII, with H12 values between 1.0 × 10³ and 1.5 × 10³ cm-1. The reorganization energy contributions seem to be the same for the three species, even when the spectra were recorded in different media. This observation also applies for the CoIII-substituted compound. The computed potential energy surfaces (PES) of the ground state for these complexes show only one stationary point, suggesting that the FeII-RuIII-FeIII (or FeII-RuIII-CoIII) electronic isomers are not thermally accessible. One-electron reduction leads to asymmetric trans-[(NC)5FeII(μ-CN)RuIIL4(μ-NC)FeIII(CN)5]5- compounds with potentially two DACT bands involving the RuII and the FeII donor fragments. These species reveal a similar degree of electronic mixing but the PES shows three minima. We explore the role of the bridging fragment in the long-range thermally induced electron transfer between the distant iron centers. The results suggest that superexchange and hopping might become competitive paths, depending on the substituents in the bridging fragment. [ABSTRACT FROM AUTHOR]

We report here the spectroscopic properties of four very closely related mixed-valence cyanide-bridged bimetallic complexes, trans-[Ru(T)(bpy)(μ-NC)Ru(L)4(CN)]3+ (T = tris(1-pyrazolyl)methane (tpm, a) or 2,2';6',2"-terpyridine, (tpy, b), and L = pyridine (py, 1) or 4-methoxypyridine (MeOpy, 2)). In acetonitrile all the complexes present intervalence charge transfer (IVCT) transitions in the NIR region, but their intensities are widely different, with the intensity of the transition observed for 1a-b3+ around four times larger than that observed for 2a-b3+. This contrasting behavior can be traced to the different nature of the dπ acceptor orbitals involved in these transitions, as confirmed by (TD)DFT calculations. The spectroscopy of 1a-b3+ provides evidence that the spin density is delocalized over the two ruthenium ions, such as a narrowing of the IVCT bands that results in the resolution of the expected three bands, and a weak solvent dependence of the energy of these transitions. The spectroscopy of 2a-b3+ instead indicates that the spin density is localized on one ruthenium ion. The IVCT in these systems is particularly weak due to the configuration of the Ru(III), where the vacant orbital is perpendicular to the cyanide bridge. [ABSTRACT FROM AUTHOR]

In this article, we report the structural, spectroscopic, and electrochemical properties of the cyanide-bridged complex salts trans-[(NC)RuII(L)4(μ-CN)RuII(py)4Cl]PF6 and trans-[RuIIL)4{(μ-CN)-RuII(py)4Cl}2] (PF6)2 (L = pyridine or 4-methoxypyridine). The mixed-valence forms of these compounds show a variety of metal-to-metal charge-transfer bands, including one arising from charge transfer between the remote ruthenium units. The latter is more intense when L = 4-methoxypyridine and points to the role of the bridging ruthenium unit in promoting mixing between the du orbitals of the terminal fragments. [ABSTRACT FROM AUTHOR]

We report on the synthesis and properties of a family of linear cyanide bridged mixed-valence heptanuclear complexes with the formula: trans-(L4RuII((μ-NC)FeIII(NC)4(μ-CN)RuIIL'4(μ-NC)FeIII(CN)5)2]6-- (with L and L' a para substituted pyridine). We also report on the properties of a related pentanuclear complex. These oligomers were purified by size exclusion chromatography, characterized by electrospray ionization (ESI) mass spectrometry and elemental analysis, and their linear shape was confirmed by scanning tunneling microscopy (STM). These complexes present a rich electrochemistry associated with the seven redox active centers. The redox potential split of identical fragments indicates that there is considerable communication along the cyanide bridged backbone of the compounds, even for centers more than 3 nm apart. This small attenuation of the interaction at long distances make these cyanide bridged compounds good candidates for molecular wires. Interestingly, the extent of the communication depends on the relative energy of the fragments, as evaluated by their redox potentials, providing a guide for improvement of this interesting property. [ABSTRACT FROM AUTHOR]

We report the synthesis, characterization, and spectroscopic properties of a family of trinuclear cyano-bridged mixed-valent compounds, trans-[RuIIL4{NCFeIII(CN)5}2]4-, trans-[RuIIL4{CNFeIII(CN)5}2]4-, and cis-[RuII(bpy)2{NCFeIII(CN)5}2]4- (L = pyridine, 4-tert-butylpyridine, and 4-methoxypyridine). Tetraphenylphosphonium salts of complexes trans-[RuIIL4{NCFeIII(CN)5}2]4- (L = pyridine and 4-tert-butylpyridine) crystallize in the space groups C2 and P21/c, respectively, and show a linear arrangement of the metal units and an almost completely eclipsed configuration of the equatorial ligands. An intense band (ϵ ≈2000-9000 M-1 cm-1) is observed for all of the compounds in the NIR region of the spectrum, not present in the separated building blocks, and strongly solvent dependent. We assign it as a metal-to-metal charge transfer (MMCT) from the Ru(II) to the terminal Fe(III) moieties in the context of a simplified three-center model. The electrochemistry measurements reveal a splitting of the redox waves for the reduction of the iron centers for some of the complexes with a trans configuration between the metal units, ranging from 100 to 260 mV, depending on the substituting pyridine ligand and the solvent, suggesting long-range metal-metal interactions. These interactions are rationalized in terms of the energy matching between the pi-symmetry orbitals of the metals and the cyanide bridge. The one- and two-electron reduced species derived from compounds trans-[RuIIL4{NCFeIII(CN)5}2]4-,5-,6- were characterized in methanolic solution. The mixed-valent FeII-RuII-FeIII system exhibits an intense red shifted band in the NIR region of the spectrum, arising from the superposition of MMCT bands from the central Ru(II) to the terminal Fe(III) fragments and from the 1 nm distant Fe(II) to Fe(III) centers. [ABSTRACT FROM AUTHOR]