Cyanide-bridged Mixed-valence Research Articles

Synthesis, structural and metal-to-metal charge transfer properties of cyanide-bridged compound [FeII/III-NC-RuII-CN-FeII/III

Cyanide-bridged mixed-valence complexes trans-[Cp(dppe)Fe(NC)RuII(tbupy)4(CN)Fe(dppe)Cp][PF6]n (n = 2, 3 and 4, respectively, 1–3) were systematically synthesized and characterized in three distinct redox states.

Synthesis, crystal structure and magnetic properties of a new cyanide-bridged mixed-valence copper(I)/copper(II) clathrate

Abstract A unique cyanide-bridge mixed-valence CuI/CuII clathrate of formula [CuI2(CN)3][{CuII(tren)}2(μ-CN)](CF3SO3)2 [tren = tris(2-aminoethyl)amine] containing cyanide-bridged [{CuII(tren)}2(μ-CN)]3 + binuclear cations stacked between anionic honeycomb layered copper(I) cyanide networks, was synthesized and structurally characterized by single crystal X-ray diffraction. Variable-temperature magnetic susceptibility studies showed that the cyanide bridge mediates a strong antiferromagnetic interaction between the copper(II) centers (J = − 160 cm− 1, the spin Hamiltonian being defined as H = −J SA⋅SB).

Solvent and metal dependent 1H NMR hyperfine shifts in paramagnetic pentaamminemetal cyanide-bridged mixed-valence complexes

(1)H NMR resonances, in several aprotic solvents, are reported for axial and equatorial ammonias coordinated to a single spin paramagnetic centre in the Robin-Day Class II cyanide-bridged mixed-valence cations [(OC)(5)Cr(μ-CN)M(NH(3))(5)](2+) (M = Ru, Os) as well as in the complex [(OC)(5)Re(μ-CN)Ru(NH(3))(5)](3+), whose synthesis and properties are reported herein. Using the appropriate isotropic hexaammine complex as a reference, the chemical shift difference between the ammonia protons, δ(ax) - δ(eq), is found to be very sensitive to the paramagnetic metal (M), the remote diamagnetic metal (Cr or Re) and also to the donor properties of the solvent (as well as the counter-ion) as a result of hydrogen bonding interactions. The difference varies linearly with the MMCT energy, and in [(OC)(5)Re(μ-CN)Ru(NH(3))(5)](3+) can be tuned from positive (δ(ax) > δ(eq)) to negative (δ(ax) < δ(eq)) through zero (δ(ax) = δ(eq)) by the choice of solvent. This reflects the sign and magnitude of the axial ligand field parameter which is in turn a result of changes in the π-donor-acceptor interactions between the donor-cyanide bridging group and the pentaammine metal unit.

Photomagnetic effect in a cyanide-bridged mixed-valence {FeII2FeIII2} molecular square

The self-assembly of [Fe(III)(Tp)(CN)(3)](-) and [Fe(II)(bik)(2)(S)(2)](2+) affords the cyanide-bridged mixed valence {Fe(III)(2)Fe(II)(2)}(2+) molecular square, which exhibits a photomagnetic effect under laser light irradiation at low temperature and also shows thermal spin-state conversion near ambient temperature.

Solvent dependence of the g-anisotropy in the ESR of cyanide-bridged mixed-valence complexes

The low temperature (approximately 5 K) X-band ESR spectra are reported of the cyanide-bridged mixed-valence complexes [(OC)5Cr(mu-CN)M(NH3)5]X2 (M = Ru, Os; X = PF6(-)) in frozen matrices formed from nitromethane, acetonitrile and dimethylformamide with toluene. The anisotropy (g paralell-g perpendicular) is greater for the ruthenium than for the osmium complex. It is positive in all cases and is strongly dependent on the hydrogen-bonding interaction between the solvent matrix and the metal-ammine fragment, decreasing in the order nitromethane > acetonitrile > dimethylformamide. The axial ligand field parameter, Delta, is quite insensitive to the ammine metal (M) and is mainly determined by the solvent matrix. Density functional calculations, together with a simplified MO model, show that: (a) The value of Delta is dominated by the interaction between the filled cyanide pi-orbitals and the ammine-metal d(xz,yz) orbitals, (b) Delta decreases with increasing solvent donicity because the resulting positive shift of the d-orbital energies reduces this interaction, (c) the insensitivity of Delta to the ammine-metal arises because an increase in the energy mismatch between the cyanide pi-orbitals and the d-orbitals in osmium compound is offset by an increase in the 5d resonance integrals relative to those in the 4d shell. Semi-quantitative values are obtained for the pi and pi* resonance integrals. We point out that g paralell determines that portion of the ammine-metal spin population that interacts with the cyanide bridge, and should therefore be correlated with the degree of metal-metal charge transfer in low-spin d6-d5 intervalence compounds. X-band ESR spectra of the polycrystalline powders (M = Ru, Os; X = CF3SO3(-)) are rhombic with similar axial and rhombic ligand field parameters. The rhombicity is interpreted as resulting from asymmetric cation-anion hydrogen-bonding that is apparent in the crystal structures of these isomorphous compounds.

Cyanide 13C NMR hyperfine shifts in paramagnetic cyanide-bridged mixed-valence complexes

Paramagnetic (hyperfine) NMR shifts in the (13)C cyanide bridge and (31)P resonances in a set of mixed valence complexes [(eta(5)-C(5)R(5))Ru(PPh(3))L((13)CN)Ru(NH(3))(5)](n+) (R = H; L = PPh(3), CO, NO(+); R = Me; L = PPh(3)) are sensitive to the extent of intermetallic charge-transfer, and are strongly solvent dependent.

Effective Charge Transfer Distances in Cyanide-Bridged Mixed-Valence Transition Metal Complexes

Stark (electroabsorption) spectroscopy can provide quantitative information on the change in dipole moment and polarizability for an electronic transition. In the case of mixed-valence transitions, the change in dipole moment associated with the intervalence charge-transfer band can be used to establish the effective charge-transfer distance required for estimating the intermetallic electronic coupling using Hush theory (Oh; Boxer J. Am. Chem. Soc.1990, 112, 8161). Stark spectra are reported for a series of cyanide-bridged complexes with -Ru III (NH3)5 as the acceptor and different metal/ligand combinations as the donor. The origins of differences between the effective charge-transfer distance based on the intermetallic distance and the dipole moment differences measured by Stark spectroscopy are discussed. The possible difference in the effective charge-transfer distances for spin-orbit states in ((NC)5Os II -CN-Ru III (NH3)5) - , recently described by Karki and Hupp (J. Am. Chem. Soc. 1997, 110, 4070), is reevaluated, and it is shown that these distances are the same within experimental error for these spin-orbit states. These data provide informative examples of methods used to evaluate Stark data and the power of using higher-order Stark spectroscopy (Lao et al. J. Phys. Chem. 1995, 99, 496) to measure the change in dipole moment for broad and relatively weak transitions often encountered in mixed-valence systems.

Synthesis and characterisation of cyanide-bridged heterobinuclear mixed-valence compounds based on cyclopentadienylorganophosphine-ruthenium(II) and -osmium(II) cyano and pentaammine-ruthenium(III) and -osmium(III) moieties

Six novel cyanide-bridged mixed-valence complexes. [(η5-C5H5)(PPh3)2M′(µ-CN)M(NH3)5][CF3SO3]3(M = Ru, M′= Ru or Os; M = Os, M′= Ru or Os) and [(η5-C5R5)(PPh3)2Ru(η-CN)Ru(NH3)5][CF3SO3]3(C5R5= C5H4Me or C5Me5), have been synthesised using a simple coupling reaction and characterised by electronic and infrared absorption spectroscopy and by cyclic voltammetry. They exhibit moderately intense (Iµmax≈ 2000–4000 dm3 mol–1 cm–1), broad (Δν½≈ 5000 cm–1) intervalence charge-transfer transitions in the visible spectrum, analysis of which reveals Robin–Day Class II behaviour (α2≈ 0.8–2.0%, Hrp≈ 1700–2000 cm–1). Outer-sphere effects upon the cyanide-bridge stretching frequency and all the intervalence charge-transfer band characteristics are reported and interpreted using linear correlations with respect to Gutmann solvent donicity, where appropriate, and simple perturbation arguments. The weak solvent dependence of the coupling element, Hrp, indicates that the charge-transfer mechanism proceeds primarily through an electron, rather than hole, transfer pathway. The intervalence charge-transfer bands of the cyclopentadienylosmium complexes exhibit a pronounced spin-orbit splitting, the relative intensities of the components also showing solvent dependence.

Electrochemical variational study of donor/acceptor orbital mixing and electronic coupling in cyanide-bridged mixed-valence complexes

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTElectrochemical variational study of donor/acceptor orbital mixing and electronic coupling in cyanide-bridged mixed-valence complexesYuhua Dong and Joseph T. HuppCite this: Inorg. Chem. 1992, 31, 14, 3170–3172Publication Date (Print):July 1, 1992Publication History Published online1 May 2002Published inissue 1 July 1992https://doi.org/10.1021/ic00040a034RIGHTS & PERMISSIONSArticle Views97Altmetric-Citations34LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (384 KB) Get e-Alerts Get e-Alerts